Post by: Star One on 02/16/2017 06:42 pm
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Scientists believe they are on the verge of obtaining the first ever picture of a black hole.
They have built an Earth-sized "virtual telescope" by linking a large array of radio receivers - from the South Pole, to Hawaii, to the Americas and Europe.
There is optimism that observations to be conducted during 5-14 April could finally deliver the long-sought prize.
In the sights of the so-called "Event Horizon Telescope" will be the monster black hole at the centre of our galaxy.
Although never seen directly, this object, catalogued as Sagittarius A*, has been determined to exist from the way it influences the orbits of nearby stars.
These race around a point in space at many thousands of km per second, suggesting the hole likely has a mass of about four million times that of the Sun.
But as colossal as that sounds, the "edge" of the black hole - the horizon inside which an immense gravity field traps all light - may be no more than 20 million km or so across.
And at a distance of 26,000 light-years from Earth, this makes Sagittarius A* a tiny pinprick on the sky.
The Event Horizon Telescope (EHT) team is nonetheless bullish.
"There's great excitement," said project leader Sheperd Doeleman from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
"We've been fashioning our virtual telescope for almost two decades now, and in April we're going to make the observations that we think have the first real chance of bringing a black hole's event horizon into focus," he told BBC News.
http://www.bbc.co.uk/news/science-environment-38937141
Post by: Nomadd on 02/16/2017 08:07 pm
Post by: Star One on 02/16/2017 08:22 pm
Post by: AegeanBlue on 02/16/2017 08:30 pm
Post by: as58 on 02/16/2017 10:12 pm
There's also a new telescope being constructed on top of Greenland's ice sheet, which will be used for EHT.
Post by: Star One on 02/17/2017 06:43 am
Spect-R works at much longer wavelengths. There are not that many observatories working at ~1 mm. Nobeyama is the only one that comes to mind immediately that is not (AFAIK) already/soon used in EHT.
There's also a new telescope being constructed on top of Greenland's ice sheet, which will be used for EHT.
Are the wavelengths it operates in a result of it being an orbital rather than ground based observatory?
Good article on the history of observing Sagittarius A*.
http://www.airspacemag.com/space/12_fm2017-mysteries-of-sagittarius-a-180961673/
Post by: as58 on 02/17/2017 10:42 am
Spect-R works at much longer wavelengths. There are not that many observatories working at ~1 mm. Nobeyama is the only one that comes to mind immediately that is not (AFAIK) already/soon used in EHT.
There's also a new telescope being constructed on top of Greenland's ice sheet, which will be used for EHT.
Are the wavelengths it operates in a result of it being an orbital rather than ground based observatory?
Sort of - interferometry gets harder at shorter wavelengths, and making a space-based (sub-)mm interferometer would be extremely difficult. It's already hard enough to make it work on the ground. Being in space would be a big advantage to sub-mm observations in general because atmosphere, in particular water vapour, absorbs quite strongly at these wavelengths. That's why the observatories are at high altitude in places with a dry atmosphere.
Post by: Sesquipedalian on 02/17/2017 07:06 pm
Post by: meekGee on 02/18/2017 06:04 am
Preliminary image of the black hole:SMH..... :)
Post by: as58 on 02/18/2017 08:28 pm
Preliminary image of the black hole:
They should zoom out a bit.
Post by: AegeanBlue on 10/09/2018 06:36 am
https://www.youtube.com/watch?v=mYsHk4fWrxU
The results from the 2017 campaign will be published in early 2019, including an image as reconstructed from the interferometry.
Post by: Star One on 04/01/2019 03:22 pm
The European Commission, European Research Council, and the Event Horizon Telescope (EHT) project will hold a press conference to present a groundbreaking result from the EHT.
When: On 10 April 2019 at 15:00 CEST
Where: The press conference will be held at the Berlaymont Building, Rue de la Loi (Wetstraat) 200, B-1049 Brussels, Belgium. The event will be introduced by European Commissioner for Research, Science and Innovation, Carlos Moedas, and will feature presentations by the researchers behind this result.
What: A press conference to present a groundbreaking result from the EHT.
RSVP: This invitation is addressed to media representatives. To participate in the conference, members of the media must register by completing an online form before April 7 23:59 CEST. Please indicate whether you wish to attend in person or if you will participate online only. On-site journalists will have a question-and-answer session with panellists during the conference. In-person individual interviews immediately after the conference will also be possible.
The conference will be streamed online on the ESO website, by the ERC, and on social media. We will take a few questions from social media using the hashtag #AskEHTeu.
An ESO press release will be publicly issued shortly after the start of the conference at 15:07 CEST. Translations of the press release will be available in multiple languages, along with extensive supporting audiovisual material.
A total of six major press conferences will be held simultaneously around the globe in Belgium (Brussels, English), Chile (Santiago, Spanish), Shanghai (Mandarin), Japan (Tokyo, Japanese), Taipei (Mandarin), and USA (Washington, D.C., English).
The European Commissioner for Research, Science and Innovation, Carlos Moedas will speak in Brussels, the President of the Academia Sinica, James Liao, will speak in Taipei, the ALMA Director Sean Dougherty and the ESO Director General Xavier Barcons will speak in Santiago, and the NSF Director France A. Córdova will speak in Washington DC.
Due to the importance of this result, we encourage satellite events in the different ESO Member States and beyond. If you wish to arrange a satellite event please contact Katharina Königstein ([email protected]) for details on the live feed. There are satellite-events currently planned in Madrid, Rome, Gothenburg, Nijmegen and Pretoria.
For any further information and updates, please also check the Event Horizon Telescope webpage at https://eventhorizontelescope.org.
Post by: Star One on 04/01/2019 03:32 pm
NSF press conference on first result from Event Horizon Telescope project (https://www.nsf.gov/news/news_summ.jsp?cntn_id=298155&org=NSF&from=news)
The Event Horizon Telescope (EHT) project and the National Science Foundation (NSF) will hold a press conference to announce a groundbreaking result.
What: Press conference on groundbreaking result from the Event Horizon Telescope.
Who: NSF Director France Córdova will deliver remarks. A panel of EHT researchers will also deliver remarks and answer questions:
Sheperd Doeleman, EHT Director, Harvard University Senior Research Fellow, Center for Astrophysics at Harvard & Smithsonian
Daniel Marrone, University of Arizona, Department of Astronomy, Steward Observatory
Avery Broderick, University of Waterloo, Department of Physics and Astronomy, Perimeter Institute for Theoretical Physics
Sera Markoff, University of Amsterdam, Anton Pannekoek Institute for Astronomy, Gravitation and AstroParticle Physics Amsterdam
When: Wednesday, April 10, 2019, 9 a.m. EDT
Where: The National Press Club, 529 14th St N.W., Washington, D.C., 20045. The event will also be streamed live online.
RSVP: Credentialed press can register to attend the event in person by contacting [email protected]. To attend, media must register by 6:00 p.m. EDT on Monday, April 8. Details about submitting questions or scheduling interviews will be sent to journalists following registration.
Immediately following the press conference, panelists and other experts from the EHT collaboration will be available for interviews.
NSF will issue a press release the morning of the press conference. Translations of the press release will be available in multiple languages, along with extensive supporting audiovisual material.
In addition to the press briefing in the U.S, press conferences will be held simultaneously in Brussels, Santiago, Shanghai, Taipei and Tokyo. Speakers in some of the locations to include:
The European Commissioner for Research, Science and Innovation, Carlos Moedas, will speak in Brussels.
President of the Academia Sinica, James Liao, will speak in Taipei.
Director of the Atacama Large Millimeter/submillimeter Array, Sean Dougherty, and European Southern Observatory Director General Xavier Barcons will speak in Santiago.
If you wish to embed the press conference in your online feed, you may do so from either the NSF Black Holes Special Report or the NSF direct livestream link. The NSF Special Report includes additional information about exploring and studying black holes.
For further information about EHT, please check the Event Horizon Telescope webpage.
Post by: Star One on 04/01/2019 03:55 pm
Post by: ugordan on 04/01/2019 04:11 pm
Post by: Star One on 04/01/2019 04:37 pm
I've been looking forward to this for some time now. I hope the results are worth this hype!
Some online have complained that announcing this on April Fools day wasn’t a good idea, seemingly ignoring the fact that I don’t believe all countries have such a day.
Post by: ugordan on 04/01/2019 05:44 pm
I've been looking forward to this for some time now. I hope the results are worth this hype!
Some online have complained that announcing this on April Fools day wasn’t a good idea, seemingly ignoring the fact that I don’t believe all countries have such a day.
Well, isn't that the primary function of the internet now anyway? People complaining and getting offended/triggered by stuff?
Who cares what those people think, I'm here for the science.
