• Question: who discovered black holes

    Asked by Frankie to Daniel, Hannah, Maggie, Ry, Scott on 7 Nov 2017.
    • Photo: Hannah Middleton

      Hannah Middleton answered on 7 Nov 2017:


      In 2015, the LIGO collaboration (the Laser Interferometer Gravitational wave Observatory, a team of over 1000 scientists) observed gravitational waves from the collision and merger of two black holes. That was the first time two black holes had been observed orbiting each other and then merged together to make a new bigger black hole.

      But before that, there was lots of evidence for the existence of black holes. Some of the best evidence came from looking at stars in the very centre of our galaxy. The stars look like they are orbiting a very massive object that cannot be seen. By watching the paths of the stars, astronomers can tell that the mass of the object there is a million times more massive than our Sun, and so we believe it must be a black hole (Sagittarius A*). I’m not sure who made the discovery that it is a black hole, but some of the first to make observations of Sagittarius A* were astronomers Bruce Balick and Robert Brown in the 70’s.

      In terms of black hole theories, the first idea of black holes was probably John Michell and Pierre-Simon Laplace way back in the 18th century, thinking about the idea of some sort of “dark star”. Then in 1915, Albert Einstein made a theory of gravity called General Relativity and in 1916, Karl Schwarzschild found a solution to Einstein’s equations leading to the theoretical indication of black holes.

    • Photo: Scott Melville

      Scott Melville answered on 7 Nov 2017:


      Hannah’s answer is just fab – it covers everything really well ๐Ÿ™‚
      From the theory side, I’ll just add that one important thing was the realization that light is affected by gravity. Newton thought that gravity only acts on things with mass, and therefore it shouldn’t do anything to light (which is massless). So he didn’t care how heavy a star was (how strong it’s gravity was), it would always shine happily away. But when Einstein and friends developed the theories that Hannah mentioned (around 1915), they realized that light still gets ‘pulled’ by gravity (because it has energy, and E=mc^2!), and so if a star was heavy enough it could pull so strongly that no light could escape – then it would look ‘black’ ๐Ÿ™‚
      (but the experiments are super important, because at first no one really believed that such heavy stars could exist! But now we know there are loads of them out there)

    • Photo: Maggie Lieu

      Maggie Lieu answered on 7 Nov 2017:


      Einstein said that nothing could travel faster than the speed of light. Then some other smart people (Schwarzchild et al) calculated that if the gravity of an object is large enough, even light can’t escape it and this would be a singularity called a black hole, where all known laws of physics breaks down!

      But no one really believed that black holes existed then. It wasn’t until we had big enough telescopes to observe stars orbiting at the centre of our galaxy, that scientists realised they were orbiting around an invisible thing and at such speeds that it must be a black hole!

      But that’s still indirect observation because we don’t see the black hole only the stars. Recently (2015) however we detected our first black holes with gravitational waves. Gravitational waves are radiation that are emitted when 2 black holes collide (among many other things), many of these signals have been detected now so I guess 2015 was when we really discovered black holes!

    • Photo: Ry Cutter

      Ry Cutter answered on 7 Nov 2017:


      Most of the others have covered this really well!
      Karl Schwarzchild has a really sad story and I don’t think it’s told enough. He was signed up to fight in world war 1 when he was 40, and fought for almost two years. While he was in Russia he got very ill and had to go to hospital. While in his sick bed he got hold of a copy of Einstein’s general relativity. Here he did some incredible maths and was the first person to solve Einsteins equations (and predict a plausible black hole!). Less than a year after getting this work out, Schwarzchild died of his illness :(. I like to wonder how much more he could have done for gravity theory had he survived.

      Anyway! We have had other indirect evidence of black holes. When a black hole eats up another star it forms a disk. Depending on how strong the gravity is determines how bright the disk will be. Cygnus X-1 is a super bright x-ray source and it can only be that bright if the gravity is created by something as heavy as a black hole! Stephen Hawking lost a bet, he thought that it wasn’t a black hole ๐Ÿ˜€ It was discovered in 1971 and is considered the first ever known black hole.

      Great question,

      Ryan

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