Astronomers just found a 2nd galaxy containing no dark matter — and it may change everything we knew about how galaxies are formed

Mar 2019
2,574
576
Texas
#1
Business Insider

According to Keck Observatory, both DF2 and DF4 belong "to a relatively new class of galaxies called ultra-diffuse galaxies." They're roughly the same size as the Milky Way but have far fewer stars, "making them appear fluffy and translucent, therefore difficult to observe."
Despite the lack of dark matter in these galaxies, the researchers say their existence bolsters the dark-matter theory, backing up the idea that dark matter is independent of "normal" matter.
This is very thought provoking findings. It makes myself wonder what role dark matter plays in our lives.
 
Oct 2010
67,701
27,586
Colorado
#4
Yes, we have no idea what dark matter even is yet we know they don't have any?

Makes me want to pound my head into the wall.
Understood. This explains how we got to this point pretty well:

If you go back to high school physics class, you may remember that the more mass something has, the greater its gravitational pull. If galaxies were only made up of the stuff we can see, there wouldn't be enough gravity to keep them together, much less to keep the stars in the sparse outer edges orbiting just as fast as those in the center. In fact, scientists reckon that normal matter makes up less than five percent of the universe. Dark matter seems to make up a whopping 27 percent. (The rest is a mysterious force called dark energy.)​
..You can also see its mass in the warping of spacetime itself. According to Einstein's theory of general relativity, matter curves the fabric of spacetime the way a bowling ball curves the fabric of a trampoline. When light travels toward that curve, it doesn't go in a straight line. Instead, it follows the curve, bending around the massive object before continuing on its path. That warp in spacetime turns into a sort of cosmic magnifying glass in a phenomenon known as gravitational lensing. But yet again, the gravitational lensing produced by a galaxy or a galaxy cluster is too great to be explained by the matter we can see. This effect is yet another piece of evidence for the existence of dark matter.​
You can also see its mass in the warping of spacetime itself. According to Einstein's theory of general relativity, matter curves the fabric of spacetime the way a bowling ball curves the fabric of a trampoline. When light travels toward that curve, it doesn't go in a straight line. Instead, it follows the curve, bending around the massive object before continuing on its path. That warp in spacetime turns into a sort of cosmic magnifying glass in a phenomenon known as gravitational lensing. But yet again, the gravitational lensing produced by a galaxy or a galaxy cluster is too great to be explained by the matter we can see. This effect is yet another piece of evidence for the existence of dark matter.​

More: How Do We Know Dark Matter Really Exists?