Tag Archives: event horizon

The Event Horizon Telescope (EHT) collaboration, who produced the first ever image of a black hole released in 2019, has today a new view of the massive object at the centre of the Messier 87 (M87) galaxy: how it looks in polarised light. This is the first time astronomers have been able to measure polarisation, a signature of magnetic fields, this close to the edge of a black hole. (EHT Collaboration)

Black Hole Seen Clearly in Historic New Direct Image

Using the Event Horizon Telescope (EHT) to observe the supermassive black hole at the centre of the galaxy Messier 87 (M87), astronomers have once again produced another first in the field of astronomy and cosmology.

Following up on the image of M87’s black hole published two years ago–the first time a black hole was imaged directly–astronomers at the EHT collaboration have captured a stunning image of the same black hole, this time in polarized light.

The achievement marks more than just an impressively sharp and clear second image of this black hole however–it also represents that first-time researchers have been able to capture the polarization of light around such an object.

Not only does this reveal details of the magnetic field that surrounds the supermassive black hole, but it also could give cosmologists the key to explaining how energetic jets launch from the core of this distant galaxy.

The Event Horizon Telescope (EHT) collaboration, who produced the first ever image of a black hole released in 2019, has today a new view of the massive object at the centre of the Messier 87 (M87) galaxy: how it looks in polarised light. This is the first time astronomers have been able to measure polarisation, a signature of magnetic fields, this close to the edge of a black hole. (EHT Collaboration)
The Event Horizon Telescope (EHT) collaboration, which produced the first-ever image of a black hole released in 2019, has today a new view of the massive object at the centre of the Messier 87 (M87) galaxy: how it looks in polarised light. This is the first time astronomers have been able to measure polarisation, a signature of magnetic fields, this close to the edge of a black hole.  This image shows the polarised view of the black hole in M87. The lines mark the orientation of polarisation, which is related to the magnetic field around the shadow of the black hole. (EHT Collaboration)

“M87 is a truly special object!  It is tied for the largest black hole in the sky with the black hole in our galaxy–Sagittarius A*, ” Geoffrey C. Bower, EHT Project Scientist and assistant research astronomer at the Academia Sinica Institute of Astronomy and Astrophysics, tells ZME Science. “It’s about one thousand times further away but also one thousand times more massive.

“The M87 black hole’s home is in the centre of the Virgo Cluster, the nearest massive cluster of galaxies, each with its own black hole. This makes it a great laboratory for studying the growth of galaxies and black holes.”

Geoffrey C. Bower, Academia Sinica Institute of Astronomy and Astrophysics.

Along with Monika Mościbrodzka, Coordinator of the EHT Polarimetry Working Group and Assistant Professor at Radboud University, Netherlands, Bower is one of the authors on two papers detailing the breakthrough published in the latest edition of The Astrophysical Journal Letters.

Messier 87 (M87) is an enormous elliptical galaxy located about 55 million light years from Earth, visible in the constellation Virgo. It was discovered by Charles Messier in 1781, but not identified as a galaxy until 20th Century. At double the mass of our own galaxy, the Milky Way, and containing as many as ten times more stars, it is amongst the largest galaxies in the local universe. Besides its raw size, M87 has some very unique characteristics. For example, it contains an unusually high number of globular clusters: while our Milky Way contains under 200, M87 has about 12,000, which some scientists theorise it collected from its smaller neighbours. Just as with all other large galaxies, M87 has a supermassive black hole at its centre. The mass of the black hole at the centre of a galaxy is related to the mass of the galaxy overall, so it shouldn’t be surprising that M87’s black hole is one of the most massive known. The black hole also may explain one of the galaxy’s most energetic features: a relativistic jet of matter being ejected at nearly the speed of light. The black hole was the object of paradigm-shifting observations by the Event Horizon Telescope. The EHT chose the object as the target of its observations for two reasons. While the EHT’s resolution is incredible, even it has its limits. As more massive black holes are also larger in diameter, M87's central black hole presented an unusually large target—meaning that it could be imaged more easily than smaller black holes closer by. The other reason for choosing it, however, was decidedly more Earthly. M87 appears fairly close to the celestial equator when viewed from our planet, making it visible in most of the Northern and Southern Hemispheres. This maximised the number of telescopes in the EHT that could observe it, increasing the resolution of the final image. This image was captured by FORS2 on ESO’s Very Large Telescope as part of the Cosmic Gems programme, an outreach initiative that (ESO)
Messier 87 (M87) is an enormous elliptical galaxy located about 55 million light-years from Earth, visible in the constellation Virgo and home of the black hole imaged by the EHT team (ESO)

