Farewell with a 'most massive explosion.'
By Amanda Jermyn

Astronomers have recently discovered the most massive explosion ever observed in the universe. Taking the form of powerful jets of radiation, this explosion occurred in the Ophiuchus galaxy cluster, about 390 million light-years from Earth. A galaxy cluster is a group of thousands of galaxies held together by gravity and bathed in gas so hot it radiates X-rays.

In 2016 a team of astronomers led by Norbert Werner discovered an enormous donut-shaped hole in this galaxy cluster, theorizing that it could have been carved out by strong jets of radiation coming from a black hole. However the team eventually discarded this theory because if it were correct, it would mean they had discovered the most powerful explosion ever observed in the universe, which at the time seemed unlikely. Yet more recently, a team led by Simona Giacintucci of the Naval Research Laboratory in Washington DC was able to confirm that this is exactly what Werner’s team had discovered. Using data from NASA’s Chandra X-Ray Observatory, the European Space Agency’s XMM-Newton X-Ray satellite, as well as radio telescopes in Australia and India, the team found evidence that the giant hole in the Ophiuchus galaxy cluster was indeed created by jets emerging from a supermassive black hole in the cluster’s central galaxy.

This black hole is several billion times the mass of the sun, and the mighty jets emanating from it blasted a crater in the surrounding gas more than a million light years wide. Dr. Giacintucci notes that “you could fit 15 Milky Way galaxies in a row” into a crater this size. The explosion was the equivalent of a billion supernova explosions, emitting about five times the energy of the previous record holder. And it occurred over a long period of time, about 100 million years.

We normally think of black holes as invisible monsters, sucking in all the matter and light that venture too close to them, but they can also emit powerful radiation. A black hole’s strong gravity attracts nearby dust, gas and stars, which over time form an accretion disk that swirls around it and spirals inwards towards its center. This process generates tremendous friction, heat and gravitational stresses as the material is compressed by gravity, resulting in the emission of powerful radiation, some of which we view as light. This radiation is generated in the accretion disk, outside the event horizon, the spherical boundary of the black hole beyond which nothing can escape.

According to Norbert Werner, in the case of the Ophiuchus explosion, for a blast this size to have occurred, the black hole must have attracted material about 270 million times the mass of our sun. The resulting explosion sent out jets of radiation that blasted out the hot gas in its path, leaving an enormous cavity, with only a smattering of electrical particles in it. Any stars or planets in the path of these powerful jets would have been obliterated, and no new ones could form in their wake.

This explosion occurred a mere 390 million light-years away, in our cosmic backyard, so to speak. Given the vastness of the universe, it is likely that many other giant explosions, some perhaps much larger than this one, are out there, just waiting to be discovered.

On a personal note, this will be my last Reach for the Stars column, as I’ve decided to move on to other ventures. I’ve learned so much in the process of writing it, and I thank you for being such appreciative readers. It’s been a wondrous, magical ride through the universe. And as Stephen Hawking once said: “Remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist.”

In these difficult times, be well and stay safe!