Astronomers now think the largest component making up the Universe is ??? In this scenario, clusters of galaxies should stop growing early in the history of the Universe and look virtually indistinguishable from those of today. Most astronomers believe that we live in a low-density Universe in which a mysterious substance known as ‘dark energy’ accounts for 70% of its content, and therefore, pervades everything. The largest galaxies in the universe are giant elliptical galaxies which may have more than 1 trillion stars. Astronomers create the largest map of the universe This artist’s impression shows a quasar — the hot disk of material around the supermassive black hole that resides in the center of a galaxy. Elliptical galaxies appear reddish, indicating that they are formed by stars which are older and cooler than our own sun. What evidence supports an acceleration in the expansion rate of the universe? The size of this structure is beyond fascinating. Some elliptical galaxies are as much as 20 times bigger than the Milky Way. Theoretical models also suggest that in the early universe… Astronomers have recently announced the discovery of the largest structure ever seen in the known universe, and its 1 Billion Light Years long, making it the largest structure ever discovered. Astronomers now think that nearly all galaxies—with possible exceptions—are embedded in huge haloes of dark matter. NEW YORK — All the stars, planets and galaxies that can be seen today make up just 4 percent of  the universe. The discovery that type Ia supernova in distant galaxies are 25 percent fainter than expected.