What is a Supernova?

A supernova is the largest and brightest explosion that can occur in the universe. It happens when a massive star dies and releases an enormous amount of energy and matter into space. A supernova can emit more light than an entire galaxy for a brief period of time.

Supernovae are very important phenomena for astrophysics, because they are the source of heavy elements that form through nuclear fusion or through neutron capture. These elements scatter through space and can become part of new generations of stars or planets. In addition, supernovae can leave behind very interesting remnants, such as nebulae, neutron stars, or black holes.

There are two main types of supernovae, according to their origin and their mechanism:

Type I supernovae are those produced by the thermonuclear explosion of a white dwarf. A white dwarf is the remnant of a low- or medium-mass star that has exhausted its nuclear fuel and has been left without pressure to counteract gravity. If a white dwarf is part of a binary system, it can steal matter from its companion star and increase its mass. When it exceeds a critical limit, called the Chandrasekhar limit, the white dwarf becomes unstable and begins to fuse the carbon and oxygen it holds inside. This triggers a chain reaction that makes the white dwarf explode completely and release a large amount of energy and heavy elements into space. Type I supernovae are divided into subtypes according to their spectrum and their luminosity. The most common subtype is Ia, which is used as a standard candle to measure cosmic distances.

Type II supernovae are those produced by the collapse of the core of a massive star. A massive star is one that has more than 8 or 9 times the mass of the Sun and that burns its nuclear fuel very quickly. When the star consumes all the hydrogen in its core, it begins to fuse other heavier elements, such as helium, carbon, oxygen, or iron. Each time it changes element, the star forms concentric layers like an onion. However, when it reaches iron, nuclear fusion no longer releases energy but consumes it. This causes the core to contract and increase its temperature and pressure until it becomes unstable and collapses on itself in a fraction of a second. The collapse generates a shock wave that bounces off the core and sends the outer layers of the star hurtling into space with great violence. The core can be left as a neutron star or a black hole, depending on its mass. Type II supernovae are also divided into subtypes according to their spectrum and their luminosity. The most common subtype is II-P, which shows a plateau in its light curve.

It is estimated that about 2 or 3 type II supernovae occur each century in our galaxy, the Milky Way, and about 6 or 7 times fewer of type Ia. However, thanks to modern telescopes we can detect supernovae in other, more distant galaxies. The first historically recorded supernova was observed by Chinese astronomers in the year 185 AD. The last supernova visible to the naked eye from Earth was SN 1987A, which occurred in the Large Magellanic Cloud, a galaxy neighboring our own.

If you love supernovae and want to learn more about them and about other astronomical phenomena, we invite you to visit San Pedro de Atacama and book an astronomical tour with www.atacamastargazing.com. You will be able to admire the clearest, starriest sky in the world with professional telescopes and expert guides who will explain anything you want to know about the universe.

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