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Stellar Collisions Create Planets from RemnantsBP Piscium mystery revealed! |
By Gabriel Gache, Science News Editor
9th of February 2008, 08:50 GMT
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Astronomers reveal the mystery behind the BP Piscium star located in the Pisces constellation, an old star that appears to have recently spawned a new star formation process. A new study reveals that the accretion disk of matter spinning around it formed during a stellar collision and merging of two stars.
Usually, stars determine a star formation process during early life, however light
spectroscopy on the surface of BP Piscium has showed that it contains relatively low amounts of lithium in its composition, meaning that it has already processed most of its lithium into heavier chemical elements.
The original study published by graduate student Carl Melis, from the University of California, in January this year, presented only the fact that the star was incredibly old for it to be able to form new planets. Now, the UCLA team, led by Benjamin Zuckerman and Carl Melis, brings a massive update to the earlier study, in an online issue.
Zuckerman writes that the most probable explanation for the existence of the new accretion disk of matter around the old star is that, in fact, BP Piscium is the result of a merger between a red giant and a smaller stellar companion orbiting around it. As stars deplete the hydrogen reserves at their cores, they lose the ability to balance the forces resulted from nuclear fusion reactions and gravity, and experience a severe inflation, before suffering a supernova explosion.
As the volume of BP Piscium grew, it eventually swallowed the smaller star orbiting around it. BP Piscium lies about 1,000 light years away from Earth, and appears to have a weight of about 1.8 times that of the Sun, which basically means that the accretion disk of matter spinning around it could contain as much mass as about 50 times that of the Earth.
During the collision, most of the material of the smaller star was engulfed by the red giant, the rest being ejected into space, forming the accretion disk. In the same study published by Melis in January, he also mentions a second star with similar features in the Ursa Major constellation, dubbed TYCHO 4144 329 2. Zuckerman says that it also may have suffered a stellar collision with another star, in its early past.
Young stars go through a stage in their lives when they emit high amounts of X-ray radiation, an extremely useful property when trying to determine a star's life. However, none of the two stars currently under study are emitting a great amount of X-ray radiation, which makes measurements on their age very difficult. Nonetheless, BP Piscium and TYCHO 4144 329 2 will continue to be studied with the help of the Hubble Space Telescope and the Chandra X-ray Space Telescope to find out more about the properties of the two systems.
The curious thing is that TYCHO 4144 329 2 is already part of a binary system, orbited by a star with a mass comparable to that of the Sun, which does not seem to present evidence of an accretion disk of matter.
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