Supernova: The Biggest Explosion Mankind Has Ever Seen

Yashdeep Podder
SRM Astrophilia
Published in
7 min readApr 2, 2023

“Supernovas, they’re brighter than the brightest galaxies. They die, but everyone watches them go.”

― Jodi Picoult

Chandra, the Supernova Remnant from the Small Magellanic Cloud Galaxy

All stars, no matter their size, shape or color, greet their end with a massive explosion- a Supernova. The death of a star is characterized by immense matter rushing through space at 9,000 to 25,000 miles per second.

Supernovas are characterized by a tremendous, intense brightening lasting for weeks, followed by a slow dimming. When a star ‘goes supernova’, huge amounts of its matter, which equals the material of its star, is blasted into space with such energy that the exploding star outshines its entire home galaxy itself!

Supernova explosions not only release tremendous amounts of radio waves and X-rays but also cosmic rays. Some gamma-ray bursts have been associated with Supernovas. Spectral analysis shows that abundances of the heavier elements are greater than normal, indicating that these elements form during the course of the explosion.

Did you know that elements like iron and other heavy elements that are only produced in Supernovas, which make up our planet and are a crucial part of human metabolism are produced by these blasts? This means that all human beings carry the remnants of these huge and distant explosions within our own bodies.

Supernova Explosion image from Hubble Space Telescope

Let us now take a walk through the collapse of a star.

Supernovas are the “last hurray” of a dying star. This happens when a star at least five times the mass of our sun goes out with a fantastic bang! Huge amounts of nuclear fuel at their cores are burnt by massive stars. The core of a star constantly converts hydrogen, its fuel supply, into helium and subsequent heavier elements. This process, called nuclear fusion, makes stars shine brightly.

After billions of years of burning, a star will eventually use up its hydrogen fuel supply. When nuclear fusion stops, gravity pulls the star inward onto itself. This produces tons of energy until the center gets very hot. This heat generates pressure and this pressure created by stellar nucleosynthesis (hydrogen burning), keeps that star from collapsing.

A star is in balance between two opposite forces. The star’s gravity squeezes the star into the smallest, compact sphere possible. But the nuclear fuel burning inside the core creates a strong outward pressure which resists the inward pull of gravity.

When a massive star runs out of fuel, it cools off. This causes the pressure to drop. Gravity wins and the star suddenly collapses. Imagine something one million times the mass of Earth collapsing in 15 seconds! The collapse happens so quickly that it creates enormous shock waves that cause the outer part of the star to explode!

Usually, a very dense core is left behind, along with an expanding cloud of hot gas called a nebula. A supernova of a star more than about 10 times the solar mass may leave behind the densest objects in the universe — black holes.

The Brief history of Supernovas

The Lonely Neutron Star in Supernova E0102 72.3

Historically, only seven supernovas were recorded before the 17th century. The most famous of them occurred in 1054 and was seen in one of the horns of the constellation Taurus. The remnants of this explosion are visible today as the Crab Nebula, which is composed of glowing ejected material of gases flying outward in an irregular fashion and a rapidly spinning, pulsating neutron star — called a pulsar, in the centre. It was bright enough to be seen during the day, and its great luminosity lasted for weeks. The closest and most easily observed supernova was first sighted on the morning of 24 February 1987, by the Canadian astronomer Ian K. Shelton while working at the Las Campanas Observatory in Chile. Designated as SN 1987A. This formerly extremely faint object attained a magnitude of 4.5 within just a few hours, thus becoming visible to the unaided eye. The newly appearing supernova was located in the LMC at a distance of about 160,000 light-years (1.5137 X 1018 km). It immediately became the subject of intense observation by astronomers throughout the Southern Hemisphere and was observed by the Hubble Space Telescope. SN 1987A’s brightness peaked in May 1987, with a magnitude of about 2.9, and slowly dimmed in the following months.

Supernova Explosion

Types of Supernova

Life Cycle of a Star

Astronomers have classified supernovae into two broad classifications: Type I and Type II.

