Atomic Hydrogen Also Fuels Star Formation, New Study Finds

It has been long believed by astronomers that hydrogen molecules fuels star formation. Nevertheless, new research shows that hydrogen atoms are also responsible for the formation of stars.

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Understanding the processes that are involved in the birth of a star is one of the biggest challenges in astrophysics. While observations at several wavelengths, especially radio and infrared have resulted in great advances in the knowledge about the subject, there are still many mysteries existing around the exact physics involved. Moreover, an extensive theoretical and computational work also contributed greatly to clarifying the physical process underlying star formation.

Stars are formed from the molecular clouds of gas in several areas of space called stellar nurseries. These clouds of gas comprise hydrogen and heavier substances that act as a source of fuel for the lifetime of a star. The clouds are in an equilibrium between two forces; one of them that tries to expand the cloud and the other that acts to collapse it. Nonetheless, if the equilibrium is disturbed, the molecular cloud starts experiencing gravitational collapse. During the process of collapse, the cloud can break down into smaller masses. When these small masses collapse further, their temperature begins to rise and the hot gas inside is at a pressure high enough to prevent further collapse. The star then starts forming, initiating as a protostar that continues to grow by accumulating the remaining mass from the fragments and probably more mass from the surrounding area.

Nevertheless, all the molecular clouds do not end up developing into new stars. And all the masses in the cloud do not go into the stars. The processes involved in star formation are only partially understood. They interact in complex ways that cannot be accurately explained with pencil and paper calculations.

Until now, astronomers have been believing that hydrogen molecules fuels star formation. However, new research reveals that hydrogen atoms may be equally important to star formation. Most hydrogen found in galaxies exist as individual atoms. While scientists assumed that younger galaxies would be comprised of fewer hydrogen atoms and more of hydrogen molecules, a cosmic survey suggests that even the earliest galaxies were richly comprised of hydrogen atoms. A new study by the researchers at the University of Western Australia and the International Center for Radio Astronomy Research (ICRAR) says that even galaxies with high rates of star formation are rich in atomic hydrogen. This also holds true for galaxies under conditions cosmic noon galaxies. Cosmic noon refers to a period about seven billion years after the Big Bang when the rate of star formation in the universe reached its peak.

Until now, most astronomers believed that there was negligible space left for hydrogen atoms in these star-filled galaxies. However, scientists found it difficult to confirm their claims. Even the powerful telescopes are unable to detect individual gas atoms at such great distances.

Scientists recently discovered galaxies three million years younger than the Milky Way with molecular gas reservoirs as large as cosmic noon galaxies. These galaxies are much closer, thus allowing astronomers to locate individual hydrogen atoms using the world’s largest radio telescopes, Puerto Rico’s Arecibo Observatory and the European Southern Observatory’s Atacama Large Millimeter/submillimeter Array in Chile. “What we found is that despite hosting 10 billion solar masses of molecular gas these young galaxies turn out to be very, very rich in atomic hydrogen as well,” said Luca Cortese, an astrophysicist with ICRAR. “The balance between atomic and molecular hydrogen is pretty much the same as in the Milky Way. In other words, it’s still dominated by atomic gas.”

It is crucial to understand the process of star formation in astrophysics as it is necessary for understanding the evolution of stars, galaxies and the universe. Life can survive only in planets and the creation of planetary systems can only be studied as a part of the star-forming process.

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