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Betelgeuse is one of the largest stars known in our galaxy, a red supergiant, and now astronomers have taken the highest-resolution image ever so far. They used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile for their observations, and not only was it the first time that ALMA had observed this star, but it succeeded in producing the highest-resolution of Betelgeuse currently available.
Not only is Betelgeuse gigantic, about 1,400 times the radius of the Sun, it is also very active. In 2013, astronomers saw plumes of gas erupting from the star, which were almost as large as our Solar System. There is also a huge "bubble" boiling away on the star's surface. These observations show how gas and dust are being shredded by the star at an incredible rate.
Betelgeuse is about 640 light-years away in the constellation Orion. Even though it is so massive, it is young, being only an estimated 8 million years old (compared to about 4.6 billion for our Sun). But it is also already nearing the end of its life and is thought to be on the verge of becoming a supernova. Whenever that happens, estimated to be within the next 100,000 years or so, the explosion would be bright enough to be seen in daytime on Earth, although it is too far away to pose any danger to us.
Betelgeuse is large enough that its disk can be resolved by telescopes, while most stars still only look like tiny points of light, even in the biggest telescopes.
Betelgeuse compared to our Solar System
The new image shows a large bright spot, and the orange color isn't what you would see with your eyes since ALMA observes stars in wavelengths beyond what human eyes can detect. An odd feature is the apparent "lump" on the left side of the star - that isn't a real physical part of the star, it is simply an area where the star is hotter and denser. There is other gas around the region of the lump, but ALMA can't see it; the gas in the lump area, however, is warm enough for it to be visible in the ALMA images. The bright spot may be a similar region of warmer gas, but is being viewed against the surface of the star itself. Phil Plait explains all of this nicely in his latest blog post.
Specifically, ALMA studies the hot gases in Betelgeuse's lower chromosphere at sub-millimeter wavelengths - this is where localized increased temperatures help to explain why the star does not appear symmetric.
According to astronomer Dr. Eamon O’Gorman at the Dublin Institute for Advanced Studies, “The chromosphere of Betelgeuse has a lower opacity than our Sun and so our ALMA observations are most likely probing very close to the temperature minimum.”
“This is unambiguous proof for the existence of an inversion of the mean temperature in the atmosphere of a red supergiant,” Dr. O’Gorman added. “The emission in the star’s atmosphere is clearly not spherically symmetric with two notable deviations from a uniform disk detected in both the images and visibilities.”
The results show that the star's inner atmosphere is not uniform, as well as the surface.
“We have known for decades that the visible surface of Betelgeuse is not uniform, but ALMA has now shown us in detail that the temperature in its inner atmosphere is also not uniform,” said O'Gorman.
The new findings will help astronomers better understand giant stars like Betelgeuse - both their characteristics and how their lives eventually end. Like other similar giant stars, Betelgeuse's life will come to a close not with a whimper, but with a huge bang.
The new paper detailing the observations is available here.