Super-K |
Extra-Terrestrial Physics Laboratories
Because of their astronomical sizes, stars offer unique opportunities to
study physics under extreme conditions. Here, I mention two ways
in which stars are used to probe physics under conditions not accessible
or not easily accessible to experimenters on Earth.
Properties of Sub-Nuclear Matter
Interestingly, stars, those massive and monstrous beasties, allow us to
study the physics of materials on sub-nuclear scales. For example,
there are exotic stars known as Neutron Stars
and
Strange Stars.
Neutron
stars are stars roughly as massive as the Sun, i.e., 2x1030
kilograms
or roughly 1057 particles
(neutrons, protons, and electrons) but with
sizes on the order of Eugene (10-20 kilometers in diameter). The Sun has
a diameter of 1.4 million kilometers. The large mass and small size means
that neutron stars have extremely
high densities.
Roughly speaking, the density of a neutron star is so high that
the particles are only
3 x 10-13 centimeters
apart. This is roughly the separation between the protons and neutrons
in the nuclei of atoms.
Neutron stars, in a certain sense, can be viewed
as huge nuclei whose structures are determined by
the Nuclear Force and the Gravitational Force.
This is an important feature of neutron stars
because the nature of the
Strong (Nuclear) Force is not well-understood at high densities.
The study of
neutron stars
may someday be able to shed light on the question of the nature
of one of the fundamental forces of the sub-nuclear Universe.
An even more exotic possibility is known as strange
stars. Strange stars exist in the density range between neutron stars
and black holes. Matter, such as protons and neutrons, are composed of
fundamental particles known as quarks. At very high densities, it is more
favorable for the quarks to be free and stars composed of quarks have
been theorized to exist. However, it is more complicated
than this as particles
known as
strange quarks dominate the stars. The
up and
down quarks
form the ordinary neutrons and protons (sometimes called nucleons).
In a loose sense, strange stars
may be viewed as huge hadrons.
Strange stars have not been shown to exist conclusively, but there are
suggestions that they may exist in nature
(
strange stars,
Chandra site).
Properties of Sub-Nuclear Particles
Stars are very large, high energy
nuclear reactors (much larger than any which can be
produced on the Earth), as such, they offer the possibility of studying
processes not easily accessible in Terrestrial accelerators. One example of
this is the long-running
Solar Neutrino Experiment.
The Sun (as do around 90 % of the stars in the Universe) produces energy by
fusing 4 hydrogen nuclei into 1 helium nucleus. In this process, a small
amount of mass is converted into energy which accounts for the huge luminosity
of the Sun. In addition to the energy (radiation), small sub-atomic particles
known as neutrinos are produced.
In the 1960's, Ray Davis proposed
an experiment designed to detect solar neutrinos. In his experiment
he placed a vat of 100,000 gallons of cleaning fluid (which contains
chlorine) deep in an old mine to detect neutrinos. The interaction between
neutrinos and chlorine is so weak that Davis expected to detect
only a neutrino or so per day!! This and other more recent neutrino experiments
are very difficult, but are extremely important experiments because:
The energy (radiation) is produced by nuclear reactions in the core of the
Sun and the energy must slowly work its way outward to the surface of the
Sun in order to be radiated into space. Due to the great size and density
of the Sun, this trip takes on the order 170 thousand years to complete.
What this means is that the light we
see coming from the Sun today was produced in the distant past.
The radiation we receive from the Sun is thus not a good indicator of what
is going on in the core of the Sun today.
Neutrinos on the other hand are ghost-like particles which
interact with matter only very weakly.
This means that neutrinos will essentially pass straight through the
dense layers of the Sun; reaching the Earth in only 8.3 minutes. The
neutrinos are thus very sensitive probes of the current state of
Sun's interior. It is important for us to confirm that the Sun produces
neutrinos at the correct rate. There are currently
ongoing
Solar Neutrino
Experiments, in addition, to many completed experiments.
The startling result of the early experiments was that the
number of neutrinos detected was only 1/2 to
1/3 of that predicted by our theoretical models of the Sun.
Naively, this would have forced us to
conclude that nuclear reactions, although on-going
in the center of the Sun, were proceeding at a slower rate than
predicted (based on observations of the luminosity of the Sun)!
Was this conclusion correct? Well, no.
Based on more recent experiments, it appears that there were
problems with our understanding of the properties of the
neutrino.
There are newer theories that postulate that
neutrinos are not mass-less and that they are chamaeleon-like in nature in
that they can switch between various forms. The early experiments were
sensitive to primarily the form of neutrinos known as electron neutrinos.
They were much less sensitive to other forms of neutrinos, such as
tau neutrinos and muon neutrinos.
