Hawking: Black holes store information

Black holes preserve information about the stuff that falls into them, according to Prof Stephen Hawking.

Physicists have long argued about what happens to information about the physical state of things that are swallowed up by black holes.

This information was thought to be destroyed, but it turned out that this violated laws of quantum physics.

Prof Hawking now says the information may not make it into the black hole at all, but is held on its boundary.

In broad terms, black holes are regions in space where the gravity is so strong that nothing that gets pulled in – even light – can escape.

At the same time, the laws of quantum mechanics dictate that everything in our world can be broken down into information, for example, a string of 1s and 0s. And according to those laws, this information should never disappear, not even if it gets sucked into a black hole.

But according to Einstein’s theory of general relativity, the information must be destroyed. This quandary is known as the information paradox.

Prof Hawking believes the information doesn’t make it inside the black hole at all.

“The information is not stored in the interior of the black hole as one might expect, but in its boundary – the event horizon,” he told a conference at the KTH Royal Institute of Technology in Stockholm, Sweden.

The event horizon is a boundary, or point of no return, where escape from the gravitational pull of the black hole becomes impossible.

Hawking has been working with Cambridge colleague Prof Malcolm Perry and Harvard professor Andrew Strominger on the problem. They believe that information at the event horizon is transformed into a 2D hologram – a phenomenon known as a super translation.

“The idea is the super translations are a hologram of the ingoing particles,” Hawking explained.

“Thus, they contain all the information that would otherwise be lost.”

Prof Marika Taylor, a theoretical physicist at the University of Southampton, told BBC News: “Einstein’s theory says that matter gets sucked into the black hole, falling behind its event horizon.

“Holography seems to suggest that Einstein’s picture of black holes isn’t right. In particular, it’s not clear that there is actually an ‘inside’ to black holes at all – matter which gets sucked in might get stuck at the event horizon and hang around as a hologram there.”

But she added that there was no consensus on this.

On the question of matter getting stuck at the event horizon, she said: “Nobody really understands the details of how this happens – this is what Hawking is trying to work out and what other related ideas ‘fuzzball’ and ‘firewall’ explore too.”

There’s currently little additional detail on the maths behind Prof Hawking’s talk, but he and his collaborators plan to publish a scientific paper in coming weeks.

Light particles – or photons – can be emitted from black holes due to quantum fluctuations, a concept known as Hawking radiation. Information from the black hole might be able to escape via this route.

But, Prof Hawking says it would be in “chaotic, useless form,” adding: “For all practical purposes the information is lost.”

If the information was not in this chaotic form, an observer might be able to reconstruct everything that had fallen into the black hole if they were able to wait for a vast amount of time.

Follow Paul on Twitter.

Dozen black holes found at galactic centre

A dozen black holes may lie at the centre of our galaxy, the Milky Way, researchers have said.

A new analysis provides support for a decades-old prediction that “supermassive” black holes at the centres of galaxies are surrounded by many smaller ones.

However, previous searches of the Milky Way’s centre, where the nearest supermassive black hole is located, have found little evidence for this.

Details appear in the journal Nature.

Charles Hailey from Columbia University in New York and colleagues used archival data from Nasa’s Chandra X-ray telescope to come to their conclusions.

They report the discovery of a dozen inactive and low-mass “binary systems”, in which a star orbits an unseen companion – the black hole.

The supermassive black hole at the centre of the Milky Way, known as Sagittarius A* (Sgr A*), is surrounded by a halo of gas and dust that provides the perfect breeding ground for the birth of massive stars. These stars live, die and could turn into black holes there.

In addition, black holes from outside the halo are believed to fall under the influence of Sgr A* as they lose their energy, causing them to be pulled into its vicinity, where they are held captive by its force.

Some of these bind – or “mate” – to passing stars, forming binary systems.

Previous attempts to detect this population of black holes have looked for the bright bursts of X-rays that are sometimes emitted by black hole binaries.

