Tag: black hole

For the first time, physicists have calculated exactly what kind of singularity lies at the center of a realistic black hole.

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by Steve Nadis

In January 1916, Karl Schwarzschild, a German physicist who was stationed as a soldier on the eastern front, produced the first exact solution to the equations of general relativity, Albert Einstein’s radical, two-month-old theory of gravity. General relativity portrayed gravity not as an attractive force, as it had long been understood, but rather as the effect of curved space and time. Schwarzschild’s solution revealed the curvature of space-time around a stationary ball of matter.

Curiously, Schwarzschild noticed that if this matter were confined within a small enough radius, there would be a point of infinite curvature and density — a “singularity” — at the center.

Infinities cropping up in physics are usually cause for alarm, and neither Einstein, upon learning of the soldier’s result, nor Schwarzschild himself believed that such objects really exist. But starting in the 1970s, evidence mounted that the universe contains droves of these entities — dubbed “black holes” because their gravity is so strong that nothing going into them, not even light, can come out. The nature of the singularities inside black holes has been a mystery ever since.

Recently, a team of researchers affiliated with Harvard University’s Black Hole Initiative (BHI) made significant progress on this puzzle. Paul Chesler, Ramesh Narayan and Erik Curiel probed the interiors of theoretical black holes that resemble those studied by astronomers, seeking to determine what kind of singularity is found inside. A singularity is not a place where quantities really become infinite, but “a place where general relativity breaks down,” Chesler explained. At such a point, general relativity is thought to give way to a more exact, as yet unknown, quantum-scale description of gravity. But there are three different ways in which Einstein’s theory can go haywire, leading to three different kinds of possible singularities. “Knowing when and where general relativity breaks down is useful in knowing what theory [of quantum gravity] lies beyond it,” Chesler said.

The BHI group built on a major advance achieved in 1963, when the mathematician Roy Kerr solved Einstein’s equations for a spinning black hole — a more realistic situation than the one Schwarzschild took on since practically everything in the universe rotates. This problem was harder than Schwarzschild’s, because rotating objects have bulges in the center and therefore lack spherical symmetry. Kerr’s solution unambiguously described the region outside a spinning black hole, but not its interior.

Kerr’s black hole was still somewhat unrealistic, as it occupied a space devoid of matter. This, the BHI researchers realized, had the effect of making the solution unstable; the addition of even a single particle could drastically change the black hole’s interior space-time geometry. In an attempt to make their model more realistic and more stable, they sprinkled matter of a special kind called an “elementary scalar field” in and around their theoretical black hole. And whereas the original Kerr solution concerned an “eternal” black hole that has always been there, the black holes in their analysis formed from gravitational collapse, like the ones that abound in the cosmos.

First, Chesler, Narayan and Curiel tested their methodology on a charged, non-spinning, spherical black hole formed from the gravitational collapse of matter in an elementary scalar field. They detailed their findings in a paper posted on the scientific preprint site arxiv.org in February. Next, Chesler tackled the more complicated equations pertaining to a similarly formed rotating black hole, reporting his solo results three months later.

Their analyses showed that both types of black holes contain two distinct kinds of singularities. A black hole is encased within a sphere called an event horizon: Once matter or light crosses this invisible boundary and enters the black hole, it cannot escape. Inside the event horizon, charged stationary and rotating black holes are known to have a second spherical surface of no return, called the inner horizon. Chesler and his colleagues found that for the black holes they studied, a “null” singularity inevitably forms at the inner horizon, a finding consistent with prior results. Matter and radiation can pass through this kind of singularity for most of the black hole’s lifetime, Chesler explained, but as time goes on the space-time curvature grows exponentially, “becoming infinite at infinitely late times.”

The physicists most wanted to find out whether their quasi-realistic black holes have a central singularity — a fact that had only been established for certain for simple Schwarzschild black holes. And if there is a central singularity, they wanted to determine whether it is “spacelike” or “timelike.” These terms derive from the fact that once a particle approaches a spacelike singularity, it is not possible to evolve the equations of general relativity forward in time; evolution is only allowed along the space direction. Conversely, a particle approaching a timelike singularity will not inexorably be drawn inside; it still has a possible future and can therefore move forward in time, although its position in space is fixed. Outside observers cannot see spacelike singularities because light waves always move into them and never come out. Light waves can come out of timelike singularities, however, making them visible to outsiders.

Of these two types, a spacelike singularity may be preferable to physicists because general relativity only breaks down at the point of singularity itself. For a timelike singularity, the theory falters everywhere around that point. A physicist has no way of predicting, for instance, whether radiation will emerge from a timelike singularity and what its intensity or amplitude might be.

