ICRAR: Star Clusters Discovery Could Upset the Astronomical Applecart

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bystander
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ICRAR: Star Clusters Discovery Could Upset the Astronomical Applecart

Postby bystander » Tue Mar 07, 2017 4:14 pm

Star Clusters Discovery Could Upset the Astronomical Applecart
International Centre for Radio Astronomy Research | 2017 Mar 06

The discovery of young stars in old star clusters could send scientists back to the drawing board for one of the universe’s most common objects.

Dr. Bi-Qing For, from the International Centre for Radio Astronomy Research in Perth, said our understanding of how stars evolve is a cornerstone of astronomical science. “There are a billion trillion stars in the universe and we’ve been observing and classifying those we can see for more than a century,” she said. “Our models of stellar evolution are based on the assumption that stars within star clusters formed from the same material at roughly the same time.”

A star cluster is a group of stars that share a common origin and are held together by gravity for some length of time. Because star clusters are assumed to contain stars of similar age and composition, researchers have used them as an “astronomical laboratory” to understand how mass affects the evolution of stars. “If this assumption turns out to be incorrect, as our findings suggest, then these important models will need to be revisited and revised,” Dr. For said.

The discovery involves a study of star clusters located in the Large Magellanic Cloud, a neighbouring galaxy to the Milky Way. By cross-matching the locations of several thousand young stars with the locations of stellar clusters, the researchers found 15 stellar candidates that were much younger than other stars within the same cluster. ...

A Discovery of Young Stellar Objects in Older Clusters of the Large Magellanic Cloud - Bi-Qing For, Kenji Bekki
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Re: ICRAR: Star Clusters Discovery Could Upset the Astronomical Applecart

Postby Ann » Tue Mar 07, 2017 7:21 pm

IC 2602 with Theta Carina.
Photo: Roberto Mura.
Young stellar objects in older clusters is nothing new. In the cluster known as "the Southern Pleiades", IC 2602, the brightest member is younger than the other members of the cluster.

Wikipedia wrote about binary star Theta Carina:

The primary component in this system is a blue straggler, which is a type of star that is created by the interaction between two or more stars. Most likely the source of this mass transfer was the secondary member of the system, and what is now the primary star was probably once the secondary component. At an estimated age of 4 million years,[6] this star is much younger than the age of the surrounding IC 2602 cluster, which is consistent with it being a straggler.


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Re: ICRAR: Star Clusters Discovery Could Upset the Astronomical Applecart

Postby BDanielMayfield » Tue Mar 07, 2017 9:55 pm

Hi Ann. I agree, and this doesn't really "upset the astronomical applecart" at all. Headline hype. The Wikipedia link you kindly provided reports that Theta Carina is a very close orbit binary with a 2.2 day orbit. Mass transfer would be a given for massive stars in close orbits. The age they report (4 million years) seems misleading too. If this binary formed along with all the other members of the open cluster that they are imbedded in (the most reasonable assumption) the true age for both stars would still be the same age as cluster IC 2602, which is about 50 million years.

Therefore this blue beauty isn't being honest about her age. She's had work done, a facelift of sorts preformed by her sister!

Bruce
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Re: ICRAR: Star Clusters Discovery Could Upset the Astronomical Applecart

Postby Ann » Wed Mar 08, 2017 4:48 am

BDanielMayfield wrote:Hi Ann. I agree, and this doesn't really "upset the astronomical applecart" at all. Headline hype. The Wikipedia link you kindly provided reports that Theta Carina is a very close orbit binary with a 2.2 day orbit. Mass transfer would be a given for massive stars in close orbits. The age they report (4 million years) seems misleading too. If this binary formed along with all the other members of the open cluster that they are imbedded in (the most reasonable assumption) the true age for both stars would still be the same age as cluster IC 2602, which is about 50 million years.

Therefore this blue beauty isn't being honest about her age. She's had work done, a facelift of sorts preformed by her sister!

Bruce


I like the "facelift" quip! :D

I would guess that the spectral characteristics of Theta Carina suggests that it can't be more than about 4 million years. A massive but unevolved star of spectral type B0V should be young, and if it was born with all the mass it has today, it couldn't possibly be 50 million years. It shouldn't be that old, anyway!

But like you said... I guess Theta Carina is another example of the classic Algol case. One star steals mass from its close companion and ends up being bright and blue, looking much younger than it really is.

To be honest, however, this isn't quite the scenario that bystander described. Blue stragglers inside globular clusters (and even populous open clusters) are already well known. I think the text refers to stars that were born from mass that was expelled from older stars.

The Cat's Eye Nebula and surrounding halo.
Photo: Nordic Optical Telescope and Romano Corradi.
Consider the picture at left of the well-known planetary nebula, the Cat's Eye Nebula. The small bright nebula is surrounded by a huge halo of expelled gas and dust. I think the text that bystander refers to suggests that new stars could form from this kind of expelled mass from old stars.

It would take very special circumstances for this kind of expelled gas and dust to become dense and cool enough to be ripe for star formation. Perhaps two asymptotic giant branch stars expelling dust at the same time could do the trick together, if their expelled dust was colliding.

In any case, I believe that only quite low-mass stars could form this way, and it should be a rare occurrence anyway.

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Re: ICRAR: Star Clusters Discovery Could Upset the Astronomical Applecart

Postby BDanielMayfield » Wed Mar 08, 2017 1:03 pm

Ah. I see what happened here. The star and cluster Ann brought up was not from the study this topic is discussing. Any excuse will do to talk about blue, eh Ann? :lol2: Oh well, glad you liked the quip.

Ok then, so the applecart was rocked, but only just a little. A second, very limited bout of star formation in clusters can occur, fed by mass loss from AGB stars. Cool. Think three dimensionally: the intersection of the spherically expanding wind fronts from 3 AGB stars would be a good place for gas & dust to pile up ...

Bruce
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Re: ICRAR: Star Clusters Discovery Could Upset the Astronomical Applecart

Postby neufer » Wed Mar 08, 2017 2:22 pm

Click to play embedded YouTube video.
BDanielMayfield wrote:
Ah. I see what happened here. The star and cluster Ann brought up was not from the study this topic is discussing. Any excuse will do to talk about blue, eh Ann? :lol2: Oh well, glad you liked the quip.

Ok then, so the applecart was rocked, but only just a little. A second, very limited bout of star formation in clusters can occur, fed by mass loss from AGB stars. Cool. Think three dimensionally: the intersection of the spherically expanding wind fronts from 3 AGB stars would be a good place for gas & dust to pile up ...
Art Neuendorffer

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Re: ICRAR: Star Clusters Discovery Could Upset the Astronomical Applecart

Postby Ann » Wed Mar 08, 2017 2:55 pm

BDanielMayfield wrote:Ah. I see what happened here. The star and cluster Ann brought up was not from the study this topic is discussing. Any excuse will do to talk about blue, eh Ann? :lol2: Oh well, glad you liked the quip.

Bruce


O f course I liked the quip, and of course I'll take any chance to talk about blue! :D I couldn't resist Robert Mura's picture of Theta Carina and IC 2602, particularly because it really showed us that Theta Carina itself is bluer than the other stars in the cluster! : happy blue smiley:

Oh, and Billie Holiday is fine too, but I prefer blue as blue...

Ann
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