Edge of darkness: looking into the black hole at the heart of the Milky Way


A black hole as depicted in the 2014 film Interstellar. Director Christopher Nolan consulted astrophysicists to get a ‘realistic’ image.
A black hole as depicted in the 2014 film Interstellar. Director Christopher Nolan consulted astrophysicists to get a ‘realistic’ image.

At the heart of our galaxy, a vast black hole is devouring matter from the dust clouds that surround it. Little by little, expanses of interstellar material are being swallowed up by this voracious galactic carnivore that, in the process, has reached a mass that is 4m times that of our sun.

The Milky Way’s great black hole is 25,000 light years distant, surrounded by dense clusters of stars, shrouded by interstellar dust and, like all other black holes, incapable of emitting light.

Yet scientists believe they will soon be able to take a photograph of this interstellar behemoth – an extraordinarily ambitious feat that will involve the creation of a radio telescope that has the effective size of our entire planet and whose operation will involve scientists from four continents.

“It is going to be very, very hard to take this photograph but we think we now have the technological capability to do it,” says Manchester University astronomer Tom Muxlow, based at the Jodrell Bank observatory in Cheshire.

“To be precise, we are not going to take a direct photograph of the black hole at our galaxy’s heart. We are actually going to take a picture of its shadow. It will be an image of its silhouette sliding against the background glow of radiation of the heart of the Milky Way. That photograph will reveal the contours of a black hole for the first time.”

Our galaxy’s great black hole is also known as Sagittarius A*, because it lies in the constellation Sagittarius and the data collection that will be used to create its image is set to take place in April. However, it will probably require a further six months of work to put together the observations made by all of the Event Horizon Telescope project’s component telescopes, which include instruments at the south pole and in the Andes, Hawaii and Europe.

The resulting image, say scientists, could look very much like the one created by director Christopher Nolan for the film Interstellar. Working with US astrophysicist Kip Thorne, Nolan went to considerable pains to develop something that looked like a “realistic” black hole. Gargantua, as it is named in the film, is depicted as a round black patch that hangs menacingly in the sky with swirling, luminous strands of matter pouring into it.

These strands of matter are known as an accretion disc. “In fact, the accretion disc around the black hole in our galaxy’s core is likely to be much thicker, geometrically, than the one in Interstellar, and so look somewhat different,” says Thorne. Nevertheless, most astronomers believe the film’s black hole is a good representation of what might be seen when the Event Horizon Telescope does its work.

A black hole is a region of space where matter has collapsed in on itself and become compressed into an incredibly small region. Its gravitational pull is so great nothing can escape from it – not even light. The point of no return, the boundary at which a black hole’s gravitational pull becomes so great nothing can emerge, is known as an event horizon.

“The event horizon is a surface in space-time, and if you go beyond that then you cannot get out again,” says Robert Laing, of the European Southern Observatory, a partner in the project. “Not even light can get out.”

The fact that light cannot escape black holes makes them tricky to observe, to say the least. However, we know they exist because they affect nearby dust clouds, stars and galaxies. As discs of material swirl around black holes they become extremely hot and give off electromagnetic radiaiton that can be detected in telescopes. “That radiation will provide the background against which we hope to see the shadow of the black hole at our galaxy’s heart,” adds Muxlow.

US astrophysicist Kip Thorne helped design the black hole for the film Interstellar.
US astrophysicist Kip Thorne helped design the black hole for the film Interstellar.

Astronomers study black holes for several reasons. They are crucial to our attempts to understand the formation of galaxies, for example, and the EHT should provide vital observations for this work. However, its main purpose is simply to test general relativity. Einstein’s great theory has stood up well to scientific scrutiny over the last century – the recent discovery of gravitational waves, predicted by general relativity, being a good example. Black holes are also predicted by Einstein’s work and although astronomers have gleaned enough information to be sure they exist, their exact structures and shapes are unclear. The Event Horizon Telescope should put that right.

“We want to see whether the idea of a black hole having an event horizon is actually right and whether the quantitative predictions of what its shadow should look like are correct,” says Laing. “If general relativity is wrong in some way, you should eventually be able to see deviations from its predictions in the shape of the shadow and behaviour of our galaxy’s great black hole.”

In other words, if Einstein’s equations break down anywhere, they are most likely to do so at the edge of a black hole, where the fabric of space-time is being stretched more severely than any other place in the cosmos. As Laing says: “It’s the ultimate test.”

For example, if the shadow is precisely circular, this would indicate our galaxy’s black hole is not rotating. However, most predictions suggest that it should be spinning – which would produce a disc that has a dent.

The production of this evidence will strain the ingenuity and technological expertise of astronomers to their limits. Vast amounts of data, collected from observatories across the planet, will have to be combined to create a single image, an international collaboration that is being led by Shep Doeleman at the Harvard Smithsonian Center for Astrophysics.

“We are going to take advantage of the fact that all the gas and dust that is trying madly to fall into the black hole heats up to billions of degrees and the black hole casts a shadow against that intense light,” Doeleman said in a recent interview. “With the Event Horizon Telescope we capture light at different points on the Earth’s surface because our telescopes will be watching the same black hole at the same time. We freeze that light. We record it on hard-disk drives and then fly them back to a central computing cluster.” The computer will then create the image of the black hole.

