Life, Unbounded

Life, Unbounded

Discussion and news about planets, exoplanets, and astrobiology

Interstellar Space Can Be Pebbly


Are there interstellar pebbles here? Red strands indicate dense interstellar grains seen with the Green Bank radio telescope (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.)

We're used to thinking of the space between the stars as void, bereft of all but the most sparsely distributed atoms and molecules, or the occasional microscopic grain of silicon or carbon dust. Even the densest cores of nebula - molecular clouds - only attain average densities of a few million atoms or molecules per cubic centimeter (by comparison, the air you're breathing right now contains roughly 10 to the power of 19 - or ten million trillion - molecules).

Only when this 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. At least this is what we'd generally assumed.

Now, a new study using the Green Bank Telescope in West Virginia has found unexpectedly bright millimeter-wave radiation emanating from filamentary regions extending over a distance of 10 light years in the heart of the Orion nebula, a place of on-going stellar birth. The best (but not only) explanation is that instead of the usual microscopic dust particles mixed in with molecular gas, there are 'pebbles' as large as a centimeter across littering this interstellar region. These larger objects are more efficient at radiating away their thermal energy in the form of millimeter radio waves.

To put this in perspective. It's as if you expected snowflakes but instead got ten meter icebergs falling from the sky.

The truly remarkable thing is that, if real, these 'pebbles' exist in a region that should have at least another 100,000 years to go before it starts making new stars and planets. There are two possible answers. First is that the pebbles actually represent the leftovers from much earlier episodes of star and planet formation; an ancient gravel repository. The second, more exciting possibility is that these filaments, or streams, of material have condensed in-situ within the cool, slow moving zones of the nebula.

If that's the case it's a very important addition to our picture of how stars and planets can form, and the gestational stages that take place. If Nature's making new worlds, the progress may be a lot faster if you start with pebbles rather than with dust.

The views expressed are those of the author and are not necessarily those of Scientific American.

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