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Black holes

Do you know that stars also die? What happens when a star dies?  Yes! Stars can die; when a star dies they form a massive whole called the Black holes. When a star has exhausted the internal thermonuclear fuels in its core at the end of its life, the core becomes unstable and gravitationally collapses inward upon itself, and the star's outer layers are blown away leading to the creation of black hole.

The existence of black hole was first predicted by ALBERT Einstein in 1916, through his general theory of relativity. The term "black hole" was coined many years later in 1967 by American astronomer John Wheeler. After decades of black holes being known only as theoretical objects, the first physical black hole ever discovered was spotted in 1971. 

Then, in 2019 the Event Horizon Telescope (EHT) collaboration released the first image ever recorded of a black hole. The EHT saw the black hole in the center of galaxy M87 while the telescope was examining the event horizon, or the area past which nothing can escape from a black hole. The image maps the sudden loss of photons (particles of light). It also opens up a whole new area of research in black holes, now that astronomers know what a black hole looks like.

 

 

 

 

There are four types of black holes: stellar, intermediate, supermassive, and miniature. The most commonly known way a black hole forms is by stellar death. Black holes are some of the strangest and most fascinating objects in outer space. They're extremely dense; with such strong gravitational attraction that even light cannot escape their grasp if it comes near enough. 

Stellar black holes — small but deadly

 

When a star burns through the last of its fuel, the object may collapse, or fall into itself just like the roof of a building collapsing into itself. For smaller stars (those up to about three times the sun's mass), the new core will become a neutron star or a white dwarf. But when a larger star collapses, it continues to compress and creates a stellar black hole.

Black holes formed by the collapse of individual stars are relatively small, but incredibly dense. One of these objects packs more than three times the mass of the sun into the diameter of a city. This leads to a crazy amount of gravitational force pulling on objects around the object. Stellar black holes then consume the dust and gas from their surrounding galaxies, which keeps them growing in size.

According the Harvard-Smithsonian Center for Astrophysics," the Milky Way contains a few hundred million" stellar black holes.

 

 

Super massive black holes — the birth of giant

Imaging a hole whose size is over millions and billions the size of the sun! Super massive black holes are enormous black holes whose size is over millions or even billions of times as massive as the sun, but are about the same size in diameter. Such black holes are thought to lie at the center of pretty much every galaxy, including the Milky Way.

Scientists aren't certain how such large black holes spawn. Once these giants have formed, they gather mass from the dust and gas around them, material that is plentiful in the center of galaxies, allowing them to grow to even more enormous sizes.

Super massive black holes may be the result of hundreds or thousands of tiny black holes that merge together. Large gas clouds could also be responsible, collapsing together and rapidly accreting mass. A third option is the collapse of a stellar cluster, a group of stars all falling together. Fourth, super massive black holes could arise from large clusters of dark matter. This is a substance that we can observe through its gravitational effect on other objects; however, we don't know what dark matter is composed of because it does not emit light and cannot be directly observed.

 

 

Intermediate black holes  — stuck in the middle

Scientists once thought that black holes came in only small and large sizes, but recent research has revealed the possibility that midsize, or intermediate, black holes (IMBHs) could exist. Such bodies could form when stars in a cluster collide in a chain reaction. Several of these IMBHs forming in the same region could then eventually fall together in the center of a galaxy and create a super massive black hole.

In 2014, astronomers found what appeared to be an intermediate-mass black hole in the arm of a spiral galaxy.

"Astronomers have been looking very hard for these medium-sized black holes," study co-author Tim Roberts, of the University of Durham in the United Kingdom, said in a statement. "There have been hints that they exist, but IMBHs have been acting like a long-lost relative that isn't interested in being found."

Newer research, from 2018, suggested that these IMBHs may exist in the heart of dwarf galaxies (or very small galaxies). Observations of 10 such galaxies (five of which were previously unknown to science before this latest survey) revealed X-ray activity — common in black holes — suggesting the presence of black holes of from 36,000 to 316,000 solar masses. The information came from the Sloan Digital Sky Survey, which examines about 1 million galaxies and can detect the kind of light often observed coming from black holes that are picking up nearby debris.

 

What do black holes look like? 

Black holes are strange regions where gravity is strong enough to bend light, warp space and distort time. 

Black holes have three "layers": the outer and inner event horizon, and the singularity.

The event horizon of a black hole is the boundary around the mouth of the black hole, past which light cannot escape. Once a particle crosses the event horizon, it cannot leave. Gravity is constant across the event horizon.

The inner region of a black hole, where the object's mass lies, is known as its singularity, the single point in space-time where the mass of the black hole is concentrated.

Scientists can't see black holes the way they can see stars and other objects in space. Instead, astronomers must rely on detecting the radiation black holes emit as dust and gas are drawn into the dense creatures. But super massive black holes, lying in the center of a galaxy, may become shrouded by the thick dust and gas around them, which can block the telltale emissions.

