Table of Contents
INTRODUCTION OF BLACK HOLE
Black Hole is a cosmic body which is strangest and most fascinating object found in space. It has intense gravity, from which nothing can escape even light. In our galaxy, Milky Way could contain more than 100 million black holes. A supermassive black hole is located at the centre of the Milky Way – “Sagittarius A*“, which have a mass more than 4 million times than mass of Sun and lies at a distance approximately 26,000 light-years away from Earth. Albert Einstein’s general theory of relativity first predicted the actual existence of black hole in 1916. The term “black hole” was given by an American astronomer John Wheeler in 1967. But at that time, the concept of black is only theoretical; there is no evidence of the existence of a black hole. The closest black hole to Earth is Gaia-BH1, which is near about 1,560 light years away. The mass of Gaia-BH1 is around 9.6 times of the sun.
FORMATION OF BLACK HOLE & SCHWARZSCHILD RADIUS
- The life of a star is a continuous struggle between gravity and pressure radiation. Gravity compresses the star, while the radiation due to nuclear fusion pushes its matter outwards. When the fuel is exhausted, the star stops burning. If, the star doesn’t have much mass — like our own Sun — it will become fainter, cooling down as a white dwarf. However, if its initial mass is about eight times that of the Sun, it will collapse, bounce back and detonate in a supernova. Neutron stars form in this way. And if the original mass exceeds about 25 times of solar masses, at the end nothing can counteract gravity and the whole mass is squeezed into a point of zero volume and infinite density. This point is called a singularity. Physicists say that the singularity is not “naked”, in the sense that it is surrounded by a boundary, called an event horizon. Hence what is left at the explosive end of the life of a very massive star is a singularity surrounded by an event horizon — a black hole.
- The Schwarzschild radius is the radius of event horizon that surrounds a non rotating black hole. Any object having a physical radius smaller than its Schwarzschild radius will be converted into a black hole. This equation was first derived by Karl Schwarzschild in 1916. The equation is written as follows
Rs = 2GM/c²
where, Rs is the Schwarzschild radius, G is the gravitational constant, M is the mass of the object and, c is the speed of light.
For sun the Schwarzschild radius is near about 3 km, that means if sun converted into a black hole, then radius of its event horizon is 3 kilometers. And for earth it will be 8.7 mm.
| Initial Stellar Mass | Final Stellar Mass | End Product |
|---|---|---|
Less than 8 M☉ | Less than 1.4 M☉ | White dwarf |
8 — 25 M☉ | 1.4 — 3 M☉ | Neutron star |
Greater than 20 — 25 M☉ | Greater than 3 M☉ | Stellar-mass black hole |
TYPES OF BLACK HOLE
Astronomers generally divide black holes into three major categories according to their mass: 1. Stellar, 2. Supermassive, and 3. Intermediate-mass. Cosmologists are suspect a fourth type, primordial black holes which formed during the beginning of the universe.
- Stellar Black Holes: Stellar Black Holes are formed when a star having more than eight times of the Sun’s mass runs out of fuel, its core collapses, rebounds, and explodes as a supernova. And if it had around 20 times of the Sun’s mass or more, the star’s core collapses into a Stellar-mass black hole. Generally this types of black holes are formed by collapsing of individual stars, which are relatively small but incredibly dense. One of these objects having more than three times mass of sun with the diameter of a city. As a result, it has huge amount of gravitational force which pulls the objects into this.
- Supermassive Black Holes: Almost every galaxy, including our Milky Way galaxy, has a supermassive black hole at its heart. These objects have hundreds of thousands to billions of times the mass of Sun. In our center of the Milky Way galaxy Sagittarius A*, is 4 million times mass of the sun. This mass is relatively small compared to other black holes found in different foreign galaxies. For an example, the black hole at the center of galaxy Holmberg 15A having at least 40 billion solar masses. And TON 618 is the most massive black hole which have ever observed, with 66 billion times the mass of the sun. It is located 18.2 billion light years from earth.
- Intermediate Black Holes: Scientists thought that black holes came only in small and large sizes, but research has shown the possibility that midsize, or intermediate, black holes could exist. Such black holes could form when stars in a cluster collide in a chain reaction. These should range from around one hundred to hundreds of thousands of times of the Sun’s mass – depending on how supermassive black holes are defined. Research, in 2018, suggested that these midsize, or intermediate, black holes may exist in the center of dwarf galaxies or very small galaxies.
