Cutting through the spin on supermassive black holes

It's the week for submission of Discovery Projects, our main funding route through the Australian Research Council. Our current proposal is almost 150 pages long, and I feel like we've been working on it since the Cosmological Dark Ages. It will be good to submit it, but don't think that means I get a break. No, it's time to catch up on all the stuff that has been on the back-burner when grant writing :)

So, a quick post today on an article I wrote for The Conversation called "Cutting through the spin on supermassive black holes". As the name suggests, I describe how astronomers can not only measure the mass of black holes, but can also calculate their spin.

I must admit that the article is a little long compared to others I've written for The Conversation, and what is published is the shortened version. It's a topic that I think is pretty cool and I put in too much detail.

I'll let you read the article, and will happily answer any questions below. The crux is that supermassive black holes spin, and often appear to be spinning as fast as they can.
Just I'll just mention part of the article that was cut due to space limitations. Essentially, the modern idea of black holes was born firstly by Einstein in his Theory of Relativity, and then properly launched by Schwarzschild working on the Eastern Front in 1917, with the spinning black hole metric being found by Kerr almost half a century later. We can now use this mathematical framework, which was initiated by a young man pondering what would happen if you could move at the speed of light, to calculate what we would see if we had gas whizzing around a spinning, billion solar mass black hole many millions of light years away.

And it works!

And to me, that shows the power of science and the human mind. Amazing.


Location: Sydney NSW, Australia

Comments

  1. Ggreybeard5 March 2013 at 12:43

    A fascinating article, Geraint. :)

    1. When astrophysicists talk about a 'spinning black hole' does that refer to the whole caboodle - include properties such as the event horizon and everything else going on inside it? Or are you referring to the singularity itself?

    2. How can a dimensionless singularity have spin properties?

    3. "We find the spinning black hole gives space-time a twist not seen around stationary black holes." Does this effect on space-time affect all dimensions equally?

    4. "Such space-time twists influence the motion of stuff moving close to the black hole." Are these 'twists' observed only from a remote perspective? If I was able to survive as part of the 'stuff' would I notice the twists? or would I continue through my my own reference frame without seeing anything abnormal?

    ReplyDelete
  2. Cusp5 March 2013 at 21:12

    OK -

    1) If you have a spherical mass, the the space-time structure outside of the body is different if the mass is stationary or rotating, and the more rotation, the mo re the different. The different space-time results in a different gravity. When the mass collapses down, this signature is fossilized on the gravitational field and so what we mean is that we measure the spin, we mean that we measure the signature of spin on the space=time.

    2) The same way a dimensionless electron or quark has mass, spin, charge etc. The singularity is really a place where the maths falls over, and so when we really understand gravity (i.e quantum gravity) there should be no singularities.

    3) Nope, the biggest effect is in the equator of the spin, and minimum along the poles. So there are different effects based on how you orbit the black hole.

    4) Yes, you would notice! you would rotate with respect to the rest of the Universe, and once you get across the ergosphere, ou would find how much you fire a rocket, you would be forced to orbit the black hole. You would notice the spin!

    ReplyDelete
  3. Ggreybeard6 March 2013 at 00:01

    1. Got it, thanks.

    2. OK. (but I would have asked the same question if you were talking about dimensionless particles). I suppose you are saying that 'Dimensionless spin' is probably no more weird a property than 'dimensionless' itself is.

    3. Understood, thanks - I guess that's one reason why you get polar jets (it's a 'weak' spot); but what I really meant in my question was "At any location, does this 'space-time twist' manifest itself equally in both time and space or is it stronger in either time or space?" I guess I'm just still trying to understand more about the nature of space-time, after your previous post.

    4. Thanks.

    There are also some great questions and answers on 'The Conversation' article itself!

    ReplyDelete
  4. Cusp6 March 2013 at 08:23

    Ah - I get what you mean now - There are "twist" terms in both the time and space parts of the space-time - of about the same magnitude, so it influences both.

    ReplyDelete

Post a Comment

Popular posts from this blog

Falling into a black hole: Just what do you see?

Image
Everyone loves black holes. Immense gravity, a one-way space-time membrane, the possibility of links to other universes. All lovely stuff. A little trawl of the internets reveals an awful lot of web pages discussing black holes, and discussions about spaghettification, firewalls, lost information, and many other things. Actually, a lot of the stuff out there on the web is nonsense, hand-waving, partly informed guesswork. And one of the questions that gets asked is "What would you see looking out into the universe?" Some (incorrectly) say that you would never cross the event horizon, a significant mis-understanding of the coordinates of relativity. Other (incorrectly) conclude from this that you actually see the entire future history of the universe play out in front of your eyes. What we have to remember, of course, is that relativity is a mathematical theory, and instead of hand waving, we can use mathematics to work out what we will see. And that's what I did.
Read more

Journey to the Far-Side of the Sun

Image
There was a movie, in the old days, Journey to the Far-Side of the Sun  (also known as Doppleganger) which (spoiler alert) posits that there is a mirror version of the Earth hidden on the other side of the Sun, sharing the orbit with our Earth. The idea is that this planet would always be hidden behind the Sun, and so we would not know it there there. This idea comes up a lot, over and over again. In fact, it came up again last week on twitter. But there's a problem. It assumes the Earth is on a circular orbit. I won't go into the details here, but one of the greatest insights in astronomy was the discovery of Kepler's laws of planetary motion , telling us that planets move on elliptical orbits. With this, there was the realisation that planets can't move at uniform speeds, but travel quickly when closer to the Sun, while slowing down as their orbits carry them to larger distance.  There has been a lot of work examining orbits in the Solar System, and you can  s
Read more

Proton: a life story

Proton: a life story  by Geraint F. Lewis 10 35 years: I’ve lived a long and eventful life, but I know that death is almost upon me. Around me, my kind are slowly melting into the darkness that is now the universe, and my time will eventually come. I’ve lived a long and eventful life… 10 -43 seconds: A time of unbelievable light, unbelievable heat! I don’t remember the time before I was born, but I was there, disembodied, ethereal, part of the swirling, roaring fires of the universe coming in to being. But the universe cooled. From the featureless inferno, its character crystalized into a seething sea of particles and forces. Electrons and quarks tore about, smashing and crashing into photons and neutrinos. The universe continued to cool. 1 second: The intensity of the heat steadily died away, and I was born. In truth, there was no precise moment of my birth, but as the universe cooled my innards, free quarks, bound together, and I was suddenly there! A p
Read more