“We are now seeing the next crucial piece of evidence to understand how magnetic fields behave around black holes, and how activity in this very compact region of space can drive powerful jets that extend far beyond the galaxy,” says Mościbrodzka.

“We have never see magnetic fields directly so close to the event horizon,” the astronomer tells ZME Science.


“We now, for the first time, have information on how magnetic field lines are oriented close to the event horizon and how strong these magnetic fields are. All this information is new.”

Deeper Into the Heart of M87

The release of the first image of a black hole on the 10th of April 2019 marked a milestone event in science, and ever since then, the team behind that image has worked hard to delve deeper into M87’s black hole. This second image is the culmination of this quest. The observation of the polarized light allows us to better understand the information in that prior image and the physics of black holes.

This composite image shows three views of the central region of the Messier 87 (M87) galaxy in polarised light. The galaxy has a supermassive black hole at its centre and is famous for its jets, that extend far beyond the galaxy.  One of the polarised-light images, obtained with the Chile-based Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, shows part of the jet in polarised light. This image captures the part of the jet, with a size of 6000 light years, closer to the centre of the galaxy. The other polarised light images zoom in closer to the supermassive black hole: the middle view covers a region about one light year in size and was obtained with the National Radio Astronomy Observatory’s Very Long Baseline Array (VLBA) in the US.  The most zoomed-in view was obtained by linking eight telescopes around the world to create a virtual Earth-sized telescope, the Event Horizon Telescope or EHT. This allows astronomers to see very close to the supermassive black hole, into the region where the jets are launched.  The lines mark the orientation of polarisation, which is related to the magnetic field in the regions imaged.The ALMA data provides a description of the magnetic field structure along the jet. Therefore the combined information from the EHT and ALMA allows astronomers to investigate the role of magnetic fields from the vicinity of the event horizon (as probed with the EHT on light-day scales) to far beyond the M87 galaxy along its powerful jets (as probed with ALMA on scales of thousand of light-years). The values in GHz refer to the frequencies of light at which the different observations were made. The horizontal lines show the scale (in light years) of each of the individual images. (EHT Collaboration)
This composite image shows three views of the central region of the Messier 87 (M87) galaxy in polarised light. The galaxy has a supermassive black hole at its centre and is famous for its jets, that extend far beyond the galaxy.  (EHT Collaboration)

“Light is an electromagnetic wave which has amplitude and direction of oscillation or polarization,” explains Mościbrodzka. “With the EHT we observed that light in the M87’s surrounding ring is polarized meaning that waves oscillation have a preferred direction.”

This polarization is a property of synchrotron radiation that is produced in the vicinity of this black hole. Polarization occurs when light passes through a filter–think of polarized sunglasses blocking out light and thus giving you a clearer view–thus the polarization of light in this picture accounts for this clearer view of M87’s black hole, which reveals a great deal of information about the black hole itself.

“The polarization of the synchrotron light tells us about the orientation of magnetic fields. So by measuring light polarization we can map out the magnetic fields around the black hole.”

Monika Mościbrodzka, Coordinator of the EHT Polarimetry Working Group and Assistant Professor, Radboud University

Capturing such an image of polarized light at a distance of 55 million light-years is no mean feat, and is only possible with the eight linked telescopes across the globe that comprise the EHT. Together these telescopes–including the 66 antennas of the Atacama Large Millimeter/submillimeter Array (ALMA)–form a virtual telescope that is as large as the Earth itself with a resolution equivalent to reading a business card on the Moon.