The group found that for both types of black holes they examined, there is indeed a central singularity, and it is always spacelike. That was assumed to be the case by many, if not most, astrophysicists who held an opinion, Chesler noted, “but it was not known for certain.”

The physicist Amos Ori, a black hole expert at the Technion in Haifa, Israel, said of Chesler’s new paper, “To the best of my knowledge, this is the first time that such a direct derivation has been given for the occurrence of a spacelike singularity inside spinning black holes.”

Gaurav Khanna, a physicist at the University of Massachusetts, Dartmouth, who also investigates black hole singularities, called the BHI team’s studies “great progress — a quantum leap beyond previous efforts in this area.”

While Chesler and his collaborators have strengthened the case that astrophysical black holes have spacelike singularities at their cores, they haven’t proved it yet. Their next step is to make more realistic calculations that go beyond elementary scalar fields and incorporate messier forms of matter and radiation.

Chesler stressed that the singularities that appear in black hole calculations should disappear when physicists craft a quantum theory of gravity that can handle the extreme conditions found at those points. According to Chesler, the act of pushing Einstein’s theory to its limits and seeing exactly how it fails “can guide you in constructing the next theory.”

https://www.quantamagazine.org/black-hole-singularities-are-as-inescapable-as-expected-20191202/?utm_source=Nature+Briefing&utm_campaign=6cddda34dd-briefing-dy-20191206&utm_medium=email&utm_term=0_c9dfd39373-6cddda34dd-44039353

Historic Image of Black Hole Said to Prove Einstein’s Theory of Relativity

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BY LI YEN, EPOCH TIMES

France Córdova, National Science Foundation director, said in a statement: “Black holes have sparked imaginations for decades. They have exotic properties and are mysterious to us.”

In fact, the mysterious black holes, dubbed as “monsters” by scientists, are not empty space, according to NASA. They are instead, as presented in Albert Einstein’s theory of general relativity, made up of “a great amount of matter packed into a very small area,” mostly formed from “the remnants of a large star that dies in a supernova explosion.”

Einstein predicted the existence of massive and dense black holes in the universe, where the gravitational fields are so strong that even light can’t escape.

The German-born American physicist, widely regarded as a genius today, made known this theory to the world more than a century ago on Nov. 25, 1915, at the Prussian Academy of Sciences.

“About a hundred years ago, Albert Einstein gave us a new description of the force of gravity, in which gravity exerts its influence through warps and curves in the fabric of space and time,” Brian Greene, a physicist at Columbia University, said in a video for the World Science.

After Einstein’s death, the scientific community discovered that black holes do exist, and there are countless such black holes spreading throughout the universe.

On April 10, the genius’s century-old theory of general relativity was further reaffirmed—the existence of the gravitational and light-sucking cosmic objects was reported to be true.

“Today, general relativity has passed another crucial test, this one spanning from horizons to the stars,” Avery Broderick, Event Horizon Telescope (EHT) team member of the University of Waterloo and the Perimeter Institute for Theoretical Physics in Canada, said during a press conference in Washington, D.C.

“You can see the ring Einstein’s relativity predicts,” Vincent Fish, a research scientist at MIT’s Haystack Observatory in Westford, and also one of the 200 scientists who was involved in the project, told the Boston Herald. “You know exactly how big that ring should be. This was the first opportunity to test that hypothesis.”

Dimitrios Psaltis, Professor of Astronomy and Physics at the University of Arizona, and EHT project scientist, said in a press release: “The Event Horizon Telescope allows us for the very first time to test the predictions of Einstein’s General Theory of Relativity around supermassive black holes in the centers of galaxies. The predicted size and shape of the shadow theory match our observations remarkably well, increasing our confidence in this century-old theory.”

“If immersed in a bright region, like a disc of glowing gas, we expect a black hole to create a dark region similar to a shadow—something predicted by Einstein’s general relativity that we’ve never seen before,” Heino Falcke of Radboud University, the Netherlands, chair of the EHT Science Council, said.

Some Refute Einstein’s Theory

Despite the theory that shot Einstein to fame, some scientists have said the theory doesn’t explain everything, and requires revision.

Speaking about gravity, Austrian physicist Andrea Ghez, who led a 20-year-long black hole experiment, told Express News: “You can hark back to the days of Newton—who had the previous best description of gravity—and at some point we realized we had to move beyond Newton, to get a more complete vision.”

Ghez added: “As we explore these more and more extreme conditions we see that there is something missing.

“the closer you get to the heart of the galaxy, the shorter the time scales become.”