Faint and steady

“The galactic centre is so far away from Earth that those bursts are only strong and bright enough to see about once every 100 to 1,000 years,” said Prof Hailey.

Instead, the Columbia University astrophysicist and his colleagues decided to look for the fainter but steadier X-rays emitted when these binaries are in an inactive state.

“Isolated, unmated black holes are just black – they don’t do anything,” said Prof Hailey.

“But when black holes mate with a low mass star, the marriage emits X-ray bursts that are weaker, but consistent and detectable.”

A search for the X-ray signatures of low-mass black hole binaries in the Chandra data turned up 12 within three light-years of Sgr A*.

By extrapolating from the properties and distribution of these binaries, the team estimates that there may be 300-500 low-mass binaries and 10,000 isolated low-mass black holes surrounding Sgr A*.

Prof Hailey said the finding “confirms a major theory”, adding: “It is going to significantly advance gravitational wave research because knowing the number of black holes in the centre of a typical galaxy can help in better predicting how many gravitational wave events may be associated with them.”

Gravitational waves are ripples in the fabric of space-time. They were predicted by Albert Einstein’s general theory of relativity and detected by the Ligo experiment in 2015. One way these ripples arise is through the collision of separate black holes.

Farthest monster black hole found

Astronomers have discovered the most distant “supermassive” black hole known to science.

The matter-munching sinkhole is a whopping 13 billion light-years away, so far that we see it as it was a mere 690 million years after the Big Bang.

But at about 800 million times the mass of our Sun, it managed to grow to a surprisingly large size in just a short time after the origin of the Universe.

The find is described in the journal Nature.

The newly discovered black hole is busily devouring material at the centre of a galaxy – marking it out as a so-called quasar.

Matter, such as gas, falling onto the black hole will form an ultra-hot mass of material orbiting around it known as an accretion disk.

“Quasars are among the brightest and most distant known celestial objects and are crucial to understanding the early Universe,” said co-author Bram Venemans of the Max Planck Institute for Astronomy in Germany.

This quasar is interesting because it comes from a time when the Universe was just 5% of its current age.

At this time, the cosmos was beginning to emerge from a period known as the dark ages – just before the first stars appeared.

“Gathering all this mass in under 690 million years is an enormous challenge for theories of supermassive black hole growth,” said co-author Eduardo Bañados, from the Carnegie Institution for Science.

The quasar’s distance is described by a property called its redshift – a measurement of how much the wavelength of its light is stretched by the expansion of the Universe before reaching Earth.

The newly discovered black hole has a redshift of 7.54. The higher the redshift, the greater the distance, and the farther back astronomers are looking in time when they observe the object.

Prior to this discovery, the record-holder for the furthest known quasar existed when the Universe was about 800 million years old.

“Despite extensive searches, it took more than half a decade to catch a glimpse of something this far back in the history of the Universe,” said Dr Bañados.

The discovery of a massive black hole so early on may provide key clues on conditions that abounded when the Universe was young.

“This finding shows that a process obviously existed in the early Universe to make this monster,” Dr Bañados explained.

“What that process is? Well, that will keep theorists very busy.”

The unexpected discovery is based on data amassed from observatories around the world. This includes data from the Gemini North observatory on Hawaii’s Maunakea volcano and a Nasa space telescope called the Wide-field Infrared Survey Explorer (Wise).

Event Horizon Telescope ready to image black hole

Scientists believe they are on the verge of obtaining the first ever picture of a black hole.

They have built an Earth-sized “virtual telescope” by linking a large array of radio receivers – from the South Pole, to Hawaii, to the Americas and Europe.

There is optimism that observations to be conducted during 5-14 April could finally deliver the long-sought prize.

In the sights of the so-called “Event Horizon Telescope” will be the monster black hole at the centre of our galaxy.

Although never seen directly, this object, catalogued as Sagittarius A*, has been determined to exist from the way it influences the orbits of nearby stars.

These race around a point in space at many thousands of km per second, suggesting the hole likely has a mass of about four million times that of the Sun.

