Stars appear to regulate their own masses during formation

Clouds of bright gases swirl in deep space in an illustration produced by the simulation software Starforge.
A simulation of a star-forming region where massive stars drive away gas reserves. (Image credit: Starforge)

Astrophysicists may have discovered that stars set their own mass during star formation. 

The revelation may finally solve the mystery of why stars that are born in radically different conditions across the universe throughout billions of years come to have similar masses, despite the fact the opposite should be true. This puzzle is one that has confounded scientists for decades.

The findings were revealed in the highest resolution 3D simulations of star formation ever created which show that stellar birth seems to be a self-regulating process with feedback from stars determining mass ranges.

Related: Stars: Facts about stellar formation, history and classification

The simulations are the work of the STARFORGE project, which was founded by astrophysicists from a range of institutions including Northwestern University. 

As well as helping astrophysicists between model the mass distribution of stars  — also known as the initial mass function (IMF)  —  the findings could have important implications for the understanding of the life processes of stars and the evolution of galaxies

"Understanding the stellar initial mass function is such an important problem because it impacts astrophysics across the board  —  from nearby planets to distant galaxies," Northwestern astronomer and STARFORGE team member Claude-André Faucher-Giguère said in a statement. "This is 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."

Faucher-Giguère added that this means that the distribution of stellar masses is therefore critical in understanding if planets that orbit stars can potentially sustain life, as well as what distant galaxies look like.

Stars are born in regions of space filled with giant cool clouds of gas and dust when gravity causes the formation of dense clumps of material. As the matter in these clumps falls inwards, it collides, generating heat that helps to birth a new star, or 'protostar.'

These protostars are surrounded by rotating discs of dust and gas, with such a disc capable of forming planets, just as happened in our solar system around 4.6 billion years ago. Whether the planets that form this protoplanetary disc can sustain life depends in part on the mass of their parent star.

Related: Giant galactic bubble is driving star formation, new study finds

That means that star formation and our understanding of it is key to figuring out if life can exist elsewhere in the universe and where this search should be focused in the future. 

"Stars are the atoms of the galaxy," University of Texas at Austin astronomer Stella Offner said in the statement. "Their mass distribution dictates whether planets will be born and if life might develop."

Yet modeling IMF has been difficult for researchers. This is in part because scientists have discovered that no matter where they look in the Milky Way, be it young star clusters or those that are billions of years old, the same ratios of star mass  —  the IMF  —  holds. 

Stars much larger than the sun make up only one percent of newborn stars. For each of these, there are 10 stars with masses like the sun and 30 dwarf stars. This balance is the same in star clusters in our galaxy and in surrounding dwarf galaxies, even though the conditions are very different. The IMF should vary radically too, but it doesn't. Instead, it seems to be universal. 

"For a long time, we have been asking why," Guszejnov said. "Our simulations followed stars from birth to the natural endpoint of their formation to solve this mystery."

The STARFORGE simulations  —  the first to zero in on and follow the formation of single stars in giant gas clouds  —  show that stellar feedback in the form of light emissions and the loss of mass through stellar winds and jets allows young stars to interact with their surroundings. This feedback acts to oppose gravity and shapes mass towards the same distribution. 

Other simulations have accounted for stellar feedback but these are the first to simultaneously model star formation, evolution and dynamics along with feedback and nearby supernova activity to see how these separate elements affect star formation.

The team's research is published in the latest edition of the journal the Monthly Notices of the Royal Astronomical Society.

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Robert Lea
Senior Writer

Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.