The James Webb Space Telescope (often referred to as Webb) is the world’s largest, most powerful, and most complex space science telescope ever built. And guess what? It detected what is believed to be a new supernova about 3 to 4 billion light-years away during its first week of operation.

This is a big deal because Webb wasn’t specifically designed to search for new supernovae — and they are really hard to detect. But the telescope looked in the exact right direction at precisely the right time. Let’s break down the discovery by starting with the basics.

What Is a Supernova?

The “super” half of the name is obvious — it is really big and impressive — and the nova half means “new.” From our perspective on Earth, a new supernova looks like a sudden, short-lived brightening so intense that it looks like a new star being created.

But the supernova doesn’t happen during the birth of a star. No, just the opposite. A supernova represents a star’s self-detonation near the end of its evolution. It can be either the final moments of a massive star’s life as it runs out of fuel — the explosion of a dying star — or the result of a star accumulating matter from a nearby neighbor until a runaway nuclear reaction ignites.

A supernova occurs when a massive star explodes and collapses into either a neutron star or a black hole. As the star runs out of fuel, the pressure drops and gravity causes the star to collapse inward. The outer layers then rebound during the collapse and explode violently. This explosion releases huge amounts of debris and particles.

Supernovae are one of the brightest events in the entire cosmos. At its peak brightness, a supernova can be as luminous as an entire galaxy. But new supernovae are relatively rare events, occurring on average about once every 50 years in the Milky Way.

How Do Astronomers Find Supernovae?

Normally, astronomers find new supernovae by using a telescope that makes surveys by searching large swaths of sky. But people have been finding them since at least 185 A.D., the oldest appearance of a supernova recorded by mankind.

In the year 1054, before telescopes, Chinese astronomers recorded a supernova in the Crab Nebula that was so bright they could even see it in the daytime. Scientists are still studying it today. Another supernova, Kepler’s Supernova, was discovered in 1604. Kepler’s Supernova is the most recent supernova to be discovered in our Milky Way galaxy, and it was observed with the naked eye.

Since the development of the telescope in 1608, the field of supernova discovery has expanded. In 1933, a team from Caltech used a 45-cm telescope at Palomar Observatory to discover 12 new supernovae within three years. They did this by comparing new photographic plates to reference images of extragalactic regions.

Using the comparison technique, the Earth-based telescopes that usually look for supernovae take images of the same wide areas of the sky every few nights. Data-processing software compares every new image with previous images of the same area, looking for anything that might have changed. By the 1960s, astronomers began using computer-controlled searches to discover even more supernovae, and by the 1990s, several automated programs searched the skies for supernovae. Even amateur astronomers have used the comparison technique to discover new supernovae.

In more recent years, supernovae have been detected by looking for neutrino emissions, and the remnants of supernovae could be found by looking for gamma rays from the decay of titanium-44. On May 21, 2008, astronomers were able to catch a supernova on camera for the first time just as it was exploding. They were looking at a galaxy 88 million light-years from Earth when they noticed a burst of X-rays by chance.

A variety of telescopes were aimed in that direction just in time to capture it.

Webb’s Infrared Camera

The Webb telescope was built to look very closely into deep, small areas of the universe to find details from an area as small as a grain of sand — not to scan the skies for new supernovae. Astronomers planned to use Webb to look at light from the earliest stars and galaxies that formed in the universe in the short hundred million years after the Big Bang. That’s why finding a supernova right away was such a surprise. Astronomers were extraordinarily lucky to happen upon a supernova at the perfect moment in time as it exploded.

Webb’s primary imager uses a Near Infrared Camera (NIRCam) that was designed to focus with unprecedented resolution on the near-infrared and mid-infrared wavelength range of 0.6 to 5 microns, which is outside the visible range. These wavelengths are important for peering through gas and dust to see distant objects that would otherwise be hidden.

Unlike the short, tight wavelengths of visible light, longer wavelengths of infrared light penetrate the dense molecular clouds of dust that block most of the visible light. Because of this, the dust is transparent in these infrared wavelengths, meaning stars and planets going through the process of formation will come into clear view with Webb.

The Latest Find

Just a few days after the start of its science operations, Webb’s NIRCam instrument spotted an unexpected bright object, which dimmed over a five-day period. This is classic supernova behavior and suggests that it could have been a supernova caught by sheer luck. The object was discovered in a galaxy that’s between 3 and 4 billion light-years away from Earth, which means that astronomers are seeing an explosion that happened over 3 billion years ago.

The Webb team used software to compare the new observations with images of the same galaxy taken from the Hubble Space Telescope in 2011 to show that this bright object was indeed new. Scientists are careful and want to be extra sure before they confirm that what Webb saw really was a supernova, so they’ll continue to collect time series data.

What Else Can the James Webb Space Telescope Do?

Since astronomers were able to detect such a special event in the first week of operations, does this mean Webb could spot supernovae regularly? Each of Webb’s deep field images includes hundreds of galaxies representing hundreds of opportunities to spot a supernova. Additionally, Webb’s deep view could make the aftermath of a supernova easier to track. Astronomers could watch how light from the supernova dims over time or measure its spectra to reveal what chemical elements made up the parent star that exploded.

Webb was designed to see the earliest galaxies that formed in the universe in the first 100 million years after the Big Bang. Just imagine what scientists could learn if Webb was able to capture the death throes of one of the universe’s first generations of giant stars. Those early stars — made almost entirely of hydrogen and helium — would have been massive, about 200 to 300 times the mass of our sun. They would have burned hot and fast and exploded into enormous supernova.

As Webb continues its investigations of the early universe, it’s sure to rewrite all the textbooks and fundamentally change our understanding of the universe.

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