August 10, 2012 – Brown Dwarfs, Strange New Objects of the Universe: Brown dwarfs begin their lives like stars but they never accumulate enough mass to fuse atoms steadily at their cores and shine with bright starlight — as our sun does so well. Instead, they fade and cool with time, giving off most of their light in infrared wavelengths. Three types of “Brown Dwarfs” are pictured above: L, T and Y. The objects are progressively cooler in atmospheric temperatures as you move from left to right. Y dwarfs are the newest and coldest class of brown dwarfs. The picture, above, illustrates what brown dwarfs of different types probably look like.
Astronomers hunted these dark objects for many years without success. When viewed with a visible-light telescope, they are nearly impossible to see. On December 14, 2009, NASA launched its Widefield Infrared Survey Explorer (WISE) telescope. WISE spent over a year imaging the entire sky. WISE orbited the Earth several hundred miles above the dividing line between night and day on Earth, carrying an extremely sensitive infrared telescope, that was kept very cold (below -430ºF) by a solid hydrogen ice pack. WISE scanned the entire sky for these and other objects, and was able to spot their feeble light with its highly sensitive infrared vision, the spectrum at which these bodies emit most of their light.
The three types of brown dwarfs have very different atmospheric temperatures. A typical L dwarf has a temperature of 2,600 degrees Fahrenheit (1,400 degrees Celsius). A typical T dwarf has a temperature of 1,700 degrees Fahrenheit (900 degrees Celsius). The coldest Y dwarf, so far identified by WISE, has a temperature of 80 degrees Fahrenheit (25 degrees Celsius). The atmospheres of brown dwarfs are similar to those of gas-giant planets like Jupiter, but they are easier to observe because they are alone in space, away from the blinding light of a parent star.
The L dwarf is seen as a dim red orb to the eye. The T dwarf is even fainter and appears with a darker reddish, or magenta, hue. The Y dwarf is dimmer still. Because astronomers have not yet detected Y dwarfs at the visible wavelengths we see with our eyes, the choice of a purple hue is done mainly for artistic reasons. But they are not certain what color Y dwarfs are, since these objects have not been detected at visible wavelengths. The purple color shown here was chosen mainly for artistic reasons.
Strangely, brown dwarfs all have the same dimensions, roughly the size of the planet Jupiter, regardless of their mass. This mass disparity can be as large as fifteen times or more when comparing an L to a Y dwarf, despite the fact that both objects have the same radius. Mass is a measurement of the amount of matter something contains. In other words, a bowling ball and beach ball may both have the same size but the bowling ball has a much higher mass than the beach ball.
So far, 100 brown dwarfs have been found, six of which are Y Dwarfs. They are located from nine to 40 light-years away. By comparison, the star closest to our solar system, Proxima Centauri, is about four light-years away.
Brown dwarfs are sometimes referred to as “failed” stars. The Y’s are the coldest members of the brown dwarf family. What little light they do emit is at infrared wavelengths.
The Master of Disaster