Calcium-rich supernovae

Calcium-rich supernovae (or Calcium-rich transients, Ca-rich SNe) are a subclass of supernovae that, in contrast to more well-known traditional supernova classes, are fainter and produce unusually large amounts of calcium. Since their luminosity is located in a gap between that of novae and other supernovae, they are also referred to as "gap" transients. Only around 15 events have been classified as a calcium-rich supernova (as of August 2017) – a combination of their intrinsic rarity and low luminosity make new discoveries and their subsequent study difficult. This makes calcium-rich supernovae one of the most mysterious supernova subclasses currently known.

Origins and classification

A peculiar group of supernova that were unusually rich in calcium were identified by Alexei Filippenko and collaborators. Although they appeared somewhat similar to Type Ib and Ic supernovae, their spectra were dominated by calcium, without other signatures often seen in Type Ib and Ic supernovae, and the term calcium-rich was coined to describe them.[1] Subsequent discoveries led to the classification of empirically similar supernovae.[2][3] They share characteristics such as quickly rising and fading light curves that peak in luminosity between novae and supernovae, and spectra that are dominated by calcium 2–3 months after initial explosion.[4]

Explosion mechanism

The exact nature of the stellar systems and their subsequent explosions that give rise to calcium-rich supernovae are unknown. Despite appearing similar to Type Ib supernovae, it was noted that a different explosion mechanism was likely to be responsible for calcium-rich supernovae.[2] Since a large proportion of the galaxies from which they are thought to originate are early-type galaxies, and thus composed of old stellar populations, they are unlikely to contain many young, massive stars that give rise to Type Ib supernovae.[5] Supernova explosions in old stellar populations generally involved a white dwarf since these are old systems that can undergo thermonuclear explosion under the right circumstances, as is the case for Type Ia supernovae. However, because calcium-rich supernovae are much less luminous and fade more quickly than normal Type Ia supernovae, it is unlikely that the same mechanism is at play for both.

Another peculiarity of calcium-rich supernovae is that they appear to explode far away from galaxies, even reaching intergalactic space. Searches for faint dwarf galaxies at their locations have ruled that they are exploding in very low density environments, unlike other supernova types.[6][7] Multiple suggestions have been made to try and explain this behaviour. Binary systems of high-velocity stars, such as two white dwarfs or a white dwarf and a neutron star, that have been ejected from their galaxy either due to a neutron star kick[8][9] or interaction with the supermassive black hole in their galaxy[10][11] could produce explosions when they eventually merge (due to gravitational wave radiation) that would preferentially occur far from galaxies. Alternatively they have been suggested to be due to stars that reside in the intracluster medium within large galaxy groups or clusters, having been expelled from their galaxy during mergers or interactions.[7] The explosion would then be caused by the detonation of a low mass white dwarf during a merging event as part of a binary system, or the detonation of a helium shell on a white dwarf.

A calcium-rich supernova event expels several tenths of a solar mass in material at thousands of kilometres per second and reaches a peak luminosity equal to around 100–200 million times that of the Sun. Despite calcium-rich supernovae being comparatively rare and diminutive compared to other supernova types, they are thought to make a significant contribution to the production of calcium in the Universe.[12]

