If
we observe the course of the evolution of the stars, we will see that there are
billions of stars in the universe at different stages in their stellar journey.
Neutron star is a form of a star located in such a state. Today we will try to
know and understand this neutron star a bit.
In
December 1933, the German scientist Walter Baade and the Swiss scientist Fritz
Zwicky first time suggested that the neutron star could exist. Nearly three and
a half decades after this event, in 1967, the Italian scientist Franco Pacini
noted that neutron stars emit electromagnetic waves by rotating at high speeds
on their axis. Later in the decade, two British scientists, Anthony Hewish and
Jacelyn Bell, discovered the neutron star, which completely corroborated the
earlier estimates of neutron stars given by various scientists. This newly
discovered neutron star was actually a pulsar. Since then, different scientists
have discovered different types of neutron stars in different constellations of
the universe. Some notable facts are that in 1974, American scientists Joseph
Taylor and Russell Hulse first discovered binary neutron stars called
PSR-B1913+16, in 2003, Italian scientist Marta Burgay and her assistant
scientists discovered a binary neutron stars, both of which are neutron stars.
The name of this binary neutron star is PSR-J0737-3039 etc. Apart from this,
scientists from different parts of the world are also working tirelessly in
this regard.
A
star has to go through various stages from creation to its final state. One
such phase is the acquisition of the neutron phase of a star. However, not all
stars have this phase. It depends on the mass of the star. In this case, if the
stages before the neutron phase are not discussed, then this discussion will
remain somewhat incomplete.
In
stars, regardless of their mass, the main driving force is the nuclear fusion
reaction going on inside the star. In this case the hydrogen molecule acts as
fuel and the combination of two hydrogen atoms produces helium. Helium is the
first substance to be produced by the process of nuclear fusion reaction inside
the core of a star. If the size of a star is so large that its mass will
naturally be greater, then there will be a situation inside that star when iron
will be produced by this type of reaction. This iron is the last element to be
formed by the nuclear fusion reaction inside a giant star. So naturally it is
understood that iron will no longer take part in this reaction, that is, the
process of nuclear fusion is stopped forever after iron is produced inside the
core of a star. At this point the temperature of the star reaches 5 X 109
Kelvin. At that high temperature the process of photodisintegration begins (Photodisintegration:
The occurrence of the separation of alpha particles from the nucleus of iron
atoms under the influence of high energy gamma rays) As long as this
reaction continues, the two opposite forces inside the star resist each other
and give the star equilibrium. This event induces a shock wave in the star
which causes a very strong explosion in the star. (Shock Wave: A wave
that occurs when there is a drastic change of pressure between an elastic
object such as air, water, or a star) This explosion is called a supernova
in the term of space science. This supernova also occurs in the case of stars
of medium or small mass. There, however, the last element produced by the
nuclear fusion reaction is carbon and the star turns into a white dwarf star
after the supernova. But in the case of large-sized stars, one of the two
states of the star is obtained after the supernova. If the mass of the original
star is between 10 and 29 times the mass of the sun, or in other words the mass
of the remnant of the star after the supernova explosion is between 1.4 and
2.16 times the mass of the sun, then the remnant of that star becomes a neutron
star and If the mass of the star or star-residue is greater than the value,
mentioned here previously, then a black hole will be created. The
largest neutron star ever discovered is the PSR-J0740-6620, which has a mass
between 2.01 to 2.15 times the mass of the sun. Measuring distances in 2019, it
was found that this neutron star in the Milky Way galaxy is 4,600 light years
away from our earth (Light Year: The distance light travels in a year)
The
neutron star is one of the gradually cooling dense stars in the universe. The
diameter of a neutron star is limited to 10 to 20 km. Due to its small size;
the concentration of matter in these stars is very high. The density of this
type of star varies from 8 X 1013 to 2 X 1015 gram per
cubic cm. These types of stars do not have heat generation capacity but tend to
cool over time. Various cosmic models have suggested that this type of star has
gained larger size after the cosmic collisions. It is worth mentioning here
that a neutron is one of the particles of an atom which is inert and its mass is
a little more than that of a proton. Normally, during the formation of a
neutron star, the protons (positively charged particle) and electrons (negatively
charged particle) of the atom come together to form neutron particles.
