Why Don’t Black Holes Swallow All of Space? This Explanation Is Blowing Our Minds


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Black holes are great at sucking up matter. So great, in fact, that not even light can escape their grasp (hence the name).

But given their talent for consumption, why don’t black holes just keep expanding and expanding and simply swallow the Universe? Now, one of the world’s top physicists has come up with a new explanation.

Conveniently, the idea could also unite the two biggest theories in all of physics.

The researcher behind this latest explanation is none other than Stanford University physicist Leonard Susskind, also known as one of the fathers of string theory.

He recently gave his two cents on the paradox in a series of papers, which basically suggest that black holes expand by increasing in complexity inwardly – a feature we just don’t see connected while watching from afar.

In other words, they expand in, not out.

Weirder still, this hypothesis might have a parallel in the expansion of our own Universe, which also seems to be growing in a counterintuitive way.

“I think it’s a very, very interesting question whether the cosmological growth of space is connected to the growth of some kind of complexity,” Susskind was quoted in The Atlantic.

“And whether the cosmic clock, the evolution of the universe, is connected with the evolution of complexity. There, I don’t know the answer.”

Susskind might be speculating on the Universe’s evolution, but his thoughts on why black holes grow in more than they do out is worth unpacking.

To be clear though, for now this work has only been published on the pre-print site arXiv.org, so it’s yet to be peer reviewed. That means we need to take it with a big grain of salt for now. On top of that, this type of research is, by its very nature, theoretical.

But there are some pretty cool idea in here worth unpacking. To do that, we need to go back to basics for a moment. So … hang tight.

For the uninitiated, black holes are dense masses that distort space to the extent that even light (read: information) lacks the escape velocity required to make an exit.

The first solid theoretical underpinnings for such an object emerged naturally out of the mathematics behind Einstein’s general relativity back in 1915. Since then physical objects matching those predictions have been spotted, often hanging around the centre of galaxies.

A common analogy is to imagine the dimensions of space plus time as a smooth rubber sheet. Much as a heavy object dimples the rubber sheet, mass distorts the geometry of spacetime.

The properties of our Universe’s rubber sheet means it can form deep gravity funnel that stretches ‘down’ without stretching much further ‘out’.

Most objects expand ‘out’ as you add material, not ‘in’. So how do we even begin to picture this? Rubber sheets are useful analogies, but only up to a certain point.

To understand how matter behaves against this super stretchy backdrop, we need to look elsewhere. Luckily physics has a second rulebook on ‘How the Universe Works’ called quantum mechanics, which describes how particles and their forces interact.

The two rule books of GR and QM don’t always agree, though. Small things interpreted through the lens of general relativity don’t make much sense. And big things like black holes produce gibberish when the rules of quantum mechanics are applied.

This means we’re missing something important – something that would allow us to interpret general relativity’s space-bending feature in terms of finite masses and force-mediating particles.

One contender is something called anti-de Sitter/conformal field theory correspondence, which is shortened to Ads/CFT. This is a ‘string theory meets four dimensional space’ kind of idea, aiming to bring the best of both quantum mechanics and general relativity together.

Based on its framework, the quantum complexity of a black hole – the number of steps required to return it to a pre-black hole state – is reflected in its volume. The same thinking is what lies behind another brain-breaking idea called the holographic principle.

The exact details aren’t for the faint hearted, but are freely available on arXiv.org if you want to get your mathematics fix for the day.

It might sound a bit like downloading movies onto your desktop only to find it’s now ‘bigger’ on the inside. As ludicrous as it sounds, in the extreme environment of a black hole more computational power might indeed mean more internal volume. At least this is what Susskind’s Ads/CFT modelling suggests.

String theory itself is one of those nice ideas begging for an empirical win, so we’re still a long way from marrying quantum mechanics and general relativity.

Susskind’s suggestion that quantum complexity is ultimately responsible for the volume of a black hole has physicists thinking through the repercussions. After all, black holes aren’t like ordinary space, so we can’t expect ordinary rules to apply.

But if anybody is worth listening to on the subject, it’s probably this guy.

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Black holes and soft hair: why Stephen Hawking’s final work is important


Malcolm Perry, who worked with Hawking on his final paper, explains how it improves our understanding of one of universe’s enduring mysteries

Star torn apart by black hole
An artist’s impression of a star being torn apart by a black hole.
Photograph: Nasa’s Goddard Space Flight Center

The information paradox is perhaps the most puzzling problem in fundamental theoretical physics today. It was discovered by Stephen Hawking 43 years ago, and until recently has puzzled many.

Starting in 2015, Stephen, Andrew Strominger and I started to wonder if we could understand a way out of this difficulty by questioning the basic assumptions that underlie the difficulties. We published our first paper on the subject in 2016 and have been working hard on this problem ever since.

The most recent work, and perhaps the last paper that Stephen was involved in, has just come out. While we have not solved the information paradox, we hope that we have paved the way, and we are continuing our intensive work in this area.

