Avi Blizovsky
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The largest and most massive stars known are 150 times more massive and 5 million to 40 million times brighter than the Sun, but these giants are destined to live short lives and then disintegrate in a supernova explosion.
Astronomer Steven Eikenberry of the University of Florida says the star, known as LBV1806-20, is at the edge of a star cluster at the other end of the Milky Way, about 45 light-years from us. In a presentation Monday to the American Astronomical Society's annual meeting, Eikenberry said the star burns at temperatures of 30 to 60 degrees and is 200 times more inflated than the Sun.
This giant star dispelled theories of massive star formation, he said. Massive stars usually do not grow larger than 100 solar masses. At this point the energy flow is so strong that any extra matter flies out.
But LBV1806-20 was formed near an area where a supernova exploded in the past. Eikenberry says this explosion likely compressed gas and dust, allowing the star to grow far beyond the normal size of a stellar giant.
He said the same region includes baby stars in the process of formation as well as several other large stars, all of which likely formed as a result of the early supernova.
Eikenberry says that massive stars only shine for about 2 million years and LBV1806-20 is now in the middle of its life, at about a million years old. Eventually, he says, such stars blow themselves into pieces and without such explosions, Earth-like planets and life on them could not exist.
"Most of the material we use in our daily lives, including the oxygen we breathe and the carbon in our skin comes from the cores of the most massive stars, where these materials are formed," he said. "Massive stars," Eikenberry says, "live short, troubled lives, exploding themselves in a supernova and their material spreading throughout the galaxy. The next generation of stars and planets will then form with these elements in it." For comparison, the age of the Sun is about 6 billion years - about half of its expected lifespan.
In another presentation at the AAS meeting, two astronomers reported the discovery of a young star speeding through space at 75 km/h, 40 times faster than a rifle bullet.
The star, called PV Ceph, was blasted like a cannonball out of a cluster of stars and is now 30 light-years from its quarry. It took him only half a million years to make the journey. PV Ceph was exiled from its home, thrown out before it even finished forming," says Alyssa Goodman of the Harvard Smithsonian Center for Astrophysics. She and her colleague Hector Acre of the California Institute of Technology are co-discoverers of the runaway star.
Goodman said the star formed inside a young cluster and probably got too close to a larger star. The effect of gravity acted like a bow shooting an arrow, and it accelerated PV Ceph to a speed 10 times greater than that of a normal star traveling through the galaxy.
Astronomers say that the star spits out gas emissions as it passes through the sky. By tracking these emissions, like waves created by a ship in the ocean, they were able to track the star's orbit and find the cluster in which it was born. The cluster, called NGC7023, also includes an orbit devoid of gas and dust, which was probably cleaned by PV Ceph in its passage.
"There is an exit-like hole in NGC7023 from which we believe the young star was shot out.
PV Ceph has found a warm new home, she said. The star is in an area rich in gas and dust and continues to grow.
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