Observations
of neutron stars have shown that it is warm enough. However, over time, these
stars gradually cooled down due to lack of heat-generating activity. Their
magnetic field is 108 to 1015 times stronger than the earth's
magnetic field. The gravitational field on the surface of a neutron star is 200
billion or 20,000 crore times stronger than the earth's gravitational field.
The escape velocity of this type of star can range from 1,00,000 km/s
(36,000,000,000 km/h) to 150,000 km/s (54,000,000 km/h). This velocity is about
one-third to one-half of the speed of light. (Escape
velocity: The minimum velocity that a moving
body must have to escape from the
gravitational field of a celestial body and move outward into space) This type of strong gravity acts as a
gravitational lensing in space (Gravitational Lens: A gravitational
lens can occur when a huge amount of matter, like a cluster of galaxies,
creates a gravitational field that distorts and magnifies the light from
distant galaxies that are behind it but in the same line of sight) Calculations
show that if an object with a diameter of 12 km falls freely from a height of 1
m above the surface of a neutron star, the velocity of the object at the moment
of touching the surface will be 1,400 km per second. However, before the object
touches the surface of the star, it will be shattered by the force of a strong
gravitational force. If the mass of our entire earth is compared to that of a
neutron star, then the whole earth would fit effortlessly in a sphere 305 meter
in diameter. For this intense gravity the time dilation here is a normal thing (Time
Dilation: The “slowing down” of a clock as determined by an observer who
is in relative motion with respect to that clock) If it were possible to
take one teaspoon of matter from here, its mass could be compared to that of
our entire Himalaya mountain range.
The
range of magnetic field energy from the surface of a neutron star ranges from
104 Tesla to 1011 Tesla (Tesla: The measurement of magnetic field energy
in SI unit) The strongest magnetic
field neutron star is the Magnetar whose magnetic field energy value ranges
from 108 to 1011. However, the source of this magnetic
field is still unknown to us. Although there are various theories about this at
different times, the real reason is still shrouded in mystery.
The
boundary for the mass of a neutron star that has been determined is called the
Tolman-Oppenheimer-Volkoff Limit. Its maximum value is 2.16 times the mass of
the sun. This value is completely consistent with the value of Chandrasekhar
Limit where it is said that if the mass of a star remaining after a supernova
explosion is less than 1.4 times the mass of the sun then we will mark the
remaining part as white dwarf star. If this mass exceeds the specified amount
of mass, mentioned earlier, then the rest of the star will become either
neutron star or black hole.
This
type of star has a very high rate of rotation on its own axis, so the neutron
star rotates on its own axis hundreds of times per second. The PSR-2446ad is
the fastest rotating neutron star as far as we know. This star rotates on its
own axis 716 times per second or 42,960 times per minute which is about one
fourth of the velocity of light. As time goes on, the neutron star loses its
energy and its rotational speed decreases at a certain rate even if it is
small. This phenomenon is called spin down. In any case, if a neutron star
receives matter from its companion star or another star, then its mass
increases and its rotational speed also increases accordingly. This phenomenon
is called spin up. In addition to this, if there is a starquake due to internal
cause, then the rotational speed of the star suddenly increases a little, and
sometimes the rotation speed of a neutron star decreases for no reason even if
the energy is not significantly reduced. It is a very mysterious thing that is
not yet understood.
Our
galaxy is thought to have about 100 million or 10 crore neutron stars. However,
this number is estimated based on the size of the star in the supernova
explosion. Of these, only 3,200 neutron stars have been identified so far.
