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 planet.
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.
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