Galaxies

We know about that can be grouped together in open or globular clusters. These stars are grouped in this way because they formed from the same cloud and gravity kept them in close proximity to each other. What happens if these clouds are much larger? Galaxies form.


In fact, it is believed that galaxies were the first large-scale features to form before stars and clusters. Older galaxies (i.e. galaxies formed long ago) also tend to be active (very bright to be seen over long distances).


Galaxies come in three basic types:

• Elliptical galaxies which look like globular clusters but on a much larger scale

Elliptical Galaxy NGC 4150

Image Credit:

NASA, ESA, R.M. Crockett (University of Oxford, U.K.), S. Kaviraj (Imperial College London and University of Oxford, U.K.), J. Silk (University of Oxford), M. Mutchler (Space Telescope Science Institute, Baltimore), R. O'Connell (University of Virginia, Charlottesville), and the WFC3 Scientific Oversight Committee

• Spiral galaxies which look like whirlpools

Andromeda Galaxy (nearest major galaxy to ours)

Image Credit:

NASA/JPL-Caltech

Barred Spiral Galaxy NGC 1300
Image Credit:

APOD

 Hubble Heritage Team, ESA, NASA



• Irregular galaxies which are kinda like open clusters, but again on much larger scale.

Large Magellanic Cloud

Image Credit:

APOD

Yuri Beletsky (ESO)

Small Magellanic Cloud with two globular clusters

Image Credit:

APOD

Stéphane Guisard

LMC (upper right center) and SMC (lower left)

Image Credit:

NASA, Axel Mellinger (Central Michigan University)

We will discuss the three types in more detail over the next few days.