Astronomers have made an extraordinary discovery by accident: they found millimeter radiation being produced right near the heart of a supermassive black hole.
This breakthrough, led by Matus Rybak of Leiden University in the Netherlands, combines two natural cosmic magnifying effects and is giving scientists a sharper view of black holes than ever before.
The story begins in 2015, when Rybak and his colleagues were studying a distant galaxy called RXJ1131-1231.
This galaxy is a quasar, which means it has an extremely bright center powered by a supermassive black hole.
What makes this galaxy special is that there is another galaxy sitting between it and Earth.
That foreground galaxy bends and magnifies the light of RXJ1131-1231 in a process called macrolensing.
Thanks to this cosmic lens, the quasar appears three times larger in our telescopes than it really is.
The researchers used the ALMA telescope in northern Chile, which is designed to detect faint millimeter and submillimeter radiation.
When they looked at RXJ1131-1231, they noticed something odd: the three separate magnified images of the galaxy did not stay the same brightness.
Instead, they flickered independently. This was a clear sign of microlensing, another magnifying effect caused when a single star in the foreground galaxy bends the light from the distant quasar.
Together, macrolensing and microlensing created what the astronomers call a “double zoom.” Rybak compares it to stacking two magnifying glasses on top of each other, allowing scientists to see details that would otherwise be invisible, even with the most advanced telescopes in the world.
When the team returned in 2020 to continue their study, they found that the quasar was flickering in millimeter radiation over timescales of years. That was surprising.
Normally, millimeter radiation comes from calm clouds of dust and gas, not from something that changes rapidly.
The team concluded that the flickering must be coming from the corona, a superheated, magnetic ring of material swirling close to the black hole.
Until now, astronomers had seen millimeter radiation near black holes, but they could not be sure whether it came from dust or from more energetic processes. This research provided the first clear evidence that it comes from the black hole’s immediate environment.
Rybak worked closely with Dominique Sluse in Leuven and Frédéric Courbin in Barcelona, who pioneered microlensing studies in visible light back in 2008. Now, nearly two decades later, the technique has been successfully applied to millimeter radiation for the first time.
The team has also been granted time with NASA’s Chandra X-ray Telescope to continue their work. Ultimately, they hope to use microlensing to measure the temperature and magnetic fields near the black hole.
These conditions shape the way the black hole interacts with its host galaxy, and understanding them may help unlock new mysteries of how galaxies grow and evolve.
