Supernovas and neutrino formation in our galaxy and the Large Magellanic Cloud [1]
Supernovas are now recognised as being instrumental in neutrino formation, and Supernova 1987A, a supernova in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, whose demise is illustrated on the previous page, was the first occasion in which neutrinos have been observed from an astronomical source other than the sun. As a result, scientists detected 25 neutrinos in Japan, the U.S. and Russia. Three hours later optical light came from a shock wave breaking through the star's surface. By November x-rays and gamma rays arrived from decaying radioactive elements and infrared light came from new heavy elements, all created in the explosion. [2]
The number may have been small, some two dozen in all, but their significance was immensely greater, for they allow astronomers and astrophysicists a peek at the interior of a massive star towards the end of its life. They also provide a rare opportunity to understand how these particles behave under extreme conditions that cannot be replicated in a laboratory. For these reasons, scientists are waiting none too patiently for the next supernova explosion which may take place hopefully nearby and maybe even within our own galaxy.
Somewhat surprisingly no supernova has been seen in the Milky Way since 1604 when observers including Johannes Kepler, noticed a “new star”’ in the constellation Ophiuchus. At its peak, this supernova was so bright that it was visible during daytime. Three decades earlier, in 1572, observers in Europe, including Tycho Brahe, had witnessed another. The current evidence is that both these supernova resulted from the explosion of a stellar cinder known as a white dwarf, which either cannibalised material from a companion star or merged with another white dwarf, rather than from the core collapse of a massive star at the end of its life.
Should present day scientists be fortunate enough to witness similar events in our galaxy, detectors will record how the number and energy of the arriving neutrinos evolve over time, which will provide valuable information about how the explosion evolves. Scientists will also be able to determine whether the star’s core collapses all the way into a black hole, from which nothing – not even neutrinos – can escape, or whether it stops short, forging a neutron star instead. If a black hole were to form, the stream of neutrinos racing outward from the supernova would come to a sudden halt. If however the result is a neutron star, this “stellar cinder” would continue emitting neutrinos for about 10 seconds while it cools down, so the neutron stream should dwindle slowly instead of cutting off abruptly.
A galactic supernova would also shed light on the nature of the neutrinos themselves – whether there are two heavy mass states plus one light state or the reverse. If there are any anomalies in their behaviour they may well point to new physics beyond the Standard Model. Scientists may also be able to pin point the exact moment the neutron star forms. Current detectors are sensitive only to one variety of neutrinos, the electron antineutrino. (Remember that they come in 3 varieties or flavours: electron, muon and tau).
All the evidence suggest that aging, giant stars such as Betelgeuse and Eta Carinae will meet their demise in the “near future”, but in cosmic terms this could still mean several thousand years. The waiting game goes on!
[1] For this material, see Ray Jayawardhana, “Coming soon: A Supernova near you”, Scientific American, December 2013, 60 at 64-5. See also “From a galaxy far, far away, scientists redefine universe”, SMH, 23-24 Nov 2013. For neutrinos, see also The path to the standard model
[2] Ann Finkbeiner, "Messengers from the sky" Scientific American, May 2018.
The number may have been small, some two dozen in all, but their significance was immensely greater, for they allow astronomers and astrophysicists a peek at the interior of a massive star towards the end of its life. They also provide a rare opportunity to understand how these particles behave under extreme conditions that cannot be replicated in a laboratory. For these reasons, scientists are waiting none too patiently for the next supernova explosion which may take place hopefully nearby and maybe even within our own galaxy.
Somewhat surprisingly no supernova has been seen in the Milky Way since 1604 when observers including Johannes Kepler, noticed a “new star”’ in the constellation Ophiuchus. At its peak, this supernova was so bright that it was visible during daytime. Three decades earlier, in 1572, observers in Europe, including Tycho Brahe, had witnessed another. The current evidence is that both these supernova resulted from the explosion of a stellar cinder known as a white dwarf, which either cannibalised material from a companion star or merged with another white dwarf, rather than from the core collapse of a massive star at the end of its life.
Should present day scientists be fortunate enough to witness similar events in our galaxy, detectors will record how the number and energy of the arriving neutrinos evolve over time, which will provide valuable information about how the explosion evolves. Scientists will also be able to determine whether the star’s core collapses all the way into a black hole, from which nothing – not even neutrinos – can escape, or whether it stops short, forging a neutron star instead. If a black hole were to form, the stream of neutrinos racing outward from the supernova would come to a sudden halt. If however the result is a neutron star, this “stellar cinder” would continue emitting neutrinos for about 10 seconds while it cools down, so the neutron stream should dwindle slowly instead of cutting off abruptly.
A galactic supernova would also shed light on the nature of the neutrinos themselves – whether there are two heavy mass states plus one light state or the reverse. If there are any anomalies in their behaviour they may well point to new physics beyond the Standard Model. Scientists may also be able to pin point the exact moment the neutron star forms. Current detectors are sensitive only to one variety of neutrinos, the electron antineutrino. (Remember that they come in 3 varieties or flavours: electron, muon and tau).
All the evidence suggest that aging, giant stars such as Betelgeuse and Eta Carinae will meet their demise in the “near future”, but in cosmic terms this could still mean several thousand years. The waiting game goes on!
[1] For this material, see Ray Jayawardhana, “Coming soon: A Supernova near you”, Scientific American, December 2013, 60 at 64-5. See also “From a galaxy far, far away, scientists redefine universe”, SMH, 23-24 Nov 2013. For neutrinos, see also The path to the standard model
[2] Ann Finkbeiner, "Messengers from the sky" Scientific American, May 2018.