# what happens when black holes meet? **URL:** \ **Category:** Factual Questions\ **Created:** [August 6, 2001, 12:38pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103 "2001-08-06T12:38:23Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![paulberserker](https://avatars.discourse-cdn.com/v4/letter/p/c4cdca/32.png) [@paulberserker](https://boards.straightdope.com/u/paulberserker)\ **Post date:** [August 6, 2001, 12:38pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/1 "2001-08-06T12:38:23Z")
what would occur, theoretically or otherwise, if two black holes met or collided, or came close to each other in space? I’m aware that 3 types exist, but lets assume they are of equal size and graviational pull. would they cancel each other out and remain equidistant, or merge and form an even larger black hole? also, what the hell is negative gravity and what does anti- matter have to do with it? cheers pauly ---
**Author:** ![Jukeball](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@Jukeball](https://boards.straightdope.com/u/Jukeball)\ **Post date:** [August 6, 2001, 1:03pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/2 "2001-08-06T13:03:16Z")
That and other 'unfound’answers of black holes coming within the next decade. ---
**Author:** ![Phobos](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@Phobos](https://boards.straightdope.com/u/Phobos)\ **Post date:** [August 6, 2001, 1:16pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/3 "2001-08-06T13:16:52Z")
The two black holes would merge into one larger/more massive black hole (although, strangely enough, with slightly less mass than the sum of the two original black holes). good link… [http://itss.raytheon.com/cafe/qadir/q859.html](http://itss.raytheon.com/cafe/qadir/q859.html) ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [August 6, 2001, 1:29pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/4 "2001-08-06T13:29:14Z")
> [@](#): > > \*Originally posted by Phobos \* > **(although, strangely enough, with slightly less mass than the sum of the two original black holes).** That doesn’t seem strange at all since the link you provided explains the difference. As the two black holes approach they will begin dumping a lot of energy in the form of gravitational waves. Since energy and mass are equivalent this is the same as dumping mass. The linked article said the resultant black hole would be about 10% less of the sum of the mass of the two balck holes when they were separate. ---
**Author:** ![JeffB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jeffb/32/188_2.png) [@JeffB](https://boards.straightdope.com/u/JeffB)\ **Post date:** [August 6, 2001, 1:51pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/5 "2001-08-06T13:51:57Z")
> [@](#): > > \*Originally posted by Phobos \* > **The two black holes would merge into one larger/more massive black hole (although, strangely enough, with slightly less mass than the sum of the two original black holes).** Wouldn’t it also be possible for two black holes to orbit each other (if they come close rather than collide)? Are there such things as binary black holes? ---
**Author:** ![Phobos](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@Phobos](https://boards.straightdope.com/u/Phobos)\ **Post date:** [August 6, 2001, 1:58pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/6 "2001-08-06T13:58:37Z")
> [@](#): > > \*Originally posted by JeffB \* > Wouldn’t it also be possible for two black holes to orbit each other (if they come close rather than collide)? Are there such things as binary black holes? With enough distance, a black hole is just another mass…so yes, safe orbits are possible. Up close, space gets funky (e.g., frame dragging) so fewer safe orbits are to be found. I have not heard of any discovered binary black hole systems. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [August 6, 2001, 2:04pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/7 "2001-08-06T14:04:56Z")
> [@](#): > > \*Originally posted by JeffB \* > \*\*Wouldn’t it also be possible for two black holes to orbit each other (if they come close rather than collide)? Are there such things as binary black holes? \*\* Not only possible but some suspect that they do. [This](http://www.sciencedaily.com/releases/2000/06/000605153643.htm) link talks about it. The quick and dirty of it is some astrophysicists believe that lots of galaxies collided back in the early ‘days’ of the universe. It is known that supermassive black holes seem to be a regular feature at the center of most galaxies. If two galaxies collide and merge you have two of these black holes the will tend towards the center of the galaxy. > [@](#): > > “A majority of astrophysicists had previously assumed that the two black holes would rapidly coalesce following a galaxy merger,” said Merritt. “Our work suggests that the black holes do fall rapidly to the center of the resulting merged galaxy, but then form a binary system that persists over time with some degree of stability. The black holes orbit about their common center of mass.” > > \ > > The two black holes then remain in orbit about each other with a separation of roughly one parsec, or three light-years, that remains nearly fixed for billions of years. ---
