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New phenomenon could reveal how stars are born

Light from the cosmic clouds where stars and planets are born could soon reveal secrets about these mysterious formative regions, a new study suggests.
Image: Coreshine
Coreshine from the Lynds Dark Nebula 183 [or L183 or LDN183]. The heart of the cloud is revealed by the strong scattering of mid-infrared light by micrometer-sized grains. This phenomenon is present in half of the studied objects.Laurent Pagani/Data: NASA
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Light from the cosmic clouds where stars and planets are born could soon reveal secrets about these mysterious formative regions, a new study suggests.

Cold molecular clouds are the cradles of stars and planets, where dense clusters of gas collapse to form protostars and immense clumps of dust grains can become Earth-like worlds. But just how this happens is largely unknown, in part because the clouds shroud what’s going on, so astronomers can’t see the action in visible light.

Now light dubbed "coreshine" that emerges from the center of these clouds might reveal clues about how the stars and planets develop over time, researchers say.

In 2005, NASA's Spitzer Space Telescope discovered infrared light emerging from the core of a cold, starless molecular cloud roughly 400 light-years away. This cloud, known as L183, is roughly 80 times the mass of the sun.

The infrared beams detected from L183 were likely the result of starlight passing through the cloud that got scattered off dust in its core, the cloud's densest region. The specific wavelength of the rays suggest the dust grains had to be at least 1 micron in size, or roughly a hundredth the width of a human hair.

"You can think of the grains as small mirrors," said researcher Laurent Pagani, an astrophysicist at the Paris Observatory. "If the mirror is much smaller than the wavelength, the light will not notice the mirror."

This size would make each grain about 10 times wider than the average dust motes thought to make up these clouds. As such, this radiation could yield insights regarding how the construction blocks of stars and planets grow.

Now the scientists reveal this coreshine effect is not limited just to L183. Instead, it is actually common in many molecular clouds across the galaxy. Pagani and his colleagues used Spitzer to investigate the cores of 110 different molecular clouds, and about half of them clearly gave off coreshine.

Further analysis of coreshine should reveal details about the properties of the grains causing this light. Since the size of the dust grains should grow over time, the coreshine should also shed light on the age of clouds, Pagani said, and the location of this radiation within the cloud could yield insights regarding its internal structure.

All this information could ultimately help scientists understand how planets and stars form.

"For a long time, models of dust growth were far too slow — typical times of hundreds of million years — and were not trustworthy," Pagani explained. He said a new model designed by his colleague Chris Ormel of the Max Planck Institute for Astronomy in Heidelberg, Germany may prove more accurate and match the recent observations.

Pagani and his team detailed their findings in the Sept. 24 issue of the journal Science.

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