Author Topic: ESA - Gaia updates  (Read 123667 times)

Offline eeergo

Re: ESA - Gaia updates
« Reply #140 on: 04/25/2018 12:52 pm »
I had never seen such a map before (I suppose some previous version of it, even with a rough spatial binning, existed?) but I like it :)
-DaviD-

Offline jebbo

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Re: ESA - Gaia updates
« Reply #141 on: 04/25/2018 12:57 pm »
I had never seen such a map before (I suppose some previous version of it, even with a rough spatial binning, existed?) but I like it :)

I've not seen anything like that before either, and it was the thing that most surprised me: spatial galactic radial velocity differences.
« Last Edit: 04/25/2018 12:57 pm by jebbo »

Offline eeergo

Re: ESA - Gaia updates
« Reply #142 on: 04/25/2018 01:18 pm »
I had never seen such a map before (I suppose some previous version of it, even with a rough spatial binning, existed?) but I like it :)

I've not seen anything like that before either, and it was the thing that most surprised me: spatial galactic radial velocity differences.

It makes sense these "counter-currents" are located as shown, since it has been known for a long time the Sun lies in the periphery of a galactic arm (in fact, one of the first science-related trivia I remember from when I was a child was this one nugget!). However, our location almost precisely at the boundary between such large volumes of opposite movement -2 kpc wide no less, 6500 light-years!- really drives home the relative uniqueness of our neighborhood. I wonder what effects, if any, this "borderland" condition has on the dynamics and compositions of our local neighborhood or Solar System.

Relative because there's probably more than half a Mpc's worth of such "unique" areas in the combined Milky Way's arm boundaries :)
-DaviD-

Offline Star One

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Re: ESA - Gaia updates
« Reply #143 on: 04/25/2018 03:17 pm »
How many hypervelocity stars are there in the catalogue?

Offline jebbo

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Re: ESA - Gaia updates
« Reply #144 on: 04/25/2018 03:30 pm »
It makes sense these "counter-currents" are located as shown, since it has been known for a long time the Sun lies in the periphery of a galactic arm (in fact, one of the first science-related trivia I remember from when I was a child was this one nugget!).

I'm not at all sure this is related to the spiral structure. The colours are Vr (i.e. radial velocity relative to the galactic centre).  As all the stars are orbiting the centre in roughly circular orbits, this spatial distributiuon is surprising - at least to me, but I must admit to not knowing much about galaxies ...

--- Tony


Offline Star One

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Re: ESA - Gaia updates
« Reply #145 on: 04/25/2018 03:41 pm »
New data release sparks astronomy revolution

Quote
Astronomy professor Helmi lead author of one of six papers describing the quality of the Gaia data

Quote
The data shows, for example, two satellite galaxies with a very similar trajectory. This suggests they share a common origin. The trajectories of satellite galaxies are also governed by how the mass of the Milky Way is distributed, especially in the halo. ‘We can now estimate the mass distribution in the halo of the Milky Way more accurately, and this is where dark matter dominates and dictates the motion of stars, globular clusters and satellite galaxies. This means we should be able to probe much more directly the nature of dark matter and test whether the law of Gravity needs modification.

https://www.rug.nl/news/2018/04/new-data-release-sparks-astronomy-revolution

Offline as58

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Re: ESA - Gaia updates
« Reply #146 on: 04/25/2018 03:47 pm »
It makes sense these "counter-currents" are located as shown, since it has been known for a long time the Sun lies in the periphery of a galactic arm (in fact, one of the first science-related trivia I remember from when I was a child was this one nugget!).

I'm not at all sure this is related to the spiral structure. The colours are Vr (i.e. radial velocity relative to the galactic centre).  As all the stars are orbiting the centre in roughly circular orbits, this spatial distributiuon is surprising - at least to me, but I must admit to not knowing much about galaxies ...

--- Tony

Where's the map from? I can't find it on the ESA site and I'd like to see some explanation about it.

Offline jebbo

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Re: ESA - Gaia updates
« Reply #147 on: 04/25/2018 03:50 pm »
Where's the map from? I can't find it on the ESA site and I'd like to see some explanation about it.

It was shown in the press conference, but I can't find it on the site [ and they talked about it as galactic radial velocity, which matches the VbarR on the plot ].  The lady presenting likened it to ripples in a pond.

