Category: Cosmology

First Ever Image of Black Hole Supports Einstein’s Theory of Relativity

First Ever Image of Black Hole Supports Einstein’s Theory of Relativity

Introduction to Black Hole

Black holes are supermassive objects from where nothing can escape, not even light. The edges of black hole are the point of no return called event horizon. But scientists finally succeeded in designing the first ever image of the shadowy edge of a supermassive black hole. This huge discovery in the history of mankind has led us to a different way of understanding the universe.

Although we have got an image of a black hole, the topic of black hole is not new. The existence of black hole was predicted by Albert Einstein’s general theory of relativity more than 100 years ago. Many scientists supported it including latest great scientist, Stephen Hawking. Now we have got a solid proof the existence of black hole after about 65 years of passage of Einstein.

First ever image of black hole
First Image of Black Hole

About First Image of Black Hole

On Wednesday, April 10, 2019, scientists have released the image of an active supermassive black hole which is located in the center of an elliptical galaxy. The black hole is named as Meisser 87 (M87)and is present about 15 million light years from us. It is 6.5 billion times the solar mass and 40 billion kilometers across. The image was captured by using the Event Horizon Telescope (EHT).

It is circular but on one side, light is brighter because the light is approaching the earth.

“The image had an orange, yellow and black ring which was obviously a black hole and its surrounding”, said Havard’s shepherd Doelemon, Director of EHT team.

An EHT team member and astronomer at University of Waterloo, Broderick said,” The shadow exists in nearly circular and the inferred mass matches estimates due to dynamics of stars 100,000 times farther away.”

Prediction by Einstein’s General Theory of Relativity

It was theoretically predicted by Einstein’s general theory of relativity more than 100 years ago. The image of black hole fully supports the theory of relativity. It is crescent – shaped as predicted by Einstein. The circular disc is an event horizon from where nothing can escape. The portion is the core of black hole and is totally black. Einstein’s prediction about the shape and glow of a big black hole is also proved right.

Einstein’s theory has not only passed this test but every challenge over the last 100 years. He has been right all along.

E.g. Einstein predicted gravitational wave which is created by massive accelerating objects.
In 2015, LIGO (Laser Interferometer Gravitational Waves Observatory) confirmed the ripples in space-time which were gravitational waves.
It was observed when two small black holes were merging.

Conclusion

After a decade, we have finally figured out about black hole which Einstein explained earlier. It took a lot of efforts for many scientists working for years and collecting millions of GBs of data to create a single picture of black hole. Hats off to all the scientists who theorized, supported, researched and proved about the existence of black hole.

Life Cycle of a Star

Life Cycle of a Star

Introduction to Star

You must have seen a number of stars in the sky at clear night. Have you ever tried to count them?
Obviously, impossible.
But, have you ever thought that from where these stars come from?
How do they appear to us although they are thousands of light years away?
Some are even millions and billions of light years away form us.
There are trillions of stars in our universe. Our nearest star is alpha centauri after sun. The collecion of a large number of stars forms a galaxy and collection of many galaxies forms the whole universe.
Well let’s see, how these stars are formed ,how do they die and how the life cycle of a star is completed.

A star has a life span of billions of years. So, it is not possible for one to observe its complete life from its birth to death. However, by observing different stars, their ages and their other characters, scientists have given an acceptable model for the life cycle of a star form its birth to its death.
Firstly, let’s look upon the formation of a star.

Image of life cycle of a star
Life cycle of a star
Image credit: cyberphysics.uk

Formation of a star

There are a lot of cloud clusters and dust particles present in the space. These matters start to come close to each other and attract each other.. Slowly they form a large mass of cloud and dust. It is called Nebula.

Nebula has extremely low temperature and mainly consists of hydrogen. Their mass is usually more than an average star mass. They are opaque to visible light and don’t reflect light at all. So they must be detected by the IR and UV-rays. The nebula begins to contract by the action of its own internal gravitational force. It becomes more denser and denser. This process continues for million of years depending upon the size of nebulae.

he temperature of the nebula starts to rise slowly and becomes highly packed. As a result, formation of protostar takes place. Protostar has relatively high density and temperature. When its temperature reaches to certain limit, nuclear binding energy of its constituent particle breaks and nuclear fusion reaction initiates. After the initiation of the nuclear reaction, large quantity of heat energy is produced. This results in the birth of a star.

