The James Webb Space Telescope (JWST) has imaged a galaxy neighboring the Milky Way in stunning detail.
Positioned around 1.5 million light-years away from Earth, the irregular-shaped galaxy, NGC 6822, is the Milky Way’s closest galactic neighbor — barring some small satellite galaxies, corresponding to the Large and Small Magellanic Clouds, that lie in its close orbit.
Created using the James Webb Space Telescope’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI), the image shows the gas and mud of NGC 6822 glowing in green and gold while billowing across a dense field of stars. Brilliant galaxies of assorted sizes and shapes also punctuate the image.
This nearby galaxy is especially interesting since it’s what astronomers call “metal-poor,” meaning it lacks elements heavier than hydrogen and helium, based on a European Space Agency (ESA) statement. For context, astronomers call all elements heavier than those two, that are the lightest elements, “metals.”
Such a composition makes NGC 6822 an awesome proxy for studying galaxies within the early universe, that are too far-off to see intimately. That is because early galaxies are also thought to have had low-metallicities. When galaxies and stars first began to form within the universe, space was populated by just hydrogen, helium and a tiny smattering of heavier elements. Thus the primary stars were similarly metal-poor.
Throughout their lifetimes, the primary stars in our universe forged heavier elements of their cores via the nuclear fusion of hydrogen and helium. When these stars exhausted that fusion fuel, they ended their lives in supernova explosions which dispersed the heavy elements all across their cosmic vicinities.
These elements were then integrated into interstellar clouds of gas and mud that eventually collapsed to birth recent stars. This next generation of stars was thus more metal-rich. That very same process repeated with the third generation of stars becoming much more enriched with metals. Actually, the sun is an example of one among these third-generation metal-rich stars.
The low-metallicity galaxy, NGC 6822, thus offers astronomers a probability to watch how the evolution of stars and interstellar gas and mud clouds proceeded within the metal-poor environments of the early universe.
Other stars within the Milky Way range in metalicity, with probably the most metal-rich stars present in its central bulge and the more metal-poor stars mostly positioned in its disk and spiral arms.
NGC 6822 is not any stranger to astronomers.
The irregular galaxy is a known focal point since it doesn’t fit the template of galaxies with well-defined shapes. It doesn’t quite resemble a spiral galaxy, corresponding to the Milky Way, or an elliptical galaxy.
First discovered by American astronomer E. E. Barnard in 1884, it was even initially misidentified as an “exceedingly faint nebula.” This confusion regarding NGC 6822 continued for several a long time, with disagreements raging about its size and its brightness. These disparities arose from the actual fact astronomers had yet to account for the way different objects would seem to different telescopes.
The controversy was settled in 1925, when Edwin Hubble confirmed the existence of astronomical objects beyond the boundaries of the Milky Way. Hubble himself acknowledged the importance of NGC 6822 on this revelation, writing: “N.G.C. 6822, [was] the primary object definitely assigned to a region outside the galactic system.”
Until the 2000s, probably the most definitive work regarding NGC 6822 was a 1966 paper by Susan Kayser, who was the primary woman to receive a Ph.D. in astronomy from Caltech.
Now, the JWST is constructing on the work of Hubble and Kayser, strengthening our knowledge of our metal-poor next-door neighbor while allowing us to marvel at its beauty.