Science: The Assembly of Galaxies

    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 James Webb Space Telescope 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.

    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.

    This process of galaxy assembly is still occurring today. In fact, we see many examples of galaxies colliding and merging to form new galaxies. In our own local neighborhood of space, the Andromeda galaxy is headed toward the Milky Way for a possible future collision - many billions of years from now!

    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.

    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.

    The James Webb Space Telescope will observe galaxies far back in time and hopefully answer these questions. By studying some of the earliest galaxies and comparing them to today's galaxies we may be able to understand their growth and evolution. Webb will also allow scientists to gather data on the types of stars that existed in these very early galaxies. Follow-up observations using spectroscopy of hundreds or thousands of galaxies will help researchers understand how elements heavier than hydrogen were formed and built up as galaxy formation proceeded through the ages. These studies will also reveal details about merging galaxies and shed light on the process of galaxy formation itself.

    Image credits: M81 - NASA/JPL-Caltech/S. Willner (Harvard-Smithsonian Center for Astrophysics), "Tuning Fork" - University of Washington, Hubble Deep Field - Rogier Windhorst and Simon Driver (Arizona State University), Bill Keel (University of Alabama), and NASA

    Want to know more? Visit the James Webb Space Telescope project home page.