--- Tony

Offline jebbo

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Re: ESA - Gaia updates
« Reply #148 on: 04/25/2018 04:18 pm »
This one is also very nice, clearly showing the rotation of the galaxy.

--- Tony

Offline Star One

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ESA - Gaia updates
« Reply #149 on: 04/25/2018 05:06 pm »
Gaia second data release

« Last Edit: 04/25/2018 05:07 pm by Star One »

Offline eeergo

Re: ESA - Gaia updates
« Reply #150 on: 04/26/2018 12:52 am »
It makes sense these "counter-currents" are located as shown, since it has been known for a long time the Sun lies in the periphery of a galactic arm (in fact, one of the first science-related trivia I remember from when I was a child was this one nugget!).

I'm not at all sure this is related to the spiral structure. The colours are Vr (i.e. radial velocity relative to the galactic centre).  As all the stars are orbiting the centre in roughly circular orbits, this spatial distributiuon is surprising - at least to me, but I must admit to not knowing much about galaxies ...

--- Tony

Where's the map from? I can't find it on the ESA site and I'd like to see some explanation about it.

https://twitter.com/rdrimmel/status/989083026213785601

My intuitive and not at all specialized understanding leads me to think the denser, star-rich arm regions are moving in roughly circular orbits with a small component that draws them inwards towards the center, while the more sparsely populated areas outside the arms get pushed outwards. No idea what the implications are for this, or if it was expected based on prior knowledge though.
-DaviD-

Offline ugordan

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Re: ESA - Gaia updates
« Reply #151 on: 04/26/2018 07:08 am »
This is pretty neat, Kepler original field of view with Gaia-supplied proper motions extrapolated 500 000 years into the past and into the future:

https://twitter.com/meg_bedell/status/989322975261396992

Video attached

Offline jebbo

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Re: ESA - Gaia updates
« Reply #152 on: 04/26/2018 08:01 am »
The papers are now available on Arxiv.  List here

Offline Alpha_Centauri

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Re: ESA - Gaia updates
« Reply #153 on: 04/26/2018 11:11 am »
It makes sense these "counter-currents" are located as shown, since it has been known for a long time the Sun lies in the periphery of a galactic arm (in fact, one of the first science-related trivia I remember from when I was a child was this one nugget!).

I'm not at all sure this is related to the spiral structure. The colours are Vr (i.e. radial velocity relative to the galactic centre).  As all the stars are orbiting the centre in roughly circular orbits, this spatial distributiuon is surprising - at least to me, but I must admit to not knowing much about galaxies ...

--- Tony

Where's the map from? I can't find it on the ESA site and I'd like to see some explanation about it.
It's in the paper "Gaia Data Release 2: Mapping the Milky Way disc kinematics"

https://arxiv.org/pdf/1804.09380.pdf

Offline Star One

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Re: ESA - Gaia updates
« Reply #154 on: 04/26/2018 07:54 pm »
Article summing up some of the groups working on the Gaia data.

https://blogs.scientificamerican.com/observations/the-milky-way-revealed-as-never-before/

Offline Phil Stooke

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Re: ESA - Gaia updates
« Reply #155 on: 04/26/2018 08:25 pm »
The elliptical map (Mollweide projection of the sky) is in galactic coordinates.  The plane of the galaxy, if you like, the galactic equator, is the line running horizontally through the middle of the ellipse.  The center of the galaxy is in the middle of the map.  If you are looking towards the middle of the galaxy, the stars orbiting closer to the center are moving away from us to the left and towards us to the right of center, producing the red and blue shifts.  If you turn around and face outwards, away from the galactic center, you are now looking at the hemisphere of the sky which, in this projection, is split and appended to the left and right ends of the elliptical whole-sky map.  We are moving faster than the more distant stars, so the ones to our left (but on the right half of the map) are falling behind, moving away from us, so are red-shifted.  The stars to our right (looking outwards), on the left half of the map, are the ones we are 'overtaking', so they are getting closer and are blue-shifted. 

If the division of the sky like this seems puzzling, look at a Mollweide projection of Earth - the middle region is one hemisphere, the crescent-shaped appendages on each side are the opposite hemisphere.