This image shows the contribution of ALMA and APEX to the EHT. The left hand image shows a reconstruction of the black hole image using the full array of the Event Horizon Telescope (including ALMA and APEX); the right-hand image shows what the reconstruction would look like without data from ALMA and APEX. The difference clearly shows the crucial role that ALMA and APEX played in the observations. (EHT Collaboration)
This image shows the contribution of ALMA and APEX to the EHT. The left hand image shows a reconstruction of the black hole image using the full array of the Event Horizon Telescope (including ALMA and APEX); the right-hand image shows what the reconstruction would look like without data from ALMA and APEX. The difference clearly shows the crucial role that ALMA and APEX played in the observations. (EHT Collaboration)

“As a virtual telescope that is effectively as large as our planet the EHT has a resolution power than no other telescope has,” says Mościbrodzka. “The EHT is observing the edge of what is known to humans, the edge of space and time. And for the second time, it has allowed us to bring to the public the images of this black hole.”

This image–as the above comparison shows– has had its clarity enhanced immensely by calibration with data provided by the Atacama Pathfinder EXperiment (APEX).

Of course, these magnetic fields are responsible for much more than just giving us a crystal clear image of the black hole they surround. They also govern many of the physical processes that make black holes such powerful and fascinating events–including one of M87’s most mysterious features.

How Magnetic Fields Help Black Holes ‘Feed’

The M87 galaxy–55 million light years from Earth– is notable for its powerful astrophysical jets that blast out of its core and extend for 5000 light-years. Researchers believe that these jets are caused when some of the matter at the edge of the black hole escapes consumption.

Whilst other matter falls to the surface of the central black hole and disappears to the central singularity, this escaping matter is launched into space as these remarkable jets.

This artist’s impression depicts the black hole at the heart of the enormous elliptical galaxy Messier 87 (M87). This black hole was chosen as the object of paradigm-shifting observations by the Event Horizon Telescope. The superheated material surrounding the black hole is shown, as is the relativistic jet launched by M87’s black hole. 9ESO/M. Kornmesser)
This artist’s impression depicts the black hole at the heart of the enormous elliptical galaxy Messier 87 (M87). This black hole was chosen as the object of paradigm-shifting observations by the Event Horizon Telescope. The superheated material surrounding the black hole is shown, as is the relativistic jet launched by M87’s black hole. 9ESO/M. Kornmesser)

Even though this is a more than plausible explanation, many questions still remain about the process, namely, how an area that is no bigger than our solar system creates jets that are greater in length than the entire galaxy that surrounds it.

This image of the polarized light around M87’s black hole which offers a glimpse into this inner region finally gives scientists a chance to answer these mysteries.

“Our planet’s magnetosphere prevents ionized particles emitted by the Sun from reaching the Earth’s surface.  In the same way, strong black hole magnetic fields can prevent or slow down the accretion of matter onto the black hole,” Bowers says. “Those strong magnetic fields are also powerful for generating the jets of particles that flow at near the speed of light away from the black hole.”

By mitigating the feeding process of their central black holes, however, these magnetic fields may have an influence that like the jets they create may extend even further than M87 itself. They could be affecting the entire galactic cluster.

“Magnetic fields can play a very important role in how black holes ‘eat.’  If the fields are strong enough, they can prevent inflowing material from reaching the black hole.  They are also important in funnelling matter out into the relativistic jets that burst from the black hole region.  These jets are so powerful that they influence gas dynamics amongst the entire cluster of galaxies surrounding M87.”

Geoffrey C. Bower, Academia Sinica Institute of Astronomy and Astrophysics.

This means a better understanding of the magnetic fields around M87’s black hole also gives researchers an improved understanding of how the matter behaves at the edge of that black hole and perhaps of how such things affect neighbouring galaxies and their evolution.

And from the image of M87’s black hole the EHT team have developed, it looks clear that of the various models that cosmologists have developed to describe the interaction of matter at the edge of black holes, only those featuring strongly magnetized gases can account for its observed features.

“We have now a better idea about the physical process in the ring visible in the image,” Mościbrodzka says. “We now know more precisely how strong magnetic fields can be near a black hole. We also know more accurately at what rate the black hole is swallowing matter. And we have a better idea of what the black hole might look like in the future.”