In terms of light, central to Einstein’s Theory of General Relativity is that the speed of light is constant everywhere.

One counter theory by researchers suggests that the speed of light is varied, and that light traveled faster in the wake of the Big Bang—a significant blow to Einstein’s theory.

“The idea that the speed of light could be variable was radical when first proposed, but with a numerical prediction, it becomes something physicists can actually test. If true, it would mean that the laws of nature were not always the same as they are today,” cosmologist and theoretical physicist João Magueijo told news.com.au.

Location of the Historic Finding

The black hole that was discovered resides at the heart of a huge galaxy known as Messier 87 or M87, near the Virgo galaxy cluster, 55 million light years from Earth.

The first snapshot of the black hole was captured by scientists using a global network of eight linked telescopes that were stationed over five continents in April 2017 for a week-long observation of black holes, according to Event Horizon Telescope.

“This is an extraordinary scientific feat accomplished by a team of more than 200 researchers,” said Sheperd Doeleman, director of the EHT Collaboration.

The enormous black hole captured in the image is predicted to have a mass 6.5 billion times bigger than our sun. Researchers believe it may be the biggest black hole that can be viewed from Earth.

“M87’s huge black hole mass makes it really a monster, even by supermassive black hole standards,” Sera Markoff, an astrophysicist at the University of Amsterdam, told The Verge. “You’re basically looking at a supermassive black hole that’s almost the size of our entire Solar System.”

https://www.theepochtimes.com/historic-image-of-black-hole-said-to-prove-einsteins-theory-of-relativity_2876829.html

Using black holes to conquer space: The halo drive

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by Matt Williams

The idea of traveling to another star system has been the dream of people long before the first rockets and astronauts were sent to space. But despite all the progress we have made since the beginning of the Space Age, interstellar travel remains just that – a dream. While theoretical concepts have been proposed, the issues of cost, travel time and fuel remain highly problematic.

A lot of hopes currently hinge on the use of directed energy and lightsails to push tiny spacecraft to relativistic speeds. But what if there was a way to make larger spacecraft fast enough to conduct interstellar voyages? According to Prof. David Kipping, the leader of Columbia University’s Cool Worlds lab, future spacecraft could rely on a halo drive, which uses the gravitational force of a black hole to reach incredible speeds.

Prof. Kipping described this concept in a recent study that appeared online (the preprint is also available on the Cool Worlds website). In it, Kipping addressed one of the greatest challenges posed by space exploration, which is the sheer amount of time and energy it would take to send a spacecraft on a mission to explore beyond our solar system.

Kipping told Universe Today via email: “Interstellar travel is one of the most challenging technical feats we can conceive of. Whilst we can envisage drifting between the stars over millions of years – which is legitimately interstellar travel – to achieve journeys on timescales of centuries or less requires relativistic propulsion.”

As Kipping put it, relativistic propulsion (or accelerating to a fraction of the speed of light) is very expensive in terms of energy. Existing spacecraft simply don’t have the fuel capacity to get up to those kinds of speeds, and short of detonating nukes to generate thrust à la Project Orion, or building a fusion ramjet à la Project Daedalus, there are not a lot of options available.

In recent years, attention has shifted toward the idea of using lightsails and nanocraft to conduct interstellar missions. A well-known example is Breakthrough Starshot, an initiative that aims to send a smartphone-sized spacecraft to Alpha Centauri within our lifetime. Using a powerful laser array, the lightsail would be accelerated to speeds of up to 20 percent of the speed of light – thus making the trip in 20 years.

“But even here, you are talking about several terra-joules of energy for the most minimalist (a gram-mass) spacecraft conceivable,” said Kipping. “That’s the cumulative energy output of nuclear power stations running for weeks on end… so this is why it’s hard.”

To this, Kipping suggests a modified version of the “Dyson Slingshot,” an idea proposed by venerated theoretical physicist Freeman Dyson, the theorist behind the Dyson Sphere. In the 1963 book Interstellar Communications (Chapter 12: “Gravitational Machines”), Dyson described how spacecraft could slingshot around compact binary stars in order to receive a significant boost in velocity.

As Dyson described it, a ship would be dispatched to a compact binary system where it would perform a gravity-assist maneuver. This would consist of the spaceship picking up speed from the binary’s intense gravity, adding the equivalent of twice their rotational velocity to its own, and is then flung out of the system.

While the prospect of harnessing this kind of energy for the sake of propulsion was highly theoretical in Dyson’s time (and still is), Dyson offered two reasons why “gravitational machines” were worth exploring:

“First, if our species continues to expand its population and its technology at an exponential rate, there may come a time in the remote future where engineering on an astronomical scale may be both feasible and necessary. Second, if we are searching for signs of technologically advanced life already existing elsewhere in the universe, it is useful to consider what kind of observable phenomena a really advanced technology might be capable of producing.”

