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The Assembly of Galaxies

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JWST's unprecedented infrared sensitivity will help astronomers to compare the faintest, earliest galaxies to today's grand spirals and ellipticals, helping us to understand how galaxies assemble over billions of years.

Why Is It Important to Understand Galaxies?

Galaxies show us how the matter in the universe is organized on large scales. In order to understand the nature and history of the universe, scientists study how the matter is currently organized and how that organization has changed through out cosmic time. In fact, scientists examine how matter is distributed and behaves at multiple size scales in our quest for this understanding. From peering into the way matter is constructed at the subatomic particle level to the immense structures of galaxies and dark matter that span the cosmos, each scale gives us important clues as to how the universe is built and evolves.

Spirals and Ellipticals

Telescopes like the Hubble have captured many beautiful images of majestic spiral galaxies, like this one, which is called NGC 3344.

Galaxy in a spin
Credit: ESA/Hubble & NASA

But galaxies have not always looked this way. The grand spirals we are so familiar with (indeed including our own) were formed over the course of billions of years by several different processes, including the collisions of smaller galaxies. Giant elliptical galaxies are thought to also be formed by the process of similar-sized galaxies colliding [see videos linked at the bottom of the page], disrupting each other, and merging. In fact, it is thought that nearly all massive galaxies have undergone at least one major merger since the Universe was 6 billion years old.

Giant elliptical galaxy, M87, Credit: ESA/Hubble & NASA

How Do the Oldest Galaxies Differ?

When we look at very distant galaxies, we see a completely different picture. Many of these galaxies tend to be small and clumpy, often with a lot of star formation occurring in the massive knots. The question of how these clumpy galaxies evolve and develop structure over time is a big open question in astronomy, and JWST will help astronomers to learn more.

Clumpy Galaxy
Clumpy galaxy spied by the Hubble. Via Galaxy Zoo.

Clumpy Galaxies
Clumpy galaxies spied by the Hubble. Via Galaxy Zoo.

Open Questions About Galaxies

Other unanswered questions about galaxies include the following. How did the first galaxies form? How did we end up with the large variety of galaxies we see today? (We see not only organized and structured spiral galaxies in the modern universe, we also see those giant ellipticals we mentioned earlier, and galaxies in a wide variety of irregular shapes and sizes.)

We now know that extremely large black holes live at the centers of most galaxies – but what is the nature of the relationship between the black holes and the galaxy that hosts them? There is also more to understand about the mechanisms that cause star formation-- whether it happens internal to a galaxy or because of an interaction with another galaxy or merger.

One thing we do know is that galaxies are still forming and assembling today. There are many, many examples of galaxies colliding and merging to form new galaxies. And in our own local neighborhood of space, the Andromeda galaxy is headed toward the Milky Way for a likely future collision – many billions of years from now! (Fun fact: space is so big that when galaxies collide, the stars within them rarely do.)

Visible light Hubble data combined with infrared data from Spitzer, to create this stunning
image of M51, the Whirlpool galaxy. M51, as you can see, is actually two interacting
galaxies (formally NGC 5194 and 5195). Credit: vdHoeven/NASA/JPL-Caltech/R. Kennicutt
(Univ. of Arizona)/DSS

More Images and Videos of Galaxy Mergers

Hubble View of Galaxy Merger II Zw 096
Hubble's view of the merging galaxies known collectively as II Zw 096. This is
multiwavelength, from the far-ultraviolet to the near-infrared. Credit:NASA/JPL-Caltech/
STScI/H. Inami (SSC/Caltech)

Hubble's newest camera takes a deep look at two merging galaxies
"The Mice," a pair of colliding galaxies, were given this name because of the long tails
of stars and gas trailing each galaxy. They will someday be a single giant galaxy. Hubble
image, Credit: NASA, Holland Ford (JHU), the ACS Science Team and ESA

Interacting galaxies
Interacting galaxies can create some unique and strange shapes, as seen in these Hubble
images. Image: NASA/ESA/Hubble Heritage Team/STScI/AURA/A Evans/University of
Virginia/NRAO/Stony Brook University/K Noll/J Westphal)

Hubble - Interacting Galaxies
And if those weren't enough for you, here are more! (Be sure to look at the larger image!)
Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration,
A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University), W. Keel
(University of Alabama, Tuscaloosa), K. Noll, B. Whitmore and M. Stiavelli (STScI),
G. Ostlin (Stockholm University), and J. Westphal (Caltech)

This video, by Dr. Frank Summers, which shows a comparison of a simulation of a galaxy collision with five Hubble observations of galaxy collisions:

Here are several videos about how JWST will help us to better understand galaxy collisions, galaxy formation, and the evolution of the early universe.

Go to: More Detail page on The Assembly of Galaxies