In Search of Glowing Interstellar Gas: Our Discovery of 49 Previously Unknown Galaxies

In Search of Glowing Interstellar Gas: Our Discovery of 49 Previously Unknown Galaxies

Stars are formed from large clouds of hydrogen gas in space. Astronomers study this gas to gain insights into the formation and growth of stars and galaxies.

Hydrogen gas emits a faint glow that is not visible to the human eye but can be detected using radio telescopes. Recently, a group of astronomers used the MeerKAT radio telescope in South Africa to search for hydrogen gas in a specific galaxy. Despite observing for a relatively short period of time, they made an unexpected discovery. Instead of finding hydrogen gas in the targeted galaxy, they identified it in 49 previously unknown galaxies. The findings have been published in the Monthly Notices of the Royal Astronomical Society.

Gas plays a crucial role in the life cycle of stars and galaxies. Nebulae, which are giant clouds of gas, serve as the birthplace of stars. When stars die, they release their gas into the surrounding environment, where it cools and forms new nebulae. Galaxies are like factories where this cycle repeats itself. To fully understand galaxies and their evolution, astronomers must consider both the stars and the gas within them.

One area of interest is “merger events,” which occur when two galaxies collide and merge into a larger galaxy. These events can impact the gas and trigger star formation. Studying gas can also provide insights into a galaxy’s history, as gas often extends beyond the boundaries of stars. Disturbed gas trails are indicative of recent galaxy mergers or interactions. However, optical telescopes are not effective at detecting galactic gas. Fortunately, radio telescopes, such as MeerKAT, are well-suited for this task.

MeerKAT is a radio telescope located in South Africa and is considered a precursor to the larger Square Kilometre Array (SKA) project. In its five years of operation, MeerKAT has achieved significant results, including detecting giant radio galaxies and studying the Milky Way’s center. Several large survey projects are currently underway with MeerKAT, focusing on studying star-forming hydrogen gas in galaxies. These surveys involve extensive observation time and are designed specifically to detect hydrogen gas.

However, MeerKAT can also be used for other scientific inquiries. Astronomers can propose “open time” observations to explore different research questions or goals. The recent discovery of the 49 previously unknown galaxies came about through one such open time observation. While the astronomers were hoping to find hydrogen gas in a specific galaxy, they stumbled upon gas located away from the target. Further investigation using techniques developed for larger surveys led to the detection of 49 gas-rich galaxies.

Each detection of gas in these galaxies was a new finding. In just over two hours of observation, MeerKAT unveiled several groups of neighboring galaxies, some of which were interacting with each other. These interactions were not evident from optical images of the stars alone. For example, one galaxy was observed stealing gas from two companion galaxies to fuel its own star formation. The collection of galaxies has informally been nicknamed the “49ers.”

The discovery required the use of various tools, including the ilifu cloud supercomputer for data reduction and the CARTA data visualization tool for the initial discovery. The astronomers also utilized iDaVIE-v, a virtual reality software for viewing astronomical datasets in 3D.

Finding 49 new galaxies in such a short observation time is remarkable, even with a powerful telescope like MeerKAT. However, astronomers believe there are more galaxies waiting to be discovered in future MeerKAT observations. In recent work, traces of gas were found in over 80 galaxies across three separate observations. Each observation initially focused on a single galaxy, similar to the open time observation that led to the discovery of the 49ers. With MeerKAT and its successor, the SKA telescope, astronomers are confident that many more exciting discoveries lie ahead.

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