Post by: jgoldader on 04/01/2019 06:24 pm
Post by: Star One on 04/01/2019 06:52 pm
IIRC, they were looking first at Sgr A* in our own galactic center and the black hole in the nucleus of M87. Wonder which one they finished with first?
I thought they wouldn’t announce the results until they had done both?
Post by: ugordan on 04/01/2019 06:53 pm
Post by: as58 on 04/01/2019 07:20 pm
I'm thinking Sgr A*, just because it's a bigger impact as it's in our backyard and not some "random" galaxy out there.
Actually, are there any other plausible targets? Messier 87 is by far the closest of the really massive ones.
Post by: ugordan on 04/01/2019 07:33 pm
I'm thinking Sgr A*, just because it's a bigger impact as it's in our backyard and not some "random" galaxy out there.
Actually, are there any other plausible targets? Messier 87 is by far the closest of the really massive ones.
There's a third one I've seen mentioned in a talk by Avery Broderick (one of the panelists for the press conference), but he said it's not radio-active so we're out of luck. Those two are the best candidates nearby.
Post by: Star One on 04/01/2019 08:21 pm
Post by: jgoldader on 04/02/2019 01:19 am
I'm thinking Sgr A*, just because it's a bigger impact as it's in our backyard and not some "random" galaxy out there.
Actually, are there any other plausible targets? Messier 87 is by far the closest of the really massive ones.
M87 is the best one besides Sgr A*, and I would be surprised if there are many (any?) others that could be resolved. The angular size of the event horizon is proportional to the linear diameter divided by the distance; yet because the linear diameter of the event horizon is proportional to the black hole mass, M87's greater mass almost compensates for its greater distance. The end result is that the angular diameter of the M87 black hole's event horizon should be a little less than that of Sgr A*.
I'm trying not to get too hopeful; the renders in "Interstellar" were based on real physics (tweaked for cinematography) and seeing a ring would be just spectacular.
Post by: as58 on 04/02/2019 05:06 am
Are there any plans to add the Tianyan radio telescope to this collective?
No, it works at much longer wavelengths than the telescopes that are used in EHT.
Post by: hoku on 04/02/2019 10:08 am
Sgr A*:
mass: 4.2 million solar masses
RADIUS: 12.5 million km
DIAMETER: 25 million km (15.5 million miles)
angular DIAMETER (for a distance Sun to Sgr A* of 8200 pc): 20 micro-arcsec
RADIUS of innermost stable orbit (for non-rotating black hole): 3 * Scharzschild radius = 30 micro-arcsec
EHT (present configuration?):
observing frequency: 230 GHz (i.e. observing wavelength 1.3mm)
angular resolution EHT for, e.g., Hawaii - ALMA baseline: 28 micro-arcsec
(see https://eventhorizontelescope.org/building-larger-array (https://eventhorizontelescope.org/building-larger-array))
Results of previously highest angular resolution radio (at 86 GHz, i.e. 3.5 millimeter) observations of Sgr A*:
https://www.mpifr-bonn.mpg.de/pressreleases/2019/1 (https://www.mpifr-bonn.mpg.de/pressreleases/2019/1)
Post by: Star One on 04/06/2019 12:04 pm
How to See a Black Hole: The Universe’s Greatest Mystery (https://www.bbc.co.uk/programmes/m00042l4)
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Documentary following researchers as they try to take the first-ever picture of a black hole. They must travel the globe to build a revolutionary telescope that spans planet Earth.
Post by: Star One on 04/06/2019 07:21 pm
Recounting the work of Jean-Pierre Luminet amongst others in the depiction of black holes.
Post by: eeergo on 04/10/2019 01:00 pm
Post by: eeergo on 04/10/2019 01:08 pm
Post by: eeergo on 04/10/2019 01:09 pm
Post by: eeergo on 04/10/2019 01:10 pm
Post by: eeergo on 04/10/2019 01:13 pm
Post by: FutureSpaceTourist on 04/10/2019 01:14 pm
Post by: eeergo on 04/10/2019 01:15 pm
Post by: Star One on 04/10/2019 01:16 pm
Post by: eeergo on 04/10/2019 01:19 pm
Post by: eeergo on 04/10/2019 01:20 pm
Post by: eeergo on 04/10/2019 01:22 pm
Post by: eeergo on 04/10/2019 01:23 pm
Post by: eeergo on 04/10/2019 01:23 pm
Highlighting how cooperation between countries was the only way to get these images.
EDIT: Adding a diagram of the interferometry telescope subtended throughout the Western hemisphere by the EHT to perform this observation.
Post by: eeergo on 04/10/2019 01:27 pm
Any news about the imaging of sagittarius a?
Just confirmed SgA* analysis is ongoing and are confident they will soon be able to release images. Probably hindered by a much more dirty background.
Post by: eeergo on 04/10/2019 01:33 pm
Post by: Star One on 04/10/2019 01:35 pm
Any news about the imaging of sagittarius a?
Just confirmed SgA* analysis is ongoing and are confident they will soon be able to release images. Probably hindered by a much more dirty background.
Thank you. Makes sense as our BH is tiny compared to this and has vast amounts of dust around.
Post by: eeergo on 04/10/2019 01:36 pm
Post by: Star One on 04/10/2019 01:43 pm
They imaged Messier-87* first because it is 1000 times larger than Sgr-A* but also 1000 times further away, so the relative size is approximately the same. This wasn't well constrained at all, so it was kind of a lucky shot. However, Sgr-A* is rotating much faster, so this makes it much more difficult to get a sharp image of it. Also mentioned how the accretion plasma is quite "optically" (in radio, obviously) thin in M87*, so they can see the shadow - which is quite an interesting result just by itself.
It’s interesting that our BH is more rapidly rotating is that a function of its smaller size/mass?
Post by: eeergo on 04/10/2019 01:47 pm
High frequencies such as the millimeter waves they studied allows you to get detailed images, but light is much more distorted and it gets difficult to identify in an undistorted way where the jets are coming from. They hypothesize, although it's still not proven, the jets originate in the Doppler-brightened spot on the bottom of the disk in the image.
The accretion disk is very thick and we're looking at it almost face-on, although the bottom is Doppler-brightened because of a slight angle towards us.
Excluding wormhole models, boson stars. Simplest explanation is consistent with Einstenian BH everywhere they've looked at.
Post by: eeergo on 04/10/2019 01:47 pm
They imaged Messier-87* first because it is 1000 times larger than Sgr-A* but also 1000 times further away, so the relative size is approximately the same. This wasn't well constrained at all, so it was kind of a lucky shot. However, Sgr-A* is rotating much faster, so this makes it much more difficult to get a sharp image of it. Also mentioned how the accretion plasma is quite "optically" (in radio, obviously) thin in M87*, so they can see the shadow - which is quite an interesting result just by itself.
It’s interesting that our BH is more rapidly rotating is that a function of its smaller size/mass?
IIRC it's just a matter of angular momentum conservation (i.e. how the forming bodies were rotating/translating with respect to each other).
Post by: eeergo on 04/10/2019 01:51 pm
For now, they have a "sense" of rotation only: its clockwise direction.
Polarization of the light is already inherent to the released data (but still not fully analyzed). It will shed light on M87*'s magnetic fields, which will also give more clues as to how it's rotating.
Post by: Star One on 04/10/2019 01:56 pm
Rotation rate is very difficult to measure with precision because of the relativistic light-bending. Think the spinning exists, and is pointing away from us (its vector) because of the energetic jets that are visible.
For now, they have a "sense" of rotation only: its clockwise direction.
Polarization of the light is already inherent to the released data (but still not fully analyzed). It will shed light on M87*'s magnetic fields, which will also give more clues as to how it's rotating.
By the way thanks for covering this news conference on here.
Post by: eeergo on 04/10/2019 02:04 pm
Rotation rate is very difficult to measure with precision because of the relativistic light-bending. Think the spinning exists, and is pointing away from us (its vector) because of the energetic jets that are visible.
For now, they have a "sense" of rotation only: its clockwise direction.
Polarization of the light is already inherent to the released data (but still not fully analyzed). It will shed light on M87*'s magnetic fields, which will also give more clues as to how it's rotating.
By the way thanks for covering this news conference on here.
My pleasure! My head hurts because I've been watching this (and trying to understand it well) while attending an important work meeting that's been going on for 2h now... thankfully I didn't have to contribute much - or so I think, because I haven't been so attentive during the last hour :D but it was definitely worth it!
