View Full Version : A Black Hole

2013-Sep-12, 11:34 PM
I would like to know how far the event horizon extends from a black hole? I know that the distance will vary due to the black holes size but an approximation would be just fine. I heard that the event horizon can extend 2 light years from the hole which would be 12 trillion miles. is this possible.

2013-Sep-13, 12:50 AM
Welcome to CQ Forum, Norman!

The Event Horizon (http://en.wikipedia.org/wiki/Event_horizon) is at the Schwarzschild radius (http://en.wikipedia.org/wiki/Schwarzschild_radius) for a non-rotating Black Hole. Per wikipedia:

The Schwarzschild radius of an object is proportional to its mass. ...
For the mass of the Sun this radius is approximately 3 kilometers and for the Earth it is about 9 millimeters.

So for a distance of 2 light years, we'd likely be talking a supermassive black hole (http://en.wikipedia.org/wiki/Supermassive_black_hole) (IE, a galactic core). And as such it's probably rotating; that means that the actual physics involved complicates things like spatial measurements well beyond my pay grade.

2013-Sep-13, 12:59 AM
My best guess is that a black hole of 3,400,000,000,000 solar masses would have an event horizon of 12,482,753,160,458 miles. It really isn't a "guess", I just don't have good short hand for "Bad at Math."

I don't know if that can actually happen.

2013-Sep-13, 01:09 AM
Black hole radius goes as 2.95km/solar mass. Or 1.83 miles/solar mass.

So for 12 trillion miles you get,
12 trillion miles / (1.83 miles / solar mass) = 6.6 trillion times the mass of the sun.

This is something like 5 times the mass of the Milky Way. Therefore, I'm going to call shenanigans!