Halo of neutrinos alters physics of exploding stars

August 21, 2012
Inside the core of a supernova explosion of a 15 solar mass progenitor star. On the left: the density in of matter in grams per cubic centimeter. On the right: the correction needed to account for halo neutrinos when calculation the evolution of neutrion flavors as they stream from the core of the star.

Sparse halos of neutrinos within the hearts of exploding stars exert a previously unrecognized influence on the physics of the explosion and may alter which elements can be forged by these violent events.

John Cherry, a graduate student at UC San Diego, models , including a type called a core-collapse . As these stars run out of fuel, their cores suddenly collapse to form a neutron star, which quickly rebounds sending seas of through the surrounding stellar envelope and out into space.

Even as the collapsed core is rebounding, the rest of the star is still falling inward. Plumes of matter sink, accreting onto the core. "This matter is actually causing some small fraction of neutrinos to bounce at wide angles and cross the of neutrinos coming from the core," Cherry said.

Astrophysicists knew that the heart of that envelope contained these scattered neutrinos, but because they are relatively few compared with the numbers streaming from the core, they thought their influence on the physics of these explosions would be so minor it could be ignored. Not so, Cherry and colleagues demonstrated in a paper they published in Physics Review Letters. They showed that neutrinos streaming from the core interacted with halo neutrinos far more often than anticipated.

Cherry calculated how often that might occur and how large a difference it would make to their models of neutrinos within . "What was so startling about this is that nowhere was the correction less than 14 percent. That's enough that you need to worry about it," he said. Indeed, the some places in the outer regions of the envelope require as much as a 10 fold correction.

Neutrinos are famously aloof particles that seldom interact with other matter. "The way neutrinos interact in matter depends on what we call 'flavor'," said George Fuller, professor of physics at UC San Diego who leads the neutrino-modeling research group and is a co-author of the paper.

When neutrinos meet, they "scatter" off one another and in the process can change their flavor. The influence is much greater than physicists thought in the outer halo of neutrinos. "Even though few neutrinos are scattered in funny directions, they can completely dominate how the neutrinos change their favors," Fuller said.

And the balance of neutrino flavors determines many important things."The neutrinos are the engine that drives the exploding star," Cherry said. "What's going on with neutrinos sets the entire stage for what's happening in the explosion."

These stars also forge new elements, and neutrino flavor influences this process as well.

"Those neutrino flavor states allow the neutrinos to change protons to neutrons or neutrons to protons." Cherry said. "What matter is produced, what kinds of atoms, elements are produced by these supernovas are changed dramatically if you change the flavor content of neutrinos."

Explore further: CERN neutrino project on target

Related Stories

CERN neutrino project on target

August 16, 2005

Scientists at CERN announced the completion of the target assembly for the CERN neutrinos to Gran Sasso project, CNGS. On schedule for start-up in May 2006, CNGS will send a beam of neutrinos through the Earth to the Gran ...

New results confirm standard neutrino theory

February 16, 2010

(PhysOrg.com) -- In its search for a better understanding of the mysterious neutrinos, a group of experimenters at DOE’s Fermi National Accelerator Laboratory has announced results that confirm the theory of neutrino oscillations ...

Neutrinos change flavors while crossing Japan

June 15, 2011

By shooting a beam of neutrinos through a small slice of the Earth under Japan, physicists say they've caught the particles changing their stripes in new ways. These observations may one day help explain why the universe ...

New software models for understanding neutrinos

June 6, 2012

Neutrinos are neutral elementary particles created by nuclear reactions such as those in our Sun and other stars. EU researchers sought to advance our understanding of their interactions in deep space with new mathematical ...

Recommended for you

'Material universe' yields surprising new particle

November 25, 2015

An international team of researchers has predicted the existence of a new type of particle called the type-II Weyl fermion in metallic materials. When subjected to a magnetic field, the materials containing the particle act ...

CERN collides heavy nuclei at new record high energy

November 25, 2015

The world's most powerful accelerator, the 27 km long Large Hadron Collider (LHC) operating at CERN in Geneva established collisions between lead nuclei, this morning, at the highest energies ever. The LHC has been colliding ...

Exploring the physics of a chocolate fountain

November 24, 2015

A mathematics student has worked out the secrets of how chocolate behaves in a chocolate fountain, answering the age-old question of why the falling 'curtain' of chocolate surprisingly pulls inwards rather than going straight ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.