The term "supernovae" comes from the Latin word "nova," which translates to "new." Nova is the name given to a different kind of exploding star. Supernovae resemble novae in several respects. Both phenomena are distinguished by an extreme and sudden increase in brightness that lasts for a couple of weeks, followed by a gradual decrease in brightness. From a spectroscopic point of view, they exhibit emission lines that have been shifted to the blue, which suggests that hot gases are being expelled. On the other hand, in contrast to a nova outburst, a supernova explosion is a catastrophic event for a star, one that, in essence, brings an end to the star's active (or energy-generating) lifetime.
When a star goes through a supernova, it transforms into either a white dwarf, a neutron star, or a black hole. White dwarf stars are created when stars of a size comparable to the sun reach their final stages of evolution. Neutron stars are formed when stars of a medium size (with a mass between two and five times that of our sun) collapse into themselves. When a star's mass is greater than five times that of the sun, it can transform into a black hole. Inside black holes, the pull of gravity is so intense that not even light can make its way out.
Chinese and Korean astronomers were the first to discover the Crab Nebula, which is widely considered to be the most famous supernova. These astronomers recorded this stellar explosion in their records in the year 1054. According to rock paintings discovered in Arizona and New Mexico, local Native Americans may have also witnessed this phenomenon. These early astronomers were able to observe the supernova that resulted in the formation of the Crab Nebula during the day because it was so bright.
An international group of astronomers led by the University of Southampton has confirmed the discovery of the most distant supernova ever detected. This supernova was a massive cosmic explosion that took place 10.5 billion years ago, which is equivalent to approximately three-quarters of the age of the Universe itself. In August of 2016, DES16C2nm was found for the first time, and in October of that same year, its distance and extreme brightness were confirmed by using three of the most powerful telescopes in the world: the Very Large Telescope in Chile, the Magellan Telescope in Chile, and the Keck Observatory in Hawaii.
A supernova is not just any cosmic explosion; rather, it is distinguished as the largest explosion that occurs in space and is known as the most powerful explosion that can occur. According to information provided by NASA, the explosion of a supernova can sometimes be so powerful that it results in the formation of a black hole. There are some supernovae that can be observed with the naked eye. Supernovae of type Ib are produced by massive stars that are in their final stages of life and have 25 times the mass of our sun. They only have a trace amount of hydrogen and a little bit of helium. Finally, Type II supernovae are produced when hydrogen- and helium-rich stars that have reached the end of their lives collapse. They have an eight times greater mass than our sun.
Imagine for a moment that a star that is at an unacceptably great distance from Earth were to explode. Consider that the supernova is located thirty light-years away. According to Mark Reid, a senior astronomer at the Harvard-Smithsonian Center for Astrophysics, the following statement was made:... if a supernova were to go off within about 30 light-years of us, that would lead to major effects on the Earth, possibly including mass extinctions. The supernova may emit X-rays in addition to more powerful gamma rays, which have the potential to destroy the ozone layer that shields us from the sun's ultraviolet rays.
Not all stars experience a supernovae. Stars with a mass that is less than five times that of our sun are incapable of undergoing this traumatic transition because they are too light. They simply do not have sufficient gravity for the structure to collapse and then rebound with such force. Instead, lighter stars go through a series of stages before finally settling down as long-lived white dwarfs after their nuclear fuel runs out. No matter what form they take in the end, stars are never extinguished entirely; they can either become neutron stars, black holes, or white dwarfs.