What happens to stars in front of a falling observer entering a black hole?

In summary, -Passing the event horizon for a large black hole is basically a non event, as the size of the tidal acceleration at the event horizon depends on the mass of the black hole. -But what happens to the stars in front of a free falling observer falling radially at escape velocity into a black hole? -Can we devise a formula that expresses the red or blue shift as seen by the observer? -For what you see after you pass through, look a bit later on the webpage, "The Schwarzschild bubble".
  • #1
Passionflower
1,543
0
It is often said that passing the event horizon for a large black hole is basically a non event as the size of the tidal acceleration at the event horizon depends on the mass of the black hole.

But let's consider something else; what happens to the stars in front of a free falling observer falling radially at escape velocity into a black hole. Can we devise a formula that expresses the red or blue shift as seen by the observer?

We have the redshift formula for stars behind us, which is:
[tex] \sqrt { \left| \left( 1-\sqrt {{\frac {r_{{s}}}{r}}} \right) \left(
1+\sqrt {{\frac {r_{{s}}}{r}}} \right) ^{-1} \right| }{\frac {1}{
\sqrt { \left| 1-{\frac {r_{{s}}}{r}} \right| }}}[/tex]
Which graphically looks like:
http://img442.imageshack.us/img442/4100/redshift.png [Broken]
But what do we measure about the stars ahead of us?
 
Last edited by a moderator:
Physics news on Phys.org
  • #2
Yes, the result is:

[itex]\lambda_{shift}[/itex] = [itex]\lambda_{0}[/itex] [itex]\sqrt{1 - R_{s}/R_{hover}{}}[/itex]

Reference: "Black Holes A Traveler's Guide", P.37, Pickover.
 
  • #3
I don't have "Traveller's guide", but the quoted expression looks like it's for a hovering observer (because of the R_hover).

The black hole itself blocks most of the light from the "other side".

For the falling case, see for instance Andrew Hamilton's webpage, http://casa.colorado.edu/~ajsh/approach.html#lensing.

Picking out the most relevant part of the webpage:

n the illustrated case, the lensing mass is a black hole. Any light rays which come within 1.5 Schwarzschild radii of the black hole fall into the black hole. Here there is a dark region, bounded by the red lines, within which images of background objects cannot appear.

For what you see after you pass through, look a bit later on the webpage, http://casa.colorado.edu/~ajsh/singularity.html, "The Schwarzschild bubble".

I've ommited some things that appear not to be directly relevant to the origianl question that are still interesting, including some interesting discussion about how and when one sees people who have previously fallen through the horizon.
 

What is the event horizon?

The event horizon is a theoretical boundary around a black hole beyond which nothing, including light, can escape due to the extreme gravitational pull of the black hole.

What happens when an object passes the event horizon?

Once an object passes the event horizon, it is pulled into the black hole and cannot escape. This is because the gravitational pull becomes infinitely strong at the singularity, the center of the black hole.

Can anything survive passing the event horizon?

No, according to current theories, nothing can survive passing the event horizon of a black hole. The intense gravitational forces would tear apart any object, including atoms, as it approaches the singularity.

How is the event horizon calculated?

The event horizon is calculated based on the mass of the black hole. It is directly proportional to the mass, meaning that the larger the black hole, the larger the event horizon. The event horizon is also affected by the rotation of the black hole.

Is it possible to see what is beyond the event horizon?

No, it is not possible to see beyond the event horizon. The intense gravitational pull of the black hole bends light and distorts the fabric of space and time, making it impossible for anything to escape or for us to see beyond the event horizon.

Similar threads

  • Special and General Relativity
2
Replies
35
Views
701
  • Special and General Relativity
Replies
11
Views
616
  • Special and General Relativity
Replies
8
Views
865
  • Special and General Relativity
Replies
3
Views
1K
Replies
35
Views
1K
  • Special and General Relativity
Replies
21
Views
1K
  • Special and General Relativity
2
Replies
57
Views
977
  • Special and General Relativity
2
Replies
67
Views
2K
  • Special and General Relativity
Replies
16
Views
1K
  • Special and General Relativity
Replies
24
Views
2K
Back
Top