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For the Iranian band, see Hypernova (band).
Eta Carinae, in the constellation of Carina, one of the nearer candidates for a future hypernova

A hypernova (pl. hypernovae or hypernovas) is a type of supernova explosion with an energy substantially higher than that of standard supernovae. An alternative term for most hypernovae is "superluminous supernovae" (SLSNe). Such explosions are believed to be the origin of long-duration gamma-ray bursts.[1]

Just like supernovae in general, hypernovae are produced by several different types of stellar explosion: some well modelled and observed in recent years, some still tentatively suggested for observed hypernovae, and some entirely theoretical. Numerous hypernovae have been observed corresponding to supernovae type Ic and type IIn, and possibly also at least one of type IIb.[2]

The word collapsar, short for collapsed star, was formerly used to refer to the end product of stellar gravitational collapse, a stellar-mass black hole. The word is now sometimes used to refer to a specific model for the collapse of a fast-rotating star, as discussed below.

History of the term[edit]

Before the 1990s, the term "hypernova" was used sporadically to describe the theoretical extremely energetic explosions of extremely massive population III stars. It has also been used to describe other extreme energy events, such as mergers of supermassive black holes.

In 1998, a paper suggesting a link between gamma-ray bursts and young massive stars[3] formally proposed to use the term "hypernova" for the visible after-glow from those gamma-ray bursts. The energy of such events was speculated to be up to several hundred times that of known supernovae.

Almost simultaneously, various over-luminous supernovae were being discovered and investigated.[4][5][6][7] These events were described as hypernovae and varied from less than five to around 50 times as energetic as other supernovae and up to 20 times as luminous as a standard type Ia supernova at its peak. This definition has become standard for the term "hypernova", although not all of them are associated with gamma-ray bursts.

Investigation of these types of luminous supernovae suggests that some of them are due to explosions of extremely massive low metallicity stars by the pair instability mechanism, although not with the energies that were speculated for them decades earlier.[8][9]

Gamma-ray bursts[edit]

Main article: Gamma-ray burst

Gamma-ray bursts are some of the most energetic events observed in the universe, but their origin was entirely speculative[10] until around the year 2000. Now, hypernova explosions are known to cause at least some gamma-ray bursts, although some gamma-ray bursts are likely from completely different events and not all hypernovae are necessarily associated with gamma-ray bursts.

A gamma-ray burst from a nearby hypernova could destroy life on Earth; however, no likely candidate progenitors are close enough to be a danger. Some have suggested[who?] that a hypernova may have caused the Ordovician–Silurian mass extinction on Earth 440 million years ago, but no categorical evidence for this hypothesis exists.[11]

Causes of hypernovae[edit]

A wide variety of models have been proposed to explain events an order of magnitude or more greater than standard supernovae. The collapsar and CSM models are widely accepted and a number of events are well-observed. Other models are still only tentatively observed or entirely theoretical.

Collapsar model[edit]

For a completely collapsed star, see stellar black hole.
Light curves compared to normal supernovae

The collapsar model is a type of hypernova that produces a gravitationally collapsed object, or black hole. When core collapse occurs in a star with a core at least around fifteen times as massive as the sun—though chemical composition and rotational rate are also significant—the explosion energy is insufficient to expel the outer layers of the star, and it will collapse into a black hole without producing a visible supernova outburst.

A star with a core mass slightly below this level—in the range of 5–15 times the sun—will undergo a supernova explosion, but so much of the ejected mass falls back onto the core remnant that it still collapses into a black hole. If such a star is rotating slowly, then it will produce a faint supernova, but if the star is rotating quickly enough, then the fallback to the black hole will produce relativistic jets. The energy that these jets transfer into the ejected shell renders the visible outburst substantially more luminous than a standard supernova. The jets also beam high energy particles and gamma rays directly outward and thereby produce x-ray or gamma-ray bursts; the jets can last for several seconds or longer and correspond to long-duration gamma-ray bursts, but they do not appear to explain short-duration gamma-ray bursts.