Physics is really about being able to predict the future given how things are now. For example, if you throw a ball, once you know its initial position and velocity, then you can figure out where it will be in the future. That kind of reasoning is fine for what we call classical physics but for small things, like atoms and electrons, the rules need some modifications, as described by quantum mechanics. In quantum mechanics, instead of describing precise outcomes, one finds that one can only calculate the probabilities for various things to happen. In the case of a ball being thrown, one would not know its precise trajectory, but only the probability that it would be in some particular place given its initial conditions.

What Hawking discovered was that in black hole physics, there seemed to be even greater uncertainty than in quantum mechanics. However, this kind of uncertainty seemed to be completely unacceptable in that it resulted in many of the laws of physics appearing to break down. It would deprive us of the ability to predict anything about the future of a black hole.

That might not have mattered – except that black holes are real physical objects. There are huge black holes at the centres of many galaxies. We know this because observations of the centre of our galaxy show that there is a compact object with a mass of a few million times that of our sun there; such a huge concentration of mass could only be a black hole. Quasars, extremely luminous objects at the centres of very distant galaxies, are powered by matter falling onto black holes. The observatory Ligo has recently discovered ripples in spacetime, gravitational waves, produced by the collision of black holes.

The root of the problem is that it was once thought that black holes were completely described by their mass and their spin. If you threw something into a black hole, once it was inside you would be unable to tell what it was that was thrown in.

These ideas were encapsulated in the phrase “a black hole has no hair”. We can often tell people apart by looking their hair, but black holes seemed to be completely bald. Back in 1974, Stephen discovered that black holes, rather than being perfect absorbers, behave more like what we call “black bodies”. A black body is characterised by a temperature, and all bodies with a temperature produce thermal radiation.

If you go to a doctor, it is quite likely your temperature will be measured by having a device pointed at you. This is an infrared sensor and it measures your temperature by detecting the thermal radiation you produce. A piece of metal heated up in a fire will glow because it produces thermal radiation.

Black holes are no different. They have a temperature and produce thermal radiation. The formula for this temperature, universally known as the Hawking temperature, is inscribed on the memorial to Stephen’s life in Westminster Abbey. Any object that has a temperature also has an entropy. The entropy is a measure of how many different ways an object could be made from its microscopic ingredients and still look the same. So, for a particular piece of red hot metal, it would be the number of ways the atoms that make it up could be arranged so as to look like the lump of metal you were observing. Stephen’s formula for the temperature of a black hole allowed him to find the entropy of a black hole.

The problem then was: how did this entropy arise? Since all black holes appear to be the same, the origin of the entropy was at the centre of the information paradox.

What we have done recently is to discover a gap in the mathematics that led to the idea that black holes are totally bald. In 2016, Stephen, Andy and I found that black holes have an infinite collection of what we call “soft hair”. This discovery allows us to question the idea that black holes lead to a breakdown in the laws of physics.

Stephen kept working with us up to the end of his life, and we have now published a paper that describes our current thoughts on the matter. In this paper, we describe a way of calculating the entropy of black holes. The entropy is basically a quantitative measure of what one knows about a black hole apart from its mass or spin.

While this is not a resolution of the information paradox, we believe it provides some considerable insight into it. Further work is needed but we feel greatly encouraged to continue our research in this area. The information paradox is intimately tied up with our quest to find a theory of gravity that is compatible with quantum mechanics.

Einstein’s general theory of relativity is extremely successful at describing spacetime and gravitation on large scales, but to see how the world works on small scales requires quantum theory. There are spectacularly successful theories of the non-gravitational forces of nature as explained by the “standard model” of particle physics. Such theories have been exhaustively tested and the recent discovery of the Higgs particle at Cern by the Large Hadron Collider is a marvellous confirmation of these ideas.

Yet the incorporation of gravitation into this picture is still something that eludes us. As well as his work on black holes, Stephen was pursuing ideas that he hoped would lead to a unification of gravitation with the other forces of nature in a way that would unite Einstein’s ideas with those of quantum theory. Our work on black holes does indeed shed light on this other puzzle. Sadly, Stephen is no longer with us to share our excitement about the possibility of resolving these issues, which have now been around for half a century.

Earliest Black Hole Gives Rare Glimpse of Ancient Universe


It weighs as much as 780 million suns and helped to cast off the cosmic Dark Ages. But now that astronomers have found the earliest known black hole, they wonder: How could this giant have grown so big, so fast?
 

Magellan Baade telescope and CMB illustration

Astronomers have at least two gnawing questions about the first billion years of the universe, an era steeped in literal fog and figurative mystery. They want to know what burned the fog away: stars, supermassive black holes, or both in tandem? And how did those behemoth black holes grow so big in so little time?

Now the discovery of a supermassive black hole smack in the middle of this period is helping astronomers resolve both questions. “It’s a dream come true that all of these data are coming along,” said Avi Loeb, the chair of the astronomy department at Harvard University.

The black hole, announced today in the journal Nature, is the most distant ever found. It dates back to 690 million years after the Big Bang. Analysis of this object reveals that reionization, the process that defogged the universe like a hair dryer on a steamy bathroom mirror, was about half complete at that time. The researchers also show that the black hole already weighed a hard-to-explain 780 million times the mass of the sun.

