What is Quasar? Why Quasars are Extremely Luminous?

     A Quasar is an Active Galactic Nucleus of very high luminosity and the most ancient objects of the Universe. Most of the galaxies have a super massive black hole in their center and that black holes are billions of solar masses. This type of black holes are surrounded by a giant gaseous circum-stellar disk. For friction the orbiting material of the disk falls inward towards the black hole. Gravitational and frictional forces squeeze the material and increases the temperature for that energy is released in the form of electromagnetic radiation to the outwards of the black hole. That event is called Quasar or Quasi-stellar object. So it is clear that a Quasar gets the energy from the super massive black hole in the same galaxy. Quasar emits immense energy across electromagnetic spectrum and it can be observed at X-ray, Ultraviolet, visible light, infrared, and radio wavelengths.
                                   

                                                  Pic courtesy: www.wikipedia.org
    Quasars are most powerful objects of the universe and the most intense sources of energy that exist. The most powerful quasars have the luminous intensity of 10 to the power 41 W and it is 1000 times greater than an ordinary galaxy. Quasars are not larger than the solar system but they are brighter than hundreds of galaxies together. They are in the edge of the universe, the farthest objects of the known Universe. If we observe them with infrared then we see their energy is greater than any other objects. The brightest known Quasars  swallow 1000 of solar masses of matter each year.
      As of 2017 most farthest discovered Quasar is ULAS J1342+0928 and it is 29.36 Giga light years away from us and the closest known Quasar is 730 million light years away from the earth and it is known as IC2497. The first Quasar was discovered in 1950 and it was 3C273.

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info courtesy: www.wikipedia.org

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What is a Black Hole? How does it Form?

     Black holes are one of the strangest thing in the Universe. A black hole is a region of space-time exhibiting such strong gravitational effects that nothing even any particles and electromagnetic radiation like light can't escape from inside of a black hole. Stars are massive collection of mostly Hydrogen atoms that collapse gas cloud under their own gravity. In the core nuclear fusion crashes Hydrogen atoms into Helium and release tremendous amount of energy and this energy in the form of radiation pushes against gravity maintaining balance into the two forces. As long the fusion happens in the core of the star remains stable enough. But the heat and pressure of the core allow to fuse heavier elements until they rejoin each other. The fusion process  mostly creates Iron that doesn't create energy and iron builds up the center of the star until it reaches to a critical amount. The balance between radiation and gravity is suddenly broken and the core collapses with in a fraction of a second  the star implodes and moves into the quarter speed of light and core becomes more massive. Then the star dies in a supernova explosion, scattering much of its matter throughout the universe and produces either a neutron star or if the star is massive enough then entire mass of the core collapses into a black hole. All the matter of a non-rotating black hole collapses into a single point called singularity and for rotating black holes the mass collapses into a circle because of rotation and that is called ring singularity. A massive black hole can swallow a star hole, black hole can also grow by colliding and merging with other black holes.
                                                   

                                                       Pic courtesy: www.wikipedia.org         

    

    A black hole is a black sphere that reflects nothing and anything is to close to a black hole is completely disappeared from view. The surface of the sphere of a black hole is called Event horizon if anything passes the Event horizon needs to be travelling faster than the speed of light to escape,  anything crosses the Event horizon from outside of black hole then it will be hidden from the rest of the universe. If the mass of a black hole stays the same of the dying star then it is called Stellar mass black hole. A galaxy contains billion and billion stars and all orbiting a central point. The center of most galaxy there is a black hole and that is called super massive black hole because of is tremendous masses, the mass of this type black hole is billions of solar masses. The black hole which is in the center of our Milky way galaxy is 4 million times of solar masses. Different star rotate in different speed. Suppose a star has a mass of 1.5 solar masses now radius has increased and mass stays same then its spinning speed will be decreased but angular momentum never changes it remains constant even a star collapse into a black hole its still have angular momentum. Because of angular momentum black hole creates spinning curve into the space-time. Black hole also has electric charge either positive or negative but until and unless the over all charge becomes neutralized it acts on opposite charged particle of the universe.

                     
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What are Gravitational Waves?

