OT Science: On the verge of explaining "Dark Matter"? Do MACHOs beat WIMPS?

Geeky science post, intended for non-scientists.  This could be a very, very big deal in the world of astrophysics.

Some recent science might answer a very long-standing debate, about a fundamental structure of 25% of our universe we KNOW exists but don't know a DAMN thing about.  And its a MACHO, not a WIMP.  Let's explain?

For many years, scientists are pretty sure that 25% of the entire energy of the Universe is made of something called "dark matter."  It's something that has gravity, but NO light -- it neither emits light, nor reflects it.  So it's there, but you can't see it.  You can only tell its there by how it affects the motion of large things, primarily galaxies.  Most galaxies spin incorrectly, meaning, given the mass they have (based on stars we can see), they ought to all fly apart.  But most galaxies spin as a single unit, which doesn't make sense unless they have a lot more mass than we can observe.  It's believed most galaxies sit in the middle of clouds or pools of "dark matter."  Dark matter's effects can also be shown by "gravitational lensing" -- how light from farther-away galaxies is bent by the mass of closer galaxies, but the amount of bending requires the closer galaxies to have more mass than they appear to have.

So we know it's there, but have never known WHAT it is.  There have been two theories:

MACHOs -- "massive compact halo objects."  (This is one of those acronyms, like Marvel's SHIELD, that is made up because the acronym itself sounds cool.)  Maybe all the dark matter is made of large objects that just don't give off light and are too small be be observed by our telescopes -- like lots and lots of planets, space rocks, etc.?  But that would require SO MANY of them... and, there is simply no theory of stellar evolution to explain so many "dark" objects that didn't create an equally large or far larger number of stars that we could observe.  (Consider that, in our own solar system, >99% of the mass is in the Sun; <1% makes up the "dark" rest.  How could you end up with a galaxy of 80% dark stuff and only 20% stars?  You can't.)

WIMPS -- "weakly interacting massive particles."  The alternative theory is that dark matter is made of some kind of special and very-abundant subatomic particles, which (a) don't interact with light, but (b) have soooo much mass to them, that they add up to account for tons and tons of dark matter.  With MACHOs not being realistic, the scientific braintrust has largely assumed dark matter is made of some kind of WIMP.  The problem is:  every attempt to find these particles has failed.  Miserably.  Our list of possible candidates for WIMPs has been whittled down to... well, nothing.

Are we stumped?  Maybe not...enter, a MACHO no one previously considered:  black holes.  And special ones at that.

Maybe, just maybe, dark matter is made of black holes that were created at the beginning of the Universe (called "primordial black holes").  Theories about evolution of the universe say that primoridal black holes should be 25-35 times the mass of the Sun.  And, if they evolved, there would be lots and lots of them.  In hindsight, black holes make good candidates for dark matter.  They (a) are dark, they eat light and don't give any off (well, nothing much), and (b) they are really heavy.  So if you had lots of black holes, you'd see the effects as dark matter.

Two recent, independent scientific results now point to primoridal black holes as the leading candidates to be dark matter.

(1)  The LIGO experiiment that proved gravity waves (discussed on Mgoblog a few weeks ago) showed two black holes merging, each about 25-35X the mass of the Sun.  That number struck some astronomers as curious.  Stars that form black holes won't ever create black holes that mass, but only primordial black holes would be that mass.

(2) Some surveys of X-ray and infrared light across in the universe (after light from galaxies are removed) shows that concentrations of both kinds of light map on top of each other, which to the experts apparently can mean they can only come from black holes.  This means black holes are scattered in large numbers across the universe.

Adding these together... and the candidacy of primordial black holes to be dark matter gains traction.

Not everyone is convinced, of course.  And recent tests at the CERN atom-smasher in Europe have, very recently, produced new results that suggest supermassive particles we didn't know existed, so maybe there is a WIMP candidate for dark matter after all.

But these are exciting times if you're a fan of MACHOs.  Or primordial black holes.

Further reading:

http://www.space.com/33122-dark-matter-black-hole-connection.html

https://www.washingtonpost.com/news/speaking-of-science/wp/2016/05/25/c…