Papers: https://iopscience.iop.org/journal/2041-8205 (https://iopscience.iop.org/journal/2041-8205)
Post by: Star One on 04/10/2019 02:33 pm
https://www.nsf.gov/news/special_reports/blackholes/downloads/A-Consensus.jpg
Useful video.
https://www.youtube.com/watch?v=A0HKL10lMck&ab_channel=AntonPetrov
Post by: Star One on 04/10/2019 03:53 pm
Documentary to be shown on BBC 4 in the U.K. on the 10th April.
How to See a Black Hole: The Universe’s Greatest Mystery (https://www.bbc.co.uk/programmes/m00042l4)
Quote
Documentary following researchers as they try to take the first-ever picture of a black hole. They must travel the globe to build a revolutionary telescope that spans planet Earth.
Post by: ugordan on 04/10/2019 04:11 pm
Post by: seawolfe on 04/10/2019 04:17 pm
Just a reminder about this documentary showing in the U.K. tonight.
Documentary to be shown on BBC 4 in the U.K. on the 10th April.
How to See a Black Hole: The Universe’s Greatest Mystery (https://www.bbc.co.uk/programmes/m00042l4)QuoteDocumentary following researchers as they try to take the first-ever picture of a black hole. They must travel the globe to build a revolutionary telescope that spans planet Earth.
How about someone record this and either put it in L2 or on NSF's YouTube site?
Post by: ugordan on 04/10/2019 04:35 pm
Just imagine, a mere 3 years ago black holes were basically accepted as things that exist in our universe, but no one really had any *direct* evidence for it. Then came LIGO and the detection of gravitational waves and now this, the first ever image of the "shadow" of a supermassive black hole, unremarkable how it may or may not seem to the layman's eye. There are days I think it's good to be alive. This is one of them.
Also, how 'bout that old Einstein guy? Of course, this is still far from a precise test of GR in the strong gravity regime, but the fact that it's not *completely* and obviously different to what the theory predicts is remarkable. I'm not sure if I should be happy or sad for all the theoreticians who are seeking to unify GR and QM and could use any extra hint they could to guide their way.
Post by: ugordan on 04/10/2019 04:49 pm
https://www.youtube.com/watch?v=Qrly-3_FNpc
Post by: RonM on 04/10/2019 04:54 pm
Just a reminder about this documentary showing in the U.K. tonight.
Documentary to be shown on BBC 4 in the U.K. on the 10th April.
How to See a Black Hole: The Universe’s Greatest Mystery (https://www.bbc.co.uk/programmes/m00042l4)QuoteDocumentary following researchers as they try to take the first-ever picture of a black hole. They must travel the globe to build a revolutionary telescope that spans planet Earth.
How about someone record this and either put it in L2 or on NSF's YouTube site?
Can't do it because that would be a copyright violation. We don't want to get NSF in trouble.
Post by: RotoSequence on 04/10/2019 05:01 pm
Also, how 'bout that old Einstein guy?
Let's also hear it for Roy Kerr, who found the solution for a rotating black hole :D
Post by: Star One on 04/10/2019 05:03 pm
Just a reminder about this documentary showing in the U.K. tonight.
Documentary to be shown on BBC 4 in the U.K. on the 10th April.
How to See a Black Hole: The Universe’s Greatest Mystery (https://www.bbc.co.uk/programmes/m00042l4)QuoteDocumentary following researchers as they try to take the first-ever picture of a black hole. They must travel the globe to build a revolutionary telescope that spans planet Earth.
How about someone record this and either put it in L2 or on NSF's YouTube site?
Can't do it because that would be a copyright violation. We don't want to get NSF in trouble.
The program should appear on that link I posted. I am not sure as regards viewed outside the UK.
Post by: ugordan on 04/10/2019 05:14 pm
Also, how 'bout that old Einstein guy?
Let's also hear it for Roy Kerr, who found the solution for a rotating black hole :D
Well, technically, I'd also need to give a shout-out to my dawg* Karl Schwarzschild then :D
*(and by my dawg, I mean we're totally unrelated)
Post by: ugordan on 04/10/2019 05:19 pm
Post by: Star One on 04/10/2019 07:39 pm
https://www.youtube.com/watch?v=TdZdqfD0LTI
The incredible story behind the first image of a black hole (https://www.wired.co.uk/article/black-hole-photo-image)
Quote
The EHT has also been observing Sagittarius A*, the supermassive black hole at the centre of the Milky Way. However, our galaxy is much 'messier' than M87 - meaning there is much more gas and dust that obscure the picture. The collaboration is still processing how to mitigate the effects of the matter lying between the Solar System and the Galactic centre. To help with that process, four more observatories are now joining the EHT.
"When Apollo [8] turned and took a picture of the Earth, we had this wonderful moment of seeing a picture that had not been seen before," Psaltis says, adding that the first image of a black hole might carry a similar emotional weight. "It's something that inspires and excites us."
Natarajan agrees. "Black holes have this incredible gravitational pull for us. It's amazing that one happens to be alive at a time right when we're learning so much about black holes."
Love this quote from today.
" VLBI allows the EHT to achieve an angular resolution of 20 micro-arcseconds -- enough to read a newspaper in New York from a sidewalk café in Paris."
Post by: Star One on 04/10/2019 08:44 pm
https://www.eso.org/public/archives/images/original/eso1907a.tif
Quote
I’ve also heard they started with M87 because it’s 1000X more massive than Sgr A*. Plasma is whipping around our local black hole, potentially brightening and dimming the image in a matter of minutes. Things unfold more slowly out at M87, so it makes sense to start there first.
https://mobile.twitter.com/fcain/status/1116032370916741120
Post by: jgoldader on 04/10/2019 10:51 pm
It's funny, since the Milky Way black hole is not bright in the near-IR, appearing as a faint, flickering source (though it is very bright in the radio). I'd heard of it being described as "starving," in comparison with other galaxies' central black holes with high accretion rates.
But I guess the small radius, just 12 million km or so, hurts. In fact, a paper by the GRAVITY collaboration found signs consistent with material orbiting near the innermost stable orbit at v~0.3 c with period of about 45 +/- 15 minutes (https://arxiv.org/abs/1810.12641). So if you're trying to combine observations taken over a period of hours, and the source is changing over a lesser period... yeah, I see how that's a problem.
Post by: CuddlyRocket on 04/11/2019 03:51 am
This YouTube video by Veritasium has an image of Sgr A* (at 4:19), which came from Goethe University, who also put up a YouTube video:
Using VLBI to create an Image of the black hole in the center of our Galaxy (https://www.youtube.com/watch?v=VnsZj9RvhFU).
Post by: Star One on 04/11/2019 05:50 am
Post by: as58 on 04/11/2019 06:51 am
Isn’t that just a simulation and I watched that video and he didn’t point that out in it?
Yes it is. It's confirmed in the comments of the original video from Goethe University by a person working there.
Post by: Star One on 04/11/2019 07:04 am
Isn’t that just a simulation and I watched that video and he didn’t point that out in it?
Yes it is. It's confirmed in the comments of the original video from Goethe University by a person working there.
But not in the one from Veritasium that used the image, sorry I should have been clearer what one I meant.
Would it be possible for them to ever produce animations from the data they receive?
And do they have plans to observe any other SMBH?
What the Sight of a Black Hole Means to a Black Hole Physicist (https://www.quantamagazine.org/what-the-sight-of-a-black-hole-means-to-a-black-hole-physicist-20190410/)
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The astrophysicist Janna Levin reflects on the newly unveiled, first-ever photograph of a black hole.
Post by: eeergo on 04/11/2019 08:09 am
Post by: joncz on 04/11/2019 09:51 am
The human side, from FB: https://m.facebook.com/ScienceNaturePage/photos/a.693601310772130/1630872857044966/?type=3&source=48
https://www.youtube.com/watch?v=BIvezCVcsYs
Post by: eeergo on 04/11/2019 10:15 am
XKCD does it again (comparison of our Solar System, Voyager-1 included, superimposed on M87*)
Post by: eeergo on 04/11/2019 10:19 am
https://twitter.com/Alex_Parker/status/1116070667068170240
Post by: joncz on 04/11/2019 10:58 am
Post by: joncz on 04/11/2019 10:59 am
Personal Recollections (1972-2002)
Jean-Pierre Luminet
https://arxiv.org/ftp/arxiv/papers/1902/1902.11196.pdf (https://arxiv.org/ftp/arxiv/papers/1902/1902.11196.pdf)
Post by: eeergo on 04/11/2019 01:22 pm
An Illustrated History of Black Hole Imaging :
Personal Recollections (1972-2002)
Jean-Pierre Luminet
https://arxiv.org/ftp/arxiv/papers/1902/1902.11196.pdf (https://arxiv.org/ftp/arxiv/papers/1902/1902.11196.pdf)
Beautiful how poetic insight can bring striking similarities to unimaginable reality. In 1854 (!), French poet Gérard de Nerval wrote in "Le Christ aux oliviers":
« En cherchant l’œil de Dieu, je n’ai vu qu’un orbite
Vaste, noir et sans fond, d’où la nuit qui l’habite
Rayonne sur le monde et s’épaissit toujours ;
« Un arc-en-ciel étrange entoure ce puits sombre,
Seuil de l’ancien chaos dont le néant est l’ombre,
Spirale engloutissant les Mondes et les Jours !
