by Prasad Ganti
Stars are born, they live, and then they die. Like any living beings. They are born when lot of gas and dust comes together under the influence of gravity and a nuclear furnace gets lit. Hydrogen powers a star. The star glow converts hydrogen to helium in a nuclear reaction termed as fusion. When the hydrogen supply is exhausted, the star starts to die. The type of death depends on the size of the star.
Stars come in different sizes. Small and medium stars live longer and die a calmer death and end up as white dwarfs. While the heavier stars live for shorter time and die a violent death. Of course, there are some fireworks when a star dies. Smaller stars have smaller fireworks while the bigger ones have fireworks comparable to Disney World fireworks or the Fourth of July fireworks !
Towards the end of their lives, the stars give off the matter as gas and dust into surrounding space. This remnants form the raw material for the birth of the next star. Or even a next generation star. The process of giving out matter also results in radiation, like light, gamma rays etc. This results in an explosive end. Heavier stars light up as a supernova before finally becoming a neutron star or a black hole. Both the neutron star and a black hole are gravitationally intense astronomical objects.
Supernova forms the death throes of a heavy star. Our Sun being a middle sized star will not result in one. Several solar masses are required to form a supernova. Supernovae are not very common. Occurring about two a century in our Milky Way galaxy. Fortunately, none of them in our solar neighborhood. If it occurs so close by, we would not exist to notice it. They occur at a safe distance away from us.
The supernovae occurring in our galaxy are visible to the naked sky. But the ones in other galaxies need a telescope to watch. The brightest portion lasts for a short period of time. About days and months. Chinese astronomers observed a supernova in 1054 AD. This supernova has cooled off since then and is visible now as Crab Nebula in the constellation of Taurus.
A supernova was observed in 1987 and is named as 1987a, which was visible in the region of Large Magellanic Cloud. This cloud can be seen only from the southern hemisphere. A 13 second burst of neutrinos was observed and detected by several observatories all over the world. This was the grandest supernova observed since the invention of the telescope. Which one is next ?
Betelgeuse is a dying red supergiant star. It lies in one of the corners of the constellation Orion, the Hunter. It is visible to the naked eye with a tinge of redness. At about 640 light years away, given its massive size, it is not that far. But not close either because this star will end up its life as a supernova. When it happens, it will be the brightest object in the night sky, next to the Sun and the Moon. It will produce great Cosmic fireworks. When will it happen ?
Despite all the advances in astronomy, it is very difficult to predict when a star will become a supernova. It is very much like predicting the death of an individual human being. A patient may be on his or her last legs in the Intensive Care Unit. But when would the end come is anyone’s guess. Betelgeuse may explode in our life time, or in the next hundred years or even a thousand years or a hundred thousand years. Not likely to be millions of years.
One more reminder that astronomical distances are so huge that even light takes some time to travel across. Betelgeuse is 640 light years away. Which means that when we look at this star, we are looking at it as it existed 640 years ago. How does it look today ? We will have to wait 640 years to know the answer ! It will take 640 years before we know that Betelgeuse has exploded.