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This star already blew its top, but it’s still here

Published Apr 25th, 2021 10:23AM EDT
hubble star

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Stars come in many shapes and sizes. Our Sun, for example, is massive compared to Earth, but it’s far from the largest or most impressive. Using the Hubble Space Telescope, NASA and the European Space Agency are able to observe many nearby stars and those surveys have helped scientists learn a great deal about how stars of all types are born, live, and die. In a new post on NASA’s website, the space agency highlights Hubble’s 31-year sightseeing campaign by targeting one of the brightest stars in the Milky Way, and it’s downright beautiful.

The star, which is called AG Carinae, looks quite a bit different than our Sun, and that’s because the two are only very distant cousins. AG Carinae is a type of star known as a luminous blue variable, a rare and massive type of star that is maintaining a delicate balance to prevent its total destruction. The image you see is a combination of exposures from Hubble that combine to reveal the unstable nature of the star, which is estimated to be 70 times as massive as our own Sun.

As NASA explains, luminous blue variable stars keep their cool for years at a time before experiencing violent outbursts. The impressive halo around AG Carinae is absolutely huge, measuring approximately three light-years across. To put that in perspective, the distance from the Sun to its nearest neighbor star, Proxima Centauri, is roughly the same size. This star and its boiling sphere of hot gas and dust occupy a lot of space, and NASA even refers to it as a “celebrity star” because of its high visibility within our galaxy.

Its halo was created during one or more previous outbursts, and it continues to radiate an incredible amount of energy into space. The only thing holding it together is gravity, and it’s not doing a very good job. The star, and others like it, appear to be constantly on the edge of total destruction but somehow maintain their shape.

“It’s an arm-wrestling contest between radiation pressure from within the star pushing outward and gravity pressing inward,” NASA explains. “This cosmic match results in the star expanding and contracting. The outward pressure occasionally wins the battle, and the star expands to such an immense size that it blows off its outer layers, like a volcano erupting. But this outburst only happens when the star is on the verge of coming apart. After the star ejects the material, it contracts to its normal size, settles back down, and becomes quiescent for a while.”

Of all the stars that scientists have observed both in our home galaxy and other nearby systems, less than 50 luminous blue variables have been spotted, making them one of the rarest types of stars. They’re also some of the most brilliant.