In the UK, our astronomers’ main involvement in the project is channelled through our membership of the European Southern Observatory, which runs an array of 66 radio telescopes in the Andes called Alma (the Atacama Large Millimeter/submillimeter Array). This is one of the main instruments involved in the Event Horizon Telescope.

“To see through the dust and other material that lies between us and the centre of our galaxy, we have to use radiation that is about a millimetre in wavelength,” says Professor Tim O’Brien, another Jodrell Bank astronomer. “That compares with the wavelength of the light that we detect in our eyes, which is hundreds of times shorter in wavelength.”

The Milky Way, at whose centre lies the supermassive black hole Sagittarius A*.
The Milky Way, at whose centre lies the supermassive black hole Sagittarius A*.

This difference has a crucial consequence. Studying radiation with longer wavelengths makes it easier to peer through the dusty hearts of galaxies, including our Milky Way. However, to detect and study such radiation, astronomers need instruments that have far bigger collecting dishes than optical telescopes require. For an instrument designed to study millimetre-length radiation, you will need a telescope that is hundreds of times larger than a normal optical telescope, which gathers radiation of a much shorter wavelength. “In fact, if you want to observe, in detail, an object that is so distant and so obscured by dust as the black hole at the galaxy’s centre, you will have to design one that is as big as an entire planet,” says O’Brien.

Building a planet-sized telescope suggests all sorts of practical difficulties. Fortunately, there are ways round the problem. By combining the observations of a number of telescopes from different parts of the world, it is possible to create a machine that has equivalent gathering power to an Earth-sized device. The technique is known as very long baseline interferometry or VLBI and, in this case, it will create an instrument of unprecedented observing power. “The Event Horizon Telescope is the equivalent of a telescope that would allow you to read a newspaper headline on the moon while standing on the Earth,” says Muxlow.

The Event Horizon Telescope has not been designed solely to study our Milky Way’s black hole, however. Astronomers have other targets for it to observe. In particular, they plan to use it to try to take images of an even more remote object: a super-giant, elliptical galaxy in the constellation Virgo known as the M87 galaxy. It is 53m light years from the Earth and it also has a black hole at its heart.

“M87’s black hole is much larger than our galaxy’s but it is much further away, so it is going to be just as hard to study as the one that is inside the Milky Way,” said Laing. “However, the M87 black hole is much more active than our black hole. It is sucking in matter from surrounding space and ejecting it again in a spectacular jet, while our black hole is fairly quiescent at present. It will be very useful to compare the two black holes. black holes.”

Some of the antennas of the Atacama Large Millimeter/submillimeter Array (Alma) in the Atacama desert, Chile.
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Some of the antennas of the Atacama Large Millimeter/submillimeter Array (Alma) in the Atacama desert, Chile. Photograph: Alamy

Just when we will get a chance to see these shadowy images of black holes is a different matter. Data from the different observatories that make up the Event Horizon Telescope will fill dozens of hard drives, the equivalent of 10,000 laptops’ worth of information. Shipping these from the South Pole Telescope, the project’s remotest instrument, is likely to take weeks, if not months. Then the data has to be combined on computers. “I think it will take at least nine months after we take our observations before we compile our first images,” says Muxlow.

Other problems that could affect the telescope’s cross-galactic photo bid in April include the weather, or to be more precise the levels of water vapour in the atmosphere. Water vapour plays havoc with observations made at millimetre wavelengths. Hence the placing of the Alma observatory high in the Andes – Atacama is one of the world’s driest places. Similarly, the south pole has a desert climate, almost never receiving any precipitation. These aid the EHT’s observing prowess but can occasionally be disrupted by weather that brings in unexpected clouds of water vapour. “We remain hopeful we will get our image in the next year, nevertheless,” says Laing.

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An Earth-Sized Clump of Matter Was Pulled Into a Black Hole Faster Than We’ve Ever Seen Before


A team of researchers in the UK have observed matter falling into a black hole at 30 percent the speed of light. This is much faster than anything previously observed.

The high velocity is a result of misaligned discs of material rotating around the black hole.

main article image

The galaxy in the study is named PG211+143 and it’s about a billion light years away from our Solar System. It’s a Seyfert galaxy, which means it is very bright and has a supermassive black hole (SMBH) in its center.

Matter falling into the hole from accretion discs causes its high energy output. But no matter has ever been observed falling this quickly into a black hole.

The team behind the study is led by Professor Ken Pounds of the University of Leicester. Pounds and the other authors used data from the European Space Agency’s XMM-Newton observatory, which was launched in 1999 to observe interstellar x-ray sources.

The study supports theoretical work already done.

“We were able to follow an Earth-sized clump of matter for about a day, as it was pulled towards the black hole, accelerating to a third of the velocity of light before being swallowed up by the hole.” explains Pounds.

Black holes are called ‘black’ because they have such strong gravitational force that not even light escape them. They are the subject of intense scrutiny because of their over-all importance in astronomy and astrophysics.

