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An excess of 'failed' stars is a bad sign for alien life

From Engadget - July 10, 2017

Brown dwarfs are too hot and big to be planets, but do not quite qualify as stars as they lack the mass to fuse hydrogen to helium in a "main sequence" reaction. It's thought that they glow and emit infrared light, plus a very small amount of visible light, thanks to less energetic fusion of deuterium (2H) or lithium, provided their mass is above a certain threshold. Because they ca not sustain a stable fusion reaction, they are often called "failed" stars.

Despite the reduced of opportunity for life, the discovery is still exciting. Astronomers always thought that brown dwarf stars were out there, but never actually imaged one until 1994 thanks to improved infrared telescope imaging. In 2013, a NASA team used the infrared cameras on the Spitzer and Hubble space telescopes, and found that there are up to 70 billion of them in the Milky Way galaxy.

Astronomers from the University of Hull thought that figure seemed high, so they scanned a young, massive cluster 5,000 light years away using Europe's ground-based Very Large Telescope (VLT). Surprisingly, they found that the density of brown dwarfs could be even higher, with up to 100 billion of them in the Milky Way. That's a lot, because researchers think our galaxy only holds up to 100 billion to 400 billion stars of all types, total.

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