Orion Molecular Cloud Complex
August 28, 2014

Researchers Find Pebble-Size Particles Of Interstellar Dust In The Orion Molecular Cloud Complex

April Flowers for redOrbit.com - Your Universe Online

Current theories suggest that rocky planets like Earth start their lives as microscopic bits of dust tinier than a grain of sand.

Filaments of star-forming gas near the Orion Nebula might be full of pebble-sized particles, according to a new study released by astronomers using the National Science Foundation's (NSF) Green Bank Telescope (GBT).

These pebbles are planetary building blocks 100 to 1,000 times larger than the dust grains typically found surrounding protostars. The researchers say that if these pebble-sized particles are confirmed, they could represent a distinctly new, mid-sized class of interstellar particles used to jump-start planet formation. The results of the study were published in a recent issue of the Monthly Notices of the Royal Astronomical Society.

"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). "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 GBT observations encompass the northern region of the Orion Molecular Cloud Complex. The Complex is a star-forming area of the cosmos that includes the Orion Nebula. The section studied by the GBT is called the OMC-2/3, and inside this region, the star forming material has condensed into long, dust-rich filaments dotted with dense knots called cores. The cores are in different stages of development, with some just starting to coalesce while others are already forming protostars — the first step on the road to star formation. During the next 100,000 to 1 million years, astronomers predict that this roughly 10 light-year long region — located approximately 1,500 light-years from Earth — will evolve into a new star cluster.

Previous studies, using the IRAM 30 meter radio telescope in Spain, created maps that led the current astronomers to expect a certain brightness to the dust emissions in OMC-2/3 when they observed the filaments at GBT's slightly longer wavelengths. They were surprised to discover that the area was much brighter than predicted 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."

Dust grains that are a few millimeters to a few centimeters are incredibly small when compared to even the smallest asteroid. For young star forming regions, however, they are huge. The unique properties of the Orion Molecular Cloud Complex's environment have suggested two possible theories to the research team.

First, the dust grains were encouraged to grow to such unusual sizes by the filaments themselves. The filament areas have lower temperatures, higher densities, and lower velocities. These characteristics would all encourage grain growth.

Second, the current rocky particles are leftovers from a previous generation of cores, or from protoplanetary disks. The material could have escaped during the formation of the new star system to return to the molecular cloud.

"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."

GBT's high frequency imaging camera, MUSTANG, was used to gather the data for this study, which was compared to previous studies and temperature estimates collected 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. "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."


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