A team led by Eduardo Bañados, an astronomer at the Carnegie Institution for Science in Pasadena, found the new black hole by searching through old data for objects with the right color to be ultradistant quasars — the visible signatures of supermassive black holes swallowing gas. The team went through a preliminary list of candidates, observing each in turn with a powerful telescope at Las Campanas Observatory in Chile. On March 9, Bañados observed a faint dot in the southern sky for just 10 minutes. A glance at the raw, unprocessed data confirmed it was a quasar — not a nearer object masquerading as one — and that it was perhaps the oldest ever found. “That night I couldn’t even sleep,” he said.

The new black hole’s mass, calculated after more observations, adds to an existing problem. Black holes grow when cosmic matter falls into them. But this process generates light and heat. At some point, the radiation released by material as it falls into the black hole carries out so much momentum that it blocks new gas from falling in and disrupts the flow. This tug-of-war creates an effective speed limit for black hole growth called the Eddington rate. If this black hole began as a star-size object and grew as fast as theoretically possible, it couldn’t have reached its estimated mass in time.

Other quasars share this kind of precocious heaviness, too. The second-farthest one known, reported on in 2011, tipped the scales at an estimated 2 billion solar masses after 770 million years of cosmic time.

These objects are too young to be so massive. “They’re rare, but they’re very much there, and we need to figure out how they form,” said Priyamvada Natarajan, an astrophysicist at Yale University who was not part of the research team. Theorists have spent years learning how to bulk up a black hole in computer models, she said. Recent work suggests that these black holes could have gone through episodic growth spurts during which they devoured gas well over the Eddington rate.

Bañados and colleagues explored another possibility: If you start at the new black hole’s current mass and rewind the tape, sucking away matter at the Eddington rate until you approach the Big Bang, you see it must have initially formed as an object heavier than 1,000 times the mass of the sun. In this approach, collapsing clouds in the early universe gave birth to overgrown baby black holes that weighed thousands or tens of thousands of solar masses. Yet this scenario requires exceptional conditions that would have allowed gas clouds to condense all together into a single object instead of splintering into many stars, as is typically the case.

Cosmic Dark Ages

Even earlier in the early universe, before any stars or black holes existed, the chaotic scramble of naked protons and electrons came together to make hydrogen atoms. These neutral atoms then absorbed the bright ultraviolet light coming from the first stars. After hundreds of millions of years, young stars or quasars emitted enough light to strip the electrons back off these atoms, dissipating the cosmic fog like mist at dawn.

Infographic of the timeline of the universe

Lucy Reading-Ikkanda/Quanta Magazine

Astronomers have known that reionization was largely complete by around a billion years after the Big Bang. At that time, only traces of neutral hydrogen remained. But the gas around the newly discovered quasar is about half neutral, half ionized, which indicates that, at least in this part of the universe, reionization was only half finished. “This is super interesting, to really map the epoch of reionization,” said Volker Bromm, an astrophysicist at the University of Texas.

When the light sources that powered reionization first switched on, they must have carved out the opaque cosmos like Swiss cheese. But what these sources were, when it happened, and how patchy or homogeneous the process was are all debated. The new quasar shows that reionization took place relatively late. That scenario squares with what the known population of early galaxies and their stars could have done, without requiring astronomers to hunt for even earlier sources to accomplish it quicker, said study coauthor Bram Venemans of the Max Planck Institute for Astronomy in Heidelberg.

More data points may be on the way. For radio astronomers, who are gearing up to search for emissions from the neutral hydrogen itself, this discovery shows that they are looking in the right time period. “The good news is that there will be neutral hydrogen for them to see,” said Loeb. “We were not sure about that.”

The team also hopes to identify more quasars that date back to the same time period but in different parts of the early universe. Bañados believes that there are between 20 and 100 such very distant, very bright objects across the entire sky. The current discovery comes from his team’s searches in the southern sky; next year, they plan to begin searching in the northern sky as well.

“Let’s hope that pans out,” said Bromm. For years, he said, the baton has been handed off between different classes of objects that seem to give the best glimpses at early cosmic time, with recent attention often going to faraway galaxies or fleeting gamma-ray bursts. “People had almost given up on quasars,” he said.

What Did Stephen Hawking Do? The Physicist’s 5 Biggest Achievements


On Wednesday, world-renowned astrophysicist Stephen Hawking died at age 76 in his home in Cambridge, England. He lived for 55 years with the neurological disease amyotrophic lateral sclerosis (ALS), and as a result, he spent most of his life using a wheelchair, which, for the last decade, also included hands-free communication capability that gave him the computerized voice with which so many people now associate him.

As a working physicist and prolific public figure, Hawking helped revolutionize the field of astrophysics. His scholarship helped elucidate our modern understanding of the universe and its origins, and he was quick to share his views on humanity and society. While his achievements are many, there are five in particular worth noting.

Space

5. Stephen Hawking Theorized How Black Holes Emit Information

Black holes are notoriously hungry phenomena, distorting spacetime and sucking in any matter that passes within their event horizon. But Hawking theorized that black holes actually radiate energy as a result of quantum effects near the event horizon. We could only observe this theoretical energy, which is referred to as “Hawking radiation,” in smaller black holes that are about the same mass as our sun. In larger black holes, it would be overwhelmed by the gas falling into the black hole. Hawkin’s hypothesized phenomenon hasn’t been directly observed, but as Inverse previously reported, physicists are working on it.