Translated freely by J.P. Luminet in the (wonderful) linked article as:
"In seeking the eye of God, I saw nought but an orbit
Vast, black, and bottomless, from which the night which there lives
Shines on the world and continually thickens
A strange rainbow surrounds this somber well,
Threshold of the ancient chaos whose offspring is shadow,
A spiral engulfing Worlds and Days!"
Post by: ugordan on 04/11/2019 06:19 pm
Post by: Star One on 04/11/2019 09:21 pm
Three Radio Telescopes will be Added to the Black Hole Imaging Array (https://www.nextbigfuture.com/2019/04/three-radio-telescopes-will-be-added-to-the-black-hole-imaging-array.html)
Post by: Star One on 04/13/2019 02:29 pm
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The new name, "Pwehi," means "embellished dark source of unending creation" in the indigenous Hawaiian language, and it was selected by Larry Kimura, a Hawaiian language professor at the University of Hawaii, Hilo (UH), according to a statement released by the university on April 10.
https://www.space.com/how-to-name-black-holes.html
Post by: Star One on 04/16/2019 07:21 pm
Quote
"It turns out that even now, with what we have, we may be able, with certain prior assumptions, to look at rotational signatures [evidence of the accretion disk swirling around the event horizon]," Doeleman said. "And then, if we had many more stations, then we could really start to see in real time movies of the black hole accretion and rotation." [9 Ideas About Black Holes That Will Blow Your Mind]
Post by: Star One on 04/18/2019 08:25 pm
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There's a bright magnetar photobombing the supermassive black hole at the center of the Milky Way, frustrating astronomers' efforts to study the black hole — called Sagittarius A* — using X-ray telescopes.
SagA* is the nearest known supermassive black hole to Earth. And while it's far smaller, quieter and dimmer than the recently imaged black hole at the center of the galaxy Messier 87, it still represents one of the best opportunities astronomers have for understanding how black holes behave and interact with their surrounding environments. But back in 2013, a magnetar — an ultradense star (also called a neutron star) wrapped in powerful magnetic fields — between SagA* and Earth lit up, and ever since has been messing with efforts to observe the black hole using X-ray telescopes.
Post by: Star One on 05/10/2019 01:55 pm
[MEDIA=youtube]uyMtsyzXWd4[/MEDIA]
Post by: Star One on 05/10/2019 08:00 pm
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The concept called the Event Horizon Imager (EHI) was dreamed up by a team of astronomers at Radboud University in the Netherlands. They’re hoping to make their project a reality with help from the European Space Agency (ESA).
“There are lots of advantages to using satellites instead of permanent radio telescopes on Earth, as with the Event Horizon Telescope (EHT),” said Freek Roelofs, a PhD candidate at Radboud University and the lead author of the article, in a statement. “In space, you can make observations at higher radio frequencies, because the frequencies from Earth are filtered out by the atmosphere.”
Post by: speedevil on 05/11/2019 06:53 pm
Simulations of imaging the event horizon of Sagittarius A* from space
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An initial design study of the concept has been presented as the Event Horizon Imager (EHI). The EHI may be suitable for imaging Sgr A* at high frequencies (up to ~690 GHz), which has significant advantages over performing ground-based VLBI at 230 GHz. The concept EHI design consists of two or three satellites in polar or equatorial circular Medium-Earth Orbits with slightly different radii. Due to the relative drift of the satellites along the individual orbits, this setup will result in a dense spiral-shaped uv-coverage with long baselines (up to ~60 Glambda), allowing for extremely high-resolution and high-fidelity imaging of radio sources.(https://i.imgur.com/ViajLiD.jpg)
The resolution would be several times better than EHT - though I am unsure if the suggested 25m dishes have any open space heritige.
Post by: SgtPoivre on 05/11/2019 08:12 pm
The resolution would be several times better than EHT - though I am unsure if the suggested 25m dishes have any open space heritige.
Orion/Mentor SIGINT spy satellites are rumored to have deployable dishes with a diameter in excess of 100m in deployed configuration : https://en.m.wikipedia.org/wiki/Orion_%28satellite%29?wprov=sfla1
Post by: hop on 05/12/2019 01:42 am
Orion/Mentor SIGINT spy satellites are rumored to have deployable dishes with a diameter in excess of 100m in deployed configurationThe requirements for a 600+ ghz dish are a lot more demanding than a typical communication bands. IIRC ALMA antennas have a tolerance of something like 25 micrometers.
Post by: Star One on 09/05/2019 07:31 pm
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The Event Horizon Telescope (EHT) team took humanity to the heart of darkness when it unveiled the world’s first direct image of a black hole in April1,2,3,4,5,6. That feat has now earned the team one of this year’s US$3-million Breakthrough prizes — one of the most lucrative awards in science and mathematics.
https://www.nature.com/articles/d41586-019-02659-5
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The team that took the first ever image of a black hole has announced plans to capture "razor sharp" full colour video of the one at the centre of our galaxy.
Satellites would be launched to supplement the existing network of eight telescopes to make this movie.
The researchers say the upgraded network will be able to see the supermassive black hole consuming the material around it.
https://www.bbc.com/news/science-environment-49571917
Post by: eeergo on 05/12/2022 09:03 am
https://www.youtube.com/watch?v=rIQLA6lo6R0
Post by: eeergo on 05/12/2022 01:03 pm
Stars around the supermassive black hole have shown orbits that they are indeed orbiting such an object, but it has so far not been seen yet.
Eight radio-observatories around the world, with a network that has expanded to eleven today. Important to remember the necessity to cooperate and work together, especially relevant today with the isolationist nationalistic tendencies and violence in Europe. 300 people in the teams signing the papers.
First direct evidence that SagA* is a black hole.
Black hole at the center, surrounded by the very hot gas swirls of accretion that emit radio waves detected by the EHT.
62 micro-arcseconds is the size of the image, as small as a doughnut on the Moon seen from Earth (3 million times as sharp as a human eye, also equivalent to seeing the bubbles on a New Yorker beer glass from Munich). But the actual black hole is the size of Mercury's orbit, with a mass of 4 million solar masses.
Amazed this image looks so similar to M87*'s, but SagA* is one thousandth of M87*'s mass, and consumes much less gas (reason for which M87* also ejects jets of plasma). Comparing M87* to the Allianz Arena stadium vs a doughnut for SagA*. Note the correct scale in the second side-to-side image.
Post by: eeergo on 05/12/2022 01:32 pm
The period of the innermost stable circular orbit, which depends on the mass and spin of the black hole corresponds to 5 days to 1 month for M87*, but, for Sgr A*, the range is only 4–30 minutes - so the source structure can evolve within a single night.
The main image is an average, but the thousands of images are distributed in 4 main classes, three of which are ring-like and another one which looks fuzzier. 52 microarseconds is the common feature of the ring-like images and precisely that foreseen by General Relativity for the deduced mass (within 10%).
Built the largest (PByte size) database of synthetic BH images, in order to compare with the results from the telescope.
Accretion disk is FACE ON to us (approximately), inferred from the simulations. Accretion rate is a millionth less than M87*'s (handwavely compared to eating a grain of rice every million years for a human's body mass, roughly... so starving is an understatement ;D ), and it is spinning as expected.
Combination of forces from ALMA in Chile (largest collecting area = sensitivity for weakest signals), 30-m IRAM antenna in Spain (sharpest resolution), APEX in Chile for precision calibration, and NOEMA in France to boost collection and sensitivity at the edge of the interferometer. Integration of NOEMA and the African Millimeter Telescope will enable further studies of SagA*, providing enough data for movies, as well as studies of jets from other holes, check the magnetic fields and precision test relativity.
Post by: eeergo on 05/12/2022 01:50 pm
https://twitter.com/planet4589/status/1524745386287681537
Post by: eeergo on 05/12/2022 02:18 pm
https://twitter.com/Alex_Parker/status/1116070667068170240
Post by: eeergo on 05/12/2022 02:36 pm
https://twitter.com/hfalcke/status/1524737908560863234
Post by: Hobbes-22 on 05/12/2022 02:40 pm
62 micro-arcseconds is the size of the image, as small as a doughnut on the Moon seen from Earth (3 million times as sharp as a human eye, also equivalent to seeing the bubbles on a New Yorker beer glass from Munich). But the actual black hole is the size of Mercury's orbit, with a mass of 4 million solar masses.
for reference, JWST NIRCam's long-wavelength channel has a resolution of 62 milliarcseconds.
