We've wanted to break down black holes on the AirSpace podcast for a while now - if only so that we could better understand them ourselves (they’re among the most mysterious phenomena in the universe, can you blame us?).
The concept of black holes isn't new — scientists first theorized their existence in the early 20th century. But in the last few years, our knowledge of black holes has expanded exponentially — from the confirmation of supermassive black holes at the center of galaxies to the first ever image of a black hole captured by the Event Horizon Telescope.
To learn more, we spoke with two experts: Dr. Andrea Ghez and Dr. Sheperd Doeleman. Ghez shared the 2020 Nobel Prize in Physics for her work in proving the existence of the black hole at the center of our galaxy, Sagittarius A*. And Doeleman is the Founding Director of the Event Horizon Telescope and heads the team that imaged the black hole at the center of galaxy M87.
Our conversations with Doeleman and Ghez convinced us that black holes are even more mind-bogglingly cool than we could have ever imagined. We dare you to think otherwise.
Here are some of our favorite mind-blowing black hole facts:
We can’t see black holes, so we must observe them indirectly
Black holes by their very definition are invisible. They represent regions of space where the pull of gravity is so intense nothing can escape it, not even light. So how can you imagine, let alone study, the unseeable?
“[A black hole] is nature’s invisibility cloak. It is where gravity is so intense that even light can’t escape from that object, so we have to observe it through its effect on other things - on matter, on light. We can only see it indirectly… by its diaphanous presence.” - Doeleman
Scientists can “see” black holes by observing their gravitational influence on the things around them. By observing the stars near the center of the Milky Way, Ghez was able to study the gravitational field distorting their orbits, revealing a supermassive black hole. We now think there are black holes at the center of most galaxies.
“Where I do my work at the center of the galaxy the environment is so different than elsewhere in the galaxy. I like to call the center of the galaxy the crowded, urban area compared to the suburbs where we live… What makes the center of the galaxy so exciting to study is things impact each other because it’s so crowded and so extreme.” -Ghez
Black holes are both massive and infinitesimally small at the same time
Einstein’s theory of gravity predicts that the singularities at the center of black holes are the smallest objects in the universe, and their extreme gravity pulls all nearby mass into a surprisingly compact cosmic package. This, along with their distance from Earth, can make black holes even harder to spot (even if you could see them).
“In the center of our own galaxy, the black hole… is four million times the mass of our Sun. And if you were to see it, it would be the equivalent of seeing an orange on the Moon.” -Doeleman
So, in order to image one, you need to build a really big telescope. And that’s exactly what Doeleman and his team did.
“The idea behind the Event Horizon Telescope was to turn the Earth into a telescope.” - Doeleman
The Event Horizon Telescope links synchronized radio dishes around the globe. Each of these radio telescopes records data from the black hole at their geographic locations, effectively forming a planet-sized telescope array. The data is then combined and played back to create an image of a black hole.
So, that begs the question, can you build a telescope that’s even bigger than the Earth? Doeleman says yes. If you launch telescopes into Earth orbit, you could make a telescope as large as the distance between telescopes on the ground and the one in space, increasing the sharpness of the images you can create.
Black holes are some of the brightest things in the universe (wait, what?)
But I thought you can’t see them? Yes, okay, you can’t see the black hole itself. But all the matter just outside the black hole is compressed and heated so much that it glows extremely brightly.
“Because of the deep gravity well that attracts matter, gas, dust, everything into a very small volume, all the matter that approaches them is compressed and it’s heated through friction, just in the same way that when you rub your hands they heat up. So, the gas that surrounds the black hole is at a temperature of hundreds of billions of degrees.” -Doeleman
The more we learn about black holes, the more mysterious they become
There are so many questions that remain about black holes. This inspires scientists to continue growing our understanding.
“I think black holes are so interesting because we know so little still. There are so many questions that remain. And, in fact, I would say the work that we’ve done at the center of the galaxy… has opened up so many other questions because almost everything we could predict about what we would expect to see near the black hole has been inconsistent with the observations. So, this is really fun because it really gives you a path forward.” -Ghez
And just last month, the Event Horizon Telescope team released a new image of M87 in polarized light, showing the magnetic fields being generated around the event horizon. What does this mean? No one knows (yet)— but it may help explain why some star-stuff falls into a black hole's abysmal gravity-well, while other material is jetted out into space in spectacular fountains of matter and energy. But wait, I thought you said nothing can escape a black hole? We did! The more we learn, the weirder it gets. And for all their unfathomable contradictions, black holes have a (nearly) irresistible attraction that keeps us coming back for more.
Want to learn more? Listen to the latest episode of the AirSpace podcast to hear from Dr. Ghez and Dr. Doeleman and expand your black hole knowledge. Listen below or on your favorite podcast app.