We’ve come a long way: on the left the first image of the M87 black hole, released in 2019. On the right this new much sharper image. (EHT)

In terms of what is next for black hole imaging, both Mościbrodzka and Bowers are clear; they have their sights set on a black hole that is closer to home than M87–the one that sits at the centre of the Milky Way, which despite being closer to home, could be a tougher nut to crack in terms of imaging.

“We’re hard at work on a problem that we know everyone wants to see; an image of the black hole at the centre of our galaxy,” says Bowers. “This is really tricky because the gas around the black hole moves so fast that the image may be changing on same the time scale that it takes to snap our picture. We think we know how to handle this problem but it requires a lot of technical innovation.”

Given the advancements already made by the EHT collaboration team, it would be unwise to bet against them achieving this lofty goal at some point in the not too distant future.

“We’ve gone from imagining what happens around black holes to actually imaging it!” Bowers concludes. “In the near future, we’ll be able to show a movie of material orbiting the black hole and getting ejected into a jet. I never thought I would see anything like this.

“Black holes are the simplest but most enigmatic objects in the Universe.  These observations are just the beginning of the road to understanding them.”

Geoffrey C. Bower, Academia Sinica Institute of Astronomy and Astrophysics.

Scientists create a sonic black hole in the lab, confirm Stephen Hawking’s theory

Physicists in Israel have devised a black hole analogue — only, rather than being a gravitational fortex that doesn’t allow light to escape, this particular object is a sonic black hole that doesn’t allow sound waves to escape. In the process, the researchers measured the long-theorized Hawking radiation, with important consequences for physics.

A black hole is a region of spacetime where gravity pulls so strongly that even light cannot get out once it crosses a point of no return, known as the event horizon — but you probably knew that already. What may be new to you is that almost 50 years ago, Stephen Hawking proposed a more nuanced view whereby black holes can also generate light.

According to Hawking, black holes can spontaneously emit photons at the event horizon thanks to transient quantum fluctuations known as virtual particles. Despite their name, virtual particles are indeed real particles — it’s just that they pop in and out of existence for a fleeting time.

Virtual particles appear in pairs and in the vast majority of cases they annihilate each other almost immediately. However, if they appear in the vicinity of a black hole, Hawking suggested that it is possible for one particle in a pair to get absorbed by the black hole, while the other escapes into space.

This stream of particles is known as stationary Hawking radiation, but since this phenomenon is so subtle, it’s virtually impossible for our instruments to detect it. But, with some thinking outside the box, it is possible to gain insight into this elusive cosmic phenomenon.

In order to study Hawking radiation, scientists from Technion-Israel Institute of Technology designed a scaled-down version of a black hole, or analogue, in the lab. An example of a black hole analogue can be found in your very own home: a bathtub vortex. The water swirling down the drain can be compared to black hole accretion of matter — but this isn’t what the physicists in Israel used.

Instead, the team cooled down 8,000 rubidium atoms to nearly absolute zero and trapped them in place with a laser beam. This nearly static gas was in an exotic state of matter known as Bose-Einstein Condensate (BEC), in which atoms become so densely packed they behave like one super atom, acting in unison. 

A second laser beam created a stream of potential energy that caused the BEC gas to flow like water rushing down a waterfall. The boundary between the region where one half of the gas was flowing faster than the speed of sound while the other half flowed slowly was the event horizon of the sonic black hole.

Rather than pairs of photons spontaneously forming in the gas, the researchers were looking for pairs of phonons — quantum sound wave particles. Phonons in the faster half of the gas flow, beyond the event horizon, are trapped by the speed of the flowing gas. Just like in a black hole that has trapped light particles crossing the event horizon, the phonon cannot return to the other side of the sonic black hole’s event horizon.

“Essentially, the event horizon is a black hole’s outer sphere, and inside it, there’s a small sphere called the inner horizon,” Prof. Jeff Steinhauer of Technion’s Physics Department said in a statement. “If you fall through the inner horizon, then you’re still stuck in the black hole, but at least you don’t feel the weird physics of being in a black hole. You’d be in a more ‘normal’ environment, as the pull of gravity would be lower, so you wouldn’t feel it anymore.”