However, most neutron stars are old and cool in nature and their radiation is
very low. It is possible to identify them in certain situations. Identifying
single neutron star that rotates slowly is almost a difficult task. However, in
1996 the Hubble Telescope discovered a neutron star called RXJ185635-3754, the
closest neutron star to earth. Its distance from the earth is 150 to 200 light
years. A few neutron stars have since been detected by means of thermal
radiation near it.
The internal temperature of
a newly formed neutron star can range from 1011 Kelvin to 1012
Kelvin. However, the large number of neutrinos (a type of particle) radiated
from a single neutron star consumes so much energy that within a few years the
temperature of that neutron star drops to 106 Kelvin. At these low
temperatures most of the radiation produced by neutron stars is X-rays. Based
on this heat dissipation and mass, scientists have divided the neutron star into
several classes, the first of which is the star with the lowest rate of mass
loss and cooling. Neutron star radiation, however, is the most talked about,
and based on that, the classification of neutron stars is the most popular
among space enthusiasts. Neutron stars are generally of three types in terms of
radiation.
i.
This type of star participates in
electromagnetic radiation. The first direct evidence of neutron stars was found
in 1967, when electromagnetic radiation by neutron stars, was first detected.
This kind of star is called pulsar. This electromagnetic radiation or radio
radiation is thought to be from the magnetic polar region of the neutron star,
and when the axis of rotation and the magnetic axis of the neutron star are
separated, the electromagnetic radiation travels into space at regular
intervals instead of coming continuously. They are called pulsars for the gap
of specific period of time in radiation.
ii.
In a vibrating neutron star, the difference
in brightness usually increases and decreases periodically. However, this
difference is very small. This type of characteristic is most often seen in young
and cool neutron stars. All of these stars are thought to be potentially strong
sources of X-rays.
iii.
A spectrum is a type of neutron star from
which visible light, X-rays, infrared, ultraviolet ray; gamma rays, etc. are
emitted. They have different names based on the emission of different type of
electromagnetic waves.
Apart
from this, the later classification of neutron star has been based on this
radiation in more details.
Despite
the advances in science, we still have to rely on some mathematical models to
learn more about neutron stars, because their vast distances from the earth and
the cosmic dust layer make it difficult to observe directly. According to this
model, the surface of a neutron star is made up of ordinary molecular nuclei.
These nuclei are usually iron. If the surface temperature is higher than 106
Kelvin, then the surface of the neutron star may be liquid. If a neutron star
had something like the atmosphere, its density could be only a few micrometer
(1 micro meter = 0.0000001 meter), but we still do not know what its components
might be. If anything can go deeper of the neutron star, it can find that the
density of neutrons will increase, that is, the greater numbers of free
neutrons are present there. This density is highest at the core of the neutron
star. However, this information is expressed according to the scientific model,
but it is not yet possible to know what is in reality.
About
5 percent of all neutron stars discovered so far are in binaries, meaning they
may have pair with a black hole or a white dwarf star or a red giant star or a
normal active star or a neutron star. The reason why neutron stars will be
paired with any type of star is because of their complex nature. This type of
neutron star emits large amounts of X-rays. This type of neutron star is
usually called X-ray binary. Over time, the distance between the stars of these
binaries decreases and at some point of time they merge completely with each
other.
Although
a little surprising to hear, it is true that neutrons may have planets. Between
1992 to 1994, three planets were discovered in the PSR B1257+12 neutron star.
Their names are Draugr, Poltergeist and Phobetor, respectively. Among them,
Draugr is the smallest planet whose mass is twice the mass of our moon. Planets
have also been discovered in the PSR B1620-26 neutron star. The planet orbits
the neutron star and its companion white dwarf star at the centre.
As far as we know about neutron stars, it is nothing compared to reality. Like the black hole, this cosmic object is no less mysterious. One of the properties of science is to move forward with the reality of reason by penetrating through the unknown mysteries. It may take a while, it may be decades or even centuries, but this unknown, unfamiliar celestial object of the universe will be very familiar to us.
DECLARATION: All The Images Have Been Sourced From Google.
