Mysterious hot spots observed in a cool red supergiant

Apr 24, 2013
Comparison between the red supergiant Antares and the Sun, shown as the tiny dot toward the upper right. The black circle is the size of the orbit of Mars. Arcturus is also included in the picture for size comparison. Credit: Wikipedia.

(Phys.org) —Astronomers have released a new image of the outer atmosphere of Betelgeuse – one of the nearest red supergiants to Earth – revealing the detailed structure of the matter being thrown off the star.

The new image, taken by the e-MERLIN operated from the Jodrell Bank Observatory in Cheshire, also shows regions of surprisingly hot gas in the star's outer atmosphere and a cooler arc of gas weighing almost as much as the Earth.

Betelgeuse is easily visible to the unaided eye as the bright, red star on the shoulder of Orion the Hunter. The star itself is huge – 1,000 times larger than our Sun – but at a distance of about 650 it still appears as a tiny dot in the sky, so special techniques combining telescopes in arrays are required to see details of the star and the region around it.

The new e-MERLIN image of Betelgeuse – published in the journal Monthly Notices of the Royal Astronomical Society, shows its atmosphere extends out to five times the size of the visual surface of the star. It reveals two within the outer atmosphere and a faint arc of cool gas even farther out beyond the radio surface of the star.

The hot spots are separated by roughly half the visual diameter of the star and have a temperature of about 4,000-5,000 Kelvin, much higher than the of the radio surface of the star (about 1,200 Kelvin) and even higher than the visual surface (3,600 Kelvin). The arc of cool gas lies almost 7.4 billion kilometres away from the star – about the same distance as the farthest Pluto gets from the Sun. It is estimated to have a mass almost two thirds that of the Earth and a temperature of about 150 Kelvin.

Lead author Dr Anita Richards, from The University of Manchester, said that it was not yet clear why the hot spots are so hot. She said: "One possibility is that , caused either by the star pulsating or by convection in its outer layers, are compressing and heating the gas. Another is that the outer atmosphere is patchy and we are seeing through to hotter regions within. The arc of cool gas is thought to be the result of a period of increased mass loss from the star at some point in the last century but its relationship to structures like the hot spots, which lie much closer in, within the star's , is unknown."

The mechanism by which supergiant stars like Betelgeuse lose matter into space is not well understood despite its key role in the lifecycle of matter, enriching the interstellar material from which future stars and planets will form. Detailed high-resolution studies of the regions around massive stars like the ones presented here are essential to improving our understanding.

Dr Richards, who is based in Manchester's School of Physics and Astronomy, added: "Betelgeuse produces a wind equivalent to losing the mass of the Earth every three years, enriched with the chemicals that will go into the next generation of star and planet formation. The full detail of how these cool, evolved launch their winds is one of the remaining big questions in stellar astronomy.

"This is the first direct image showing hot spots so far from the centre of the star. We are continuing radio and microwave observations to help decide which mechanisms are most important in driving the stellar wind and producing these hot spots. This won't just tell us how the elements that form the building blocks of life are being returned to space, it will also help determine how long it is before explodes as a supernova."

Future observations planned with e-MERLIN and other arrays, including ALMA and VLA, will test whether the hotspots vary in concert due to pulsation, or show more complex variability due to convection. If it is possible to measure a rotation speed this will identify in which layer of the star they originate.

Explore further: Young binary star system may form planets with weird and wild orbits

More information: 'e-MERLIN resolves Betelgeuse at wavelength 5 cm: hotspots at 5R*,' Monthly Notices of the Royal Astronomical Society, 2013.

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User comments : 8

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Ophelia
1 / 5 (4) Apr 24, 2013
What is that image of size comparisons of Antares doing with this article about Betelgeuse? Antares isn't even mentioned in the article, just the caption!

Hire some editors. These types of errors are rampant here.
Q-Star
1.9 / 5 (9) Apr 24, 2013
Antares was shown to relate how much larger Betelgeuse is compared to the "typical" red supergiant. So it was not an error, it was a very good example to show how extremely large Betelgeuse is.

By the By; Your umbrage should be directed to the University of Manchester, they wrote the article and provided the illustrations.

Be that as it may,,, wouldn't be just an awesome thing to be alive when Betelgeuse goes supernova?
Ophelia
1 / 5 (7) Apr 24, 2013
At Q-star:
Antares was shown to relate how much larger Betelgeuse is compared to the "typical" red supergiant. So it was not an error, it was a very good example to show how extremely large Betelgeuse is.
Nothing in the article relates Antares to Betelgeuse in any way. That makes the image inclusion an error or any omission of relating language an error. No words such as "typical" found.

Your umbrage should be directed to the University of Manchester, they wrote the article and provided the illustrations.
While the University isn't off the hook, that doesn't excuse sloppily passing on unedited nonsensical press releases here. Nothing is apparently ever edited. I just finished another article on this site where bits and pieces of two or three different sentences talking about different things were all mashed together to produce absolute gibberish.
Kaymen
1.5 / 5 (6) Apr 25, 2013
Could these hotspots be what is left of planets?
antialias_physorg
5 / 5 (2) Apr 25, 2013
Could these hotspots be what is left of planets?

That still wouldn't explain why they appear hotter than the general atmosphere of the star.

wouldn't be just an awesome thing to be alive when Betelgeuse goes supernova?

I dunno. Betelgeuse is at the sort of distance where it could affect us (if we happen to be caught in th GRB shooting out the poles. Which is pretty unlikley, but still...)

It would also play hob with "The Hitchhiker's Guide to the Galaxy" timeline...
yyz
5 / 5 (3) Apr 25, 2013
"Betelgeuse is at the sort of distance where it could affect us (if we happen to be caught in th GRB shooting out the poles. Which is pretty unlikley, but still...)"

Fortunately a 1998 study of Betelgeuse using spatially resolved UV spectra from Hubble suggested that the poles are inclined ~20 degrees to our line of sight: http://iopscience...ulltext/

The UV flux of the star in a SN outburst has also been estimated to be lower than that of the Sun. But it should put on an amazing light show for observers on Earth, with an estimated apparent magnitude of -12: http://en.wikiped...upernova
antialias_physorg
5 / 5 (2) Apr 25, 2013
20 degrees is uncomfortably close. A bit of a wobble ... (OK, for stuff that magnitude such a 'bit' of a wobble is unlikely but then again: supernova explosions are pretty violent by all acconuts)

The shere scale of Betelgeuse boggles the mind. And to think there are even bigger stars out there (for comparison: VY Canis majoris has a radius about twice as big..and Westerlund 1 may be even bigger than that)
Q-Star
1.8 / 5 (10) Apr 25, 2013
Well if it has to happen, I would rather go out seeing a red supergiant go supernova than say, something as mundane as a super asteroid or comet crashing into my world (or house even). And it would place me (us) in a very elite group of humanity (being the last of that paltry group.)

I mean if ya have to go, it may as be extraordinary, right?