Radio/optical composite of the Orion Molecular Cloud Complex showing the OMC-2/3 star-forming filament. GBT data is shown in orange. Uncommonly large dust grains there may kick-start planet formation. Credit: S. Schnee, et al.; B. Saxton, B. Kent (NRAO/AUI/NSF); We acknowledge the use of NASA's SkyView Facility located at NASA Goddard Space Flight Center.
Zoom in of the OMC-2/3 region
Credit: S. Schnee, et al.; B. Saxton, B. Kent (NRAO/AUI/NSF); We acknowledge the use of NASA's SkyView Facility located at NASA Goddard Space Flight Center. 
GBT data of the filaments in OMC-2/3 region
Credit: S. Schnee et al.; B. Saxton (NRAO/AUI/NSF)
Rocky planets like Earth start out as microscopic bits of dust tinier than a grain of sand, or so theories predict.
Astronomers using the National Science Foundation’s (NSF) Green Bank Telescope
(GBT) have discovered that filaments of star-forming gas near the Orion
Nebula may be brimming with pebble-size particles -- planetary building
blocks 100 to 1,000 times larger than the dust grains typically found
around protostars. If confirmed, these dense ribbons of rocky material
may well represent a new, mid-size class of interstellar particles that
could help jump-start planet formation.
"The large dust grains seen by the GBT would suggest that at least
some protostars may arise in a more nurturing environment for planets,"
said Scott Schnee, an astronomer with the National Radio Astronomy
Observatory (NRAO) in Charlottesville, Virginia. "After all, if you want
to build a house, it’s best to start with bricks rather than gravel,
and something similar can be said for planet formation."
The new GBT observations extend across the northern portion of the
Orion Molecular Cloud Complex, a star-forming region that includes the
famed Orion Nebula. The star-forming material in the section studied by
the GBT, called OMC-2/3, has condensed into long, dust-rich filaments.
The filaments are dotted with many dense knots known as cores. Some of
the cores are just starting to coalesce while others have begun to form
protostars -- the first early concentrations of dust and gas along the
path to star formation. Astronomers speculate that in the next 100,000
to 1 million years, this area will likely evolve into a new star
cluster. The OMC-2/3 region is located approximately 1,500 light-years
from Earth and is roughly 10 light-years long.
Based on earlier maps of this region made with the IRAM 30 meter
radio telescope in Spain, the astronomers expected to find a certain
brightness to the dust emission when they observed the filaments at
slightly longer wavelengths with the GBT.
Instead, the GBT discovered that the area was shining much brighter than expected in millimeter-wavelength light.
"This means that the material in this region has different properties
than would be expected for normal interstellar dust,” noted Schnee. “In
particular, since the particles are more efficient than expected at
emitting at millimeter wavelengths, the grains are very likely to be at
least a millimeter, and possibly as large as a centimeter across, or
roughly the size of a small Lego-style building block."
Though incredibly small compared to even the most modest of
asteroids, dust grains on the order of a few millimeters to a centimeter
are incredibly large for such young star-forming regions. Due to the
unique environment in the Orion Molecular Cloud Complex, the researchers
propose two intriguing theories for their origin.
The first is that the filaments themselves helped the dust grains
grow to such unusual proportions. These regions, compared to molecular
clouds in general, have lower temperatures, higher densities, and lower
velocities -- all of which would encourage grain growth.
The second scenario is that the rocky particles originally grew
inside a previous generation of cores or perhaps even protoplanetary
disks. The material could then have escaped back into the surrounding
molecular cloud rather than becoming part of the original newly forming
star system.
"Rather than typical interstellar dust, these researchers appear to have detected vast streamers of gravel -- essentially a long and winding road in space," said NRAO astronomer Jay Lockman, who was not involved in these observations. "We've known about dust specks and we have known that there are things the size of asteroids and planets, but if we can confirm these results it would add a new population of rocky particles to interstellar space."
"Rather than typical interstellar dust, these researchers appear to have detected vast streamers of gravel -- essentially a long and winding road in space," said NRAO astronomer Jay Lockman, who was not involved in these observations. "We've known about dust specks and we have known that there are things the size of asteroids and planets, but if we can confirm these results it would add a new population of rocky particles to interstellar space."
The most recent data were taken with the Green Bank Telescope's high
frequency imaging camera, MUSTANG. These data were compared with earlier
studies as well as temperature estimates obtain from observations of
ammonia molecules in the clouds.
"Though our results suggest the presence of unexpectedly large dust
grains, measuring the mass of dust is not a straightforward process and
there could be other explanations for the bright signature we detected
in the emission from the Orion Molecular Cloud," concluded Brian Mason,
an astronomer at the NRAO and co-author on the paper. "Our team
continues to study this fascinating area. Since it contains one of the
highest concentrations of protostars of any nearby molecular cloud it
will continue to excite the curiosity of astronomers."
A paper detailing these results is accepted for publication in the Monthly Notices of the Royal Astronomical Society.
The GBT is the world's largest fully steerable radio telescope. Its location in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone protects the incredibly sensitive telescope from unwanted radio interference.
Later this year, the GBT will receive two new, more advanced high frequency cameras: MUSTANG-1.5, the even-more-sensitive successor to MUSTANG, and ARGUS, a camera designed for mapping the distribution of organic molecules in space.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
A paper detailing these results is accepted for publication in the Monthly Notices of the Royal Astronomical Society.
The GBT is the world's largest fully steerable radio telescope. Its location in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone protects the incredibly sensitive telescope from unwanted radio interference.
Later this year, the GBT will receive two new, more advanced high frequency cameras: MUSTANG-1.5, the even-more-sensitive successor to MUSTANG, and ARGUS, a camera designed for mapping the distribution of organic molecules in space.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
