Monday, April 28, 2014

Astronomer Discovers the Fourth Closest Star System to Us -- And It's Cool!



Just last year, I posted the news that astronomer Kevin Luhman of Penn State had discovered the third closest star system to our own.  It consisted of a pair of failed stars -- stars containing too little material to shine consistently with visible light and thus commonly called brown dwarfs.

Now Luhman has done it again.  He recently announced the discovery of the fourth closest system -- this one consisting of the coldest brown dwarf ever found.  Known only by a long catalog number giving its cosmic "latitude and longitude" (WISE J085510.83-071442.5), the wanna-be star is 7.2 light years away.  That's right in our neighborhood as far as astronomical objects are concerned.

Our best estimate of its mass is that it weighs only as much as 3 to 10 Jupiters.  So, really, it could be more of a free-floating planet rather than a brown dwarf.  But since brown dwarfs are more common (planets are found more frequently around stars than by themselves), the discoverer is betting it's just a very cold and poorly endowed brown dwarf.

The image accompanying this note is just an artist's conception of what such a cold, failed star might look like.  After observing it with a variety of space-based telescopes (such as WISE and Spitzer, which are sensitive to infra-red or heat rays and not light), Luhman and his colleagues estimate that the outer temperature of this strange neighbor is as cold as the Earth's North Pole.  (Estimates vary from -54 to 9 degrees Fahrenheit, or -48 to 13 Centigrade.)   So its outer layers are like those of the giant planets far from our Sun, and nothing like a real star.  Stars have temperatures thousands of degrees hot.

What is remarkable to me is that, after 400 years of using telescopes, and more than 50 years of instruments in space, we are still discovering our closest neighbors!  It's not our fault, of course -- this neighbor was very shy, not shining with the kind of rich light power that our closest neighbor, the triple star system Alpha Centauri, gives off.  And in space, as on Earth, it's often the show-offs that get the attention.

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