They are intensely energetic, and are the most efficient objects at extracting energy from matter. And they get that energy from gas falling into the black hole.

Galaxies like PG211+143, and like our own Milky Way, have super massive black holes in their center. These monsters have millions or billions times as much matter as our Sun.

They can become intensely energetic when enough matter flows into them, and then they’re called active galactic nuclei (AGN).

Black holes dwarf the Sun in terms of mass, but they are tiny, compact objects. They are surrounded by swirling discs of gas, but the black hole’s small size means that gas only falls in slowly.

Most of the gas orbits the black hole, slowly and gradually spiralling into the hole through an accretion disc. An accretion disc is a sequence of circular orbits of decreasing size.

As the gas gets closer and closer to the black hole, it speeds up and becomes hot and luminous.

This is how black holes turn matter into energy. The intense gravity of the hole causes the gas in the disc to move faster and faster, until it starts radiating energy.

Astronomers assumed that these discs of in-flowing gas are in alignment with each other, like the planets on the ecliptic in our Solar System. But that’s not always the case.

Clouds of gas and dust can fall into the black hole from any direction, so there’s really no reason that these accretion discs can’t be misaligned. The question has been, how do misaligned discs affect the in-fall of gas into a black hole?

This is where Professor Pounds and his team of collaborators come in. They used XMM-Newton to examine x-ray spectra from PG211+143.

They found that spectra was red-shifted and the matter they were observing was falling into the black hole at about 100,000 km/s (62,000 mps), or about 30 percent of the speed of light.

In astronomical terms the matter was very close to the hole. Its distance from the hole is only 20 times the size of the hole itself, and the matter had barely any rotational energy.

Theoretical work done using the Dirac supercomputer facility in the UK agrees with these observations. That work shows how accretion rings of gas can break off and collide with each other.

That cancels out the rotational velocity of the gas, allowing the gas to fall into the black hole much more quickly. But until now, it has never been observed.

“The galaxy we were observing with XMM-Newton has a 40 million solar mass black hole which is very bright and evidently well fed. Indeed some 15 years ago we detected a powerful wind indicating the hole was being over-fed,” explains Pounds.

“While such winds are now found in many active galaxies, PG1211+143 has now yielded another ‘first’, with the detection of matter plunging directly into the hole itself.”

The study not only spotted this high-velocity in-flow of matter into a black hole, but in doing so it shed light on another mystery in astronomy. In the early universe, black holes quickly gained very large masses, but it was never clear why.

Misaligned discs and the chaotic accretion of matter could be responsible for the fast-growing black holes in the early days of the universe.

Why Stephen Hawking’s Black Hole Puzzle Keeps Puzzling


The renowned British physicist, who died at 76, left behind a riddle that could eventually lead his successors to the theory of quantum gravity.
 

The physicist Stephen Hawking in 1979 in Princeton, New Jersey.

The physicist Stephen Hawking in 1979 in Princeton, New Jersey.

The renowned British physicist Stephen Hawking, who died today at 76, was something of a betting man, regularly entering into friendly wagers with his colleagues over key questions in theoretical physics. “I sensed when Stephen and I first met that he would enjoy being treated irreverently,” wrote John Preskill, a physicist at the California Institute of Technology, earlier today on Twitter. “So in the middle of a scientific discussion I could interject, ‘What makes you so sure of that, Mr. Know-It-All?’ knowing that Stephen would respond with his eyes twinkling: ‘Wanna bet?’”

And bet they did. In 1991, Hawking and Kip Thorne bet Preskill that information that falls into a black hole gets destroyed and can never be retrieved. Called the black hole information paradox, this prospect follows from Hawking’s landmark 1974 discovery about black holes — regions of inescapable gravity, where space-time curves steeply toward a central point known as the singularity. Hawking had shown that black holes are not truly black. Quantum uncertainty causes them to radiate a small amount of heat, dubbed “Hawking radiation.” They lose mass in the process and ultimately evaporate away. This evaporation leads to a paradox: Anything that falls into a black hole will seemingly be lost forever, violating “unitarity” — a central principle of quantum mechanics that says the present always preserves information about the past.

Hawking and Thorne argued that the radiation emitted by a black hole would be too hopelessly scrambled to retrieve any useful information about what fell into it, even in principle. Preskill bet that information somehow escapes black holes, even though physicists would presumably need a complete theory of quantum gravity to understand the mechanism behind how this could happen.

Physicists thought they resolved the paradox in 2004 with the notion of black hole complementarity. According to this proposal, information that crosses the event horizon of a black hole both reflects back out and passes inside, never to escape. Because no single observer can ever be both inside and outside the black hole’s horizon, no one can witness both situations simultaneously, and no contradiction arises. The argument was sufficient to convince Hawking to concede the bet. During a July 2004 talk in Dublin, Ireland, he presented Preskill with the eighth edition of Total Baseball: The Ultimate Baseball Encyclopedia, “from which information can be retrieved at will.”

