NASA's James Webb Space Telescope (JWST) never fails to enthral the world with its spellbinding images. With its infrared sensitivity, Webb, the world's most powerful telescope, has resolved faint stars in the nearby dwarf galaxy Wolf-Lundmark-Melotte (WLM). The galaxy is located near the Milky Way. WLM is our galactic neighbour and located three million light-years away from Earth.
Also, the dwarf galaxy is antisocial, which means it has not interacted with nearby galaxies. According to NASA, WLM is 'old school', which means it has a chemical makeup similar to early universe galaxies. As a result, WLM is an ideal candidate to study how stars in the early universe may have formed and evolved.
What are resolved stellar populations?
In a statement released by NASA, Kristen McQuinn, one of the lead scientists who focused on resolved stellar populations, said WLM is a dwarf galaxy fairly close to the Milky Way, but it is relatively isolated. Resolved stellar populations are large groups of stars, including stars within WLM. These larger groups of stars are close enough for Webb to differentiate between individual stars, but far enough for Webb to capture a large number of stars at once.
What does Webb’s image of dwarf galaxy WLM mean?
NASA's Spitzer Space Telescope, which ended operations in January, 2020, had also captured a portion of WLM. The Spitzer image, captured by the telescope's Infrared Array Camera, shows 3.6-micron light in cyan and 4.5-micron in orange. Webb's image has been captured by the Near-Infrared Camera (NIRCam). The new image of WLM showcases Webb's remarkable ability to resolve faint stars outside the Milky Way, and includes 0.9-micron light shown in blue, 1.5-micron light in cyan, 2.5-micron light in yellow, and 4.3-micron light in red.
Webb's NIRCam "makes the whole place shimmer", according to NASA.
Why is WLM ideal for studying galactic evolution in early universe?
McQuinn said astronomers think WLM has not interacted with other systems, which makes it really nice for testing the theories of galaxy formation and evolution. Since many of the other nearby galaxies are intertwined and entangled with the Milky Way, they are harder to study.
WLM's gas is similar to the gas that made up galaxies in the early universe, McQuinn said. It is fairly enriched, chemically speaking, which means that it is poor in elements heavier than hydrogen and helium.
Why is WLM poor in certain elements?
The reason WLM is poor in elements heavier than hydrogen and helium is that the galaxy has lost many of these elements through something called galactic winds. WLM has been forming stars throughout cosmic time, and those stars have been synthesising new elements. However, some of the material gets expelled from the galaxy when the massive stars explode. McQuinn explained that supernovae can be powerful and energetic enough to push material out of small, low-mass galaxies like WLM.
WLM can help astronomers study how stars form and evolve in small galaxies like those in the ancient universe.
What does Webb’s image reveal?
McQuinn said that in Webb's image, one can see a myriad of individual stars of different colours, sizes, temperatures, ages and stages of evolution, interesting clouds of nebular gas within the galaxy, foreground stars with Webb's diffraction spikes, and background galaxies with neat features like tidal tails, which are thin, elongated regions of star and interstellar gas extending into space from a galaxy.
Some of WLM’s stars formed in early universe
McQuinn said researchers aim to reconstruct the star formation history of WLM. The fact that low-mass stars can live for billions of years means that some of the stars seen in WLM today formed in the early universe. One can gain insight into what was happening in the very distant past by determining the properties of these low-mass stars. By looking at high-redshift (displacement of spectral lines towards longer wavelengths in radiation from distant galaxies) systems, one can learn about the early formation of galaxies. These systems help astronomers see galaxies as they existed when they first formed.
McQuinn said her team is checking the calibration of NIRCam and stellar evolution models, and developing software to measure star brightness.
The researchers are using WLM as a sort of standard of comparison to make sure they understand the Webb observations, and to make sure they are measuring the stars' brightnesses accurately and precisely.
The team is developing a public software tool to measure the brightness of all the resolved stars in the NIRCam images. It is a "bedrock tool" for astronomers around the world, McQuinn said.