An Elliptical galaxy is one of four main types of galaxies that exist in the Universe. The other types are Spiral, Lenticular and Irregular. The best way to describe an Elliptical is that it is ball or oval shaped. Our galaxy, the milky way is a spiral galaxy and not an Elliptical. The image below by Nova Celestia shows the different types of galaxy, it shows you where Elliptical galaxies are in the classification.
Galaxy classification was devised by Edwin Hubble, the same American scientist that Hubble Space Telescope was named after. Although you can see from the diagram, but it doesn't hurt in spelling it out, elliptical galaxies are graded from 0 to 7. The more round the galaxy it is, the lower the number. A perfect circular galaxy would be zero.
Elliptical galaxies and Spiral Galaxy have one thing in common apart from stars is that they both have a Supermassive Black Hole at the centre of the galaxy.
Stars in a spiral galaxy orbit round the central point, the Supermassive Black Hole but with elliptical galaxies, there is no order, stars orbits can be random. The shape of the galaxy can be determined by the speed of the stars. Swinborne
Elliptical galaxies will tend to have old stars, having used up most of their dust and gas. There might be some star formation going on but they won't be anything like they used to. CalTech As there is not much star forming going on, they are not as bright as spiral galaxy which because of star-formation makes them brighter.
You can tell if the galaxy is old or new. A newer galaxy's spectral colours will appear more blue indicating a youthful galaxy where as a redder colour, one that is cooler is indicative of older galaxies. Colours and age also apply to star ages too.
The most well known Elliptical Galaxy is IC 1101 which happens to be the largest known Elliptical galaxy known to exist. In fact, the galaxy is the largest galaxy of any type known to exist. Not only can they be the large, there are also pretty small elliptical galaxies out there.
Elliptical Galaxies are seen as being at the end of their lives because of not much star formation going on. IC 1101 is an old galaxy and a greedy one too, it is believed to grown in size by consuming passing galaxies. Galactic cannibalism isn't limited to ellipticals, our galaxy is believed to be consuming the Canis Major Dwarf Galaxy. As the CMa Dwarf Galaxy is small, there is not much influence on our galaxy from consuming it.
Some of the small galaxies are Elliptical Galaxies as well, often referred to as Dwarf Ellipticals. They can be no larger than a Star Clusters. These elliptical are usually found in galaxy clusters or as satellite galaxies round larger galaxies. These dwarf elliptical can contain just a mere ten million stars which is nothing to compared to Milky Way with a believed 250 billion stars.
The MIlky Way Galaxy as mentioned above is believed to be a spiral galaxy, although no one has seen it, it is believed to be so. The Andromeda Galaxy is also a spiral galaxy. The two galaxy are currently moving towards one another and in a few billion years, the two galaxies will collide with one another. When the collision happens, it is believed that the resulting outcome will be an ellpitcal galaxy.
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