Thorne, however refused to concede, and it seems he was right to do so. In 2012, a new twist on the paradox emerged. Nobody had explained precisely how information would get out of a black hole, and that lack of a specific mechanism inspired Joseph Polchinski and three colleagues to revisit the problem. Conventional wisdom had long held that once someone passed the event horizon, they would slowly be pulled apart by the extreme gravity as they fell toward the singularity. Polchinski and his co-authors argued that instead, in-falling observers would encounter a literal wall of fire at the event horizon, burning up before ever getting near the singularity.

At the heart of the firewall puzzle lies a conflict between three fundamental postulates. The first is the equivalence principle of Albert Einstein’s general theory of relativity: Because there’s no difference between acceleration due to gravity and the acceleration of a rocket, an astronaut named Alice shouldn’t feel anything amiss as she crosses a black hole horizon. The second is unitarity, which implies that information cannot be destroyed. Lastly, there’s locality, which holds that events happening at a particular point in space can only influence nearby points. This means that the laws of physics should work as expected far away from a black hole, even if they break down at some point within the black hole — either at the singularity or at the event horizon.

To resolve the paradox, one of the three postulates must be sacrificed, and nobody can agree on which one should get the axe. The simplest solution is to have the equivalence principle break down at the event horizon, thereby giving rise to a firewall. But several other possible solutions have been proposed in the ensuing years.

David Kaplan explores one of the biggest mysteries in physics: the apparent contradiction between general relativity and quantum mechanics.

Video: David Kaplan explores one of the biggest mysteries in physics: the apparent contradiction between general relativity and quantum mechanics.

Filming by Petr Stepanek. Editing and motion graphics by MK12.

For instance, a few years before the firewalls paper, Samir Mathur, a string theorist at Ohio State University, raised similar issues with his notion of black hole fuzzballs. Fuzzballs aren’t empty pits, like traditional black holes. They are packed full of strings (the kind from string theory) and have a surface like a star or planet. They also emit heat in the form of radiation. The spectrum of that radiation, Mathur found, exactly matches the prediction for Hawking radiation. His “fuzzball conjecture” resolves the paradox by declaring it to be an illusion. How can information be lost beyond the event horizon if there is no event horizon?

Hawking himself weighed in on the firewall debate along similar lines by way of a two-page, equation-free paper posted to the scientific preprint site arxiv.org in late January 2014 — a summation of informal remarks he’d made via Skype for a small conference the previous spring. He proposed a rethinking of the event horizon. Instead of a definite line in the sky from which nothing could escape, he suggested there could be an “apparent horizon.” Information is only temporarily confined behind that horizon. The information eventually escapes, but in such a scrambled form that it can never be interpreted. He likened the task to weather forecasting: “One can’t predict the weather more than a few days in advance.”

In 2013, Leonard Susskind and Juan Maldacena, theoretical physicists at Stanford University and the Institute for Advanced Studies, respectively, made a radical attempt to preserve locality that they dubbed “ER = EPR.” According to this idea, maybe what we think are faraway points in space-time aren’t that far away after all. Perhaps entanglement creates invisible microscopic wormholes connecting seemingly distant points. Shaped a bit like an octopus, such a wormhole would link the interior of the black hole directly to the Hawking radiation, so the particles still inside the hole would be directly connected to particles that escaped long ago, avoiding the need for information to pass through the event horizon.

Physicists have yet to reach a consensus on any one of these proposed solutions. It’s a tribute to Hawking’s unique genius that they continue to argue about the black hole information paradox so many decades after his work first suggested it.

This Year, We’ll See a Black Hole for the First Time in History


IN BRIEF

Using data collected from their network of telescopes, the Event Horizons Telescope team hopes to produce the first ever image of a black hole in 2018.

FIRST LOOK AT A BLACK HOLE

Within the next 12 months, astrophysicists believe they’ll be able to do something that’s never been done before, and it could have far-reaching implications for our understanding of the universe. A black hole is a point in space with a gravitational pull so strong that not even light can escape from it. Albert Einstein predicted the existence of black holes in his theory of general relativity, but even he wasn’t convinced that they actually existed. And thus far, no one has been able to produce concrete evidence that they do. The Event Horizon Telescope (EHT) could change that.

The EHT isn’t so much one telescope as it is a network of telescopes around the globe. By working in harmony, these devices can provide all of the components necessary to capture an image of a black hole.

“First, you need ultra-high magnification — the equivalent of being able to count the dimples on a golf ball in Los Angeles when you are sitting in New York,” EHT Director Sheperd Doeleman told Futurism.

Next, said Doeleman, you need a way to see through the gas in the Milky Way and the hot gas surrounding the black hole itself. That requires a telescope as big as the Earth, which is where the EHT comes into play.

The Large Millimeter Telescope in Mexico at sunrise. Image Credit: Ana Torres Campos
The Large Millimeter Telescope in Mexico at sunrise. Image Credit: Ana Torres Campos

The EHT team created a “virtual Earth-sized telescope,” said Doeleman, using a network of individual radio dishes scattered across the planet. They synchronized the dishes so that they could be programmed to observe the same point in space at the exact same time and record the radio waves they detected onto hard disks.

The idea was that, by combining this data at a later date, the EHT team could produce an image comparable to one that could have been created using a single Earth-sized telescope.

