• Question: What is the cause of a black hole?

    Asked by QWERTYUIOPASDFGHJKLZXCVBN to Alice, Bose, Christian, Emma, Steve on 4 Mar 2016. This question was also asked by Ella.
    • Photo: Alice Harpole

      Alice Harpole answered on 4 Mar 2016:

      Short answer: we don’t really know, and it’s likely different black holes form in different ways.

      Long answer: there are several ways black holes are thought to form. The first is through gravitational collapse, or when an object gets so dense it collapses under its own gravity. This is what happens in some supernovae, when very big, massive stars come to the end of their life and explode.

      They could also form if two objects collide at extremely high energy. It was believed by some people before the Large Hadron Collider (LHC) was switched on that the particles in the experiment may collide at such high energies that micro black holes may form (note: we haven’t detected any of these yet!).

      There is a also certain type of black holes called primordial black holes – these are thought to have formed in the early universe when the pressure and temperature were extremely high, such that even a small fluctuation could produce high enough density for a black hole to form.

    • Photo: Christian Killow

      Christian Killow answered on 4 Mar 2016:

      Lots and lots of matter in a small space! There are various ways this might happen, as Alice explained, but once a certain amount of matter has collapsed into a certain volume of space, a black hole will result.

    • Photo: Steve Marsden

      Steve Marsden answered on 4 Mar 2016:

      A very high density of mass or energy. How dense? For the sun to be a black hole, its entire mass would have to be compressed to less than 6 km across. Earth would have to be compressed to less than 2 cm across. A person would have to be less than a billionth of the width of a proton. Most of the time the mass must be about 10,000 times the mass of our sun, but that’s not necessarily always the case.

      I work on the LHC, where we collide protons together which large amounts of kinetic energy. Our best understanding of gravity states that there is no way to create a black hole there, as when the protons ‘collide’, they are still separated by too much for their energy to form a black hole. However, because gravity is so weak compared with the other fundamental forces we’ve never been able to measure it interacting with subatomic particles. So gravity may well behave differently at small distances. (In actuality we’ve not been able to measure gravitational interactions under about 1 mm, so there’s plenty of room for new physics to develop before we get to the subatomic scale). If we were to see black holes being produced (and subsequently boiling away) at the LHC, this would show that gravity is much stronger at small distances than we think.

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