Black Holes and the Event Horizon?

  • Thread starter TDS
  • Start date
  • #1
TDS
29
0
My questions are these: When a Black Hole is detected, Is it found by its Event Horizon? Is the Event Horizon located in relation to the stars equitorial plane? If I were to approach a Black Hole from its "North Pole" or "South Pole", would I be affected by its Event Horizon?
 

Answers and Replies

  • #2
1,997
5
TDS said:
My questions are these: When a Black Hole is detected, Is it found by its Event Horizon? Is the Event Horizon located in relation to the stars equitorial plane? If I were to approach a Black Hole from its "North Pole" or "South Pole", would I be affected by its Event Horizon?
The event horizon is a sphere surrounding the center of a black hole.
 
  • #3
George Jones
Staff Emeritus
Science Advisor
Gold Member
7,428
1,071
Consider the region of spacetime from which it possible for a photon to escape to (future null) infinity. Now consider he complement of this region, i.e., a region of spacetime from which it is not possible for a photon to escape to infinity. This latter region is the black hole region.

The boundary between the two regions is the event horizon.

Unfortunately, there are no warning makers that tell you when you cross an event horizon.
 
  • #4
TDS
29
0
I had not though about the Event Horizon as being spherical! What a concept!

Would you happen to know of any books or links where I could read more about this!


MeJennifer said:
The event horizon is a sphere surrounding the center of a black hole.
 
  • #5
TDS
29
0
So is it safe to say that the Accretion Disk and the Event Horizon are two different things? I had thought that they were the same thing.


George Jones said:
Consider the region of spacetime from which it possible for a photon to escape to (future null) infinity. Now consider he complement of this region, i.e., a region of spacetime from which it is not possible for a photon to escape to infinity. This latter region is the black hole region.

The boundary between the two regions is the event horizon.

Unfortunately, there are no warning makers that tell you when you cross an event horizon.
 
  • #6
George Jones
Staff Emeritus
Science Advisor
Gold Member
7,428
1,071
TDS said:
IWould you happen to know of any books or links where I could read more about this!

In my opinion, https://www.amazon.com/dp/0316483419/?tag=pfamazon01-20 has the best popular-level treatrment of black holes - I can't recommend it highly enough. Great diagrams.
 
Last edited by a moderator:
  • #7
George Jones
Staff Emeritus
Science Advisor
Gold Member
7,428
1,071
TDS said:
So is it safe to say that the Accretion Disk and the Event Horizon are two different things? I had thought that they were the same thing.

Yes, they are different. The accretion disk lies outside the event horizon.

Sorry, gotta run! I'll try and add some more details tonight.

Are asking about evidence for an event horizon that can be seen from afar, or evidence as you cross an event horizon?
 
  • #8
TDS
29
0
George Jones,

Thanks for this link! My home library has just gained mass!:biggrin:
If you have more links or suggestions, feel free to send them to me. The more that I learn - the better I will be!


George Jones said:
In my opinion, https://www.amazon.com/dp/0316483419/?tag=pfamazon01-20 has the best popular-level treatrment of black holes - I can't recommend it highly enough. Great diagrams.
 
Last edited by a moderator:
  • #9
TDS
29
0
Any information that you can provide on both will be more than I have at the moment. Basically what I am trying to understand is this; everytime you see a depiction of a Black Hole, you see a ring of "light" that signifies the event horizon around the Black Hole. And in the same breath the narrator starts talking about the accretion disk. I would like to understand the difference. As for your questions - both.



George Jones said:
Yes, they are different. The accretion disk lies outside the event horizon.

Sorry, gotta run! I'll try and add some more details tonight.

Are asking about evidence for an event horizon that can be seen from afar, or evidence as you cross an event horizon?
 
  • #11
541
3
TDS said:
Any information that you can provide on both will be more than I have at the moment. Basically what I am trying to understand is this; everytime you see a depiction of a Black Hole, you see a ring of "light" that signifies the event horizon around the Black Hole. And in the same breath the narrator starts talking about the accretion disk. I would like to understand the difference. As for your questions - both.

Accretion disk are swirling matters being pulled into the black hole. They glow as the result of being heated up by the friction. The event horizon is a spherical boundary which you can't escape once you get passed. You can't see the event horizon, at least not directly. If you have a black hole sitting around a region with not much matter, there will be no accretion disk. But the event horizon is always there.
 
  • #12
TDS
29
0
@pervect,

Thanks for the book link! There goes the mass of my bookshelf again!

@yenchin,

Thanks for clearing up my questions about the Event Horizon and the Accretion Disk!

Now for the really big question. Since the Event Horizon is spherical, is the Accretion Disk also spherical or does it exhist along the equitorial plane of the Black Hole?
 
  • #13
George Jones
Staff Emeritus
Science Advisor
Gold Member
7,428
1,071
TDS said:
Now for the really big question. Since the Event Horizon is spherical, is the Accretion Disk also spherical or does it exhist along the equitorial plane of the Black Hole?

No, the acretion disk is a disk, i.e, it lies in a plane, for roughly the same reason that the orbits of all the planets lie in a plane.

For accretions disks, I can do no better than to quote from Gravity: An Introduction to Einstein's General Relativity, by James Hartle.

Hartle said:
Consider for example, a black hole or neutron star in mutual orbit with a more normal companion star - one like the Sun for instance. The binary pair can lose orbit energy - by gravitational radiation among among other mechanisms - decreasing the size of the orbit. The orbit can bcome small enought that the outermost layer of the companion is more strongly attracted to the compact object than to its own center. In that case the more normal star will shed mass, which will fall (accrete) onto the compact object. Conservation of its initial orbital angular momentum means that the accreting material does not fall directly onto the compact object but rather forms a disk around it called an accretion disk. Various dissipative mechanisms associated with interactions between the particles in the disk cause them to slowly lose energy and angular momentum and gradually spiral towards the object. They spiral slowly inward on nearly circular orbits until they reach the innermost stable circular orbit, after which they fall rapidly into the compact object. The energy they lose leaves the disk as radiation - characteristically at X-ray wavelengths for compact objects around a solar mass.
 
  • #14
TDS
29
0
First let me say THANKS to all that has posted answers to my questions on this thread!!!:biggrin:

I have received more answers in two days on this site than I did in my first semester of Astronomy! This is a good thing for you folks, a sad thing for the school that I went to.

Now for another question.

Would it be possible to observe a Black Hole so long as the probe stayed outside of the Accretion Disk?

I know that the only thing that could actually be observed would be the Accretion Disk unless the probe had a device to detect Hawking Radiation.
 
  • #15
541
3
Yes. If you stay sufficiently far away at a safe distance, you can observe the accretion disk. Hawking radiation is too weak to be detected as it is many times weaker than the microwave background radiation.
 
  • #17
TDS
29
0
@chronon,

My thanks goes out to you as well! If this keeps up I shall need to get another bookshelf!:biggrin:


chronon said:
I've a list of books related to black holes (and in particular Hawking Radiation) at Black Hole Evaporation - useful books
 

Related Threads on Black Holes and the Event Horizon?

  • Last Post
Replies
4
Views
4K
  • Last Post
Replies
11
Views
6K
Replies
142
Views
23K
Replies
6
Views
2K
Replies
5
Views
809
  • Last Post
Replies
5
Views
647
Replies
99
Views
20K
Replies
38
Views
7K
Replies
5
Views
970
Replies
12
Views
2K
Top