A question about Supermassive Black Holes and Hypernovae.

[THEHOOLIGANJEDI]

I was thinking: Since it is believed that the Milky Way and Andromeda Galaxies will collide with each other in few billion years that made me think.
A) It is believed that two very dense stellar objects (i.e. Neutron Stars and Black Holes) merging will cause a Gamma Ray burst. It is also believed that this type merging causes Hypernova events. (Hypernovae are said to be the most powerful explosions in space next to the Big Bang)
B)It is Believed that many Galaxies have Supermassive Black Holes at their center. It is also said that even a fairly distant Gamma Ray Burst (say 2 Million LY away) would be very bad for the Earth.

Which comes to my question:
Wouldn't the Collision of our Galaxy and Andromeda lead to a very powerful Gamma Ray Burst/Hypernova? If so how powerful would it be and what be the effects on the scale of a Galactic Cluster.

[Jawawithagun]

Nothing says they collide centre-on and those black holes get in any touching distance of each other.

[THEHOOLIGANJEDI]

Nothing says they collide centre-on and those black holes get in any touching distance of each other.

Let's just say for the sake of the thread that they do touch and merge.

[The Spartan]

Nothing says they collide centre-on and those black holes get in any touching distance of each other.

Let's just say for the sake of the thread that they do touch and merge.

They wouldn't even necessarily have to hit center on would they? If there's a neutron star on the fringe of Andromeda and it collides with a blackhole closer to the center of our galaxy it would still create the hypernova.

Just out of curiosity, suppose the two did hit center on, what would 2 supermassive blackholes colliding do? Absorb each other, or cause a hypernova event?

[THEHOOLIGANJEDI]

Nothing says they collide centre-on and those black holes get in any touching distance of each other.

Let's just say for the sake of the thread that they do touch and merge.

They wouldn't even necessarily have to hit center on would they? If there's a neutron star on the fringe of Andromeda and it collides with a blackhole closer to the center of our galaxy it would still create the hypernova.

Just out of curiosity, suppose the two did hit center on, what would 2 supermassive blackholes colliding do? Absorb each other, or cause a hypernova event?

That's my question. What would happen? Would the hypernova event be bigger than a standard one? (involving Stellar Black holes and Neutron Stars)

[GrandMasterTerwynn]

I was thinking: Since it is believed that the Milky Way and Andromeda Galaxies will collide with each other in few billion years that made me think.
A) It is believed that two very dense stellar objects (i.e. Neutron Stars and Black Holes) merging will cause a Gamma Ray burst. It is also believed that this type merging causes Hypernova events. (Hypernovae are said to be the most powerful explosions in space next to the Big Bang)
B)It is Believed that many Galaxies have Supermassive Black Holes at their center. It is also said that even a fairly distant Gamma Ray Burst (say 2 Million LY away) would be very bad for the Earth.

Which comes to my question:
Wouldn't the Collision of our Galaxy and Andromeda lead to a very powerful Gamma Ray Burst/Hypernova? If so how powerful would it be and what be the effects on the scale of a Galactic Cluster.

No. The distances between individual stars and stellar-mass bodies in a galaxy are many millions of times the diameters of those bodies, even though the distances between galaxies in the universe are only a few tens to a few thousand times those of the diameters of the individual galaxies. The merging of Andromeda and the Milky Way would be akin to two clouds of smoke colliding. While the gravitational interaction between the two galaxies will induce massive amounts of star formation (since the gas clouds in the galaxies are large enough to be substantially affected,) the individual stars will only see their orbits changed. The end result will be a large elliptical galaxy with strands of stars flung into intergalactic space.

