What is a supernova?

Oh, to be a star born and perish in the most spectacular of explosions.

When a star reaches the end of its life, it explodes in a bright explosion of light, resulting in a supernova. Supernovae may outshine whole galaxies for a brief moment and emit more energy than our sun would in its entire lifetime. They are also the universe's principal supplier of heavy materials.According to NASA, supernovae are the "largest explosions that occur in space."

 

Long before the invention of the telescope in the 17th century, several civilizations observed supernovae. RCW 86, discovered by Chinese astronomers in A.D. 185, is the oldest reported supernova. According to NASA, this "guest star" was visible in the sky for eight months.

The Crab Nebula, possibly the most famous supernova, was discovered in 1054 by Chinese and Korean astronomers who documented the stellar explosion in their records. According to rock drawings discovered in Arizona and New Mexico, Native Americans may have witnessed it as well. The Crab Nebula was generated by a supernova that was so brilliant that early astronomers could view it during the day.

Other supernovae detected prior to the invention of the telescope happened in the years 393, 1006, 1181, 1572 (examined by noted astronomer Tycho Brahe), and 1604. In his work "De nova stella(opens in new tab)," Brahe described his observations of the "new star," which gave origin to the term "nova."

The word "supernova" was coined by Walter Baade and Fritz Zwicky at Mount Wilson Observatory(opens in new tab) in reference to an explosive event known as S Andromedae (also known as SN 1885A) in the Andromeda Galaxy. Supernovas, according to the experts, occur when regular stars collapse into neutron stars.

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When Stars Die

According to European Space Agency studies, a supernova will occur once every 50 years in a galaxy the size of the Milky Way(opens in new tab). According to the US Department of Energy, this indicates that a star bursts every 10 seconds or so somewhere in the cosmos.

A cluster of supernovae generated the "Local Bubble" around 10 million years ago, a 300-light-year long, peanut-shaped bubble of gas in the interstellar medium that surrounds our solar system.

The manner in which a star dies is determined in part by its mass. Our sun, for example, lacks the mass to explode as a supernova. (However, the news for Earth isn't good because after the sun runs out of nuclear fuel, which might happen in a couple billion years, it will inflate into a red giant that would likely annihilate our planet before gradually cooling into a white dwarf. A star, on the other hand, can burn out in a blazing explosion if it has enough mass.

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A supernova can occur in one of two ways:

1.     Type I supernova: A star collects materials from a neighboring star until a runaway nuclear reaction sparks.

2.     Type II supernova: The star exhausts its nuclear fuel and crashes under its own gravity.

Type I supernova

Type I supernovae have no hydrogen signature in their light spectra and are assumed to be the result of a near binary star system (opens in new tab). As the partner star's gas accumulates on the white dwarf, it becomes increasingly squeezed, eventually triggering a runaway nuclear reaction within that leads to a spectacular supernova explosion.

Because all Type Ia supernovae are considered to blaze with similar brightness at their peaks, astronomers use them as "standard candles" to estimate cosmic distances.

Type Ib and Ic supernovae experience core-collapse in the same way as Type II supernovae do, but they have lost the majority of their outer hydrogen layer. In 2014, astronomers discovered a weak, difficult-to-find companion star to a Type Ib supernova. The hunt lasted two decades since the companion star was far fainter than the brilliant explosion.

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Type II supernova

Let's start with the more interesting Type II. A star must be several times more massive than the sun in order to explode as a Type II supernova (estimates range from eight to fifteen solar masses). It, like the sun, will ultimately deplete its hydrogen and then helium fuel reserves in its core. It will, however, have enough mass and pressure to fuse carbon.

Following that, heavier elements progressively accumulate in the core, and the star creates onion-like layers of material, with components becoming lighter toward the star's periphery. When the core of a star reaches a particular mass (known as the Chandrasekhar limit), it begins to collapse. As a result, these Type II supernovae are sometimes referred to as core-collapse supernovae.

The implosion eventually rebounds back off the core, releasing the star material into space and forms the supernova. What remains is an ultra-dense object known as a neutron star, a city-sized object with the mass of the sun packed into a compact area.

Light curves, which explain how the intensity of the light varies over time, are used to classify Type II supernova sub-categories. The brightness of Type II-L supernovae gradually fades following the explosion, but the light of Type II-P supernovae remains stable for a longer time before fading. Both varieties have a hydrogen signature in their spectra.

Astronomers believe that stars far more massive than the sun (between 20 and 30 solar masses) may not explode as a supernova. They instead collapse to generate black holes.

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Watching a Supernova

According to recent research, supernovae vibrate like huge speakers and generate an audible hum before exploding.

For the first time, astronomers observed a supernova exploding(opens in new tab) in 2008. Astronomer Alicia Soderberg anticipated to observe a faint light smudge of a month-old supernova while staring at her computer screen. Instead, she and her coworker witnessed a bizarre, highly brilliant five-minute burst of X-rays.