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Photo Suggests Planet Under Construction
By Jeanna Bryner
(LiveScience.com, Mar. 26, 2008)
Astronomers have peered into the womb of a stellar disk to capture an
image of material falling onto what could be a planet in an early
stage of formation.
The new image shows a somewhat horseshoe-shaped void in the disk
surrounding a young star called AB Aurigae. Within the void, a barely
visible bright spot could indicate a developing object that's
currently between 5 and 37 times the mass of Jupiter.
"The deficit of material could be due to a planet forming and sucking
material onto it, coalescing into a small point in the image and
clearing material in the immediate surroundings," said researcher Ben
Oppenheimer, an astrophysicist at the American Museum of Natural
History in New York. "It seems to be indicative of the formation of a
small body, either a planet or a brown dwarf."
A brown dwarf is considered a star that's not massive enough to
generate the thermonuclear fusion that powers real stars.
To date, no confirmed extrasolar planet has been imaged or seen
directly, as no one yet has succeeded in effectively blocking the
light from the parent star that overwhelms the faint glow of a nearby
If this object is a planet, the image does not show the planet itself.
Oppenheimer said the image shows what's thought to be dust accreting
onto the object.
"The main problem is that the stars are hundreds of millions to
billions of times brighter than the planets that orbit them,"
Oppenheimer told SPACE.com. "So the glare of the star wipes out any
hope of really seeing the planets."
Planet-formation theorist Alan Boss of the Carnegie Institution of
Washington called the finding "an intriguing situation." He added:
"And given that it's a fairly massive disk with big spiral features,
there's a good chance that something is forming in it." Based on the
apparent intensity of the object along with its distance from the
primary star (about 100 times the distance from Earth to the sun),
Boss speculates the object is more likely a brown dwarf.
Oppenheimer and his colleagues blocked out most of the stellar glare
by attaching a coronagraph they had developed to a U.S. Air Force
telescope on Maui, Hawaii. They also used polarization filters, which
show light scattered off the disk.
The observations, set to be detailed in the June issue of the
Astrophysical Journal, could fill a gap in astronomers' understanding
of planet formation, which they are pretty confident occurs within the
disks of material surrounding young stars. While the exact ways in
which gas giant planets and brown dwarfs form are not known, it's
possible both objects develop in the same manner in the material that
swirls around a newborn star.
Boss calls the finding a "great step forward toward trying to
understand how planets form and being able to image planets in
formation as well as mature planets."
The star AB Aurigae is quite young, estimated to be between 1 million
and 3 million years old. Our sun, by comparison, is 4.6 billion years
old, but most of the planet formation in our solar system is thought
to have taken place in the first hundred million years or so.
Past observations of stars slightly older than AB Aurigae indicate
that at some point during planet formation, gas is removed from the
dusty disk surrounding the stars. How the gas exits has remained a
mystery. The situation at AB Aurigae could represent an intermediate
stage in which some mechanism is clearing out the gas from the disk's
center and leaving behind mainly dust.
"The image produced speaks directly to the biggest, unresolved
question of planet formation how the thick disk of debris and gas
evolves into a thin, dusty region with planets," said National Science
Foundation Program Manager Julian Christou.
The research was funded in part by the NSF, U.S. Air Force, NASA's
Terrestrial Planet Finder Program and individual donors.