A Living Star

After the birth of a star, the star starts its life of a billion of years. The life of a star depends upon the amount of matter it is composed of. Small stars have low temperature and use up their fuel slowly while large stars use up their fuel in vast amount and have very high temperature. Colour of a star also changes constantly along with the life cycle of a star. It changes as:

  • Violet
  • Indigo
  • Blue
  • Green
  • Yellow
  • Orange
  • Red

Our sun is now somewhere in the yellow-orange phase and is going to end up. But we don’t have to worry about it, because it will take several billions of years to finish the life of the sun.

Finally, the fuel of the stars become almost finished and the star starts its journey towards death.

Final Stage of a star

After the red-phase of a star, there comes possibility of formation of two types of stars, red supergiant star and red giant star. It depends upon the mass of the star.

1. Star having the mass less than five times the mass of our sun

Formation of Red Giant Star

Formation of Red Giant Star during life cycle of a star
Red Giant Star

If the star has the mass less than five times the mass of our sun, the star starts to contract. The star becomes dense. But some of the remnants hydrogen in the outer parts of star starts of fuse and produce large quantity of heat energy. Due to this, the star enlarges. This star of this stage is called red giant star.

Formation of Planetary Nebula

After the hydrogen of the star is completely used up, upper layers will expand and eject the materials to its surrounding while its core starts to shrink. This process continues until the pressure becomes equal to the central electron cloud. It results in the formation of a nebula called as planetary nebula.

2. Star having the mass more than five times the mass of our sun

Formation of Red Supergiant Star

Formation of red supergiant star during life cycle of a star
Red Supergiant Star

If the mass of the star is more than the five times the mass of our sun, the star expands enormously and changes into red supergiant.

The red supergiant cannot balance its inner and outer pressure and hence it explodes. This explosion of red supergiant star is called supernova.

After supernova, either neutron star or a black hole is formed.

For small remnant of supernova:

Formation of Neutron Star

If the remaining mass is relatively less, it starts forming the neutron star. The remaining hydrogen of the mass is converted into the helium. Its mass is large enough to convert helium into carbon and carbon into other elements like silicon, iron, etc. The core becomes so dense that even electrons cannot remain in the orbit. The electron then combines with the protons forming neutrons. Then the star becomes a ball of neutrons, which is called neutron star.
The neutron star has only neutrons as its constituents. So, it has a very large mass and small volume. Typically, a neutron star weighs about 5-10 solar masses and a radius of 10-20 KM. Its escape velocity also becomes very high ( about 108 m/s ).

For large remnant of supernova:

Formation of Black Hole

If the remnant of supernova is more than about 3 times the solar mass, the force towards the centre cannot be balanced by the repulsive force of neutrons. As a result, the mass further shrinks and forms a tiny mass. It causes the formation of black hole.
The black hole is a body whose escape velocity is more than that of the speed of light. So, even light cannot escape from the black hole and anything inside the black hole cannot be observed form outside the event horizon.

Concluding the life cycle of a star

Hence, a life of a star starts form the dust particles and clouds, passes through different phases and finally end up being white dwarf, neutron star or black hole, depending upon its size.

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Theory of Light

Theory of Light

Introduction to light

Generally, light is a electromagnetic radiation of visible wavelength. Visible light ranges from the wavelength of 400 to 700 nm (nanometer). But in scientific context, light refers to whole electromagnetic spectrum of any wavelength. Theory of light describes how and why light shows its properties and nature .Light is composed of elementary particle called photon. It is produced by different luminous sources like fire, light bulb, etc.

Light shows different properties like reflection, refraction, diffraction, interference, photoelectric effect, etc. Optics is the branch of science which deals with these kinds of optical phenomena.
Ray optics deals with the geometric of the light like reflection, refraction, rectilinear propagation of light etc. while physical optics deals with the production, emission, propagation of light like interference, diffraction and polarization of light.

