When we delve into certain realms of astronomy, the scale of events and objects are often impossibly large to imagine. If we think of planets like Earth and Mars we can at least get some sort of grasp as to their size, as we can consider them relative to other bodies. As we get to bigger objects, like Jupiter and the Sun, our understanding gets somewhat muddled, but we can still comprehend how enormous they are by using Earth as a starting point (for example, the Sun is over 100 times the size of Earth).
It’s when we get to the larger celestial occurrences, like supergiant stars and black holes, however, that things really start to get unfathomable. When it comes to mammoth celestial events like supernovas, it’s hard to get our heads around just how large and powerful they are.
Supernovas have fascinated astronomers for millennia, appearing out of nowhere in the night sky and outshining other stars with consummate ease. The first recorded supernova, known today as SN 185, was spotted by Chinese astronomers in 185 CE and it was apparently visible for almost an entire year.
While this is the first recorded sighting, there have doubtless been many supernovas in preceding years that confounded Earth dwellers who were unable to explain the sudden appearance of a bright new star in the sky.
One of the most notable supernova events likely occurred about 340,000 years ago when a star known as Geminga went supernova. Although it was unrecorded, astronomers have been able to discern the manner of its demise from the remnant neutron star it left behind.
Geminga is the closest known supernova to have exploded near Earth, as little as 290 light years away. Its proximity to Earth meant that it might have lit up the night sky for many months, casting its own shadows and rivalling the moon for brightness, turning night into day. So bright and large was this supernova that the ancients would have seen the light of it stretching from horizon to horizon.
Left behind after this supernova was a neutron star rapidly rotating at about four times a second, the nearest neutron star to Earth and the third-largest source of gamma rays to us in our observations of the cosmos. Other notable stellar explosions include Supernova 1987A, a star located in the Large Magellanic Cloud that went supernova in 1987. This originated from a supergiant star known as Sanduleak -69°202. It almost outshone the North Star (Polaris) as a result of its brightness, which was comparable to 250 million times that of the Sun.
It is a testament to the scale of these explosions that even ancient civilizations with limited to no astronomical equipment were able to observe them. Supernovas are bright not only visually but in all forms of electromagnetic radiation. They throw out X-rays, cosmic rays, radio waves and, on occasion, may be responsible for causing giant gamma-ray bursts, the largest known explosions in the universe. It is by measuring these forms of electromagnetic radiation that astronomers are able to glean such a clear picture of the formation and demise of supernovas. In fact, it is estimated that 99 percent of the energy that a supernova exerts is in various forms of electromagnetic radiation other than visible light, making the study of this invisible (to the naked eye at least) radiation incredibly important, and something to which many observatories worldwide are tuned.
Another type of stellar explosion you may have heard of is a nova. This is similar in its formation to a supernova, but there is one key difference post-explosion: a supernova obliterates the original star, whereas a nova leaves behind an intact star somewhat similar to the original progenitor of the explosion.
Our understanding of the universe so far suggests that pretty much everything runs in cycles. For example, a star is born from a cloud of dust and gas, it undergoes nuclear fusion for billions of years, and then destroys itself in a fantastic explosion, creating the very same dust and gas that will lead to the formation of another star. It is thanks to this cyclic nature of the universe that we are able to observe events that would otherwise be extremely rare or non-existent. If stars were not constantly reforming, there would be none left from the birth of the universe 13.7 billion years ago.
As destructive as they may be, supernovas are integral to the structure and formation of the universe. It is thought that the solar system itself formed from a giant nebula left behind from a supernova while, as mentioned earlier, supernovas are very important in the life cycle of stars and lead to the creation of new stars as the old ones die out. This is because a star contains many of the elements necessary for planetary and stellar formation including large amounts of helium, hydrogen, oxygen and iron, all key components in the structure of celestial bodies. On top of these, many other elements are thought to form during the actual explosion itself.
There’s no doubt that supernovas are one of the most destructive forces of the universe, but they’re also one of the most essential to the life cycle of solar systems. As we develop more powerful telescopes over the coming years, we will be able to observe and study them in more detail, and possibly discover some that do not fall into our current classifications. The study of supernovas alone can unlock countless secrets of the universe, and we’ll be able to learn more about the cosmos as a whole.
