Question

When a star erupts in a supernova explosion, huge numbers of electron neutrinos are formed in nuclear reactions. Such neutrinos from the 1987A supernova in the relatively nearby Magellanic Cloud were observed within hours of the initial brightening, indicating they traveled to earth at approximately the speed of light. Explain how this data can be used to set an upper limit on the mass of the neutrino, noting that if the mass is small the neutrinos could travel very close to the speed of light and have a reasonable energy (on the order of MeV).

a) Neutrinos with mass travel slower
b) Neutrinos with mass have lower energy
c) Massless neutrinos travel at the speed of light
d) Neutrinos with mass cannot reach the Earth

Answer 1

The observation of neutrinos from the 1987A supernova reaching Earth at nearly the speed of light can be used to set an upper limit on their mass.

Step-by-step explanation:

Neutrinos are subatomic particles that are created in huge numbers during a supernova explosion.

The observation of electron neutrinos from the 1987A supernova in the Magellanic Cloud, which is relatively close to Earth, within hours of the initial brightening suggests that these neutrinos traveled to Earth at approximately the speed of light.

This data can be used to set an upper limit on the mass of the neutrino.

If neutrinos have a significant mass, they would not be able to travel at the speed of light.

However, if the mass of the neutrino is small, it would be possible for them to travel very close to the speed of light and have a reasonable energy.

Therefore, based on the observation of neutrinos from the supernova reaching Earth at nearly the speed of light, we can conclude that neutrinos are either massless or have a very small mass.