The SNO group group has
announced results of an experiment that is sensitive to all types of
neurtinos. Their results support the idea of
neutrino oscillations. This is a major breakthrough in our knowledge of
fundamental particles.
Because of their astronomical sizes, stars offer unique opportunities to study physics under extreme conditions. Here, I mention two ways in which stars are used to probe physics under conditions not accessible or not easily accessible to experimenters on Earth.
Interestingly, stars, those massive and monstrous beasties, allow us to
study the physics of materials on sub-nuclear scales. For example,
there are exotic stars known as Neutron Stars
and
Strange Stars.
|
|
Neutron stars are stars roughly as massive as the Sun, i.e., 2x1030 kilograms or roughly 1057 particles (neutrons, protons, and electrons) but with sizes on the order of Eugene (10-20 kilometers in diameter). The Sun has a diameter of 1.4 million kilometers. The large mass and small size means that neutron stars have extremely high densities. Roughly speaking, the density of a neutron star is so high that the particles are only 3 x 10-13 centimeters apart. This is roughly the separation between the protons and neutrons in the nuclei of atoms. Neutron stars, in a certain sense, can be viewed as huge nuclei whose structures are determined by the Nuclear Force and the Gravitational Force. This is an important feature of neutron stars because the nature of the Strong (Nuclear) Force is not well-understood at high densities. The study of neutron stars may someday be able to shed light on the question of the nature of one of the fundamental forces of the sub-nuclear Universe. |
An even more exotic possibility is known as strange stars. Strange stars exist in the density range between neutron stars and black holes. Matter, such as protons and neutrons, are composed of fundamental particles known as quarks. At very high densities, it is more favorable for the quarks to be free and stars composed of quarks have been theorized to exist. However, it is more complicated than this as particles known as strange quarks dominate the stars. The up and down quarks form the ordinary neutrons and protons (sometimes called nucleons). In a loose sense, strange stars may be viewed as huge hadrons. Strange stars have not been shown to exist conclusively, but there are suggestions that they may exist in nature ( strange stars, Chandra site).
Stars are very large, high energy nuclear reactors (much larger than any which can be produced on the Earth), as such, they offer the possibility of studying processes not easily accessible in Terrestrial accelerators. One example of this is the long-running Solar Neutrino Experiment.
The Sun (as do around 90 % of the stars in the Universe) produces energy by fusing 4 hydrogen nuclei into 1 helium nucleus. In this process, a small amount of mass is converted into energy which accounts for the huge luminosity of the Sun. In addition to the energy (radiation), small sub-atomic particles known as neutrinos are produced. In the 1960's, Ray Davis proposed an experiment designed to detect solar neutrinos. In his experiment he placed a vat of 100,000 gallons of cleaning fluid (which contains chlorine) deep in an old mine to detect neutrinos. The interaction between neutrinos and chlorine is so weak that Davis expected to detect only a neutrino or so per day!! This and other more recent neutrino experiments are very difficult, but are extremely important experiments because:
|
|
The energy (radiation) is produced by nuclear reactions in the core of the Sun and the energy must slowly work its way outward to the surface of the Sun in order to be radiated into space. Due to the great size and density of the Sun, this trip takes on the order 170 thousand years to complete. What this means is that the light we see coming from the Sun today was produced in the distant past. The radiation we receive from the Sun is thus not a good indicator of what is going on in the core of the Sun today. |
Neutrinos on the other hand are ghost-like particles which interact with matter only very weakly. This means that neutrinos will essentially pass straight through the dense layers of the Sun; reaching the Earth in only 8.3 minutes. The neutrinos are thus very sensitive probes of the current state of Sun's interior. It is important for us to confirm that the Sun produces neutrinos at the correct rate. There are currently ongoing Solar Neutrino Experiments, in addition, to many completed experiments.
The startling result of the early experiments was that the number of neutrinos detected was only 1/2 to 1/3 of that predicted by our theoretical models of the Sun. Naively, this would have forced us to conclude that nuclear reactions, although on-going in the center of the Sun, were proceeding at a slower rate than predicted (based on observations of the luminosity of the Sun)! Was this conclusion correct? Well, no. Based on more recent experiments, it appears that there were problems with our understanding of the properties of the neutrino. There are newer theories that postulate that neutrinos are not mass-less and that they are chamaeleon-like in nature in that they can switch between various forms. The early experiments were sensitive to primarily the form of neutrinos known as electron neutrinos. They were much less sensitive to other forms of neutrinos, such as tau neutrinos and muon neutrinos.
The SNO group group has announced results of an experiment that is sensitive to all types of neurtinos. Their results support the idea of neutrino oscillations. This is a major breakthrough in our knowledge of fundamental particles.