Offline AegeanBlue

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Re: ESA - Gaia updates
« Reply #156 on: 04/30/2018 06:10 pm »
UK's contribution to Gaia:

https://stfc.ukri.org/news/3-d-map-of-the-milky-way/

So the UK Space Agency is funding £4 million a year in processing. Considering that the project is computationally very intensive and getting a result is an issue of getting crunching power and not just good software, this is good news. Now, if only the other countries that are members of Gaia DPAC would put out this sort of press release.


Offline AlexA

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Re: ESA - Gaia updates
« Reply #158 on: 05/01/2018 10:17 am »
Interesting paper:

https://arxiv.org/abs/1804.08351

Quote
SETI with Gaia: The observational signatures of nearly complete Dyson spheres

Erik Zackrisson, Andreas J. Korn, Ansgar Wehrhahn, Johannes Reiter

(Submitted on 23 Apr 2018)

A star enshrouded in a Dyson sphere with high covering fraction may manifest itself as an optically subluminous object with a spectrophotometric distance estimate significantly in excess of its parallax distance. Using this criterion, the Gaia mission will in coming years allow for Dyson-sphere searches that are complementary to searches based on waste-heat signatures at infrared wavelengths. A limited search of this type is also possible at the current time, by combining Gaia parallax distances with spectrophotometric distances from ground-based surveys. Here, we discuss the merits and shortcomings of this technique and carry out a limited search for Dyson-sphere candidates in the sample of stars common to Gaia Data Release 1 and RAVE Data Release 5. We find that a small fraction of stars indeed display distance discrepancies of the type expected for nearly complete Dyson spheres. To shed light on the properties of objects in this outlier population, we present follow-up high-resolution spectroscopy for one of these stars, the late F-type dwarf TYC 6111-1162-1. The spectrophotometric distance of this object is about twice that derived from its Gaia parallax, and there is no detectable infrared excess. While our analysis largely confirms the stellar parameters and the spectrophotometric distance inferred by RAVE, a plausible explanation for the discrepant distance estimates of this object is that the astrometric solution has been compromised by an unseen binary companion, possibly a rather massive white dwarf (≈1 M ⊙  ). This scenario can be further tested through upcoming Gaia data releases.

Offline Star One

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Re: ESA - Gaia updates
« Reply #159 on: 05/01/2018 04:53 pm »
Interesting paper:

https://arxiv.org/abs/1804.08351

Quote
SETI with Gaia: The observational signatures of nearly complete Dyson spheres

Erik Zackrisson, Andreas J. Korn, Ansgar Wehrhahn, Johannes Reiter

(Submitted on 23 Apr 2018)

A star enshrouded in a Dyson sphere with high covering fraction may manifest itself as an optically subluminous object with a spectrophotometric distance estimate significantly in excess of its parallax distance. Using this criterion, the Gaia mission will in coming years allow for Dyson-sphere searches that are complementary to searches based on waste-heat signatures at infrared wavelengths. A limited search of this type is also possible at the current time, by combining Gaia parallax distances with spectrophotometric distances from ground-based surveys. Here, we discuss the merits and shortcomings of this technique and carry out a limited search for Dyson-sphere candidates in the sample of stars common to Gaia Data Release 1 and RAVE Data Release 5. We find that a small fraction of stars indeed display distance discrepancies of the type expected for nearly complete Dyson spheres. To shed light on the properties of objects in this outlier population, we present follow-up high-resolution spectroscopy for one of these stars, the late F-type dwarf TYC 6111-1162-1. The spectrophotometric distance of this object is about twice that derived from its Gaia parallax, and there is no detectable infrared excess. While our analysis largely confirms the stellar parameters and the spectrophotometric distance inferred by RAVE, a plausible explanation for the discrepant distance estimates of this object is that the astrometric solution has been compromised by an unseen binary companion, possibly a rather massive white dwarf (≈1 M ⊙  ). This scenario can be further tested through upcoming Gaia data releases.

https://forum.nasaspaceflight.com/index.php?PHPSESSID=aco9gun18v8geg40198mkbtb86;topic=43914.msg1814143#msg1814143

I didn’t post it in here as I know some forum members are hyper allergic to any mention of SETI.

Tags: gaia 
 

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