Author Topic: Astronomy Thread  (Read 35996 times)

Offline Star One

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Exoplanet Thread
« Reply #60 on: 06/13/2017 08:24 AM »
I still can't help wonder if there are more planets in the large gap.
« Last Edit: 06/13/2017 08:31 AM by Star One »

Offline Bynaus

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Re: Exoplanet Thread
« Reply #61 on: 06/13/2017 08:36 AM »
Sounds like a 55 Cancri analogue system. A few gas giants on closely packed orbits, with a large, slightly eccentric jovian at ca. 5 AU. The resonance of the innermost two jovians at 55 Cnc is closer to 3:1, and there are more known planets in the 55 Cnc system (a hot super-Earth and a light-weight gas giant in the "gap"), but the similarities are striking (surprisingly, the authors do not mention that in their paper).
« Last Edit: 06/13/2017 08:37 AM by Bynaus »

Offline Star One

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Re: Exoplanet Thread
« Reply #62 on: 06/13/2017 08:35 PM »
New evidence that all stars are born in pairs

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Did our sun have a twin when it was born 4.5 billion years ago?

Almost certainly yes — though not an identical twin. And so did every other sunlike star in the universe, according to a new analysis by a theoretical physicist from the University of California, Berkeley, and a radio astronomer from the Smithsonian Astrophysical Observatory at Harvard University.

Many stars have companions, including our nearest neighbor, Alpha Centauri, a triplet system. Astronomers have long sought an explanation. Are binary and triplet star systems born that way? Did one star capture another? Do binary stars sometimes split up and become single stars?

Astonomers have even searched for a companion to our sun, a star dubbed Nemesis because it was supposed to have kicked an asteroid into Earth’s orbit that collided with our planet and exterminated the dinosaurs. It has never been found.

The new assertion is based on a radio survey of a giant molecular cloud filled with recently formed stars in the constellation Perseus, and a mathematical model that can explain the Perseus observations only if all sunlike stars are born with a companion.

“We are saying, yes, there probably was a Nemesis, a long time ago,” said co-author Steven Stahler, a UC Berkeley research astronomer.

“We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud, and the only model that could reproduce the data was one in which all stars form initially as wide binaries. These systems then either shrink or break apart within a million years.”

http://news.berkeley.edu/2017/06/13/new-evidence-that-all-stars-are-born-in-pairs/

Offline Star One

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Re: Exoplanet Thread
« Reply #63 on: 06/14/2017 07:46 PM »
Mistaken brown dwarf is actually two planets orbiting each other

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Finding massive planets is nothing new these days. But finding them orbiting each other instead of orbiting a star is unprecedented. An object initially thought to be a single brown dwarf is actually a pair of giant worlds. It’s not yet clear how this binary system formed, but the discovery may help redefine the line between planets and brown dwarfs – failed stars with tens of times the mass of Jupiter.

This pair of planets is made up of two balls of gas the size of Jupiter but almost four times more massive, separated by some 600 million kilometres, and slowly circling each other once per century or so. The young couple only emits light at infrared wavelengths, with residual heat from their formation, just 10 million years ago.

Observations with the 10-metre Keck II telescope, by a team led by William Best of the University of Hawaii, uncovered the binary system, with the help of adaptive optics that correct for the blurring effects of Earth’s atmosphere.

https://www.newscientist.com/article/2134712-mistaken-brown-dwarf-is-actually-two-planets-orbiting-each-other

Offline CuddlyRocket

Re: Exoplanet Thread
« Reply #64 on: 06/14/2017 11:51 PM »
Quote
But are they really planets? Maybe not. In the past, the dividing line between planets and brown dwarfs was generally placed at 14 Jupiter masses, when nuclear fusion of deuterium in the object’s core sets in.

But Latham argues that the best way to distinguish between the two is not by their mass but by how they form: brown dwarfs result from collapsing clouds of gas and dust, while planets form out of a stellar disk.

