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Interstellar Space Can Be Pebbly

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

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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.

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His books include Gravity's Engines (2012) and The Copernicus Complex (2014) (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

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

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  1. 1. NickCohen 4:38 pm 08/29/2014

    Imagine the restrictions that pebbles in space would place on interstellar space travel!

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  2. 2. And Then What? 5:47 pm 09/11/2014

    This is all very interesting, of course, and since I once had to present a lecture in an undergraduate Astrophysics and Stellar Astronomy course many, many moons ago I have a passing knowledge of the subject of interstellar dust and its effects on light travelling through Space but, what I really want to know is Space-Time itself pebbly? i.e. is the density of Space-Time uniform or does it vary and if it does why does it and what effect would such Density variations have on its expansion and consequently on the evolution of the Universe itself? Really what I am asking is the “Energy Density of Space-Time Uniform?”. I am not even sure if that is a valid question but anyway it is in my head so I let it out.

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