The analog black hole created by the researchers. Credit: Kolobov et al.

It took 97,000 iterations of this experiment over 124 consecutive days for the physicists led by Steinhauer to confirm Hawking radiation. Luckily for them, their patience paid off.

“The experimental results of Prof. Steinhauer are of great importance and interest,” Prof. Amos Ori, a general relativity and black hole expert at the Technion Physics Department, said in a statement. 

“Jeff measures stationary Hawking radiation emitted from a sonic black hole, in agreement with Hawking’s theoretical prediction. This gives very significant experimental support to Hawking’s analysis, which gets experimental approval for the first time in Jeff’s experiments.”

The experiments also revealed new insights that weren’t predicted during Hawking’s lifetime. After a certain time, the radiation emitted by the system began to intensify. This is likely due to the development of stimulated radiation following the formation of the inner horizon, the physicists explained in the journal Nature Physics.


“Our new long-term goal,” Steinhauer concluded, “is to see what happens when one goes beyond the approximations used by Hawking, in which the Hawking radiation is quantum, but space-time is classical. In other words, we would take into account that the analogue black hole is composed of point-like atoms.”

The supermassive black hole at the heart of the Milky Way just got very hungry

This artist’s impression shows the path of the star S2 as it passes very close to the supermassive black hole at the center of the Milky Way. As it gets close to the black hole the very strong gravitational field causes the color of the star to shift slightly to the red, an effect of Einstein’s general theory of relativity. Credit:
ESO/M. Kornmesser.

Like virtually all other galaxies, the Milky Way houses a supermassive black hole at its center with a mass millions of times greater than the sun. It constantly gobbles up enormous amounts of gas and dust from its surroundings but scientists have noticed that even for its gargantuan appetite, this black hole is now unusually hungry.

“We have never seen anything like this in the 24 years we have studied the supermassive black hole,” said Andrea Ghez, UCLA professor of physics and astronomy and a co-senior author of the research. “It’s usually a pretty quiet, wimpy black hole on a diet. We don’t know what is driving this big feast.”

The astronomers employed more than 13,000 observations of the black hole, called Sagittarius A*, performed by the W.M. Keck Observatory in Hawaii and the European Southern Observatory’s Very Large Telescope in Chile since 2003.

Although black holes cannot be imaged directly since their massive gravity allows nothing to escape their grasp, not even light, astronomers can see brightness at the edge of the black hole’s point of no return — the event horizon.

The brightness is generated by radiation from gas and dust that are accelerated to huge speeds as they circle the event horizon. Moving at close to the speed of light, the matter generates powerful jets of plasma containing electrons and positrons that ricochet off the event horizon and get hurled outward along the black hole’s axis of rotation. It is these enormous jets of energetic subatomic particles that emit light, which our telescopes can see. Last year, researchers were able to produce the first image of a black hole’s event horizon.

Observations of Sagittarius A* performed on May 13 showed that its brightness had enhanced considerably.

“The first image I saw that night, the black hole was so bright I initially mistook it for the star S0-2, because I had never seen Sagittarius A* that bright,” said UCLA research scientist Tuan Do, the study’s lead author. “But it quickly became clear the source had to be the black hole, which was really exciting.”

Astronomers aren’t sure what’s gone into Sagittarius A* but it’s possible that the extreme brightness swings may have been triggered after a nearby star called S0-2 made a close approach to the black hole during 2018. In the process, it should have discharged a large quantity of gas.

Another hypothesis is that G2, a binary star system was stripped off its outer layer during a close approach to the black hole in 2014. This may explain the black hole’s sudden variations in brightness just outside of it.

Alternatively, very large asteroids that ventured too close to the black hole may have contributed to the jump in brightness, the astronomers noted in a recent paper published in The Astrophysical Journal.

Whatever may be the case, the anomaly is no threat to life on Earth. The black hole is located about 26,000 light-years away from Earth and its radiation would have to be 10 billion times brighter to affect us in a significant way.

