What are Pulsars
What are Pulsars
(A blog on the universe and the cosmos above and the nature of it determined by great scientists.)
Pulsars are extremely dense objects which are the final stage in the life cycle of a star. These are simply neutron stars which rotate in specific time periods and give off powerful radio bursts with each rotation. Being so dense and rotating at fixed time intervals with such great precision, they provide scientists opportunities for detecting Exoplanets, Graviational waves and also to sudy dense forms of matter.
Contents :-
- Neutron stars
- Chandrashekhar limit
- Pulsars
- Types of Pulsars
- Uses made of Pulsars
Neutron stars :
There are different types of stars that are formed in the universe ranging from the smallest brown dwarfs ( not really considered as stars ) to the medium range where or sun lies being a yellow dwarf right to the largest stars ie: the blue hypergiants. The very basic difference between these stars is in their sizes while at the time they are formed in the stellar nebulae. There are also differences that are observed between their life spans as larger stars die out pretty quickly as compared to low mass ones. There is also a difference between the various elements that are present inside those stars.
However, the very basic difference that is the difference in their masses is what determines the evolutionary path that the stars follow. Stars that are large in size right from the beginning grow even larger in their later evolutionary stages before dying out, while the stars which are formed with a low initial mass evolve in their life spans too much greater masses, but still, these masses are far smaller when compared with the size of large stars at the same evolutionary stage.
Some of these stars that are pretty huge in size right from the beginning reach the last stage of their evolution pretty fast and after they are left with no elements for fusion ( ie: iron. Though there is iron present in them, it can no longer e fused to form new elements ), they burst to open their outer shells in what is called a supernova explosion. After the supernova explosion, what is left is their extremely dense core which is mainly made up of Neutrons, thus giving them their name - neutron stars. These neutron stars are extremely dense; so much so, a spoonful of material from these stars would weigh a few tons on the Earth. These objects are the densest objects in the known universe only after Black holes. Moreover, if a star can evolve into a neutron star or not can e determined with the star's initial mass and the Chandrashekhar limit.
The Chandrashekhar limit:
The Chandrashekhar limit is a mathematical wonder that was produced by an Indian scientist by the name Suraminan Chandrashekhar. This limit is what expresses the relation between the mass of the stars and whether or not they will become a black hole or a neutron star after the supernova explosion they will produce after they are left with no more atoms to fuse.
According to the Chandrashekhar limit, any star with a mass more than about 1.4 times that of our own star, the sun will go through a supernova explosion. After the supernova explosion, it merely depends upon how big the star was that results in either the core of the star collapsing upon itself and forming a black hole or the core are able to sustain itself and this leads to the formation of a neutron star.
Pulsars:
Pulsars are types of neutron stars themselves. The only difference between a neutron star and a Pulsar is that Pulsar is a rotating neutron star. Pulsars are very interesting objects in the universe. There is not much that is known in regards to them. However, these are a kind of neutron stars that are the remnant of a huge dead star. These pulsars rotate at extreme speeds and the most important characteristic of these stars is that they constantly give off radio waves with each rotation that they make.
These Pulsars are an important source of radio waves in the sky and are of extreme importance for radio astronomy. Though pulsars produce radio waves in abundance, they also produce light of other wavelengths which consists of x - rays as well as gamma rays in small yet considerable proportions.
These pulsars are magnetized, that is they produce a strong magnetic field around their poles which results in the particles of light being magnetized and glow. These glowing radiations of light are then shot into space as radiation. Other light radiations like gamma rays are also shot into space from these pulsars, however, the exact process which leads to these gamma-ray bursts from the pulsars is still a big question that the science community is trying their level best to solve.
Pulsars as a star are pretty complex with their extraordinary rotations and their speed, the radiation that it radiates into space, and also have some distinguishable characteristics among them which enable us to group them into different types. The main characteristic of differentiation between pulsars is based upon the time intervals between 2 successive radio bursts. Based on the time between these bursts ( that is measured in very small units of time like seconds and milliseconds ), pulsars can be classified into 2 major types which are described below.
The difference in the time intervals between successive radio bursts is caused due to differences in the speed at which they rotate. This is a very important property of pulsars that make them different from their counterparts, neutron stars. Though the exact reason as to why pulsars rotate is not yet known to scientists, a possible reason taken into account by scientists worldwide is that the pulsars rotate as they are able to conserve the angular momentum, that is the momentum ( a net product of mass and velocity ) produced by the star in a specific angle at which it spins before it bursts out in a supernova explosion to for the pulsar.
Stars do rotate on their axis of spin and thus generate angular momentum ( because stars have both mass and speed at a particular angle ). Pulsars are created when the product formed when such rotating stars die out is able to conserve its rotational property. This is the very property of pulsars that set them apart from neutron stars. Pulsars are just neutron stars that are able to conserve the angular momentum of the star from which it is formed and thus rotates giving radio bursts at set intervals of time, while neutron stars are non-rotating dense form a product that is left behind after a supernova explosion.
