# Can the centers of galaxies act as particle accelerators?

At the centers of galaxies, the amount of dark matter is much higher than that of ordinary matter. So the centers can effectively gravitationally attract and accelerate ordinary matter- without much resistance - to much higher speeds than a similar mass of purely ordinary matter would, since ordinary matter interacts very weakly with dark matter. Is this reasoning correct?

If my above reasoning is correct, (and assuming the matter doesn't fall all the way into the super-massive black hole) then can the energy of the particles reach values higher than that in the LHC and other particle accelerators? Can we draw any conclusions about beyond-the-standard-model particle physics by astronomical observations of galactic centers?

• The black hole which is usually located in the center of galaxies is the dominant "source of gravity" in the central zone, it makes dark matter contribution negligible there. Dark matter is more important when you go at the edges of galaxies and you find always less visible matter and the gravitational effects of dark matter, which is distributed in a way bigger space than the visible galaxy, are dominant. So no, the center of a galaxy can't do that. – Run like hell Jun 7 '17 at 18:47
• In terms of energies, AGN are actually the best accelerators. Sadly, we have no control over them so we're stuck with what they give us (which generally isn't a lot) – Kyle Kanos Jun 7 '17 at 19:13
• – Kyle Kanos Jun 7 '17 at 19:17
• AGN? Active Galactic Neucleii? – CriglCragl Feb 1 '18 at 12:08

## 2 Answers

Galactic centers can be quite powerful emitters of many RF frequencies from radio waves to IR, visible and UV radiation, to X and gamma rays, if they are active. Active means that they are most likely supermassive black holes (BHs), a million to ten billion or more solar mass BHs,that are accreting huge amounts of mass off a disc spinning g around the BH. They can be the core of Seifert galaxies, as well as the quasars and X Ray and gamma ray sources.

If a BH is feeding on a disc of material orbiting the BH, they will be radiating huge amounts of energy. The energy has to be released somehow so the rest of the mass can fall into the galactic nucleus. It may have collimated emissions in the axis parallel to the BH rotation. See https://en.m.wikipedia.org/wiki/Active_galactic_nucleus

Cosmic rays detected on earth or near space can be quite powerful also, actually more than the gamma rays because the massive particles can can augment their mass energy with kinetic energy. Cosmic rays are mostly protons, alpha particles, electrons, and some of the light nucleuses. The largest energy cosmic ray detected was 40 million times more energetic than the LHC energy particles, at about tens of millions of TEV. So, yes, there is in fact significant efforts to detect them and their decays and collision debris.

See UCLA BSM physics combining particle and astroparticle physics at http://www.pa.ucla.edu/content/theory-elementary-particles-astroparticle-physics-and-phenomenology-tepapp

and a popular article about using cosmic and gamma rays also at https://www.forbes.com/sites/startswithabang/2016/11/29/cosmic-rays-may-reveal-new-physics-just-out-of-lhcs-reach/#4b620ae669bf

Edited correction on 2/3/18Due to @Kyle Kanos comment which is correct. Some cosmic rays are believed to come from supernova explosions, and the most energetic ones more than likely from active galactic centers (AGN) which are powered by accretion into supermassive black holes. Since most will also have rotation the magnetic fields and rotation will accelerate the particles. They've been detected at up to energies of about $10^{21}$ ev.

• The last paragraph is wrong. Most galactic CRs are believed to come from the remnants of supernovae, not the explosions themselves. The extragalactic CRs are believed to be accelerated in AGN (see the link I provided in a comment for details). – Kyle Kanos Feb 1 '18 at 12:35
• Out of topic. Bob if you have time can you look at the answers here physics.stackexchange.com/q/1048 , particularly the recent one by Meredith which claims "amateurs?"self publications. – anna v Feb 12 '18 at 14:22
• @anna v. Yes, just read it. It's not only a reference to their own self publication (in Quora), but it also makes no attempt at comparing what it would predict numerically for the CMB with the measured values, or with the results of publications which use the CMB measurement to determine limits on rotation. The comments sya inflation is pure speculation, and that the rotation can explain other things (I just read it but forget The speculations) like dark energy (?). I have no seen the real papers with rotation limits based on the CMB, but what Meredith wrote was an un backed personal theory – Bob Bee Feb 16 '18 at 2:19
• BTW I don't mind self publications, in your own blog. I didn't think Quora allowed that, but the quality of postings in Quora is generally pretty bad in my Opinion. Plus I've seen some postings there that are pretty much self promotion, yes even in physics – Bob Bee Feb 16 '18 at 2:26
• Thanks. I thought so, but am not sure of my cosmological knowledge, the only gravitational course I followed was back in 1975 .I have flagged it. – anna v Feb 16 '18 at 4:58

In short yes there is some scope for this, but as pointed out by another post the active research on dark matter is generally focused on the edges of galactic disks.

However. Galactic nucleii are likely to be the main source of new fundamental physics. Cosmic rays hit the Earth with -as also previously posted- far higher energies not only than the LHC, but than any particular possible Earth-based particle accelerator, just not predictably and conveniently where we want them. Until now.

LIGO is just the first generation gravitational observatory, and the first collision generated hundreds if not thousands of papers (one paper had 4,000 authors, indicating the scale of this research). A space-based gravity wave observatory already planned will increase the information dramatically. And knowing where black holes and neutron stars are colliding, we can point other detectors there and learn about vastly more energetic events than through the LHC.

One of the things we may be able to do with this, is compare expected and actual transmission of different signals. And get a far clearer more objective map of masses between us and such events, potentially ruling out or in some of the ideas about dark matter.

In the long run, galactic nucleii will be second only to the Big Bang itself as a place to look for new physics. In various ways, that must include answers relating to dark matter and energy.