Re:Milky Way’s Black Hole Just Flared, Growing 75 Times as B...
by scatters on Wednesday August 14, 2019 @05:48AM
(#20693990)
The Lorentz factor here is 1/sqrt(3/4), around 15% over unity. So the elapsed time for you to see the flare is 2/1.15 * 26ky, or 45 ky. In general, for any λ multiple of c, the elapsed time multiple is sqrt(1 - λ^2) / (1 - λ), which reduces to 1 + λ in the λ << 1 case. You can try plotting it for λ from -1 (c directly towards the event) to +1 (c directly away from the event) to get a feel for how it behaves.
Re:Milky Way’s Black Hole Just Flared, Growing 75 Times as B...
by taneq on Wednesday August 14, 2019 @08:17AM
(#20694689)
That's great, thanks! For anyone else who wanted to see the graph, here's mine: https://www.desmos.com/calculator/kihnh5ohrv
Re:Milky Way’s Black Hole Just Flared, Growing 75 Times as B...
by roywiggins on Wednesday August 14, 2019 @12:06AM
(#20692644)
If you (somehow) keep accelerating in one direction, there are events you will never observe. It's called a Rindler horizon. Your world-line traces a hyperbola... which will always outpace photons from certain spacetime locations.
Say we're both on Earth 26,000 years ago. You stay on Earth and I shoot off at C/2 in a direction away from the SMBH. You wait 26,000 years and then see the flare. How long do I wait in my own reference frame before I see the flare?
My guess intuitively is that time dilation and the extra distance cancel out and I still wait exactly 26,000 years (no matter how fast I go), but I'd have to dig out my old physics textbook to figure it out properly. Also, what happens if instead I shoot off towards the SMBH? Or at 90 degrees? I'd obviously see the flare sooner in my reference frame, but how much?
It seems like there's a general rule that, by moving, you can decrease the time until you see events (at least those communicated by light) but you can never increase it.