INTRODUCTION
Black Holes
Black Holes are stranger than anything dreamed up by science fiction writers. It is a place in space where gravity pulls so much that even light cannot get out of it.They have more matter stuffed into least space. They are too compact and has very strong gravity. In other words a Black hole is a region space-time where gravity is so strong that nothing, no particles or even electromagnetic radiation such as light can escape from it.
History of a Black Hole:
The idea of a massive body that even light could not escape was briefly proposed by astronomical pioneer and English clergyman John Michell in a letter published in November 1784. In 1915, Albert Einstein developed his theory relativity, having shown that gravity does influence light's motion. Further, Albert Einstein wrote a paper in 1939 claiming that stars could not collapse under gravity because matter could not be compressed beyond a certain point.
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John Michell used the term 'dark star', and in the early 20th century, physicists used the term 'gravitationally collapsed object'. Earlier Black Holes were termed as ‘Frozen Stars’. John Wheeler introduced the term ‘black hole’ in 1967. In his work in the 1950s and 1960s, he emphasized that many stars would eventually collapse, and pointed out the problems that possibility posed for theoretical physics. He also foresaw many of the properties of the objects which collapsed stars become – that is, black holes. This name meant something dark and mysterious.
ALL ABOUT BLACK HOLES
How do they form?
During most of the life of a normal star, over many billions of years, it will support itself against its own gravity by thermal pressure, caused by nuclear processes which convert hydrogen into helium. Nuclear Fusion accounts for outward pressure. The own gravity of star accounts for inward pressure. Eventually, the star will exhaust its nuclear fuel and star gets contracted. It becomes a denser object. More Denser object results in having more gravity. In simple words. Black holes are expected to form when very massive stars collapse at the end of their life cycle.
- The star would contract to a single point of Infinite density and we call it as singularity.
- A singularity is what we end up with when a giant star is compressed to an unimaginably small point.
- It also refers not only to the end of a star but also to a fundamental idea about the starting-point for the formation of the entire universe.
- This singularity is the defining theme of Stephen Hawking’s Career.
How do they look like and what do they do?
A black hole has a boundary, called the event horizon. This is where gravity is just strong enough to drag light back and prevent it escaping. Because nothing can travel faster than light, everything else will get dragged back also. The strong Gravity effects the stars and gases around the black hole.
After a Black hole is formed, it continue to grow by absorbing mass from its surroundings. Stars passing too close to the black hole can be shred into streamers that shine very brightly before being swallowed. Gravitational waves are emerged when black holes merge. Imagine a giant drain with water spiralling down into it. If something slips over the edge, there is no way to come out.
How are they witnessed?
In Space no one can hear us SCREAM. In Black hole no one can see us DISAPPEAR. Black hole reflects no Light! Light can’t get out of it. Hence special tools are employed to find Black Holes. These tools examine how stars that are very close to black holes act differently than other stars. Experimental results shows that stars and gases around black holes shine brightly before being swallowed.
Space agencies are using satellites and telescopes that are traveling in space to learn more about black holes. These telescopes study the peculiarity in the behaviour of stars when they are nearer to a Black Hole.
Types of BLACK HOLES
Black Holes are broadly classified into two categories based on the mass of the stars with respect to our Sun. They are:
- Stellar Mass Black Holes
- Super Massive Black Holes
Stellar mass Black Holes
The mass of these Black Holes is 20 times more than the mass of Sun. These kind of Black Holes are formed when stars burns up all its fuel and then it explodes. The left over substance turns into a super compact object.
Super Massive Black holes
These Black holes mass is more than one million Suns. Formation and other properties of these Black Holes is under research. A Black Hole named Sagittarus A* is at the core of MILKY WAY Galaxy. It is a stellar mass Black Hole having a mass of 4 million Suns.
URRENT ADVANCEMENTS
Hawking Radiation:
Outstanding contribution was done in the field of Black Holes by “Stephen Hawking”. As far as the real world is concerned a Black hole takes everything into it and whatever goes into a Black Hole is lost for ever. But Stephen Hawking, world’s renowned late physicist have found that Black holes seemed to emit particles at a steady rate. In his investigations, he found that wavelengths of outgoing particles from the Black holes is thermal in nature. His calculations estimated that Black holes create and emit particles at a steady rate with a temperature that is proportional to surface gravity and inversely proportional to mass of the Black Hole.
According to quantum mechanics whole space is filled with pairs of virtual particles and anti- particles. The particles are termed to be virtual because they cannot be detected with the existing particle detectors, but their indirect effects can be measured. When one of the paired particle falls into a Black hole, the other particle in the pair has a chance to escape falling into the infinity and may appear as radiation emitted by a Black hole.
The appearance and disappearance of these particles remain unnoticed. The emissions suggested by this theory is treated as “Hawking Radiation”. A Black hole with the mass of sun emits radiations which are impossible to detect. A mountain sized Black Hole may emit radiations in the X-ray detector range i.e. tiny black holes would give off X-rays and gamma rays, but till date researchers haven’t found the existence of such tiny Black holes.
Black Holes nearer to us:
A Black Hole Sagittarus A* at the core of MILKY WAY Galaxy. Its mass is about mass of 4 million Suns. Our Sun will never become Black hole .It doesn’t have such matter to form a Black Hole.
BLACK HOLES- THE UNANSWERED QUESTIONS
Black hole is not only end of the star, but a far more fundamental idea about starting point for the formation of entire UNIVERSE. Black Hole a Million Dollar question: The Science of Black Holes is not yet completely explored and it is under investigation and research. The research done till date made people anxious about Black holes. There are many unanswered questions in this field. Few of them are:
- What happens to particles and poor astronauts that feel into BLACK HOLE?
- Can they re-emerge?
- Whether it is possible to fall into a black hole and come out in another UNIVERSE?
- Are we falling into a BLACK HOLE?
- Or are we travelling through a BLACK HOLE?
Stephen Hawking, who dedicated his entire life for the research in the field of Black Holes concluded that, there may be something on the other side of a Black Hole.
REFERENCES
- Stephen Hawking (2016) Black Holes- The BBC Reith Lectures, Bantam Book
- https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
- https://www.nasa.gov/mission_pages/chandra/news/black-hole-image-makes-history
- https://en.m.wikipedia.org/wiki/Black_hole
- https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
- https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
- https://www.nasa.gov/mission_pages/chandra/news/black-hole-image-makes-history
- https://en.m.wikipedia.org/wiki/Black_hole
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