Stars Eating/Giving Birth to New Planets

"Stars stay young by eating planets"

A new research has indicated that stars can slow down their aging process by consuming Jupiter-sized planets.

According to a report in New Scientist , most stars eventually become white dwarfs, but along the way expand into red giants, while their cores shrink and undergo a short but intense phase of helium fusion.

"Yet gobbling up a Jupiter-sized planet as they expand can affect that process," said Brad Hansen at the University of California, Los Angeles.

Calculations by Hansen suggest that if the planet is swallowed at the right moment, its gravity can peel off the star's outer layers.

Then, the star's exposed core never gets hot enough to fuse helium, so the resulting white dwarf is less massive and looks younger than it should for its age.

A group of white dwarfs with precisely those characteristics was observed three years ago in the star cluster NGC 6791.

The work was presented at the annual American Astronomical Society meeting in Austin, Texas last week.
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"Amazing old stars give birth again"

http://www.usatoday.com/tech/science/space/2008-01-21-old-stars-birth_N.htm

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."