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Oct 22nd 2017
Black holes are some of the strangest and most fascinating objects found in outer space. They are objects of extreme density, with such strong gravitational attraction that even light cannot escape from their grasp if it comes near enough.
Albert Einstein first predicted black holes in 1916 with his general theory of relativity. The term "black hole" was coined in 1967 by American astronomer John Wheeler, and the first one was discovered in 1971.
There are three types: stellar black holes, supermassive black holes and intermediate black holes.
Stellar black holes — small but deadly
When a star burns through the last of its fuel, it may collapse, or fall into itself. For smaller stars, up to about three times the sun's mass, the new core will be 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. Such an object packs three times or more the mass of the sun into a city-size range. This leads to a crazy amount of gravitational force pulling on objects around it. Black holes consume the dust and gas from the galaxy around them, growing in size.
According the Harvard-Smithsonian Center for Astrophysics, "the Milky Way contains a few hundred million" stellar black holes.
Supermassive black holes — the birth of giants
Small black holes populate the universe, but their cousins, supermassive black holes, dominate. Supermassive black holes are millions or even billions of times as massive as the sun, but have a radius similar to that of Earth's closest star. 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 they've 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 enormous sizes.
Illustration of a young black hole, such as the two distant dust-free quasars spotted recently by the Spitzer Space Telescope. More photos of black holes of the universe
Supermassive 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.
Intermediate black holes – stuck in the middle
Scientists once thought black holes came in only small and large sizes, but recent research has revealed the possibility for the existence of mid-size, or intermediate, black holes (IMBHs). Such bodies could form when stars in a cluster collide in a chain reaction. Several of these forming in the same region could eventually fall together in the center of a galaxy and create a supermassive 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," 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 IMBH's have been acting like a long-lost relative that isn't interested in being found."
Black hole theory — how they tick
Black holes are incredibly massive, but cover only a small region. Because of the relationship between mass and gravity, this means they have an extremely powerful gravitational force. Virtually nothing can escape from them — under classical physics, even light is trapped by a black hole.
Such a strong pull creates an observational problem when it comes to black holes — scientists can't "see" them the way they can see stars and other objects in space. Instead, scientists must rely on the radiation that is emitted as dust and gas are drawn into the dense creatures. Supermassive black holes, lying in the center of a galaxy, may find themselves shrouded by the dust and gas thick around them, which can block the tell-tale emissions.
Black holes are strange regions where gravity is strong enough to bend light, warp space and distort time. [See how black holes work in this SPACE.com infographic.
Credit: Karl Tate, SPACE.com contributor
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 itself remains unseen, these powerful jets can be viewed from great distances.
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 where light loses its ability to 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 its mass lies, is known as its singularity, the single point in space-time where the mass of the black hole is concentrated.
Under the classical mechanics of physics, nothing can escape from a black hole. However, things shift slightly when quantum mechanics are added to the equation. Under quantum mechanics, for every particle, there is an antiparticle, a particle with the same mass and opposite electric charge. When they meet, particle-antiparticle pairs can annihilate one another.
If a particle-antiparticle pair is created just beyond the reach of the event horizon of a black hole, it is possible to have one drawn into the black hole itself while the other is ejected. The result is that the event horizon of the black hole has been reduced and black holes can decay, a process that is rejected under classical mechanics.
Scientists are still working to understand the equations by which black holes function.
Shining light on binary black holes
In 2015, astronomers using the Laser Interferometer Gravitational-wave Observatory (LIGO) made the first detection of gravitational waves. Since then, the instrument has observed several other incidents. The gravitational waves spotted by LIGO came from merging stellar black holes.
"We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses — these are objects we didn't know existed before LIGO detected them," MIT's David Shoemaker said in a statement. Shoemaker is the spokesperson for the LIGO Scientific Collaboration (LSC), a body of more than 1,000 international scientists who perform LIGO research together with the European-based Virgo Collaboration.
LIGO's observations also provide insights about the direction a black hole spins. As a pair of black holes spirals around one another, they can spin in the same direction or they can be completely different.
"This is the first time that we have evidence that the black holes may not be aligned, giving us just a tiny hint that binary black holes may form in dense stellar clusters," said LIGO researcher Bangalore Sathyaprakash of Penn State and Cardiff University.
There are two theories on how binary black holes form. The first suggests that they formed at about the same time, from two stars that were born together and died explosively at about the same time. The companion stars would have had the same spin orientation, so the black holes they left behind would, as well.
Under the second model, black holes in a stellar cluster sink to the center of the cluster and pair up. These companions would have random spin orientations compared to one another. LIGO's observations of companion black holes with different spin orientations provide stronger evidence for this formation theory.
"We're starting to gather real statistics on binary black hole systems," said LIGO scientist Keita Kawabe of Caltech, who is based at the LIGO Hanford Observatory. "That's interesting because some models of black hole binary formation are somewhat favored over the others even now and, in the future, we can further narrow this down."
Interesting 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 singularity. But a 2012 study in Nature suggests that quantum effects would cause the event horizon to act much like a wall of fire, instantly burning anyone to death.
· Black holes do not "suck." Suction is caused by pulling something into a vacuum, which the massive black hole definitely is not. Instead, objects fall into them.
