Show Notes
About This Episode
A black hole is not what most of us picture. It is not a dark void pulling everything into oblivion. It is mostly empty space, with all its mass theoretically concentrated at a single mathematical point with no volume. It is an object that slows time, bends light back on itself, and almost certainly exists in the millions within our own galaxy, yet we have directly photographed exactly one.
Ole Eggers Bjælde is an astrophysicist at Aarhus University in Denmark. He studies the universe and the physical processes that shape it, and black holes sit close to the centre of what makes his field endlessly interesting. In this episode, he sits down with Mikkel Svold to work through the physics of black holes in terms that are precise without requiring a physics degree.
The conversation covers the structure of a black hole from the event horizon to the singularity at its core, the counterintuitive behaviour of time near an object of extreme gravity, white holes and wormholes and why theory permits them while reality probably does not, and the recent breakthrough that allowed scientists to photograph a black hole using a telescope effectively the size of the Earth. It also covers something less often discussed: there are millions of black holes in the Milky Way, and we have observed a tiny fraction of them. Most, we will probably never see.
In This Episode
- What astrophysics actually is and how scientists study objects that existed billions of years ago
- How a black hole forms from the collapse of a massive star, and why the resulting object is mostly empty
- Why all of a black hole's mass is theoretically concentrated in a single point of infinite density
- What the event horizon is and why it is not a physical surface but a point of no return
- How time slows near a black hole, and what an outside observer sees when watching something fall in
- What white holes and wormholes are, and why theory allows them while reality probably does not
- How Stephen Hawking predicted black holes would slowly evaporate, and why it would take 10 to the power of 66 years for a Sun-mass black hole
- Why the Milky Way likely contains millions of black holes, of which we have directly observed almost none
- How the first image of a black hole was captured using a telescope array the size of the Earth
Chapters
- What astrophysics is and how it works
- What is a black hole
- Inside a black hole and the singularity
- White holes, wormholes, and the event horizon
- Time dilation near a black hole
- Hawking radiation and how black holes die
- Millions of black holes we cannot see
- The first image of a black hole
- Future research and what comes next
Key Quotes
"There are literally millions of black holes in our Milky Way galaxy. And we have maybe observed a little more than a handful of these."
"If someone came and told me that these objects exist and I didn't have the background and I didn't know anything about it, I would probably not believe them. I would probably say, okay, in Sci-fi, sure. But not in reality."
"The most part of the black hole is actually completely empty."
"Time passes slower, closer to the center of the Earth. So if you're standing on a mountain and you have your wristwatch and you look at it, and if you compare that to someone standing next to the sea, they will be different."
About Ole Eggers Bjælde
Ole Eggers Bjælde is an astrophysicist at Aarhus University in Denmark. His research focuses on the universe and the physical processes that govern it. He is an active science communicator who gives popular science talks on topics ranging from black holes to the broader structure and history of the cosmos, and he takes a particular interest in making the counterintuitive aspects of modern physics accessible to general audiences.
Resources Mentioned
- NASA — imagery and research on black holes; search "NASA black hole" for updated visuals and research summaries
- Event Horizon Telescope collaboration — the team behind the first direct image of a black hole
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