Post by: Greg Hullender on 05/12/2022 03:18 pm
Post by: Star One on 05/12/2022 03:36 pm
Astronomers reveal first image of the black hole at the heart of our galaxy
Today, at simultaneous press conferences around the world, including at the European Southern Observatory (ESO) headquarters in Germany, astronomers have unveiled the first image of the supermassive black hole at the centre of our own Milky Way galaxy. This result provides overwhelming evidence that the object is indeed a black hole and yields valuable clues about the workings of such giants, which are thought to reside at the centre of most galaxies. The image was produced by a global research team called the Event Horizon Telescope (EHT) Collaboration, using observations from a worldwide network of radio telescopes.
The image is a long-anticipated look at the massive object that sits at the very centre of our galaxy. Scientists had previously seen stars orbiting around something invisible, compact, and very massive at the centre of the Milky Way. This strongly suggested that this object — known as Sagittarius A* (Sgr A*, pronounced "sadge-ay-star") — is a black hole, and today’s image provides the first direct visual evidence of it.
Although we cannot see the black hole itself, because it is completely dark, glowing gas around it reveals a telltale signature: a dark central region (called a shadow) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun.
“We were stunned by how well the size of the ring agreed with predictions from Einstein’s Theory of General Relativity," said EHT Project Scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei. "These unprecedented observations have greatly improved our understanding of what happens at the very centre of our galaxy, and offer new insights on how these giant black holes interact with their surroundings." The EHT team's results are being published today in a special issue of The Astrophysical Journal Letters.
Because the black hole is about 27 000 light-years away from Earth, it appears to us to have about the same size in the sky as a doughnut on the Moon. To image it, the team created the powerful EHT, which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope [1]. The EHT observed Sgr A* on multiple nights in 2017, collecting data for many hours in a row, similar to using a long exposure time on a camera.
In addition to other facilities, the EHT network of radio observatories includes the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile, co-owned and co-operated by ESO on behalf of its member states in Europe. Europe also contributes to the EHT observations with other radio observatories — the IRAM 30-meter telescope in Spain and, since 2018, the NOrthern Extended Millimeter Array (NOEMA) in France — as well as a supercomputer to combine EHT data hosted by the Max Planck Institute for Radio Astronomy in Germany. Moreover, Europe contributed with funding to the EHT consortium project through grants by the European Research Council and by the Max Planck Society in Germany.
“It is very exciting for ESO to have been playing such an important role in unravelling the mysteries of black holes, and of Sgr A* in particular, over so many years,” commented ESO Director General Xavier Barcons. “ESO not only contributed to the EHT observations through the ALMA and APEX facilities but also enabled, with its other observatories in Chile, some of the previous breakthrough observations of the Galactic centre.” [2]
The EHT achievement follows the collaboration’s 2019 release of the first image of a black hole, called M87*, at the centre of the more distant Messier 87 galaxy.
The two black holes look remarkably similar, even though our galaxy’s black hole is more than a thousand times smaller and less massive than M87* [3]. "We have two completely different types of galaxies and two very different black hole masses, but closeto the edge of these black holesthey look amazingly similar,” says Sera Markoff, Co-Chair of the EHT Science Council and a professor of theoretical astrophysics at the University of Amsterdam, the Netherlands."This tells us that General Relativity governs these objects up close, and any differences we see further away must be due to differences in the material that surrounds the black holes.”
This achievement was considerably more difficult than for M87*, even though Sgr A* is much closer to us. EHT scientist Chi-kwan (‘CK’) Chan, from Steward Observatory and Department of Astronomy and the Data Science Institute of the University of Arizona, USA, explains: “The gas in the vicinity of the black holes moves at the same speed — nearly as fast as light — around both Sgr A* and M87*. But where gas takes days to weeks to orbit the larger M87*, in the much smaller Sgr A* it completes an orbit in mere minutes. This means the brightness and pattern of the gas around Sgr A* were changing rapidly as the EHT Collaboration was observing it — a bit like trying to take a clear picture of a puppy quickly chasing its tail.”
The researchers had to develop sophisticated new tools that accounted for the gas movement around Sgr A*. While M87* was an easier, steadier target, with nearly all images looking the same, that was not the case for Sgr A*. The image of the Sgr A* black hole is an average of the different images the team extracted, finally revealing the giant lurking at the centre of our galaxy for the first time.
The effort was made possible through the ingenuity of more than 300 researchers from 80 institutes around the world that together make up the EHT Collaboration. In addition to developing complex tools to overcome the challenges of imaging Sgr A*, the team worked rigorously for five years, using supercomputers to combine and analyse their data, all while compiling an unprecedented library of simulated black holes to compare with the observations.
Scientists are particularly excited to finally have images of two black holes of very different sizes, which offers the opportunity to understand how they compare and contrast. They have also begun to use the new data to test theories and models of how gas behaves around supermassive black holes. This process is not yet fully understood but is thought to play a key role in shaping the formation and evolution of galaxies.
“Now we can study the differences between these two supermassive black holes to gain valuable new clues about how this important process works,” said EHT scientist Keiichi Asada from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei. “We have images for two black holes — one at the large end and one at the small end of supermassive black holes in the Universe — so we can go a lot further in testing how gravity behaves in these extreme environments than ever before.”
Progress on the EHT continues: a major observation campaign in March 2022 included more telescopes than ever before. The ongoing expansion of the EHT network and significant technological upgrades will allow scientists to share even more impressive images as well as movies of black holes in the near future.
Notes
[1] The individual telescopes involved in the EHT in April 2017, when the observations were conducted, were: the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder EXperiment (APEX), the IRAM 30-meter Telescope, the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope Alfonso Serrano (LMT), the Submillimeter Array (SMA), the UArizona Submillimeter Telescope (SMT), the South Pole Telescope (SPT). Since then, the EHT has added the Greenland Telescope (GLT), the NOrthern Extended Millimeter Array (NOEMA) and the UArizona 12-meter Telescpe on Kitt Peak to its network.
ALMA is a partnership of the European Southern Observatory (ESO; Europe, representing its member states), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan, together with the National Research Council (Canada), the Ministry of Science and Technology (MOST; Taiwan), Academia Sinica Institute of Astronomy and Astrophysics (ASIAA; Taiwan), and Korea Astronomy and Space Science Institute (KASI; Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, the Associated Universities, Inc./National Radio Astronomy Observatory (AUI/NRAO) and the National Astronomical Observatory of Japan (NAOJ). APEX, a collaboration between the Max Planck Institute for Radio Astronomy (Germany), the Onsala Space Observatory (Sweden) and ESO, is operated by ESO. The 30-meter Telescope is operated by IRAM (the IRAM Partner Organizations are MPG [Germany], CNRS [France] and IGN [Spain]). The JCMT is operated by the East Asian Observatory on behalf of The National Astronomical Observatory of Japan; ASIAA; KASI; the National Astronomical Research Institute of Thailand; the Center for Astronomical Mega-Science and organisations in the United Kingdom and Canada. The LMT is operated by INAOE and UMass, the SMA is operated by Center for Astrophysics | Harvard & Smithsonian and ASIAA and the UArizona SMT is operated by the University of Arizona. The SPT is operated by the University of Chicago with specialised EHT instrumentation provided by the University of Arizona.
The Greenland Telescope (GLT) is operated by ASIAA and the Smithsonian Astrophysical Observatory (SAO). The GLT is part of the ALMA-Taiwan project, and is supported in part by the Academia Sinica (AS) and MOST. NOEMA is operated by IRAM and the UArizona 12-meter telescope at Kitt Peak is operated by the University of Arizona.
[2] A strong basis for the interpretation of this new image was provided by previous research carried out on Sgr A*. Astronomers have known the bright, dense radio source at the centre of the Milky Way in the direction of the constellation Sagittarius since the 1970s. By measuring the orbits of several stars very close to our galactic centre over a period of 30 years, teams led by Reinhard Genzel (Director at the Max –Planck Institute for Extraterrestrial Physics in Garching near Munich, Germany) and Andrea M. Ghez (Professor in the Department of Physics and Astronomy at the University of California, Los Angeles, USA) were able to conclude that the most likely explanation for an object of this mass and density is a supermassive black hole. ESO's facilities (including the Very Large Telescope and the Very Large Telescope Interferometer) and the Keck Observatory were used to carry out this research, which shared the 2020 Nobel Prize in Physics.
[3] Black holes are the only objects we know of where mass scales with size. A black hole a thousand times smaller than another is also a thousand times less massive.
