Collective Oscillations, Neutrinos, and Stars
Neutrinos are elementary particles that are very small. These particles, which come in three flavors, have the rare capacity to switch flavors through neutrino oscillations on a regular basis. Neutrinos have mass and act as quantum mechanics predicts, according to the discovery of neutrino oscillation in the 1990s.
Massive stars that explode at the conclusion of their lives are known as supernovas. Nuclear processes create a significant quantity of neutrinos. The three flavors are made using different spectra, or uneven abundances of energy and emission direction. The majority of these neutrinos escape the star, but some return their energy and aid in the formation of heavy nuclear elements. Neutrino oscillations may become unstable in a dense star environment, with their amplitude increasing exponentially over time. These new instabilities, which were predicted by Jim Pantaleone, Alan Kostelecky, and Stuart Samuel in the 1990s and Ray Sawyer in the 2000s, are collective oscillations in which all neutrinos oscillate at the same time. A dense flock of birds, a school of fish, or a mob at the railway station have all been likened to how they are driven to go in the same direction.
A crucial issue remained: what are the circumstances that allow for exponential increase of taste conversions? Basudeb Dasgupta of the Tata Institute of Fundamental Research in Mumbai has published a paper in Physical Review Letters demonstrating that exponential growth may only occur when the spectra of two neutrino flavors overlap at certain energy or emission angle. This conclusion, which is based on a technique developed by Taiki Morinaga of Waseda University, ensures that studying neutrino oscillation instabilities will disclose new information from deep inside the star.
Present and Future Observations
The study of neutrinos from supernovae, as well as their influence on star heating and nucleosynthesis, will reveal insight on neutrinos deep inside them.
A supernova just beyond our galaxy emitted roughly 20 neutrinos in 1987. Astronomers have never observed neutrinos from a dense star before. Unfortunately, these few neutrinos were insufficient to expose the instabilities in collective oscillations.
Existing neutrino observatories, such as Super-K in Japan and IceCube in Antarctica, are expected to record more than ten thousand neutrinos from a supernova in our galaxy in the future. Such an event, which is only projected to happen a few times per century, would be a gold mine for researchers studying neutrinos and supernovae. Insight into these probable neutrino oscillation instabilities would be a major and unique result of a galactic supernova observation, and it would also be the first direct proof for neutrino interactions with each other.
Multi-messenger neutron star merger detections, such as the gravitational wave interferometer LIGO’s detection of the GW170817 event and subsequent studies by optical and infrared instruments, provided precise information regarding the synthesis of heavier elements in these stellar collisions. Several groups of astronomers have deduced from this fact that rare elements like gold and silver, as well as medically vital elements like oxygen, calcium, and iodine, are mostly created in star collisions. The efficiency of synthesis of these elements is affected by neutrino oscillations in the neutron star merger environment. The observed pattern of constituent abundances may offer evidence for collective neutrino oscillation instabilities in future investigations of binary neutron star mergers.
Neutrinos are known for surprising people and resolving discrepancies in particle physics theories. “Experimental discovery of collective oscillations will offer a new window into the depths of distant stars,” adds Dr. Dasgupta, “putting yet another feather in the crown of neutrinos — the great problem solver among elementary particles.”
IMAGE: ARTIST’S IMPRESSION
CREDIT: BASUDEB DASGUPTA