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Huge, bright star will have short life

The largest and brightest star faces a short life that will end in a supernova explosion, despite being  millions of times more luminous and 150 times more massive than the sun.
The star LBV 1806-20 is at least 150 times larger and 5 million times brighter than the sun. The two are shown for size comparison in this artist's conception.
The star LBV 1806-20 is at least 150 times larger and 5 million times brighter than the sun. The two are shown for size comparison in this artist's conception.Meghan Kennedy / University of Florida
/ Source: The Associated Press

The most massive and brightest star known is 5 million to 40 million times more luminous than Earth's own star, the sun, and about 150 times more massive, but this stellar giant is destined to live a short life and then to erupt in a supernova explosion.

Astronomer Stephen Eikenberry of the University of Florida said the star, known as LBV1806-20, is on the edge of a cluster of stars on the far side of the Milky Way, 45,000 light-years from the solar system.

In a presentation Monday at the national meeting of the American Astronomical Society, Eikenberry said the star burns at a temperature of 30,000 degrees to 60,000 degrees Fahrenheit and has ballooned out to a diameter 200 times that of the sun.

The huge star actually defies theories of massive star formation, he said. Usually massive stars grow no bigger than about 100 solar masses. At that point, the energy outflow is so powerful that additional material is blown away.

LBV1806-20, however, formed near where a supernova exploded in the past. Eikenberry said this explosion may have compressed gas and dust, enabling the star to grow far beyond the usual size of stellar giants. He said the same area contains a baby star in the process of formation, along with several other large stars, all of which may have formed as the result of the earlier supernova.

Connection to life on Earth
Eikenberry said massive stars generally only shine for about 2 million years, and LBV1806-20 is now middle-aged, about a million years old. Eventually, he said, such stars blow themselves apart. Scientists say that without such explosions there would be no planets capable of sustaining life as we know it.

"Most of the material that we deal with on a daily basis, including the oxygen you are breathing and the carbon in your skin, comes from the core of the most massive stars. That's where that materials are formed," he said.

Massive stars, said Eikenberry, "live a short and troubled life, blow themselves apart in a supernova and spread that material through out the galaxy."

The next generation of stars and planets then form out of that material and incorporate those elements.

"That is what the earth is made of, and you and I are made of," he said.

By comparison, the sun is around 6 billion years old, about halfway through its expected lifetime.

Speeding young star
In another presentation at the AAS meeting, two astronomers reported on the discovery of a young star that is streaking through space at nearly 50,000 miles per hour, 45 times faster than a speeding bullet.

The star, called PV Ceph, was flung like a rock from a slingshot from a cluster of stars and is now 30 light-years from its place of origin. It took about a half-million years to make the journey.

"PV Ceph was exiled from its home, thrown out before it even finished forming," said Alyssa Goodman of the Harvard-Smithsonian Center for Astrophysics. She and Hector Arce of the California Institute of Technology are co-discoverers of the speeding star.

Goodman said the star was forming as part of a young cluster and apparently moved too close to a larger star. The gravitational effect, acting like a slingshot, accelerated PV Ceph and flung it across space at about 10 times the normal speed of a moving star.

The astronomers said the star belched bursts of gas as it raced across the sky. By following traces of these emissions, like the wake of a ship on the ocean, they were able to trace the path of star and find its birth home cluster. The cluster, called NGC 7023, also contained a path empty of gas and dust, apparently cleared by the departing PV Ceph.

"There's a hole, like an exit wound, in NGC7023 where we think this young star was shot out," said Goodman.

PV Ceph has found a happy new home, she said. The star is now in an area rich with gas and dust and is continuing to grow.