Are There Dark Matter Black Holes?

The Coma Cluster of Galaxies, where Zwicky first found evidence for dark matter. Image Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona

The question: Dark matter is supposed to interact with gravity. Does that mean dark matter is sucked into black holes? And are there dark matter black holes?

A complete answer requires an explanation of why astronomers think there is dark matter in the universe, and what astronomers think constitutes the dark matter.

Why Astronomers Think Dark Matter Exists

The first evidence for the existence of dark matter came from Fritz Zwicky in 1933.

Zwicky studied the orbits of galaxies in the Coma cluster of galaxies. These galaxies orbit the center of the cluster, however the total mass of the cluster required to explain the orbital properties of individual galaxies in the cluster is about 10 times the mass of the galaxies visible in the cluster.

Hence, 90 percent of the gravitationally-detected mass in the Coma cluster is matter that is too dark to be visible. At the time, astronomers widely ignored Zwicky’s work.

Starting in the late 1960s, Vera Rubin, using a sensitive spectrometer built by Kent Ford, studied the orbits of individual stars in spiral galaxies. Rubin found that the orbital properties of the individual stars in a galaxy required a total mass of the galaxy that is roughly 10 times the visible mass of the galaxy. Again 90% of the gravitationally-detected mass in galaxies is unseen dark matter.

Since these early observations, evidence for the existence of dark matter has continued to grow. It seems that about 90% of the matter in the universe is invisible dark matter that astronomers can only detect by its gravitational effect on visible matter.

What Is Dark Matter?

Astronomers do not yet know what dark matter is made of, but they have plenty of theories. Two of the most likely possibilities are MACHOs and WIMPs.

WIMPs, Weakly Interacting Massive Particle, are postulated elementary subatomic particles that interact primarily via the weak nuclear force. As all elementary particles, WIMPs have microscopic masses, but if enough exist they might account for the dark matter. Because they do not interact significantly with the electromagnetic force or less exotic subatomic particles, WIMPs do not emit light or other electromagnetic radiation. Hence we don’t see them. WIMPS are also extremely difficult to detect, so particle physicists searching for possible WIMPs with particle accelerators have yet to find particles that might explain dark matter.

Artist’s conception of the distribution of dark matter in the halo surrounding the Milky Way Galaxy. Image Credit: ESO/L. Calçada

MACHOs, Massive Astrophysical Compact Halo Objects, are celestial objects that might be distributed in spherical halos around spiral galaxies, but are too faint to be observed directly. Possible MACHOs include faint white dwarfs, neutron stars, isolated black holes, and substellar objects such as brown dwarfs or free floating giant planets. Astronomers are trying to indirectly detect MACHOs from their gravitational lensing effects. Current data suggest that MACHOs might explain some but not all of the dark matter.

The mystery of what constitutes the dark matter remains unsolved.

Black Holes and Dark Matter

The fact that astronomers detect dark matter via its gravitational effects means that dark matter does indeed interact gravitationally with ordinary matter.

Dark matter in the form of either WIMPs or MACHOs could quite easily fall into black holes. Black holes do not emit light, but material falling into black holes usually emits X-rays, so such events might be detected with X-ray telescopes.

Because one possibility for MACHOs is isolated black holes, it is quite possible that black holes, originally formed from ordinary matter, constitute at least some of the dark matter in the universe.

© Copyright 2012 Paul A. Heckert, Ph.D., All rights Reserved. Written For: Decoded Science
  • Colin Denman-Jones

    Thanks, I was just wondering about this. If I understand correctly, one possibility then is that WIMPs could coalesce into a black hole, which then could be classed as a type of MACHO?

  • http://migratingblackholes.blogspot.nl/ Leo Vuyk

    You probably would be surprized if somebody postulate that all dark matter is hidden inside black holes of different sizes.
    I do.

  • david-dougherty@comcast.net

    If WIMPs do not interact with anything besides gravity how can they form a black hole? How is energy conserved? Charged particle will emit X-rays which leak energy out , letting the rest of the massive particle relax in closer to each other. (Like when a free electron drops in on a high Z nucleus to settle in an inner shell state. Without the X-ray, the electon would orbit back to its intial radius.). Imagine a spherical cloud of WIMPS with initial velocity zero. Under gravity the cloud collapses, but then it will rebound since none of the particles can lose any energy.

    Hey I’m just an electrical engineer, what do I know? I would be very interested in hearing from someone who does though!

