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coffeecofeecoffee t1_je72gpf wrote

Reply to comment by amitym in Ultramassive black hole over 30 billion times mass of our sun has been spotted. The discovery had been made possible thanks to a phenomenon known as gravitational lensing — the first time a black hole has been spotted in such a way. by Wagamaga

Maybe I don't understand but shouldnt the escape velocity at the event horizon be the speed of light?

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FrickinLazerBeams t1_je7ez4s wrote

Yes. He made some kind of math error on that point. Everything else he said is correct though.

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amitym t1_jea8msl wrote

Yes, and it will of course be slightly less than that in an orbit just outside the event horizon.

But escape velocity isn't the same as local orbital velocity, right? Escape velocity is the speed you have to start out at if you want to coast the rest of the way and still escape the orbit of your primary. Your orbital velocity in your local frame of reference should be much less than the speed of light in this case.

So you should be able to exit your secret black hole lair through gradual velocity changes, from continuous acceleration or other means. The reason I mention that is that it seems technologically somewhat more feasible than stipulating, "okay well first off, you start by going at the speed of light...."

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