# Can black holes ever have a glancing collision?

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• 1 month ago

They can come at each other at any angle. But if one comes closer than 3 times the event horizon radius, there are no circular or elliptical or hyperbolic orbits. So the black holes must combine and merge.

(Note: the 3 times event horizon radius comes out of a general relativity calculation. It doesn't come from Newton's mechanics.)

• 1 month ago

Not likely at all. it would take speed of light differences before the gravity were dominated by kinetic energy.

The more likely thing, is locking to each other as a binary system.

On a theory, a direct impact the singularities would merge becoming a new mass with the sum of both. There would be one hell of a lot of energy release but couldn't escape inside event horizon.

https://cosmos-images1.imgix.net/file/spina/photo/...

• Zardoz
Lv 7
1 month agoReport

Glancing does not mean bouncing off. It means contacting at a low angle.

• YKhan
Lv 7
1 month ago

If by glancing you mean they touch and bounce off of each other, then the answer is no. There are two reasons.

First, there is no surface on a black hole to touch. The event horizon is a fictitious surface, just a mathematical border with no special properties than any other region of space. It just marks the point at which light can't escape anymore, but nothing special beyond that.

The second reason is that BH's are so extreme, you can't describe them with standard Newtonian gravity anymore, you need to use Einstein's General Relativity. In GR, gravity starts behaving differently as you draw closer. In GR, gravity actually starts sucking the orbital energy out of the orbiting black holes, making them draw even closer until they merge (this doesn't happen in Newtonian gravity). This is the basis of what gravitational waves are. Orbital energy is being radiated away as gravitational waves. At a certain point black holes will be so close to each other that there will be no escape from each other, they will 100% likely fall into each other.

• Zardoz
Lv 7
1 month ago

Almost certainly always.

Unless the black holes were heading directly toward each other with unbridled precision well before their mutual attraction became the dominant force acting upon them then they will not smack into each other like a car crash, but spiral in and contact at a shallow angle; i.e., glancingly.

Source(s): [n] = 10ⁿ
• 1 month ago

When two galaxies collide, the supermassive black holes at their centers do not hit head-on but would shoot past each other on hyperbolic trajectories