<p>Using 1 CM from the Event Horizon of Super Massive Black Hole, SGR A, as the reference point. The particles within the accretion disk are traveling at extreme high speeds.  Assume this speed increases as the particles orbit closer and closer to the EH. </p>

<p>Are the particles within the accretion disk of Super Massive BH SGR A subject to time dilation both from 1) the gravitational field of SGR A at 1 cm from Event Horizon ...and 2) from the the acceleration of the particles traveling around the BH as they approach the EH?   </p>

<p>Does the acceleration of particles act as an interference to the affects of the gravitational time dilation?  And if not, or if these two types of time dilation affect the time intervals for this group of particles,  When would an observer 1 light year from the EH see the particles enter the EH?  A) Before Impacting the EH, B) After impacting the EH,  or C) Never?  </p>

CC BY-SA 4.0
2019-10-20T11:36:02.020Z
There's some info about time dilation near rotating black holes in [this Physics.SE answer](https://physics.stackexchange.com/q/146105/123208). A recent estimate of the spin parameter of the Sagittarius A* black hole is $a=0.65\pm0.05$; there are no stable orbits 1 cm from its event horizon.
PM 2Ring
CC BY-SA 4.0
2019-10-20T13:28:52.647Z
Thank You for your answer,
Richard
CC BY-SA 4.0
2019-10-20T13:37:53.870Z
Please assume there are hot clumps of gas that orbit the  BH SGR A at 30% of C -  All should  agree when answering this question there are no stable orbits when we think in terms of planets orbiting our sun, or moons orbiting our planet; as the conditions at this relative point would break up matter this close to the EH.   I am speaking solely about the particles traveling within the accretion disk at speeds up to 30% of the speed of light.  Does the time dilation at 1 CM from SGA's BH stack on top of the time dilation from the velocity of the particles in the accretion disk?
Richard
CC BY-SA 4.0
2019-10-20T13:49:57.317Z
Matter in an accretion disk *is* in orbit, so the inner radius of the accretion is at the ISCO - the innermost stable circular orbit. Of course, some of the matter in the accretion disk is being pulled into the BH, so it doesn't *have* a stable orbit. OTOH, Sgr A* (fortunately) doesn't really have much of an accretion disk, just the gas clouds you mentioned. There are several stars that are orbiting it, although at a fair distance from the event horizon.
PM 2Ring
CC BY-SA 4.0
2019-10-20T13:56:23.240Z
You may like to browse the existing questions about rotating [black holes](https://astronomy.stackexchange.com/search?q=%5Bblack-hole%5D+rotating). We have many more pages here on black holes, but they generally assume that the BH is a simple  Schwarzschild BH, not a rotating Kerr BH. The Physics stack also has many pages on black holes & general relativity. The quick answer to your question is, yes, for bodies orbiting a BH there's time dilation due to velocity and time dilation due to gravity. Hopefully, one of our professionals will give you a more complete answer.
PM 2Ring
CC BY-SA 4.0
2019-10-20T13:59:12.773Z
Thank You PM 2Ring.  Does the  acceleration of the particles traveling "in orbit" within the accretion disk at the ISCO (not sure if this is possible at 1 cm from EH) dilate time as well?
Richard
CC BY-SA 4.0
2019-10-20T14:07:23.247Z
I believe I  am wrong about the speed being 30% of the speed of light.  At 1 CM from the EH this speed will be higher.
Richard
CC BY-SA 4.0
2019-10-20T14:15:06.013Z
It gets tricky talking about speed near a BH. Because of time dilation, a distant observer never sees anything cross the EH, although if you were falling into a BH your speed approaches lightspeed as you approach the EH. And it gets even more complicated with a Kerr BH, since spacetime itself is getting dragged around the BH at a high speed. I don't want to say too much more, in case I make a mistake. ;)
PM 2Ring
CC BY-SA 4.0
2019-10-20T14:31:02.773Z
Thank You PM 2Ring.    I reviewed the links referenced in your post.  I will research more on Kerr BH.   My underlying curiosity and reason for the question is I want to know if the combined affects for time dilation due to gravity and velocity have the observed result of moving the particles backwards in time.
Richard
CC BY-SA 4.0
2019-10-20T14:39:01.733Z
The recent discovery of the higher than expected pressure at the edge of our solar system's Heliopause by Voyager spacecraft may suggest more particles exist in interstellar space than previously thought.  Wondering where (or when) they came from.  :)
Richard
CC BY-SA 4.0
2019-10-20T15:35:29.463Z
No, time dilation can never reverse the direction of time. In theory, general relativity *does* permit closed timelike curves ("time loops"), but they require special topology, and are unlikely to actually exist.
PM 2Ring
<time><time-dilation>
Does Gravitational Time Dilation stack on top of Time Dilation caused by Velocity?
Richard
# Does Gravitational Time Dilation stack on top of Time Dilation caused by Velocity?

