- Designations: Boomerang Nebula, PGC 3074547, Centaurus Bipolar Nebula, Bow Tie Nebula
- Object: Protoplanetary nebula
- Constellation: Centaurus
- Right ascension: 12h 44m 45.45s
- Declination: −54° 31′ 11.4″
- Apparent size: 1.445′ × 0.724′
- Radius: 1 light year
- Distance: 5,000 light years
The Boomerang Nebula is a protoplanetary nebula located in the constellation Centaurus, around 5,000 light years away from the Solar System. It is the coldest place in the universe, with a temperature of only 1 Kelvin (-272.15°C or -458°F). The nebula is even colder than the faint −270 °C background glow of the Big Bang.
The Boomerang Nebula is believed to be a star system evolving toward the planetary nebula phase. It was formed by a star in the late stage of its life shedding its mass to form clouds of dust and gas and illuminating the clouds with its light.
The central star continues to expel material from its surface and outflowing gas continues to move outwards, so the nebula continues to form. It is expanding at a rate of 164 km/s. In the last 1,500 years, the star has lost almost one and a half times the mass of the Sun and is shedding it’s mass about 10 times faster than similar stars that are expelling gas.
The preplanetary nebula stage lasts only about a thousand years. As the gas from the central star continues to expand, this is what gives the nebula it’s extremely low temperature. As of mid-2017, it is believed that the star at the center of the nebula is a dying red giant.
The nebula was revealed to be the coldest natural object in the universe in 1995. Astronomers used the 15 meter Swedish-ESO Submilimetre Telescope (SEST), which is a radio telescope at the La Silla Observatory in Chile, when they made the discovery.
The Boomerang Nebula has an interesting shape different to many other nebulae. It is hourglass shaped when viewed from Earth. This is the result of the nebula’s central region being obscured by dust.
The structure of the nebula consists of a large, round molecular gas cloud which is rapidly expanding and a considerably denser cloud of dust surrounding the central star. The smaller, doughnut-shaped dust cloud blocks the light radiating from the star’s equator, which is why the nebula appears double-lobed. There is also a hollow cylindrical nebula around the dying star. This is suspected to have been formed by jets of hydrogen or helium gas emanating from the star’s poles, eroding the surrounding gas and carving out a tunnel in it.
The nebula was given its name by Keith Taylor and Mike Scarrott in 1980, after they had observed it with the 3.9-metre Anglo Australian Telescope at the Siding Spring Observatory near Coonabarabran in New South Wales, Australia. They were only able to see the slightly curved shape of the nebula’s asymmetrical lobes, which resembled the shape of a boomerang.
Later, more detailed images taken by NASA’s Hubble Space Telescope in 1998 revealed that the bow tie shape was an illusion and that the cloud of gas surrounding the central star was in fact spherical.
In 2013, observations of the ALMA radio interferometer revealed that the visible double lobe of the Boomerang Nebula is surrounded by a larger spherical volume of cold gas seen only in sub-millimeter radio wavelengths. The nebula’s outer layers appear to be gradually warming.
- Boomerang Nebula – By ESA/NASA – http://www.spacetelescope.org/images/heic0301a/, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2128416