ABOUT SUPERNOVAE

Astronomers describe stars that explode, becoming 100 mil­lions times brighter than the sun during the process, as supernovae. They are extremely rare phenomena. Only three have been noticed within our own galaxy although they have been observed at fairly regular intervals in other galaxies. These violent explosions are believed to be caused when a star runs out of hydrogen and contracts under its own gravitational field. The contraction creates a sufficiently high temperature in the interior for thermonuclear reactions to occur produc­ing heavy elements. The formations of heavy elements with atomic numbers higher than about 40 absorbs energy and the star collapses inwards increasing its speed of rotation and ultimately flinging a large portion of its matter into the depths of space. Some astrophysicists believe that the planets of the solar system consist of matter thrown into space by a supernova which was subsequently gathered by the sun’s gravitational field. The residue of the supernova explosion is a white dwarf star.

In 1006 something strange happened in the Constellation Lupus. Suddenly a new star was born. But it was no ordinary star. It was a supernova Wolf, which was very brilliant and almost turned night into day.

As indicated above since 1006 only three supernovae have been seen in our galaxy, the explosion in 1054 that made the Crab Nebula, Tycho’s Star of 1572 and Kepler’s Star of 1604. However they cannot be compared with the Star of the Wolf which exploded in 1006.

There are two types of supernovas: Type-1 and Type- 2.Type-l supernovae may be two Star systems, a normal star coupled with a White dwarf, a small dense star in an advanced stage of evolution with a strong pull of gravity. The White dwarf behaves life a stellar thief. It draws away material from its unfortunate companion and eventually becomes so massive that it collapses into an even smaller denser object made up of neutrons. At this stage the degenerate White dwarf releases an amazing amount of energy creating what we observe as a supernova spectacle. Apparently the 1572 and 1604 stars were of this kind.

Type-2 supernovae involve only one massive star which has reached the end of its energy-producing career and has collapsed. The outer envelope of the star implodes and rushes toward the collapsed core where the temperature is nearly a billion degrees. There is a shock-wave, rapid compression, a further sharp increase in temperature, and a cataclysmic nuclear outburst, that results in the ejection of about four fifths of the star’s mass. (we must appreciate that when we refer to a supernova we are talking in terms of energies hundreds of thousands of times that of volcanoes or hydrogen bombs !) All that remains is an expanding gas cloud together with the supernova remnant. Made up of neutrons, the remnant rotates fast producing rapidly varying radio signals called “pulsars”.

The question arises why the most brilliant supernova Wolf, occurred in the constellation Lupus, in 1006. The probable reason is that the Wolf Star was only about 3000 to 4000 light-years away from the earth (a light year is the distance travelled by light at the speed of 186000 miles per second for a whole year- it works out to 4.879 multiplied by 10 raised to the power of 12). Radio astronomers have identified along wave-length source known as PKS 1459-41 which they think is a remnant of the supernova. Since it was discovered in 1965 by a giant radio telescope in Australia; it has also been detected at X-ray wave-lengths and is visible as a faint optical object.

Supernovae are so bright that we can identify them in other galaxies millions of light-years away. In 1885 a supernova named S. Andromedae in the Andromeda Spiral (Messier 31) attained what is known in astronomical parlance as the “Sixth” magnitude. One Hungarian Baroness who was looking through a small telescope on her lawn is also believed to have witnessed the phenomenon! For a few days the supernova reached the fringe of naked eye visibility. But in 1885 its nature was not appreciated. No supernova explosion has been observed in our galaxy since the invention of telescopes and astronomers have been champing at the bit for centuries.

Supernovas may not last long but at their peak they give off as much energy as is produced by all other stars in the galaxy in which they are embedded. The effect would be most unpleasant if an outburst were to happen in our own region of space. Some scientists have theorised that a supernova like the one that created the Crab Nebula in 1054 had wiped out the dinosaurs.

What are the chances of anything similar happening again. Supernovae are not common occurrences as we said earlier but by the law of averages our galaxy is certainly due for another. One possible candidate is the extraordinary Eta Carinae which during the past 2 centuries has fluctuated widely between magnitude—One and half (as bright as any normal star), and seven, below naked eye-visibility. (Astrono­mers have been measuring the brightness of a star by the term “magnitude” according to an ancient system which is still in use with some modifications and refinements. The brighter the star the lower the magnitude as per this classification. The measure goes from positive to zero and beyond to even negative numbers!) However if Eta Carinae did explode, it could not damage us because it is thousands of light-years away from us.

Within our own region of galaxy, there are no stars that can be expected to explode as supernovae. Even the Red giant stars well advanced in their evolution are too far away. The closest of them—Mira Ceti the famous long-period variable star in the constellation Cetus (the whale)—is more than 100 light-years away.). And the supreme example of a bright red super-giant Betelgeuse, in Orion, lies at well over a distance of 400 light years. If Betelgeuse should turn into a supernova it would indeed provide a magnificent sight for the Gods as well as human beings.