A multitude of civilizations recorded multiple supernovas long before the telescope was invented. The oldest supernova that was recorded is called RCW 86, which was seen by some Chinese astronomers in A.D. 185. According to NASA, their records show that this star stayed in the sky for only 8 months. Before telescopes became available, in the 17th century, there were only 7 recorded supernovas according to Encyclopedia Britannica. The Crab Nebula is the most famous supernova we know of today. Some Chinese and Korean astronomers recorded this star explosion in 1054, and it is possible that southwestern Native Americans may have seen it as well, according to rock paintings seen in Arizona and New Mexico. The supernova that formed the Crab Nebula was so bright that astronomers could see it during the day. Many other supernovas were observed before the telescope was invented such as in 393, 1006, 1181, 1572, and 1604. Famous astronomer Tycho Brahe was the one who observed the supernova in 1572 and he wrote about his observations of the so-called “new star” in his book called “De nova stella,” which was where the name 'nova' came from. However, a nova and a supernova are different. Although both are sudden bursts of brightness as hot gases are blown outward, a supernova’s explosion is cataclysmic and signifies the end of a star’s life.
On average, a supernova will occur once every 50 years in a galaxy the size of the Milky Way. A star explodes every second or so somewhere in the universe, and some of those are close to Earth. Roughly 10 million years ago, a cluster of supernovas created what is known as the “Local Bubble,” which is a 300-light-year-long, peanut-shaped bubble of gas in the interstellar medium that surrounds the solar system. The way a star dies is dependent in part on its mass. For example, our sun doesn’t have enough mass to explode into a supernova, however, once the sun runs out of its nuclear fuel, perhaps in a couple of billion years, it will swell into a red giant that will likely vaporize our world, before gradually cooling into a white dwarf. However, with the right amount of mass, a star can burn out in a fiery explosion. There are two ways in which a star can go supernova: Type I supernova, which is when a star accumulates matter from a nearby neighbor until a runaway nuclear reaction ignites, and Type II supernova, which is when a star runs out of nuclear fuel and collapses under its own gravity.
The more exciting type of supernova is Type II supernova. For a star to explode as a Type II supernova, it must be several times more massive than the sun, roughly 8-15 solar masses. Like the sun, it will eventually run out of hydrogen and then helium fuel at its core. However, it will have enough mass and pressure to fuse carbon. Then, gradually heavier elements build up at the center, and it becomes layered like an onion, with elements becoming lighter toward the outside of the star. Once the star’s core surpasses a certain mass, the star begins to implode, and for this reason, they are also known as core-collapse supernovas. The core heats up and becomes denser. Eventually, the implosion bounces back off the core, expelling the stellar material into space, forming the supernova. Finally, what’s left is an ultra-dense object called a neutron star, which is a city-sized object that can pack the mass of the sun in a small space. There are two subcategories of Type II supernovas, classified based on their light curves. The light of Type II-L supernovas declines steadily after the explosion, while Type II-P’s light stays steady for a time before diminishing. Both types have the signature of hydrogen in their spectra. An interesting fact is that astronomers think that stars much more massive than the sun, roughly 20 to 30 solar masses, might not explode as a supernova, but rather collapse to form black holes.
Type I supernovae differ from Type II supernovae in many ways but the most significant is that they don’t have a hydrogen signature in their light spectra. Type Ia supernovae are usually thought to originate from white dwarf stars in a close binary system. As the gas of the companion star accumulates onto the white dwarf, the white dwarf is progressively compressed, and eventually sets off a runaway nuclear reaction inside that eventually leads to a cataclysmic supernova outburst. Astronomers use Type Ia supernovae as “standard candles” to measure cosmic distances because all are thought to blaze with equal brightness at their peaks. Type Ib and Ic supernovae also undergo core-collapse just as Type II supernovae do, but they have lost most of their outer hydrogen envelopes. In 2014, scientists detected the faint, hard-to-locate companion star to a Type Ib supernova. The search consumed two decades, as the companion star shone much fainter than the bright supernova.
Recent studies have found that supernovas vibrate like giant speakers and emit an audible hum before exploding. In 2008, scientists caught a supernova in the act of exploding for the first time. While peering at her computer screen, astronomer Alicia Soderberg expected to see the small glowing smudge of a month-old supernova. But what she and her colleague saw instead was a strange, extremely bright, five-minute burst of X-rays. With this observation, they became the first astronomers to catch a star in the act of exploding. The new supernova was dubbed SN 2008D. Further study has shown that the supernova had unusual properties.
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By: Zubin Sidhu
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References: Thompson, Andrea. “What Is a Supernova?” Space.Com, 9 Feb. 2018, www.space.com/6638-supernova.html.
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