Slashdot Mirror
Can Primordial Black Holes Alone Account For Dark Matter?
thomst writes: Slashdot stories have reported extensively on the LIGO experiments' initial detection of gravity waves emanating from collisions of primordial black holes, beginning, on February 11, 2016, with the first (and most widely-reported) such detection. Other Slashdot articles have chronicled the second LIGO detection event and the third one. There's even been a Slashdot report on the Synthetic Universe supercomputer model that provided support for the conclusion that the first detection event was, indeed, of a collision between two primordial black holes, rather than the more familiar stellar remnant kind that result from more recent supernovae of large-mass stars.
What interests me is the possibility that black holes of all kinds -- and particularly primordial black holes -- are so commonplace that they may be all that's required to explain the effects of "dark matter." Dark matter, which, according to current models, makes up some 26% of the mass of our Universe, has been firmly established as real, both by calculation of the gravity necessary to hold spiral galaxies like our own together, and by direct observation of gravitational lensing effects produced by the "empty" space between recently-collided galaxies. There's no question that it exists. What is unknown, at this point, is what exactly it consists of.
The leading candidate has, for decades, been something called WIMPs (Weakly-Interacting Massive Particles), a theoretical notion that there are atomic-scale particles that interact with "normal" baryonic matter only via gravity. The problem with WIMPs is that, thus far, not a single one has been detected, despite years of searching for evidence that they exist via multiple, multi-billion-dollar detectors.
With the recent publication of a study of black hole populations in our galaxy (article paywalled, more layman-friendly press release at Phys.org) that indicates there may be as many as 100 million stellar-remnant-type black holes in the Milky Way alone, the question arises, "Is the number of primordial and stellar-remnant black holes in our Universe sufficient to account for the calculated mass of dark matter, without having to invoke WIMPs at all?"
I don't personally have the mathematical knowledge to even begin to answer that question, but I'm curious to find out what the professional cosmologists here think of the idea.
What interests me is the possibility that black holes of all kinds -- and particularly primordial black holes -- are so commonplace that they may be all that's required to explain the effects of "dark matter." Dark matter, which, according to current models, makes up some 26% of the mass of our Universe, has been firmly established as real, both by calculation of the gravity necessary to hold spiral galaxies like our own together, and by direct observation of gravitational lensing effects produced by the "empty" space between recently-collided galaxies. There's no question that it exists. What is unknown, at this point, is what exactly it consists of.
The leading candidate has, for decades, been something called WIMPs (Weakly-Interacting Massive Particles), a theoretical notion that there are atomic-scale particles that interact with "normal" baryonic matter only via gravity. The problem with WIMPs is that, thus far, not a single one has been detected, despite years of searching for evidence that they exist via multiple, multi-billion-dollar detectors.
With the recent publication of a study of black hole populations in our galaxy (article paywalled, more layman-friendly press release at Phys.org) that indicates there may be as many as 100 million stellar-remnant-type black holes in the Milky Way alone, the question arises, "Is the number of primordial and stellar-remnant black holes in our Universe sufficient to account for the calculated mass of dark matter, without having to invoke WIMPs at all?"
I don't personally have the mathematical knowledge to even begin to answer that question, but I'm curious to find out what the professional cosmologists here think of the idea.
See this link: Content of the Universe 2016
So, the problem is that there is so much of it, you would think we'd see it perturbing stallar orbits more, it it were concentated in many, many discrete points of star gravitational influence. There would be a lot more stars orbiting pulsar type objects, perhaps?
A real cosmologist would know the odds of the galaxy looking the way it does if all the extra mass were in scattered black holes of a certain size. Probably low.
https://phys.org/news/2015-03-... http://www.sciencemag.org/news... If dark matter were simply some existing form of baryonic matter, even if trapped in black holes, then a phenoma like this where dark matter halos separate from collided galaxies and behave under different rules to continue on their existing path should not be possible at all, because it, like all the other ordinary matter involved, it should have followed the same paths gravitationally bound.
There is evidence for more matter than visible in the galaxies, which is completely independent of Dark Energy. The most prominent evidence is the rotational characteristics of the outer parts of a galaxy. The stars there are circling the center of the galaxy much faster than expected from a Keplerian point of view. Instead of falling with r^2/3, as Kepler's Third law of motion predicts, the speed of stars remains roughly constant if you get to the outer parts of the galaxy. This means that the mass of the galaxy inside the respective orbits of the stars has to grow much faster than the mass from the additional stars within outer orbits.
(Be careful not to confuse the speed of stars on their orbit with their angular speed! A star twice the distance from the center of a galaxy needs twice the time to complete a circle than a star closer to the center. Thus the angular speed halves, but the linear speed on the orbit keeps the same. With Kepler's Third law, we would expect the time to complete an circle for the outer star to be 2*sqrt(2) of the time the inner star needs.)
Here's a result of a 5 second Google search: Could black holes be the dark matter?
Not really. There's areas of mass where there's little to no ordinary matter, where galaxies have collided and the gas has slowed down, but the dark matter has kept on going. This is demonstrated by gravitational lensing effects of the invisible mass. This doesn't really fit with MOND theories.