What’s perhaps more fascinating than this anomaly, however, is the way the astronomers were able to track the black hole’s feeding patterns all of these years.

In 2004, Ghez and colleagues helped pioneer a crucial piece of technology, called adaptive optics, which corrects the distorting effects of Earth’s atmosphere in real-time. This allowed them to observe more than 3,000 stars in the vicinity of Sagittarius A*.

However, astronomers have been observing Sagittarius A* since long before adaptive optics were invented. In order to make good use of observations made prior to 2004, Ghez developed a new technique called speckle holography that can use faint information from 24 years of data recorded on the black hole and fill in the blanks. The technique was recently described in The Astrophysical Journal Letters and allowed the researchers to determine that the black hole’s brightness is at an all-time high since we’ve been observing it.

Remarkably, the technique also allowed the astronomers to test Einstein’s theory of general relativity near the black hole. The researchers observed the black hole’s effects on S0-2 at it completed an orbit; effects which mirrored Einstein’s predictions.

“It was like doing LASIK surgery on our early images,” Ghez said. “We collected the data to answer one question and serendipitously unveiled other exciting scientific discoveries that we didn’t anticipate.”

Picture showing a black hole's shadow found at the centre of galaxy M87. Credit: EHT Collaboration. EHT Collaboration

Black hole picture shown for the first time

Picture showing a black hole's shadow found at the centre of galaxy M87. Credit: EHT Collaboration. EHT Collaboration

Picture showing the shadow of a black hole found at the center of galaxy M87. Credit: EHT Collaboration.
EHT Collaboration

On Wednesday, a huge collaboration of international scientists made a historic announcement: they have captured the first picture of a black hole. The image was constructed from data gathered by observatories all over the globe, which were combined to create a virtual telescope as big as the Earth.

“We have seen what we thought was unseeable,” said Sheperd Doeleman, an astronomer at Harvard University and the Harvard-Smithsonian Center for Astrophysics, who directed the project behind the black hole image. “We’ve exposed a part of our universe we’ve never seen before,” he added during a press conference at the National Press Club in Washington, D.C.

The Eye of Sauron

The picture shows a dark circle surrounded by swirling, bright features, all eerily similar to the Eye of Sauron from the Lord of the Rings. What we’re seeing is actually the event horizon of the supermassive black hole that sits at the very center of a distant galaxy known as Messier 87, about 53.5 million light-years away, in the constellation Virgo. This means that the picture of the black hole we’re seeing now is what it used to look like exactly 53.5 million years ago — the time it took for its light to reach us. Researchers also made observations of another supermassive black hole, the one at the center of the Milky Way, Sagittarius A*, located only 26,000 light-years away.

The epic picture was produced over the course of many years by a collaboration of more than 200 scientists known as the Event Horizon Telescope (EHT) project.

Black holes are the dark remnants of collapsed stars whose gravity is so intense that nothing, not even light, can escape. Because light cannot escape the gravitational pull of a black hole, it is virtually impossible to image or photograph one. However, matter and energy aggregate around the edge of a black hole, a ring-shaped feature known as the event horizon — and this can be imaged because some light manages to escape and reach us.

But it wasn’t easy. For instance, the Sagittarius A* event horizon “is so small that it’s the equivalent of seeing an orange on the moon or being able to read the newspaper in Los Angeles while you’re sitting in New York City,” Doeleman said during the SXSW event last month.

In order to image an object as small as Sagittarius A*, you need a really big telescope. In this case, the researchers turned the whole planet into a huge telescope by combining data from eight radio telescopes located all around the world. Using a technique called Very Long Baseline Interferometry, or VLBI, the instruments of all these observatories located thousands of miles from one another were linked to form a “virtual telescope”, whose resolving power is as big as the space between the disparate dishes.

Simulation of a black hole's event horizon. Credit: Hotaka Shiokawa/YouTube.

Simulation of a black hole’s event horizon. Credit: Hotaka Shiokawa/YouTube.