  • Leo Vuyk

    INDEED; Dark Matter Black Holes exist:

    The Splitting Dark Matter- Black Hole- Big Bang and the Cyclic Multiverse.

    According to Quantum FFF Theory, the FORM and MICROSTRUCTURE of elementary particles, is supposed to be the origin of FUNCTIONAL differences between Higgs- Graviton- Photon- and Fermion particles. As a result, a NEW paradigm of splitting-, accelerating- and pairing Black Hole seems to be able to accelerate itself by a -Zero Point Energy driven-self created plasma tails ( by a new Quantum Fluctuation process), to form dumbbell systems, of two or even more black holes. Inside Nebula these dumbbell systems are called Herbig Haro systems. Inside the early universe however these systems are observed as dumbbell shaped radio lobes at both sides of early galaxies (Faint B3 radio galaxies).
    Recent cosmic observations of the infra red and x-ray background radiation of the universe by Chandra and Spitzer space telescopes (CIB and CXB), suggest that even direct after the big bang ABUNDANT black holes already existed.
    This can be interpreted as a support for a Black Hole splitting Big Bang and a Black Hole pairing Big Crunch before, thus there is reason to propose a cyclic Universe. In Quantum FFF theory, the chirality of the universal vacuum lattice is proposed to be the origin of negative- or positive charged black holes and the origin of the formation of matter over anti-matter around negative charged black holes as in our universe seems to be the case.
    The chirality of the oscillating Higgs vacuum is supposed to be the origin of preferred Positron attachment with three different shaped monopole Gluon/photons for easy Quark formation without a lot of particle annihilation back into the Higgs vacuum. At the same time, the possibility of a chiral universal vacuum is reason to support the idea of a super symmetric raspberry shaped multiverse, with multiversal copy universes, instant entangled down to all quantum systems.

  • Mike Coleman

    Consider this. Space is a “fabric”. Matter warping the fabric “downward” is called gravity. Everything we can detect (matter, particles, light, etc) is on one side of the fabric. Now, what if, something on the other side of the fabric affects what we detect. Maybe this so-called dark matter which is “the extra gravity” which keeps galaxies from flying apart is concentrations of matter (which exist on the other side of the black hole). Now, Black holes seem to suck up our matter. Let’s assume that the theory that matter/energy can not be destroyed is true. When black holes suck up our matter, some of it gets spit back out as quasars. The rest of the “stuff” stays on the other side of the fabric. Some of it clumps together “below” the galaxy (causing extra gravity) to keep the galaxy together. The rest of it disperses. But as the “matter” on our side of the fabric gets sucked to the other side, it displaces existing matter on the other side. This displacement pushes upward. This displacement upwards causes galaxies overall to side away from each other (like stuff sliding down a mountain). So locally, this dark matter keeps a galaxy together, but the displacement pushes our galaxies apart. So maybe this “dark matter” / “dark energy” is actually the same thing which is stuff on the other side of the fabric. I don’t believe that we can ever detect dark matter because it “does not exist” on our side of the fabric. We can only detect its “effect” on our side of the fabric (bending of light and gravitational effects). Just my thoughts.

  • MadSat

    Wimps don’t have an electric charge, so they don’t interact in that way. They just drop in and stay.

  • DaveD5145

    Why do they ‘drop in and stay’ if they have no charge or any other interaction? They will ‘drop in and drop back out’.
    In the spherical distribution above, I guess if all the particles were aimed precisely so they would pass within the eventual Schwarzchild radius, then it would form a black hole. But the odds of hitting a 10km target from even a few A.U. is ridiculously small, and they would all have to do ti. Even slightest deviation from a sphere would create enough angular momentum so the impact parameter would miss the target radius for collapse.

  • Michael Ball

    Dave, go study angular momentum.

  • Michael Ball

    At sixty-four and having been a hard-core science fan since I was seventeen, I have to say you have good imagination. But, little of what you suggest is grounded in reality.

  • Michael Ball

    After having read over a few comments, I can say it’s wonderful that people have such imaginations. Little to none of the suggestions here are grounded in reality.
    If you’re going to suggest an entity (a force or particle) that is unknown to science, have a theory (math and a scientific explanation) that explains the process.
    I can just postulate that the Big Bang created atomic sized fields of gravitation that are not actually particles, just gravitational energy.
    Wow! I just solved it.
    Then again, maybe not.
    Try applying your imagination to the real world and solve some important problems here.