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How viruses shape our world. The era of greyhound racing in the U. See how people have imagined life on Mars through history. I'll explain that in a minute. The important thing is that this image shows a very nearby brown dwarf, maybe 18 - 30 light years away the distance is hard to determine, but observations taken over the next year or so should pin it down.
That's really close! The nearest known star, Proxima Centauri a faint red dwarf is 4. You'd think think we'd have a pretty good idea of all the stars near us, since they'd be among the brightest in the sky. But in fact brown dwarfs are so faint that to optical telescopes they can escape detection even if they're our cosmic neighbors.
WISE, however, looks in the infrared, where brown dwarfs glow considerably brighter. And that brings me to the weird colorful adjectives we use for these objects. The color of a star depends mostly on its temperature and the way our eyes see the mixed colors from stars, which is complicated, and I will ignore here. Very hot stars are blue, middlin' hot are white like the Sun , cooler ones are orange, and very cool ones are red. Brown dwarfs are even milder than red dwarfs, and their spectrum actually peaks in the infrared.
But it's a bit more complicated than that. These have surface temperatures of about 1, K — 2, K. They are cool enough that lithium and other alkali metals are present in their atmosphere. Below the L category are T dwarfs, with surface temperatures of about K — 1, K. These are brightest in the near infrared, and are cool enough for methane and other molecules to build up in their atmosphere.
But even the T class dwarfs are not the coolest stars. Recently the WISE infrared telescope discovered six very cool brown dwarf stars. Since they all have temperatures less than K, they are placed in a new spectral type known as Y dwarfs.
The coolest of these has an atmospheric temperature of only K, or about room temperature. Hertzsprung-Russell Diagram, shows relationship of star color and temperature source. It also shows us which are the biggest stars , and which are smaller, as well as where we can find the dimmest stars. In the H-R Diagram, the hottest temperatures are on the left, coolest on the right. Where the exponent is negative, e. Main sequence stars are burning hydrogen atoms in their cores to create helium atoms.
Our own Sun is an example of a main-sequence star. The Hertzsprung-Russell Diagram also shows that the coolest stars on the main sequence, i. This shows us that bright, hot blue stars tend to be younger because they are burning their hydrogen violently fast and tend not to live for very long. Redder, cooler stars are the opposite. They are turning their hydrogen into helium much more slowly and can exist in that state for a very long time.
Our own sun, a pretty average star by all accounts, is around halfway through its ten billion year life. When a star has used up its hydrogen, it leaves the main-sequence and becomes a different type of star.
A star with a mass less than 0.
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