This Thursday is Halloween…and Dark Matter Day! Dark matter-themed events are being organized by labs and institutions around the world doing this research. They range from live webcasts with researchers to dark matter scavenger hunts to a Reddit AMA. Find a sortable list at www.darkmatterday.com/events-list

Scientists believe that dark matter, which we have so far only detected through its gravity-based effects in space, makes up about a quarter (26.8 percent) of the total mass and energy of the universe, and something that is driving the universe’s accelerating expansion, which scientists call dark energy, accounts for another 68.3 percent.

The ordinary matter, like stars and planets and galaxies, makes up just 4.9 percent of the total mass and energy of the universe.

So there’s a BIG part of the universe that we don’t know much about. We’re not sure if dark matter is made up of undiscovered particles, or if it can be explained by tweaking the known laws of physics. Its makeup could teach us much about the history and structure of our universe.

Could dark matter play a role in the composition of newly detected spiral galaxies that dwarf our Milky Way? Recently discovered Super Spiral Galaxies are 180,000 to 440,000 light years across! Our Milky Way is a pretty big galaxy as galaxies go, but it’s a mere 100,000 light years across. These super spirals have so much mass that they spin up to three times faster than galaxies the size of our Milky Way. The spin seems to be much faster than the visible mass should allow. No worries, researchers have pinned the blame on, you guessed it, Dark Matter!

Astronomer Vera Rubin postulated that galaxies had large amounts of unseen mass that affected their gravitational component: What we now know as dark matter. The extraordinary rotational speeds could be accounted for if there’s a halo of dark matter surrounding the enormous galaxy. The largest of the observed galaxies seems to have 40 trillion solar masses worth of dark matter; that’s 40 trillion suns worth, more than 100 times the amount of stars in Milky Way type galaxies! 100 of these galaxies have been identified so far.