'Big Bang Theory' loved its nerdy celeb cameos, and Stephen Hawking's was an absolute treasure.

4. Stephen Hawking Proposed That the Singularity Was an Essential Element of the Big Bang Theory

The Big Bang Theory — the physics one, not the television one — proposes the universe began with a powerful expansion that started with one point, the singularity. Before Hawking’s time, physicists tried to reconcile the apparent paradox of the singularity. The idea of a single point of infinite density simply didn’t mesh with the conventional views of physics in the middle of the 20th century. In 1970, though, Hawking co-authored a paper with Roger Penrose that began to reconcile this notion.

This paper, titled “The singularities of gravitational collapse and cosmology,” countered the widely discussed notion that the Big Bang was preceded by the universe contracting. Physicists generally accept this version of the Big Bang Theory, in which there was nothing before the beginning of the universe.

Ripples in spacetime.

3. Stephen Hawking Proposed There Was No Meaningful Distinction Between Space and Time in the Early Universe

In his 1988 best-selling book, A Brief History of Time, Hawking proposed that at the very beginning of the universe, space existed, but time as we know it did not yet exist. Astrophysicists continue to describe space and time as being intrinsically tied to one another, but Hawking hypothesized that at the very beginning of everything there was no meaningful distinction. The curious public digested this hypothesis in Hawking’s book, but physicists continue to debate his idea.

Stephen Hawking, Big Bang

2. Stephen Hawking Provided Evidence That Time Travel Is Impossible

Back in 2009, Hawking hosted a time traveler party, inviting time travelers to join him for a reception to celebrate their achievements. Here’s the catch, though: He didn’t send out the invitations until the next day. The idea was that anyone who actually showed up would clearly be legit since nobody knew about the party before it happened. On Hawking’s 75th birthday in 2017, he announced that nobody had shown up to his party. While this isn’t definitive proof that time travel doesn’t exist, it’s pretty strong evidence. After all, if you discovered how to travel through time, wouldn’t Hawking’s time travel party be one of your first destinations?

Stephen Hawking on 'The Simpsons'

1. Stephen Hawking Played Himself Four Times on The Simpsons

Sure, revolutionizing astrophysics is great, but what about having your cartoon avatar immortalized for posterity? In addition to playing himself on Star Trek, Hawking appeared on The Simpsons four times between 1999 and 2010. Sure, this achievement wasn’t scientific, strictly speaking, but it does embody the character and public image of one of the best-known scientists in modern history. As a physicist, Hawking didn’t create much original work in his later years. But as a science popularizer, he continued to inspire people to learn about the world around them. And as far as monumental achievements go, that one’s hard to overstate.

We Finally Have Evidence That Black Holes Drive Winds Shaping Their Entire Galaxy


Black holes are so weird and so mysterious, it’s possible we’re never going to unravel all their puzzles. But this new one is pretty fantastic – the first evidence that supermassive black holes at galactic cores actively shape their environments, something suspected but never before confirmed.

 

Not just that, but they way they do so – by generating powerful winds that blow far and wide – influences where new stars form. This means the influence exerted by black holes reaches much farther than expected, right into the far reaches of their galaxies.

That supermassive black holes blow powerful winds into the space around them is well known. There may be no air in space, but there is plasma, gas and other matter in the interstellar medium.

Previous studies have concluded that these winds, which are powerful enough to spread throughout entire galaxies, can suppress the formation of new stars across the region.

This new study marks the first time this phenomenon has been observed.

“Supermassive black holes are captivating,” said astrophysicist Shelley Wright from the University of California, San Diego.

“Understanding why and how galaxies are affected by their supermassive black holes is an outstanding puzzle in their formation.”

The black hole in question is visible as part of a quasar, in host galaxy 3C 298 some 9.3 billion light-years away.

This means the phenomena we’re detecting happened quite early in the history of the Universe, which is around 13.8 billion years old.

3C298 multi color final 604 800Image of the quasar host galaxy (A. Vayner and team)

The black hole itself can’t be seen, since no light escapes it, but it’s in the centre of a large accretion disc of dust and gas that is swirling around the black hole at tremendous speeds.

This generates friction and heat, which gives off immense light. In fact, quasars are some of the brightest objects in our universe.

In the image above, the green colours highlight the energetic gas across the galaxy that is being illuminated by the quasar, while the blue colour represents powerful winds blowing throughout the galaxy.

The supermassive black hole itself is in that orange-bordered bright circle slightly below the middle of the image.

The quasar stage of a galaxy’s life is usually the early, very active stage, before the black hole settles down into a more conventional adulthood, having consumed all the nearby matter.

Most of the galaxies nearby to the Milky Way today show a correlation between the size of the supermassive black hole at the centre and the size of the galaxy. But 3C 298 is disproportionate.

Using data from the Keck Observatory’s infrared spectrograph OSIRIS and the Atacama Large Millimeter/submillimeter Array, the research team found that it has 100 times less mass than expected, given the size of its black hole.

Putting together the pieces of the puzzle, this indicates that the black hole was formed and established well before the galaxy coalesced around it.