More information
This research was presented in six papers published today in The Astrophysical Journal Letters.
The EHT collaboration involves more than 300 researchers from Africa, Asia, Europe, North and South America. The international collaboration aims to capture the most detailed black hole images ever obtained by creating a virtual Earth-sized telescope. Supported by considerable international efforts, the EHT links existing telescopes using novel techniques — creating a fundamentally new instrument with the highest angular resolving power that has yet been achieved.
The EHT consortium consists of 13 stakeholder institutes; the Academia Sinica Institute of Astronomy and Astrophysics, the University of Arizona, the Center for Astrophysics | Harvard & Smithsonian, the University of Chicago, the East Asian Observatory, Goethe-Universitaet Frankfurt, Institut de Radioastronomie Millimétrique, Large Millimeter Telescope, Max Planck Institute for Radio Astronomy, MIT Haystack Observatory, National Astronomical Observatory of Japan, Perimeter Institute for Theoretical Physics, and Radboud University.
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
APEX, Atacama Pathfinder EXperiment, is a 12-metre diameter telescope, operating at millimetre and submillimetre wavelengths — between infrared light and radio waves. ESO operates APEX at one of the highest observatory sites on Earth, at an elevation of 5100 metres, high on the Chajnantor plateau in Chile’s Atacama region. The telescope is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO), and ESO.
The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration in astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates APEX and ALMA on Chajnantor, two facilities that observe the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society.
Links
Main papers:
Paper I: The Shadow of the Supermassive Black Hole in the Center of the Milky Way
Paper II: EHT and Multi-wavelength Observations, Data Processing, and Calibration
Paper III: Imaging of the Galactic Center Supermassive Black Hole
Paper IV: Variability, Morphology, and Black Hole Mass
Paper V: Testing Astrophysical Models of the Galactic Center Black Hole
Paper VI: Testing the Black Hole Metric
Supplementary papers:
Selective Dynamical Imaging of Interferometric Data
Millimeter Light Curves of Sagittarius A* Observed during the 2017 Event Horizon Telescope Campaign
A Universal Power Law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows
Characterizing and Mitigating Intraday Variability: Reconstructing Source Structure in Accreting Black Holes with mm-VLBI
ESO EHT web page
EHT Website & Press Release
Images of ALMA
Images of APEX
Contacts
Geoffrey Bower
EHT Project Scientist, Institute of Astronomy and Astrophysics, Academic Sinica, Taipei and University of Hawaii at Mnoa, US
Tel: +1-808-961-2945
Email: [email protected]
Huib Jan van Langevelde
EHT Project Director, JIVE and University of Leiden
Leiden, The Netherlands
Tel: +31-521-596515
Email: [email protected]
Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: [email protected]
Connect with ESO on social media
https://www.eso.org/public/news/eso2208-eht-mw/
Post by: eeergo on 05/12/2022 04:11 pm
I wonder why it's so tilted with respect to the galactic plane? I'd have expected it to have little or no tilt in that respect--meaning it would be edge-on to us. But, according to the paper, they eliminated all edge-on (aka "high-inclination") models (https://iopscience.iop.org/article/10.3847/2041-8213/ac6674#:~:text=All%20edge%2Don%20(high%20inclination)%20models%20fail%20the%20combined%20set%20of%20EHT%2Donly%20constraints%20for%20at%20least%20one%20simulation) and ended up with ones that were more face-on. That really surprises me.
Note that in the paper they are much more cautious than the casual language they used during the media event. The observations "disfavor" reconstruction simulations with high inclination (>50º) and strongly disfavor edge-on orientations. Still, that doesn't mean we're looking down its rotation axis.
Personally (and while admitting my expertise on this matter is very scant), the animation I posted above zooming in through the Galaxy towards SagA* in radio wavelengths left me intrigued as of the nature of the "ricochet-like" structures surrounding the black hole and their relative size. Wild guess probably any researcher in the field can cast lots of doubt upon in a couple of minutes - but I wonder if they are remnants of weak jets from slightly more active periods in SagA*'s life, or otherwise some ejection from it. They would seem to point to a non-zero inclination from a completely naïve point of view.
Post by: rsnellenberger on 05/12/2022 04:32 pm
I wonder why it's so tilted with respect to the galactic plane? I'd have expected it to have little or no tilt in that respect--meaning it would be edge-on to us. But, according to the paper, they eliminated all edge-on (aka "high-inclination") models (https://iopscience.iop.org/article/10.3847/2041-8213/ac6674#:~:text=All%20edge%2Don%20(high%20inclination)%20models%20fail%20the%20combined%20set%20of%20EHT%2Donly%20constraints%20for%20at%20least%20one%20simulation) and ended up with ones that were more face-on. That really surprises me.That struck me as well, but I'd guess it has a lot to do with the genesis and development of the galaxy -- e.g., how material in the proto-nebula entered the initial black hole, the resulting spin after past galactic mergers, etc.
I'll also be interested in whether the earlier analyses of interactions between the objects orbiting in close proximity to the hole will be revisited now that we have a better idea of the size and orientation of the accretion disk.
Post by: Star One on 05/12/2022 04:35 pm
Couldn’t it have got ‘disarranged’ by previous galactic mergers. We now have evidence for several of these and wouldn’t the black holes from the merging galaxies have sunk towards the centre and merged with Sagittarius-A*.I wonder why it's so tilted with respect to the galactic plane? I'd have expected it to have little or no tilt in that respect--meaning it would be edge-on to us. But, according to the paper, <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ac6674#:~:text=All%20edge%2Don%20(high%20inclination)%20models%20fail%20the%20combined%20set%20of%20EHT%2Donly%20constraints%20for%20at%20least%20one%20simulation">they eliminated all edge-on (aka "high-inclination") models</a> and ended up with ones that were more face-on. That really surprises me.That struck me as well, but I'd guess it has a lot to do with the genesis and development of the galaxy -- e.g., how material in the proto-nebula entered the initial black hole, the resulting spin after past galactic mergers, etc.
I'll also be interested in whether the earlier analyses of interactions between the objects orbiting in close proximity to the hole will be revisited now that we have a better idea of the size and orientation of the accretion disk.
Post by: eeergo on 05/12/2022 04:54 pm
Couldn’t it have got ‘disarranged’ by previous galactic mergers. We now have evidence for several of these and wouldn’t the black holes from the merging galaxies have sunk towards the centre and merged with Sagittarius-A*.I wonder why it's so tilted with respect to the galactic plane? I'd have expected it to have little or no tilt in that respect--meaning it would be edge-on to us. But, according to the paper, <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ac6674#:~:text=All%20edge%2Don%20(high%20inclination)%20models%20fail%20the%20combined%20set%20of%20EHT%2Donly%20constraints%20for%20at%20least%20one%20simulation">they eliminated all edge-on (aka "high-inclination") models</a> and ended up with ones that were more face-on. That really surprises me.That struck me as well, but I'd guess it has a lot to do with the genesis and development of the galaxy -- e.g., how material in the proto-nebula entered the initial black hole, the resulting spin after past galactic mergers, etc.
I'll also be interested in whether the earlier analyses of interactions between the objects orbiting in close proximity to the hole will be revisited now that we have a better idea of the size and orientation of the accretion disk.
Quote from one of the "forefathers" of this image:
https://twitter.com/hfalcke/status/1524749672715194377
Post by: Greg Hullender on 05/12/2022 05:04 pm
Or perhaps there was an off-center merger with the black hole from another galaxy sometime in the past. I wonder how destructive that would have been to the rest of the galaxy. Yes, that depends on the mass of the other black hole, but it needed to be massive enough to knock Sag. A* out of kilter, so probably a million solar masses or more.
Post by: rsnellenberger on 05/12/2022 07:21 pm
He's speaking to the large-scale structure in that quote, and I'm sure he's correct. What I was referring to is the merging of two galactic black holes with different sizes, spins, and orientations. If the nuclei of Andromeda and the Milky Way are gravitationally captured during the coming encounter, their central black holes will eventually merge into a black hole that reflects the spin and orientation of the components.Couldn’t it have got ‘disarranged’ by previous galactic mergers. We now have evidence for several of these and wouldn’t the black holes from the merging galaxies have sunk towards the centre and merged with Sagittarius-A*.I wonder why it's so tilted with respect to the galactic plane? I'd have expected it to have little or no tilt in that respect--meaning it would be edge-on to us. But, according to the paper, <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ac6674#:~:text=All%20edge%2Don%20(high%20inclination)%20models%20fail%20the%20combined%20set%20of%20EHT%2Donly%20constraints%20for%20at%20least%20one%20simulation">they eliminated all edge-on (aka "high-inclination") models</a> and ended up with ones that were more face-on. That really surprises me.That struck me as well, but I'd guess it has a lot to do with the genesis and development of the galaxy -- e.g., how material in the proto-nebula entered the initial black hole, the resulting spin after past galactic mergers, etc.
