Chalmers: Red Giant Image Gives Glimpse of Sun's Future

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Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby bystander » Tue Nov 07, 2017 5:02 pm

ALMA’s Image of Red Giant Star Gives a Surprising Glimpse of the Sun’s Future
Chalmer's University of Technology | 2017 Nov 07

A Chalmers-led team of astronomers has for the first time observed details on the surface of an aging star with the same mass as the Sun. ALMA's images show that the star is a giant, its diameter twice the size of Earth’s orbit around the Sun, but also that the star’s atmosphere is affected by powerful, unexpected shock waves. The research is published in Nature Astronomy on 30 October 2017.

​A team of astronomers led by Wouter Vlemmings, Chalmers University of Technology, have used the telescope ALMA (Atacama Large Millimetre/Submillimetre Array) to make the sharpest observations yet of a star with the same starting mass as the Sun. The new images show for the first time details on the surface of the red giant W Hydrae, 320 light years distant in the constellation of Hydra, the Water Snake.

W Hydrae is an example of an AGB (asymptotic giant branch) star. Such stars are cool, bright, old and lose mass via stellar winds. The name derives from their position on the famous Hertzsprung-Russell diagram, which classifies stars according to their brightness and temperature. ...

The Shock-Heated Atmosphere of an Asymptotic Giant Branch Star Resolved by ALMA - Wouter Vlemmings et al
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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby BDanielMayfield » Tue Nov 07, 2017 5:55 pm

The article makes a big deal out of W_Hydrae, https://en.wikipedia.org/wiki/W_Hydrae being the same mass as the Sun. However, the mass of this star is so vaguely known that no estimate of its mass is even given in the current referenced Wikipedia article. That may change soon of course, but the claim that this star would be an accurate predictor of the Sun's far future fate is questionable. Even if it can be shown that this star is the Sun's mass now, it must have been quite a bit more massive in the past when it was as old as Sol is now. (Editted because, the more massive a star is, the faster it evolves off the MS.)

Therefore it wouldn't be sound science to conclude that our Sun will bloat out to a size of twice the Earth's orbit from this star's current size. There are just too many unknowns.

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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby geckzilla » Tue Nov 07, 2017 6:20 pm

BDanielMayfield wrote:The article makes a big deal out of W_Hydrae, https://en.wikipedia.org/wiki/W_Hydrae being the same mass as the Sun. However, the mass of this star is so vaguely known that no estimate of its mass is even given in the current referenced Wikipedia article. That may change soon of course, but the claim that this star would be an accurate predictor of the Sun's far future fate is questionable. Even if it can be shown that this star is the Sun's mass now, it must have been quite a bit more massive in the past when it was as old as Sol is now.

Therefore it wouldn't be sound science to conclude that our Sun will bloat out to a size of twice the Earth's orbit from this star's current size. There are just too many unknowns.

I'm wondering if you read the papers referenced by the article or just Wikipedia. It appears to me that Wikipedia is not a comprehensive source regarding this particular star. Much more is known regarding the mass of gas surrounding the star than is reflected by what is presented at Wikipedia.
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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby BDanielMayfield » Tue Nov 07, 2017 6:43 pm

That's a fair question geck. I had read the abstract of the paper that the article bystander referred to to open this thread. Here it is:
Our current understanding of the chemistry and mass-loss processes in solar-like stars at the end of their evolution depends critically on the description of convection, pulsations and shocks in the extended stellar atmosphere. Three-dimensional hydrodynamical stellar atmosphere models provide observational predictions, but so far the resolution to constrain the complex temperature and velocity structures seen in the models has been lacking. Here we present submillimeter continuum and line observations that resolve the atmosphere of the asymptotic giant branch star W Hya. We show that hot gas with chromospheric characteristics exists around the star. Its filling factor is shown to be small. The existence of such gas requires shocks with a cooling time larger than commonly assumed. A shocked hot layer will be an important ingredient in the models of stellar convection, pulsation and chemistry that underlie our current understanding of the late stages of stellar evolution.
The underline is mine, to point out the only connection to the Sun made in the abstract. Then I scanned though the paper, looking for anything about this star's mass. This is all I could find, toward the end of the article:
The highest outflow velocity that matches the spectra is ~20 km s-1 which equal to the escape velocity from W Hya at 1.8 R★, assuming the star has a mass of ~1 M¤ (29).