They also observed quasar-driven winds changing the density of molecular gas, lessening it considerably – clouds of which are vital to stellar formation. This means that the quasar was limiting star formation.

The findings are the first results from a survey on distant quasars, and the effect they have on galactic growth and star formation. But even though it gave up magnificent evidence of a long-suspected mechanism, there’s still work to be done.

For example, it’s still unclear whether quasar galaxies can be included in the scaling models used for nearby galaxies.

It’s also unclear how stellar formation can occur, since the quasar’s winds have removed most of the necessary gas from the galaxy. The team proposes that a galactic merger, or gas from the intergalactic medium, will bring the galaxy up to the mass expected for the size of its black hole.

“The most enjoyable part of researching this galaxy has been putting together all the data from different wavelengths and techniques,” said one of the team, astronomer Andrey Vayner.

“Each new dataset that we obtained on this galaxy answered one question and helped us put some of the pieces of the puzzle together.

“However, at the same time, it created new questions about the nature of galaxy and supermassive black hole formation.”

Meet Sabrina Pasterski, The 23-Year-Old “New Einstein”


At 23, Sabrina Pasterski has a standing job offer from NASA. Her research has been cited by Stephen Hawking, and it’s been nearly a decade since she built her first plane engine. Kind of makes us wonder what we’re doing with our lives.

 

A Talent for Building Spacecraft

 Sabrina Pasterski has her eye on the prize: the 23-year-old Harvard PhD student (and top MIT grad) has never had an alcoholic drink or a cigarette, and isn’t on any form of social media, from Facebook to LinkedIn. She doesn’t even own a smartphone. “I’d rather stay alert, and hopefully I’m known for what I do and not what I don’t do,” Pasterski told OZY.

And what she does is incredible: Pasterski researches black holes, spacetime, and quantum gravity, and her papers have been cited by the likes of Andrew Strominger (her advisor at Harvard) and Stephen Hawking. One of the special skills she lists on her résumé? “Spotting elegance within the chaos.”

Pasterski had an interest in designing spacecraft from a young age: “It’s a freedom like nothing else you can compare it to,” she told Chicago Tonight. She built her first single-engine plane at the young age of 14, and has a standing job offer from Jeff Bezos, founder of Amazon.com and the aerospace research and development company called Blue Origin.

But it wasn’t all smooth sailing: Pasterski was rejected from Harvard and waitlisted at MIT in the spring of 2010, before eventually being accepted. From there, she graduated with the highest honors and entered the prestigious Harvard PhD program, gaining accolades such as a $250,000 Hertz Foundation fellowship for her research.

Into the Future

 Right now, Pasterski is focused on grappling with physics problems that excite her, learning as much as she can from the rich resources she has access to. But with standing job offers from NASA and Blue Origin, Pasterski might eventually make a big impact on aircraft travel–specifically, space travel. Companies like Blue Origin and SpaceX are looking for bright young minds to shape the future of space exploration and push us into the next frontier. And Pasterski’s potential is far from unnoticed: Forbes named her to their 30 under 30 All Star list.

Still, Pasterski remains humble about her success. “I am just a grad student. I have so much to learn. I do not deserve the attention,” she writes.

Source:curiosity.com

This Mind-Bending Theory Joins Black Holes, Gravitational Waves & Axions to Find New Physics


We haven’t seen physicists this excited for a while.

Scientists have proposed a new theory that combines some of the most mysterious phenomena in the Universe – black holes, gravitational waves, and axions – to solve one of the most confounding problems in modern physics. And it’s got experts in the field very excited.

The theory, which imagines a Universe filled with colossal ‘gravitational atoms’ that are capable of producing vast clouds of dark matter, predicts that it could be possible to detect entirely new kinds of particles using a giant gravitational wave detector called LIGO.

 “This is probably the most promising paper I’ve seen so far on the new physics we might probe with gravitational waves,” MIT particle physicist Benjamin Safdi, who wasn’t involved in the research, told Nature.

“It’s an awesome idea,” adds particle astrophysicist Tracy Slatyer, also from MIT. “The [LIGO] data is going to be there, and it would be amazing if we saw something.”

Before we dive headfirst into the crazy physics of this new theory, let’s run through the major players.

Black holes are an easy one – vast, matter-annihilating objects that are so remarkably strange, when Albert Einstein’s equations first predicted their existence, he didn’t believe they could actually be real.

Black holes maintain such powerful gravitational fields, when two of them collide with each other, they produce gravitational waves.

Confirmed for the first time last year, but predicted by Einstein more than a century ago, gravitational waves are ripples in the fabric of space-time that emanate from the most violent and explosive events in the Universe.

 And axions? Well, they’re a bit more tricky, because unlike black holes and gravitational waves, we’re not even sure if axions exist – and we’ve been searching for them for the past four decades.

Axions are one of the many candidates that have been proposed for dark matter – a mysterious, invisible substance whose gravity appears to hold our galaxies together, and is predicted to make up 85 percent of all matter in the Universe.

Axions are predicted to weigh around 1 quintillion (a billion billion) times less than an electron, and if we can prove their existence, these super-light particles could solve some major theoretical problems with the standard model of physics.