In short, gravitational machines are worth studying in case they become possible someday, and because this study could allow us to spot possible extraterrestrial intelligences (ETIs) by detecting the technosignatures such machines would create. Expanding upon this, Kipping considers how black holes, especially those found in binary pairs, could constitute even more powerful gravitational slingshots.

This proposal is based in part on the recent success of the Laser Interferometer Gravitational-Wave Observatory (LIGO), which has detected multiple gravitational wave signals since 2016. According to recent estimates based on these detections, there could be as many as 100 million black holes in the Milky Way galaxy alone.

Where binaries occur, they possess an incredible amount of rotational energy, which is the result of their spin and the way they rapidly orbit one another. In addition, as Kipping notes, black holes can also act as a gravitational mirror – where photons directed at the edge of the event horizon will bend around and come straight back at the source. As Kipping put it:

“So the binary black hole is really a couple of giant mirrors circling around one another at potentially high velocity. The halo drive exploits this by bouncing photons off the “mirror” as the mirror approaches you, the photons bounce back, pushing you along, but also steal some of the energy from the black hole binary itself (think about how a ping pong ball thrown against a moving wall would come back faster). Using this setup, one can harvest the binary black hole energy for propulsion.”

This method of propulsion offers several obvious advantages. For starters, it offers users the potential to travel at relativistic speeds without the need for fuel, which currently accounts for the majority of a launch vehicle’s mass. And there are many, many black holes that exist throughout the Milky Way, which could act as a network for relativistic space travel.

What’s more, scientists have already witnessed the power of gravitational slingshots thanks to the discovery of hyper-velocity stars. According to research from the Harvard-Smithsonian Center for Astrophysics (CfA), these stars are a result of galactic mergers and interaction with massive black holes, which kick them out of their galaxies at one-tenth to one-third the speed of light – around 30,000 to 100,000 km/s (18,600 to 62,000 mps).

But of course, the concept comes with innumerable challenges and more than a few disadvantages. In addition to building spacecraft that can endure being flung around the event horizon of a black hole, a tremendous amount of precision is required – otherwise, the ship and crew (if it has one) could be pulled apart in the maw of the black hole. Additionally, there’s simply the matter of reaching one:

“[T]he thing has a huge disadvantage for us in that we have to first get to one of these black holes. I tend to think of it like a interstellar highway system – you have to pay a one-time toll to get on the highway, but once you’re on, you can ride across the galaxy as much as you like without expending any more fuel.”

The challenge of how humanity might go about reaching the nearest suitable black hole will be the subject of Kipping’s next paper, he indicated. And while an idea like this is about as remote to us as building a Dyson Sphere or using black holes to power starships, it does offer some pretty exciting possibilities for the future.

In short, the concept of a black hole gravity machine presents humanity with a plausible path to becoming an interstellar species. In the meantime, the study of the concept will provide SETI researchers with another possible technosignature to look for. So until the day comes when we might attempt this ourselves, we will be able to see if any other species have already made it work.

Read more at: https://phys.org/news/2019-03-black-holes-conquer-space-halo.html#jCp

Deep-space photo reveals thousands of supermassive black holes

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A new deep-space study by NASA shows the vast void beyond our home is dotted not only with countless galaxies and stars, but also a stunning number of supermassive black holes.

Using data collected over 80 days of observations by NASA’s Chandra X-ray Observatory spacecraft, the agency released an image that shows the largest concentration of black holes ever seen. According to scientists, the density as viewed from Earth would be equivalent to about 5,000 objects that would fit into the area of the sky covered by the full moon.

“With this one amazing picture, we can explore the earliest days of black holes in the Universe and see how they change over billions of years,” study leader Niel Brandt of Pennsylvania State University in University Park, said in a statement.

The image above shows black holes emitting x-ray energy at a variety of intensities. Red indicates low energy, medium is green, and the highest-energy x-rays observed by Chandra are blue. About 70 percent of the objects in the image are supermassive black holes, with masses estimated to range anywhere from 100,000 to 10 billion times the mass of our sun. Many date back billions of years, forming just after the Big Bang.