I think a lot (most, probably) of astronomers who have an opinion would say that these are not planets because they don't orbit a star or stellar remnant. But they're probably not rogue planets either, because it seems unlikely they were ejected from a stellar system as a binary couple. The problem with Latham's suggestion would seem to be how do you tell the difference between a solo brown dwarf and a solo rogue planet? And is there a minimum size, or is every pebble a brown dwarf? (Though this may not matter in practice as it would probably be difficult to detect anything smaller than a gas giant.)

Offline clongton

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Re: Exoplanet Thread
« Reply #65 on: 06/16/2017 12:20 AM »
... how do you tell the difference between a solo brown dwarf and a solo rogue planet?

I suspect that would be the core temperature. A brown dwarf would be quite a bit warmer than a rogue planet, even a rocky one with a molten core.
« Last Edit: 06/16/2017 12:22 AM by clongton »
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Offline jebbo

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Re: Exoplanet Thread
« Reply #66 on: 06/19/2017 09:37 AM »
An announcement from the Pale Red Dot team is expected at 11am CET:

https://twitter.com/Pale_red_dot/status/876530355523776513

Almost certainly to do with their Barnard's Star campaign (which started a couple of months ago)

--- Tony

Offline Alpha_Centauri

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Re: Exoplanet Thread
« Reply #67 on: 06/19/2017 10:22 AM »
Sounds like it is just announcing the search rather than any discoveries yet.

Offline jebbo

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Re: Exoplanet Thread
« Reply #68 on: 06/19/2017 10:40 AM »
Yes.  Search started on June 15th. I got the impression from one of the team that they started looking at Barnard's Star earlier, but apparently not.

They will also be looking at Ross 154 (a flare star).  Home to "Glory Station" in Cherryh's Alliance/Union setting.

--- Tony
« Last Edit: 06/19/2017 10:42 AM by jebbo »

Offline Star One

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Exoplanet Thread
« Reply #69 on: 06/19/2017 10:49 AM »
Sounds like it is just announcing the search rather than any discoveries yet.

I was under the impression there has been an ongoing examination of Barnard's star?

Yes.  Search started on June 15th. I got the impression from one of the team that they started looking at Barnard's Star earlier, but apparently not.

They will also be looking at Ross 154 (a flare star).  Home to "Glory Station" in Cherryh's Alliance/Union setting.

--- Tony

Seems a bit pointless to prioritise a flare star in the search.
« Last Edit: 06/19/2017 10:50 AM by Star One »

Offline Alpha_Centauri

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Re: Exoplanet Thread
« Reply #70 on: 06/19/2017 10:56 AM »
Proxima is a flare star too, many M dwarfs are.  It's the occupational hazard.

Speaking of which they will also be observing Proxima again for further planets.  Data to be released in real-time.
« Last Edit: 06/19/2017 11:03 AM by Alpha_Centauri »

Offline jebbo

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Re: Exoplanet Thread
« Reply #71 on: 06/19/2017 11:03 AM »
Seems a bit pointless to prioritise a flare star in the search.

Why? The point of this is to find the nearest planets (i.e. that are the most susceptible to follow-up).

Flare stars (well all M dwarfs really) are a bit problematic for habitability, but - depending on the initial water fraction - it is not ruled out.

--- Tony

Offline Star One

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Exoplanet Thread
« Reply #72 on: 06/19/2017 11:20 AM »
Seems a bit pointless to prioritise a flare star in the search.

Why? The point of this is to find the nearest planets (i.e. that are the most susceptible to follow-up).

Flare stars (well all M dwarfs really) are a bit problematic for habitability, but - depending on the initial water fraction - it is not ruled out.

