Q&A: Galaxies, Galaxy Clusters, AGN, and Quasars

Q:
If the center of a galaxy is so much bigger and brighter than all of its stars, why is it that we cannot see the light it emits from earth with the naked eye; or, is it so far away that it only looks like another star in the night sky?

A:
Thanks for your good question. The center of our galaxy is very bright, but because the solar system is located in the plane of the galaxy, there is a lot of gas and dust that blocks our view of the middle of the galaxy. For example, in the southern hemisphere in winter the middle of the galaxy is directly above you in the sky. You can see a lot of stars, but you can also see dark patches because of dust and gas.

If we were to travel upwards or downwards out of the plane of the galaxy, you would see the middle of the galaxy getting much brighter. But this journey is well beyond our capabilities.

I should point out that this discussion applies to optical radiation that we see with our eyes. Radiation at different wavelengths can do a better job at penetrating dust and gas, so the middle of the galaxy can look much brighter.