Elliptical Galaxies

Elliptical galaxies are the oldest galaxies in the universe, though they are not the oldest structures in the universe.*

     * That honor goes to galactic clusters

What exactly are elliptical galaxies?

• They are spherical in shape
• They tend to be both larger and smaller than spiral galaxies
• They are typically older - red stars with low metallicities
• They do not have a lot of gas and dust - no star formation going on.

We don't see elliptical galaxies near our galaxy because they are older with lower metallicities. Our region of space is "younger" in that objects are closer to us than the elliptical galaxies we see. The Andromeda Galaxy, for example, is "only" two million light years away. Elliptical galaxies can be on the order of hundreds of millions to billions of light years away from our galaxy. We know that there are more metals in our region of space because we see them in the spectra of nearby objects, where we don't see metals in ellipticals.



Giant elliptical galaxies can be up to a million parsecs in diameter (our Milky Way is only 30,000 parcsecs in diameter) and contain trillions of stars. They also can be tiny, called dwarf ellipticals, roughly the size of a large globular cluster (~ 1000 parsecs).



Ellipticals are broken up based on the flatness of the ellipticals. Spherical ellipticals are E0 and the number increases with flatness up to E7. A unique thing about this classification is that an E0 could actually be from an E0 to an E7 depending on the orientation. If we see an E7, it can only be an E7. No orientation will make it look more spherical.

The way I used to describe this is to image an American football: oblong in one direction, round from the end. When you see the football lengthwise, it will appear as an E7. From the end, it looks like an E0.

Ellipticals may house a supermassive black hole in their centers which may lead to a subclass of galaxies - active galaxies.