eso8704 — Comunicato Stampa Scientifico
Brightest Supernova since Four Hundred Years Explodes in Large Magellanic Cloud
25 Febbraio 1987
Astronomers all over the world are highly excited about the sudden explosion of a supernova in the Large Magellanic Cloud (LMC), a small satellite galaxy to our own Milky Way Galaxy. The LMC is the nearest, external galaxy; its distance is only about 180.000 light years.
Almost at magnitude 4, this supernova is easily visible with the naked eye to observers in the southern hemisphere. It has been given the designation 1987A and is the brightest to be observed since the 1604 supernova in our own Galaxy, observed by Johannes Kepler. In 1885, a magnitude 7 supernova was seen in the Andromeda Nebula, another neighbour galaxy. The current event is therefore a most unique, once-in-a-lifetime opportunity for astronomers.
The supernova was seen first during the night between February 23 and 24, apparently almost simultaneously by observers in South America, Australia and New Zealand. According to professional astronomers in Chile and Australia, it had risen very rapidly in brightness, becoming at least 1500 times brighter within the previous 24 hours.
An emergency programme was immediately put into action at the ESO La Silla observatory. At least eight ESO telescopes have been observing the supernova during the past night (February 24 - 25). The following is a brief summary of the information which was transmitted this morning from La Silla to the ESO Headquarters:
The supernova was nearly constant in brightness, during five hours of accurate photometric observations; the visual magnitude is found to be 4.60. There is a slight indication of further brightening, so perhaps it has not yet reached maximum brightness. The colour is very blue. Spectra were obtained at medium resolution which show very broad features, as normally seen in a Type I supernova. High resolution spectra (resolution 100.000, Calcium ion lines at 393 and 397 nm) show narrow absorption lines from at least 12 intergalactic clouds, situated between the LMC and our Galaxy, and most of which were not known before.
By chance, colour photographs were obtained at ESO of the LMC, a few days before the supernova explosion. More colour photos were made last night, now showing the bright supernova. It is expected that they will become available from the ESO Information and Photographic Service early next week.
Some general information about supernovae:
Supernovae are believed to represent a late evolutionary stage of massive stars in which the star runs out of atomic fuel. It can no longer support its own weight and collapses. Immediately thereafter follows a dramatic thermonuclear explosion during which the outer layers are blown into the surrounding space. A small and very compact object may remain at the center. The best known historical supernova was seen in the year 1054, giving birth to the Crab Nebula and an associated neutron star, which was detected as a radio pulsar in 1967. Most, if not all heavy elements in the universe have been generated in the exceedingly hot interiors of stars in the supernova phase. Supernovae are very rarely discovered before they reach their maximal brightness and little is known about the early phases. Currently, about 20 - 25 supernovae are detected per year in exterior galaxies; the last one in our own galaxy, the Milky Way, appears to be the one found by Kepler in the constellation Ophiocus in 1604. A 12 mag supernova was observed last May in the peculiar galaxy NGC 5128 (Centaurus A), see ESO Press Release eso8607 of 13 May 1986. It was about 1500 times fainter than the present one in LMC.
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