While invisible to the naked eye, black holes emit x-rays due to captured matter heating up as it spins faster and faster towards the object’s all-consuming center or event horizon.

http://www.mnn.com/earth-matters/space/blogs/deep-space-photo-reveals-thousands-supermassive-black-holes

Albert Einstein’s special mark on the universe

On By A.P.In Albert Einstein, Theory of Special RelativityLeave a comment

By Jeffrey Bennett

It has been exactly 100 years since Albert Einstein presented his theory of general relativity to an audience of scientists on November 25, 1915. While virtually everyone has heard of Einstein and his theory, very few people have any idea of what the theory actually is.

This is a shame, not only because there is a great public thirst for understanding of it, but also because relativity is important, for at least four major reasons.

General relativity provides our modern understanding of space, time and gravity — which means it’s crucial to almost everything we do in physics and astronomy. For example, you cannot understand black holes, the expansion of the universe or the Big Bang without first understanding the basic ideas of relativity. Though few people realize it, Einstein’s famous equation E = mc2 is actually part of the theory of relativity, which means that relativity also explains how the sun shines and how nuclear power works.

A second reason everyone should know about relativity lies in the way it changes our perception of reality. Relativity tells us that our ordinary perceptions of time and space are not universally valid. Instead, space and time are intertwined as four-dimensional space-time.

In our ordinary lives, we perceive only three dimensions—length, width and depth—and we assume that this perception reflects reality. However, in space-time, the four directions of possible motion are length, width, depth and time. (Note that time is not “the” fourth dimension; it is simply one of the four.)

Although we cannot picture all four dimensions of space-time at once, we can imagine what things would look like if we could. In addition to the three spatial dimensions of space-time that we ordinarily see, every object would be stretched out through time. Objects that we see as three-dimensional in our ordinary lives would appear as four-dimensional objects in space-time. If we could see in four dimensions, we could look through time just as easily as we look to our left or right. If we looked at a person, we could see every event in that person’s life. If we wondered what really happened during some historical event, we’d simply look to find the answer.

To see why this is so revolutionary, imagine that you met someone today who deeply believed that Earth is the center of the universe. You would probably feel sorry for this person, knowing that his or her entire world view is based on an idea disproven more than 400 years ago.

Now imagine that you met someone who still believed that time and space are independent and absolute — which, of course, describes almost everyone — even though we’ve known that’s not the case for a century now. Shouldn’t we feel equally sorry for all who hold this modern misconception?

It seems especially unfortunate once you realize that the ideas of relativity are not particularly difficult to understand. Indeed, I believe we could begin teaching relativity in elementary school in much the same way that we teach young children about the existence of atoms, even though few will ever study quantum mechanics.

My third reason for believing relativity is important lies in what Einstein’s discovery tells us about human potential. The science of relativity may seem disconnected from most other human endeavors, but I believe Einstein himself proved otherwise. Throughout his life, Einstein argued eloquently for human rights, human dignity and a world of peace and shared prosperity. His belief in underlying human goodness is all the more striking when you consider that he lived through both World Wars, that he was driven out of Germany by the rise of the Nazis, that he witnessed the Holocaust that wiped out more than six million of his fellow Jews, and that he saw his own discoveries put to use in atomic bombs.

No one can say for sure how he maintained his optimism in the face of such tragedies, but I see a connection to his discovery of relativity. Einstein surely recognized that a theory that so challenged our perceptions of reality might have been dismissed out of hand at other times in history, but that we now live in a time when, thanks to the process that we call science, the abundant evidence for relativity allowed for its acceptance.

This willingness to make judgments based on evidence shows that we are growing up as a species. We have not yet reached the point where we always show the same willingness in all our other endeavors, but the fact that we’ve done it for science suggests we have the potential.

Finally, on a philosophical level, relativity is profound. Only about a month before his death in 1955, Einstein wrote: “Death signifies nothing … the distinction between past, present and future is only a stubbornly persistent illusion.” As this suggests, relativity raises interesting questions about what the passage of time really means.

Because these are philosophical questions, they do not have definitive answers, and you will have to decide for yourself what these questions mean to you. But I believe that one thing is clear. Einstein showed that even though space and time can independently differ for different observers, the four-dimensional space-time reality is the same for everyone.

This implies that events in space-time have a permanence to them that cannot be taken away. Once an event occurs, in essence it becomes part of the fabric of our universe. Every human life is a series of events, and this means that when we put them all together, each of us is creating our own, indelible mark on the universe. Perhaps if everyone understood that, we might all be a little more careful to make sure that the mark we leave is one that we are proud of.

So there you have it. Relativity is necessary to comprehend the universe as we know it, it helps us understand the potential we all share when we put our brains to work for the common good, and if we all understood it we might treat each other a little more kindly.

http://www.cnn.com/2015/11/25/opinions/bennett-einstein-theory-of-relativity/index.html