# The Naked Scientists Forum

### Author Topic: How close should I be to BH to see objects passing event the horizon  (Read 1091 times)

#### flr

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##### How close should I be to BH to see objects passing event the horizon
« on: 29/07/2013 20:00:20 »
Let's consider a non-rotating black hole.

A far away observer will never see an object passing the event horizon of the black hole. He will see the objects getting closer and closer and as if it "freezes in time" as it gets closer and closer to event horizon, but it will not see the actual passing thorough event horizon. I hope I understood this correctly.

Would that change is the observer moves closer to black hole?

Will an observer located close to event horizon (but still outside) see the falling object actually disappearing?
If yes, is it there a certain distance from event horizon from which an observer can see actual disappearance beyond event horizon, as opposed to a far away observer that will never the the actual disappearance?

PS. By "disappearance"  I mean the actual passing through event horizon.

#### evan_au

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##### Re: How close should I be to BH to see objects passing event the horizon
« Reply #1 on: 30/07/2013 22:33:24 »
For an observer distant from the event horizon, seeing something pass the event horizon is an "asymptotic" process (just like you can get closer & closer to the speed of light, but you can never quite make it):
• He sees it getting closer & closer to the event horizon
• More & more red-shifted
• Dimmer & dimmer
• Until he can't really see anything
• ...but he still hasn't seen light from the object passing the event horizon

If you want to see something pass the event horizon, try dropping with the object.
At least on a galactic-mass black hole, you can achieve this without getting "spaghettified", or ending up so far apart in your orbit that you can't see the object that you originally dropped with.

The main problem is that after taking this wonderful video content, you won't be able to play it on prime-time TV - because it will now be inside the black hole.

#### CliffordK

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##### Re: How close should I be to BH to see objects passing event the horizon
« Reply #2 on: 30/07/2013 23:24:49 »
The black hole may bend light to such an extent that falling on a parallel path to an object, the object would no longer be visible as it passes the event horizon.

The only way to truly watch it fall into the black hole might be to be below the object as it falls into the black hole, or at least further into the black hole than the object being observed.
« Last Edit: 30/07/2013 23:27:30 by CliffordK »

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##### Re: How close should I be to BH to see objects passing event the horizon
« Reply #2 on: 30/07/2013 23:24:49 »