Largest yellow hypergiant star spotted

Mar 12, 2014
HR 5171, the brightest star just below the centre of this wide-field image, is a yellow hypergiant, a very rare type of stars with only a dozen known in our galaxy. Its size is over 1,300 times that of the Sun -- one of the 10 largest stars found so far. Observations with ESO's Very Large Telescope Interferometer have shown that it is actually a double star, with the companion in contact with the main star. Credit: ESO/Digitized Sky Survey 2

ESO's Very Large Telescope has revealed the largest yellow star—and one of the 10 largest stars found so far. This hypergiant has been found to measure more than 1,300 times the diameter of the Sun, and to be part of a double star system, with the second component so close that it is in contact with the main star. Observations spanning over 60 years also indicate that this remarkable object is changing very rapidly.

Using ESO's Very Large Telescope Interferometer (VLTI), Olivier Chesneau (Observatoire de la Côte d'Azur, Nice, France) and an international team of collaborators have found that the yellow hypergiant star HR 5171 A is absolutely huge—1300 times the of the Sun and much bigger than was expected. This makes it the largest yellow star known. It is also in the top ten of the largest known—50% larger than the famous red supergiant Betelgeuse—and about one million times brighter than the Sun.

"The new observations also showed that this star has a very close binary partner, which was a real surprise," says Chesneau. "The two stars are so close that they touch and the whole system resembles a gigantic peanut."

The astronomers made use of a technique called interferometry to combine the light collected from multiple individual telescopes, effectively creating a giant telescope up to 140 metres in size. The new results prompted the team to thoroughly investigate older observations of the star spanning more than sixty years, to see how it had behaved in the past.

Yellow hypergiants are very rare, with only a dozen or so known in our galaxy—the best-known example being Rho Cassiopeiae. They are among the biggest and brightest stars known and are at a stage of their lives when they are unstable and changing rapidly. Due to this instability, yellow hypergiants also expel material outwards, forming a large, extended atmosphere around the star.

Despite its great distance of nearly 12 000 light-years from Earth, the object can just about be seen with the naked eye by the keen-sighted. HR 5171 A has been found to be getting bigger over the last 40 years, cooling as it grows, and its evolution has now been caught in action. Only a few stars are caught in this very brief phase, where they undergo a dramatic change in temperature as they rapidly evolve.

By analysing data on the star's varying brightness, using observations from other observatories, the astronomers confirmed the object to be an eclipsing binary system where the smaller component passes in front and behind the larger one as it orbits. In this case HR 5171 A is orbited by its companion star every 1300 days. The smaller companion is only slightly hotter than HR 5171 A's surface temperature of 5000 degrees Celsius.

Chesneau concludes "The companion we have found is very significantas it can have an influence on the fate of HR 5171 A, for example, stripping off its outer layers and modifying its evolution."

This new discovery highlights the importance of studying these huge and short-lived yellow hypergiants, and could provide a means of understanding the evolutionary processes of massive stars in general.

Explore further: Bright star reveals new exoplanet

More information: This research was presented in a paper "The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in the common envelope phase", by Chesneau et al., to appear in the journal Astronomy & Astrophysics. arxiv.org/pdf/1401.2628v2.pdf

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antialias_physorg
5 / 5 (12) Mar 12, 2014
"The two stars are so close that they touch and the whole system resembles a gigantic peanut."

Oh, to have a probe close by and get some live video of one star churning through another's chromosphere (or even photosphere). That would be an awesome sight to behold.
marklade
Mar 12, 2014
This comment has been removed by a moderator.
Tuxford
1.3 / 5 (12) Mar 12, 2014
Very massive, and very active, and ejecting a lot of material. Fits the model, of growing from within.

Otherwise you can go with the conventional very weak explanation: that it is unstable because it is big. And leave it at that. Whew...

HOW did it get so big??? And with a very close companion? Is it swarmed by other companions just dying to join the party? Is that how? Don't tell me it is accumulating gas, while blowing gas at the same time. Better to just ignore these questions, like this article does.

I am beginning to understand the illogical nature of physical scientists. Glad I became an aerospace engineer instead.
antialias_physorg
4.4 / 5 (14) Mar 12, 2014
I am beginning to understand the illogical nature of physical scientists.


So let me get this straight:
Fits the model, of growing from within.

Making shit up is better than solid calculations?

Riiiiight.
Tuxford
1 / 5 (9) Mar 12, 2014
Yes, I understand your confusion. For the simple-minded with limited powers of insight, it must seem like magic.

http://starburstf...mulator/
Skepticus
not rated yet Mar 12, 2014
This is 12,000 years old news.
RealScience
5 / 5 (10) Mar 12, 2014
Glad I became an aerospace engineer instead.


@Tuxford - Do you commercial airplanes, and, if so, which company do you work for?
thermodynamics
4.7 / 5 (12) Mar 12, 2014
Glad I became an aerospace engineer instead.


@Tuxford - Do you commercial airplanes, and, if so, which company do you work for?


RealScience: Thank you for this public service announcement. You can help us improve air safety with questions like this. I will be looking forward to Tuxford's reply so I can decide what not to fly on. Thank you again for saving lives.
Solon
not rated yet Mar 12, 2014

Oh, to have a probe close by and get some live video of one star churning through another's chromosphere (or even photosphere). That would be an awesome sight to behold.

I've been waiting a long time hoping to see a live video of [i]our[/i] Sun, from space. Or the Moon even.
Vietvet
4.2 / 5 (5) Mar 13, 2014
@thermodynamics, best post I've read today!
RealScience
5 / 5 (3) Mar 13, 2014

... so I can decide what not to fly on...


Exactly - but I figured that if I put that into the question, Tuxford would be less likely to answer.