Darkish matter continues to withstand our greatest efforts to pin it down. Whereas darkish matter stays a dominant concept of cosmology, and there’s numerous proof to help a universe stuffed with chilly darkish matter, each seek for darkish matter particles yields nothing. A brand new research continues that custom, ruling out a spread of darkish matter candidates.
If darkish matter particles exist, we all know they will’t work together strongly with gentle. They need to work together gravitationally, and so they may work together by way of the sturdy and weak nuclear forces as effectively. We additionally know they will’t be extremely huge particles. In the event that they have been, they’d decay over time into lighter particles, and we see little proof of this. This leaves three broad candidates: small black holes, sterile neutrinos, or some kind of sunshine boson. This newest work focuses on the third possibility.
Identified elementary particles of matter may be positioned in one in every of two classes: fermions and bosons. So, electrons, quarks, and neutrinos are fermions, whereas photons and gluons are bosons. Inside the usual mannequin of particle physics, there are not any bosons that will match the invoice for darkish matter. However some various fashions predict particles that may very well be darkish matter. Supersymmetry fashions, for instance, predict that each recognized fermion should have a corresponding boson and vice versa. Thus, the electron would have a counterpart boson often called the selectron, the photon would have a counterpart fermion often called the photino, and so forth. One other chance are axions, which have been proposed in 1977 to deal with delicate elements of how quarks work together.
Each axions and supersymmetry particles may very well be low-mass bosons and would fulfill the wants of darkish matter. But when both exists, they haven’t been discovered up to now. Nonetheless, these gentle bosons would work together with common matter gravitationally, therefore this newest research.
If darkish matter is made of sunshine bosons, then these particles could be unfold throughout the universe, together with close to black holes. A black gap would gravitationally seize close by bosons, thus rising its mass. If a black gap is rotating, the seize of darkish matter particles would additionally are inclined to decelerate its rotation. You may think about kids at a playground that has a merry-go-round. If kids soar onto the merry-go-round as it’s spinning, the merry-go-round will decelerate barely due to the added mass. The identical could be true for black holes.
In different phrases, darkish matter bosons would restrict the speed that black holes rotate. The crew realized that heavier bosons would restrict black holes extra, and lighter bosons would constrain them much less. So that they regarded on the LIGO and Virgo information of black gap mergers, which tells us the rotation price of black holes earlier than they merge. It seems that a few of these black holes rotated so rapidly that it guidelines out the existence of ultra-light darkish matter bosons. Primarily based on this research, darkish matter can’t be axions or gentle supersymmetry particles.
So as soon as once more, a seek for darkish matter has proven us not what darkish matter is, however what it isn’t. It’s extraordinarily irritating, and doubtlessly thrilling as a result of we’re rapidly operating out of choices for darkish matter.
Reference: Ng, Ken KY, et al. “Constraints on Ultralight Scalar Bosons within Black Hole Spin Measurements from the LIGO-Virgo GWTC-2.” Bodily Evaluate Letters 126.15 (2021): 151102.