WATCH: Rise and shine: Scientists watch black hole 'wake up' and emit light in far-off galaxy

Scientists have managed to watch a supermassive black hole awaken before their very eyes, watching the core of a distant galaxy shine brighter than ever before, according to a new study.

The phenomenon that was observed is known as an active galactic nucleus, which is when the supermassive black hole start to shine even brighter due to the activity at the galactic core.

The findings of this study were published in the peer-reviewed academic journal Astronomy & Astrophysics.

Shine bright like a... black hole? Why black holes can make bright galaxies

When one thinks of black holes, the last thing they tend to think of is "bright lights." After all, black holes are called as such because they are essentially holes of complete darkness, totally invisible to observation since their gravity is so intense that nothing can escape - not even light.

However, black holes are also responsible for some of the brightest things in the universe, active galactic nuclei and quasars. 

How do these two contradictory facts make sense?

Well, it's complicated - as astrophysics so often is.

To understand this, we need to understand a bit about what black holes do, and how they function in galactic formation and function. 

Most galaxies are essentially built around even larger black holes, known as supermassive black holes, which sit at the cores of these galaxies consuming all matter unfortunate enough to come near it. These supermassive black holes end up fuelling brightness that can form in these galactic cores, as is the case with this recent study. 

This is because while the black hole itself is invisible, the act of it consuming matter isn't.

Black holes are surrounded by an accretion disk, which is filled with gas and minerals that it ends up devouring, growing bigger as everything that comes close to it gets ripped apart. All the material in the disc creates friction and gravitational stress as it tumbles to the event horizon, the point of no return in the black hole's grasp. All this friction and stress translates into energy.

But if that explains why some galaxies are bright, why aren't some other galaxies? 

This has to do with the amount of material in the accretion disk. If there isn't enough matter in the disk, then it won't be able to light up.

Without the necessary amount of fuel to get it going, these supermassive black holes essentially stay silent, slumbering away and passively consuming what relatively little matter passes by. 

This is also the case with Sagittarius A*, the supermassive black hole at the center of the Milky Way Galaxy, which is currently asleep and not actively accreting enough matter to light up.

Certain events can cause the galactic cores to temporarily light up, such as a supernova or a star being ripped apart by a black hole - something known as a tidal disruption event. But these won't last long enough to become an active galactic nucleus. 

Now that we understand that, we can look at what makes this recent discovery so amazing. 

The study in question centers around SDSS1335+0728, a galaxy 300 million light years away from Earth. 

While previously a relatively unnotable galaxy, SDSS1335+0728 started to suddenly shine in December 2019 - and scientists were eager to know why.

“Imagine you’ve been observing a distant galaxy for years, and it always seemed calm and inactive,” said Paula Sánchez Sáez, an astronomer at the European Southern Observatory (ESO) in Germany and lead author of the study. “Suddenly, its [core] starts showing dramatic changes in brightness, unlike any typical events we've seen before.” 

Nearly five years later, and SDSS1335+0728 is still going strong. Observations taken by the ESO's Very Large Telescope (VLT) in Chile showed that not only is it emitting more infrared, optical, and ultraviolet light, but as of February 2024, it's also emitting X-rays. 

So the scientists got to work trying to figure out what caused this galaxy's supermassive black hole to suddenly wake up. If it was a supernova or a star being consumed, it would likely have dimmed out by now, so for it to stay so bright is unprecedented. 

The researchers went through all possibilities and ultimately had to rule almost everything out. 

Ultimately, there were just two possibilities: Either this is some kind of never-before-seen tidal disruption event, or this is the start of an active galactic nucleus turning on for the first time, and this option seems the most likely.

“The most tangible option to explain this phenomenon is that we are seeing how the [core] of the galaxy is beginning to show... activity,” said co-author Lorena Hernández García, from MAS and the University of Valparaíso in Chile. “If so, this would be the first time that we see the activation of a massive black hole in real time.”

Aside from being a visual spectacle, this also provides some very useful new data about black holes and galactic evolution. More research is needed to figure out exactly how this happened, which the ESO's upcoming Extremely Large Telescope (ELT) could hopefully shed light on.