References

  1. ^ "IAUC 8159: 2003gh; 2001co, 2003H, 2003dg,, 2003dr". www.cbat.eps.harvard.edu. Retrieved 2017-08-10.
  2. ^ a b Perets, H. B.; Gal-Yam, A.; Mazzali, P. A.; Arnett, D.; Kagan, D.; Filippenko, A. V.; Li, W.; Arcavi, I.; Cenko, S. B. (2010-05-20). "A faint type of supernova from a white dwarf with a helium-rich companion". Nature. 465 (7296): 322–325. arXiv:0906.2003. Bibcode:2010Natur.465..322P. doi:10.1038/nature09056. ISSN 0028-0836. PMID 20485429.
  3. ^ Brown, Eryn (2010-05-19). "Supernova is rich in calcium". Los Angeles Times. ISSN 0458-3035. Retrieved 2017-08-10.
  4. ^ Kasliwal, Mansi M.; Kulkarni, S. R.; Gal-Yam, Avishay; Nugent, Peter E.; Sullivan, Mark; Bildsten, Lars; Ofer Yaron; Perets, Hagai B.; Arcavi, Iair (2012). "Calcium-rich Gap Transients in the Remote Outskirts of Galaxies". The Astrophysical Journal. 755 (2): 161. arXiv:1111.6109. Bibcode:2012ApJ...755..161K. doi:10.1088/0004-637X/755/2/161. ISSN 0004-637X.
  5. ^ Smartt, Stephen J. (2009). "Progenitors of Core-Collapse Supernovae". Annual Review of Astronomy and Astrophysics. 47 (1): 63–106. arXiv:0908.0700. Bibcode:2009ARA&A..47...63S. doi:10.1146/annurev-astro-082708-101737.
  6. ^ Lyman, J. D.; Levan, A. J.; James, P. A.; Angus, C. R.; Church, R. P.; Davies, M. B.; Tanvir, N. R. (2016-05-11). "Hubble Space Telescopeobservations of the host galaxies and environments of calcium-rich supernovae". Monthly Notices of the Royal Astronomical Society. 458 (2): 1768–1777. arXiv:1602.08098. Bibcode:2016MNRAS.458.1768L. doi:10.1093/mnras/stw477. ISSN 0035-8711.
  7. ^ a b Lunnan, R.; Kasliwal, M. M.; Cao, Y.; Hangard, L.; Yaron, O.; Parrent, J. T.; McCully, C.; Gal-Yam, A.; Mulchaey, J. S. (2017). "Two New Calcium-rich Gap Transients in Group and Cluster Environments". The Astrophysical Journal. 836 (1): 60. arXiv:1612.00454. Bibcode:2017ApJ...836...60L. doi:10.3847/1538-4357/836/1/60.
  8. ^ Lyman, J. D.; Levan, A. J.; Church, R. P.; Davies, M. B.; Tanvir, N. R. (2014-11-01). "The progenitors of calcium-rich transients are not formed in situ". Monthly Notices of the Royal Astronomical Society. 444 (3): 2157–2166. arXiv:1408.1424. Bibcode:2014MNRAS.444.2157L. doi:10.1093/mnras/stu1574. ISSN 0035-8711.
  9. ^ Parnell, Brid-Aine. "Lonely Supernovae May Have Been Kicked Out Of Their Galaxies". Forbes. Retrieved 2017-08-10.
  10. ^ Foley, Ryan J. (2015-09-21). "Kinematics and host-galaxy properties suggest a nuclear origin for calcium-rich supernova progenitors". Monthly Notices of the Royal Astronomical Society. 452 (3): 2463–2478. arXiv:1501.07607. Bibcode:2015MNRAS.452.2463F. doi:10.1093/mnras/stv789. ISSN 0035-8711.
  11. ^ "HubbleSite: News - NASA's Hubble Finds Supernovae in 'Wrong Place at Wrong Time'". hubblesite.org. Retrieved 2017-08-10.
  12. ^ Mulchaey, John S.; Kasliwal, Mansi M.; Kollmeier, Juna A. (2014). "Calcium-rich Gap Transients: Solving the Calcium Conundrum in the Intracluster Medium". The Astrophysical Journal Letters. 780 (2): L34. arXiv:1401.7017. Bibcode:2014ApJ...780L..34M. doi:10.1088/2041-8205/780/2/L34. ISSN 2041-8205.

External links

History of supernova observation

The known history of supernova observation goes back to 185 AD, when supernova SN 185 appeared, the oldest appearance of a supernova recorded by humankind. Several additional supernovae within the Milky Way galaxy have been recorded since that time, with SN 1604 being the most recent supernova to be observed in this galaxy.Since the development of the telescope, the field of supernova discovery has expanded to other galaxies. These occurrences provide important information on the distances of galaxies. Successful models of supernova behavior have also been developed, and the role of supernovae in the star formation process is now increasingly understood.

NGC 5714

NGC 5714 is a spiral galaxy located 130 million light-years away in the constellation of Boötes (the Herdsman). It was discovered by William Herschel in 1787.

SN 2005E

SN 2005E (aka 2005-1032) was a calcium-rich supernova first observed in January 2005 that scientists concluded was a new type of cosmic explosion. The explosion originated in the galaxy NGC 1032, approximately 100 million light years away.Location: RA 02° 39' 14.34" Dec+01hr 05' 55.0" [Epoch J2000]

Supernova

A supernova ( plural: supernovae or supernovas, abbreviations: SN and SNe) is a transient astronomical event that occurs during the last stellar evolutionary stages of the life of a massive star, whose dramatic and catastrophic destruction is marked by one final, titanic explosion. This causes the sudden appearance of a "new" bright star, before slowly fading from sight over several weeks or months or years.

Supernovae are more energetic than novae. In Latin, nova means "new", referring astronomically to what appears to be a temporary new bright star. Adding the prefix "super-" distinguishes supernovae from ordinary novae, which are far less luminous. The word supernova was coined by Walter Baade and Fritz Zwicky in 1931.

Only three Milky Way, naked-eye supernova events have been observed during the last thousand years, though many have been observed in other galaxies. The most recent directly observed supernova in the Milky Way was Kepler's Supernova in 1604, but the remnants of recent supernovae have also been found. Observations of supernovae in other galaxies suggest they occur on average about three times every century in the Milky Way, and that any galactic supernova would almost certainly be observable with modern astronomical telescopes.

Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a degenerate star or the sudden gravitational collapse of a massive star's core. In the first instance, a degenerate white dwarf may accumulate sufficient material from a binary companion, either through accretion or via a merger, to raise its core temperature enough to trigger runaway nuclear fusion, completely disrupting the star. In the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy as a supernova. While some observed supernovae are more complex than these two simplified theories, the astrophysical mechanics have been established and accepted by most astronomers for some time.

Supernovae can expel several solar masses of material at speeds up to several percent of the speed of light. This drives an expanding and fast-moving shock wave into the surrounding interstellar medium, sweeping up an expanding shell of gas and dust observed as a supernova remnant. Supernova nucleosynthesis is a major source of elements heavier than nitrogen in the interstellar medium, and the expanding shock waves can directly trigger the formation of new stars. Supernova remnants might be a major source of cosmic rays. Supernovae might produce strong gravitational waves, though, thus far, the gravitational waves detected have been from the merger of black holes and neutron stars, such as those that can be left behind by supernovae.

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