How Neutrinos Aid In the Death of Massive Stars
Why in News?
- Many stars, towards the end of their lifetimes, form supernovas – massive explosions that send their outer layers shooting into the surrounding space.
- Most of the energy of the supernova is carried away by neutrinos – tiny particles with no charge and which interact weakly with matter.
- Researching the mechanisms of the so called Type II supernovas, a team from IIT Guwahati has come up with new insights into the part played by neutrinos in this dramatic death of massive stars.
Fate of the star
- All stars burn nuclear fuel in their cores to produce energy.
- The heat generates internal pressure which pushes outwards and prevents the star from collapsing inward due to the action of gravity on its own mass.
- But when the star ages and runs out of fuel to burn, it starts to cool inside.
- This causes a lowering of its internal pressure and therefore the force of gravity wins; the star starts to collapse inwards.
- This builds up shock waves because it happens very suddenly, and the shock wave sends the outer material of the star flying.
- This is what is perceived as a supernova. This happens in very massive stars.
- In stars that are more than eight times as massive as the Sun, the supernova is accompanied by a collapsing of the inner material of the dying star – this is also known as core collapse supernova or Type II supernova.
- The collapsing core may form a black hole or a neutron star, according as its mass.
Three flavours
- Neutrinos come in three ‘flavours’, another name for ‘types’, and each flavour is associated with a light elementary particle.
- For instance, the electron-neutrino is associated with the electron; the muon-neutrino with the muon and the tau-neutrino with the tau particle.
- As they spew out of the raging supernova, the neutrinos can change from one flavour to another in a process known as neutrino oscillations.
- Due to the high density and energy of the supernova, several interesting features emerge as this is a nonlinear phenomenon:
- “This [phenomenon] may generate neutrino oscillations happening simultaneously over different energies (unlike normal neutrino oscillation), termed collective neutrino oscillation.
- The oscillation result may dramatically change when one allows the evolution with the angular asymmetry, the oscillations can happen at a nanosecond time scale, termed fast oscillation.
- Models of this process, dubbed the effective two-flavour models, have only taken into account the asymmetry between electron neutrino and the corresponding antineutrino.
- Researchers from IIT Guwahati claim that a three-flavour model is needed to predict well the dynamics of the supernova.
Fast oscillations
- The fast oscillations are important because the researchers find that these can decide the flavour information of the supernova neutrinos.
- So far, this has not been done, and models have only kept terms involving a neutrino and its corresponding anti-neutrino.
- Find that fast nonlinear oscillations of neutrinos are sensitive to three flavours, and neglecting the third flavour may yield the wrong answer.
- “Thus, the presence of …[asymmetry between] the muon neutrinos and antineutrinos will be crucial for the neutrino oscillations, in turn influencing the supernova mechanism.”
- Understanding this is important when one wants to measure the influence of neutrinos and their oscillations on supernova mechanism and heavy element synthesis in stellar environments.
The Hindu