Sometimes, as matter is drawn toward a black hole, it ricochets off the event horizon and is hurled outward, rather than being tugged into the maw. Bright jets of material traveling at near-relativistic speeds are created. Although the black hole remains unseen, these powerful jets can be viewed from great distances.

The Event Horizon Telescope's image of a black hole in M87 (released in 2019) was an extraordinary effort, requiring two years of research even after the images were taken. That's because the collaboration of telescopes, which stretches across many observatories worldwide, produces an astounding amount of data that is too large to transfer by internet. 

With time, researchers expect to image other black holes and build up a repository of what the objects look like. The next target is likely Sagittarius A*, which is the black hole in the center of our own Milky Way galaxy. Sagittarius A* is intriguing because it is quieter than expected, which may be due to magnetic fields smothering its activity, a 2019 study reported. Another study that year showed that a cool gas halo surrounds Sagittarius A*, which gives unprecedented insight into what the environment around a black hole looks like.

 

Weird facts about black holes

·         If you fell into a black hole, theory has long suggested that gravity would stretch you out like spaghetti, though your death would come before you reached the singularity. But a 2012 study published in the journal Nature suggested that quantum effects would cause the event horizon to act much like a wall of fire, which would instantly burn you to death.

·         Black holes don't suck. Suction is caused by pulling something into a vacuum, which the massive black hole definitely is not. Instead, objects fall into them just as they fall toward anything that exerts gravity, like the Earth.

·         The first object considered to be a black hole is Cygnus X-1. Cygnus X-1 was the subject of a 1974 friendly wager between Stephen Hawking and fellow physicist Kip Thorne, with Hawking betting that the source was not a black hole. In 1990, Hawking conceded defeat.

·         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.

·         Astronomers estimate that the Milky Way has anywhere from 10 million to 1 billion stellar black holes, with masses roughly three times that of the sun.

·         Black holes remain terrific fodder for science fiction books and movies. Check out the movie "Interstellar," which relied heavily on Thorne to incorporate science. Thorne's work with the movie's special effects team led to scientists' improved understanding of how distant stars might appear when seen near a fast-spinning black hole.

 

 

10 FUN FACTS ABOUT BLACK HOLES!

1. You Can’t Directly See a Black Hole.

A black hole is called a black hole because of it’s color, especially since light can’t escape. What we can see, though, is the effects of a black hole. Analyzing the surrounding area of a black hole, we can see its effects upon its environment. For example, a star that’s close enough to a black hole can be seen being ripped apart.

2. Our Milky Way Probably Has a Black Hole.

But, don’t be alarmed, Earth isn’t in danger! The major black hole that astronomists believe to be within our Milky Way is light years away from Earth.

3. Dying Stars Lead to Stellar Black Holes.

The death of large stars lead to black holes, because a star’s gravity will overwhelm the star’s natural pressure that it maintains to keep its shape. When the pressure from the nuclear reactions collapses, gravity overwhelms and collapses the star’s core, and the star’s other layers are thrown off into space, and this process is also known as a supernova. The remainder of the core collapses, a spot overcome by density and without volume – a black hole.

·         4. There are Three Categories of Black Holes.

·          Primordial Black holes – These are the smallest of black holes and range from an atom’s size to a mountain’s mass.

·          Stellar Black Holes – These are the most common of black holes and they can be up to 20 times more massive than the Sun. There are also a variety of these all over the Milky Way.

·          Supermassive Black Holes – These are the largest of black holes, being more than 1 million times more massive than the Sun.

·          Black Holes Are Funky.

·         Say someone falls into a black hole and there’s an observer that witnesses this. The person who fell into the black hole’s time slows down, relative to the person watching. This is explained by Einstein’s Theory of General Relativity, which states that time is affected by how fast you are going when you’re at extreme speeds close to light.

·          The First Black Hole Wasn’t Discovered Until X-Ray Astronomy was Used.

·         Cygnus X-1 was the first black hole discovered in the 1960’s, and it’s 10 times more massive than the Sun.

·          The Closest Black Hole is Probably Not 1,600 Light-Years Away.

·         V4647 Sagitarii was thought to be 1,600 light-years away, but is further away than expected. Scientists now believe that this black hole is about 20,000 light years away.

·         We Don’t Know if Wormholes Exist.

·         We don’t know if this event exists, since we don’t know too much about physics, but that also means that anything may be possible.

·          Black Holes Are Only Dangerous if You Get Too Close.

·         Black holes are safe to observe from a lengthy distance, but not if you get too close, which also means that it’s unlikely for a black hole to consume an entire universe.

·          Black Holes Are Constantly Used in Science Fiction.