Simulations show why stars formed in different environments have similar masses

Last year, a team of astrophysicists, including key members from Northwestern University, launched STARFORGE, a project producing the most realistic, high-resolution 3D simulations of star formation to date. Now scientists have used the highly detailed simulations to uncover what determines the masses of stars, a mystery that has captivated astrophysicists for decades.

In a new study, the team found that star formation is a self-regulating process. In other words, the stars themselves fix their own masses. This helps explain why stars formed in different environments always have the same mass. This new discovery could give scientists a better understanding of star formation in our own Milky Way and other galaxies.

The study was published last week in Royal Astronomical Society Monthly Notices. The collaborative team included experts from Northwestern, the University of Texas at Austin (UT Austin), Carnegie Observatories, Harvard University, and the California Institute of Technology. The lead author of the new study is Dávid Guszejnov, a postdoc at UT Austin.

“Understanding the initial mass function of stars is such an important question because it affects astrophysics at all levels—from nearby planets to distant galaxies,” said Claude-André Faucher-Giguère of Northwestern, co-author of the study. “That’s because stars have relatively simple DNA. If you know the mass of a star, then you know most things about the star: how much light it emits, how long it will live, and what will happen to it when it dies. The distribution of stellar masses is therefore crucial for knowing whether planets orbiting stars can potentially support life, as well as for knowing what distant galaxies look like. »

Faucher-Giguère is an associate professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and a member of the Interdisciplinary Center for Exploration and Research in Astrophysics (CIERA).

Outer space is filled with giant clouds made up of cold gas and dust. Slowly, gravity pulls distant particles of this gas and dust together to form dense clumps. Materials from these clusters fall inward, smash together and heat up to create a newborn star.

Surrounding each of these “protostars” is a rotating disc of gas and dust. Every planet in our solar system was once specks in such a disk around our newborn sun. Whether the planets orbiting a star can support life depends on the star’s mass and how it formed. Therefore, understanding star formation is crucial to determining where life can form in the universe.

“Stars are the atoms of the galaxy,” said Stella Offner, associate professor of astronomy at UT Austin. “Their mass distribution dictates whether planets will be born and whether life can develop. »

Every subfield of astronomy depends on the mass distribution of stars – or initial mass function (IMF) – which has proven difficult for scientists to model correctly. Stars much larger than our Sun are rare, representing only 1% of nascent stars. And for each of these stars, there are up to 10 Sun-like stars and 30 dwarf stars. Observations have revealed that no matter where we look in the Milky Way, these conditions (ie the IMF) are the same, both for newly formed star clusters and for those billions of years old.

This is the mystery of the IMF. Every population of stars in our galaxy and in all the dwarf galaxies around us has the same balance – even though their stars were born under vastly different conditions over billions of years. In theory, the IMF should vary widely, but it is practically universal, which has baffled astronomers for decades.

“For a long time we asked why,” Guszejnov said. “Our simulations followed stars from their birth to the natural endpoint of their formation to solve this mystery. »

However, the new simulations showed that stellar feedback, in an attempt to counteract gravity, pushes stellar masses towards the same mass distribution. These simulations are the first to track the formation of individual stars in a giant collapsing cloud, while also capturing how these newly formed stars interact with their surroundings by emitting light and losing mass via jets and winds – a phenomenon called ” star feedback”. »

The STARFORGE project is a multi-institutional initiative led by Guszejnov and Michael Grudić of Carnegie Observatories. Grudić was a CIERA postdoc at Northwestern when the project was launched. STARFORGE simulations are the first to simultaneously model star formation, evolution, and dynamics while accounting for stellar feedback, including jets, radiation, winds, and nearby supernova activity. While other simulations have incorporated individual types of stellar feedback, STARFORGE brings them all together to simulate how these different processes interact to affect star formation.

The collaboration is funded by the National Science Foundation, NASA, Research Corporation for Science Advancement, Extreme Science and Engineering Discovery Environment, CIERA and the Harvard Institute for Theory and Computation. The research was completed on two supercomputers at UT Austin’s Texas Advanced Computing Center.


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