A star with a 5–15 solar mass core has an approximate total mass of 25–90 suns if the star has not undergone mass loss. Such a star will still have a hydrogen envelope and will explode as a type II supernova. Faint type II supernovae have been observed, but no definite candidates for a type II hypernova (except type IIn, which are not thought to be jet supernovae). Only the very lowest metallicity population III stars will reach this stage of their life with little mass loss. Other stars, including most of those visible to us, will have had most of their outer layers blown away by their high luminosity to become a Wolf-Rayet star and will explode as type Ib or type Ic supernovae. Many observed hypernovae are type Ic and those associated with gamma-ray bursts are almost all type Ic, and these are very good candidates for having relativistic jets produced by fallback to a black hole. Not all type Ic hypernovae correspond to observed gamma-ray bursts but the burst would only be visible if one of the jets were aimed towards us.

In recent years a great deal of observational data on long-duration gamma-ray bursts has significantly increased our understanding of these events and made clear that the collapsar model produces explosions that differ only in detail from more or less ordinary supernovae and have energy ranges from approximately normal to around 100 times larger. Nevertheless, they continue sometimes to be referred to in the literature as hypernovae. The word hypernova itself was coined by S.E. Woosley.[12]

A good example of a collapsar hypernova is Sn1998bw,[13] which was associated with the gamma-ray burst GRB 980425. It is classified as a type Ic supernova due to its distinctive spectral properties in the radio spectrum, indicating the presence of relativistic matter.

CSM model[edit]

Almost all observed hypernovae have had spectra similar to either a type Ic or type IIn supernova. The type Ic hypernovae are thought to be produced by jets from fallback to a black hole, but type IIn hypernovae have significantly different light curves and are not associated with gamma-ray bursts. Type IIn supernovae are all embedded in a dense nebula probably expelled from the progenitor star itself, and this circumstellar material (CSM) is thought to be the cause of the extra luminosity.[14] When material expelled in an initial normal supernova explosion meets dense nebular or material or dust close to the star, the shockwave converts kinetic energy efficiently into visible radiation. Thus we see an extremely luminous supernova of extended duration even though the initial explosion energy was the same as that of a normal supernova.

Although any supernova type could potentially produce a type IIn hypernova, given suitable surrounding CSM, the constraints on the size and density of the CSM mean that it will almost always be produced from the star itself immediately prior to the supernova explosion. Such stars are hypergiants and LBVs undergoing substantial mass loss due to Eddington instability, for example SN2005gl.[15]

Pair-instability supernova[edit]

Another type of hypernova is a pair-instability supernova, of which SN 2006gy[16] may possibly be the first observed example. This supernova event was observed in a galaxy about 238 million light years (73 megaparsecs) from Earth.

The theoretical basis for pair-instability collapse has been known for many decades[17] and was suggested as a dominant source of higher mass elements in the early universe as super-massive population III stars exploded. In a pair-instability supernova, the pair production effect causes a sudden pressure drop in the star's core, leading to a rapid partial collapse. Gravitational potential energy from the collapse causes runaway fusion of the core which entirely destroys the star, leaving no remnant.

Current models show that this phenomenon only happens in stars with extreme low metallicity and masses between about 140 and 260 times the sun, making observing them in the local universe extremely unlikely. Although originally expected to produce hypernova explosions hundreds of times greater than a supernova, they actually produce luminosities ranging from about the same as a normal core collapse supernova to perhaps 50 times brighter, although remaining bright for much longer.[18]

Magnetar energy release[edit]

Models of the creation and subsequent spin down of a magnetar yield much higher luminosities than regular supernova[19][20] events and match the observed properties[21] of at least some hypernova. In cases where pair-instability supernova may not be a good fit for explaining a hypernova,[22] a magnetar explanation is more plausible.

Other models[edit]

There are still models for hypernova explosions produced from binary systems, white dwarf or neutron stars in unusual arrangements or undergoing mergers, and some of these are proposed to account for gamma-ray bursts.

See also[edit]

References[edit]