   Gravity is a curve in a surface called Space-time. Gravitational Waves are the disturbance in the curvature of Space-time generated by accelerated masses and propagate as wave outward from their source at the speed of light. Gravity is the force that any two objects pull together. The object which has more mass its gravitational pull stronger. Every mass in the universe has an effect on every other mass no matter how small, then changes of gravity can tell about what those objects are doing.
   Variation in the gravity coming from the Universe are called gravitational waves. A mass in space creates a depression in space-time and a massive sphere rolling across a depression will curve like it's being attracted to the other mass. The bigger mass creates deeper depression and stronger gravity. When the mass making the depression moves that sends out waves in space time, these are gravitational waves.
  Suppose two massive black holes are pulling each other, now one of them becomes more massive then it will pull more the other and once they will make a collision and will merge into single black hole when the collision will happen then there will create some disturbance in the space-time and will vibrate the space-time by waves it is also the example of Gravitational wave.
                                         

                                                  Pic courtesy: www.wikipedia.org
      On September 14, 2015 two black-holes were collided. they had been orbiting each other by millions of years, as they got closer they circled each other faster and faster, finally the collision between them happened and they merged and became into a more massive and bigger one. A fraction of a second before their crash they sent a vibration across the universe at the speed of light and billion of years later it was detected by LIGO ( Laser Interferometer Gravitational-Wave Observatory) on the Earth.

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Why does Light Bend? What is Slow Light, Fast Light, and Stopped Light?

   Suppose a light is coming on earth from a star and when it is visible to us the photon already emitted from the star before several times because light takes time to travel light does not travel in a infinite speed. So when we see the star actually it is back in time. Let there is a very massive object with high gravity like black hole in between the star and the earth, now light that left the star which would normally miss the earth entirely but it bends by the black hole and comes and hits to the earth.    Light itself is effective by Gravity. As of General relativity black hole or any massive object creates a curvature on space time, suppose black hole is sitting on a sheet of a space time it bend the space time where it is sitting, like a ball on a sheet makes an arc. Photon also travels through the space time so it also bends.
  Some object which has mass will be bend by the gravitational field of a black hole when it will pass the black hole now photon has energy E, we know E=mc^2, m=E/c^2  so photon has a mass then it will be definitely bend by the gravitational field of a black hole.
                                 

                                         Pic courtesy: www.wikipedia.org
 Slow Light:Suppose a pulse of a light interact with a slow medium i.e. the molecules of the medium has slow velocity then propagation of light will be slower than c.
 Fast Light:A pulse of a light interact with a fast velocity molecules medium then the propagation of light will be faster than c. but actually nothing is greater than c.
 Stopped light:If a pulse of a light stopped by the medium then it is called stopped light.
 
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What is Gravitational Singularity?-The Infinite gravity

  A Gravitational Singularity or Space time singularity is a location in Spacetime where the gravitational field of a celestial body becomes infinite that does not depend on coordinate.  Something is singular when it is one, odd, not just any individual or single. A singularity is like the answer to a question for which there is no answer. 

We know that,
         r_s = 2GM/c²

^{c=speed of light} 

^{G=gravitational constant}

^{M=mass of the object}

 ^{r_s =Schwarzschild radius}

 ^{here c and G are constants.}

^{Now if a sphere shape mass M is squeezed then mass will be the same but its volume  gets smaller. If it is squeezing more then it will become tiny but stay as massive as before. All the molecules compressed close to each other until it reaches a critical size and that is the Schwarzschild radius-the radius of a sphere mass when all masses of the object are compressed within the sphere, the escape velocity from the surface of the sphere would equal the speed of light this means in order to escape the gravitational pull of the object have to move faster than speed of light but it is not possible because only light can travel in this speed.}

^{Now the radius of earth is 6371 km the Schwarzschild radius will be only 8 mm. How massive a sphere object is it does not matter because it will be divided by the square of velocity of light that is huge.}

                                                           Pic courtesy: www.wikipedia.org

   

     If the object's radius is less than Schwarzschild radius  i.e.r<rs 

then it becomes a black hole.
Schwarzschild metric has the form with signature coordinate (1,-1,-1,-1)
$}$
where,

• when dτ² is positive, τ is the proper time (time measured by a clock moving along the same world line with the test particle),
• c is the speed of light,
• t is the time coordinate (measured by a stationary clock located infinitely far from the massive body),
• r is the radial coordinate (measured as the circumference, divided by 2π, of a sphere centered around the massive body),
• θ is the colatitude (angle from north, in units of radians),
• φ is the longitude (also in radians), and
• r_s is the Schwarzschild radius of the massive body, a scale factor which is related to its mass M 

what happens if the object's radius is zero.i.e. r=0
we know Y=f(x), Y=1/x and if x→0 then Y→∞  if x=0 then Y=∞ 
rs /0 =∞ 
  so the equation will be the infinite, in the middle of a black hole r becomes zero so the gravitational field becomes infinite. So in the middle of a black hole is an example of gravitational Singularity.

