Astronomers using the Karl G. Array have discovered that their new study of neighboring galaxy M33 indicates that fast-moving cosmic ray electrons can drive winds blowing the gas needed to form new stars.
Such winds are responsible for slowing down the rate of star formation as galaxies evolve over time. However, shock waves from supernova explosions and energetic black hole-powered jets of material from galactic cores are the primary drivers of those winds. Cosmic rays were thought to be secondary contributions, especially in galaxies such as M33 that contain regions of abundant star formation.
Fatemeh Tabatabaei, from the Institute for Research in Basic Sciences in Iran said.
Tabatabai and an international team of scientists have made detailed multi-wavelength VLA observations of M33, a spiral galaxy about 3 million light-years away and part of the Local Group of galaxies that includes the Milky Way. They also used data from previous observations using the VLA, Germany’s Eiffelsberg Radio Telescope, and millimeter-wave, visible-light, and infrared telescopes.
Stars with a mass much greater than the Sun speed up through their life cycles, eventually exploding as supernovae. Explosive shock waves can accelerate particles to nearly the speed of light, producing cosmic rays. Enough of these cosmic rays could generate pressure that drives winds carrying the gas needed to continue star formation.
“VLA observations have indicated that cosmic rays in M33 are escaping from the regions where they were born, making them capable of driving more extensive winds,” said William Cotton, of the National Radio Astronomy Observatory.
Based on their observations, the astronomers concluded that the many supernova explosions and supernova remnants in the giant M33 complexes of exuberant star formation made such cosmic-ray-driven winds more likely.
“This means that cosmic rays may have been a general cause of galactic winds, especially at earlier times in the history of the universe, when star formation was occurring at a much higher rate,” Tabatabai said. “This mechanism has thus become a more important factor in understanding the evolution of galaxies over time,” she added.
Tabatabai, Cotton and their colleagues report their findings in the October 25 issue of the journal Monthly Notices of the Royal Astronomical Society.
S Tabatabaei et al., Cloud-scale radio surveys of star formation and reactions in the Triangulum Galaxy M 33: VLA, 2005; Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac2514
Submitted by the National Radio Astronomy Observatory
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