  • Type-I

Type I supernova occurs when either a white dwarf in a binary star system accumulates too much energy from its companion star causing it to explode or when a larger star runs out of nuclear fuel and collapses under its own gravity. A type Ia supernova is most commonly observed in outer space, thanks to its brightness, it acts like a candle light helping us observe distances across the deep dark unknown.

The exact nature of the explosion mechanism in Type I generally is still uncertain and is thought to originate in binary systems consisting of a moderately massive star and a white dwarf, with material flowing to the white dwarf from its larger companion. A thermonuclear explosion results if the flow of material is sufficient to raise the mass of the white dwarf above the Chandrasekhar limit (maximum mass theoretically possible for a stable white dwarf star) of 1.44 solar masses. Radioactive elements, notably nickel-56 are formed. When nickel-56 decays to cobalt-56 and later to iron-56, significant amounts of energy is released, providing the brightest light emitted during the weeks following the explosion.

Type Ia supernovae are useful probes of the structure of the universe, since they all have the same luminosity, and by measuring the apparent brightness of these objects, one can also measure the expansion rate of the universe and its variation with time.

Type Ib’s are formed after a large star collapses under its own core gravity where the outer region of the star’s hydrogen is stripped away, leaving behind only a second layer of helium.

Type Ic’s lack both the hydrogen and helium layer when they explode, although the difference here has been debated as not being significant enough to differentiate a type Ib from a Ic.

Type I supernova will often be on the smaller side for a supernova explosion, where a white dwarf is in Chandrashekhar limit. This means that they typically won’t have enough mass to result in stellar remnants other than neutron stars.

Hubble Space Telescope image of supernova 1994D in galaxy NGC 4526.
  • Type-II

These are formed when a star between 8–50 times the Sun’s mass collapses into itself and causes a huge explosion that produces a neutron star or a black hole. These larger stars will first go through a red giant phase, and convert hydrogen to helium via nuclear fusion. This takes place under a billion years where the star will continue converting hydrogen for as long as it can, until the energy produced by the nuclear fusion is unable to sustain balance with the inwards force of itself, causing the star to collapse and explode. In essence, anything above 20 times the size of our Sun can potentially result in a black hole whilst a white dwarf star that is 1.44 solar masses or between 10–20 times the mass of our Sun would produce a neutron star instead.

“A supernova is born from the explosive impact between Superman and Nova.” Source: Trust me, bro

How do scientists study Supernovas?

NASA scientists use a number of different types of telescopes to search and then study supernovas. One example is the NuSTAR (Nuclear Spectroscopic Telescope Array) mission, which uses X-ray vision to investigate the universe. NuSTAR is helping scientists observe supernovas and young nebulas to learn more about what happens leading up to, during, and after these spectacular blasts.

What can we learn from Supernovas?

Scientists have learned a lot about the universe by studying supernovas. They use the Type II supernova like a ruler, to measure distances in space.

They have also learned that stars are the universe’s factories. Stars generate the chemical elements needed to make everything in our universe. At their cores, stars convert simple elements like hydrogen into heavier elements. These heavier elements, such as carbon and nitrogen, are the elements needed for life.Only massive stars can make heavy elements like gold, silver, and uranium. When explosive supernovas happen, stars distribute both stored-up and newly-created elements throughout space.

A star shedding layers of gas and dust, just before exploding in a Supernova

Supernovas are important because they help create new elements and distribute them throughout the universe.

Approximately, every second, a supernova comes into existence. Supernovae happen more often than you might imagine. Luckily, the Milky Way only has an average of two supernovae per century, so trying to observe one at the moment it happens is a tricky task. The last supernova that was directly observed in our galaxy was over 400 years ago. Its viewer and namesake, Johannes Kepler, referred to it as SN 1604.

They are also the Creators of incredibly beautiful remnants. The result of immense and apparently destructive forces are often stunning. Some of the most magnificent stellar objects in existence were created by supernovas that occurred hundreds and thousands of epochs ago, like neutron stars, star-forming nebulae, pulsars and black holes.

In the end, the sight of a supernova explosion might be awful and mesmerizing at the same time, as the beauty of destruction is not always euphoric, yet these humbling events are the celestial distributors of seeds, the explosive pillars of creation.

--

--