--- Tony

I assumed obviously mistakenly by the fact that the OP classed it as a flare star that they were indicating that even amongst M dwarfs it's was very active, otherwise why mention it?
« Last Edit: 06/19/2017 11:44 AM by Star One »

Offline jebbo

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Re: Exoplanet Thread
« Reply #73 on: 06/19/2017 11:55 AM »
I assumed obviously mistakenly by the fact that the OP classed it as a flare star that they were indicating that even amongst M dwarfs it's was very active, otherwise why mention it?

It is more active than most - it is a UV Ceti type star, with major flares every couple of days or so - which I thought worth mentioning, that's all.

Its age is thought to be <1Gyr so it is a fairly young star, but this age is poorly constrained (gyrochronology!), and M dwarfs become less active with age.

And from a different angle, looking at active flare stars will help us understand the effects of flares.

--- Tony

Offline Star One

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Exoplanet Thread
« Reply #74 on: 06/19/2017 12:02 PM »
As a general point are they going to try and tie down Proxima C which I believe is meant to be a larger planet further out than b?
« Last Edit: 06/19/2017 12:02 PM by Star One »

Offline jebbo

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Re: Exoplanet Thread
« Reply #75 on: 06/19/2017 12:25 PM »
As a general point are they going to try and tie down Proxima C which I believe is meant to be a larger planet further out than b?

The ESO presser talks about more than one terrestrial sized planet, and there is a linear trend in the Proxima b RV data, so it will help. But whether the campaign will be long enough to confirm a "c" and its period is another question

Edit: there are variations in the 200-300 days and ~40day periods as well. A post is forthcoming on their website.

--- Tony
« Last Edit: 06/19/2017 12:27 PM by jebbo »

Offline Star One

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Re: Exoplanet Thread
« Reply #76 on: 06/19/2017 08:34 PM »
Article on the same.

Pale Red Dot: Campaign 2

https://www.centauri-dreams.org/?p=37964

Offline CuddlyRocket

Re: Exoplanet Thread
« Reply #77 on: 06/20/2017 06:11 AM »
Cross-posting to provide links to relevant posts in the Kepler Updates thread:

NASA Releases Kepler Survey Catalog with Hundreds of New Planet Candidates
Here is the briefing material ... [and] the archived video of the press conference:

Quote
... precise measurements of thousands of planets, [reveals] two distinct groups of small planets ... a clean division in the sizes of rocky, Earth-size planets and gaseous planets smaller than Neptune. Few planets were found between those groupings. ...

“We like to think of this study as classifying planets in the same way that biologists identify new species of animals,” said Benjamin Fulton, doctoral candidate at the University of Hawaii in Manoa, and lead author of the second study. “Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree.”

It seems that nature commonly makes rocky planets up to about 75 percent bigger than Earth. For reasons scientists don't yet understand, about half of those planets take on a small amount of hydrogen and helium that dramatically swells their size, allowing them to "jump the gap" and join the population closer to Neptune’s size.

This is what is being called by some (not Benjamin - though he possibly doesn't object! :) ) the Fulton Gap. He gives an explanation in the video as to why it might arise.

Offline jebbo

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Re: Exoplanet Thread
« Reply #78 on: 06/20/2017 10:36 AM »
This is what is being called by some (not Benjamin - though he possibly doesn't object! :) ) the Fulton Gap. He gives an explanation in the video as to why it might arise.

The original paper is here https://arxiv.org/abs/1703.10375, and predates the latest DR25 release.

The gap is also known as the "photoevaporation desert" ;-)

--- Tony




Offline Alpha_Centauri

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Re: Exoplanet Thread
« Reply #79 on: 06/20/2017 11:16 AM »
The photoevaporation desert and the Fulton gap are separate as far as I know. You can see this in the bottom diagram page 12. The photoevaporation desert is the noticeable lack of Neptunes in the very highest insolations, top left. The Fulton gap is the distinct relatively low occurrence gap marked by the crossing point between the two lines denoting the atmospheric loss and gas poor models (the point being the data did not rule out either cause).
« Last Edit: 06/20/2017 11:17 AM by Alpha_Centauri »