Now, there are many factors upon which the rotational speed of these pulsars depends upon. These factors include their mass, age, and their overall internal structure itself. Pulsars themselves slow down as they age, also being the last stage of life in the life cycle of a star, they don't evolve any further, and thus there is no way that they can regain their speed or evolve into some other kind of celestial object over the period of time. This rate at which the pulsars slow down can be referred to as the slow down rate and according to some scientists is heavily dependent on the diamagnetic radiation that is produced by the pulsars.
Though the rotational speed of these pulsars gets slower with time there is superfluid that is present between their outer crust and core. To explain in simple terms, superfluidity is the characteristic property of fluids with zero viscosity To make it simple even further, viscosity can be determined to be the measure of resistivity that is offered towards deformation. One can imagine this with an example of water and some other thick fluids like honey. When one pours water into a container, it rather flows pretty smoothly without halting. However, when one does the same with honey, it forms kind of layers rather than flowing in a continuous manner and forming a homogenous mixture like water does.
In the structure of a pulsar, the inner crust located between the outer crust and the core has nuclei having an abundant amount of neutrons present in them, in other words, these nuclei are rich in neutrons. These neutron-rich nuclei are located in a sea of free neutrons in the inner crust. Of these, the free neutrons present as a medium in which the nuclei are located are in a state of superfluidity as the temperature at these levels inside the pulsars matches the temperatures that are required for the neutrons to be in the state of superfluidity and thus behave like a fluid that has a total of zero viscosity and thus can flow without any of its kinetic energy being lost.
This superfluidity shown by these neutrons is what acts as a reservoir of the angular momentum. Thus, when the overall rotational speed of the pulsar becomes low, the total angular momentum of these neutrons in the state of superfluidity does not get affected ( though we need to take into consideration the temperature and the age of the pulsar for coming to this conclusion ). Some of the theories given by scientists also predict that when the difference in the rotational speeds of the physical pulsar and the neutrons present inside it in the state of superfluidity increases to a certain critical level, the neutrons transfer their momentum to the pulsar thus increasing its speed. However, these theories have reportedly proved to be very uncertain and thus scientists still think that the rotational speed of pulsars does slow down with time.
Types of Pulsars :
As said above, the rotational speed of one pulsar doesn't only differ from another one but also from itself when we compare it taking into account 2 different time periods. As the speed of rotation changes, the rate at which radio wave bursts are given off by that pulsar also changes simultaneously. Thus, on the basis of the difference in the time intervals between successive radio bursts given off by a pulsar, it can be segregated into the following 2 major types of pulsars :
1. Second Pulsar : There are divisions that are made between the different types of pulsars upon the time they require for completing on rotation. As the name describes, the second pulsars are types of pulsars that rotate on their axis of spin once every second. With each rotation per second made by pulsars of this type, pulses of radio waves are shot out in the space, that is, radio waves are emitted per second by such pulsars.
2. Millisecond Pulsars : The pulsars following under this category are much faster than the pulsars that lie under the category of the second pulsar. As the name suggests, these types of pulsars rotate around their axis of spin once every millisecond and thus give off radio pulses at a regular interval of 1 millisecond. Most of these millisecond pulsars have a rotational speed of less than a 10 millisecond and so is their rate at which they give out radio bursts into space around. Scientists have also proved theoretically that such high speed of rotation along the axis of rotation can actually cause the energy being transferred and thus speeding up the rotational speed of the pulsar making it move at such great speeds that it can make more than about 100 rotations per second, hence theoretically proving the existence of such high radio wave radiating pulsars in the extents of the universe.
Uses of Pulsars :
Pulsars are pretty fascinating objects present in the universe with all the unusual properties that they have, which we have already discussed above. But, apart from just being fascinating objects, they also have some practical uses for scientists and help them up to quite an extent with different jobs. Some of such areas in which pulsars prove to e useful are as follows :
1. Finding exoplanets :
Pulsars are the final evolutionary stage in the life cycle of a star that started off with a pretty big mass. Thus, just like any other star, one can also expect to find exoplanets revolving around pulsars. According to the various studies performed/undertaken by scientists across the world, we today know 3 planets which revolve around a pulsar just like they would have around any other normal star. Such planets are termed as pulsar planets. Till date, scientists have found success in mapping a total of 3 pulsar planets across the observable universe. Information about each is given below :-
|
|
||
|
|
||
|
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||
|
|
|
|
|
|
||
|
|
|
2. Detecting Gravitational Waves :
Pulsars, especially the ones belonging to the millisecond pulsar category are used by experts in method known as Pulsar Timing Array ( PTA ) which is used to identify and note even the most subtle disturbances in the space and Gravitational waves are one of those cosmic phenomenon that can be detected by using such methods. Thus, scientists are able to detect gravitational waves by especially using millisecond which emit radio pulses at an insanely constant rate in a relatively lower time period.
Comments
Loved ur blog very much!
All the very best for future ones
Would like to learn a lot form u
- Om Bakshi