Webb and Our Galaxy

Our galaxy, the Milky Way, contains a supermassive black hole at its core surrounded by a central bulge of old, yellowish stars. Beyond that are bluish spiral arms filled with younger stars, newly forming stars, and dark lanes of dust.

It is just one of billions of galaxies in our universe, but the Milky Way is our galaxy, our home in the universe. The Milky Way contains the closest examples of stars, planets, nebulae, black holes, and other objects that likely reside in every galaxy throughout the cosmos. By studying the Milky Way in the infrared, the Webb Telescope will be able to teach us a great deal about our galaxy and others. Webb will improve our understanding of all stages of star formation — from birth to death and back again to the rise of the next stellar generation. Astronomers know that stars form out of collapsing clouds of gas and dust, but they don't yet know the exact sequence of how stars are born. What triggers a cloud to collapse and a star to begin forming? How much of that mother cloud does a star use up when it forms? How and when do planets begin to form around a newborn star?
At the end of their lives, stars die in a variety of exciting and interesting ways — from gentle exhales of material to violent explosions expelling stellar shrapnel into the galaxy. Many dying stars and stellar corpses are embedded in their ejected material, which shrouds our view in visible light but can be penetrated with Webb's infrared vision. Webb will help us probe and understand both this residual material and the stars that died. It will help astronomers test their theories for how stars end their lives and how the heavier elements forged within these dying stars are recycled into the galactic environment to help create the next generation of stars.

Omega Centuari is one of the largest globular star clusters residing in the outskirts of our galaxy.

Counting Stars

Webb will help us understand just how many stars there are and how those stars are distributed throughout the galaxy. The most common stars in the Milky Way are "dwarf" stars that are often too dim for Hubble to observe in visible light, but that glow brighter in infrared light. Webb will help astronomers get a firmer grip on just how many of these stars exist, and perhaps help us learn more about them. Knowing how many stars there are of different types also tells us how quickly or efficiently stars formed at various stages in the galaxy's history.
Webb will also study giant stellar swarms called globular clusters, which reside at the outskirts of the Milky Way and contain the oldest stars in the galaxy. Webb will analyze the composition of these ancient stars, and perhaps reveal whether globular clusters formed along with our galaxy or originated somewhere else, and were later absorbed into the galaxy.

Looking Inward and Outward

This X-ray image shows the region around our galaxy's central supermassive black hole, known as Sagittarius A* (or Sgr A*). Credit: NASA/CXC/Univ. of Wisconsin/Y. Bai et al.

Webb will help us understand what's going on at the very heart of the Milky Way. In our galaxy's core lies a supermassive black hole surrounded by gas, dust, and a densely packed swarm of stars. However, this central black hole does not seem to be consuming as much material as its peers in other galaxies are. Astronomers aren't sure why. Webb’s infrared observations could give us a clearer view of the material and stars near the black hole, and perhaps uncover the reason why our galaxy's black hole is so quiet. Webb's sharp and powerful infrared vision will allow it to peer farther into the Milky Way with greater clarity than infrared telescopes before it — uncovering parts of the galaxy that were once too dim, too distant, or too concealed to study. These investigations will not only help us understand our own Milky Way, but myriad galaxies throughout the universe.