A team of astronomers using the Atacama Large Millimeter / submillimeter Array (ALMA) carried out the first census of molecular clouds in the nearby Universe, revealing that contrary to previous scientific opinion, these stellar nurseries did not all look the same and do not act the same. In fact, they are as diverse as the people, homes, neighborhoods and regions that make up our own world.
Stars are formed from clouds of dust and gas called molecular clouds or stellar nurseries. Each star nursery in the Universe can form thousands or even tens of thousands of new stars during its lifetime. Between 2013 and 2019, astronomers from the PHANGS project – Physics at High Angular Resolution in Nearby Galaxies – conducted the first systematic study of 100,000 stellar nurseries in 90 galaxies in the neighboring Universe to better understand how they connect to their mother galaxies .
“We used to think that all the stellar nurseries in each galaxy must look more or less the same, but this investigation found that this is not the case, and the stellar nurseries change from place to place. “said Adam Leroy, associate professor of astronomy. at Ohio State University (OSU), and lead author of the article presenting the PHANGS ALMA survey. “This is the first time that we are taking millimeter wave images of many nearby galaxies that have the same sharpness and quality as optical images. And while optical images show us starlight, these revolutionary new images show us the clouds that form these stars. “
Scientists compared these changes to the way people, homes, neighborhoods and cities have similar characteristics but change from region to region and country to country.
“To understand how stars are formed, we need to relate the birth of a single star to its place in the Universe. It is like connecting a person to their home, neighborhood, city, and region. If a galaxy represents a city, then the neighborhood is the spiral arm, the home the star-forming unit, and neighboring galaxies are neighboring towns in the region, ”said Eva Schinnerer, astronomer at the Max Planck Institute of Astronomy (MPIA) and PHANGS Collaboration Principal Investigator “These observations have taught us that ‘neighborhood’ has small but pronounced effects on the location and number of stars born.”
To better understand star formation in different types of galaxies, the team observed similarities and differences in the properties of molecular gases and the star formation processes of galaxy disks, star bars, spiral arms, and star formation. galaxy centers. They confirmed that location, or neighborhood, plays a critical role in star formation.
“By mapping different types of galaxies and the diverse range of environments that exist within galaxies, we map the full range of conditions under which star-forming gas clouds live in the present Universe. This allows us to measure the impact that many different variables have on how star formation occurs, ”said Guillermo Blanc, astronomer at the Carnegie Institution for Science and co-author of the article.
“How stars form and how their galaxy affects this process are fundamental aspects of astrophysics,” said Joseph Pesce, National Science Foundation program manager for NRAO / ALMA. “The PHANGS project utilizes the exquisite observational power of the ALMA Observatory and provided remarkable insight into the history of star formation in a new and different way.”
Annie Hughes, astronomer at the Institute for Research in Astrophysics and Planetology (IRAP), added that this is the first time scientists have had a glimpse of what star-forming clouds really look like in across such a wide range of different galaxies. “We discovered that the properties of stellar clouds depend on their location: clouds in dense central regions of galaxies tend to be more massive, denser and more turbulent than clouds that reside in the periphery. The life cycle of clouds also depends on their environment. The speed at which a cloud forms stars and the process that eventually destroys the cloud both seem to depend on where the cloud lives .
This is not the first time that stellar nurseries have been observed in other galaxies using ALMA, but almost all previous studies have focused on individual galaxies or part of a galaxy. Over a period of five years, PHANGS has assembled a comprehensive view of the population of nearby galaxies. “The PHANGS project is a new form of cosmic mapping that allows us to see the diversity of galaxies in a whole new light, literally. We finally see the diversity of star gas across many galaxies and are able to understand how they change over time. It was impossible to make these detailed maps before ALMA, “said Erik Rosolowsky, associate professor of physics at the University of Alberta and co-author of the research.” This new atlas contains 90 of the best maps ever carried out that reveal where the next generation of stars will form. “
For the team, the new atlas does not mean the end of the road. While the survey answered questions about what and where, it raised others. “This is the first time that we have had a clear view of the stellar nursery population throughout the neighboring Universe. In that sense, it’s a big step towards understanding where we came from,” Leroy said. “While we now know that stellar nurseries vary from place to place, we still do not know why or how these variations affect the stars and planets formed. These are questions we hope to answer in the near future. . “
Ten papers detailing the results of the PHANGS survey are presented this week at the 238th meeting of the American Astronomical Society.