190
R. N. Mohapatra
25.1 Why Look for Neutrinos from Extra-Solar
Sources and Extra-Galactic Sources
There is a lot to be learned about the various stars and galaxies in the universe.
That includes their evolution, the nature of stellar collapse, the mechanism of
supernova explosion, and more. The more we learn, the more we expand the
frontier of knowledge and the better off we are as a society. Deeper knowledge
helps us in making useful decisions. The only tool we had before for probing
the universe was looking at electromagnetic waves (such as light) from the
various distant sources in the sky, using Earth-based telescopes. We had and
still have telescopes of different strengths, the famous Hubble Space Telescope
being a shining example. We had infrared telescopes and radio telescopes in
the past. Major discoveries were made using these devices e.g. the first binary
pulsars were discovered by Hulse and Taylor using 1000 ft. diameter radio
telescopes. Quasars and exoplanets are other examples of discoveries made
using radio telescopes. Also recently, a new class of mysterious cosmic objects
known as “fast radio bursts” have been discovered using radio telescopes. All
these have inspired a great deal of theoretical activity regarding the nature of
different astrophysical objects. The infrared telescopes, such as SPITZER and
IRAS telescopes, made their mark with important discoveries like previously
unknown rings of Saturn (discovered by Spitzer). Then there is the James
Webb Space Telescope, (JWST) being made ready by NASA, which is going
to be launched soon. Using both optical and infrared frequencies, JWST will
look further back into the universe to see the first galaxies that formed in the
universe. This will throw light on the origin of galaxies and how they originally
formed from the almost uniform cosmic soup.
However, these devices involving electromagnetic radiation of different
wavelengths have limitations: they get light that is scattered and absorbed in its
path from the source to the Earth where the telescopes are. Similarly, these light
beams only provide information about the surface of the source and not the
interior, since the light from the interior gets distorted in its path through the
outer layers of the emitting object. While they are useful and have provided
invaluable information about galaxies, stars, and planets, better devices are
called for to learn more. For example, what is going on in the solar core cannot
be fully understood using light.
The neutrinos on the other hand have very little interaction with the
medium they travel through in their journey from the source to the Earth,
and therefore preserve the information more accurately. Thus, if we want to
understand in great detail the stars and galaxies, neutrinos provide a more
R. N. Mohapatra
25.1 Why Look for Neutrinos from Extra-Solar
Sources and Extra-Galactic Sources
There is a lot to be learned about the various stars and galaxies in the universe.
That includes their evolution, the nature of stellar collapse, the mechanism of
supernova explosion, and more. The more we learn, the more we expand the
frontier of knowledge and the better off we are as a society. Deeper knowledge
helps us in making useful decisions. The only tool we had before for probing
the universe was looking at electromagnetic waves (such as light) from the
various distant sources in the sky, using Earth-based telescopes. We had and
still have telescopes of different strengths, the famous Hubble Space Telescope
being a shining example. We had infrared telescopes and radio telescopes in
the past. Major discoveries were made using these devices e.g. the first binary
pulsars were discovered by Hulse and Taylor using 1000 ft. diameter radio
telescopes. Quasars and exoplanets are other examples of discoveries made
using radio telescopes. Also recently, a new class of mysterious cosmic objects
known as “fast radio bursts” have been discovered using radio telescopes. All
these have inspired a great deal of theoretical activity regarding the nature of
different astrophysical objects. The infrared telescopes, such as SPITZER and
IRAS telescopes, made their mark with important discoveries like previously
unknown rings of Saturn (discovered by Spitzer). Then there is the James
Webb Space Telescope, (JWST) being made ready by NASA, which is going
to be launched soon. Using both optical and infrared frequencies, JWST will
look further back into the universe to see the first galaxies that formed in the
universe. This will throw light on the origin of galaxies and how they originally
formed from the almost uniform cosmic soup.
However, these devices involving electromagnetic radiation of different
wavelengths have limitations: they get light that is scattered and absorbed in its
path from the source to the Earth where the telescopes are. Similarly, these light
beams only provide information about the surface of the source and not the
interior, since the light from the interior gets distorted in its path through the
outer layers of the emitting object. While they are useful and have provided
invaluable information about galaxies, stars, and planets, better devices are
called for to learn more. For example, what is going on in the solar core cannot
be fully understood using light.
The neutrinos on the other hand have very little interaction with the
medium they travel through in their journey from the source to the Earth,
and therefore preserve the information more accurately. Thus, if we want to
understand in great detail the stars and galaxies, neutrinos provide a more