In April 2017, the EHT team put their telescope to the test for the first time. Over the course of five nights, eight dishes across the globe set their sights on Sagittarius A* (Sgr A*), a point in the center of the Milky Way that researchers believe is the location of a supermassive black hole.

Data from the South Pole Telescope didn’t reach the MIT Haystack Observatory until mid-December due to a lack of cargo flights out of the region. Now that the team has the data from all eight radio dishes, they can begin their analysis in the hopes of producing the first image of a black hole.

PROVING EINSTEIN RIGHT (OR WRONG)

Not only would an image of a black hole prove that they do exist, it would also reveal brand new insights into our universe.

“The impact of black holes on the universe is huge,” said Doeleman. “It’s now believed that the supermassive black holes at the center of galaxies and the galaxies they live in evolve together over cosmic times, so observing what happens near the event horizon will help us understand the universe on larger scales.”

In the future, researchers could take images of a single black hole over time. This would allow the scientists to determine whether or not Einstein’s theory of general relativity holds true at the black hole boundary, as well as study how black holes grow and absorb matter, said Doeleman.

Still, the April observations of Sgr A* are just the first using the EHT, and Doeleman is keeping expectations in check.

“Of course, we have no guarantee of what we’ll see, and nature could throw us a curve ball. However, the EHT is now up and running, so over the next several years, we will work towards making an image to see what a black hole really looks like,” he told Futurism.

While the entire team is excited about the prospect of producing that never-before-seen image, they are also making sure to work carefully and deliberately on the data, said Doeleman, and have, therefore, not set a date for when results will be ready.

Still, we’re closer than ever before to finally capturing an image of a black hole, and there’s no harm in hoping the EHT team crosses the finish line in 2018.

For The First Time, Astronomers Caught a Black Hole Spewing Out Matter Twice


We’ve never seen anything like this.

Black holes don’t just sit there munching away constantly on the space around them. Eventually they run out of nearby matter and go quiet, laying in wait until a stray bit of gas passes by.

 

Then a black hole devours again, belching out a giant jet of particles. And now scientists have captured one doing so not once, but twice – the first time this has been observed.

The two burps, occurring within the span of 100,000 years, confirm that supermassive black holes go through cycles of hibernation and activity.

It’s actually not as animalistic as all that, since black holes aren’t living or sentient, but it’s a decent-enough metaphor for the way black holes devour material, drawing it in with their tremendous gravity.

But even though we’re used to think how nothing ever comes back out of a black hole, the curious thing is that they don’t retain everything they capture.

When they consume matter such as gas or stars, they also generate a powerful outflow of high-energy particles from close to the event horizon, but not beyond the point of no return.

“Black holes are voracious eaters, but it also turns out they don’t have very good table manners,” said lead researcher Julie Comerford, an astronomer at the University of Colorado Boulder.

“We know a lot of examples of black holes with single burps emanating out, but we discovered a galaxy with a supermassive black hole that has not one but two burps.”

The black hole in question is the supermassive beast at the centre of a galaxy called SDSS J1354+1327 or just J1354 for short. It’s about 800 million light-years from Earth, and it showed up in Chandra data as a very bright point of X-ray emission – bright enough to be millions or even billions of times more massive than our Sun.

The team of researchers compared X-ray data from the Chandra X-ray observatory to visible-light images from the Hubble Space Telescope, and found that the black hole is surrounded by a thick cloud of dust and gas.

“We are seeing this object feast, burp, and nap, and then feast and burp once again, which theory had predicted,” Comerford said. “Fortunately, we happened to observe this galaxy at a time when we could clearly see evidence for both events.”

That evidence consists of two bubbles in the gas – one above and one below the black hole, expulsions particles following a meal. And they were able to gauge that the two bubbles had occurred at different times.

The southern bubble had expanded 30,000 light-years from the galactic centre, while the northern bubble had expanded just 3,000 light-years from the galactic centre. These are known as Fermi bubbles, and they are usually seen after a black hole feeding event.

From the movement speed of these bubbles, the team was able to work out they occurred roughly 100,000 years apart.

So what’s the black hole eating that’s giving it such epic indigestion? Another galaxy. A companion galaxy is connected to J1354 by streams of stars and gas, due to a collision between the two. It is clumps of material from this second galaxy that swirled towards the black hole and got eaten up.

“This galaxy really caught us off guard,” said doctoral student Rebecca Nevin.

“We were able to show that the gas from the northern part of the galaxy was consistent with an advancing edge of a shock wave, and the gas from the south was consistent with an older outflow from the black hole.”

The Milky Way also has Fermi bubbles following a feeding event by Sagittarius A*, the black hole in its centre. And, just as J1354’s black hole fed, slept, then fed again, astronomers believe Sagittarius A* will wake to feed again too.

The research was presented at the 231st meeting of the American Astronomical Society, and has also been published in The Astrophysical Journal.

Are gravitational waves kicking this black hole out of its galaxy?


