First giant molecular cloud simulation for star formation that includes jets, radiation, winds, supernovae
Star formation is arguably the most important process in the universe. During their lifetime, and then upon death, stars produce all chemical elements except hydrogen and helium (produced in the Big Bang). In their youth, stars fuel the birth of planets and smaller bodies, and their demise results in supernovas, super-dense bodies such as black holes, neutron stars or white dwarfs, and nebulae.
Stars radiate their abundant energy into the cosmos at wavelengths across the spectrum, warming the surfaces of planets, facilitating interstellar chemistry and illuminating galaxies in all cosmic eras. Star formation, by determining the locations, abundances and relative masses of stars, regulates the palette of the sky and its rainbow of attributes.
Stars in the universe form, at least in our current era, when massive clouds of molecular gas collapse through gravity. But in the Milky Way, this process is very inefficient; only about 1% of the available material ends up in a star. Astronomers believe that one reason is that star-forming cores cannot develop due to the outward pressure of turbulent supersonic gas movements (that is, gas moving faster than the speed of sound) and from outflows from supernovae, winds or jets produced by an earlier generation of stars. At least this is the picture for low mass stars.
However, observations of young massive stars sometimes suggest the opposite conclusion, which is that high-mass stars form exactly where gas turbulence prevents the development of low-mass stars until enough mass is accumulated to give birth to massive stars. The many complex, intertwined physical processes involved leave many puzzles, including why stars form with low efficiency, why they have the specific mass they have, why and how they form in clusters, and why some are in multiple systems and some are not. †
Computer simulations can provide fundamental insights into these questions. Astronomers have been refining their codes for decades and comparing them with observations. The task is daunting: Not only are many different physical processes at work, they influence each other, as critical steps take place over spatial scales from hundreds of light years to the immediate vicinity of the embryonic star, and time scales from millions of years to days. A realistic simulation of star formation should somehow accurately explain all of this.
CfA astronomer Anna Rosen and her colleagues have developed the first giant molecular cloud simulation that tracks the formation of individual stars and their feedback from jets, radiation, wind and supernovae. It builds on their previous codes that included gravity, magnetic fields and turbulence, but yielded an unrealistically high star-forming efficiency and produced an excess of massive stars.
The new numerical simulation traces star formation in a cloud over about 8 million years, using about 160 million steps, some separated by times of just a day. It bypasses the flaws of previous codes, but maintains overall consistency with their more accurate results. It also comes to important conclusions, including that protostellar jets are a dominant source of feedback that inhibits star birth — supernova feedback occurs too late in the birth cycle to seriously disrupt the development of other stars in the nursery.
Published in Monthly Notices from the Royal Astronomical Societythis landmark achievement is the first numerical simulation of any kind to model the formation of a stellar cluster while tracking the formation, accretion, motion, evolution and feedback of individual stars and protostars, with feedback from all major channels: protostellar jets, stellar winds, stellar radiation and collapse supernovas.
‘Yoyo stars’ responsible for cosmic bubbles outside the center
Michael Y Grudić et al, The dynamics and outcome of star formation with jets, radiation, winds and supernovae in concert, Monthly Notices from the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac526
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