When we look at our galaxy, we find it has more mass than the matter we see. Much more. This is the first clue that there must be dark matter in the Universe.
Raising the Bar
By measuring the distribution of hydrogen in our galaxy, we know that our galaxy is a barred spiral.
21 Centimeters
The 21cm line is a commonly used wavelength in astronomy. We can use it to measure the distribution of hydrogen in the Milky Way.
Mapping the Galaxy
Radio signals from pulsars are delayed slightly by the ionized plasma in our galaxy. This allows us to measure the amount of plasma in our galaxy by observing the pulses of more than 2000 pulsars in our galaxy.
Heart of the Dragon
We can observe the motion of stars in the center of our galaxy, and it is clear from their motion that our galaxy has a supermassive black hole.