The eventual merging of the two supermassive black holes at the center of each galaxy, however, will generate two very strong jets of relativistic high-energy particles shooting out at right angles of the plane of the black holes' orbits. These two jets will be strong sources of x-rays and radio waves, making the newly formed active elliptical galaxy look like a quasar to an observer in a distant galaxy (that is to say, you'd have an otherwise normal galaxy with an extremely bright and active nucleus. However, the process would likely take many hundreds of millions of years to unfold, as the galactic nuclei first have to merge, and then the two supermassive black-holes have to merge as well . . . and as the supermassive black holes are stellar-sized objects, in spite of their enormous mass, this will take a while.

[kheegster]

A hypernovae is a term used to denote a class of large supernovae, i.e. the explosion occuring when a star reaches the end of its fusion and collapses under its own gravity. As such, a collision between galaxies wouldn't have any effect on the likelihood of hypernovae occurences.

[kheegster]

A hypernovae is a term used to denote a class of large supernovae, i.e. the explosion occuring when a star reaches the end of its fusion and collapses under its own gravity. As such, a collision between galaxies wouldn't have any effect on the likelihood of hypernovae occurences.

Addendum: the spurt in star formation means that immediately following the 'collision', the populations of hot, massive stars would be increased, which would, indeed, correspondingly increase the probability of hypernovae.

[Dooey Jo]

Nothing says they collide centre-on and those black holes get in any touching distance of each other.

Well they would have to collide eventually. We're talking about objects possibly massing billions of solar-masses. They may not collide directly during the first stages of the collision, but eventually they are going to start orbiting each other. This is believed to cause significant gravitational radiation (because of the huge accelerating masses), which will send the holes spiralling in towards each other. It may take millions of years, but it will happen eventually...

Whether it will cause a gamma ray burst or not is unknown, but either way, it will probably be bad news for any complex organic lifeforms in the galaxy...


By the way (not to hijack the thread or anything), if two supermassive black holes were to orbit each other within their own event horizon, would the gravitational waves generated be detectable from outside of the holes? Or would they somehow "fall back down", because of the waves travelling at c, and all?

[GrandMasterTerwynn]

Nothing says they collide centre-on and those black holes get in any touching distance of each other.

Well they would have to collide eventually. We're talking about objects possibly massing billions of solar-masses. They may not collide directly during the first stages of the collision, but eventually they are going to start orbiting each other. This is believed to cause significant gravitational radiation (because of the huge accelerating masses), which will send the holes spiralling in towards each other. It may take millions of years, but it will happen eventually...

Whether it will cause a gamma ray burst or not is unknown, but either way, it will probably be bad news for any complex organic lifeforms in the galaxy...

No, it won't cause a gamma ray burst. These are black holes, not time-bombs(*). What it will cause are powerful gravitational waves like the sort we eventually hope to detect with gravitational telescopes now being built.

(* - Not in the time-scales involved. Eventually, they will liberate most of their mass via Hawking radiation and vanish in a flash of gamma rays, but for black holes that massive, this process is expected to take many, many, many times the current age of the universe.)

[Surlethe]

By the way (not to hijack the thread or anything), if two supermassive black holes were to orbit each other within their own event horizon, would the gravitational waves generated be detectable from outside of the holes? Or would they somehow "fall back down", because of the waves travelling at c, and all?

If two black holes are within each others' event horizons, how can we tell there's two and not one?

[wolveraptor]

I thought you couldn't maintain a stable orbit within the event horizon without exceeding the speed of light?

[Kuroneko]

If two black holes are within each others' event horizons, how can we tell there's two and not one?

It's in principle possible to distinguish the two cases by the shape of the apparent horizon. It will quickly become a single black hole, however.

I thought you couldn't maintain a stable orbit within the event horizon without exceeding the speed of light?

You are correct. In fact, there aren't stable orbits for a certain radius outside the event horizon, either.

[Gil Hamilton]

Isn't how it works inside an event horizon that no matter which way you go, you are actually always heading toward the center?

[Surlethe]

Isn't how it works inside an event horizon that no matter which way you go, you are actually always heading toward the center?

Yeah. The description I heard was "time flows into the singularity" -- i.e., it's always in your future.