Boomerang Nebula
The Boomerang Nebula is a protostellar nebula located 5,000 light-years from Earth in the constellation Centaurus . It is also known as the Sagittarius Nebula and is cataloged as LEDA 3074547. The nebula has a temperature of 1 Kelvin (−272.15 ° C −457.87 ° F ), making it the coldest known natural location in the universe.
The Boomerang Nebula is thought to be a star system evolving into a fertile planetary cloud. It continues to form and evolve as gas streams out from its center. Millimeter-scale dust grains obscure part of the center of the nebula so that most of the visible light coming out of the nebula is from opposite poles forming a distinctive hourglass shape as seen from Earth. The outgoing gas is moving at a speed of about 164 km/s, which indicates that it is expanding rapidly; this expansion is the reason for the nebula's unusually low temperature.
The Boomerang Nebula was first observed by astronomers Keith Taylor and Mike Scarrott in 1980 using the Anglo-Australian Telescope at Siding Spring Observatory . The astronomers were unable to see it clearly, but only saw a slight distortion at the nebula's poles indicating a curved, lightning-like shape. The nebula was imaged in high detail with the Hubble Space Telescope in 1998, revealing the nebula's more symmetrical hourglass shape.
In 1995, astronomers used the 15-meter Swedish-European Southern Supermillimeter Telescope in Chile to measure the nebula's temperature to be one degree above absolute zero (−272.15 degrees Celsius). This makes it the coldest place in the universe ever found, besides temperatures created in laboratories. Even the Big Bang's 2.7 Kelvin background radiation is warmer than the nebula. It is the only object ever found that naturally has a temperature lower than the background radiation.
In 2013, the Atacama Large Millimeter/submillimeter Array's visible radio interferometric observations of the Boomerang Nebula revealed other features. The nebula's visible double arcs were observed to be surrounded by a larger sphere of cold gas that can only be seen at sub-radio wavelengths . The outer edges of the coil appear to be gradually heating up.
As of mid-2017, the bright star at the center of the nebula is thought to be a dying red giant .
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