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Brown dwarfs hiding in plain sight

Brown dwarfs are like stars, but too small to ignite fusion in their cores and so shine as stars do. If you saw one, it wouldn’t be brown. It’d be magenta.

Astronomers led by Jasmin Robert of Université de Montréal announced on September 6, 2016 that they’ve discovered 165 ultracool brown dwarfs, several in our own solar neighborhood. They said that, although hundreds of ultracool brown dwarfs have already been discovered, they felt before starting their recent survey that many more remained to be found. So they surveyed 28 percent of the sky and found the 165 ultracool brown dwarfs, about a third of which have unusual compositions or other peculiarities, and so didn’t show up on earlier surveys. These findings are published in The Astrophysical Journal.

When talking about brown dwarfs, ultracool means temperatures under about 3,500 Fahrenheit or 2,200 kelvin.

Prior to their study, the techniques used to identify ultracool brown dwarfs were overlooking those with unusual compositions. Study co-author Jonathan Gagné of the Carnegie Institution of Science commented:

The search for ultracool brown dwarfs in the neighborhood of our own solar system is far from over. Our findings indicate that many more are hiding in existing surveys.

The astronomers’ September 6 statement explained why astronomers want to study brown dwarfs, and also provided the video at the top of this post, which gives some background. The statement said:

Cool brown dwarfs are a hot topic in astronomy right now. Smaller than stars and bigger than giant planets, they hold promise for helping us understand both stellar evolution and planet formation. New work from a team including Carnegie’s Jonathan Gagné has discovered several ultracool brown dwarfs in our own solar neighborhood. Their findings are published in The Astrophysical Journal.

Brown dwarfs are sometimes called failed stars. They are too small to sustain the hydrogen fusion process that powers stars, so after forming they slowly cool, contract, and dim over time. Their temperatures can range from nearly as hot as a star to as cool as a planet and their masses also range between star-like and giant-planet-like.

They’re fascinating to astronomers for a variety of reasons, mostly because they can serve as a bridge between stars and planets and how the former influences the latter, particular when it comes to composition and atmospheric properties.

But much about them remains unknown.

Read more via Carnegie Institution of Science.

Bottom line: Astronomers announce 165 newly discovered ultracool brown dwarfs and provide background, plus a video, explaining why they want to study them.

Deborah Byrd