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HI! THIS IS VISHWADEEP SINGH AND I WANT TO SHARE WITH YOU SOME INTERESTING KNOWLEDGE ABOUT SUPERNOVAE. ALTHOUGH THIS TERM MAY NOT BE A NEW ONE FOR YOU, YET AFTER READING THIS ARTICLE YOU WILL FIND MANY NEW INTERESTING FACTS.
SUPERNOVA is one of the most violent phenomena that occur in the universe. Although a supernova is about 10 billion times as luminous as the Sun, it tends to fade over a couple of months or years. No doubt, the energy output of a supernova surpasses that of the galaxy as a whole! The brightest supernova, perhaps, in recorded human history, occured in 1006 A.D, the remnant of which is still visible to modern astronomers in the southerly constellation of Lupus. Another supernova event was recorded in the year 1054 by a Chinese chronicler, Ming Taun-Lin, which is today seen as the Crab Nebula. Then in 1572, Tycho Brahe observed a cosmic explosion that is today popular as Tycho's Supernova Remnant.The last supernova to be seen in our Galaxy, the Milky Way, was in 1604 by the famous astronomer, Kepler. The brightest since then was, however, supernova 1987A, which happened on 24 February 1987 in the Large Magellanic Cloud, a small satellite galaxy of our Milky Way.
Catching a supernova at its peak proves splitting hair, as one cannot predict their occurence and schedule the observing time using the world's largest telescopes. Moreover, they are fleeting and must be observed carefully multiple times within the few weeks. If they are discovered after passing the peak brightness that will be of little use as the peak brightness is essential for calibration.
Supernovae come in two main observational varieties. The classification is generally done on the basis of optical spectra. The first two main classes of SNe were identified by Minkowski in 1941 based on the presence or absence of hydrogen lines in their optical spectra. Supernova whose optical spectra exhibit hydrogen lines are classified as Type II, while hydrogen- deficient SNe are designated Type I. SNe I are further subdivided according to the detailed appearance of their early time spectrum. SNe Ia are characterized by strong absorption near 6150 Angstrom corresponding to SiII, for example, supernova SN 1996X. SNe Ib lack this feature but instead they shows prominent HeI lines like supernova SN 1999dn. SNe Ic, such as SN 1994I, have neither the SiII nor the HeI lines. In many cases, there is little distinction between the latter two types and they are designated as SN Ib/c.
Four subclasses of SN II are known, namely, IIP, IIL, IIb and IIn. SN IIP (plateau) and SN IIL (Linear) constitute the bulk of all SN II and are often referred to as normal SN II. Celebrated SN1987 A belongs to this class. The subclassification is made according to the shape of optical light curves. The luminousity of SN IIP stops declining shortly after maximum plateau 2-3 months long. SN IIL, on the other hand, show a linear, uninterrupted luminousity decline. Indeed there is no clear spectral difference between these two types, but their progenitors do differ by the amount of hydrogen they have in their envelope. A few objects have been found to have early time spectra similar to Type II and late time spectra similar to Type Ib/c. For this reason they have been called SN IIb. The first such was SN 1987M. A number of peculiar SN II have been grouped into the class of SN IIn, where n stands for 'narrow emission lines'. the spectra of these objects have a slow evolution and are dominated by strong Balmer emission lines. Supernovae SN Ib/c and SN IIn, also called hypernovae, are associated with Gamma Ray Bursts.
Physically,there are two fundamental types of supernova,based on what mechanism powers them; the thermonuclear SNe and the core-collapse ones.Only SNe Ia are thermonuclear types the rest are formed by core-collapsing of a massive star.SNe Ia are discovered in all types of galaxies and are not associated with the arms of spirals as strongly as other supernovae.The other type SNe mostly apper in spiral galaxies and have been associated with parent population of massive stars.
It is believed that SNe Ia are formed as a result of a white dwarf accreting matter from a nearby companion star,typically a red giant, until it reaches the Chandrasekhar limit .If a white dwarf is in a close binary system with a main sequence star,the latter starts dumping gas onto the white dwarf whan it expands into a giant or supergiant. When the mass of the white dwarf is nudged up to the Chandrasekhar limit,it is no longer stable, as its radius decrease resulting in increase of temperature and density. At higher density and temperature ,the fusion of carbon and oxygen into iron occurs in a runaway fashion. The white dwarf is thus converted into a fusion bomb, and is blown off completely by the explosion without leaving any remnent behind.The amount of energy released in this explosion is about 10 the power 40 joules, which is as much energy as the sun has radiated away during its entire lifetime.