Sunday, September 23, 2012
Stars outside the solar system too have planets, says Nasa
FIRST PLANETS FOUND AROUND SUN-LIKE STARS IN A CLUSTER
NASA-funded astronomers have, for the first time,
spotted planets orbiting sun-like stars in a crowded cluster of
stars. The findings offer the best evidence yet planets can sprout up
in dense stellar environments. Although the newfound planets are not
habitable, their skies would be starrier than what we see from Earth.
The starry-skied planets are two so-called hot Jupiters, which are
massive, gaseous orbs that are boiling hot because they orbit tightly
around their parent stars. Each hot Jupiter circles a different
sun-like star in the Beehive Cluster, also called the Praesepe, a
collection of roughly 1,000 stars that appear to be swarming around a
common center, says a Nasa statement.
The Beehive is an open cluster, or a grouping of stars born at about
the same time and out of the same giant cloud of material. As such,
the stars share a similar chemical composition. Unlike the majority
of stars, which spread out shortly after birth, these young stars
remain loosely bound together by mutual gravitational attraction.
"We are detecting more and more planets that can thrive in diverse and
extreme environments like these nearby clusters," said Mario R.
Perez, the NASA astrophysics program scientist in the Origins of
Solar Systems Program. "Our galaxy contains more than 1,000 of these
open clusters, which potentially can present the physical conditions
for harboring many more of these giant planets."
The two new Beehive planets are called Pr0201b and Pr0211b. The star's
name followed by a "b" is the standard naming convention for planets.
"These are the first 'b's' in the Beehive," said Sam Quinn, a graduate
student in astronomy at Georgia State University in Atlanta and the
lead author of the paper describing the results, which was published
in the Astrophysical Journal Letters.
Quinn and his team, in collaboration with David Latham at the
Harvard-Smithsonian Center for Astrophysics, discovered the planets
by using the 1.5-meter Tillinghast telescope at the Smithsonian
Astrophysical Observatory's Fred Lawrence Whipple Observatory in
Arizona to measure the slight gravitational wobble the orbiting
planets induce upon their host stars. Previous searches of clusters
had turned up two planets around massive stars but none had been
found around stars like our sun until now.
"This has been a big puzzle for planet hunters," Quinn said. "We know
that most stars form in clustered environments like the Orion nebula,
so unless this dense environment inhibits planet formation, at least
some sun-like stars in open clusters should have planets. Now, we
finally know they are indeed there."
The results also are of interest to theorists who are trying to
understand how hot Jupiters wind up so close to their stars. Most
theories contend these blistering worlds start out much cooler and
farther from their stars before migrating inward.
"The relatively young age of the Beehive cluster makes these planets
among the youngest known," said Russel White, the principal
investigator on the NASA Origins of Solar Systems grant that funded
this study. "And that's important because it sets a constraint on how
quickly giant planets migrate inward. And knowing how quickly they
migrate is the first step to figuring out how they migrate."
The research team suspects planets were turned up in the Beehive
cluster because it is rich in metals. Stars in the Beehive have more
heavy elements such as iron than the sun has.
According to White, "Searches for planets around nearby stars suggest
that these metals act like a 'planet fertilizer,' leading to an
abundant crop of gas-giant planets. Our results suggest this may be
true in clusters as well."