How can black holes shine?

April 6, 2015 by Fraser Cain, Universe Today
Artistic view of a radiating black hole. Credit: NASA

We hear that black holes absorb all the light that falls into them. And yet, we hear of black holes shining so brightly we can see them halfway across the Universe. What's going on? Which is it?

I remember back to a classic episode of the Guide to Space, where I provided an extremely fascinating and concise explanation for what a quasar is. Don't recall that episode? Well, it was super. Just super. Alright slackers, let's recap.

Quasars are the brightest objects in the Universe, visible across billions of light years. Likely blanching life from everything in the path of the radiation beam from its lighthouse of death. They occur when a is actively feeding on material, pouring out a mountain of radiation. Black holes, of course, are regions of space with such intense gravity where nothing, not even light itself, can escape.

But wait, not so fast "recap" Fraser Cain. I call shenanigans. If black holes absorb all the radiation that falls into them, how can they be bright?

You, Fraser Cain of days of yore, cannot have it both ways. It's either a vortex of total destruction gobbling all the matter and light that fall into them OR alternately light can escape, which still sounds good. I mean, it could be WHERE NO STUFF CAN ESCAPE, except light.

If you'll admit that you of the past was wrong, we'll put you in the temporal cone of shame and move on with the episode. Right? Right? Wrong.

Let's review. Black holes are freaky complicated beasts, with many layers. And I don't mean that in some abstract Choprian "many connections on many different levels". They're a gobstopper from a Sam Neill Event Horizon style hellscape. Let's take a look at the anatomy of a black hole, and everything should fall into place, including the terror.

At the very heart of the black hole is the singularity. This is the region of compressed matter that used to be a star, or in the case of a supermassive black hole, millions or billions of times the mass of a star. Astronomers have no idea what the singularity looks like or behaves, because our understanding of physics completely breaks down, along with the rest of our brains.

It's possible that the singularity is a sphere of exotic matter, or maybe it's constantly compressing down into an infinitely small size. It could also be a pork pie. We'll never know, because nothing goes fast enough to escape from a black hole, not even light.

Maybe you'd need to be going 10 times the speed of light to escape. Or maybe a trillion times the speed of light. Which makes it easy; as far as we can tell, nothing can go faster than the speed of light, and so nothing is escaping.

As you get further from the singularity, the force of gravity decreases. Initially, it'll still requires that you go faster than light. You'll finally reach a very specific point where the escape velocity is exactly the speed of light. This is the , and it's a different distance from the singularity with every black hole. That's the line. Within the event horizon, the light is doomed, outside the event horizon, it can escape. This is the hard candy shell surrounding the chocolately unimaginable nightmare of physics.

Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. Credit: NASA/CXC/M.Weiss

So when see bright black holes, like a quasar, we're not actually seeing light coming from inside the black hole itself or reflected of its surface. What we're seeing is the material that's piling up just outside the event horizon. For all its voracious hunger, a black hole's gravitational eyes are much bigger than its stomach, and it can only feed so quickly. Excess stuff piles up around the black hole's face and forms a vast disk of material, just like me at a Pizza Hut's $5 all you can eat buffet. This pizza heats up until it's like the core of a star, and starts blasting out radiation into space.

Everything I've said is for non-spinning black holes, by the way. Physicists will always make this point with great emphasis. Stay your angry comments astrophysicists, for I have said the magic stone-cutter appeasement code-word, "Non-rotating".

A WFPC2 image of a spiral-shaped disk of hot gas in the core of active galaxy M87. HST measurements show the disk is rotating so rapidly it contains a massive black hole at its hub.

Of course, black holes do rotate, and can rotate at nearly the speed of light. And this rotation changes the nature of the black hole's event horizon in ways that make difficult math even harder. All this spinning generates powerful magnetic fields around the black hole, which focuses jets of material that blast out for hundreds of thousands of light-years. When we see these bright quasars, we're staring right at these jets with our delicate little eyeballs.

So how can we see light coming from black holes when black holes absorb all light? It's not coming from . It's coming from the super-heated region of junk all around the black hole. And still, anything that falls through the event horizon, whether it be , junk, you, me or Grumpy Cat it will never been seen again.

Explore further: How fast do black holes spin?

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14 comments

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Benni
1 / 5 (6) Apr 06, 2015
This by the author: "At the very heart of the black hole is the singularity. This is the region of compressed matter that used to be a star" versus this by the author: "As you get further from the singularity, the force of gravity decreases".

@Fraser Cain- you need to learn a lot more about the force of gravity at the center of BH versus the compressive forces at the center where the Singularity exists. Gravity is at the maximum on the surface of a stellar body & zero at the center, it does not decrease the further you get from the center which is the point at which the Singularity exists, this is true for any planetoid or stellar body.

At the point of the center, compressive & gravity forces are inversely proportional to one another via the Inverse Square Law.
Uncle Ira
1 / 5 (1) Apr 06, 2015
This by the author: "At the very heart of the black hole is the singularity. This is the region of compressed matter that used to be a star" versus this by the author: "As you get further from the singularity, the force of gravity decreases".

@Fraser Cain- you need to learn a lot more about the force of gravity at the center of BH versus the compressive forces at the center where the Singularity exists. Gravity is at the maximum on the surface of a stellar body & zero at the center, it does not decrease the further you get from the center which is the point at which the Singularity exists, this is true for any planetoid or stellar body.

At the point of the center, compressive & gravity forces are inversely proportional to one another via the Inverse Square Law.


