Astronomers have discovered a galaxy as big as the Milky Way that consists almost entirely of dark matter, a mysterious and invisible substance that scientists have been trying to figure out for decades. Only one-hundredth of one percent of the galaxy is ordinary, visible

Hanneke Weitering SPACE.com 8-26-16

matter like stars and planets. The other 99.99 percent of the stuff in this galaxy can't be seen.

No one really knows what dark matter is made of, but scientists believe it exists because they can see the effects of its gravity on other things in space. Whatever it may be, about 80 percent of the mass in the universe is dark matter. ...
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The galaxy’s empire has a new colony. Astronomers have detected a dwarf galaxy orbiting the Milky Way whose span stretches farther than nearly all other Milky Way satellites. It may belong to a small group of galaxies that is falling into our own.

By Ken Croswell www.newscientist.com 4-14-16

[...]

Now, Gabriel Torrealba at the University of Cambridge and his colleagues have found a new galaxy about 380,000 light years away in the constellation Crater. “It’s the fourth largest satellite of the Milky Way,” Torrealba says.

Named the Crater 2 dwarf, the new galaxy is not apparent to human eyes, though individual stars within the galaxy are visible. The team were only able to find it this January by using a computer to look for over-densities of stars in data from images taken by a telescope in Chile.


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