I'll also be interested in whether the earlier analyses of interactions between the objects orbiting in close proximity to the hole will be revisited now that we have a better idea of the size and orientation of the accretion disk.
Quote from one of the "forefathers" of this image:
https://twitter.com/hfalcke/status/1524749672715194377
Post by: deadman1204 on 05/12/2022 08:09 pm
Yes, the black hole is small compared to the Milky Way, but I'm not sure how that's relevant. You'd think that the material falling into it over the past 12 billion years would, on average, give it angular momentum with a spin axis pretty close to that of the galaxy itself.
Or perhaps there was an off-center merger with the black hole from another galaxy sometime in the past. I wonder how destructive that would have been to the rest of the galaxy. Yes, that depends on the mass of the other black hole, but it needed to be massive enough to knock Sag. A* out of kilter, so probably a million solar masses or more.
I've heard that the milky way is rather odd in that Sag A* is so small compared to the size of the galaxy. Our merger history is gentler and doesn't include alot of dwarf galaxies with their own super massive black holes.
Post by: eeergo on 05/13/2022 08:22 am
Yes, the black hole is small compared to the Milky Way, but I'm not sure how that's relevant. You'd think that the material falling into it over the past 12 billion years would, on average, give it angular momentum with a spin axis pretty close to that of the galaxy itself.
Or perhaps there was an off-center merger with the black hole from another galaxy sometime in the past. I wonder how destructive that would have been to the rest of the galaxy. Yes, that depends on the mass of the other black hole, but it needed to be massive enough to knock Sag. A* out of kilter, so probably a million solar masses or more.
Local movement (more specifically, the closest visible objects to the black hole, the S-stars - see for instance: https://en.wikipedia.org/wiki/Sagittarius_A (https://en.wikipedia.org/wiki/Sagittarius_A)*#/media/File:SgrA2018.gif) is pretty randomized. If they are representative of older objects since accreted by the hole, and I see no reason why they wouldn't be a priori, then it's not so counter-intuitive a thought that the angular momentum imparted to the hole by its progenitor masses would be completely randomly-oriented with respect to the large-scale structure of the Galaxy. Think also of how gravitational interactions in a much less dynamic environment, our own Solar System, can send things flying off out of the ecliptic plane fairly easily.
It takes a bit more perspective to think in these scales. By the same measure, first intuition would lead to believe that exosolar systems should have their planes aligned among themselves and with the galactic plane. Obviously that isn't true.
Alsol, see this important caveat:
https://twitter.com/TM_Eubanks/status/1524849743377080320
Post by: hoku on 05/13/2022 08:48 am
<snip>I think that scientists have been (and still are) trying to do this. One problem is to identify which of the many features in the Galactic Center environment might trace back to Sgr A*. The GC region is a very dynamic and energetic environment, as visualised in the attached MeerKAT radio images. Massive and very luminous stars add lots of "energy" in form of stellar winds and ionising radiation, and create bubbles and shockwaves once they go supernova. Ionised matter also attaches to magnetic fields (like, e.g., the "radio arc" feature to the "left" of the center).
... but I wonder if they are remnants of weak jets from slightly more active periods in SagA*'s life, or otherwise some ejection from it. They would seem to point to a non-zero inclination from a completely naïve point of view.
Note that the EHT image displays structures on scales of 50 micro-arc-seconds, while 1 pixel in the first attached MeerKAT image corresponds to 1 arc-seconds, i.e. a factor of more than 20 000 difference in angular resolution.
https://apod.nasa.gov/apod/ap220202.html (https://apod.nasa.gov/apod/ap220202.html)
Post by: eeergo on 05/13/2022 08:55 am
<snip>I think that scientists have been (and still are) trying to do this. One problem is to identify which of the many features in the Galactic Center environment might trace back to Sgr A*. The GC region is a very dynamic and energetic environment, as visualised in the attached MeerKAT radio images. Massive and very luminous stars add lots of "energy" in form of stellar winds and ionising radiation, and create bubbles and shockwaves once they go supernova. Ionised matter also attaches to magnetic fields (like, e.g., the "radio arc" feature to the "left" of the center).
... but I wonder if they are remnants of weak jets from slightly more active periods in SagA*'s life, or otherwise some ejection from it. They would seem to point to a non-zero inclination from a completely naïve point of view.
Note that the EHT image displays structures on scales of 50 micro-arc-seconds, while 1 pixel in the first attached MeerKAT image corresponds to 1 arc-seconds, i.e. a factor of more than 20 000 difference in angular resolution.
https://apod.nasa.gov/apod/ap220202.html (https://apod.nasa.gov/apod/ap220202.html)
Yeah, MeerKAT images are relevant to this discussion, but I was actually referring to the zoom-in of the central area. It shows a remarkably wispy, corkscrewy structure that may be FAR too small to be related to jets, I suspect, but still appears possibly correlated with the BH:
Post by: Star One on 05/13/2022 11:02 am
I thought it was the case that a lot of the merger history was with dwarf galaxies that may not have had central black holes.Yes, the black hole is small compared to the Milky Way, but I'm not sure how that's relevant. You'd think that the material falling into it over the past 12 billion years would, on average, give it angular momentum with a spin axis pretty close to that of the galaxy itself.
Or perhaps there was an off-center merger with the black hole from another galaxy sometime in the past. I wonder how destructive that would have been to the rest of the galaxy. Yes, that depends on the mass of the other black hole, but it needed to be massive enough to knock Sag. A* out of kilter, so probably a million solar masses or more.
I've heard that the milky way is rather odd in that Sag A* is so small compared to the size of the galaxy. Our merger history is gentler and doesn't include alot of dwarf galaxies with their own super massive black holes.
Post by: Star One on 05/13/2022 11:05 am
I certainly wouldn’t want to be an alien civilisation trying to exist in that environment.<snip>I think that scientists have been (and still are) trying to do this. One problem is to identify which of the many features in the Galactic Center environment might trace back to Sgr A*. The GC region is a very dynamic and energetic environment, as visualised in the attached MeerKAT radio images. Massive and very luminous stars add lots of "energy" in form of stellar winds and ionising radiation, and create bubbles and shockwaves once they go supernova. Ionised matter also attaches to magnetic fields (like, e.g., the "radio arc" feature to the "left" of the center).
... but I wonder if they are remnants of weak jets from slightly more active periods in SagA*'s life, or otherwise some ejection from it. They would seem to point to a non-zero inclination from a completely naïve point of view.
Note that the EHT image displays structures on scales of 50 micro-arc-seconds, while 1 pixel in the first attached MeerKAT image corresponds to 1 arc-seconds, i.e. a factor of more than 20 000 difference in angular resolution.
https://apod.nasa.gov/apod/ap220202.html (https://apod.nasa.gov/apod/ap220202.html)
Post by: ttle2 on 05/13/2022 01:41 pm
Post by: eeergo on 05/13/2022 02:03 pm
To keep things interesting, this appeared recently on arXiv: https://arxiv.org/abs/2205.04623. The authors have done an independent image reconstruction using the public M87 EHT data and claim that the famous ring could be an artifact.
Won't pretend to really follow their argument, much less be able to critique their result, but this claim should be pretty easy to disprove by the EHT Collaboration: just use test or calibration images of any other source known not to exhibit this annular shape and use the same procedures to show it doesn't mainly reconstruct as a ring no matter the FOV and reconstruction details supposedly biasing the final image into this shape.
Would be shocked if this claim hadn't crossed anyone's mind among 300 collaborators from different countries and affiliations, when the underlying cause is quite intuitive and they've had years to check and recheck, moreover after claims that remind of those unfounded ones thrown on LIGO regarding GW detection (against the arguments presented by only 3 researchers from interrelated institutions, who use the EHT's public data while most certainly missing some of the processing and calibration nuances, and whose reconstruction does look quite funky with artifacts).
Also the timing is suspicious -why publish a critique of M87*'s image at this very moment if not to call for attention- and the concluding remark too strong for a good-faith rebuke IMO.
Post by: Hobbes-22 on 05/13/2022 03:16 pm
Post by: eeergo on 05/13/2022 03:56 pm
On some other sites, I'm seeing claims that the original data for these images is only 2x3 pixels. Is there any merit to that claim?
