Astrophysicists have an concept that would assist to unravel two mysteries: the explanation for the weird abundance of super-high-energy radiation taking pictures from the middle of our galaxy and the id of invisible stuff referred to as dark matter that has perplexed the world since its discovery some 50 years in the past.
And the concept has a super-cool title: gravity portals. The thought goes, when two darkish matter particles (no matter they’re) get sucked into one among these portals, they obliterate one another and spit out shockingly sturdy gamma rays.
This line of pondering can probably clarify why the galactic heart — the place dense clusters of darkish matter are thought to lurk — is stuffed with gamma rays; and it may make clear how the darkish matter behaves and would possibly often work together with the traditional matter of our universe.
What darkish matter needs to be
Greater than 80% of the matter in our universe is of a type unknown to the usual mannequin of particle physics. Scientists name it “darkish matter,” as a result of it doesn’t work together with gentle. The primary trace of darkish matter’s existence got here within the 1970s, when astronomer Vera Rubin seen that galaxies had been rotating far too shortly — with out an extra, hidden supply of gravity, they need to have torn themselves aside eons in the past.
For many years, astronomers did not know in the event that they wanted to vary their understanding of gravity, add extra regular-but-really-dim matter to the universe, or embrace a model new ingredient. However yr after yr, remark after remark have restricted the alternatives. No principle of modified gravity can clarify all observations. And physicists have positioned agency limits on the quantity of regular matter (vibrant, dim and every part in between) within the cosmos.
That leaves darkish matter to elucidate the speedy galaxies. This matter can be a brand new sort of particle, with some unknown id (or identities). It would not work together with gentle, in any other case we might’ve seen it by now. It would not work together with the strong nuclear force — which binds collectively particles of matter — in any other case scientists would have detected its affect in atomic experiments. It’d discuss to the weak nuclear pressure, however that pressure is so feeble and short-range that observing any deviations within the anticipated outcomes is difficult.
Trillions of darkish matter particles could also be streaming via you proper now, invisible and silent.
Nonetheless, darkish matter betrays its presence via gravity, as a result of each single type of mass and vitality within the universe exerts some kind of gravitational affect. So the one surefire solution to research darkish matter is thru its gravitational interactions with regular matter, such because the motions of stars inside galaxies.
However there could also be one other method.
The case of the surplus electrons
In a research revealed Jan. 28 to the preprint database arXiv, physicists proposed a brand new principle to elucidate what darkish matter is and the way it behaves. However earlier than diving into their concept, we now have to introduce yet one more clue into this dark-matter hunt. The clue comes within the type of an odd abundance of gamma rays noticed emanating from the middle of our Milky Manner galaxy.
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Gamma rays are the highest-energy type of radiation doable, and so they normally solely come into existence from some severely high-energy occasions, similar to stars going supernova. However there are extra gamma rays than you’d anticipate within the galactic heart given how uncommon such cataclysmic occasions there are. So, it is doable, this principle proposed, that gamma rays could emerge as a byproduct of high-energy electrons.
These high-energy electrons, that are a sort of particle often called “leptons” and far simpler to provide than gamma rays straight, emanate from some supply and journey all through the galactic heart. The electrons themselves are undetectable (they’re very, very tiny), however as they flood via interstellar house, they’ll often slam right into a random passing photon (a light-weight particle).
That photon, most probably one thing innocuous and low-energy, collides with the aggressive electron; the collision boosts the photon’s vitality a lot that it begins to present off gamma rays that we are able to see.
These collisions probably clarify the surplus gamma rays, however the place do these high-energy electrons come from?
Leaping via the portal
Let’s recap what we all know. One, darkish matter interacts solely via gravity. Two, high-energy leptons floating across the galactic heart may clarify the additional gamma rays we see there. Three, as a result of in our personal galaxy the core has the very best density of matter, we expect that there’s additionally a big focus of darkish matter there.
Coincidence? Or conspiracy?
The hyperlink between these two observations has a suitably superior title: leptophilic gravity portals, as detailed by Solar Xu-Dong and Dai Ben-Zhong, of the China Key Laboratory of Astroparticle Physics, of their arXiv paper. The research has but to be peer-reviewed.
Let’s begin with the “gravity portals” half. So far as we perceive gravity, it simply pulls on stuff. Earth pulls on the moon; the solar pulls on Earth; stars in a galaxy pull on one another, and so forth. And gravity does a extremely, actually good job of pulling.
So on the face of it, the one factor gravity can do to darkish matter is … pull.
However our understanding of gravity is incomplete. Physics can clarify gravity operates on the massive scale, however there is no so-called quantum principle of gravity, which might describe sturdy gravity working at very tiny scales. And on this regime, gravity might need some surprises in retailer.
The opposite forces of nature are able to annihilating, reworking and creating particles on a regular basis. The weak nuclear pressure, for example, can change a proton right into a neutron, triggering radioactive decay. A particle and its antiparticle can join through the electromagnetic pressure, annihilating one another in a burst of radiation.
So possibly gravity, in excessive circumstances, can convey two darkish matter particles collectively and destroy them, turning them into … something, actually.
And in line with the theoretical mannequin outlined by the researchers, possibly these darkish matter particles can rework into leptons. Therefore the “leptophilic” a part of the title, which implies “lepton-loving.”
In keeping with the brand new principle, darkish matter particles can often annihilate one another via nothing greater than likelihood gravitational interactions. These likelihood interactions are recognized within the physics jargon as “gravity portals,” since they provide a method for particles to work together via gravity alone. The product of that collision is a high-energy electron. These interactions can be rather more frequent within the galactic heart, the place the density of darkish matter is probably going highest. These electrons would then journey on, finally hanging a low-energy photon and turning right into a gamma ray, inflicting the surplus that we observe.
Sure, this concept is a stretch. However on condition that physicists are in the dead of night on the subject of the id of darkish matter, new concepts are at all times welcome. And this principle was particularly designed to match the remark of the gamma rays. However as soon as that doorway has been opened, permitting darkish matter particles to rework into common matter (leptons, on this case), extra theoretical work will be executed to see if there are different methods to check the idea.
Initially revealed on Stay Science.