Astronomers have just spied a black hole with a mass 1 billion times the sun’s hurtling toward our galaxy. But scientists aren’t worried about it making contact: It’s some 8 billion light-years away from Earth and traveling at less than 1% the speed of light. Instead, they’re wondering how it got the boot from its parent galaxy, 3C186 (fuzzy mass in the Hubble telescope image, above). Most black holes lie quietly—if voraciously—at the center of their galaxies, slurping up the occasional passing star.

But every once in a while, two galaxies merge, and the black holes in their centers begin to swirl around each other in a pas des deux that eventually leads to a devastating merger. The wandering black hole (bright spot above), may be the result of one such merger. Based on the wavelengths of spectral lines emitted by the luminous gas surrounding the black hole, the object is traveling at a speed of about 7.5 million kilometers per hour—a rate that would carry it from Earth to the moon in about 3 minutes. If the most likely scenario is true, then a massive kick from the merger of two black holes some 1.2 billion years ago would have created a ripple of gravitational waves, the researchers suggest in a forthcoming issue of Astronomy & Astrophysics. And if the precollision black holes didn’t have the same mass and rotation rate as each other, the waves would have been stronger in some directions than others, giving the resulting object a jolt equivalent to the energy of 100 million supernovae exploding simultaneously, the researchers estimate. Other runaway black holes have been proposed, but none of them has yet been confirmed.

Physicists create mind-bending ‘negative mass’ that accelerates backwards and could help explain black holes


A rubidium metal sample

Scientists have created a fluid with “negative mass” which they claim can be used to explore some of the more challenging concepts of the cosmos.

Washington State University physicists explained that this mass, unlike every physical object in the world we know, accelerates backwards when pushed.

The phenomenon, which is rarely created in laboratory conditions, shows a less intuitive side of Newton’s Second Law of Motion, in which a force is equal to the mass of an object times its acceleration (F=ma).

 Our everyday world sees only the positive effect of the law: if you push an object, it moves away from you.

“That’s what most things that we’re used to do,” said Michael Forbes, a WSU assistant professor of physics and astronomy and an affiliate assistant professor at the University of Washington. “With negative mass, if you push something, it accelerates toward you.”

To create the negative matter the WSU team cooled rubidium atoms to just above absolute zero, creating what is known as a Bose-Einstein condensate in which particles move very slowly and behave like waves.

First predicted theoretically by Satyendra Nath Bose and Albert Einstein, a Bose-Einstein condensate is a group of atoms cooled to such a low temperature that there is hardly any movement left in the group. At that point, the atoms begin to clump together becoming identical, from a physical point of view, and the whole group starts behaving as though it were a single atom.

Once scientists reached that stage, they used lasers to kick atoms back and forth until they started spinning backwards. When the rubidium rushes out fast enough, if behaves as if it had negative mass.

 “Once you push, it accelerates backwards,” said Mr Forbes, who acted as a theorist analysing the system. “It looks like the rubidium hits an invisible wall.”

The physicist explained that the ground-breaking aspect of their research is the “exquisite control” they have of the negative mass using their technique.

The heightened control gives researchers a new tool to engineer experiments to study similar behaviours in astrophysics, such as neutron stars, and cosmological phenomena like black holes and dark energy, where experiments are impossible.

“It provides another environment to study a fundamental phenomenon that is very peculiar,” Mr Forbes said.

What is a black hole?

Nasa artist’s impression of debris from a star being flung away from a black hole

A black hole is a region in space with a gravitational field so intense that even light can not get out. Because light can’t escape, black holes can’t be seen. They’re detected by the difference in behaviour of stars nearer to the black hole. Stellar black holes are formed by the collapse of the centre of a massive star. This collapse also causes a supernova, or an exploding star, that blasts part of the star into space.

Source:http://www.telegraph.co.uk

 

Astronomers To Peer Into A Black Hole For The First Time With New Event Horizon Telescope.


Ever since first mentioned by Jon Michell in a letter to the Royal Society in 1783, black holes have captured the imagination of scientists, writers, filmmakers and other artists. Perhaps part of the allure is that these enigmatic objects have never actually been “seen”. But this could now be about to change as an international team of astronomers is connecting a number of telescopes on Earth in the hope of making the first ever image of a black hole. The Conversation

Black holes are regions of space inside which the pull of gravity is so strong that nothing – not even light – can escape. Their existence was predicted mathematically by Karl Schwarzchild in 1915, as a solution to equations posed in Albert Einstein’s theory of general relativity.

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We don’t know what the black hole at the centre of the Milky Way will look like.

Astronomers have had circumstantial evidence for many decades that supermassive black holes – a million to a billion times more massive than our sun – lie at the hearts of massive galaxies. That’s because they can see the gravitational pull they have on stars orbiting around the galactic centre. When overfed with material from the surrounding galactic environment, they also eject detectable plumes or jets of plasma to speeds close to that of light. Last year, the LIGO experiment provided even more proof by famously detecting ripples in space-timecaused by two medium-mass black holes that merged millions of years ago.

But while we now know that black holes exist, questions regarding their origin, evolution and influence in the universe remain at the forefront of modern astronomy.

