NAOC Researchers Participated in Discovering Pebble-Size Dust Grains in Orion Nebula, Advancing Understanding of Planet Formation

Sep 10, 2014     Email"> PrintText Size

The large-size dust particles (millimeter- to centimeter-sized) were considered as the start point of the planet formation. The growth of the dust particles were thought to be a slow process, and only when the interstellar material collapses under its own weight for millions of years – gravity overwhelming pressure – can densities reach much higher levels. Stellar atmospheres, ices, and rocks, all condense out of matter’s gas phase in the great swirls of proto-stellar, or proto-planetary disks at the endpoint of this collapse. In addition, around a star or a brown dwarf, it’s expected that drag forces cause large particles to lose kinetic energy and spiral in toward the star. This process should be relatively fast, but since planets are fairly common, many astronomers have put forth theories to explain how dust hangs around long enough to form planets. One such theory is the so-called dust trap: a mechanism that herds together large grains and keeps them from spiraling inward.

In a new study led by Dr. Scott Schnee in the National Radio Astronomical Observatory (NRAO) focused on northern portion of the Orion Molecular Cloud Complex, a star-forming region that spans hundreds of light-years with ongoing stellar birth. The researchers performed a combined analysis of the dust emissions with the recently published high-resolution temperature map over the Orion Nebular by Dr. LI Di, chief scientist in the research group of “ISM evolution and star formation” in National Astronomical Observatories (NAOC) of the Chinese Academy of Sciences. The research work shows that the dust emissivity in the millimeter wavelengths is unexpectedly bright. The best (but not the only) explanation is that instead of the usual microscopic dust particles mixed with molecular gas, there are "pebbles" as large as a centimeter littering this interstellar region. These large objects are more efficient at radiating away their thermal energy and would emit bright millimeter radio waves. With the presence of centimeter-size pebbles, the progress of the planet formation would be much faster and more efficient than in the case with only small-size dust.

The observational data of the current result is obtained with the Green Bank Telescope (GBT), and the result has been reported by a few leading science medias over the world including Science American and Universe Today.

Figure: A radio (orange) and optical composite of the Orion Molecular Cloud Complex showing the OMC-2/3 star-forming filament. (Image by S. Schnee, et al. / B. Saxton, B. Kent, NRAO/AUI/NSF)