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Four Stars Found in Amazingly Tight Bunch

January 10, 2008

AUSTIN, Texas — A quartet of stars has been
discovered in an intimate cosmic dance, swirling around each other within a
region about the same as Jupiter’s orbit around the sun.

Astronomers
say a gaseous disk might have once engulfed and pushed the stars into their
tight orbits
.

Though bright,
the stellar system was thought to be a single star dubbed BD -22°5866. Now,
research presented here today at a meeting of the American Astronomical Society
reveals the pinpoint of light is a rare system of four closely orbiting stars.
The group is located about 166 light-years from the sun. In our sky, they are
just south of the constellation Aquarius.

Each of the
stars is about half as massive as the sun and older than 500 million years. The
sun, by comparison, is 4.6 billion years old.

Since most
stars form as part of a multiple-star
system
, the new findings could have implications for understanding the
evolution of stars.

Evgenya
Shkolnik of the University of Hawaii’s Institute for Astronomy and NASA
Astrobiology Institute and colleagues spotted the foursome while surveying
hundreds of nearby low-mass stars with the Keck I telescope and the
Canada-France-Hawaii telescope, both on the summit of Mauna Kea.

At the time
of the observations, two of the stars were orbiting each other at 300,000 mph
(483,000 kilometers per hour), taking a under a mere five days to complete an
orbit. The other couple had an orbit speed of 120,000 miles per hour (193,000
kilometers per hour) and takes about 55 days for a complete jaunt around their
common gravitational midpoint in space.

The first
pair has an orbit radius of at most .06 astronomical units (AU), where one AU
is the average distance between Earth and the sun. The second pair has a
maximum radius of .26 AU.

The two
pairs also promenade each other in less than nine years with a maximum radius
of just 5.8 AU. Jupiter, to compare, is 5.2 AU from the sun.

The
researchers say that fewer than 1 in 2,000 stars observed might be involved in
such intimately
bound systems
.

“The
extraordinarily tight configuration of this stellar system tells us that there
may have been a single gaseous disk that forced them into such small orbits
within the first 100,000 years of their evolution,” Shkolnik said,
“as the stars could not have formed so close to one another.”

In fact,
the spin energy of the more rapidly rotating pair, mixed with the gravitational
interaction between the two pairs, has pushed the other pair farther away over
the years.

“At
one point early in its history, it was even closer than we see now,”
Shkolnik told SPACE.com.

The
research has been submitted to the Astrophysical Journal Letters.


Source: imaginova