Catching a tiny spot on the sky

On April 5-14 2017, the team behind the Event Horizon Telescope hopes to test the fundamental theories of black-hole physics by attempting to take the first ever image of a black hole’s event horizon (the point at which theory predicts nothing can escape). By connecting a global array of radio telescopes together to form the equivalent of a giant Earth-sized telescope – using a technique known as Very Long Baseline Interferometry and Earth-aperture synthesis – scientists will peer into the heart of our Milky Way galaxy where a black hole that is 4m times more massive than our sun – Sagittarius A* – lurks.

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Sagittarius A*. This image was taken with NASA’s Chandra X-Ray Observatory. Ellipses indicate light echoes.
Astronomers know there is a disk of dust and gas orbiting around the black hole. The path the light from this material takes will be distorted in the gravitational field of the black hole. Its brightness and colour are also expected to be altered in predictable ways. The tell-tale signature astronomers hope to see with the Event Horizon Telescope is a bright crescent shape rather than a disk. And they may even see the shadow of the black hole’s event horizon against the backdrop of this brightly shining swirling material.

The array connects nine stations spanning the globe – some individual telescopes, others collections of telescopes – in Antarctica, Chile, Hawaii, Spain, Mexico and Arizona. The “virtual telescope” has been in development for many years and the technology has been tested. However, these tests initially revealed a limited sensitivity and an angular resolution that was insufficient to probe down to the scales needed to reach the black hole. But the addition of sensitive new arrays of telescopes – including the Atacama Large Millimeter Array in Chile and the South Pole Telescope – will give the network a much-needed boost in power. It’s rather like putting on spectacles and suddenly being able to see both headlights from an oncoming car rather than a single blur of light.

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The Atacama Large Millimeter submillimeter Array ALMA by night under the Magellanic Clouds.

The black hole is a compact source on the sky – its view at optical wavelengths (light that we can see) is completely blocked by large quantities of dust and gas. However, telescopes with sufficient resolution and operating at longer, radio millimetre wavelengths can peer through this cosmic fog.

The resolution of any kind of telescope – the finest detail that can be discerned and measured – is usually quoted as a small angle corresponding to the ratio of an object’s size to its distance. The angular size of the moon as seen from the Earth is about half a degree, or 1800 arc seconds. For any telescope, the bigger its aperture, the smaller the detail that can be resolved.

The resolution of a single radio telescope (typically with an aperture of 100 metres) is roughly about 60 arc seconds. This is comparable to the resolution of the unaided human eye and about a sixtieth of the apparent diameter of the full moon. But by connecting many telescopes, the Event Horizon Telescope will be about to achieve a resolution of 15-20 microarcsecond (0,000015 arcseconds), corresponding to being able to spy a grape at the distance of the moon.

What’s at stake?

Although the practice of connecting many telescopes in this way is well known, particular challenges lie ahead for the Event Horizon Telescope. The data recorded at each station in the network will be shipped to a central processing facility where a supercomputer will carefully combine all the data. Different weather, atmospheric and telescope conditions at each site will require meticulous calibration of the data so that scientists can be sure any features they find in the final images are not artefacts.

If it works, imaging the material inside the black hole region with angular resolutions comparable to that of its event horizon will open a new era of black hole studies and solve a number of big questions: do event horizons even exist? Does Einstein’s theory work in this region of extreme strong gravity or do we need a new theory to describe gravity this close to a black hole? Also, how are black holes fed and how is material ejected?

It may even even be possible to image the black holes at the centre of nearby galaxies, such as the giant elliptical galaxy that lies at the heart of our local cluster of galaxies.

Ultimately, the combination of mathematical theory and deep physical insight, global international scientific collaborations and remarkable, tenacious long-term advances in cutting edge experimental physics and engineering look set to make revealing the nature of spacetime a defining feature of early 21st century science.

Source:http://www.huffingtonpost.co.uk/

Stephen Hawking says he has a way to escape from a black hole.


Hawking outside the KTH Royal Institute of Technology in Stockholm yesterday
Hawking outside the KTH Royal Institute of Technology in Stockholm yesterday

Stuff that falls into a black hole is gone forever, right? Not so, says Stephen Hawking.

“If you feel you are in a black hole, don’t give up,” he told an audience at a public lecture in Stockholm, Sweden, yesterday. He was speaking in advance of a scientific talk today at the Hawking Radiation Conference being held at the KTH Royal Institute of Technology in Stockholm. “There’s a way out.”

You probably know that black holes are stars that have collapsed under their own gravity, producing gravitational forces so strong that even light can’t escape. Anything that falls inside is thought to be ripped apart by the massive gravity, never to been seen or heard from again.

What you may not know is that physicists have been arguing for 40 years about what happens to the information about the physical state of those objects once they fall in. Quantum mechanics says that this information cannot be destroyed, but general relativity says it must be – that’s why this argument is known as the information paradox.

Now Hawking says this information never makes it inside the black hole in the first place. “I propose that the information is stored not in the interior of the black hole as one might expect, but on its boundary, the event horizon,” he said today.

