Giant Star May be Giving Birth to Planets
(Special Report from the 2001 American Astronomical Society meeting)
SAN DIEGO (Jan. 9, 2001) -- A family of planets may be taking shape in a disk of gas and dust encircling
a young, massive star in the constellation Orion, according to astronomers who
have studied the system with an array of radio telescopes in New Mexico. The
complex system spans several times the diameter of our own solar system, and
appears to include a second star that "fences in" the possible planet-forming
region.
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A disk, a ring, high-speed outflows of material, and a companion star all
surround G192.16-3.82, a massive young star in the constellation Orion,
in this artist's conception. A smaller neighbor star appears nearby.
[Boris Starosta, NRAO/AUI/NSF] (Full size image: 125K jpeg)
G192.16-3.82 looks like an elongated blob in the raw image compiled
from radio observations of the system. The size of our our solar system
is shown for comparison. [D. Shepherd, M. Claussen, S. Kurtz, NRAO/AUI/NSF] |
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Known as G192.16-3.82, the system is more than 6,000 light-years from Earth.
It is too faint to see with the unaided eye, but it produces abundant radio
energy. A team of three astronomers studied this energy late last year with
the Very Large Array, a set of 27 large dish antennas that work together as
a single telescope, combined with yet another radio dish about 30 miles away.
The combined telescopes allowed the astronomers to see rich details in G192.16-3.82.
They found that a disk of gas and dust surrounds the central star, which is
only about 200,000 years old but about 10 times the mass of the Sun. "There's
something extremely massive at the heart of this thing," said Debra Shepherd
of the National Radio Astronomy Observatory and one of the astronomers who studied
the system.
The disk is about twice the diameter of our own solar system, yet it contains
enough material to make about 20 stars as massive as our own Sun. Earth and
the other planets of our solar system probably formed from a similar but much
less-massive disk about 4.5 billion years ago, suggesting that planets could
be forming around G192.16-3.82, Shepherd said.
Computer simulations suggest that a second star orbits just outside the disk,
although astronomers have not yet seen this star. It may act as a cosmic "shepherd"
to help maintain the disk's size and shape. A large "doughnut" of
gas and dust encircles the system outside the orbit of the smaller star.
While some of the material in the central disk will fall into the star, and
more eventually form planets, much of it will be fired back into space through
"outflows" -- high-speed streams of gas and dust streaming above the
poles of central star. As gas and dust spiral toward the star, powerful magnetic
fields accelerate them and shoot them into space. These outflows currently span
about 30 light-years -- about seven times the distance from the Sun to the nearest
star system, Alpha Centauri -- and contain more than 100 times the mass of our
own Sun. "This is one of the largest and most energetic outflows in our
entire galaxy," Shepherd said.
G192.16-3.82 is the most massive star encircled by a disk yet discovered, Shepherd
added. Comparisons between this and less-massive systems may help astronomers
understand the planet-formation process and the mechanisms behind outflows of
gas from young stars. -- — Damond Benningfield
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