First high-resolution model to simulate an entire gas cloud where stars are born.
A team including Northwestern University astrophysicists has developed the most realistic, highest-resolution 3D simulation of star formation to date. The result is a visually stunning, mathematically-driven marvel that allows viewers to float around a colorful gas cloud in 3D space while watching twinkling stars emerge.
Called STARFORGE (Star Formation in Gaseous Environments), the computational framework is the first to simulate an entire gas cloud — 100 times more massive than previously possible and full of vibrant colors — where stars are born.
It also is the first simulation to simultaneously model star formation, evolution and dynamics while accounting for stellar feedback, including jets, radiation, wind and nearby supernovae activity. While other simulations have incorporated individual types of stellar feedback, STARFORGE puts them altogether to simulate how these various processes interact to affect star formation.
Using this beautiful virtual laboratory, the researchers aim to explore longstanding questions, including why star formation is slow and inefficient, what determines a star’s mass and why stars tend to form in clusters.
The researchers have already used STARFORGE to discover that protostellar jets — high-speed streams of gas that accompany star formation — play a vital role in determining a star’s mass. By calculating a star’s exact mass, researchers can then determine its brightness and internal mechanisms as well as make better predictions about its death.
Newly accepted by the Monthly Notices of the Royal Astronomical Society, an advanced copy of the manuscript, detailing the research behind the new model, appeared online on May 17, 2021. An accompanying paper, describing how jets influence star formation, was published in the same journal in February 2021.
“People have been simulating star formation for a couple decades now, but STARFORGE is a quantum leap in technology,” said Northwestern’s Michael Grudic, who co-led the work. “Other models have only been able to simulate a tiny patch of the cloud where stars form — not the entire cloud in high resolution. Without seeing the big picture, we miss a lot of factors that might influence the star’s outcome.”
“How stars form is very much a central question in astrophysics,” said Northwestern’s Claude-André Faucher-Giguère, a senior author on the study. “It’s been a very challenging question to explore because of the range of physical processes involved. This new simulation will help us directly address fundamental questions we could not definitively answer before.”
Grudic is a postdoctoral fellow at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Faucher-Giguère is an associate professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and member of CIERA. Grudic co-led the work with Dávid Guszejnov, a postdoctoral fellow at the University of Texas at Austin.
From start to finish, star formation takes tens of millions of years. So even as astronomers observe the night sky to catch a glimpse of the process, they can only view a brief snapshot.
“When we observe stars forming in any given region, all we see are star formation sites frozen in time,” Grudic said. “Stars also form in clouds of dust, so they are mostly hidden.”
For astrophysicists to view the full, dynamic process of star formation, they must rely on simulations. To develop STARFORGE, the team incorporated computational code for multiple phenomena in physics, including gas dynamics, magnetic fields, gravity, heating and cooling and stellar feedback processes. Sometimes taking a full three months to run one simulation, the model requires one of the largest supercomputers in the world, a facility supported by the National Science Foundation and operated by the Texas Advanced Computing Center.
The resulting simulation shows a mass of gas — tens to millions of times the mass of the sun — floating in the galaxy. As the gas cloud evolves, it forms structures that collapse and break into pieces, which eventually form individual stars. Once the stars form, they launch jets of gas outward from both poles, piercing through the surrounding cloud. The process ends when there is no gas left to form any more stars.
Pouring jet fuel onto modeling
Already, STARFORGE has helped the team discover a crucial new insight into star formation. When the researchers ran the simulation without accounting for jets, the stars ended up much too large — 10 times the mass of the sun. After adding jets to the simulation, the stars’ masses became much more realistic — less than half the mass of the sun.
“Jets disrupt the inflow of gas toward the star,” Grudic said. “They essentially blow away gas that would have ended up in the star and increased its mass. People have suspected this might be happening, but, by simulating the entire system, we have a robust understanding of how it works.”
Beyond understanding more about stars, Grudic and Faucher-Giguère believe STARFORGE can help us learn more about the universe and even ourselves.
“Understanding galaxy formation hinges on assumptions about star formation,” Grudic said. “If we can understand star formation, then we can understand galaxy formation. And by understanding galaxy formation, we can understand more about what the universe is made of. Understanding where we come from and how we’re situated in the universe ultimately hinges on understanding the origins of stars.”
“Knowing the mass of a star tells us its brightness as well as what kinds of nuclear reactions are happening inside it,” Faucher-Giguère said. “With that, we can learn more about the elements that are synthesized in stars, like carbon and oxygen — elements that we are also made of.”
Reference: “STARFORGE: Toward a comprehensive numerical mode of star cluster formation and feedback” by Michael Y Grudic, Dávid Guszejnov, Philip F Hopkins, Stella S R Offner and Claude-André Faucher-Giguére, 17 May 2021, Monthly Notices of the Royal Astronomical Society.
The study was supported by the National Science Foundation and NASA.
Amazing huh? Pity it’s nothing like reality.
It’s a lot like reality, it is the whole point.
Since 2018ish this is where the science edge in cosmology lies:
“Perhaps the simulations’ single biggest lesson so far is not that scientists need to revise their overarching theory of cosmology, but rather that problems lurk in their understanding of astrophysics at smaller scales. In particular, their theory of star formation comes up wanting, Springel says. To produce realistic galaxies, modelers must drastically reduce the rate at which clouds of gas form stars from what astrophysicists expect, he says. “Basically, the molecular clouds form stars 100 times slower than you’d think,” he says.”
[“Galaxy simulations are at last matching reality—and producing surprising insights into cosmic evolution”, Science]
Since then there was found a factor 10 difference in star formation rate between massive and disperse molecular clouds, and the STRAFORGE adds another factor 10:
“When the researchers ran the simulation without accounting for jets, the stars ended up much too large — 10 times the mass of the sun.”
There is also consistency on all scales:
“In summary, the authors of today’s paper have shown that the KS relation that has been used for years in extragalactic studies has a local analog. This is particularly interesting as the various clouds in their sample have a wide range of physical properties. This correlation implies that star formation is regulated by processes on small scales, including stellar outflows or turbulence, rather than galaxy-scale effects such as supernovae and galactic properties.”
[“Molecular Clouds All the Way Down”, AAS Nova]
The problem lies rather in that it is now uncertain if jet formation suffice to explain molecular cloud collapse:
“Current measurements of the amount of mass directly launched by protostars in winds or jets suggest that this additional factor is not sufficient. Measurements of the molecular gas with millimeter interferometry are needed to determine whether slower, higher-density flows entrained by the outflows are responsible for the halting of infall/accretion and the ∼30%–40% star formation efficiencies. If they are not, mechanisms other than feedback may be required.”
[ https://authors.library.caltech.edu/108886/1/Habel_2021_ApJ_911_153.pdf ]
Close, but not quite. Yet, there may be reason to uncork the champagne soon!