Ever since astronomers first gazed upon the mesmerizing spiral arms of the Milky Way, they have been intrigued by the processes that shape these extraordinary structures. These processes also account for the diverse range of galaxies in the observable universe, consisting of around 2 trillion distinct galaxies in different sizes, shapes, and compositions. To gain a deeper understanding of galactic evolution, a global team of over 100 astronomers from 80 institutions have called for the James Webb Space Telescope (JWST) to conduct an extensive, multi-epoch, multi-wavelength survey of the innermost regions of the Milky Way, also known as the Galactic Center (GC). The aim is to decode the dynamics of the Galactic Center, which could shed light on similar processes occurring in other galaxies.
Despite being one of the most extensively studied areas in the night sky, many mysteries still surround the Galactic Center. Astronomers are particularly curious about the role played by Sagittarius A*, the supermassive black hole at the heart of our galaxy, in its evolution. They are also perplexed as to why star formation within cold, dark molecular clouds in the area is slower than expected and how the galaxy’s central star clusters form.
So why do astronomers believe the JWST is the key to unraveling these mysteries? According to astronomer Adam Ginsburg from the University of Florida, the Galactic Center poses two significant challenges to observation. Firstly, its density of stars makes it difficult for smaller telescopes to differentiate between individual stars. Additionally, the view of the Galactic Center from Earth is obscured by vast clouds of dust. Ginsburg explains that the JWST overcomes these challenges due to its large size, high resolution, and ability to separate stars from one another. Moreover, its capacity to observe in the infrared spectrum enables it to penetrate the dust effectively. These regions, which appear as dark voids to the naked eye, can be seen by the JWST’s Near-infrared Camera (NIRCam) and its filter system, which separates infrared light into specific wavelengths emitted by different materials.
The JWST’s ability to observe longer wavelengths of infrared light, particularly useful for studying galaxies in the early universe, is another advantage. Light from these galaxies has undergone redshift due to the universe’s expansion, with longer wavelengths moving towards the red end of the electromagnetic spectrum. This shifting of wavelengths is known as the Doppler Effect. As infrared light has longer wavelengths and lower energy than visible light, it is invisible to humans. However, the JWST’s detectors are designed to capture this invisible light.
However, even with the JWST, a single telescope is insufficient to capture the full picture. The team’s proposal suggests combining the JWST’s observations with data from other telescopes, including the Atacama Large Millimeter Array (ALMA), the Hubble Space Telescope, the Roman Space Telescope, the European Space Observatory’s Extremely Large Telescope, and Japan’s JASMINE astrometry satellite. This collaborative effort would provide a comprehensive multi-epoch survey of the Galactic Center at different intervals.
What can astronomers hope to learn from this survey? One of the main unresolved questions involves the influence of our galaxy’s black hole, Sgr A*, on its evolution. Astronomers already know that massive black holes grow primarily by consuming the gas surrounding them in accretion disks. Since the existence of such gas is crucial for star formation, researchers believe there is a connection between Sgr A*’s growth history and the rate of star formation in the Galactic Center. The proposed multi-epoch observations should provide astronomers with valuable insights into the number of stars forming and, consequently, the rate of Sgr A*’s growth.
While active black holes emit significant amounts of electromagnetic radiation, Sgr A* appears relatively dormant in this regard, indicating it is not consuming large volumes of material. This characteristic of Sgr A*, known as a “quiescent” black hole, provides valuable clues about its past. The survey could also enhance astronomers’ estimates of the Initial Mass Function (IMF), which determines the relative number of large and small stars formed. This measurement is crucial for understanding how much light star populations produce, particularly in galaxies too distant to observe individual stars.
However, obtaining time on the JWST is highly competitive, with a substantial oversubscription rate. Astronomers are requesting far more time than is available on the telescope. Moreover, the subjectivity rule poses a challenge for the community studying the Galactic Center since most astronomers in this field wish to participate in the JWST Galactic Center surveying program. To address this issue, the team aimed to demonstrate a broad consensus on the necessity of such a survey, as there would be a lack of expert reviewers familiar with the topic.
The Milky Way’s Galactic Center is the only place we can observe a galactic core where every individual star is investigable. The more we discover about our galaxy, the more we will learn about the evolution of galaxies throughout the universe. The team behind the proposal hopes to take us on a journey from the outskirts to the heart of this bustling galactic metropolis, filled with enigma and intrigue.
(Original content retained HTML tags)
