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Scientists at Johns Hopkins hypothesize that the LIGO gravitational wave detector may have found dark matter:
The eight scientists from the Johns Hopkins Henry A. Rowland Department of Physics and Astronomy had already started making calculations when the discovery by the Laser Interferometer Gravitational-Wave Observatory (LIGO) was announced in February. Their results, published recently in Physical Review Letters , unfold as a hypothesis suggesting a solution for an abiding mystery in astrophysics.
"We consider the possibility that the black hole binary detected by LIGO may be a signature of dark matter," wrote the scientists in their summary, referring to the black hole pair as a "binary." What follows are five pages of annotated mathematical equations showing how the researchers considered the mass of the two objects LIGO detected as a point of departure, suggesting that these objects could be part of the mysterious substance known to make up about 85 percent of the mass of the universe.
A matter of scientific speculation since the 1930s, dark matter has recently been studied with greater precision; more evidence has emerged since the 1970s, albeit always indirectly. While dark matter itself cannot yet be detected, its gravitational effects can be. For example, dark matter is believed to explain inconsistencies in the rotation of visible matter in galaxies.
There is a very readable summary available, as well.
Is dark matter, then, black holes that will eventually coalesce and prompt another Big Bang?
(Score: 1) by raattgift on Monday June 20 2016, @08:47AM
Sadly we don't know that "for a fact"; we only know from microlensing studies in the foreground of the Magellanic clouds that the dark matter halo of the Milky Way does not have a mass-density distribution consistent with large numbers of ~ stellar mass compact objects. We also lack a good theory that explains the formation of early time compact objects of with more mass (thus reducing the number of expected occultations of the MCs) or much much less mass (falling below the current detectability threshold; and that limit keeps falling).
WRT your second paragraph, the CMB is mute on MACHOs. As a relic field, studying it provides useful constraints on the reheating epoch, which primarily constrains the nature of particle alternatives like WIMPs and PIDMs. The present constraints still allow for a wide range of particle dark matter, and the limit is our observation technology; forthcoming CMB laboratories and the emergence of _indirect_ gravitational astronomy (as we are more confident about the match between theory and observation in gravitational waves shed by inspiralling black holes, we can probably be a bit more confident about the match between theory and observation in the anisotropies of the CMB, where we simply aren't very confident at all (compare the BICEP mess not long ago)). For the time being though, numerous elegant particle explanations for dark matter are on the cusp of testability in the latest LHC run; medium mass gauge bosons (massive, but not nearly as massive as W or Z bosons) that arise in various supersymmetry extensions to the Standard Model (and which can arise in non-SUSY too) are of particular interest, in that mass limits interaction range, and it is perfectly plausible to consider WIMPy-DM annihilation in the bright part of galaxies generating heavy bosons that decay within 10 kpc or so into WIMPs again, solving the cusp/core problem; an additional boson that decays at Mpc scales can hide the true value of \Lambda in the early universe (i.e., up to about now) by filling inter-galactic-cluster space with energy-density of massive (but very light) gauge bosons -- this would elegantly explain the acceleration of the metric expansion without having to change \Lambda-CDM (which is fine with a false vacuum decaying in exactly this kind of way).
The constraints of Big Bang Nucleosynthesis is what drives the difference in total energy between the dark matter fields and the ordinary matter fields; the CMB provides some inputs by setting a limit on the range of interactions between any heavy WIMPs and the relic neutrino field (since that affects nucleosynthesis) and the decay modes of light WIMPs (e.g. the extent to which they can decay into electromagnetic field content when degeneracy pressure is high).
Structure formation is key to the Cold Dark Matter hypothesis of the standard cosmology, but CDM need not be any particular type, or even just one type, of particle or even emergent macroscopic system. In particular "cold" means that the free streaming length of the mass-carrying particles must be small compared to the size of early galaxies. Studies on mixed models that involve CDM and dark matter with free-streaming lengths about the size of early galaxies or much larger, constrain the contribution of non-cold DM to the relic neutrino field and not much more, otherwise we get very different cluster-scale structures than we see in the sky. There is also no evidence in particle physics for "warm" dark matter, with FSLs about the size of protogalaxies, and that poses a problem for "dark electromagnetic-like interactions" such as the non-massless (but fairly light) bosons above. :/
While DM remains an inference (from dynamics and kinematics) rather than an experimental fact, theorists are pretty free to propose all sorts of mechanisms, particle and otherwise; as long as their proposals themselves are testable and not already excluded by experimental facts or observations, they tend to be well-received. The best types of proposals are those that do not immediately become implausible but rather become constrained to form at most some percentage of the overall contribution to the inferred comoving mass density.
So I partly agree with "Sadly, that doesn't give us the first clue what dark matter is, but it does tell us what it isn't"; I mostly don't agree that we lack clues about what it is, and additionally I think the clues get better as good ideas are ruled out by observation and experiment (bye bye MSSM...).