Webb Identifies Millions of Stars in Cigar Galaxy

6 Min Read

Located 12 million light-years away and undergoing rapid star formation, edge-on spiral galaxy Messier 82 (M82) is a scientifically unique sight to behold, and now NASA's James Webb Space Telescope has revealed previously unseen details.

M82's intense star formation, thought to be the result of a galaxy merger, will be a short-lived event in astronomical terms, estimated to last a few hundred million years in its entirety. This temporary phase of extreme star formation relative to the galaxy's mass, as well as its location in the local universe, are among the factors that make M82, also known as the Cigar galaxy, a one-of-a-kind environment to study.

Image: M82 Cigar Galaxy (Webb + Hubble)

A team of astronomers recently completed an imaging survey with the Webb telescope. This program entailed a total of 65 hours of observation time with Webb's NIRCam (Near-Infrared Camera) instrument and revealed never-seen-before details of the starburst galaxy, including its distended disk structure and millions of individual stars. Webb's high-resolution imaging, specifically of the main plane of the galactic disk, has unlocked vital information for astronomers as they seek to uncover M82's formation history. Additionally, the Webb data will help scientists understand the current processes occurring within the starburst galaxy.

"M82 is a mess, but it's a beautiful mess. We don't fully understand what's going on, especially concerning its evolutionary history. What could have triggered such an elevated rate of star formation? How long has this galaxy been driving plumes of material away from its center?" said principal investigator Adam Smercina, a NASA Hubble Fellow at the Space Telescope Science Institute in Baltimore, and incoming Assistant Professor at Tufts University in Massachusetts. "M82 is an ideal galaxy evolution laboratory because it has properties that allow us to probe important physical processes, such as how stars form in such environments and how that activity drives outflows. M82 provides a simultaneous window onto many astrophysical questions, in a way that no other galaxy in the local universe can."

Image: M82 Cigar Galaxy (NIRCam Image)

Prior to Webb, many observatories looked at the starburst galaxy, including NASA's Hubble and retired Spitzer space telescopes. However, the sheer volume of dust within that galaxy limited the amount of information astronomers could acquire on M82 at high resolution. While Webb has previously looked at this galaxy, the duration of the new imaging survey, combined with the telescope's infrared sensitivity, enabled it to pierce through the thick dust.

Image: M82 Cigar Galaxy (Hubble/Webb Side-by-Side)

The telescope's near-infrared-light view is a snapshot of a scene that has been evolving over a couple hundred million years. Webb's image contains approximately 16.5 million individual stars dispersed throughout the galaxy. The light from these stellar sources is depicted as luminous blue granules. This is only a small portion of the total amount of stars astronomers think reside in a galaxy like M82, with the majority too faint to be seen.

"The sheer number of stars that we were able to resolve with Webb is incredible," said team member Benjamin Williams of the University of Washington. "It's a whole different world from what we've been able to see with other telescopes. All of these stars collectively provide a detailed fossil record of the formation and evolution of M82."

Moving inward, the increase in brightness and the asymmetrical shape of the galactic disk hints at the spiral galaxy's unique underlying structure. The differing radii between the two sides suggests that M82 has a distorted shape, which can happen during intense galaxy mergers.

"At first glance, the disk of the galaxy may seem less spectacular because Webb sees through the dust," said team member Eric Bell of the University of Michigan. "But M82 is a delightfully complex system. Webb's observations will help us address some ongoing mysteries, such as how star formation has moved within M82 over the last few billion years."

Video: M82 Cigar Galaxy (Webb + Hubble Fade)

Because of the extreme star formation within the galaxy, which is 10 times faster than the Milky Way galaxy's star formation rate, stellar birth will eventually be disrupted. M82's stellar frenzy is causing bipolar plumes of material to be ejected above and below the disk. Though it looks like a tumultuous region, the hourglass-shaped outflows appear to have a layered structure. The yellow tendrils of material closest to the galaxy's disk represent ionized gas, whereas the orange material farther away depicts small dust grains. These grains are called polycyclic aromatic hydrocarbons and are helpful in tracing material in the space between the galaxy's stars, also known as the interstellar medium.

The information collected as part of this Webb study is just one dataset scientists will analyze as they seek to piece together this starburst galaxy's formation history.

"Galaxies are such intricate ecosystems that if you truly want to understand them, you have to pull datasets from different missions together," said team member Kristen McQuinn of the Space Telescope Science Institute. "One mission cannot fully answer all of the questions we have about M82. Combining the data collected by different telescopes, like Webb and Hubble, is powerful. When you marry the datasets, you expand what you can probe, and the questions that you can pose are even more complex."

The James Webb Space Telescope is the world's premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).