BellaOnline Forums Education Astronomy What Is a Galaxy?

What is a galaxy? A great star system held together by gravity, with stars, gas and dust, black holes and dark matter. Astronomers used to think our Galaxy was the whole universe. But now that we know of billions of galaxies, they're considered to be the building blocks of the universe.

What Is a Galaxy

Here is NGC 6946. It's a face-on spiral galaxy from our point of view, Hubble type "Sc" because its spiral arms are loosely wound. It's about 10 million light years away in the constellation Cepheus. NGC 6946 has a high rate of starbirth, but it gets its nickname the "Fireworks Galaxy" because it also has a high stellar death rate in the form of supernovae, at least nine known since the early 20th century.

Composite Image Data - Subaru Telescope (NAOJ) and Robert Gendler; Processing - Robert Gendler

Have a look at this fantastic SBb type barred spiral galaxy NGC 1300. What a beauty!

Barred spirals differ from normal spiral galaxies in that the arms of the galaxy do not spiral all the way into the center, but are connected to the two ends of a straight bar of stars containing the nucleus at its center.

Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

NGC 4565 (the Needle Galaxy) is a spiral galaxy in the constellation Coma Berenices. We see it edge-on, showing how comparatively thin the galactic plane is and highlighting the central bulge. NGC 4565 lies about 40 million light-years away and spans some 100,000 light-years.

Image Credit & Copyright: Lóránd Fényes