But as colossal as that sounds, the “edge” of the black hole – the horizon inside which an immense gravity field traps all light – may be no more than 20 million km or so across.

And at a distance of 26,000 light-years from Earth, this makes Sagittarius A* a tiny pinprick on the sky.

The Event Horizon Telescope (EHT) team is nonetheless bullish.

“There’s great excitement,” said project leader Sheperd Doeleman from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

“We’ve been fashioning our virtual telescope for almost two decades now, and in April we’re going to make the observations that we think have the first real chance of bringing a black hole’s event horizon into focus,” he told BBC News.

The EHT’s trick is a technique called very long baseline array interferometry (VLBI).

This combines a network of widely spaced radio antennas to mimic a telescope aperture that can produce the resolution necessary to perceive a pinprick on the sky.

The EHT is aiming initially to get down to 50 microarcseconds. Team-members talk in analogies, describing the sharpness of vision as being the equivalent of seeing something the size of a grapefruit on the surface of the Moon.

They emphasise the still complex years of work ahead, but also trail the prospect of an imminent breakthrough.

The scientists certainly have an expectation of what they ought to see, if successful.

Simulations rooted in Einstein’s equations predict a bright ring of light fringing a dark feature.

The light would be the emission coming from gas and dust accelerated to high speed and torn apart just before disappearing into the hole.

The dark feature would be the shadow the hole casts on this maelstrom.

“Now, it could be that we will see something different,” Doeleman said.

“As I’ve said before, it’s never a good idea to bet against Einstein, but if we did see something that was very different from what we expect we would have to reassess the theory of gravity.

“I don’t expect that is going to happen, but anything could happen and that’s the beauty of it.”

Over the years, more and more radio astronomy facilities have joined the project. A key recent addition is the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

Its extraordinary state-of-the-art technology has at a stroke increased the EHT’s sensitivity by a factor of 10. Hence, the optimism ahead of April.

Even so, scientists have had to install special equipment at all the radio facilities involved in the observations.

This includes big hard drives to store colossal volumes of data, and atomic clocks to precisely timestamp it all.

Nothing happens on the spot – the hard drives must first be flown to a large computing facility at MIT Haystack Observatory in Westford, just outside Boston, Massachusetts.

“Our hard-drive modules hold the capacity of about 100 standard laptops,” said Haystack’s Vincent Fish.

“We have multiple modules at each telescope and we have numerous telescopes in the array. So, ultimately, we’re talking about 10,000 laptops of data.”

It is in Haystack’s correlator computer that the synthesis will begin.

Some very smart imaging algorithms have had to be developed to make sense of the EHT’s observations, but it will not be a quick result.

It could be the end of the year, perhaps the start of 2018, before the team releases an image in public.

Looking to the future, the scientists are already thinking about how to extend their techniques.

For example, the matter closest to the event horizon and about to disappear into Sagittarius A* should take about 30 minutes to complete an orbit.

Katie Bouman, from MIT’s Computer Science and Artificial Intelligence Laboratory, thinks it might be possible to capture this movement.

“We want to push boundaries and to try to make movies from the data,” she told BBC News.

“Maybe we can actually see some of the gas flowing around the black hole. That’s really the next stage of what we’re trying to accomplish with these imaging algorithms.”

First and foremost, the team needs good weather at the participating observing stations in April.

The strategy is to view the galactic centre at a wavelength of 1.3mm (230GHz). This has the best chance of piercing any obscuring gas and dust in the vicinity of the black hole. But if there is too much water vapour above the array’s receivers, the EHT will struggle even to see through Earth’s atmosphere.

Just getting a resolved view of Sagittarius A* would be a remarkable triumph in itself. But the real objective here is to use the imaging capability to go test aspects of general relativity.

If there are flaws to be found in Einstein’s ideas – and scientists suspect there are more complete explanations of gravity out there waiting to be discovered – then it is in the extreme environment of black holes that limitations should be exposed.

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos