Black Hole Collisions

[RyanB]

Hi there!
This is my first post here (long time reader)

I've started the Introductory Astronomy Lectures and must say I'm finding them great!

Anyhow, the reason for my post is something has been puzzling me lately.

Lets say for instance we have two Spiral Galaxys colliding, The part i cant really seem to grasp is what happens to the two central SMBHs when they meet... really i have no ideas

[neufer]

Lets say for instance we have two Spiral Galaxys colliding,
The part i cant really seem to grasp is what happens to the two central SMBHs when they meet... really i have no ideas

When two spiral galaxies collide one or both of them have their nice spiral structures torn asunder.

However, the two central SMBHs NEVER meet.

In fact, hardly any of the hundreds of billions of stars involved ever even come close to one another.

The only real collisions that take place are between large dust/gas clouds which causes condensations into new stars.
(A few dust/gas clouds may also be gobbled up by the other galaxy's central SMBH.)

However, they aren't really killing each other as much as they are mating.

[Chris Peterson]

However, the two central SMBHs NEVER meet.

Not so. In fact, when galaxies collide and merge, their central black holes virtually always collide. Such collisions have been modeled, and a few are suspected to be seen in observational data. It is also commonly believed that the massive black holes at the center of galaxies formed as the result of smaller black holes merging in ancient collisions.

Perhaps what you mean is that the central black holes in galaxies almost never collide directly when galaxies merge. They end up orbiting each other, and their death spiral may take a long time. But eventually they do collide.

When they do, they may form a new, more massive black hole, or one may be ejected (something that has not been observed, but is supported by an interesting theory).

[alter-ego]

However, the two central SMBHs NEVER meet.

Not so. In fact, when galaxies collide and merge, their central black holes virtually always collide. Such collisions have been modeled, and a few are suspected to be seen in observational data. It is also commonly believed that the massive black holes at the center of galaxies formed as the result of smaller black holes merging in ancient collisions.

Perhaps what you mean is that the central black holes in galaxies almost never collide directly when galaxies merge. They end up orbiting each other, and their death spiral may take a long time. But eventually they do collide.

When they do, they may form a new, more massive black hole, or one may be ejected (something that has not been observed, but is supported by an interesting theory).

And there is a candidate, but I haven't researched the topic beyond articles similar to this:
http://news.discovery.com/space/black-hole-galaxy.html

[Iron Sun 254]

Perhaps what you mean is that the central black holes in galaxies almost never collide directly when galaxies merge. They end up orbiting each other, and their death spiral may take a long time. But eventually they do collide.

When they do, they may form a new, more massive black hole, or one may be ejected (something that has not been observed, but is supported by an interesting theory).

As a supplemental question, are there any suspected examples of two massive black holes orbiting each other?

[neufer]

Are there any suspected examples of two massive black holes orbiting each other?

Practically every pair of interacting galaxies is a suspected example of two central black holes orbiting each other.

. http://apod.nasa.gov/apod/ap090426.html

And perhaps the twist to the jets of Centaurus A is an indication of closely orbiting central black holes:

. http://apod.nasa.gov/apod/ap110531.html
. http://apod.nasa.gov/apod/ap101107.html

"Centaurus A itself is apparently the result of a collision of two galaxies and the left over debris
is steadily being consumed by the black hole. Astronomers believe that such black hole central engines
generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies."

[alter-ego]

Are there any suspected examples of two massive black holes orbiting each other?

Practically every pair of interacting galaxies is a suspected example of two central black holes orbiting each other.

. http://apod.nasa.gov/apod/ap090426.html

And perhaps the twist to the jets of Centaurus A is an indication of closely orbiting central black holes:

. http://apod.nasa.gov/apod/ap110531.html
. http://apod.nasa.gov/apod/ap101107.html

"Centaurus A itself is apparently the result of a collision of two galaxies and the left over debris
is steadily being consumed by the black hole. Astronomers believe that such black hole central engines
generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies."

Yes, but not many are known.
http://www.nasa.gov/mission_pages/swift ... holes.html

Astronomers refer to galaxy centers exhibiting such intense emission as active galactic nuclei (AGN). Yet as common as monster black holes are, only about one percent of them are currently powerful AGN. Binary AGN are rarer still: Markarian 739 is only the second identified within half a billion light-years.