Right after the birth of the universe, the matter in space (hydrogen, helium and dark matter) was dragged together because of the influence of their mutual gravity. A few hundred million years later, enough matter agglomerate and the first stars where born. From the first matter and stars the fist galaxy’s existed. The gravity takes care that the matter inside a galaxy will stick together. Galaxy’s don’t only contain stars, but all the other objects that we can see trough our telescopes, like clusters, planets and nebulae. Galaxy’s are mostly part of a group. Our Milky Way is, together with the Andromeda Nebula, part of the Local Group for example.
There are different types of galaxies. Edwin Hubble has made a classification to classify the galaxy’s easily (see image below). Nowadays, this classification is enlarged, but we will stick to the classification of Hubble in this article. First there are elliptical galaxies, indicated with “E”. E0, for example, is globular, E7 galaxy’s are long-drawn. So elliptical galaxies have the shape of an ellipse. They don’t have spiral arms. In most of this galaxy’s there isn’t star forming anymore for a while. The stars in an elliptical galaxy are very old. Most of them are probably born in collisions between two spiral galaxies. When they merged they formed together an elliptical galaxy. About 80% of all the galaxies in our universe are elliptical galaxies.
Then we have the spiral galaxies, indicated with “S”. Sa stands for a galaxy with spiral arms close to the core, Sc galaxies have openly spiral arms. This galaxies have a thickened core, containing old stars. There is almost no new star forming in these cores. However, in the spiral arms there are much younger stars and there is star formation here.
Barred spiral galaxies are indicated with “SB”. SBa galaxies have a flat disk and a core with barred spiral arms, located close to the core. SBc galaxies have looser barred spiral arms. This spiral galaxies have a bar coming out of their core. On each side of this bar are the spiral arms located. These barres are probably temporary and it depends of the mass in the centre of the galaxy: the less mass, how longer the bar.
There are also irregular galaxies, indicated with “Ir”. These galaxies aren’t elliptical and don’t have any spiral arms. An obvious thickening in the core is also missing. Probably the most irregular galaxies were elliptical of spiral shaped in the past, but their shape is distorted by gravity, probably by passing galaxies.
Galaxies aren’t the easiest objects to observe. To make good observations you need a 10cm telescope at least. The Andromeda Galaxy is an exception though. It’s visible on dark night with the unaided eye.
Some galaxies to observe for yourself
The Andromeda Galaxy
The Andromeda Galaxy (31) is located in constellation Andromeda. The galaxy has the same shape as our Milky Way and is classified as type Sb. This galaxy is located 2.4 to 2.9 million light years from earth. That makes it the nearest galaxy. There probably is a double core in the centre. This could be the result of a collision in the past. There are two satellite galaxies known (M32 & M110): smaller galaxies that describes an orbit around the Andromeda Galaxy.
The Andromeda Galaxy has a magnitude of 4 and is the only galaxy visible with the unaided eye in very good conditions. To see more details and the two satellites of Andromeda, use a (small) telescope.
The Whirlpool Galaxy
The Wirlpool Galaxy (M51) in constellation Canes Venatici is classified as a Sc type. Because we look from above on this galaxy, we see a good example of the structure in this kind of spiral galaxies. There is a satellite galaxy, known as NGC 5195) circling around M51. Both galaxies are located 31 million light years from earth.
With a magnitude of 8, the Whirlpool Galaxy is already visible with small telescopes as a fuzzy dot. With at least 10cm telescopes, the spiral structure becomes visible.
Bodes Galaxy & the Sigar Galaxy
Bodes Galaxy (M81) is a spiral galaxy and it’s located 12 million light years from earth. In 1993 there was a supernova visible in this galaxy, which reached a magnitude of 10.5.
The Sigar Galaxy (M82) is an irregular galaxy. A lot of stars are being born inside it. This is 10 times more than in regular galaxies. This is caused by the interaction of the close encounter between M81 and M82 in the past. The cores in both galaxies are only 150.000 light years located from each other.
You find both galaxies in constellation Ursa Major. They are both visible in small telescopes, under good conditions, in the same field of view.
The Sombrero Galaxy
The Sombrero Galaxy gets its name because of its shape. Because we look from the side to this galaxy, we see a wide hump in the core. There is also a bright dust disk visible around the galaxy. Because of this, the galaxy looks like a sombrero. The galaxy is located 50 million light years from earth and contains a lot of globular clusters.
You’ll find this galaxy in constellation Virgo, its already visible trough small telescopes. With larger telescopes you can see a lot of the globular clusters.