Important clues into cause and process of death of stars revealed by IIT Guwahati researchers

Death of stars: IIT Guwahati researchers find key clues about the death of stars! Working with researchers from Germany-based Max Planck Institute for Physics and US’ Northwestern University, researchers from the eminent Indian Institute of Technology (IIT), Guwahati, have found major clues to better understand the death of stars. Moreover, they have also been able to point out the problems that existing models had. The team of researchers has revealed that the clue to the death of these stars lies in tiny subatomic particles called neutrinos in the supernovae, and have said that all the three species of neutrinos are important, instead of commonly believed two.

The finding is very important and the astrophysics community from all over the world has taken an interest in the research, which has been published in Physics Review Letters journal and accessed by Financial Express Online.

In a statement issued by IIT Guwahati, lead researcher Dr Sovan Chakraborty carried out the research with research scholar Madhurima Chakraborty, along with Max Planck Institute’s postdoctoral fellow Dr Francesco Capozzi and Northwestern University postdoctoral fellow Dr Manibrata Sen.

Supernovae and neutrinos

Supernovae are super explosions that occur when large massive stars die, and they are believed to be the origin of the synthesis of nature’s heavy elements and of new stars. When the life of a massive star ends, they collapse, which leads to a great shock wave causing it to explode. This explosion is so bright that it outshines, for a brief period of time, any other star present in the galaxy.

It is important to study such an explosion, called supernova, and the particles released during the event, because the matter making up the universe is almost entirely a result of such massive explosions.

The statement quoted Dr Sovan Chakraborty as saying that the mechanisms behind the supernovae are not yet solved in their entirety, and continue to be an enigma.

The mystery behind the core collapse mechanism, however, can be solved with the help of neutrinos, the tiny subatomic particles.

A core collapse supernova leads to several particle processes, resulting in the creation of neutrinos. The neutrinos are neutral, however, and have an extremely weak interaction with stellar matter, and thus, are able to escape, while carrying a whopping 99% of the collapsing star’s energy. Therefore, neutrinos are the only matter holding the information from the stars’ deepest interiors.

However, neutrinos in themselves are complex. In the last 70 years or so since their discovery, the scientists have been able to expand their understanding of these particles, but there is still a long way to go. One of the questions facing the scientists about these particles is their flavour structure and different neutrinos’ mass ordering. Neutrinos are of three species – electron, mu and tau – and the only natural source of the creation of neutrinos as well as antineutrinos in substantial amounts is the supernovae, leading to additional complexities.

The researchers pointed out that so far, the existing models of supernovae predicted that antineutrinos as well as the neutrinos species mu and tau were very similar in their properties and clubbed them as one species, leading to simplified problem of the supernovae and neutrinos. This meant that most studies were being carried out with researchers assuming that all these neutrinos and antineutrinos were behaving in the same way when they were ejected from the dying star.

Death of a star: Findings of the study

Dr Sovan said that in extremely dense supernovae core, neutrinos interact with each other, and they might interchange their flavours. This interchanging, however, can happen very rapidly and it can impact the process of the supernova because neutrinos of different species are emitted from the explosion with different angular distribution.

The conversion of flavours is non-linear, Dr Sovan added, and the phenomenon is not confronted in any other sources of the neutrino except the supernovae. For the first time, the research team carried out nonlinear simulations of this rapid conversion between all three species of neutrinos.

This was possible because new simulations of supernovae showed the presence of muons, leading to the production of asymmetry between antineutrinos and muon neutrinos, which was otherwise taken to be zero. This has implied three flavour effects.

Dr Manibrata Sen was quoted by the statement as saying that the study of these three flavours has changed the results drastically as against the results of existing studies. This study, Sen said, can have huge implications for particle and astrophysics of supernovae neutrinos.

The study has clearly demonstrated the relevance of all the three flavours of neutrinos, leading to an incomplete picture of fast flavour exchange if the presence of any species is ignored.