More than 100 years ago, Einstein’s equations predicted exactly what the size and shape of a black hole’s shadow would be. Researchers have also designed computer simulations and models that compute the shape of a black hole’s event horizon, which can be tested with the actual physical observation. With this most recent observation of M87, researchers said that the findings are consistent with the predictions of general relativity — this was perhaps the hardest test of general relativity yet.

The observations also shine new light about the behavior of black holes, such as how gas spirals down into a black hole singularity. The technique used to image the black hole can also be used to determine the shape of an event horizon, thus revealing whether a black hole is spinning. Perhaps most importantly, we now know that something that sounds so esoteric as an event horizon is definitely real.

The EHT researchers produced four images so far, offering the first intimate look inside one of the most mysterious objects in the universe. But these were just the first picture and those to come later will surely be better and sharper. Today marks a historical day when a whole new world might open up to us.

Simulation of a black hole's event horizon. Credit: Hotaka Shiokawa/YouTube.

The first ever photo of a black hole might be revealed this week

Simulation of a black hole's event horizon. Credit: Hotaka Shiokawa/YouTube.

Simulation of a black hole’s event horizon. Credit: Hotaka Shiokawa/YouTube.

Astronomers who are part of one of the most ambitious scientific projects in history are gearing up for a massive announcement on Wednesday. If rumors hold true, the world may soon be shown the first ever photo of a black hole’s event horizon.

Photographing an orange on the moon

Since 2017, the Event Horizon Telescope Collaboration (EHT) has been studying two supermassive black holes, one located at the center of the Milky Way, called Sagittarius A*, the other found at the core of the supergiant elliptical galaxy Messier 87.

Black holes are the dark remnants of collapsed stars whose gravity is so intense that nothing, not even light, can escape. At the center of most galaxies lies a supermassive black hole, which can have a mass billions of times greater than that of the sun, all crammed in a relatively small volume. For instance, the supermassive black hole at the center of the Milky Way, Sagittarius A*, is about the size of the orbit of Mercury.

Because light cannot escape the gravitational pull of a black hole, it is virtually impossible to image or photograph one. However, matter and energy aggregate around the edge of a black hole, known as the event horizon. It’s this ring-shaped structure that scientists are hoping to image — and this is no trivial task.

During a press conference at last month’s South by Southwest (SXSW) festival in Austin, Texas, Sheperd Doeleman, who is the director of the Event Horizon Telescope, shared a quirky anecdote so people could relate to the kind of challenges involved in this project. He said that imaging the Milky Way’s black hole is just as difficult as spotting an orange on the surface of the moon.

In order to image an object as small as Sagittarius A* lying more than 26,000-light-years away, you need a really big telescope. In this case, the researchers turned the whole planet into a huge telescope by combining eight radio telescopes located all around the world. Using a technique called Very Long Baseline Interferometry, or VLBI, the instruments of all these observatories located thousands of miles from one another were linked to form a “virtual telescope”, whose resolving power is as big as the space between the disparate dishes. Very clever, indeed!

The radio telescopes involved in the project are ALMA (Atacama Large Millimeter/submillimeter Array in Chile; APEX (Atacama Pathfinder Experiment) in Chile; IRAM 30m (Institut de RadioAstronomie Millimétrique) in Spain; LMT (Large Millimeter Telescope) in Mexico; SMT (Submillimeter Telescope) in Arizona; JCMT (James Clerk Maxwell Telescope) in Hawaii; SMA (SubMillimeter Array) in Hawaii; and SPT (South Pole Telescope) in Antarctica.

Wednesday news conference is expected to provide the first image of Sagittarius A* shadow on its accompanying disk of bright material.

The Event Horizon Telescope network. Credit: EHT.

The Event Horizon Telescope network. Credit: EHT.

Beyond the historical implications of such an achievement, imaging a black hole’s event horizon will also put Einstein’s theory of general relativity to its ultimate test. More than 100 years ago, Einstein’s equations predicted exactly what the size and shape of a black hole’s shadow would be. Researchers have also designed computer simulations and models that compute the shape of a black hole’s event horizon, which can be tested with the actual physical observation. So far, EHT researchers have run over 12,000 simulations of different black hole shadows that could differ from Einstein’s predictions. If there’s anything different from what general relativity predicts, theoretical physics could be up for quite the show.

