# SN 1987A

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SN 1987A

Supernova
name = SN 1987A

caption= Circumstellar rings around SN 1987A, with the ejecta from the supernova explosion at the center of the inner ring.
epoch = J2000.0
type = Type II-P ("unusual")
SNRtype = unknown
host = Large Magellanic Cloud (LMC)
ra = 05h 35m 28.03s (J2000) cite web | url = http://heritage.stsci.edu/1999/04/fast_facts.html | publisher = Hubble Heritage Project | title = SN1987A in the Large Magellanic Cloud | accessdate = 2006-07-25]
dec = −69° 16&prime; 11.79&Prime; (J2000)
gal = unknown
discovery = 24 February 1987 (23:00 UTC)
iauc = cite web | url = http://cfa-www.harvard.edu/iauc/04300/04316.html | title = IAUC4316: 1987A, N. Cen. 1986 | date = 24 February 1987]
mag_v = +3
distance = 168,000 light-years, or 51.4 kpc
progenitor = Sanduleak -69° 202a
progenitor_type = B3 supergiant
b-v = +0.085
notes = Closest recorded supernova
since invention of telescope

[
supernova remnant with a ring of dense material ejected by the progenitor star 20,000 years before the supernova.]

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 , close enough that it was visible to the naked eye. It could be seen from the Southern Hemisphere. It was the closest observed 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 (member of the Manchester Astronomical Society) in Zimbabwe. On March 4-12, 1987 it was observed from space by Astron, the largest ultraviolet space telescope of that time. [ [http://adsabs.harvard.edu/abs/1987PAZh...13..739B Observations on Astron: Supernova 1987A in the Large Magellanic Cloud] ]

Since 51.4 kiloparsecs is approximately 168,000 light-years, the cosmic event itself happened approximately 168,000 years prior to its observation in 1987.

Most supernovas grow dimmer with the passage of time as they release their energy. But the X-ray and radio emissions from 1987A grew brighter because its shock wave had crashed into a dense cloud of gas and dust. [ [http://newswise.com/articles/view/544695/ ‘Wild Cousin’ Emerges from Family Tree of Sueprnova] Newswise, Retrieved on September 25, 2008.]

Precursor

Soon after the event was recorded, the progenitor star was identified as Sanduleak -69° 202a, a blue supergiant. This was an unexpected identification, because at the time a blue supergiant was not considered a possibility for a supernova event in existing models of high mass stellar evolution. Current understanding is that the progenitor was a binary system, the stars of which merged about 20,000 years before the explosion, producing a blue supergiant. Difficulties persist with this interpretation. [ [http://adsabs.harvard.edu/abs/arXiv:0705.3066 Galactic Twins of the Nebula Around SN 1987A: Hints that LBVs may be supernova] May 2007]

Neutrino emissions

There were 3 neutrino bursts observed. The Mont Blanc computer detected a burst of five pulses about 8 hrs before the first optical observation, followed by a second burst of three pulses about 2 hrs later; Kamioka and Baksan reported observations of a burst made by eleven and five pulses, respectively, delayed by 4.7 hrs in comparison with the Mont Blanc burst. (Refer http://adsabs.harvard.edu/abs/1989NYASA.571..584A)

Approximately three hours before the visible light from SN 1987A reached the Earth, a burst of neutrinos was observed at three separate neutrino observatories. This is due to the neutrino emission (which occurs simultaneously with core collapse) preceding the emission of visible light (which occurs only after the shock wave reaches the stellar surface). At 7:35am Universal time, Kamiokande II detected 11 antineutrinos, IMB 8 antineutrinos and Baksan 5 neutrinos, in a burst lasting less than 13 seconds. Water-based instruments detect only antineutrinos of thermal origin [cite book
author = [http://www.physics.upenn.edu/facultyinfo/mann.html Mann, Alfred K.]
title = Shadow of a star: The neutrino story of Supernova 1987A
publisher = W. H. Freeman
date = 1997
location = New York
pages = page 127
isbn = 0716730979
] , while a gallium-71-based instrument detects only neutrinos (lepton number = +1) of either thermal or electron-capture origin.

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 $10^\left\{58\right\}$ with a total energy of $10^\left\{46\right\}$ joules. Fact|date=March 2008

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.

Missing neutron star?

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 takes sharpest images of the supernova regularly since August 1990. 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 is enshrouded in dense dust clouds so that it cannot be seen. The second is that large amounts of material fell back on the neutron star, so that it further collapsed into a black hole.

N1987A distance and the speed of light

The three bright rings around SN 1987A are material from the stellar wind of the progenitor. These rings were ionized by the ultraviolet flash from the supernova explosion, and consequently began emitting in various emission lines. These rings did not "turn on" until several months after the supernova, and the turn-on process can be very accurately studied through spectroscopy. The rings are large enough for their angular size to be measured accurately: the inner ring is 0.808 arcseconds in radius. Using the distance light must have traveled to light up the inner ring as the base of a right angle triangle, and the angular size as seen from the Earth for the local angle, one can use basic trigonometry to calculate the distance to SN1987A, which is about 168,000 light-years. [cite journal | title=New Distance Determination to the LMC | author=Panagia, N. | journal=Memorie della Societa Astronomia Italiana | volume= 69 | pages =225 | url =http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1998MmSAI..69..225P&amp;data_type=PDF_HIGH&amp;type=PRINTER&amp;filetype=.pdf]

ee also

* List of supernova remnants

References

* arxiv|archive=astro-ph|id=0505066

* [http://antwrp.gsfc.nasa.gov/apod/ap970124.html Picture of Supernova 1987A]
* [http://www.rochesterastronomy.org/snimages/sn1987a.html Rochester Astronomy discovery timeline]
* [http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/antimatterFall.html Gravitational effects on antimatter]
* [http://eros.in2p3.fr/EchoesSN1987a/ Light echoes from Sn1987a, Movie with real images by the group EROS2]
* [http://antwrp.gsfc.nasa.gov/apod/ap060125.html Animation of light echoes from SN1987A]
* [http://www.spacetelescope.org/images/archive/freesearch/SN+1987A/viewall/1 SN 1987A at ESA/Hubble]
* [http://www.wikisky.org/?ra=5.5911&de=-69.2696&zoom=16&img_source=IMG_60007:all Supernova 1987A, WIKISKY.ORG]

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