M81, Spitzer Space Telescope

How did the very first galaxies form?  How did we end up with the large variety of galaxies we see today?  We now know that extremely large black holes live at the centers of most galaxies – what is the nature of the relationship between the black holes and the galaxy that hosts them?  These are some of the fundamental questions about galaxies that the JWST will tackle.

Computer models that scientists have made to understand galaxy formation indicate that galaxies are created when dark matter merges and clumps together. Dark matter is an invisible form of matter whose total mass in the universe is roughly five times that of “normal” matter (i.e., atoms). It can be thought of as the scaffolding of the universe. The visible matter we see collects inside this scaffolding in the form of stars and galaxies. The way dark matter "clumps" together is that small objects form first, and are drawn together to form larger ones.

Want to learn more? Here is an animation that shows the dark matter distribution in the universe at the present time, based on the Millennium Simulation, the largest N-body simulation carried out thus far!

Image courtesy of University of Washington

This build-up of large systems is accompanied by the formation of luminous stars from gas and dust.  As stars evolve, and eventually die, they give way to new generations of stars. Scientists believe that the interaction of stars and galaxies with the invisible dark matter produced the present-day galaxies, organized into what is known as the "Hubble Sequence of galaxies", shown at left.

Scientists today know that galaxies existed about one billion years after the Big Bang. While most of these early galaxies were smaller and more irregular than present-day galaxies, some are very similar to those seen nearby today.

Want to learn more about the earliest galaxies? Visit the Hubble Deep Field page .

Despite all the work done to date, there are still many questions. Scientists do not really know how galaxies are formed and what gives them their shapes. Scientists do not know how the chemical elements are distributed through the galaxies, and the details of how the central black holes in galaxies influence their host galaxies.  Scientists are also still searching for answers on what happens when small and large galaxies collide or join together.