Okay, now that we have all the pieces in place, let’s get to this mind-bending new theory. (And yes, we’re calling it a theory, not a hypothesis, because it’s based on a mathematical framework. More on that here).

A team of physicists led by Asimina Arvanitaki and Masha Baryakhtar from the Perimeter Institute for Theoretical Physics in Canada have proposed that if axions exist and have the right mass, they could be produced in the form of vast clouds of particles by a spinning black hole.

This process would be enough to produce gravitational waves like the ones that were detected last year, and if so, we can use gravitational wave detectors to finally observe the signature of dark matter, and close the gaps in the standard model.

“The basic idea is that we’re trying to use black holes… the densest, most compact objects in the Universe, to search for new kinds of particles,” Baryakhtar told Ryan F. Mandelbaum at Gizmodo.

You can think of this scenario like this: a black hole is like the nucleus at the centre of a giant, hypothetical gravitational atom. Axions get stuck in orbit around this nucleus, whizzing around like electrons do in regular atoms.

“[E]lectrons interact via electromagnetism, so they let out electromagnetic waves, or light waves. Axions interact via gravity, so they let out gravitational waves,” Mandelbaum explains.

If an axion strays too close to the black hole’s event horizon, the spin of the black hole will ‘supercharge’ it, and due to a process called superradiance that has been shown to multiply photons (light particles) in many experiments in the past, this will cause the axions to multiply within a black hole.

These multiplying axions would interact with the black hole in the same way as the original axion near the event horizon, resulting in 1080 axions – “the same number of atoms in the entire Universe, around a single black hole”, says Mandelbaum.

“It’s so cool, and I haven’t read a paper that talked about [superradiance] in years,” Chanda Prescod-Weinstein, a University of Washington axion expert who wasn’t involved in the research, told him.

“[I]it was really fun to see superradiance and axions in one paper.”

These multiplying axions wouldn’t just pop into existence randomly – they’d group together in huge quantum waves like the electron clouds you see in an atom.

Within this cloud, any axions that collide with each other would produce gravitons – another hypothetical particle thought to mediate the force of gravitation.

Gravitons are to gravitational waves as photons are to light, and Baryakhtar and her team propose that they would set off continuous waves into the Universe at a frequency set by the axion’s mass.

With improved sensitivity, LIGO should be able to spot thousands of these axion signals in a single year, the researchers predict, finally giving them a way to observe the signature of dark matter – something that has eluded scientists for decades.

Of course, grand theories like these always come with some caveats – in order to work, the axions must have a very specific mass, and that mass doesn’t necessarily gel well with current predictions on dark matter.

But physicists are still excited by the idea, and with LIGO expected to increase greatly in sensitivity in the next couple of years, it might not be too long before we can test it out for real.

Source:http://www.sciencealert.com

Stephen Hawking, Given Two Years to Live in 1963, Is Going To Space Over 50 Years Later.


Article Image
Dr. Stephen Hawking delivers a speech entitled ‘Why we should go into space’ on April 21, 2008, at George Washington University’s Morton Auditorium in Washington, DC.

Stephen Hawking gave an interview to Piers Morgan on “Good Morning Britain”, where he confirmed that he’ll be going to space on Richard Branson’s Virgin Galactic spaceship. Branson actually offered him the trip in 2015 for free, and Hawking says “since that day, I have never changed my mind.”

When the flight will be we don’t yet know. Virgin Galactic’s SpaceShipTwowas previously slated to launch at the end of 2017, but no hard date has been announced yet.

Hawking’s spaceflight will be an amazing feat for the 75-year-old scientist, known for his work in physics and cosmology, adding another chapter to an already remarkable life. When he was only 21, he was diagnosed with amyotrophic lateral sclerosis (ALS) also known as Lou Gehrig’s disease. This rare neurogenerative disease is deadly and Hawking was told he had 2 years to live

50+ years later, Hawking is still going strong (and going to space). Paralyzed and confined to a wheelchair, speaking through a specially-designed computer system since 1985, the scientist has achieved more than most do in a lifetime, not letting the debilitating disease slow him down.

Hawking has done groundbreaking work on black holes, discovering (along with James Bardeen and Brandon Carter) four laws of black holes mechanics.

His 1974 “Hawking radiation” theory that black holes are slowly evaporating due to particles robbing them of energy can still land him a Nobel Prize as recent research appears to prove it.

He has also done outstanding work on gravitational singularities, one-dimensional points that have infinite mass in infinitely tiny spaces. Cooperating with mathematician Roger Penrose, Hawking proved the existence of singularities and proposed key theorems on their origins. 

hawking nasa

Stephen Hawking, date unconfirmed but likely in 1990s. 

His other scientific achievements include pioneering work on cosmic inflation and the early state of the universe (which Hawking proposed had no time or beginning). 

Hawking is also famous for being one of the world’s most popular science educators, writing numerous books like the bestseller “A Brief History of Time,” which sold more than 10 million copies. 

How did Hawking, who also has been a professor of mathematics at University of Cambridge for the 30 years, thrive despite the illness? In an interview with Scientific American, ALS expert and professor of neurology Leo McCluskey, called Hawking “an outlier”. His case is exceptional and probably represents just a few percent of ALS patients. If Hawking developed the disease while still a teenager, it could be a “juvenile-onset” variant that progresses very slowly. He has also had great care.

