Astronomers discover monster star

Astronomers have wondered for decades just how massive stars can get. Now there is a new candidate for “largest star known” and it’s a whopper – 265 times the mass of our sun – far more massive than the currently accepted mass limit for stars of 150 solar masses.

The universe never stops surprising us.

This star – called R136a1 – is thought to be hundreds of times more massive than our sun, but 10 million times more luminous.

What’s more, the star is thought to be losing weight through very powerful stellar winds from its surface, so that it started with perhaps 320 solar masses and has now dwindled to 265.

This discovery was made using a combination of instruments on the Very Large Telescope of the European Southern Observatory (ESO). Like a riddle wrapped in an enigma, the star was found inside a cluster of young, massive, hot stars – which in turn is inside the Tarantula Nebula – which is inside one of our neighboring galaxies, the Large Magellanic Cloud or LMC – 165,000 light-years away. This monster star – as astronomers are calling it – is a neighbor of ours, astronomically speaking.

There is a possibility that the monster star might really be two stars of a smaller mass, but astronomers say this isn’t likely.

I couldn’t resist running this photo of the movie star Charlize Theron, which I stumbled upon while searching for the words “monster star.” The movie Monster? Never mind.

“Unlike humans, these stars are born heavy and lose weight as they age,” said astrophysicist Paul Crowther at the University of Sheffield, who led the team that discovered R136a1. “Being a little over a million years old, the most extreme star R136a1 is already ‘middle-aged’ and has undergone an intense weight loss program, shedding a fifth of its initial mass over that time, or more than 50 solar masses.”

Astronomers say that if R136a1 replaced our sun, it would outshine the sun by as much as the sun currently outshines the full moon.

They say that if it replaced our sun, its high mass would pull Earth into a much smaller orbit, reducing the length of the Earth’s year to three weeks. At that distance, R136a1 would bathe the Earth in incredibly intense ultraviolet radiation, rendering life on our planet impossible, they say.

Astronomers are curious about these huge stars. Are they born so big? Or do smaller stars merge to create them?

Also, how do these stars end their lives? Stars between about 8 and 150 solar masses explode at the end of their short lives as supernovae, leaving behind exotic remnants, either neutron stars or black holes. Having now established the existence of stars weighing between 150 and 300 solar masses, the astronomers’ findings raise the prospect of the existence of exceptionally bright, “pair instability supernovae” that completely blow themselves apart, failing to leave behind any remnant and dispersing up to ten solar masses of iron into their surroundings. A few candidates for such explosions have already been proposed in recent years.

Not only is R136a1 the most massive star ever found, but it also has the highest luminosity too, close to 10 million times greater than the sun. “Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon,” concludes Crowther.

July 21, 2010

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