So, the only reference in this paper to this red giant's mass assumes that it is 1 solar mass today. It would have to be less than the Sun's mass today for it to be a good "glimpse of Sun's Future".

The reporter and or editor of this news drew conclusions that the authors of the paper did not make. The moral of this story: Science reports should be read with a degree of skepticism. Headline hype strikes again.

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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby geckzilla » Tue Nov 07, 2017 9:23 pm

Sure, but notice that (29) is a reference to yet <a href="https://arxiv.org/pdf/1702.02016.pdf">another paper</a>, which you would then have to check out to see how they arrived at that conclusion and decide from there if the assumption is really as vague as you think it is. I'm under the impression that the Chalmers article authors either know enough to be able to write as they did, or were in communication with the scientists who did the research. So yes, it could still be wrong, but it's not like it's a CNN article or random blog from someone who completely misunderstood it.
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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby BDanielMayfield » Tue Nov 07, 2017 11:55 pm

geckzilla wrote:Sure, but notice that (29) is a reference to yet <a href="https://arxiv.org/pdf/1702.02016.pdf">another paper</a>, which you would then have to check out to see how they arrived at that conclusion and decide from there if the assumption is really as vague as you think it is. I'm under the impression that the Chalmers article authors either know enough to be able to write as they did, or were in communication with the scientists who did the research. So yes, it could still be wrong, but it's not like it's a CNN article or random blog from someone who completely misunderstood it.

Here's what reference 29 is, from the paper being discussed here:
29. T. Danilovich, R. Lombaert, L. Decin, A. Karakas, M. Maercker, H. Oloffson, Water isotopologues in the circumstellar envelopes of M-type AGB stars, Astron. Astrophys, 602, A14, 11 pp.(2017)

I'll happily peruse that paper if a link is provided, but from its title I wouldn't think it was a study of stellar mass. They possibly where just using earlier assumptions about what W Hya's mass might be.

My gripe is that the average viewer of this:ALMA’s Image of Red Giant Star Gives a Surprising Glimpse of the Sun’s Future
Chalmer's University of Technology | 2017 Nov 07

A Chalmers-led team of astronomers has for the first time observed details on the surface of an aging star with the same mass as the Sun. ALMA's images show that the star is a giant, its diameter twice the size of Earth’s orbit around the Sun, but also that the star’s atmosphere is affected by powerful, unexpected shock waves. The research is published in Nature Astronomy on 30 October 2017.

​A team of astronomers led by Wouter Vlemmings, Chalmers University of Technology, have used the telescope ALMA (Atacama Large Millimetre/Submillimetre Array) to make the sharpest observations yet of a star with the same starting mass as the Sun. The new images show for the first time details on the surface of the red giant W Hydrae, 320 light years distant in the constellation of Hydra, the Water Snake.

W Hydrae is an example of an AGB (asymptotic giant branch) star. Such stars are cool, bright, old and lose mass via stellar winds. The name derives from their position on the famous Hertzsprung-Russell diagram, which classifies stars according to their brightness and temperature. ...
might well conclude that the Earth is toast, when that wasn't what the Astronomers doing the work where saying at all.

The work they did was great, btw. Actually resolving the gasses being blown off the surface of a star is remarkable. That's what should have been focused on.

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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby geckzilla » Wed Nov 08, 2017 12:44 am

You'd have to point to me exactly what you think is wrong, then. I don't understand. The headline seems fine and so does the content of the article.
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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby BDanielMayfield » Wed Nov 08, 2017 12:53 am

geckzilla wrote:You'd have to point to me exactly what you think is wrong, then. I don't understand. The headline seems fine and so does the content of the article.

I will, as soon as I have more time. To be continued...
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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby geckzilla » Wed Nov 08, 2017 1:31 am

No worries.
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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby BDanielMayfield » Sat Nov 11, 2017 12:20 am

BDanielMayfield wrote:
geckzilla wrote:You'd have to point to me exactly what you think is wrong, then. I don't understand. The headline seems fine and so does the content of the article.

I will, as soon as I have more time. To be continued...


