Messier 82: Unlocking the mysteries of star formation

Today’s Image of the Day from the European Space Agency features Messier 82, a starburst galaxy located in the constellation Ursa Major. This galaxy is actively forming new stars at a rate ten times that of the Milky Way.

In a study using the James Webb Space Telescope (JWST), an international team of astronomers has taken an unprecedented look at Messier 82 (M82), revealing intricate details about its frenzied star formation. 

The power of NIRCam

The study, led by Alberto Bolatto, utilized Webb’s Near-Infrared Camera (NIRCam) to penetrate the thick dust and gas covering the galaxy’s core, a region critical to understanding star formation. 

“M82 has garnered a variety of observations over the years because it can be considered as the prototypical starburst galaxy,” noted Bolatto. “With Webb’s size and resolution, we can look at this star-forming galaxy and see all of this beautiful new detail.”

Webb’s NIRCam has proven crucial for observing areas like M82’s center, where layers of dust typically obscure the view in other wavelengths. The camera’s ability to capture infrared light allows it to reveal the galaxy’s core and its dynamic processes. 

Messier 82 image

“This image shows the power of Webb. Every single white dot in this image is either a star or a star cluster. We can start to distinguish all of these tiny point sources, which enables us to acquire an accurate count of all the star clusters in this galaxy,” noted study co-author Rebecca Levy from the University of Arizona.

One of the NIRCam’s innovative features is its mode that prevents bright sources from overwhelming the detector, which was particularly useful in studying the intensely active center of Messier 82. 

In the image, dark brown tendrils of dust weave through the galaxy’s glowing white core, interspersed with small green specks that represent concentrated areas of iron from supernova remnants. Red patches highlight regions where molecular hydrogen is illuminated by the radiation from nearby young stars.

Insights into galactic winds

The study also focused on understanding how galactic wind, driven by the rapid rate of star formation and subsequent supernovae, influences M82’s environment.

The NIRCam images showed clumpy streams of gas, appearing in red, which extend above and below the galaxy’s plane, marking the path of this wind rushing out from the starburst’s core.

A key revelation came from the NIRCam’s tracing of polycyclic aromatic hydrocarbons (PAHs), sooty chemical molecules that map out the structure of the galactic wind. To the surprise of researchers, the PAH emissions closely resembled the patterns of the hot, ionized gas, suggesting a more complex interaction within the wind than previously understood. 

“It was unexpected to see the PAH emission resemble ionised gas,” said Bolatto. “PAHs are not supposed to live very long when exposed to such a strong radiation field, so perhaps they are being replenished all the time. It challenges our theories and shows us that further investigation is required.”

Future observations of Messier 82

The findings from Webb are just the beginning. The team plans to further analyze Messier 82 with additional data, including spectroscopic observations, to determine the ages of the star clusters and the duration of each star formation phase within the starburst environment. 

These observations will also assist in a broader understanding of similar processes in early galaxies, which were common in the young universe.

Broader implications of the study

Study co-author Torsten Böker of the European Space Agency emphasized the broader implications of these findings. 

“With these amazing Webb images, and our upcoming spectra, we can study how exactly the strong winds and shock fronts from young stars and supernovae can remove the very gas and dust from which new stars are forming,” explained Böker. 

“A detailed understanding of this ‘feedback’ cycle is important for theories of how the early universe evolved, because compact starbursts such as the one in M82 were very common at high redshift.”

Image Credit: ESA/Webb, NASA & CSA

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