· The first object considered to be a black hole is Cygnus X-1. Rockets carrying Geiger counters discovered eight new X-ray sources. In 1971, scientists detected radio emissions coming from Cygnus X-1, and a massive hidden companion was found and identified as a black hole.
· Cygnus X-1 was the subject of a 1974 friendly wager between Stephen Hawking and a fellow physicist Kip Thorne, with Hawking betting that the source was not a black hole. In 1990, he conceded defeat. [VIDEO: Final Nail in Stephen Hawking's Cygnus X-1 Bet?]
· 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, it can be torn apart.
· Astronomers estimate there are anywhere from 10 million to a billion stellar black holes, with masses roughly three times that of the sun, in the Milky Way.
· The interesting relationship between string theory and black holes gives rise to more types of massive giants than found under conventional classical mechanics.
· Black holes remain terrific fodder for science fiction books and movies. Check out the science behind the movie "Interstellar," which relied heavily on theoretical physicist Kip Thorne to bring real science to the Hollywood feature. In fact, work with the special effects of the blockbuster lead to an improvement in the scientific understanding of how distant stars might appear when seen near a fast-spinning black hole.
Feb 5th 2017
· NASA has found evidence of supermassive black holes in galaxies that formed when the universe was just 1.4 billion years old.
· This discovery could completely change our understanding of how black holes came together when the universe was just in its infancy.
FROM OUT OF THE DARKNESS
In some ways, astronomy is a lot like time travel. Even with the best telescopes, what we see now has already happened, and in some cases, it happened billions of years ago. The radiation and other signals we pick up take so long to travel to us that the farther away the event was, the longer it takes for us to know about it. Such information can provide scientists with a window into the past, and sometimes, even give us a glimpse at the very foundations of our universe.
Recently, NASA used the Fermi Gamma-Ray Space Telescope to intercept intense gamma radiation from some far away, ancient galaxies. The galaxies formed roughly 12 billion years ago and could clue us in to how black holes formed during the universe’s (relative) infancy.
The rays come from super energetic space objects call blazars, which are compact quasars. These objects are found at the centers of active elliptical galaxies that are also home to supermassive black holes. As matter falls into these black holes, they shoot out energy, which moves nearly at the speed of light. Knowing this, we can tell from where and when the energy came.
A DEEPER LOOK
Astronomers are excited by the prospect of studying such old black holes. “Despite their youth, these far-flung blazars host some of the most massive black holes known,” said Roopesh Ojha of NASA’s Goddard Space Flight Centre in a press release. He continued, “That they developed so early in cosmic history challenges current ideas of how supermassive black holes form and grow, and we want to find more of these objects to help us better understand the process.”
Tools such as the Fermi Space Telescope are allowing scientists to reach deeper into space than ever before. Subsequently, that means that we are able to look deeper into the universe’s past. But as with many huge discoveries, the findings present more questions than immediate answers. “The main question now is how these huge black holes could have formed in such a young universe. We don’t know what mechanisms triggered their rapid development,” said another team member, Dario Gasparrini of the Italian Space Agency’s Science Data Centre.
Given what we know about black holes, how these supermassive objects, which pump out two trillion times the energy of our Sun, were able to form is a mystery. Answers to questions like this will help us understand how the universe looked throughout its development, and maybe even what’s in store for the future. For now, NASA will continue to look for more blazars to study, as their orientation causes them to appear clearly on our high-powered equipment. According to Marco Ajello from Clemson University in South Carolina, “We think Fermi has detected just the tip of the iceberg, the first examples of a galaxy population that previously has not been detected in gamma rays.”
Black-holes are a space phenomenon that are no threat to human beings, there is one at the centre of our galaxy and whilst it is a strange and very violent place it has been there for a long long time and I could joke and say nobody has ever seen it, but we do know it’s there, scientists have told us.
As an example as to why it is no threat to us consider this. If our sun were to stop shining suddenly we would not be aware of it for a full eight minutes, because that is the time it takes for the light from the sun to reach us here on earth.
Now the nearest black hole is the one at the centre of our galaxy and our galaxy is many light years across, a light year is the way we measure the enormous distances across space. We cannot do this in miles, the numbers are just too big for our reasoning.
You can work it out, the sun is about 93 million miles away, and light travels that distance in eight minutes so divide a year by eight minutes and multiply that figure by 93 million miles and you get a large number of miles, that’s a light year.
It’s impractical to think of miles when you are thinking about space, distant stars are millions of light years distant from Earth, when we think about, photograph or record these stars, we are recording what they were like millions of light years ago, we don’t know what they are like today.
The biggest known black hole is four lights Days in diameter this equates to 70,000 million miles, and remember the sun is 93,million miles away from the Earth
How can we be sure that what science is telling us is actually a true picture of the universe? we know that as we go faster time actually slows down, we also know that the universe is expanding and everything that we are looking at are travelling at different speeds, and this means some parts have different times.
The world is a weird and wonderful place and if you include the universe in your thinking things get more weird and more wonderful the more you think about it.
But do not worry about such things, it has been like this for thousands of years and it's not likely to change soon.
The best way for me to give you information on black holes is to present you with a series of YouTube videos, here they are.