A team of astronomers using the Atacama Large Millimeter/submillimeter Array, the ALMA, has completed the first survey of molecular clouds in the near universe, revealing that contrary to previously thought, these stellar nurseries do not look alike and act in the same way. In fact, they are diverse, just as people are different, houses are different, neighborhoods and regions of our world are different.
Stars are formed in clouds of dust and gas called molecular clouds, or stellar nurseries. Every stellar nursery in the universe can form thousands or even tens of thousands of new stars during its lifetime. Between 2013 and 2019, astronomers at the Physics at high angular Resolution in Nearby GalaxieS, or PHANGS project, conducted the first systematic survey of 100,000 star nurseries in 90 nearby universe galaxies to better understand how they connect to their parent galaxies.
It is normally thought that all stellar nurseries in every galaxy are more or less alike, but this research revealed that this is not the case, stellar nurseries are different. This is the first time that millimeter wavelength images of many nearby galaxies have the same optical quality. Images taken in visible light show the light of stars, while these new images show the molecular clouds that form these stars.
Scientists have compared these changes to the same changes we have with homes, people, neighborhoods, cities and everything else we have here on our planet.
To understand how stars form, we need to link the birth of a single star to its place in the universe. It’s like linking a person to your home, your city, your region. Observations made with ALMA have shown that neighborhoods have small but pronounced effects on how and where many stars are born.
To better understand star formation in different types of galaxies, astronomers looked at similarities and differences in the properties of the molecular gas and in the star formation process of the galaxy’s disks, star bars, spiral arms, and center of galaxies. They confirmed that location, or neighborhood, plays a critical role in star formation.
By mapping the different types of galaxies and different types of environments that exist within galaxies, astronomers can trace all the conditions where star-forming clouds live in the current universe. This allows astronomers to measure the impact that different variables have on the training process.
How stars form, and how galaxies affect this process, are fundamental aspects of astrophysics. The PHANGS project utilizes the exceptional observational power of ALMA and with this it was possible to get a good idea about the history of star formation in a new and different way.
This is the first time scientists have had images of clouds forming stars in a large number of galaxies. And the properties of star-forming clouds depend on where they are located. Clouds in the dense central regions of galaxies tend to be more massive and denser and more turbulent than clouds that reside in the peripheral regions of galaxies. The lifecycle of these clouds also depends on the environment. How fast a cloud forms stars and the process that ultimately destroys the cloud both depend on where the clouds live.
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. Within five years, PHANGS has achieved a complete view of a large population of nearby galaxies. The PHANGS project is a new form of cosmic cartography that allows us to see the diversity of galaxies in a new light, literally.
Astronomers are finally seeing the diversity of star formation regions in many galaxies and are being able to understand how they change over time. Before ALMA it was impossible to see maps as detailed as these. This new atlas contains 90 of the best maps ever made that reveal where the next generation of stars is forming.
This new atlas does not represent the end of the line. While this survey answered some important questions about where and how, it raised other questions. This is the first time that we have had a clear view of the stellar nursery population across the near universe. And that’s a big step towards understanding where we came from. While we now know that stellar nurseries vary from place to place, we still don’t know why or how these variations affect the formation of stars and planets. These are the questions astronomers hope to answer in the near future.