# describe a black hole collision/merger **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [April 12, 2018, 1:15am UTC](https://boards.straightdope.com/t/describe-a-black-hole-collision-merger/812259 "2018-04-12T01:15:38Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [April 12, 2018, 1:15am UTC](https://boards.straightdope.com/t/describe-a-black-hole-collision-merger/812259/1 "2018-04-12T01:15:38Z")
There seem to be [many thousands of black holes](https://www.sciencedaily.com/releases/2018/04/180404133532.htm) orbiting Sagittarius A\*, so this kind of thing must be happening quite a lot nearby-ish, so, obviously, need answer fast. Some years ago, there was a lovely piece in Sci-Am that narrated a supernova. I enjoyed quite a bit and felt like I had a front row seat to a cataclysm. Recently, LIGO detected two black holes spinning together and merging, which made me ponder: what the hell must that be like. As I understand black holes, they are not as much of a thing in the same way that other more familiar things are things. Their interior geography is not well (or not at all) understood, just that there is a bunch of mass in there and all the interior geodesics lead to the singularity. Surrounding this, of course, is the ever-popular event horizon, the boundary between regular spacetime and weirdness. In the cases we know about, the two black holes enter a capture orbit and spin down toward each other – straight line, head on mergers seem like a thing that could happen (and probably has) but is likely to be very rare. In the spinning scenario, as long as there is separation of the event horizons, I expect that each of the black holes remains a discrete individual. When they get fairly close, there would, I think, be a literal exchange of mass via Hawking radiation, which might present some small resistance to the merger, and/or some sort of friction (like atmospheric drag or somesuch). But once the event horizons meet to form an aperture – a joining of the interior weirdness – what happens? Do they form some sort of false singularity upon which all of their geometry focuses, driving the two singularities together with all dispatch? And does the shared event horizon rapidly realign to center on the false singularity? ---
**Author:** ![PlaceboTarget](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/placebotarget/32/1073_2.png) [@PlaceboTarget](https://boards.straightdope.com/u/PlaceboTarget)\ **Post date:** [April 12, 2018, 6:20am UTC](https://boards.straightdope.com/t/describe-a-black-hole-collision-merger/812259/2 "2018-04-12T06:20:14Z")
I don’t have an answer to the question but I’m relatively curious about the process of two black holes colliding. _Relatively_ curious because much of the explanation would probably escape me. However, I would like to know whether there are relevant similarities between this phenomenon and other types of mergers, such as when solar eruptions combine or when vortices merge to form a single vortex. I also think this thread would fit better in a different section. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [April 12, 2018, 8:58am UTC](https://boards.straightdope.com/t/describe-a-black-hole-collision-merger/812259/3 "2018-04-12T08:58:39Z")
As I recall, what happens is that the two holes merge, forming a single larger one. Much of their mass is converted to gravity waves in the process; so it’s a very large energy release, but an invisible one. The resulting black hole “[rings](https://en.wikipedia.org/wiki/Binary_black_hole#Ringdown)” for a short time until stabilizing. > [@](#): > > Immediately following the merger, the now single black hole will “ring” – oscillating in shape between a distorted, elongated spheroid and a flattened spheroid. This ringing is damped in the next stage, called the ringdown, by the emission of gravitational waves. The distortions from the spherical shape rapidly reduce until the final stable sphere is present, with a possible slight distortion due to remaining spin. It also receives a large acceleration, which can throw it out of a smaller galaxy. ---
**Author:** ![snfaulkner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snfaulkner/32/433_2.png) [@snfaulkner](https://boards.straightdope.com/u/snfaulkner)\ **Post date:** [April 12, 2018, 10:08pm UTC](https://boards.straightdope.com/t/describe-a-black-hole-collision-merger/812259/4 "2018-04-12T22:08:50Z")
The sound…was of a garbage truck…dropped from the top of the Empire State Building. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 12, 2018, 10:18pm UTC](https://boards.straightdope.com/t/describe-a-black-hole-collision-merger/812259/5 "2018-04-12T22:18:50Z")
From the moment the two event horizons touch, you have one single black hole. From there, have you ever seen two soap bubbles merge? It’s exactly like that. As in, literally exactly: The same math gives the shape of the event horizon as gives the shape of the soap bubble. Now, the complicated part is right before that, in the last 3-4 orbits before the horizons touch. It’s only been in the past decade or so that we’ve figured out how to set up the math to be able to program computers to calculate it. As for the sound, it’s something like [sub]woooooooooooooooo[/sub]ooo[sup]oOP[/sup] ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 12, 2018, 10:38pm UTC](https://boards.straightdope.com/t/describe-a-black-hole-collision-merger/812259/6 "2018-04-12T22:38:16Z")
And they happen around [every 5 minutes](http://en.brinkwire.com/259661/the-background-hum-of-space-could-reveal-hidden-black-holes/). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 12, 2018, 11:03pm UTC](https://boards.straightdope.com/t/describe-a-black-hole-collision-merger/812259/7 "2018-04-12T23:03:44Z")
Oh, and is there any reason this isn’t in GQ? ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [April 12, 2018, 11:10pm UTC](https://boards.straightdope.com/t/describe-a-black-hole-collision-merger/812259/8 "2018-04-12T23:10:43Z")
Yeah, I figured there would not be a definitive answer.