Friday, June 25, 2010
Today's press release on the discovery of 14 brown dwarf stars by the Spitzer space telescope is interesting in that it spends little time talking about the discovery itself, and much more on brown dwarfs in general and the number WISE is expected to find. This discovery is important in that it gives us an idea of their frequency; theoretically brown dwarfs should be more plentiful than red dwarfs (less massive objects are always more plentiful) and thus there should be a large number of them relatively close to our own solar system, but without a proper infrared survey it's impossible to tell. Spitzer has a much narrower view of the cosmos than WISE, but the frequency of those found by Spitzer in this survey (a region in the constellation Boötes) shows that yes, there should be a large number of them near us as well - a hundred or more within 25 light years of the Sun. As you can see, the WISE survey (the bubble) is shorter but covers everything, whereas Spitzer is long and thin. Find a target discovered by WISE and one can turn the Spitzer telescope on it to find out more, but Spitzer alone would take an eternity to discover them in the first place.
Even this "hundred or more" may be a conservative guess as there are 68 stars within just 16 light years of the Sun, so the final tally within 25 light years should work out to at least hundreds, not just a hundred or more.
The most important discovery will of course be the likely discovery of a brown dwarf closer to us than Alpha Centauri. Once given the nickname Nemesis, astronomers have recently been promoting the name Tyche instead as a benevolent counterpart, not an evil twin that swoops in every once in a while and bombards the Earth with swarms of comets.
The most interesting part of the press release may be this:
The 14 objects found by Spitzer are hundreds of light-years away -- too far away and faint for ground-based telescopes to see and confirm with a method called spectroscopy. But their presence implies that there are a hundred or more within only 25 light-years of our sun. Because WISE is looking everywhere, it will find these missing orbs, which will be close enough to confirm with spectroscopy.In other words, to find out more about the most interesting brown dwarfs (those closest to us) after their discovery we won't need to wait for another infrared telescope to be launched.
Finally, one reminder: though brown dwarfs are technically sub-stellar objects, I recommend emphasizing them as being brown dwarf stars, as titles can often make the difference between great interest and outright dismissal of an object in space. Had Ceres been called a planet all this time we certainly would have seen a probe there back in the 1980s or so, not 2015 as things have worked out.