**Author:** ![Astroboy14](https://avatars.discourse-cdn.com/v4/letter/a/df705f/32.png) [@Astroboy14](https://boards.straightdope.com/u/Astroboy14)\ **Post date:** [August 6, 2001, 2:22pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/8 "2001-08-06T14:22:22Z")
They shake hands, exchange pleasantries, and go their own ways! Sheesh!:rolleyes: This whole “fighting ignorance” thing is pretty taxing, isn’t it? Whew! 😃 ---
**Author:** ![g8rguy](https://avatars.discourse-cdn.com/v4/letter/g/7cd45c/32.png) [@g8rguy](https://boards.straightdope.com/u/g8rguy)\ **Post date:** [August 6, 2001, 3:02pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/9 "2001-08-06T15:02:35Z")
> [@](#): > > also, what the hell is negative gravity and what does anti- matter have to do with it? To answer this other part of your question, negative gravity is a pop-sci term for the cosmological constant. It has the effect of making the expansion of the universe slow down less than it otherwise would, so the press calls it negative gravity because that’s a more catchy term. _sigh_ Unfortunately, we can’t tell you a lot about it yet because when people try to calculate what it should be, they get an answer that’s much much much too large (IIRC); this is one of the great embarrassments of modern cosmology. Broadly speaking, it represents the energy stored in the vacuum. Anti-matter doesn’t really have anything to do with it _per se_, and gravity can’t tell the difference between matter and anti-matter. ---
**Author:** ![mongrel\_8](https://avatars.discourse-cdn.com/v4/letter/m/e274bd/32.png) [@mongrel\_8](https://boards.straightdope.com/u/mongrel_8)\ **Post date:** [August 6, 2001, 3:17pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/10 "2001-08-06T15:17:51Z")
[QUOTE] \*Originally posted by g8rguy \* \*\* > [@](#): > > This is one of the great embarrassments of modern cosmology. \*\* I assume the other would be the shotty level of manicurists today right? ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [August 6, 2001, 4:30pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/11 "2001-08-06T16:30:17Z")
[slight hijack] > [@](#): > > negative gravity is a pop-sci term for the cosmological constant. Is this also the same thing that they’re calling “Dark Energy” ? What an AWFUL term of phrase that is ! [/slight hijack] ---
**Author:** ![g8rguy](https://avatars.discourse-cdn.com/v4/letter/g/7cd45c/32.png) [@g8rguy](https://boards.straightdope.com/u/g8rguy)\ **Post date:** [August 6, 2001, 5:06pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/12 "2001-08-06T17:06:33Z")
**Squink** and **mongrel8** : yes and yes, respectively (as far as I know). Oh, and also yes, “dark energy” is a horrible phrase, but then, you should see some of the names that physicists make up on their own! ---
**Author:** ![John\_Kentzel-Griffin](https://avatars.discourse-cdn.com/v4/letter/j/ccd318/32.png) [@John\_Kentzel-Griffin](https://boards.straightdope.com/u/John_Kentzel-Griffin)\ **Post date:** [August 6, 2001, 5:11pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/13 "2001-08-06T17:11:36Z")
> [@](#): > > _Originally posted by_\*\* paulberserker \*\* > what would occur, theoretically or otherwise, if two black holes met or collided, or came close to each other in space? According to Stephen Hawking, when two black holes merge, the area of the resulting black hole’s event horizon is greater than or equal to the sum of the areas of the two black holes event horizons. > [@](#): > > I’m aware that 3 types exist. What three types? I suspect you are thinking about the no-hair theorem. A black hole is defined by three attributes – mass, electric charge, and angular momentum (and possiblly magnetic charge). Do you mean something else? ---
**Author:** ![kniz](https://avatars.discourse-cdn.com/v4/letter/k/c37758/32.png) [@kniz](https://boards.straightdope.com/u/kniz)\ **Post date:** [August 6, 2001, 5:55pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/14 "2001-08-06T17:55:19Z")
> [@](#): > > \*Originally posted by paulberserker \* > **what would occur, theoretically or otherwise, if two black holes met or collided, or came close to each other in space?** [sup]O.K. they’ve given you the theoretical scientific answer to your question. Here’s the layman’s answer:[/sup][list][list][list][list][list][list][list][list] **BLACK OUT** …:D… ---
**Author:** ![paulberserker](https://avatars.discourse-cdn.com/v4/letter/p/c4cdca/32.png) [@paulberserker](https://boards.straightdope.com/u/paulberserker)\ **Post date:** [August 7, 2001, 12:50pm UTC](https://boards.straightdope.com/t/what-happens-when-black-holes-meet/75103/15 "2001-08-07T12:50:04Z")
the three types i mention are “supermassive”, small and something else. this is from the nasa website. i know i sound numb for not remembering, but it clears up the query of whether i ment mass time and energy etc. cheers