SN 2006gy was an extremely energetic supernova, also referred to as a hypernova or quark-nova, that was discovered on September 18, 2006. It was first observed by Robert Quimby and P. Mondol, and then studied by several teams of astronomers using facilities that included the Chandra, Lick, and KeckObservatories. In May 2007 NASA and several of the astronomers announced the first detailed analyses of the supernova, describing it as the "brightest stellar explosion ever recorded". In October 2007 Quimby announced that SN 2005ap had broken SN 2006gy's record as the brightest-ever recorded supernova, and several subsequent discoveries are brighter still.Time magazine listed the discovery of SN 2006gy as third in its Top 10 Scientific Discoveries for 2007.
Light curve of SN 2006gy (uppermost intermittent squares) compared with other types of supernovae
SN 2006gy occurred in a distant galaxy (NGC 1260), approximately 238 millionlight-years (73 megaparsecs) away. The energy radiated by the explosion has been estimated at 1051ergs (1044J), making it a hundred times more powerful than the typical supernova explosion which radiates 1049 ergs (1042 J) of energy. Although at its peak the SN 2006gy supernova was intrinsically 400 times as luminous as SN 1987A, which was bright enough to be seen by the naked eye, SN 2006gy was more than 1,400 times as far away as SN 1987A, and too far away to be seen without a telescope.
SN 2006gy is classified as a type II supernova because it showed lines of hydrogen in its spectrum, although the extreme brightness indicates that it is different from the typical type II supernova. Several possible mechanisms have been proposed for such a violent explosion, all requiring a very massive progenitor star. The most likely explanations involve the efficient conversion of explosive kinetic energy to radiation by interaction with circumstellar material, similar to a type IIn supernova but on a larger scale. Such a scenario might occur following mass loss of 10 or more M☉ in a luminous blue variable eruption, or through pulsational pair instability ejections. Denis Leahy and Rachid Ouyed, Canadian scientists from the University of Calgary, have proposed that SN 2006gy was the birth of a quark star.
Similarity to Eta Carinae
Eta Carinae (η Carinae or η Car) is a highly luminous hypergiant star located approximately 7,500 light-years from Earth in the Milky Way galaxy. Since Eta Carinae is 32,000 times closer than SN 2006gy, the light from it will be about a billion-fold brighter. It is estimated to be similar in size to the star which became SN 2006gy. Dave Pooley, one of the discoverers of SN 2006gy, says that if Eta Carinae exploded in a similar fashion, it would be bright enough that one could read by its light on Earth at night, and would even be visible during the daytime. SN 2006gy's apparent magnitude (m) is 15, so a similar event at Eta Carinae will have an m of about −7.5. According to astrophysicist Mario Livio, this could happen at any time, but the risk to life on Earth would be low.
This diagram illustrates the pair-instability process that astronomers think triggered the explosion in SN 2006gy. A sufficiently massive star can produce gamma rays of such high energy that some of the photons convert into pairs of electrons and positrons causing a runaway reaction which destroys the star.
SN2006gy (top right) in infrared
SN2006gy (top right) in ultraviolet
NASA artist's impression of the explosion of SN 2006gy
^Ofek, E. O.; Cameron, P. B.; Kasliwal, M. M.; Gal-Yam, A.; Rau, A.; Kulkarni, S. R.; Frail, D. A.; Chandra, P.; Cenko, S. B.; Soderberg, A. M.; Immler, S. (2007). "SN 2006gy: An Extremely Luminous Supernova in the Galaxy NGC 1260". The Astrophysical Journal. 659 (1): L13–L16. arXiv:astro-ph/0612408. Bibcode:2007ApJ...659L..13O. doi:10.1086/516749. S2CID 51811699.
^Smith, Nathan; Li, Weidong; Foley, Ryan J.; Wheeler, J. Craig; Pooley, David; Chornock, Ryan; Filippenko, Alexei V.; Silverman, Jeffrey M.; Quimby, Robert; Bloom, Joshua S.; Hansen, Charles (2007). "SN 2006gy: Discovery of the Most Luminous Supernova Ever Recorded, Powered by the Death of an Extremely Massive Star like η Carinae". The Astrophysical Journal. 666 (2): 1116–1128. arXiv:astro-ph/0612617. Bibcode:2007ApJ...666.1116S. doi:10.1086/519949. S2CID 14785067.
^NASA's Chandra Sees Brightest Supernova Ever, NASA Press Release on the Discovery, May 7, 2007
^Stevenson, D. S. (2014). "The Mysterious SN 2005ap and Luminous Blue Flashes". Extreme Explosions. Astronomers' Universe. pp. 239–251. doi:10.1007/978-1-4614-8136-2_10. ISBN 978-1-4614-8135-5.
^ abQuimby, R. M. (2012). "Superluminous Supernovae". Proceedings of the International Astronomical Union. 7: 22–28. Bibcode:2012IAUS..279...22Q. doi:10.1017/S174392131201263X.
^"Top 10 Scientific Discoveries: #3. Brightest Supernova Recorded", Time, 2007
^Smith, N.; Chornock, R.; Silverman, J. M.; Filippenko, A. V.; Foley, R. J. (2010). "Spectral Evolution of the Extraordinary Type IIn Supernova 2006gy". The Astrophysical Journal. 709 (2): 856–883. arXiv:0906.2200. Bibcode:2010ApJ...709..856S. doi:10.1088/0004-637X/709/2/856. S2CID 16959330.
^Leahy, Denis; Ouyed, Rachid (2008). "Supernova SN2006gy as a first ever Quark Nova?". Monthly Notices of the Royal Astronomical Society. 387 (3): 1193. arXiv:0708.1787. Bibcode:2008MNRAS.387.1193L. doi:10.1111/j.1365-2966.2008.13312.x. S2CID 15696112.