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| Image: wikimedia commoms |
It has been more than 450 million years since our sun was formed. That is, half of its age is over. And half of its fuel is gone. Our sun uses hydrogen as fuel. In the sun's core, hydrogen atoms fuse together to form helium atoms due to nuclear fusion. This is why the sun emits heat and light.
After all the hydrogen atoms in the sun are converted to helium atoms, the helium atoms begin to fuse together to form carbon atoms. Then the carbon atoms begin to combine with each other to form neon atoms. Following this, magnesium atoms are formed. Finally, magnesium atoms combine to form iron atoms. Iron atoms cannot combine with each other to form new atoms. It is at this stage that a star reaches its final phase. After this, the star becomes larger in size and becomes a red giant star.
After the star is fully grown, it undergoes a supernova explosion. Then the core of the star becomes a neutron star. These neutron stars are very small in size. An average neutron star is about 20 kilometers in diameter. We can confine it within a city. When electromagnetic waves are emitted from both poles of neutron stars, they are called "pulsars.".
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| Picture of a pulsar Image: wikimedia commoms |
When these electromagnetic waves pass through our earth, the star appears to twinkle. A neutron star is so small that it is almost invisible to our eyes. But we can see the twinkling of the star only when the electromagnetic waves emitted from its two poles pass through our earth.
These pulses were discovered in the 1960s. Let's see how a pulsar star is formed.
Formation of Pulsar Stars:
As nuclear fusion takes place in the core of a star, energy is released outwards. Thus, an outward force is also exerted. But the star's gravity pulls its surface inward. As these two forces act in opposite directions, the star is in balance.
But after the star runs out of fuel, nuclear fusion stops in its core. So no energy is dissipated. Hence no force acts outward. And now no force acts against the star's gravity. So the star begins to shrink. So the pressure on the core of this star keeps increasing. Due to the excess pressure, all the electrons that may be present in the area, along with the protons, are converted into neutrons. At the same time, the star's outer layer begins to expand and become a red giant star.
As each neutron is produced in the core of the star, each neutron is ejected. Due to the excess pressure, those neutrons will start to collide with each other. In this case, excess heat energy is dissipated. Also, its core will start spinning at an excessive speed. After a certain point, the star's core stops shrinking. Further, excess energy is ejected from the region, and the star undergoes a supernova explosion.
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| Image: wikimedia commoms |
But the core of the star keeps rotating in the same place. as a neutron star. Because of its smaller size and conservation of momentum, it's rotational speed is very high. It spins so fast that it spins around itself almost a thousand times in a second.
If the wheels of a car spin at this speed, its speed would be 7000 km/hr. So the magnetic field around this neutron star would be trillions of times greater than Earth's magnetic field.
Now, because the pressure on the surface of a neutron star is low, the neutrons there decay into electrons and protons. As these are caught in the star's magnetic field, they are thrown outwards at high speeds from both poles of the star. According to the laws of physics, electromagnetic waves are emitted from an electron when it is accelerated.
Similarly, here electrons and protons are accelerated by the magnetic field of the neutron star. Hence electromagnetic waves are emitted. These may be at wavelengths visible to our eyes or may be emitted as X-rays or even gamma rays. These electromagnetic waves emanate from both poles of the star.
These poles are slightly tilted because they are slightly off the spin axis of the neutron star. And the neutron star does not rotate with respect to these poles.
Thus, neutron stars that emit electromagnetic waves from both poles are called pulsars.
The electromagnetic waves of these pulsars can only be felt by us when they pass through our Earth.
Basic Properties:
Not all pulsar stars rotate at the same speed. Some stars rotate only 100 times per second. And these stars appear to twinkle slowly when viewed from Earth. The stronger the magnetic field of a pulsar, the more powerful electromagnetic waves are emitted.
Gamma rays are the only electromagnetic waves with maximum energy. The magnetic field of pulsars that can emit these rays would be very strong. These pulsars are called the magnetors.
The pulsars are more massive than the original star. And some planets orbiting pulsars have now been discovered.
These pulsars, or neutron stars, bend the fabric of spacetime just like a black hole. That is, you spend 10 months on the surface of a neutron star, and by the time you reach Earth, you will have spent 12 months here. According to Einstein's theory of special relativity, time slows down for an object in fast motion.
On Earth, the reason we stand at a certain weight is because of its gravity. But since the gravitational force of a neutron star is millions of times greater than that of Earth, once you land on the surface of the star, you will be pressed on the surface and merge with the ground. That is, you will be crushed.
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| Picture of a neutron star Image: flickr |
Although this neutron star does not absorb light like a black hole, it has too much mass to bend the light. As this neutron star shrinks further, it becomes a black hole.
Stars with masses greater than 20 times that of the Sun do not become neutron stars at the end of their lifetimes. Because of their mass, the pressure on the core of the stars is so high that they are turned into black holes.
But our sun will not become a neutron star or a black hole. Because the mass of our sun is very low compared to other stars. Scientists believe that our sun is unlikely to undergo a supernova explosion.
Scientists believe that our Sun is likely to become a white dwarf star after its death.
A pulsar star stops emitting electromagnetic waves from both its poles after a few million years. Then an ordinary neutron star would remain. And it is said that its spin speed will also decrease.