Is the Milky Way Unique?

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It is just one of billions of galaxies, but the Milky Way is our galaxy, our home in the universe.

Our galaxy
Our galaxy, the Milky Way, contains a supermassive black hole at its core, surrounded by a central bulge of old, yellow stars. Beyond that, young blue stars spiral out from the center, filled in with dark lanes of dust. CREDIT: NASA and STScI. GET THE FULL IMAGE IN RESOURCE GALLERY >

Our first observations of stars, beginning with the naked eye and then with successively more powerful telescopes, happened here, providing a baseline for all the discoveries—and new questions—to follow.

One major question astronomers investigate when studying galaxies is how stars form within them. The James Webb Space Telescope’s powerful infrared instruments will improve our understanding of all stages of the star “lifecycle”—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 gas cloud to collapse? How much of that “mother” cloud does a star use up when it forms? How and when do planets begin to form around a new star?

At the end of their so-called lifecycle, stars “die” in a variety of dramatic and scientifically interesting ways—from gentle exhales of material to violent supernova explosions that expel stellar shrapnel into the galaxy. Many dying stars and stellar corpses are embedded in their ejected material; this shrouds them from view in visible light, but Webb’s infrared vision penetrates the dusty haze. Webb will help us probe and understand both this residual material and the former star. It allows astronomers to test their theories for how stars burn out, and how the heavier elements forged within these stars are recycled into the galactic environment to help create the next generation of stars.

 

Counting Stars

Webb will help us get a better grip on how many stars there are in the Milky Way and how those stars are distributed throughout the galaxy. The most common stars in the Milky Way are “dwarf stars” that are too dim for the Hubble Space Telescope to observe well in visible light, but that are easily visible in the infrared wavelengths that Webb can detect. Knowing how many dwarf stars there are, as well as other types of stars, also tells us how quickly or efficiently stars formed at various stages in the galaxy’s history. This will give astronomers a much more informed local baseline from which to compare and contrast other galaxies.

Omega Centauri
Omega Centauri is one of the largest globular star clusters residing in the outskirts of our galaxy. CREDIT: NASA, ESA, and the Hubble Heritage Team (STScI, and AURA).

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 can 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 Milky Way.

Sagittarius A
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, University of Wisconsin, Y. Bai et al.

Looking Inward and Outward

Webb can 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. Astronomers aren’t sure why. Webb’s infrared observations could give us a clearer view of the dense region surrounding the black hole, and perhaps uncover the reason why our galaxy’s black hole is so quiet.

Webb’s high-resolution infrared vision allows 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.


 

Keywords:  GalaxiesMilky Way

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