Amazing Signs as old stars give birth again
Pastor Dale Morgan
Amazing Signs as old stars give birth again*
By Jeanna Bryner, SPACE.com
Two old stars appear to be gearing up for a second generation of planet
formation, a phenomenon astronomers say they have never seen before.
"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 at a recent meeting of the American Astronomical
Society in Austin, Texas.
The stars are BP Piscium in the constellation Pisces and TYCHO 4144 329
2, which resides in the constellation Ursa Major. The exact ages of the
stars are unknown, but it is estimated they are at least hundreds of
millions or possibly billions of years old, and might have already given
birth to planets long ago.
"Most astronomers now believe that most stars are accompanied by
first-generation planets of some sort, even if the planets are not
massive enough to be picked up by the radial velocity [detection]
technique," Melis said.
Second generation of planets
The unusual thing about these stars is that they appear to be giving
birth to planets again.
"We currently understand planet formation to occur around stars when
they are very young and enshrouded in dusty and gaseous disks, the
material necessary to form planetary bodies," Melis told SPACE.com.
"This material is completely used up after a couple to ten million years
after the star is born and is not replenished during the star's life. As
such, we would never expect a star to undergo planet formation late in
its life as the necessary conditions are not present."
How they can do this is still unclear, but the stars seem to have kept
many of their youthful qualities. For instance, the researchers found
orbiting disks of gas and dust extended around the stars, and, in the
case of BP Piscium, jets of gas being ejected into space. These
gas-and-dust rings provide the fodder for the making of planetesimals,
such as comets and asteroids that can merge to form larger bodies, along
with planets.
"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."
Aging stars
The lack of lithium gave away the true stellar ages. Since stars burn
lithium as they get older, younger stars should pack large stores of the
chemical element. The astronomers found, however, that BP Piscium
contained much less lithium than would be 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."
The researchers speculate that the senior stars might be borrowing
material from their neighbors to construct new worlds.
"Our team believes that these stars, as they aged and began to expand
into giant stars, engulfed very short-period companion stars orbiting
around them," Melis said. "Interactions with these companions caused
matter to be flung into disks surrounding the two stars."