  1. ^ "A Hypernova: The Super-charged Supernova and its link to Gamma-Ray Bursts". Imagine the Universe!. NASA. Retrieved 9 December 2011. 
  2. ^ Hamuy, M.; Deng, J.; Mazzali, P. A.; Morrell, N. I.; Phillips, M. M.; Roth, M.; Gonzalez, S.; Thomas-Osip, J.; Krzeminski, W.; Contreras, C.; Maza, J.; González, L.; Huerta, L.; Folatelli, G. N.; Chornock, R.; Filippenko, A. V.; Persson, S. E.; Freedman, W. L.; Koviak, K.; Suntzeff, N. B.; Krisciunas, K. (2009). "Supernova 2003bg: The First Type IIb Hypernova" (pdf). The Astrophysical Journal 703 (2): 1612–1623. arXiv:0908.1783. Bibcode:2009ApJ...703.1612H. doi:10.1088/0004-637X/703/2/1612.  edit
  3. ^ Paczyński, B. (1998). "Are Gamma-Ray Bursts in Star-Forming Regions?" (pdf). The Astrophysical Journal 494 (1): L45–L48. arXiv:astro-ph/9710086. Bibcode:1998ApJ...494L..45P. doi:10.1086/311148.  edit
  4. ^ Iwamoto, K.; Nakamura, T.; Nomoto, K. I.; Mazzali, P. A.; Danziger, I. J.; Garnavich, P.; Kirshner, R.; Jha, S.; Balam, D.; Thorstensen, J. (2000). "The Peculiar Type Ic Supernova 1997ef: Another Hypernova" (pdf). The Astrophysical Journal 534 (2): 660–669. Bibcode:2000ApJ...534..660I. doi:10.1086/308761.  edit
  5. ^ Nomoto, K.; Iwamoto, K.; Mazzali, P. A.; Umeda, H.; Nakamura, T.; Patat, F.; Danziger, I. J.; Young, T. R.; Suzuki, T.; Shigeyama, T.; Augusteijn, T.; Doublier, V.; Gonzalez, J. -F.; Boehnhardt, H.; Brewer, J.; Hainaut, O. R.; Lidman, C.; Leibundgut, B.; Cappellaro, E.; Turatto, M.; Galama, T. J.; Vreeswijk, P. M.; Kouveliotou, C.; Van Paradijs, J.; Pian, E.; Palazzi, E.; Frontera, F. (1998). "A Hypernova Model for the Supernova Associated with the Big γ-Ray Burst of 25 April 1998". Nature 395 (6703): 672–674. doi:10.1038/27155.  edit
  6. ^ Mazzali, P. A.; Deng, J.; Maeda, K.; Nomoto, K.; Umeda, H.; Hatano, K.; Iwamoto, K.; Yoshii, Y.; Kobayashi, Y.; Minezaki, T.; Doi, M.; Enya, K.; Tomita, H.; Smartt, S. J.; Kinugasa, K.; Kawakita, H.; Ayani, K.; Kawabata, T.; Yamaoka, H.; Qiu, Y. L.; Motohara, K.; Gerardy, C. L.; Fesen, R.; Kawabata, K. S.; Iye, M.; Kashikawa, N.; Kosugi, G.; Ohyama, Y.; Takada-Hidai, M.; Zhao, G. (2002). "The Type Ic Hypernova SN 2002ap" (pdf). The Astrophysical Journal 572 (1): L61–L65. Bibcode:2002ApJ...572L..61M. doi:10.1086/341504.  edit
  7. ^ Mazzali, P. A.; Deng, J.; Pian, E.; Malesani, D.; Tominaga, N.; Maeda, K.; Nomoto, K. I.; Chincarini, G.; Covino, S.; Della Valle, M.; Fugazza, D.; Tagliaferri, G.; Gal‐Yam, A. (2006). "Models for the Type Ic Hypernova SN 2003lw associated with GRB 031203" (pdf). The Astrophysical Journal 645 (2): 1323–1330. arXiv:astro-ph/0603516. Bibcode:2006ApJ...645.1323M. doi:10.1086/504415.  edit
  8. ^ Gal-Yam, A.; Mazzali, P.; Ofek, E. O.; Nugent, P. E.; Kulkarni, S. R.; Kasliwal, M. M.; Quimby, R. M.; Filippenko, A. V.; Cenko, S. B.; Chornock, R.; Waldman, R.; Kasen, D.; Sullivan, M.; Beshore, E. C.; Drake, A. J.; Thomas, R. C.; Bloom, J. S.; Poznanski, D.; Miller, A. A.; Foley, R. J.; Silverman, J. M.; Arcavi, I.; Ellis, R. S.; Deng, J. (2009). "Supernova 2007bi as a pair-instability explosion". Nature 462 (7273): 624–627. doi:10.1038/nature08579. PMID 19956255.  edit
  9. ^ Kasen, D.; Woosley, S. E.; Heger, A. (2011). "Pair Instability Supernovae: Light Curves, Spectra, and Shock Breakout" (pdf). The Astrophysical Journal 734 (2): 102. arXiv:1101.3336. Bibcode:2011ApJ...734..102K. doi:10.1088/0004-637X/734/2/102.  edit