- Primordial Black Holes: Each of the black holes that have observed till now can be categorized as one of three classifications: 1. Stellar-mass black holes, 2. Intermediate mass black holes, and 3. Supermassive black holes. Each is more massive than our Sun in our solar system and formed something like billions of But, there is one more kind of black hole astronomers haven’t yet observed and studied, however they think it could exist. These are actually termed as primordial black holes. But there is one more kind of black that haven’t yet observed and studied, however, they believe it could exist. These are actually termed as “Primordial Black Holes”. As the name implies, Primordial black holes formed very early in the universe’s existence, only a fraction of a second after the Big Bang. Years after the Big Bang, when our universe expanded and advanced, it was a time when stars, galaxies, and many types of black holes could not yet exist.
STRUCTURE OF BLACK HOLE
One of the biggest misconceptions related to a black hole is to think of it like a planet or other celestial body, in space with its surface being the event horizon. However, a black hole is not like other celestial bodies. All the mass of a blackhole is concentrated at a single point called the singularity. So basically, there are two main parts of black hole —
- Even Horizon, 2. Singularity
Event Horizon: The event horizon is the point of no return around the black hole. At this point in spacetime, nothing, including light, can escape the Black Hole and the escape velocity is near to the speed of light.
When an item approaches an event horizon, a witness will notice the item’s picture reddening and dimming as gravity distorts the light coming from it. At the event horizon, this image would fade to invisibility. “The event horizon protects us from the unknown physics surrounding a singularity.” Loeb said.
Singularity: Singularity happens when all the matters in a dying star gets compacted into the minimum possible volume. It is usually known as singularity. It is a zero-dimensional point which basically contains a massive mass in an infinitely small space, where density and gravity become infinite and the curves of space time extend infinitely, and where all the laws of physics break down. Scientists are currently engaged in research to better understanding what happens at these singularities.
STRUCTURE OF BLACK HOLE
From Einstein’s general theory of relativity, we know that the time is influenced by two things, if an object which travels near about of light speed and an object which have massive mass. Strange phenomenon that a travellar would observe close to a black hole time dilation, in which time passes slower for an object closer to the black hole than further away. This happens because massive objects create a strong gravitational field that curve and stretch the “fabric” of space time. For an example, passing a month near a black hole might be equal to passing several years back on Earth. In earth we can also see this time dilation due to the earth’s gravity but it will very small. Living on the International Space Station astronauts also experience slightly different of time because they are further from the gravitational pull of the Earth.
In movie Interstellar (2014), after passing through the wormhole (appears near planet Saturn), Coop’s team decide to land on Dr. Miller’s planet. It’s orbiting a supermassive black hole Gargantua, the massive glowing black hole which exists in the foreign galaxy. Due to Gargantua’s massive gravitational force, every hour passes on that planet is seven years on Earth (1 hour on Miller’s planet = 7 years on Earth). After a massive tidal wave hits their spacecraft which delays their exit, they could find that 23 years have passed on Earth.
CURRENT RESEARCH ON BLACK HOLE
There are probably over millions of black holes are in the Milky Way alone, orbiting like the stars, but we cannot see them. And there are many things which is still unknown, like what’s inside a black hole, mechanics of black hole. For this reason, scientists and researchers try to find out of this answer. Here are some recent research findings on black holes:
- In October 2018, astronomers observed a black hole in a foreign galaxy near about 665 million light-years from Earth. This event, called AT2018hyz and the black hole was 20 million times more massive than the sun.
- In 2021, astronomers revealed a new image of the supermassive black hole at the center of galaxy M87 in polarized light. This image shows the black hole’s ring is magnetized and the black hole in more detail.
- In May 2022, scientists revealed the first image of the supermassive black hole which lie at the center of Milky Way galaxy, “Sagittarius A*”.
- In 2023, some studies suggests that supermassive black holes at the centre of large galaxies could be the main sources of dark energy, the force that drives the universe’s expansion and is responsible for pushing things apart stronger than gravity.
- In November 2023, Astronomers have discovered the farthest black hole yet seen in X-rays, by using NASA telescopes. The black hole is at an early stage of growth that had never been seen before, where its mass is similar of its host galaxy.
- In February 2024, According to Live Science article, scientists have discovered a powerful “Black Hole Wind” which blew through a nearby galaxy for hundreds of days, reshaping the galaxy & crushing star formation.
CONCLUSIONS
Has the Earth been affected by black holes?? When a massive star explodes, it leaves behind stellar-mass black holes. These explosions propel life sustaining materials into space, including carbon, nitrogen, and oxygen. If anything, their existence helps us. Star explosions eject materials like as carbon, nitrogen, and oxygen into space, resulting in black holes. Collisions between black holes and neutron stars allow heavier metals, such as gold and platinum, to spread. These are the elements that comprise our world and ourselves.