@ Bennie-Skippy. Wrong again Cher. You should use the Google-Skippy instead of the Yahoo-Answer-Skippy before you write down the stuff you don't know you got wrong.
bluehigh
4.3 / 5 (6) Apr 06, 2015
Thanks to Fraser Cain and phys.org for this interesting and informative science news.
A well balanced and enjoyable article.
Dethe
1 / 5 (2) Apr 06, 2015
Of course, black holes do rotate, and can rotate at nearly the speed of light
Umm, ummm... How something could rotate, if its hidden beneath the event horizon (which event the light cannot reportedly escape)? Or better to ask, even if it would - how we can know about it? Has the magnetic field some hidden trick, which enables it to bypass the light speed limit?
A well balanced and enjoyable article
It actually brings nothing new, it could be written in 1950 without problem. Such an articles just conserve common scientific misinterpretation of the last decades in the layman publics.
Benni
1 / 5 (4) Apr 06, 2015
Thanks to Fraser Cain and phys.org for this interesting and informative science news.
A well balanced and enjoyable article.


But he has no comprehension of the Inverse Square Law.
Uncle Ira
3 / 5 (2) Apr 06, 2015
Thanks to Fraser Cain and phys.org for this interesting and informative science news.
A well balanced and enjoyable article.


But he has no comprehension of the Inverse Square Law.


@ Bennie-Skippy. It is you Cher that needs to do some comprehending. I am not a scientist like you are not either, but it was easy enough for Ira-Skippy to find out in about 5 minutes you are wrong with what you wrote up there. Are you embarrassed by that? You should be.

Google up the stuffs and learn something like I did. The black hole does not have a surface except the center. The event horizon thing is not a surface. Now when you get that under your belt, then read up on the "shell theorem" so you will see how the gravity attraction does always get down as you go away.

If ol Ira-Skippy can do it, anybody can. And I am not even a nuclear engineer or scientist like you are not either.
Dethe
1 / 5 (2) Apr 06, 2015
The rotation of black holes just may lead to black hole radiation, which can be understood by similar principle, like so-called gravitational brightening of fast rotating massive stars. The strong rotation makes star oblate and the gravitational force will change slower at poles. The existence of event horizon depends on gradient of gravity field, so that the fast rotating black hole may exhibit a hole in event horizon at poles. It will change into "naked singularity" or so called "white hole" there and it will become very radiative. Its light will escape in narrow cones which are known as black hole jets. Actually very fast rotating black holes are conjectured to have toroid shape of event horizon, which makes the whole situation even more apparent. The main difference from classical models is, the black hole can radiate its mass by itself, it doesn't require the accretion of matter for it.
cantdrive85
1.7 / 5 (6) Apr 06, 2015
How can black holes shine?


Because fanciful astrophysicists can make anything happen in their little world of make believe.
Dethe
2.3 / 5 (3) Apr 06, 2015
The asymmetric appearance of jets of some galaxies indicates, that the rotational axis of central black hole can be detached from its magnetic field in similar way like inside of pulsars. As the black hole is losing matter its jets weaken and vanish and the radiation of black hole may get interrupted with period of inactivity. We can observe some indicia of this even inside of Milky Way, the X-ray background of which resembles the bundle of jets under closer examination. This is another aspect, in which black holes are similar to common pulsars and variable stars.. According to american astronomer LaViolette these eruptions affected the climate at Earth in period of few dozens of thousands years.
Dethe
1 / 5 (2) Apr 06, 2015
Another interesting aspect of black hole radiation is the jet asymmetry observed. This asymmetry can be attributed to relativistic Doppler effect, when one of jets is heading toward us. But in many cases this explanation cannot apply and we should consider the CP symmetry violation as the natural cause of this asymmetry. It means, not only jet, but the whole magnetic field of black hole is missing at one pole and the whole black hole represents a giant magnetic monopole.
Ultron
5 / 5 (2) Apr 07, 2015
I didnt like that the author was writing about jets but didnt mention, that nobody knows what is causing polar jets of black holes. There are some hypothesis level attempts, but no solid theory.

reset
1 / 5 (2) Apr 07, 2015
I didnt like that the author was writing about jets but didnt mention, that nobody knows what is causing polar jets of black holes. There are some hypothesis level attempts, but no solid theory.



Except that guy who reproduced them in his plasma chamber every day for three months and videod it...but since it demonstrates no necessity for a BH to be present it isn't currently well accepted. Patience dictates that eventually the mathematical masturbation fantasy will result in some kind of climax, at which point all options will be exhausted except for the correct one.
Uncle Ira
1 / 5 (1) Apr 07, 2015
I didnt like that the author was writing about jets but didnt mention, that nobody knows what is causing polar jets of black holes. There are some hypothesis level attempts, but no solid theory.



Except that guy who reproduced them in his plasma chamber every day for three months and videod it...but since it demonstrates no necessity for a BH to be present it isn't currently well accepted. Patience dictates that eventually the mathematical masturbation fantasy will result in some kind of climax, at which point all options will be exhausted except for the correct one.


@ Reset-Skippy. How you are Cher? I'm good thanks. That's really cool what he did. How did he get the black hole to get inside his chamber thing? Did he make him in there or get him from out in space?
viko_mx
2.3 / 5 (3) Apr 07, 2015
Caste of theoretical physicists continues to amaze me with its isolation from the real world. By mathematics can be described real and imaginary physical objects and processes, so scienties should pay more attention to the facts rather than speculation in science. Still physics is not an international trading market where everyone wants to make the big deal. Besides the factors that prevent the formation and existence of such unnatural object, black holes are meaningless. Everything in the uneverse is created with design and puropose.

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