Ok, here is my problem with this news report. It hypes an overstated prediction of the Sun's future, when the scientific work being reported never even mentioned W Hydrae as a solar analog or that this star could or should be used to forecast the Sun's future. That's just something written to attract attention to the report, not something the astronomers were saying in the paper, and it misleads people into believing something that isn't true.

Look again at the paragraphs bystander first quoted, in which I've highlighted in red the problematic statements:
bystander wrote:ALMA’s Image of Red Giant Star Gives a Surprising Glimpse of the Sun’s Future
Chalmer's University of Technology | 2017 Nov 07

A Chalmers-led team of astronomers has for the first time observed details on the surface of an aging star with the same mass as the Sun. ALMA's images show that the star is a giant, its diameter twice the size of Earth’s orbit around the Sun, but also that the star’s atmosphere is affected by powerful, unexpected shock waves. The research is published in Nature Astronomy on 30 October 2017.

​A team of astronomers led by Wouter Vlemmings, Chalmers University of Technology, have used the telescope ALMA (Atacama Large Millimetre/Submillimetre Array) to make the sharpest observations yet of a star with the same starting mass as the Sun. The new images show for the first time details on the surface of the red giant W Hydrae, 320 light years distant in the constellation of Hydra, the Water Snake.

W Hydrae is an example of an AGB (asymptotic giant branch) star. Such stars are cool, bright, old and lose mass via stellar winds. The name derives from their position on the famous Hertzsprung-Russell diagram, which classifies stars according to their brightness and temperature. ...

The Shock-Heated Atmosphere of an Asymptotic Giant Branch Star Resolved by ALMA - Wouter Vlemmings et al

Just how big the Sun will get when it becomes a red giant is unknown, but reports I've come across say that the Earth might just escape engulfment, the issue is too close to call. But any casual reader of this article might well think that this is proof that now we know for sure; the Earth's going to be swallowed. I think that this would be big news, if it was right. If it was a reasonable conclusion, don't you think the authors of the paper would have made it in their paper? They didn't, because it wasn't a reasonable conclusion to make.

Now look again at the bold assertions I highlighted. The reporter (not the authors) states that W Hydrae is "an ageing star with the same mass as the Sun" and then he or she goes even further and claims that it is "a star with the same starting mass as the Sun." That would make it a true solar analog if it were true, but how the heck can that be known? That isn't a claim made by the paper's authors. Where's the proof that W Hydrae is such a close match of the Sun?

I wonder, what do the stellar lists say about W Hydrae?

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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby MargaritaMc » Sat Nov 11, 2017 6:42 pm

There's a good article here from AAVSO about W Hydrae
https://www.aavso.org/vsots_whya
But no mention of its mass.

However, we know that W Hydrae is on the Asymptotic Giant Branch so we can infer that it is an intermediate mass star, a category which comprises stars which have between either 0.6–10 solar masses (according to Wikipedia https://en.m.wikipedia.org/wiki/Asymptotic_giant_branch) or 80% and eight times the Sun's mass (according the the ESO
https://www.eso.org/public/images/0409-evolution-of-stars-individual-paths-1/)

The authors of the paper under discussion write:
https://arxiv.org/abs/1711.01153
Our current understanding of the chemistry and mass-loss processes in solar-like stars at the end of their evolution depends critically on the description of convection, pulsations and shocks in the extended stellar atmosphere.

and the phrase "solar-like" might have led to the references in the press release to W Hydrae being like the sun.

Regarding the sun's future, there is a useful set of lecture notes here
http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html
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Re: Chalmers: Red Giant Image Gives Glimpse of Sun's Future

Postby BDanielMayfield » Sun Nov 12, 2017 1:35 pm

MargaritaMc wrote:There's a good article here from AAVSO about W Hydrae
https://www.aavso.org/vsots_whya
But no mention of its mass.

However, we know that W Hydrae is on the Asymptotic Giant Branch so we can infer that it is an intermediate mass star, a category which comprises stars which have between either 0.6–10 solar masses (according to Wikipedia https://en.m.wikipedia.org/wiki/Asymptotic_giant_branch) or 80% and eight times the Sun's mass (according the the ESO
https://www.eso.org/public/images/0409-evolution-of-stars-individual-paths-1/)

The authors of the paper under discussion write:
https://arxiv.org/abs/1711.01153
Our current understanding of the chemistry and mass-loss processes in solar-like stars at the end of their evolution depends critically on the description of convection, pulsations and shocks in the extended stellar atmosphere.

and the phrase "solar-like" might have led to the references in the press release to W Hydrae being like the sun.

