Dark matter, as the name implies, is an enigma. We know that nearly a quarter of the universe is made up of this unknown substance. Only 4.5% of the universe is made of what we normally think of as matter, that is atoms. Not only do we not know what dark matter is, we’re not even sure where it is. However, that may be changing, thanks to the efforts of Shogo Masaki from Nagoya University, Masataka Fukugita and Naoki Yoshida from the University of Tokyo. They used observations of gravitational lensing and computer simulations to find dark matter. It turns out dark matter connects all the galaxies in our universe.
Gravitational lensing is the distortion in the light from distant galaxies caused by closer sources of gravity, such as nearby galaxies. You can see that illustrated below.
The two images illustrate the effect of gravitational lensing. A massive galaxy at the center of the right panel causes the images of the background galaxies (white spots) to be enlarged and brightened.
Image credit: Joerg Colberg, Ryan Scranton, Robert Lupton, SDSS
Dark matter also exerts gravitational effects on normal matter. That’s how we discovered dark matter in the first place. However, until recently, we didn’t have enough data to see just how much of an effect dark matter was having on galaxies. Luckily, the Sloan Digital Sky Survey has been steadily capturing images of galaxies for the past decade. The authors were able to put 24 million galaxy images into their computer simulation.
They found that there is effectively no empty space in the universe. The distribution of dark matter extends from galaxy to galaxy. Regions devoid of stars are not devoid of dark matter; it truly seems to be ubiquitous. Now, if we can only figure out what it is.
Hat tip: Skeptics' Guide to the Universe.