Two Old Stars Are Acting Like They Are New

Posted Jan 11, 2008 by KJ Mullins
A second wave of planet formation appears to be taking place around two older stars, BP Piscium and TYCHO 4144 329 2, possibly billions of years after planets would have initially formed around them.
The star BP Piscium (center)  in the constellation Pisces. The green and red streaks are jets of gas...
The star BP Piscium (center), in the constellation Pisces. The green and red streaks are jets of gas shot from the star. The image was obtained using the 3-meter telescope at the University of California's Lick Observatory. (Credit: Image courtesy of Univ
"This is a new class of stars, ones that display conditions now ripe for formation of a second generation of planets, long, long after the stars themselves formed," said UCLA astronomy graduate student Carl Melis, who reported the findings today at the American Astronomical Society meeting in Austin, Texas.
"If we took a rocket to one of these stars and discovered there were two totally distinct ages for their planets and more minor bodies like asteroids, that would blow scientists' minds away," said Benjamin Zuckerman, UCLA professor of physics and astronomy and co-author of the research, which has not yet been published. "We're seeing stars with characteristics that have never been seen before."
The stars are in the constellations Pisces and Ursa Major. Melis says that these two older stars have amazing properties for their age.
They are behaving like very young stars with rapid accretion of gas, extended orbiting disks of dust and gas and a large infrared excess emission. BP Piscium is also shooting jets of gas into space. Olanets, comets and asteroids form from the gas and dust particles that orbit young stars.
75 percent of BP Piscium's radiant energy is being converted into infrared light. TYCHO 4144 329 2's conversion level is at about 12 percent. This is highly unusual for stars that are as old as these two.
Scientists are looking at the heavens using Hubble and Chandra X-ray Observatory among other space based observatories and Earth based telescopes to study these two remarkable stars and search for more like them.
"With all these characteristics that match so closely with young stars, we would expect that our two stars would also be young," Melis said. "As we gathered more data, however, things just did not add up." For example, because stars burn lithium as they get older, young stars should have large quantities of lithium. The astronomers found, however, that the spectroscopic signature of lithium in BP Piscium is seven times weaker than expected for a young star of its mass.
"There is no known way to account for this small amount of lithium if BP Piscium is a young star," Melis said. "Rather, lithium has been heavily processed, as appropriate for old stars. Other spectral measurements also indicate it is a much older star."