Introduction
- A black hole is a region of spacetime where gravity is so profound that nothing can escape it, be it any particle or not even light. According to the theory of general relativity, A black hole can be formed by any compact mass.
This is a simulated view of a black hole
In November 1784, John Michell, an astronomical pioneer, suggested that a massive body almost of the density of the sun exist and nothing can escape its gravity.
What is a black hole? (Its properties and structure)
A black hole is a massive structure almost to the equal density as to the sun and no particle can escape it.
- Such supermassive but non-radiating bodies can be detected by their gravitational force on nearby visible bodies.
- Matter or stars that fall on a black hole can be shred into streamers that shine very brightly before being swallowed.
- A black hole of the stellar mass is expected to form when very massive stars collapse at the end of their life cycle.
- After a black hole has formed, it continues to grow by absorbing masses from its surroundings.
- By absorbing stars and merging in other black holes, forms a supermassive black hole. There is consensus that supermassive black holes exist in the center of most galaxies.
Properties
- Once a black hole achieves a stable condition after its formation then it has only three independent physical properties: Mass, Charge & Angular momentum.
- The black hole otherwise is featureless
- If the conjecture is true, any two black holes of the same properties are indistinguishable from one another.
- These properties are special because they are visible from the outside of the black hole.
- When any object t falls on a black hole, any information about its shape or its charge got evenly divided into black holes’ horizon and got to outside observers.
- The gravitational and electrical fields of black holes provide very less information about what went inside.
- The above image is a simple illustration of a nonspinning black hole. Here Schwarzschild radius is the gravitational radius between the particle and black hole.
Event Horizon
- An event horizon is a boundary in spacetime through which matter and light can only pass towards the mass of a black hole.
- This event horizon is referred to as because no information can reach the outside observers.
- The event horizon deforms the paths of the particles in a way that no other way left for the particles to escape.
Singularity
- Singularity is the center of a black hole which is a region where the spacetime curvature becomes infinite.
More about black hole
Once a black has formed, it continues to grow by absorbing matters.
It continuously absorbs gas and interstellar dust from its surroundings.
In 1974, Hawking stated that black holes are not black entirely. It emits some amount of radiation. This effect is known as Hawking radiation.
According to Hawking’s theory, black holes shrinks and evaporates as they lose mass by the emission of photons and other particles.
Observational Evidences
In 2015, the LIGO gravitational wave observatory made its first-ever successful direct observation of gravitational waves. The signal was consistent while the merger of two black holes.
Due to the conservation of angular momentum, gas falling into the gravitational well created by a massive object will typically form a disk-like structure around the object.
Within such a disk, friction would cause angular momentum to be transported outwards, allowing matter to fall farther inward, thus releasing energy and increasing the temperature of the gas.
When the accreting object is a neutron star, the gas in the inner accretion disc orbits at a very high speed because of its proximity to the object.
The resulting friction heats the inner disk which emits a vast amount of electromagnetic radiation.
In November 2011, the first direct observation of a quasar accretion disk around a supermassive black hole was reported.
Another way the black hole nature of an object may be tested in the future is through observation of effects caused by a strong gravitational field in their vicinity. One such effect is gravitational lensing.
The deformation of spacetime around a massive object causes light rays to be deflected much as light passing through an optic lens.
Observation has been made of weak gravitational lensing, in which light rays are deflected by only a few observed for a black hole.
Conclusion
- Blackhole exists and it is a noticeable region in spacetime where the gravitational force is so strong that no matter can escape it.
- These holes get merged to form a supermassive black hole.
- It has many unfold questions and many new aspects to come in the future related to this very known term called ‘Black-hole’.
Exercise
Q.1. What is Blackhole?
Q.2. Describe schwarzschild radius?
Q.3. What is a supermassive black hole?
Q.4. How does event horizon work?
Q.5. What is microlensing?
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