Multiple images of a background image created by gravitational lensing can be seen in the system HS 0810+2554. Credit: Hubble Space Telescope / NASA / ESA
Topics: Astronomy, Astrophysics, Dark Matter, Einstein, General Relativity
Physicists believe most of the matter in the universe is made up of an invisible substance that we only know about by its indirect effects on the stars and galaxies we can see.
We're not crazy! Without this "dark matter," the universe as we see it would make no sense.
But the nature of dark matter is a longstanding puzzle. However, a new study by Alfred Amruth at the University of Hong Kong and colleagues, published in Nature Astronomy, uses light's gravitational bending to bring us a step closer to understanding.
Invisible but omnipresent
We think dark matter exists because we can see its gravity's effects on galaxies' behavior. Specifically, dark matter seems to make up about 85% of the universe's mass, and most of the distant galaxies we can see appear to be surrounded by a halo of the mystery substance.
But it's called dark matter because it doesn't give off light or absorb or reflect it, which makes it incredibly difficult to detect.
So what is this stuff? We think it must be some kind of unknown fundamental particle, but beyond that, we're not sure. All attempts to detect dark matter particles in laboratory experiments have failed, and physicists have debated its nature for decades.
Scientists have proposed two leading hypothetical candidates for dark matter: relatively heavy characters called weakly interacting massive particles (or WIMPs) and extremely lightweight particles called axions. Theoretically, WIMPs behave like discrete particles, while axions behave more like waves due to quantum interference.
It has been difficult to distinguish between these two possibilities—but now light bent around distant galaxies has offered a clue.
New look at 'Einstein rings' around distant galaxies just got us closer to solving the dark matter debate, Rossana Ruggeri, Phys.org.