# Black holes and photons ?

1. Mar 9, 2010

### dany74q

Hello everyone,
I have a question that bothers me quite some time now,and it would be great to get an answer.

I have been reading some time now about black holes,and photons,and how black holes attract photons and different theories says it can or cannot escape the black hole,and theres some things that arent clear to me:
1.How can a black hole attract a massless particle?
2.How can we see the black hole if he "swallows" the photons ?
3.quite general - are black holes confirmed as "anti - matter" or is it an unconfirmed hypothesis?

So many thanks,
if the question is not appropriate to this section I would be grateful if one of the moderators could move it.
Danny.

2. Mar 9, 2010

### clm321

you cant see a black hole directly only by how it interacts on its surroundings and it dose not atract a particle the black holes immense gravity pulls it in

3. Mar 9, 2010

### dany74q

Thanks,though I`m still confused about the quoted sentence -
I understand that the high value force of black holes gravity pulls the photons in,but how it can affect the photons if they are massless ?
I know that when calculating the force of gravity between 2 objects when one of the masses valued zero (which it is in this case),the equation itself equal zero = no force applied on neither objects.
Am I not correct?

4. Mar 9, 2010

### clm321

well if you beleive in string theory they say graty may be causesd by gravitons and the transfer of these particle causes force if they somehow are transfered between photons you can see how gravity only depends on its mass by the amoput of particles available to give off gravitions

5. Mar 9, 2010

### DavidSullivan

Last edited: Mar 9, 2010
6. Mar 9, 2010

### dany74q

Thank you for sharing that source,some very interesting FAQ.
Though if I understood correctly the formula,then their relativistic mass is also 0,
as m-rel = gamma * m0 (rested),as m0 equal zero then m-rel will be zero as well,
plus - if m-rel is "gain in mass" and equivalent to the value of the velocity increment it will always be zero with photons,as theoretically they move in the same velocity,
or maybe I understood it wrong?

Thank you so much for your answers,
I really appreciate it.

7. Mar 9, 2010

### DavidSullivan

I don't know - I'm not a physicist and simple questions in physics seem always to have long and difficult explainations. :surprised

I found the explaination in the FAQ to be a good conceptual starting point and should narrow your search if you chose to continue digging.

Good luck!

-David

8. Mar 9, 2010

### cragar

mass or energy creates a gravitational field as stated in relativity . we know that light has energy E=hf
A photon it self has its own gravitational field.

9. Mar 9, 2010

### DaveC426913

It doesn't. Gravity is not an attraction; it is a curvature of spacetime.

All massive objects - planets and BHs alike - warp spacetime. All objects - massive or massless - follow the curve of spacetime. Around a BH, spacetime is so curved that photons follow their straight path through curved spacetime to the BH.

We do not see a BH itself. But they tend to acquire an accretion disc of infalling matter. This matter gets compressed and shines brightly, especially in X-rays.

I know of no such hypothesis. Where did you read this?

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