Different theories of light

From the very ancient time, people have been presenting different views about light. It has become one of the interesting field of research in modern world also. Scientists have made many discoveries regarding the light.

Ancient theories of light

In the ancient time, some people had purposed some theories in light . Earlier people considered it as one of the elements of nature. Later on, some assumptions were made as:

  • Light is composed of extremely small particles (though not mentioned clearly)
  • It travels at the speed of infinity
  • Light always travels in straight path
  • Colors of light are made up of darkness and brightness

However, due to lack of further supports and proofs, these assumptions are negleted now.

Corpuscular Theory of Light

This theory was given by the great scientist, Sir Issac Newton in 1678 AD. It supports the particle nature of light. Some of his assumptions on light were:

  • Light is composed of tiny, light(not heavy) and perfect elastic particles called corpuscules, emitted by luminious sources.
  • The size of corpuscules determine the colour of light.
  • The bouncing back of these corpuscules from the surfaces causes reflection of light.
  • The particles present in denser medium attract the corpuscules which cause them to accelerate. It explains the refraction of light.

He also explained that the white light is made up of seven colours (i.e. Violet, Indigo, Blue, Green, Yellow, Orange and Red) by the process of diffraction through triangular prism. Similarly, he made different optical instruments and contributed a lot in the field of physical optics. He also published a book named “Opticks” in 1704 AD.

His theory could not explain the wave nature of light like interference, polarization, diffraction etc. But this theory successfully explained particle nature of light. Since photoelectric effect was not discovered at that time, this theory was discarded.

Huygen’s Wave Theory

This theory was purposed by Christian Huygen in 1678 AD. It explains light as a longitudinal wave in which particle vibrate simple harmonically along the direction of propagation of wave. For the transmission of the longitudinal wave, a medium is necessary. So Huygen assumed that a hypothetical ether medium was present in the space which is responsible for transmission of light waves.

This theory could explain reflection, refraction, dispersion and total internal reflection of the light. Moreover, Frensnel and Young explained interference phenomenon on the basis of this wave theory.

However, this theory failed to explain the phenomena of polarization of light. Also, the existence of ether could not be verified by the experiments

Maxwell’s Electromagnetic Theory of Light

James Clerk Maxwell in 1860 AD mathematically proved that light is the electromagentic wave which travels with the speed of 3×108m/s in vacuum. He used the following equation to find out the speed of light.

Equation of Maxwell's Electromagentic Theory of Light

According to this theory of light, light is a form of electromagentic waves in which the electric and mangnetic field vectors oscillate transversely in the mutually perpendicular directions. Such wave needs no material for the propagation. So, the ether hypothesis is no longer required.

But the phenomena like compton effect, emission and absorption of light etc could not be explained by this theory. Hence, Physicists started further study of light naure.

Quantum Theory of Light

This theory considers light as a discrete packet of waves called quantum. Each quanta (singular of quantum) of light consists of a photon which carries energy equal to the product of plank’s constant and its frequency.
i.e. E = hν
where, h = 6.62607004 × 10-34 m2 kg / s
A photon travels with very high speed ( 3 × 108 m/s in vacuum). Higher will be the frequency of light, more will be the energy carried by the photon.
Quantum theory of light successfully explains the phenomena of photoelectric effect, compton effect, etc.

Conclusion

The experimental observations show that light sometime shows the behavior of wave and sometime it behaves as particle. E.g. light showed particle nature during interference while it showed particle nature during photoelectric effect.
In 1924 AD, de-Broglie suggested that a particle moving with the momentum ‘p’ has an associated wavelength of λ = h/p
i.e. λ = h/(mv)
However, light is found to have no rest mas. So the light never remains stationary and always travels with very high speed.

Hence we can conclude that light has dual nature of wave and particle. Photoelectric effect can be explained on the basis of quantum theory of light while interference, diffraction and polarization can ve explained on the basis of wave theory.


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