No idea, but I'd appreciate help on the interpretation of this paragraph in the paper, just above figure 2:
Quote
The longest baselines have an interferometric fringe spacing of 1/∣ u ∣ ≈ 24 μas, which defines the diffraction-limited angular resolution of the EHT. The visibility amplitudes have two deep minima, the first at ∣ u ∣ ≈ 3.0 Gλ and the second at ∣ u ∣ ≈ 6.5 Gλ. The amplitudes have a baseline dependence that is similar to that of an infinitesimally thin ring with a 54 μas diameter that has been blurred with a circular Gaussian kernel with 23 μas FWHM. The ring diameter is primarily constrained by the minima locations, while the width is determined by the amplitude of the secondary visibility peak between the minima.
I must admit I haven't read the other technical papers yet, and as mentioned I don't have expertise in interferometry, but - is it me or does it read as if the inteferometer is diffraction-limited at the approximate thickness of both black hole images (20-something μas), and the interference fringes are a ring of the BH's inferred angular size with smearing equivalent to its width? That would be some bias, wouldn't it? Or am I reading it wrong (most likely)? If so, how should this be interpreted?
Post by: Star One on 05/13/2022 04:17 pm
To keep things interesting, this appeared recently on arXiv: https://arxiv.org/abs/2205.04623. The authors have done an independent image reconstruction using the public M87 EHT data and claim that the famous ring could be an artifact.Didn’t we get papers like this after the first announced detection of Gravitational Waves.
Post by: ttle2 on 05/13/2022 04:28 pm
Also the timing is suspicious -why publish a critique of M87*'s image at this very moment if not to call for attention- and the concluding remark too strong for a good-faith rebuke IMO.I think timing really is (mostly, at least) a coincidence. The paper was accepted a few days ago (they claim, but there's no reason to doubt it), but a paper this long must have spent at least a couple of months in the refereeing process and posting on arxiv after acceptance to a journal is what most people do.
I agree that the conclusion is blunt, though that could be partly due to cultural differences.
Post by: Dizzy_RHESSI on 05/13/2022 05:01 pm
To keep things interesting, this appeared recently on arXiv: https://arxiv.org/abs/2205.04623. The authors have done an independent image reconstruction using the public M87 EHT data and claim that the famous ring could be an artifact.
It's worth pointing out that this isn't the first independent analysis. Carilli and Thyagarajan used the same tools (CLEAN and hybrid mapping) but found a ring.
https://ui.adsabs.harvard.edu/abs/2022NatAs...6..259A/abstract
https://ui.adsabs.harvard.edu/abs/2022ApJ...924..125C/abstract
There has also been some discussion on twitter, including Falcke from EHT.
https://twitter.com/hfalcke/status/1525055070265548803?ref_src=twsrc%5Etfw
QuoteThe longest baselines have an interferometric fringe spacing of 1/∣ u ∣ ≈ 24 μas, which defines the diffraction-limited angular resolution of the EHT. The visibility amplitudes have two deep minima, the first at ∣ u ∣ ≈ 3.0 Gλ and the second at ∣ u ∣ ≈ 6.5 Gλ. The amplitudes have a baseline dependence that is similar to that of an infinitesimally thin ring with a 54 μas diameter that has been blurred with a circular Gaussian kernel with 23 μas FWHM. The ring diameter is primarily constrained by the minima locations, while the width is determined by the amplitude of the secondary visibility peak between the minima.
I must admit I haven't read the other technical papers yet, and as mentioned I don't have expertise in interferometry, but - is it me or does it read as if the inteferometer is diffraction-limited at the approximate thickness of both black hole images (20-something μas), and the interference fringes are a ring of the BH's inferred angular size with smearing equivalent to its width? That would be some bias, wouldn't it? Or am I reading it wrong (most likely)? If so, how should this be interpreted?
They don't measure the width, it's unresolved. What happens when you don't resolve a feature? You see the true scene convolved with the beam, which in this case is 24 uas. They're just saying that their visibility amplitudes are well fit by an infinitesimally narrow annulus which is then degraded to their resolution.
Post by: eeergo on 05/13/2022 05:55 pm
Quote from: Dizzy_RHESSI link=topic=42331.msg2368398#msg2368398
QuoteThe longest baselines have an interferometric fringe spacing of 1/∣ u ∣ ≈ 24 μas, which defines the diffraction-limited angular resolution of the EHT. The visibility amplitudes have two deep minima, the first at ∣ u ∣ ≈ 3.0 Gλ and the second at ∣ u ∣ ≈ 6.5 Gλ. The amplitudes have a baseline dependence that is similar to that of an infinitesimally thin ring with a 54 μas diameter that has been blurred with a circular Gaussian kernel with 23 μas FWHM. The ring diameter is primarily constrained by the minima locations, while the width is determined by the amplitude of the secondary visibility peak between the minima.
I must admit I haven't read the other technical papers yet, and as mentioned I don't have expertise in interferometry, but - is it me or does it read as if the inteferometer is diffraction-limited at the approximate thickness of both black hole images (20-something μas), and the interference fringes are a ring of the BH's inferred angular size with smearing equivalent to its width? That would be some bias, wouldn't it? Or am I reading it wrong (most likely)? If so, how should this be interpreted?
They don't measure the width, it's unresolved. What happens when you don't resolve a feature? You see the true scene convolved with the beam, which in this case is 24 uas. They're just saying that their visibility amplitudes are well fit by an infinitesimally narrow annulus which is then degraded to their resolution.
Thanks, that explanation is highly appreciated.
If I may follow up: what is exactly meant by "visibility amplitude"? I may be lacking important terminology. I've been reading it as saying that this annulus is "built into" their image through diffraction and resolution smearing, which as you say then gets convolved with the scene - but wouldn't that then introduce the evident bias that most resolution-limited scenes would appear to show this ring, no matter their true shape... which coincidentally has the same approximate angular diameter as the observed object, which is also coincidentally the same apparent size as M87*? Where am I veering off course, since this would be too obvious a bias?
Post by: Dizzy_RHESSI on 05/13/2022 08:28 pm
Thanks, that explanation is highly appreciated.
If I may follow up: what is exactly meant by "visibility amplitude"? I may be lacking important terminology. I've been reading it as saying that this annulus is "built into" their image through diffraction and resolution smearing, which as you say then gets convolved with the scene - but wouldn't that then introduce the evident bias that most resolution-limited scenes would appear to show this ring, no matter their true shape... which coincidentally has the same approximate angular diameter as the observed object, which is also coincidentally the same apparent size as M87*? Where am I veering off course, since this would be too obvious a bias?
You're welcome.
A visibility is what is measured from correlating the output of two telescopes, it is a Fourier component of the image. Different baseline lengths probe different scales (spatial frequencies). A visibility has an amplitude and a phase, the later is generally more complicated to calibrate in VLBI. The amplitudes alone however carry a lot of information about the structure of the source. The fact that there are minima in the plot of visibility amplitude vs baseline length tells you something is resolved. Interpreting the data this way doesn't involve any imaging. The model annulus that they're comparing their visibilities to is not from their imaging, it is an idealised annulus. This is separate from their imaging, it's just a simple way of showing that the data seem to be consistent with an annulus. In the real imaging they use all the data, not just the visibility amplitudes.
Post by: catdlr on 03/27/2024 03:48 am
Quote
For those unaware: the Event Horizon Telescope team are the masterminds behind the stunning images of the Sagittarius A* & M87* black holes shown below.
So this could be a particularly interesting announcement. 😮
Quote
So apparently the Event Horizon Telescope @ehtelescope folks have a big announcement this week, and the embargo lifts Wednesday at 9am.
Post by: catdlr on 03/27/2024 06:11 pm
Quote
Breaking news: the Event Horizon Telescope team unveils strong magnetic fields spiraling at the edge of Milky Way’s central black hole, Sagittarius A*. This new image suggests that strong magnetic fields may be common to all black holes.
Post by: Blackstar on 03/27/2024 08:36 pm
Post by: Torbjorn Larsson, OM on 04/01/2024 07:19 pm
Quote
The new images reveal even more similarities Between Sgr A* and M87* than the previous. An earlier study of M87* revealed the black hole launched jets of material into space and the current results suggest that the same might be happening at Sgr A*. Moreover, the similarities suggest that some processes are similar for all black holes, regardless of differences in mass and size.
Besides once again supporting the MAD model of the magnetic fields, jets (however temporary) could help explain the Milky Way central Fermi X-ray and eROSITA gamma bubbles.
https://www.seramarkoff.com/2021/02/to-be-mad-or-not-to-be-mad/ (https://www.seramarkoff.com/2021/02/to-be-mad-or-not-to-be-mad/)
https://astrobites.org/2022/07/04/you-mad-flow-the-hot-accretion-flow-of-the-m87-supermassive-black-hole/ (https://astrobites.org/2022/07/04/you-mad-flow-the-hot-accretion-flow-of-the-m87-supermassive-black-hole/)