“Black holes ain’t as black as they are painted”

The event horizon is the sphere around a black hole from inside which nothing can escape its clutches. Hawking is suggesting that the information about particles passing through is translated into a kind of hologram – a 2D description of a 3D object – that sits on the surface of the event horizon. “The idea is the super translations are a hologram of the ingoing particles,” he said. “Thus they contain all the information that would otherwise be lost.”

So how does that help something escape from the black hole? In the 1970s Hawking introduced the concept of Hawking radiation – photons emitted by black holes due to quantum fluctuations. Originally he said that this radiation carried no information from inside the black hole, but in 2004 changed his mind and said it could be possible for information to get out.

Just how that works is still a mystery, but Hawking now thinks he’s cracked it. His new theory is that Hawking radiation can pick up some of the information stored on the event horizon as it is emitted, providing a way for it to get out. But don’t expect to get a message from within, he said. “The information about ingoing particles is returned, but in a chaotic and useless form. This resolves the information paradox. For all practical purposes, the information is lost.”

Last year Hawking made headlines for saying “there are no black holes” – although what he actually meant was a little more complicated, as he proposed replacing the event horizon with a related concept, an apparent horizon. This new idea is compatible with his previous one, which wasn’t really news to theoretical physicists, says Sabine Hossenfelder of the Nordic Institute for Theoretical Physics in Stockholm, who attending Hawking’s lecture.

“He is saying that the information is there twice already from the very beginning, so it’s never destroyed in the black hole to begin with,” she says. “At least that’s what I understood.”

More details are expected later today when one of Hawking’s collaborators Malcom Perry expands on the idea, and Hawking and his colleagues say they will publish a paper on the work next month, but it’s clear he is gunning for the idea that black holes are inescapable. It’s even possible information could get out into parallel universes, he told the audience yesterday.

“The message of this lecture is that black holes ain’t as black as they are painted. They are not the eternal prisons they were once thought,” he said. “Things can get out of a black hole both on the outside and possibly come out in another universe.”

Gravitational waves can’t solve our black hole problems, physicists warn.


When it comes to black holes, the past couple of years have seen a firestorm of disagreements about event horizons, firewalls, and the very nature of black hole life and death erupting between cosmologists. It’s admittedly been a quiet firestorm, with papers here and there carefully arguing their positions while being respectful of opposing views, but that still counts as a firestorm in science.

Some people thought that the gravitational waves observed earlier this year could put an end to the dispute, but a group of physicists now warns that we shouldn’t be so quick to jump to conclusions.

The arguments centre around two related disagreements over what we’re actually talking about when we call something a ‘black hole’.

The first is over what happens when something falls into a black hole. Traditionally, black holes are thought to be objects with a gravitational force so strong, light isn’t even going fast enough to escape their clutches. And if light – the fastest thing in the Universe – can’t escape, then neither can anything else.

A black hole is usually defined by its event horizon – the outline of the region in space where gravity is strong enough to hold light down. You wouldn’t even necessarily notice as you passed over the event horizon of a black hole, since it’s just a place in space like any other. You’d only notice when you tried to escape.

But a few years ago, a couple of papers suggested that this very simplified view leads to some problems that can’t be resolved with our current understanding of the laws of physics.

Instead, they said, there must be something special about the event horizon: just after something passed over the event horizon, it would be scrambled and burnt up beyond recognition by something called a firewall. These firewalls seemed to eliminate the theoretical problems, but they were a pretty weird solution – and not everyone was on board.

One of those not on-board was Stephen Hawking, who thought it was ridiculous. Hawking and those who agreed with him maintained that there was nothing special about the edge of a black hole.

But then Hawking went a step further, adding fuel to the second part of the debate. In his quest to disprove the firewall, he ended up with a black hole without an event horizon.

This turned the definition of a black hole upside-down: without the event horizon – the place beyond which nothing can ever escape the black hole – what even defines a black hole? Physicists weren’t exactly scrambling to the table with answers.

At the same time, there were some alternatives to black holes being developed that might still have extreme gravity but wouldn’t have a point of no return. These strange objects have been dubbed ‘black hole mimickers’.

And then there were those who kept black holes with event horizons but still refused to believe the firewall.

All of the different parties converged on the gravitational waves observed by the Laser Interferometer Gravitational-Wave Observatory (LIGO). At first glance, the gravitational waves seemed like a clear victory for the black-holes-with-event-horizons camp. The pattern of the waves seemed to exactly match their predictions of what it should look like when two black holes with event horizons collide to form another black hole with an event horizon.

They were particularly excited about the ‘ringdown’ – when the final black hole sheds some energy and settles down after all the excitement of the collision. The ringdown, they said, precisely matched what they expected and didn’t match other contradictory predictions.

But the authors of a new paper say we can’t be quite so sure. They showed that the gravitational waves LIGO detected could have been made by any of those black hole mimickers – the objects that have gravity like a black hole without having an event horizon. So it seems like we’re back to square one.

But there is hope for distinguishing between the different hypotheses. They still disagree when it comes to the ringdown, but the disagreements are going to take better measurements to resolve. With better measurements of gravitational waves and of the ringdown, we should be able to answer these fundamental questions about the nature of black holes.

Watch the video. URL:https://youtu.be/XE5PNbsUERE