The James Webb Space Telescope Early Release Science (ERS) program – first published on July 12, 2022 – has proven to be a mine of scientific knowledge and breakthroughs.
Among the many areas of research it facilitates is the study of resolved stellar populations (RSTs), which has been the theme ERS1334.
This refers to large groups of stars that are close enough that individual stars can be seen, but far enough apart that telescopes can pick up many of them at once. A good example is the Wolf Lundmark Melotte (WLM) Dwarf galaxy neighboring the Milky Way.
Kristen McQuinn, assistant professor of astrophysics at Rutgers University, is one of the principal scientists in the Webb ERS program, whose work focuses on RSTs. Lately, she spoke to Natascha Piroa senior communications specialist at NASA on how the JWST has enabled new studies of the WLM.
Webb’s improved observations have shown that this galaxy has not interacted with other galaxies in the past.
According to McQuinn, this is a great candidate for astronomers to test theories about galaxy formation and evolution. Here are the highlights of this interview.
Speaking of WLM
The WLM is about 3 million light-years from Earth, which means it’s fairly close (astronomically) to the Milky Way. However, it is also relatively isolated, leading astronomers to conclude that it has not interacted with other systems in the past.
As astronomers observed other nearby dwarf galaxies, they found that they are typically entangled with the Milky Way, suggesting they are in the process of merging.
This complicates their study, as their population of stars and gas clouds cannot be fully distinguished from our own.
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Another important thing about WLM is that it contains few elements heavier than hydrogen and helium (which were very common in the early universe). Elements such as carbon, oxygen, silicon, and iron were formed in the cores of early population stars and dissipated when those stars exploded in supernovae.
In the case of WLM, which has seen star formation throughout its history, the force of those explosions pushed those elements out over time. This process is known as “galactic winds” and has been observed in small, low-mass galaxies.
Compared to the Webb images, these offered a limited resolution, which can be seen in the direct comparison (see below).
As you can see, Webb’s infrared optics and advanced suite of instruments provide a much deeper view, allowing individual stars and features to be distinguished. As McQuinn described it:
“We can see myriads of individual stars of different colors, sizes, temperatures, ages, and evolutionary stages; interesting nebula gas clouds within the galaxy; foreground stars with Webb’s diffractive peaks; and background galaxies with pretty features like tide trails. It really is a beautiful picture.”
The ERS program
As McQuinn explained, the scientific focus of ERS 1334 is to build on previous knowledge developed with Spitzer, Hubble and other space telescopes to learn more about the history of star formation in galaxies.
Specifically, they are conducting deep multiband imaging of three resolved star systems within one megaparsec (~3,260 light-years) of Earth using Webb near infrared camera (NIRCam) and Slitless spectrograph for near infrared imaging (NIRISS).
The population of low-mass stars in WLM makes it particularly interesting because they are so long-lived, meaning some of the stars seen there today may have formed during the early Universe.
“By determining the properties of these low-mass stars (like their ages), we can gain insight into what happened in the very distant past,” McQuinn said.
“It’s very complementary to what we learn by watching about the early formation of galaxies High redshift systemswhere we see the galaxies as they existed when they first formed.”
Another goal is to use the WLM dwarf galaxy to calibrate the JWST to ensure it can measure the brightness of stars with extreme accuracy, which will allow astronomers to test models of stellar evolution in the near-infrared.
McQuinn and her colleagues are also developing and testing non-proprietary software to measure the brightness of resolved stars imaged with the NIRCam, which will be made available to the public.
The results of their ESR project will be published ahead of the Cycle 2 call for proposals (27 January 2023).
The James Webb Space Telescope has been in space for less than a year but has already proved invaluable. The stunning views of the cosmos it has provided include deep-field images, extremely precise observations of galaxies and nebulae, and detailed spectra of extrasolar planetary atmospheres.
The scientific breakthroughs it has already made possible have been nothing short of groundbreaking. Before the projected 10-year mission is over (which could be extended to 20 years), some truly paradigm-shifting breakthroughs are expected.