(Asked by: username_0 on 2019-10-20)

Using 1 CM from the Event Horizon of Super Massive Black Hole, SGR A, as the reference point. The particles within the accretion disk are traveling at extreme high speeds. Assume this speed increases as the particles orbit closer and closer to the EH.

Are the particles within the accretion disk of Super Massive BH SGR A subject to time dilation both from 1) the gravitational field of SGR A at 1 cm from Event Horizon ...and 2) from the the acceleration of the particles traveling around the BH as they approach the EH?

Does the acceleration of particles act as an interference to the affects of the gravitational time dilation? And if not, or if these two types of time dilation affect the time intervals for this group of particles, When would an observer 1 light year from the EH see the particles enter the EH? A) Before Impacting the EH, B) After impacting the EH, or C) Never?

**Tags:** time, time-dilation

> **Comments:**
> **username_1**: There's some info about time dilation near rotating black holes in [this Physics.SE answer](https://physics.stackexchange.com/q/146105/123208). A recent estimate of the spin parameter of the Sagittarius A* black hole is $a=0.65\pm0.05$; there are no stable orbits 1 cm from its event horizon.  
> **username_0**: Thank You for your answer,  
> **username_0**: Please assume there are hot clumps of gas that orbit the  BH SGR A at 30% of C -  All should  agree when answering this question there are no stable orbits when we think in terms of planets orbiting our sun, or moons orbiting our planet; as the conditions at this relative point would break up matter this close to the EH.   I am speaking solely about the particles traveling within the accretion disk at speeds up to 30% of the speed of light.  Does the time dilation at 1 CM from SGA's BH stack on top of the time dilation from the velocity of the particles in the accretion disk?  
> **username_1**: Matter in an accretion disk *is* in orbit, so the inner radius of the accretion is at the ISCO - the innermost stable circular orbit. Of course, some of the matter in the accretion disk is being pulled into the BH, so it doesn't *have* a stable orbit. OTOH, Sgr A* (fortunately) doesn't really have much of an accretion disk, just the gas clouds you mentioned. There are several stars that are orbiting it, although at a fair distance from the event horizon.  
> **username_1**: You may like to browse the existing questions about rotating [black holes](https://astronomy.stackexchange.com/search?q=%5Bblack-hole%5D+rotating). We have many more pages here on black holes, but they generally assume that the BH is a simple  Schwarzschild BH, not a rotating Kerr BH. The Physics stack also has many pages on black holes & general relativity. The quick answer to your question is, yes, for bodies orbiting a BH there's time dilation due to velocity and time dilation due to gravity. Hopefully, one of our professionals will give you a more complete answer.  
> **username_0**: Thank You username_1.  Does the  acceleration of the particles traveling "in orbit" within the accretion disk at the ISCO (not sure if this is possible at 1 cm from EH) dilate time as well?  
> **username_0**: I believe I  am wrong about the speed being 30% of the speed of light.  At 1 CM from the EH this speed will be higher.  
> **username_1**: It gets tricky talking about speed near a BH. Because of time dilation, a distant observer never sees anything cross the EH, although if you were falling into a BH your speed approaches lightspeed as you approach the EH. And it gets even more complicated with a Kerr BH, since spacetime itself is getting dragged around the BH at a high speed. I don't want to say too much more, in case I make a mistake. ;)  
> **username_0**: Thank You username_1.    I reviewed the links referenced in your post.  I will research more on Kerr BH.   My underlying curiosity and reason for the question is I want to know if the combined affects for time dilation due to gravity and velocity have the observed result of moving the particles backwards in time.  
> **username_0**: The recent discovery of the higher than expected pressure at the edge of our solar system's Heliopause by Voyager spacecraft may suggest more particles exist in interstellar space than previously thought.  Wondering where (or when) they came from.  :)  
> **username_1**: No, time dilation can never reverse the direction of time. In theory, general relativity *does* permit closed timelike curves ("time loops"), but they require special topology, and are unlikely to actually exist.  

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## 0 answers

