# How does Dark Matter interact with Black Holes? **URL:** \ **Category:** Factual Questions\ **Created:** [May 8, 2019, 9:57pm UTC](https://boards.straightdope.com/t/how-does-dark-matter-interact-with-black-holes/833687 "2019-05-08T21:57:38Z")\ **Posts on this page:** 8\ **Page:** 2
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [May 9, 2019, 3:48pm UTC](https://boards.straightdope.com/t/how-does-dark-matter-interact-with-black-holes/833687/21 "2019-05-09T15:48:37Z")
> [@naita](#): > > Those would be incredibly difficult to find, though. Agree. I wonder, though, if you could find them by looking for unexpected gravitational lensing? ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [May 9, 2019, 6:15pm UTC](https://boards.straightdope.com/t/how-does-dark-matter-interact-with-black-holes/833687/22 "2019-05-09T18:15:09Z")
> [@Telperion](#): > > Evidently there could be. The sun is a pretty small reference star, though. There are stars that are hundreds of solar masses all on their own. Those are very rare compared to one solar-mass stars. The nearest one is thousands of light years away. Nearby bright stars are much closer to the Sun’s mass. Bright A-type stars, for example Sirius, Altair, Vega, and Fomalhaut, are only about 2 solar masses. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [May 9, 2019, 6:28pm UTC](https://boards.straightdope.com/t/how-does-dark-matter-interact-with-black-holes/833687/23 "2019-05-09T18:28:25Z")
> [@Jasmine](#): > > [**How Black Holes Gobble Up Dark Matter**](https://www.space.com/8080-black-holes-gobble-dark-matter.html) > > A very interesting article and worth the read. > > This makes sense if you think about it. The Super Massive Black Hole in the center of the giant elliptical galaxy messier 87 is estimated to have a mass equivalent to six and a half BILLION solar masses! Really? It swallowed six and half billion stars to get that way? There couldn’t be that much regular matter within its gravitational influence to begin with. That’s still less than 3% of the total mass of M87. ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [May 9, 2019, 7:20pm UTC](https://boards.straightdope.com/t/how-does-dark-matter-interact-with-black-holes/833687/24 "2019-05-09T19:20:52Z")
[https://boards.straightdope.com/sdmb/showthread.php?t=850716&highlight=matter](https://boards.straightdope.com/sdmb/showthread.php?t=850716&highlight=matter) ---
**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:** [May 9, 2019, 8:05pm UTC](https://boards.straightdope.com/t/how-does-dark-matter-interact-with-black-holes/833687/25 "2019-05-09T20:05:37Z")
> [@Jasmine](#): > > [**How Black Holes Gobble Up Dark Matter**](https://www.space.com/8080-black-holes-gobble-dark-matter.html) > > A very interesting article and worth the read. > > This makes sense if you think about it. The Super Massive Black Hole in the center of the giant elliptical galaxy messier 87 is estimated to have a mass equivalent to six and a half BILLION solar masses! Really? It swallowed six and half billion stars to get that way? There couldn’t be that much regular matter within its gravitational influence to begin with. This quote suggests that dark matter doesn’t fall into black holes very much: > [@](#): > > However, dark matter very rarely falls into black holes for the same reasons that we don’t see it: it interacts very little with itself and with ordinary matter. > > \ > > For ordinary particles this is not a problem: as they get closer to the black hole, they bump and rub against each other, losing rotational energy and angular momentum such that they spiral into the black hole… > > \ > > But dark matter particles don’t “bump and rub”, by definition! This means that they can’t lose angular momentum so they rarely get close enough to the black holes to be “sucked in”. > > SOURCE: [http://curious.astro.cornell.edu/disclaimer/90-the-universe/black-holes-and-quasars/falling-into-a-black-hole/456-why-doesn-t-dark-matter-fall-into-a-black-hole-advanced](http://curious.astro.cornell.edu/disclaimer/90-the-universe/black-holes-and-quasars/falling-into-a-black-hole/456-why-doesn-t-dark-matter-fall-into-a-black-hole-advanced) ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [May 9, 2019, 8:19pm UTC](https://boards.straightdope.com/t/how-does-dark-matter-interact-with-black-holes/833687/26 "2019-05-09T20:19:21Z")
> [@Quercus](#): > > This is technically incorrect (the worst kind of incorrect). There’s no problem carrying energy into a black hole. Point a particle directly at a black hole and it will keep accelerating (turning gravitational potential energy into kinetic energy) all the way in, carrying that (now kinetic) energy right into the hole. No need to carry any energy away at all. > > What needs to be transferred away is angular momentum. If the particle is moving sideways relative to the hole, and it’s interacting only with the hole, there’s no way for that sideways motion to go away (since gravity only pulls straight towards the hole), and the particle will stay in orbit around the black hole. **The only way for it to fall in is to bang into something, slowing its sideways motion.** (bold added) That’s not quite right. It could also interact gravitationally with another object in such a way as to alter its orbit of the black hole such that its periapsis was inside the event horizon. ---
**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:** [May 9, 2019, 9:20pm UTC](https://boards.straightdope.com/t/how-does-dark-matter-interact-with-black-holes/833687/27 "2019-05-09T21:20:48Z")
It is certainly a mystery just how supermassive black holes like the one in M87 (or, for that matter, even the one in our own Galaxy, at a “mere” few million solar masses) form. It could be from a whole bunch of stars falling in one at a time (or some other similar slow-but-steady process), or it could be from mergers of intermediate-mass black holes. Both hypotheses have problems, and to my knowledge, nobody has yet been able to come up with a model that produces holes that big in the lifespan of the Universe. This is one of the specific known-unknown questions that we hope to address with gravitational-wave data. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [May 9, 2019, 10:15pm UTC](https://boards.straightdope.com/t/how-does-dark-matter-interact-with-black-holes/833687/28 "2019-05-09T22:15:36Z")
> [@Grey](#): > > The energetic jets don’t arise from gravitational interaction, they arise from electromagnetic interactions that also allows for energy to escape from the particles. DM doesn’t interact outside of gravity. So sure rub a M particle against a DM particle and you’ll get a gravitation wave but of such a mind numbingly tiny amount you would never ever notice it. The mechanism of quasars is not well-understood, but one of the most likely mechanisms (the Blandford-Znajek process) does involve the interaction of the in-falling particles EM field with the black hole’s rotation and gravitation, such that the process is powered by the black hole’s rotational energy. Of course as DM does not interact electromagnetically it cannot contribute directly to this process and I believe for a similar process to occur for dark matter it would depend heavily on the nature of DM’s self-interaction. [Previous page](https://boards.straightdope.com/t/how-does-dark-matter-interact-with-black-holes/833687.md?page=1)