Supernova or black hole: Neutrino ‘flavor’ may determine the fate of dying stars

As a star nears the end of its life, it faces two very different fates: It can explode as a supernova, leaving behind a neutron star, or collapse and become a black hole. What determines the outcome remains one of astrophysics’ great unanswered questions.

Now, a new study from the University of Copenhagen shows that neutrinos—also known as “ghost particles”—and their ability to change “flavor” may play a far greater role in determining the fate of a dying massive star.

This “flavor change”—or “neutrino flavor conversion”—means that neutrinos switch from one type to another. Their type, or flavor, affects how they interact with matter in the cores of dying stars.

“We have long known that neutrinos can switch between different flavors. But we generally assumed that this had no effect on the outcome of the explosion itself. Our new research findings suggest that this flavor can tell us something about the star’s fate,” says Mariam Gogilashvili, a postdoctoral researcher at the Niels Bohr Institute and lead author of the study.

195 simulations of dying massive stars

Although scientists have known about neutrino flavor conversion for many years, incorporating it into supernova simulations has been too computationally demanding.

“Simulating the death of a massive star is something that is pretty much at the frontier of what we can do computationally at the moment. That is because it is a problem involving a great deal of physics and it is extremely expensive computationally,” says Irene Tamborra, a professor at the Niels Bohr Institute, head of the Particle Astrophysics group and the study’s second author.

In their work published in the journal Physical Review D, the two astrophysicists developed a simplified model to investigate the significance of neutrino flavor changes in supernova simulations.

The researchers simulated the collapse of 195 stars with masses between nine and 120 times the mass of the sun. They compared models “with” and “without” neutrino flavor conversion and investigated what happened when the process was triggered at different densities within the star.

They then assessed whether the stars exploded as supernovae or collapsed into black holes. The results showed that “the behavior of neutrinos can significantly alter the outcome,” particularly for stars with masses between 16 and 30 solar masses.

“It was a really exciting moment when we put all 195 simulations side by side and saw a whole range of stars flip from exploding to failing. Seeing such a clear pattern across so many stars told us that neutrino flavor conversion is something we simply cannot leave out when we try to understand how massive stars end their lives,” says Gogilashvili.

Closer to understanding astronomical mysteries

The results of Gogilashvili and Tamborra’s study suggest that the behavior of neutrinos may help explain observations that have long challenged researchers.

These include what is known as the “supernova rate problem,” in which researchers observe significantly fewer supernovae in the universe than theoretical models predict.

“Normally, we detect a supernova because the explosion shines very brightly. But if a star collapses directly into a black hole without a visible explosion, or is obscured by dust, it can effectively ‘disappear’ from our counts. Our results therefore suggest that there is a mechanism that could make such ‘failed supernovae’ more likely,” says Gogilashvili.

“This could therefore not only give us better tools to predict a dying star’s fate, but it may also help explain why observations do not always match theoretical predictions,” adds Tamborra.

It’s all connected

Getting closer to understanding what happens when stars die is not just about black holes and neutron stars, theory and observations. It’s also about you and me.

Massive stars synthesize heavy elements during their lifetimes. When a star explodes as a supernova, these elements are released into the universe, where they later help form planets and life.

“When we study how massive stars live and die, we are also investigating the origins of many of the elements that make up the universe and ourselves. In this way, questions about dying stars are linked to questions about our own origins,” concludes Tamborra.

Who’s behind this story?

Swati Mestri

Swati Mestri holds a bachelor’s degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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