BLACK HOLE - A MYSTREY IN ASTRO PHYSICS
A.AYSHA NILOBAR M.Sc.,M.Phil.,
ASSISTANT PROFEESOR & HEAD,
DEPARTMENT OF PHYSICS,
ANNAI HAJIRA WOMEN’S COLLEGE,
MELAPALAYAM.
INTRODUCTION
John Michell
The astonishing idea about the black hole was first announced in 1783 by John Michell, an English country parson.
Although he was one of the most brilliant and original scientists of his time, Michell remains virtually unknown today, in part because he did little to develop and promote his own path-breaking ideas.
WHAT IS A BLACK HOLE?
“A black hole is a cosmic body of extremely intense gravity from which even light cannot escape. Black holes usually cannot be observed directly, but they can be “observed” by the effects of their enormous gravitational fields on nearby matter.”
Birth of Stars
Nebula and Globula
Nebula:
A Nebula is a distinct luminiscent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust.
Nabulae are often star-forming regions, called as ‘Pillars of Creation’.
Globule:
A smsll drop or a ball of a liquid
How black holes formed?
A black hole forms from the leftover mass of a dead Star.
A Star much more massive than our Sun about 3 to 8 times more massive, after the Star has consumed all of its fuel i.e. hydrogen to helium, helium to Carbon then to other heavier elements and finally to Iron.
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STRUCTURE OF A BLACK HOLE
Singularity
The singularity at the centre of a black hole is the ultimate no man’s land on: a place where matter is compressed down to an infinitely tiny point and all conceptions of time and spacecompletely break down. And it doesn’t really exist. Something has to replace the singularity, but we are not exactly sure what.
Event Horizon
The ’event horizon’ is the boundary defining the region of space around a black hole from which nothing (not even light) can escape. In other words, the escape velocity for an object within the event horizon exceeds the speed of light.
THE IMAGE OF BLACK HOLE
This image was released in 2019 and created from data collected in 2017.
Due to very high surface gravity light can not escape from its surface...So we will not be able to see it.
That is why it is called black hole. large mass makes the space curved around.
When this reaches a very high limit the light which have the highest velocity can not escape from the event horizon.
The massive black hole at the heart of the Milky Way is an ideal cosmic laboratory for all kinds of physical tests.
Its extremely strong gravitational field influences the surrounding area and has an impact on the motion of stars passing by
What makes a black hole black?
First off. Let's point out that black holes are not black, but in fact invisible. In order to see something, light must bounce off of or radiate from that something and into your eyes. In this case, that something is a black hole.
Black holes are formed when a star collapses in on itself, squeezing the majority of the star's mass into a tiny space.
Too put it into perspective, imagine our solar system's sun squeezed into a box the size of New York. This is why black holes are so dense.
Because black holes are so dense, they have a very strong gravitational pull. So strong in fact that light can't escape its grasp, pulling the light into the center of the black hole.
Schwarzschild black hole
Schwarzschild Black Hole, otherwise known as a 'static black hole', does not rotate and has no electric charge.
It is characterised solely by its mass.
Kerr black hole
A Kerr black hole is a type of black hole that possesses only mass and angular momentum (but not electrical charge – the third possible property of a black hole).
In other words, a Kerr black hole is an uncharged black hole that rotates about a central axis.
TYPES OF BLACK HOLES
There are four types of black holes:
The most commonly known way a black hole forms is by stellar death.
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Steller black hole
When a star with more than eight times the Sun’s mass runs out of fuel, its core collapses, rebounds, and explodes as a supernova.
What’s left behind depends on the star’s mass before the explosion. If it was near the threshold, it creates a city-sized, superdense neutron star. If it had around 20 times the Sun’s mass or more, the star’s core collapses into a stellar-mass black hole.
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The masses of these newly born objects can range from a few to hundreds of times the Sun’s mass, depending on star’s mass when the supernova began.
Stellar-mass black holes can continue to gain mass through collisions with stars and other black holes.
Nearly all the stellar-mass black holes observed so far have been found because they’re paired with stars.
They likely originated as mismatched stars where the more massive one evolved rapidly into a black hole.
In some cases, called X-ray binaries, the black hole pulls gas off the star into a disk that heats up enough to produce X-rays. Binaries have revealed around 50 suspected or confirmed stellar-mass black holes in the Milky Way, but scientists think there may be as many as 100 million in our galaxy alone.
Intermediate black hole
Scientists are puzzled by the size gap between stellar-mass and supermassive black holes.
They think there should be a continuum of sizes because, over cosmic time, collisions between stellar-mass black holes should have created some intermediate-mass black holes.
These should range from around one hundred to hundreds of thousands of times the Sun’s mass – or tens of thousands, depending on how supermassive black holes are defined. Scientists are actively hunting for examples of these so-called missing-link black holes. Numerous candidates have been identified but have proven difficult to confirm.
Supermassive black hole
Almost every large galaxy, including our Milky Way, has a supermassive black hole at its center.
These monster objects have hundreds of thousands to billions of times the Sun’s mass, although some scientists place the lower boundary at tens of thousands.
The one at the center of our galaxy, Sagittarius A* (pronounced ey-star), is 4 million times the mass of the Sun – relatively small compared to those found in some other galaxies. For example, the black hole at the center of galaxy Holmberg 15A holds at least 40 billion solar masses.
Scientists aren’t sure how these monster objects came to be.
Observations of distant galaxies show that some supermassive black holes formed in the first billion years after the birth of the universe.
It’s possible these black holes began with the collapse of supermassive stars in the early universe, which gave them a head start.
While their origins are mysterious, scientists know supermassive black holes can grow by feeding on smaller objects, like their stellar-mass relatives and neutron stars.
They can also merge with other supermassive black holes when galaxies collide.
Miniature black hole
Micro black holes, also called mini black holes or quantum mechanical black holes, are hypothetical tiny (<1 M ☉) black holes, for which quantum mechanical effects play an important role. The concept that black holes may exist that are smaller than stellar mass was introduced in 1971 by Stephen Hawking.
Miniature black holes may have formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, dense black holes less massive than the sun. If a star passes too close to a black hole, the star can be torn apart (opens in new tab).
How can we learn about black holes if they trap light, and can't actually be seen?
No light of any kind, including X-rays, can escape from inside the event horizon of a black hole, the region beyond which there is no return.
NASA's telescopes that study black holes are looking at the surrounding environments of the black holes, where there is material very close to the event horizon.
Matter is heated to millions of degrees as it is pulled toward the black hole, so it glows in X-rays. The immense gravity of black holes also distorts space itself, so it is possible to see the influence of an invisible gravitational pull on stars and other objects.
A mysterious black hole