For example: 1. Many black holes and neutron stars are thought to be hidden in the Milky Way. Because they can't emit visible light or hide behind dust, they can only be observed through X-ray space telescopes. Many black holes and neutron stars are thought to be hidden in the Milky Way. Because they don't emit visible light or are covered with dust, only X-ray telescopes can find them.

2.Segue2 is one of dozens of satellite galaxies orbiting the Milky Way. Segue 2 is one of dozens of "partner" galaxies orbiting the Milky Way.

From this, you can calculate the total mass of the galaxy. From this you can calculate the total mass of the galaxy.

4. The Milky Way consists of 1000 billion stars. The Milky Way galaxy consists of10 billion stars.