How will Hawking fare in space? We don’t know the details of Virgin Galactic flight yet but Hawking seems quite enthusiastic:

“I can tell you what will make me happy, to travel in space. I thought no one would take me but Richard Branson has offered me a seat on Virgin Galactic and I said yes immediately.”

Source:http://bigthink.com

Gravitational Wave Kicks Monster Black Hole Out Of Galactic Core


Gravitational Wave Kicks Monster Black Hole Out Of Galactic Core

Gravitational Wave Kicks Monster Black Hole Out Of Galactic Core
Runaway black hole is the most massive ever detected far from its central home
Normally, hefty black holes anchor the centers of galaxies. So researchers were surprised to discover a supermassive black hole speeding through the galactic suburbs. Black holes cannot be observed directly, but they are the energy source at the heart of quasars — intense, compact gushers of radiation that can outshine an entire galaxy. NASA’s Hubble Space Telescope made the discovery by finding a bright quasar located far from the center of the host galaxy.Researchers estimate that it took the equivalent energy of 100 million supernovas exploding simultaneously to jettison the black hole. What could pry this giant monster from its central home? The most plausible explanation for this propulsive energy is that the monster object was given a kick by gravitational waves unleashed by the merger of two black holes as a result of a collision between two galaxies. First predicted by Albert Einstein, gravitational waves are ripples in the fabric of space that are created when two massive objects collide.

Astronomers have uncovered a supermassive black hole that has been propelled out of the center of a distant galaxy by what could be the awesome power of gravitational waves.

Though there have been several other suspected, similarly booted black holes elsewhere, none has been confirmed so far. Astronomers think this object, detected by NASA’s Hubble Space Telescope, is a very strong case. Weighing more than 1 billion suns, the rogue black hole is the most massive black hole ever detected to have been kicked out of its central home.

Researchers estimate that it took the equivalent energy of 100 million supernovas exploding simultaneously to jettison the black hole. The most plausible explanation for this propulsive energy is that the monster object was given a kick by gravitational waves unleashed by the merger of two hefty black holes at the center of the host galaxy.

First predicted by Albert Einstein, gravitational waves are ripples in space that are created when two massive objects collide. The ripples are similar to the concentric circles produced when a hefty rock is thrown into a pond. Last year, the Laser Interferometer Gravitational-Wave Observatory (LIGO) helped astronomers prove that gravitational waves exist by detecting them emanating from the union of two stellar-mass black holes, which are several times more massive than the sun.

Hubble’s observations of the wayward black hole surprised the research team. “When I first saw this, I thought we were seeing something very peculiar,” said team leader Marco Chiaberge of the Space Telescope Science Institute (STScI) and Johns Hopkins University, in Baltimore, Maryland. “When we combined observations from Hubble, the Chandra X-ray Observatory, and the Sloan Digital Sky Survey, it all pointed towards the same scenario. The amount of data we collected, from X-rays to ultraviolet to near-infrared light, is definitely larger than for any of the other candidate rogue black holes.”

Chiaberge’s paper will appear in the March 30 issue of Astronomy & Astrophysics.

Hubble images taken in visible and near-infrared light provided the first clue that the galaxy was unusual. The images revealed a bright quasar, the energetic signature of a black hole, residing far from the galactic core. Black holes cannot be observed directly, but they are the energy source at the heart of quasars – intense, compact gushers of radiation that can outshine an entire galaxy. The quasar, named 3C 186, and its host galaxy reside 8 billion light-years away in a galaxy cluster. The team discovered the galaxy’s peculiar features while conducting a Hubble survey of distant galaxies unleashing powerful blasts of radiation in the throes of galaxy mergers.

“I was anticipating seeing a lot of merging galaxies, and I was expecting to see messy host galaxies around the quasars, but I wasn’t really expecting to see a quasar that was clearly offset from the core of a regularly shaped galaxy,” Chiaberge recalled. “Black holes reside in the center of galaxies, so it’s unusual to see a quasar not in the center.”

The team calculated the black hole’s distance from the core by comparing the distribution of starlight in the host galaxy with that of a normal elliptical galaxy from a computer model. The black hole had traveled more than 35,000 light-years from the center, which is more than the distance between the sun and the center of the Milky Way.

Based on spectroscopic observations taken by Hubble and the Sloan survey, the researchers estimated the black hole’s mass and measured the speed of gas trapped near the behemoth object. Spectroscopy divides light into its component colors, which can be used to measure velocities in space. “To our surprise, we discovered that the gas around the black hole was flying away from the galaxy’s center at 4.7 million miles an hour,” said team member Justin Ely of STScI. This measurement is also a gauge of the black hole’s velocity, because the gas is gravitationally locked to the monster object.

The astronomers calculated that the black hole is moving so fast it would travel from Earth to the moon in three minutes. That’s fast enough for the black hole to escape the galaxy in 20 million years and roam through the universe forever.

The Hubble image revealed an interesting clue that helped explain the black hole’s wayward location. The host galaxy has faint arc-shaped features called tidal tails, produced by a gravitational tug between two colliding galaxies. This evidence suggests a possible union between the 3C 186 system and another galaxy, each with central, massive black holes that may have eventually merged.

