By Jesse Emspak: Subscribe to Jesse's RSS feed
July 21, 2010 7:11 PM EDT
Astronomers have found one of the heaviest stars ever seen, helping to answer a question that has been a mystery for a century: just how big can stars get?
The answer is that nobody knows yet, but it is at least 265 times the mass of the sun and could be larger. Called R136a1, it was found with the Very Large Telescope of the European Southern Observatory, located in Chile.
The research team, led by Professor of Astrophysics at the University of Sheffield, had the telescope scan certain parts of the sky in the near-infrared. They also used archival data from the Hubble Space Telescope.
Olivier Schnurr, one of the research team at the Astrophysical Institute in Potsdam, Germany, said in looking for heavy stars, the most likely places are in globular clusters or regions where a lot of stars are forming. That's what they did, and when they looked at a cluster of stars in the Large Magellanic Cloud, they found one that weighs in at 265 times the Sun's mass.
If it were put in the Sun's place, it would cover an area in the sky thirty times larger than the sun does. It generates many times more energy, and shines in the ultraviolet and blue end of the spectrum, so sunlight would be bluish rather than white. The surface of the sun is about 5,700 degrees Celsius, or 9,900 degrees Fahrenheit. R136a1 has a surface temperature ten times higher, which would make the Earth's surface hot enough to melt many metals.
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Stars, including those like the Sun, form when clouds of gas, usually hydrogen but sometimes containing other elements, coalesce under their own gravity. As the material compresses under its own weight, the pressure becomes so great that the hydrogen starts to fuse into helium and from helium to heavier elements.
It's the same process that happens inside a hydrogen bomb, except its much bigger and lasts for millions of years. The fusion generates energy, which we see as heat and light, which generates pressure that resists the star's own gravitational pull.
But you can't just put any amount of mass into a star. Calculations done decades ago showed that beyond a certain point, stars become unstable. But those calculations were always simplified - some simulations showed stars in the early universe reaching 1,000 times the mass of the Sun. But no stars like that have ever been found.
On top of that, the more massive a star is, the shorter its life. The Sun has lasted 4.5 billion years and will last 5 billion more. R136a1 has been shining for a million years and won't last for more than another million or so before it explodes as a supernova and turns into a black hole.
R136a1 was likely 300 times the Sun's mass when it formed; it has lost about 35 solar masses worth since then. Finding this star raises a number of questions, Schnurr said, about how to model star formation, and what the internal structure of massive stars looks like. It also helps to answer what the relation is between mass and luminosity when stars get a lot bigger than run-of-the-mill stars like the Sun.
"The mass-luminosity relation for very massive stars is an open problem," he said. "We also want to know how such massive stars form."
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