<p>Light signals from an object falling into a BH are redshifted until their wavelengths are too long to observe.  Some light rays will be able to go around the horizon the long way to reach us.  If it goes in along the line of sight these rays will make a ring around the BH.  The direct path image would be very mildly magnified.</p>

CC BY-SA 4.0
2023-05-22T17:53:18.177Z
2023-05-22T18:22:00.240Z
2023-05-22T18:22:00.240Z
eshaya
<p>People often say that an object freezes over a black hole’s event horizon as it falls in. This is because only a finite amount of proper time passes for the object before it crosses the event horizon. But, as the object gets nearer and nearer the event horizon it will be traveling away from the observer at almost the speed of light; does it look to the observer that it is traveling away from them at the speed of light? Is it getting smaller and smaller as it is getting further away, or does it approach some limiting angular size so that it does actually looks like it freezes in place? Heck, with gravitational lensing does it swell up and actually appear bigger as it gets further away? In other words what is the angular size of the object as it approaches the event horizon? Assume what ever location for a stationary observer that makes answering the question easiest.</p>

<black-hole><angular-diameter>
Angular size of an object falling into a black hole
Larry_Boy
# Angular size of an object falling into a black hole

(Asked by: username_0 on 2023-05-15)

People often say that an object freezes over a black hole’s event horizon as it falls in. This is because only a finite amount of proper time passes for the object before it crosses the event horizon. But, as the object gets nearer and nearer the event horizon it will be traveling away from the observer at almost the speed of light; does it look to the observer that it is traveling away from them at the speed of light? Is it getting smaller and smaller as it is getting further away, or does it approach some limiting angular size so that it does actually looks like it freezes in place? Heck, with gravitational lensing does it swell up and actually appear bigger as it gets further away? In other words what is the angular size of the object as it approaches the event horizon? Assume what ever location for a stationary observer that makes answering the question easiest.

**Tags:** black-hole, angular-diameter

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## 1 answers

### Answer by username_1 on 2023-05-22. Score: 1

Light signals from an object falling into a BH are redshifted until their wavelengths are too long to observe. Some light rays will be able to go around the horizon the long way to reach us. If it goes in along the line of sight these rays will make a ring around the BH. The direct path image would be very mildly magnified.


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