  10. ^ Higdon, J. C.; Lingenfelter, R. E. (1990). "Gamma-Ray Bursts". Annual Review of Astronomy and Astrophysics 28: 401. Bibcode:1990ARA&A..28..401H. doi:10.1146/annurev.aa.28.090190.002153.  edit
  11. ^ Minard, Anne (April 3, 2009). "Gamma-Ray Burst Caused Mass Extinction?". National Geographic News. Retrieved 16 April 2010. 
  12. ^ Woosley, S. E.; Weaver, T. A. (1982). "Theoretical Models for Supernovae". In Rees, M. J.; Stoneham, R. J. Supernovae: A Survey of Current Research. NATO ASI Series C90. Dordrecht: D. Reidel Publishing. p. 79. Bibcode:1982sscr.conf...79W. ISBN 9789027714428. 
  13. ^ Fujimoto, S. I.; Nishimura, N.; Hashimoto, M. A. (2008). "Nucleosynthesis in Magnetically Driven Jets from Collapsars" (pdf). The Astrophysical Journal 680 (2): 1350–1358. arXiv:0804.0969. Bibcode:2008ApJ...680.1350F. doi:10.1086/529416.  edit
  14. ^ Smith, N.; Chornock, R.; Li, W.; Ganeshalingam, M.; Silverman, J. M.; Foley, R. J.; Filippenko, A. V.; Barth, A. J. (2008). "SN 2006tf: Precursor Eruptions and the Optically Thick Regime of Extremely Luminous Type IIn Supernovae" (pdf). The Astrophysical Journal 686 (1): 467–484. arXiv:0804.0042. Bibcode:2008ApJ...686..467S. doi:10.1086/591021.  edit
  15. ^ Gal-Yam, A.; Leonard, D. C. (2009). "A Massive Hypergiant Star as the Progenitor of the Supernova SN 2005gl" (pdf). Nature 458 (7240): 865–867. doi:10.1038/nature07934. PMID 19305392.  edit
  16. ^ Smith, N.; Chornock, R.; Silverman, J. M.; Filippenko, A. V.; Foley, R. J. (2010). "Spectral Evolution of the Extraordinary Type IIn Supernova 2006gy" (pdf). The Astrophysical Journal 709 (2): 856–883. arXiv:0906.2200. Bibcode:2010ApJ...709..856S. doi:10.1088/0004-637X/709/2/856.  edit
  17. ^ Fraley, G. S. (1968). "Supernovae Explosions Induced by Pair-Production Instability" (pdf). Astrophysics and Space Science 2 (1): 96–114. Bibcode:1968Ap&SS...2...96F. doi:10.1007/BF00651498.  edit
  18. ^ Kasen, D.; Woosley, S. E.; Heger, A. (2011). "Pair Instability Supernovae: Light Curves, Spectra, and Shock Breakout" (pdf). The Astrophysical Journal 734 (2): 102. arXiv:1101.3336. Bibcode:2011ApJ...734..102K. doi:10.1088/0004-637X/734/2/102.  edit
  19. ^ Woosley, S.E. (August 2010). "Bright Supernovae From Magnetar Birth". Astrophysical Journal Letters 719 (2). arXiv:0911.0698. Bibcode:2010ApJ...719L.204W. doi:10.1088/2041-8205/719/2/L204. Retrieved 27 December 2013. 
  20. ^ 2010, ApJ, 717, 245; Kasen, Daniel, Bildsten, Lars (2010). "Supernova Light Curves Powered by Young Magnetars". Astrophysical Journal 717: 245–249. arXiv:0911.0680. Bibcode:2010ApJ...717..245K. doi:10.1088/0004-637X/717/1/245. Retrieved 27 December 2013. 
  21. ^ D.A. Howell, et al. (October 2013). "Two superluminous supernovae from the early universe discovered by the Supernova Legacy Survey". Astrophysical Journal 779 (2). arXiv:1310.0470. Bibcode:2013ApJ...779...98H. doi:10.1088/0004-637X/779/2/98. Retrieved 27 December 2013. 
  22. ^ M. Nicholl, et. al (October 2013). "Slowly fading super-luminous supernovae that are not pair-instability explosions". Nature 502 (7471). arXiv:1310.4446. Bibcode:2013Natur.502..346N. doi:10.1038/nature12569. Retrieved 27 December 2013. 

Further reading[edit]


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