Astronomers have two main ideas about how elliptical galaxies formed. I first need to explain a little bit of background in order for those two methods to make better sense.
Space is relatively empty, but it does have matter spread all across it. The distribution of matter is not uniform, which means certain areas have a higher density of mass and consequently a higher gravitational force. The areas of higher gravity pulled in large clouds of dust and gas. Those are the beginnings of galaxies and nebulae. As the galaxy material collapsed, it either began spinning or didn't. Galaxies that began to spin eventually flattened out with long spiral arms. That flattening due to spinning is explained by angular momentum. Those galaxies are the spiral galaxies.
One way to form an elliptical galaxy is to have the material for the galaxy present, but not have it spin or not have enough spin to flatten itself out. It would then be a round structured galaxy with no set axis of rotation.
A second theory is that elliptical galaxies formed from the collisions of spiral galaxies. This theory works as long as an expanding universe is present. In the early universe, galaxies were much closer together; therefore, galaxy collisions happened. The spiral shape would have been destroyed, and what was left was an elliptical galaxy.
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