‘You need a little bit of alcohol to follow science, I think’, says Stefano Bellotti with a laugh. The postdoc at the Leiden Observatory is also coordinator for Astronomy on Tap. He’s particularly excited for this month’s edition of the event, which is themed around black holes and will take place at the Rijksmuseum Boerhaave.

‘A black hole is the last stage of the life of a very massive star’, explains Bellotti. ‘Throughout the lifetime of a star, there is this battle between the output of the thermonuclear reactions that power the star and gravity. At some point, the star cannot produce enough energy to counterbalance the gravity, and so collapse happens. When the star is really massive, a point of extremely high density is generated. It’s called a singularity, and it forms a black hole.’

‘If the Sun became a black hole, we would not be sucked in’, assures Bellotti. ‘The Earth would keep orbiting around it. Black holes only form from stars much larger than the Sun. Not large in terms of size per se, but more in terms of mass. Black holes are very mysterious because they convey a lot of information, but it’s hard to get this information. The gravity around black holes is so strong that not even light can come out. Because of this, they are extremely difficult to see.’

Distorted images

‘For years, there has been indirect observational evidence of where black holes were and what they were. You don’t really see a black hole, but you see what is orbiting around it. And eventually you think, ‘Oh, this star is not moving as I expect, so there must be something invisible that is making the star move in a certain way.’

In addition to being invisible, there’s another challenge to studying black holes. ‘They’re very, very distant.’ The black hole closest to us sits at the centre of our galaxy. ‘But we also have black holes in other galaxies. The distances are extremely high, which means that it’s even more difficult to see them because you may have some material in front that could blur or distort the images.’

Camera shy

All of this explains why the first image of a black hole wasn’t taken until 2019, using the Event Horizon Telescope. ‘They used a principle in physics called interferometry, for which you use different telescopes all over the earth. Using the combination of these telescopes, you basically obtain a telescope that is on a global scale. Because this telescope is so big, it means that you can see the details of very tiny objects and extreme objects. That's how they got the image. From this amazing international collaboration.’

The black hole in the 2019 image sits at the centre of galaxy M87, located 53.49 million light years away. By contrast, Sagittarius A*, the black hole at the centre of our Milky Way galaxy, is just 26,000 light years away. A massive distance considering that the edge our Solar System is two light years from the Sun. It would take NASA’s Voyager 1 spacecraft – currently the most distant human-made object – 30,000 years to travel this far.

While there are many challenges, Bellotti believes that black holes are well worth studying. ‘You can think of them as cosmic laboratories. You can literally peek into them and have a have a feeling of extreme conditions: extreme gravity, extreme density.’

‘Because black holes are regions where gravity is high, you have extreme bending of space-time. So black holes can help us understand what space-time is. How it works, how it is formed, and so on.’

‘Black holes are also the frontier of understanding quantum mechanics and quantum physics at small scales’, Bellotti adds. ‘Around them, you reach the point where you really need to understand how gravity works at the small scale. There is this debate about how we can describe gravity with the rules of quantum physics. It’s quite complicated. Black holes are really at the frontier of what pure science is.’

Misconceptions

‘As much as we can think that black holes are the vacuum cleaners of the of the universe, unless we are beyond a certain threshold, we’re not sucked in’, notes Bellotti. ‘If something falls within a certain distance, then it gets inside the black hole. Otherwise, it will orbit. 

‘They are not here forever. They shrink over time and become smaller and smaller.’ But black holes evaporate on a timescale longer than the universe has existed, so it’s unlikely we’ll witness this anytime soon.

Even as an astronomer, Bellotti still appreciates fictional representations of black holes. ‘Interstellar is probably one of the best, if not the best space-based movie’, he says. ‘It’s scientifically accurate while still being sci-fi. Entering a black hole, it’s fun because we don’t know what would happen, so they exploited the fact that we don’t know. And that’s just amazing.’