Based on this visible evidence, along with theoretical work, the researchers developed a scenario to describe how the behemoth black hole could be expelled from its central home. According to their theory, two galaxies merge, and their black holes settle into the center of the newly formed elliptical galaxy. As the black holes whirl around each other, gravity waves are flung out like water from a lawn sprinkler. The hefty objects move closer to each other over time as they radiate away gravitational energy. If the two black holes do not have the same mass and rotation rate, they emit gravitational waves more strongly along one direction. When the two black holes collide, they stop producing gravitational waves. The newly merged black hole then recoils in the opposite direction of the strongest gravitational waves and shoots off like a rocket.

The researchers are lucky to have caught this unique event because not every black-hole merger produces imbalanced gravitational waves that propel a black hole in the opposite direction. “This asymmetry depends on properties such as the mass and the relative orientation of the back holes’ rotation axes before the merger,” said team member Colin Norman of STScI and Johns Hopkins University. “That’s why these objects are so rare.”

An alternative explanation for the offset quasar, although unlikely, proposes that the bright object does not reside within the galaxy. Instead, the quasar is located behind the galaxy, but the Hubble image gives the illusion that it is at the same distance as the galaxy. If this were the case, the researchers should have detected a galaxy in the background hosting the quasar.

If the researchers’ interpretation is correct, the observations may provide strong evidence that supermassive black holes can actually merge. Astronomers have evidence of black-hole collisions for stellar-mass black holes, but the process regulating supermassive black holes is more complex and not completely understood.

The team hopes to use Hubble again, in combination with the Atacama Large Millimeter/submillimeter Array (ALMA) and other facilities, to more accurately measure the speed of the black hole and its gas disk, which may yield more insight into the nature of this bizarre object.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

Source:http://hubblesite.org

Black holes are ‘portals to other universes,’ according to new quantum results


Black holes may not end in a crushing singularity as previously thought, but rather open up passageways into whole other universes.

black hole and galaxies

According to Albert Einstein’s theory of general relativity, black holes are uninhabitable chasms of spacetime that end in a “singularity,” or a mass of infinite density. It’s a place so bleak that even the laws of physics break down there. But what if black holes aren’t so forbidding? What if they are instead some kind of intergalactic stargate, or maybe even a passageway into a whole other universe?

It may sound like the premise for a clever science-fiction movie, but new calculations by quantum physicists now suggest that the stargate idea might actually be the better theory. According to the startling new results, black holes do not culminate in a singularity. Rather, they represent “portals to other universes,” reports New Scientist.

This new theory is based on a concept known as ‘loop quantum gravity’ (or LQG). It was first formulated as a way of merging standard quantum mechanics and standard general relativity, in order to remedy incompatibilities between the two fields. Basically, LQG proposes that spacetime is granular, or atomic, in nature; It is made up of miniscule, indivisible chunks about the same size as the Planck length — which roughly amounts to 10-35 meters in size.

Researchers Jorge Pullin from Lousiana State University, and Rodolfo Gambini from the University of the Republic in Montevideo, Uruguay, crunched the numbers to see what would happen inside a black hole under the parameters of LQG. What they found was far different from what happens according to general relativity alone: there was no singularity. Instead, just as the black hole began to squeeze tight, it suddenly loosened its grip again, as if a door was being opened.

It might help to conceptualize exactly what this means if you imagine yourself traveling into a black hole. Under general relativity, falling into a black hole is, in some ways, much like falling into a very deep pit that has a bottom, only instead of hitting the bottom, you get pressed into a single point — a singularity — of infinite density. With both the deep pit and the black hole, there is no “other side.” The bottom stops your fall through the pit, and the singularity “stops” your fall through the black hole (or at least, at the singularity it no longer makes sense to say you’re “falling”).

Your experience would be much different traveling into a black hole according to LQG, however. At first you might not notice the difference: gravity would increase rapidly. But just as you were nearing what ought to be the black hole’s core — just as you’re expecting to be squashed into the singularity — gravity would instead begin to decrease. It would be as if you were swallowed, only to be spit out on the other side.

In other words, LQG black holes are less like holes and more like tunnels, or passageways. But passageways to where? According to the researchers, they could be shortcuts to other parts of our universe. Or they could be portals to other universes entirely.

Interestingly, this same principle can be applied to the Big Bang. According to conventional theory, the Big Bang started with a singularity. But if time is rewound according to LQG instead, the universe does not begin with a singularity. Rather, it collapses into a sort of tunnel, which leads into another, older universe. This has been used as evidence for one of the Big Bang’s competing theories: the Big Bounce.

Scientists don’t have enough evidence to decide whether this new theory is actually true, but LQG does have one thing going for it: it’s more beautiful. Or rather, it avoids certain paradoxes that conventional theories do not. For instance, it avoids the black hole information paradox. According to relativity, the singularity inside a black hole operates as a sort of firewall, which means that information that gets swallowed by the black hole gets lost forever. Information loss, however, is not possible according to quantum physics.

Since LQG black holes have no singularity, that information need not be lost.

“Information doesn’t disappear, it leaks out,” said Jorge Pullin.
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