Using Bright Streams to Learn about Dark Matter

Matter is what we call all of the “stuff” that makes up the universe. Ordinary matter, such as atoms, makes up only about 15% of all the matter in the universe. The other 85% is called “dark matter”—it is invisible but important enough to hold our galaxy, the Milky Way, together so it does not break apart. What is dark matter? For decades, astronomers have been thinking of ideas and trying to test these ideas by observations. One popular theory called “cold dark matter (CDM)” has been widely successful in explaining dark matter in the universe as a whole, but it still needs to be tested inside our own galaxy. In this study, we show how computer simulations can help us use streams of stars in the galaxy to determine whether CDM is the correct theory to explain dark matter.