In our universe, there are two types of galaxies: live ones and dead ones. For two decades, scientists didn't understand what could possibly kill a previously thriving galaxy, but in 2017, research may be pointing to whodunit.
It could happen to our own galaxy.
Find out what they are and how they form.
Just because it's invisible doesn't mean it's unimportant.
The known universe consists of about 70% dark energy, 25% dark matter, and 5% visible matter. 00:08
Dark energy seems to be intrinsic to empty space, which has more energy than everything else in the universe combined. 03:45
One theory of dark energy postulates that it comes from virtual particles in empty space that form and disappear constantly. 04:47
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