Astronomers using the NASA/ESA/CSA James Webb Space Telescope have captured a new image of the central starburst region of Messier 82 (M82, NGC 3034 or the Cigar Galaxy), a starburst irregular galaxy located 12 million light-years away in the constellation of Ursa Major.
Messier 82 was observed by the NASA/ESA Hubble Space Telescope in 2006, which showed the galaxy’s edge-on spiral disk, shredded clouds, and hot hydrogen gas. The NASA/ESA/CSA James Webb Space Telescope observed the core of Messier 82, capturing in unprecedented detail the structure of the galactic wind and characterizing individual stars and star clusters. Image credit: NASA / ESA / CSA / Hubble / Webb / STScI / A. Bolatto, UMD.
Messier 82 is located about 12 million light-years away. It appears high in the northern spring sky in the direction of the northern constellation Ursa Major.
First discovered by the German astronomer Johann Elert Bode in 1774, the galaxy is approximately 40,000 light-years across.
Messier 82 is also called the Cigar Galaxy because of the elongated elliptical shape produced by the tilt of its starry disk relative to our line of sight.
The galaxy is famous for its extraordinary speed in making new stars, with stars being born 10 times faster than in our Milky Way Galaxy.
University of Maryland astronomer Alberto Bolatto and his colleagues directed Webb’s NIRCam (Near-Infrared Camera) instrument toward the center of Messier 82, obtaining a closer look at the physical conditions that foster the formation of new stars.
“Messier 82 has garnered a variety of observations over the years because it can be considered as the prototypical starburst galaxy,” Dr. Bolatto said.
“Both Spitzer and Hubble space telescopes have observed this target. With Webb’s size and resolution, we can look at this star-forming galaxy and see all of this beautiful new detail.”
“Star formation continues to maintain a sense of mystery because it is shrouded by curtains of dust and gas, creating an obstacle to observing this process.”
“Fortunately, Webb’s ability to peer in the infrared is an asset in navigating these murky conditions.”
“Additionally, these NIRCam images of the very center of the starburst were obtained using an instrument mode that prevented the very bright source from overwhelming the detector.”
“While dark brown tendrils of dust are threaded throughout Messier 82’s glowing white core even in this infrared view, Webb’s NIRCam has revealed a level of detail that has historically been obscured.”
“Looking closer toward the center, small specks depicted in green denote concentrated areas of iron, most of which are supernova remnants.”
“Small patches that appear red signify regions where molecular hydrogen is being lit up by the radiation from a nearby young star.”
“This image shows the power of Webb,” said Dr. Rebecca Levy, an astronomer at the University of Arizona.
“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.”
Looking at Messier 82 in slightly longer infrared wavelengths, clumpy tendrils represented in red can be seen extending above and below the plane of the galaxy. These gaseous streamers are a galactic wind rushing out from the core of the starburst.
One area of focus for this research team was understanding how this galactic wind, which is caused by the rapid rate of star formation and subsequent supernovae, is being launched and influencing its surrounding environment.
By resolving the central region of Messier 82, the astronomers were able to examine where the wind originates, and gain insight into how hot and cold components interact within the wind.
Webb’s NIRCam instrument was well suited to tracing the structure of the galactic wind via emission from sooty chemical molecules known as polycyclic aromatic hydrocarbons (PAHs).
PAHs can be considered as very small dust grains that survive in cooler temperatures but are destroyed in hot conditions.
Much to the team’s surprise, Webb’s view of the PAH emission highlights the galactic wind’s fine structure — an aspect previously unknown.
Depicted as red filaments, the emission extends away from the central region where the heart of star formation is located.
Another unanticipated find was the similarity between the structure of the PAH emission and that of the hot, ionized gas.
“It was unexpected to see the PAH emission resemble ionized gas,” Dr. Bolatto said.
“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.”
The team’s paper will be published in the Astrophysical Journal.
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Alberto D. Bolatto et al. 2024. JWST Observations of Starbursts: Polycyclic Aromatic Hydrocarbon Emission at the Base of the M 82 Galactic Wind. ApJ, in press; arXiv: 2401.16648
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