Cosmic collisions and black hole boxing

Two pieces of tech may help astronomers get into the ring with some of the universe's most formidable foes.

It’s time to set up the universe’s boxing ring. On one end is an insane amount of matter squeezed into a small, tight space: a supermassive black hole. It is a region with a gravitational pull so strong that not even light can get out of it. An equally formidable enemy lurks on the other side of the ring: another supermassive black hole. The bell rings, and the two black holes begin spinning inward towards each other on a collision path. Two invisible regions, full of energy, rearing to meet head-on. The collision of these two behemoths is something that scientists have been dying to measure.

By 2030, two pieces of technology from the European Space Agency just might cast these cosmic car crashes in a new light. The agency announced that two of its space observatories will be timing their launches so that the instruments contained within can be used at the same time. The instruments in question? An x-ray space telescope called Athena, and a space-based gravitational wave observatory called LISA. With both Athena and LISA in the sky by 2030, scientists will be able to look at the x-rays and the gravitational waves of black hole collisions at the same time. Athena and LISA’s combined power will mean that scientists can make maps of universal events, like black hole collisions, using both x-ray and gravitational wave data. The simultaneous launch of these two tech marvels will allow scientists to understand how black holes and galaxies can co-evolve, and how the gas around black holes functions.

Athena measures x-rays in order to pin down the position of black holes in the sky—a task that is harder than it seems. Since black holes suck in all the light around them, they can’t be observed with the naked eye. Instead, scientists figure out the position of black holes based on the effects the holes have on their surroundings. Black holescan be massive, meaning that their mass can impact the objects around them by causing the objects to wobble or spin. When debris from a star falls into a black hole, the intense energy inside the hole heats it up and causes it to accelerate. The superheated debris gives off x-rays that can be measured with telescopes like Athena.

LISA, on the other hand, measures gravitational waves. These waves are like ripples in a pond coming from large space bodies, squeezing and stretching objects that they come into contact with as they travel through space time. When these waves move past earth, LISA can measure the distorting effects they have on space. The gravitational waves given off by two black holes orbiting each other are different: they slowly pinch off each other’s orbits, moving the black holes closer and closer to each other until they spiral into a collision. This cosmic crash is a little different from landing a punch in boxing: for one thing, it’s totally silent, and completely dark. However, it’s full of energy from both the black holes. Eventually, the two holes form an even more supermassive black hole, and gravitational waves undulate outwards from the scene of the crime, stretching and bending the regions around them until they can be detected by a telescope like LISA.

At the center of almost every galaxy, including our own, is a supermassive black hole. In a few billion years, the supermassive black holes inside the Milky Way and neighboring galaxy Andromeda are expected to collide, merging the two galaxies and forming an even more supermassive black hole. Athena and LISA’s measurements in 2030 are allowing us to understand black hole boxing interactions in time for our own galaxy to eventually step into the ring. Measuring the aftermath of supermassive black hole collisions today gives us the power to see a little bit into our galaxy’s chaotic future.