2 December 2014
One other day, one other new thought for what darkish matter is likely to be. This time, it’s a paper that proposes darkish matter is made of normal matter. For individuals who are acquainted with darkish matter, this would possibly elevate an eyebrow as a result of darkish matter can’t be common matter. In actual fact, what this paper reveals is that whereas observational information excludes the same old suspects for darkish matter corresponding to chilly gasoline and mud, small black holes and the like, there is likely to be a approach to shoehorn common matter into the image. The answer they suggest is, fairly actually, a bit unusual.
With all of the searches for darkish matter, we’ve truly eradicated a lot of the candidates. Low mass WIMPs (weakly interacting huge particles) have largely been excluded by underground darkish matter detectors. Primordial black holes (small, asteroid-mass black holes) would gravitationally microlens starlight when passing in entrance of a star. We haven’t noticed such an impact, so they’re largely excluded. Different small, dense our bodies corresponding to neutrons stars and brown dwarfs (collectively referred to as huge compact halo objects, or MACHOs) are excluded for related causes.
So darkish matter isn’t gasoline, mud, MACHOs, WIMPs, black holes, so what’s left? The authors suggest that it may very well be unusual matter. Most common matter is manufactured from electrons, protons and neutrons. Protons and neutrons are manufactured from two forms of quarks referred to as up and down quarks. However there are 4 different forms of quarks as effectively, and considered one of them, referred to as the unusual quark, is the closest cousin to up and down. It has been speculated that unusual quarks would possibly seem within the ultradense cores of neutron stars, and will result in the formation of quark stars.
So what if within the early moments of the universe, when protons and neutrons shaped by way of a course of referred to as baryogenesis, unusual quarks additionally appeared and produced dense clumps of unusual matter. If these clumps had the same density as neutron stars, however with lots someplace between 1 kilogram and a trillion kilograms, then they might fulfill the gravitational wants of darkish matter whereas nonetheless being allowed by present observational limits. They name these darkish matter clumps MACROs, for macroscopic darkish matter.
There are some issues with the thought. For one, unusual quarks are extraordinarily unstable. The authors argue that neutrons are additionally unstable by themselves, however secure in an atomic nucleus. Maybe the same impact would happen with unusual quarks, in order that clumping would make them secure. An even bigger downside comes from the cosmic microwave background, which clearly distinguishes darkish matter from common matter in its fluctuations. To get round this, the authors suggest that the MACROs shaped shortly, earlier than the formation of protons and neutrons. If 90% of the early quarks shaped into MACROs, then this may agree with information from the cosmic background.
If this all seems like a just-so story, you’re proper. The mannequin is sort of a wild proposal tweaked to suit the present observational limits. It additionally depends on hypothesis about how quark matter would possibly behave within the early universe. However as I’ve talked about earlier than, that is the sort of factor we want at this level. The cautious concepts have been excluded by observational information, and as extra choices get excluded we’ll maintain throwing theoretical pasta on the wall to see if any of it sticks. It’s the sort of factor that occurs when fashions and information begin critically butting heads.
And that may make for some unusual days.