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What is Antimatter and where it is?-The Mystery

   Everything we are watching beside us is matter. Every physical substance with mass is called matter.
   Then there is a other thing called Antimatter. Mass and Energy is exchangeable, mass is concentrated energy. 90 trillion joules of energy are equivalent to 1 gram of mass. New particles will come into existence if a huge amount of energy is concentrated in a tiny space. This particles always come in pairs, just because particles always have a counterpart that is an antiparticle and these are always produce in equal i.e. 50/50. Therefore during the big bang, in initial stage when a huge energy was transformed into mass there should have be similar numbers of matter and antimatter but all of the antimatter destroyed one another and producing enormous amount of radiation, it is one of the greatest mysteries of physics. In the collision between two protons billions of particles and antiparticles are produced every second at Large Hadron Collider. An electron has small mass and negative charge and its antiparticle Positron has exactly same mass but positive electric charge. Apart from opposite charges, both particles are identical and perfectly stable. The same is true for Proton and Anti-proton. So if there is a world created by Anti-proton look, feel, smell will be the same but the substance will be the anti-proton we may find anti-water, anti-gold etc.
                                     

                                               Pic courtesy: www.wikipedia.org

  Imagine there will be anti-marble now marble and anti-marble of two world's are brought together, this two apparently solid objects would completely disappear into a big flash of energy equivalent to an atomic bomb because combining of matter and antimatter would create so much energy. The energy of 1 gram of antimatter would be enough for driving a car 1000 times around the world.
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  Neutron Star-The Strange

   Hydrogen fusion is always happening in the star, fusing hydrogen nuclei gives helium and release energy and for this energy all stars are shining. When the fusion stops then the stellar evolution comes to an ends, and the star dies.
  When the stars die a low mass star ends as a white dwarf, a high mass star becomes black hole and in between white dwarf and black hole, a star dies as a new born Neutron star.
Neutron stars are primarily made by neutrals particle neutrons. Suppose a dying star is 1.5 times massive than sun and its gravity is so strong that compress electrons and protons to form neutrons and neutrinos. As Pauli exclusion principle the neutrinos dart off into space behind big sphere of neutrons and gravity continues to compress the neutrons together, but eventually hits a wall.
  Suppose a white dwarf has a mass of 1 solar mass now the mass increase to 1.4 solar masses then the gravity gets stronger white dwarf gets smaller. Gravity becomes strong enough to combine electrons and protons to make neutrons and neutrinos and the dead star becomes Neutron star from white dwarf this is called Chandrasekhar limit. Again the mass of Neutron star increase between 1.5 and 3 solar masses then the gravity becomes strong enough to breakdown the neutrons, and the Neutron star collapses into black hole this is called Tolman–Oppenheimer–Volkoff limit.
  Typically a Neutron star has a radius of 10 km and the surface gravity is 200 billion times stronger than earth. Surface temperature of a Neutron star of around 600000 K and a mass between 1.4 and 3 solar masses. The magnetic field of a Neutron star are between 100 million and 1 quadrillion times strong than earth. It is so dense that one matchbox contains of neutron star material have a mass approximately 300 billion tons.

                                                           Pic courtesy: www.wikipedia.org
Spin of a new born Neutron star is 100 times per second and the magnetic field emits beams of electromagnetic radiation called Radio Pulsar it was first observed by Susan Jocelyn Bell Burnell in 1967. The known fastest spinning Neutron star is  PSR J1748-2446ad, rotating at a rate of 716 times per second.
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Is Time Travel Possible?

Time Dilation & Time Travel Hypothesis

Time Dilation is a difference in the elapsed time measured by two observers

Time Travel is the concept of movement between certain points in time.

  If Multiverse or parallel universe exists then it is possible to get thousand copies of a person suppose we take two universes as two rooms with different gravity and it is possible to watch one universe from other. Now for different gravitational field the time dilation of two rooms are different. which room has more gravity time is slow there and time is fast in the less gravity because gravity is inversely proportional to time. If some event happen suppose someone has been murdered in the same time. But for different time dilation the event will be happened relatively different time into the rooms. It will be happened first in the fast moving time or less gravity and thereafter it will be happened in the slow moving time or more gravity. So it is possible to watch the murder from slow moving time when murder didn't occur yet in that room i.e. in which time is moving fast is the future of slow moving time.

                                             Pic courtesy: www.wikipedia.org

Some theories like general and special relativity suggest that suitable geometries of specific types of motion in space might allow time travel into the past and future if these geometries or motions were possible.
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