Hypernovae: Coruscations of the Heavens
The superluminous supernovae, also called hypernovae, are the most energetic stellar explosions that the universe has to offer and are some of the brightest objects in the universe.
Written by Graham Lau
In the vast expanse of the universe, certain phenomena stand out. It may be due to immense size like the star UY Scuti, a red hypergiant star with an estimated radius of 1.188 billion kilometers (some 1,700 times larger than our Sun). It could be due to their extreme mass like the current largest known supermassive black hole, TON 618, which is 66 billion times the mass of the Sun. But there are also phenomena like the supernovae, which are known for their powerful and luminous (i.e. super bright) explosions. And among these, hypernovae are particularly remarkable, representing some of the most powerful stellar explosions we’ve observed.
A hypernova is an exceptionally energetic supernova, resulting from the catastrophic collapse of a massive star, typically exceeding 30 times the mass of our Sun.
In this powerful event, the star’s core collapses to form a rapidly spinning black hole, emitting twin jets of highly energetic particles and surrounded by an accretion disk. The explosion releases material with kinetic energies at least an order of magnitude higher than typical supernovae. And this stellar event is exceptionally bright, releasing a lot of light into the cosmos.
To contextualize the brilliance of a hypernova explosion, it’s insightful to compare the luminosity of such an event with various objects, ranging from the darkest materials to the most luminous cosmic events.
Here’s a short list of some objects from faintest to brightest:
Vantablack: Some of the darkest artificial substances, Vantablack is a class of paint coatings that can absorb 99.965% of visible light, reflecting minimal light and appearing nearly invisible under certain conditions. Vantablack is a name derived from Vertically Aligned Nanotube Arrays (VANTA) and the color black. The coatings are composed of vertical arrays of carbon nanotubes, which capture and absorb most incoming light. While Vantablack coatings are famed for being extremely black and having a range of applications from space exploration to artistic endeavors, darker substances have been made—engineers at MIT in 2019 created a carbon nanotube (CNT) foil that was able to absorb 99.995% of light (10 times darker than the darkest Vantablack).
Incandescent Light Bulb: The concept of electric light had been around for sometime before the first continuous electric light of an arc lamp was created in 1835. But after Thomas Edison’s patents for incandescent bulbs in 1879 and 1880, the commercialization of electric light took off and before long street lamps, public buildings, and homes had their oil burning lamps replaced with incandescent light. Fun fact: Edison did not invent the light bulb nor the idea of electric light, but he and his team worked together to figure out a way to make the incandescent bulb practical by being cheaper to produce and lasting longer while also focusing on infrastructure necessary for electric light to replace the gas and oil lighting systems of the time. These days, a typical incandescent bulb emits about 800 lumens, corresponding to a luminous flux of approximately 0.001 watts.
The Sun: Our star has a luminosity of about 3.828 x 1026 watts, serving as a baseline (1 solar luminosity) for comparing stellar brightness. The Sun has slowly been increasing in luminosity over time—it’s now over 30% more luminous than it was when our solar system first formed and slowly becoming more luminous as time goes on.
Average Stars: Stars vary widely in their luminosity. For instance, Alpha Centauri A emits about 1.5 times the Sun’s luminosity, while Betelgeuse—a red supergiant—radiates approximately 100,000 times more than the Sun. Most stars on the Main Sequence have luminosities that range from being about ten thousand times dimmer than the Sun to being up to one million times brighter.
Supernovae: These stellar explosions can outshine entire galaxies temporarily. A typical Type Ia supernova releases around 1044 joules of energy, with peak luminosities reaching up to 5 billion times that of the Sun. Not only are these types of supernovae super bright, but they’re also fairly consistent and have been used as standard candles for measuring large astronomical distances.
Hypernovae: Surpassing standard supernovae, hypernovae can emit energies up to 1046 joules, with luminosities tens of times greater than typical supernovae. Due to this, these events are also called superluminous supernovae. For one example, the hypernova ASASSN-15lh reached a peak luminosity approximately 570 billion times that of the Sun, making it one of the most luminous supernova-like events recorded. The amount of light released during this event was something like 20 times brighter than all of the light released by the entire Milky Way galaxy!
Gamma-Ray Bursts (GRBs): Often associated with hypernovae, GRBs are brief but intense emissions of gamma rays. The most powerful GRBs can momentarily outshine all other gamma-ray sources in the observable universe, releasing as much energy in a few seconds as the Sun will emit over its entire 10-billion-year lifespan. GRBs are thought to be the second most energetic events in the cosmos—only being surpassed by the Big Bang itself.
Dr. Graham Lau is an astrobiologist and communicator of science. He serves as the Director of Communications and Marketing for Blue Marble Space, as a Senior Research Investigator with BMSIS, and as the Host of Ask an Astrobiologist. You can read more of his writing at The Cosmobiologist.