The universe is filled with matter: You see it all around you.
Invisible to the human eye, dark matter is a type of matter that is very different from the “ordinary” matter we know so well. Many scientists say dark matter exists because we can see the electromagnetic effects it has on stars and galaxies in the depths of space. For instance, the laws of physics tell us that the stable rotation of galaxies cannot be solely explained by the effects of visible matter. Dark matter is also determined to be responsible for the light-bending phenomenon known as gravitational lensing and the speeds at which some stars in our galaxy appear to rotate.
Most importantly, according to theory, the Milky Way would not exist without dark matter. With approximately five times the mass of visible matter with the same size, the collective gravitational pull of dark matter is said to have facilitated the formation of the Milky Way’s structure.
The Problem with Calling It “Dark Matter”
The words ‘dark matter’ may immediately bring to mind black holes. However, dark matter is not necessarily associated with the absence of light. Because light can pass through it, dark matter is actually transparent.
Truth be told, scientists probably know more about what dark matter isn’t, than what it is. Brown stars, white dwarf stars, neutron stars and black holes could all be dark matter. Or none of them could be. In fact, many researchers have said each of these objects is too rare to account for all the observed effects of dark matter.
Scientists also aren’t sure if dark matter is comprised of particles we already know, or ‘dark matter particles’ that we know nothing about. It’s possible the on-going particle experiments at CERN will eventually reveal evidence of dark matter particles.
In light of the absence of definitive proof, a few maverick scientists have offered a theory that does away with dark matter entirely, called Modified Newtonian Dynamics (MOND). Basically, the theory says the laws of physics, as we know them, do not apply on the grandest scales. MOND theory proponents say describing dark matter has been so difficult because it simply doesn’t exist. Critics of MOND say it does not sufficiently explain the universe.
Those backing the MOND theory were likely buoyed by a 2020 study from researchers at the University of Bonn in Germany that found galaxies as we know them are capable of forming without dark matter.
Detecting Dark Matter
Researchers have constructed extremely sensitive, peculiar systems to try to find physical evidence of dark matter. These detection systems include pools of liquid xenon located deep underground and telescopes trying to find dark matter particles breaking down into gamma rays and other phenomena we can measure. Part of the mission for the Hadron Collider is the detection of particles that can be associated with dark matter.
Scientists are also planning on using the Fermi Gamma-Ray Space Telescope to detect evidence of dark matter. When two particles of dark matter particles collide, they theoretically release a gamma ray and the Fermi telescope could potentially recognize the gamma ray evidence of these collisions. Launched in 2008, Fermi has yet to detect evidence of collisions between dark matter particles.