Thread by @TODreamsProject

1. Today is a very big day for black holes. So let’s talk about the first black hole we *ever* found, how it was discovered by a scientist at the University of Toronto, and how it settled Stephen Hawking’s most infamous bet. A thread...

2. This is not a photo of a black hole. This is a photo of a star with the oh-so-catchy name of HDE226868. It’s a blue supergiant, more than 20 times as big and hundreds of thousands of times as bright as the Sun.

3. It’s relatively close by — in the same part of the galaxy as we are: a thin line of stars between two of the great spiralling arms of the Milky Way — but it still takes light 1,600 years to reach us from there. It’s about 16 quadrillion kilometers away.

4. You can’t see HDE226868 with your naked eye; you need at least a small telescope to glimpse it through the clouds of interstellar gas and dust that stand between it and us. But as far as X-rays go, this patch of sky is a shining beacon.

5. The signal we get from it is stronger than pretty much anything else we can see. And since blue supergiants don’t give off that kind of radiation, scientists know those X-rays must be coming from something else. Something powerful. Something they call Cygnus X-1.

6. Charles Thomas Bolton figured Cygnus X-1 was probably another star. He was just a young astronomer back in 1971, doing his postdoc at the University of Toronto. He spent a lot of his time at the school’s astronomy facility in Richmond Hill: the David Dunlap Observatory.

7. The beautiful stone and dome complex was built in the 1930s on an estate of nearly 200 acres, just north of Toronto. When it opened, it housed the second biggest telescope in the world. Today, it's still the biggest telescope in Canada.

8. When Bolton pointed it at Cygnus X-1, he was hoping to find evidence of a neutron star. Neutron stars are small but incredibly heavy, the dense remnant of a bigger star after it dies in a supernova explosion. They give off X-rays like crazy.

9. Early observations seemed to confirm Bolton’s suspicions: HBE226868 was wobbling slightly, which meant there must be a massive source of gravity nearby. If that source of gravity was a neutron star, he’d have discovered a binary system: two stars orbiting around each other.

10. It would have been an exciting find for the young astronomer, who was particularly interested in those systems. But Cygnus X-1 was no neutron star. After a couple of months spent collecting data at the Dunlap Observatory, Bolton began to suspect the truth…

11. HBE226868 was definitely orbiting something massive, but it was orbiting at an incredible velocity: more than 200 times the speed of sound. That meant Cygnus X-1 was much smaller and much denser than a neutron star.

12. It meant Cygnus X-1 was a black hole.

13. It seems that once upon a time, there was a *really* BIG star. More than 40x bigger than the Sun big. And for most of its life, this star did what all stars do: crush hydrogen atoms together, the immensity of its gravity causing nuclear reactions to fuse them into helium.

14. In fact, this star was so big that eventually it was fusing that helium into even more complex elements, stuff like carbon and neon and oxygen and silicon. That’s where all those elements come from: every single atom forged within a star.

15. By the end of their lives, the very biggest stars make an even more complex and even heavier element: iron. And so, at the centre of this particular gigantic star, a huge iron core built up.

16. Eventually, it was so heavy its atoms couldn’t support its own weight anymore. The star imploded. The enormous mass was crushed down into a tiny space. It became so dense, and its gravity so strong, that nothing coming close to it could ever escape again — not even light.

17. It had become a black hole. Cygnus X-1 was born.

18. HDE226868 whips around Cygnus X-1 once every 5-6 days. A long tail of material gets sucked from the star down toward the black hole, heating up into a disc of plasma as it nears the event horizon—the point of no escape. That, it seems, is where all the X-rays are coming from.

19. Before Charles Thomas Bolton, no one had ever found a black hole. Einstein’s theories of relatively — and the quantum physics that followed — predicted them, but in the 1970s there were still plenty of scientists who didn’t believe they existed at all.

20. Bolton knew that going public with his discovery was going to be risky. It would either make or break his career. It wasn’t until a pair of scientists in England – and then another one in the United States – seemed to confirm his findings that he published his paper.

21. Even then, it was extremely controversial. People put forward plenty of arguments against it. It even became the subject of a famous bet between Stephen Hawking and another physicist, Kip Thorne.

22. Hawking, who had long believed in black holes, said he was 80% sure that Bolton was right, but bet against it anyway. That way, even if he’d been wrong about black holes his entire career, he’d still win something.

23. But he wasn’t wrong. In 1990, enough evidence had finally piled up to convince Hawking without a doubt. Bolton was right. Cygnus X-1 was a black hole. The David Dunlap Observatory had discovered an extraordinary phenomenon never seen before.

24. So one night, Hawking broke into Thorne’s office and signed the bet. He officially owed the physicist a one-year subscription to Penthouse magazine. And astronomy was changed forever.

25. By then, the black hole had eve made its mark on pop culture. Bolton’s discovery inspired a Rush song called “Cygnus X-1”. It’s 28-minutes long and spread across two albums — because of course it is, it’s Rush.

26. Now, the existence of black holes is a widely-accepted scientific fact and supermassive black holes, waaaay bigger than Cygnus X-1, are believed to sit at the centre of many galaxies, including the Milky Way.

27. Today, for the first time in history, we even saw a photo of one. The supermassive black hole known as M87* is 6.5 billion times more massive than our sun and sits at the core of one of the most massive galaxies in our part of the universe.

28. And as for Charles Thomas Bolton and the David Dunlap Observatory: in 2008, the University of Toronto sold the property to a private developer and Bolton was forced to leave the home where he made his thrilling discovery.

But the observatory itself was saved.

29. Today, the @Dunlap_Obs is still operating, engaging in public education and outreach. And so, more than 80 years after the observatory first turned its telescope to the sky, you can still look through it yourself.

Thanks so much for reading!

And if you're into Canadian history & science... last year, I descended two kilometers beneath the surface of the Earth to visit a dark matter lab while exploring Sudbury's extraterrestrial origins for @thisiscanadiana: