SN 1987A

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**SN 1987A**
Observation data (Epoch J2000.0)
1987A supernova remnant near the center
Supernova type	Type II-P (unusual)
Remnant type	unknown
Host Galaxy	Large Magellanic Cloud (LMC)
Constellation	Dorado
Right ascension	05^h 35^m 28.03^s (J2000) <ref name="hubble_heritage">SN1987A in the Large Magellanic Cloud. Hubble Heritage Project. Retrieved on 2006-07-25.</ref>
Declination	−69° 16′ 11.79″ (J2000) <ref name="hubble_heritage" />
Galactic coordinates	unknown
Discovery Date	24 February 1987 (23:00 UTC) ^{<ref name="iauc">IAUC4316: 1987A, N. Cen. 1986 (24 February 1987).</ref>}
Peak magnitude (V)	+3
Physical characteristics
Progenitor	Sanduleak -69° 202a
Progenitor type	B3 supergiant
Colour (B-V)	+0.085
Notable features	Closest recorded supernova since invention of telescope

Image:SN1987A 03-05 changes.gif

SN 1987A was a supernova in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a nearby dwarf galaxy. It occurred approximately 51.4 kiloparsecs from Earth <ref name="hubble_heritage" />, close enough that it was visible to the naked eye. It was the closest supernova since SN 1604, which occurred in the Milky Way itself. The light from the supernova reached Earth on February 23, 1987. As the first supernova discovered in 1987, it was labeled "1987A". Its brightness peaked in May with an apparent magnitude of about 3 and slowly declined in the following months. It was the first opportunity for modern astronomers to see a supernova up close.

It was discovered by Ian Shelton and Oscar Duhalde at the Las Campanas Observatory in Chile on February 24 1987, and independently by Albert Jones in New Zealand, and Colin Henshaw in Zimbabwe. <ref name="iauc" />

Since 51.4 kiloparsecs is approximately 168,000 light-years, the cosmic event itself happened approximately 168,000 years ago. To put this in perspective, Homo sapiens sapiens (modern humans) evolved about 200,000 years ago.

1 Neutrino emissions
2 Precursor
3 Scientific studies
4 References
5 External links

[edit] Neutrino emissions

Approximately three hours before the visible light from SN 1987A reached the Earth, a burst of neutrinos was observed at three separate neutrino observatories. It is widely thought that this is due to the neutrino emission preceding the emission of visible light rather than the neutrinos travelling faster than light. At 7:35am Universal time, Kamiokande II detected 11 neutrinos, IMB 8 neutrinos and Baksan 5 neutrinos, in a burst lasting less than 13 seconds.

Although the actual neutrino count was only 24, it was a significant rise from the previously-observed background level. This was the first time neutrinos emitted from a supernova had been observed directly, and the observations were consistent with theoretical supernova models in which 99% of the energy of the collapse is radiated away in neutrinos. The observations are also consistent with the models' estimates of a total neutrino count of <math>10^{58}</math> with a total energy of <math>10^{46}</math> joules.

One highly significant result was obtained from the data regarding gravity. It appeared that the neutrinos and antineutrinos both took the same amount of time to arrive at earth, about 168,000 years. The difference in their arrival times was less than 12 seconds. This was the first empirical evidence that matter, antimatter, and photons all react similarly to gravity, which had been widely predicted by standard theories of gravity but had not been previously shown from direct empirical data.

[edit] Precursor

Sanduleak -69° 202a, the progenitor star of SN 1987A, was a blue supergiant presumed to have a mass of about 18 solar masses. This required some revisions to models of high mass stellar evolution, which had suggested that supernovae would only result from red supergiants.

[edit] Scientific studies

Image:Sn87a.jpg

The supernova remnant formed by debris from SN 1987A is one of the most-studied astronomical objects today.

SN 1987A appears to be a core-collapse supernova, which should result in a neutron star. Since the supernova first became visible, astronomers have been searching for the collapsed core but have not detected it.

The Hubble Space Telescope took the sharpest images of the supernova to date. The images show no evidence of a neutron star. Two possibilities for the 'missing' neutron star are being considered. The first is that the neutron star isn't pulling in material from around it so it cannot be seen. The second is that the neutron star pulled in so much material that it further collapsed into a black hole. The latter option has been gaining support in recent years.

[edit] References

Graves, G.J.M, et al. (2005). "Limits from the Hubble Space Telescope on a point source in SN 1987A". Astrophysical Journal 629: 944–959. arXiv:astro-ph/0505066