That is all very interesting Margarita, thanks for that input. I note that this somewhat famous star is a loner, like our Sun. This fact would explain the lack of info on its mass, as, significantly to this discussion, it is impossible for us to accurately measure the mass of lone objects in space. The mass of stars in single star systems can only be estimated (guessed at) by comparison with other stars with known masses. In the case of stars like W Hyd that are currently undergoing rapid mass loss an accurate determination of its current and starting masses would seem to be quite beyond our ability. Sure, this star is an older, "solar-like" star, but the report goes way beyond that, basically claiming that it is exactly like the Sun except for its age. What credible source has ever made this claim? That's the big beef I have with this report. W Hyd would be way more famous than it is if it really was a true solar analog, but this is an unsupported claim.

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Kyoto: Winds Blowing Off a Dying Star

Postby bystander » Sun Nov 12, 2017 2:37 pm

Winds Blowing Off a Dying Star
Kyoto University | ALMA (NAOJ) | 2017 Nov 10

Stars like our Sun eject large amounts of gas and dust into space, containing various elements and compounds. Asymptotic giant branch -- AGB -- phase stars, near their end of life, are particularly significant sources of such substances in our galaxy.

Formation of dust around AGB stars has been considered to play an important role in triggering acceleration of stellar wind, but the detailed mechanism of this acceleration has not been well explained.

And there is yet another conundrum. In space, silicon is ten times more abundant than aluminum. However, many oxygen-rich AGB stars are rich in aluminum oxide dust -- the major carrier of aluminum -- but poor in silicate dust -- the carrier of silicon, which has puzzled researchers: why is aluminum oxide dust so abundant around oxygen-rich AGB stars?

In a paper published in Science Advances, a research team led by Aki Takigawa of Kyoto University have utilized the Atacama Large Millimeter/submillimeter Array -- ALMA, as the high spatial-resolution radio interferometer in Chile is known -- to obtain detailed images of gas molecules forming dust surrounding an AGB star. ...

These new results shed light not only on the dynamics of gas and dust surrounding stars, but also on the importance of studying both together. The team plans to continue using ALMA to elucidate gas and dust dynamics in the universe.

Dust formation and wind acceleration around the aluminum oxide–rich AGB star W Hydrae - Aki Takigawa et al
Last edited by bystander on Mon Nov 13, 2017 4:51 pm, edited 1 time in total.
Reason: Added direct Kyoto U link and NAOJ ALMA link
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Re: Kyoto: Winds Blowing Off a Dying Star

Postby BDanielMayfield » Sun Nov 12, 2017 3:25 pm

bystander wrote:Winds Blowing Off a Dying Star
Kyoto University | via EurekAlert | 2017 Nov 10

Stars like our Sun eject large amounts of gas and dust into space, containing various elements and compounds. Asymptotic giant branch -- AGB -- phase stars, near their end of life, are particularly significant sources of such substances in our galaxy.

Formation of dust around AGB stars has been considered to play an important role in triggering acceleration of stellar wind, but the detailed mechanism of this acceleration has not been well explained.

And there is yet another conundrum. In space, silicon is ten times more abundant than aluminum. However, many oxygen-rich AGB stars are rich in aluminum oxide dust -- the major carrier of aluminum -- but poor in silicate dust -- the carrier of silicon, which has puzzled researchers: why is aluminum oxide dust so abundant around oxygen-rich AGB stars?

In a paper published in Science Advances, a research team led by Aki Takigawa of Kyoto University have utilized the Atacama Large Millimeter/submillimeter Array -- ALMA, as the high spatial-resolution radio interferometer in Chile is known -- to obtain detailed images of gas molecules forming dust surrounding an AGB star. ...

These new results shed light not only on the dynamics of gas and dust surrounding stars, but also on the importance of studying both together. The team plans to continue using ALMA to elucidate gas and dust dynamics in the universe.

Dust formation and wind acceleration around the aluminum oxide–rich AGB star W Hydrae - Aki Takigawa et al

Now see, this report about work done with the same tools and the same target is a fine example of science reporting. There's no need to over hype things.

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