“What the black hole image could do for us, if we can get it, would be to take something that is the most extreme, the strangest prediction of general relativity, one of the great accomplishments of the human mind, [and] combine it with the most advanced electronics with a planetary scale collaboration with the most advanced statistics [and] new imaging techniques,” Peter Galison, a professor at Harvard University and EHT collaborator, said at SXSW. “It’s like making a new camera with a new kind of film, a new kind of lens, combining it with other cameras, all at once, and if that could happen, if we could actually get in and see right up close to the horizon.”

Wednesday’s announcement is scheduled for 9 a.m. EDT. The National Science Foundation will provide a live stream.

Nothing can escape a black hole’s clutch — and this proves Einstein’s Theory of Relativity (again)

The theory says that if you get close enough to a black hole, if you pass what is called the event horizon, there’s no turning back. Nothing, not even light can escape back from the event horizon. Even though the existence of such event horizons is all but certain, and they fit greatly into Einstein’s Theory of Relativity, they haven’t been proven yet — until now.

This is the first in a sequence of two artist’s impressions that shows a huge, massive sphere in the center of a galaxy, rather than a supermassive black hole. Image credits: Mark A. Garlick/CfA.

Researchers from the University of Texas at Austin and Harvard University have put this principle to test, showing that when matter gets pulled past an event horizon, it simply vanishes.

“Our whole point here is to turn this idea of an event horizon into an experimental science, and find out if event horizons really do exist or not,” said Pawan Kumar, a professor of astrophysics at The University of Texas at Austin.

Their research was based on supermassive black holes, the gargantuan black holes that lie at the center of most (if not all) galaxies; when scientists call something “supermassive,” you know there’s no joking — these objects have a mass ranging from hundreds of thousands to billions of solar masses. But some researchers believe that supermassive black holes are not black holes at all, but something even more bizarre: objects that have somehow managed to escape the event horizon.

Before we understand what that means, let’s get our hands dirty and sink our teeth into some basic black hole physics.

Artist’s representation of a black hole. Image credits: XMM-Newton, ESA, NASA.

Point of no return

A black hole is any region of spacetime exhibiting enough gravitational attraction that it doesn’t allow anything to escape from it. OK, we kind of know this and it’s fairly easy to comprehend, but what does it actually mean, and how do they form?

According to the theory of general relativity, any area can become a black hole, as long as it has sufficiently compact mass. Realistically though, they only have a chance of forming when a huge gravitational mass starts to collapse, as is the case of some stars. Basically, after most of their fuel is consumed, the internal pressure is not large enough to counteract the star’s own gravitational field, and the star collapses on itself. If this process starts, nothing, not a single known process can stop it. It’s interesting to note that Einstein himself thought black holes would not form as physical objects, though by the 60s, most physicists strayed from this belief.

When a black hole forms, the event horizon also takes shape. Technically, the event horizon is a boundary in spacetime after which events cannot affect an observer, and viceversa. Basically, it’s the point of no return: nothing can go past the event horizon and go back. Nothing.

At the center of a black hole, there’s what is called a singularity, a point where the gravitational field is infinite. Fun fact: according to our current understanding of the universe, before the Big Bang, the entire universe was a singularity, a single point.

Demonstrating an event horizon

Artistic representation of how a black hole might suck a star. Image via WiffleGif.

If your head’s not spinning already, we’re good to go. What the Texas and Harvard researchers did was to put the idea of a supermassive black hole to test. If it is indeed a black hole, then it would have a singularity — but this is a point, a single point without any real surface. If the other option was true, and some physical things were stuck at the event horizon, then they would have a hard surface, and this could be studied.

“Our motive is not so much to establish that there is a hard surface,” Kumar said, “but to push the boundary of knowledge and find concrete evidence that really, there is an event horizon around black holes.”

Black holes suck up things all the time, but Kumar and his colleagues decided to look for the most visible thing: stars. Every once in a while, black holes consume stars (yes, the universe is crazy). Crashing a star onto a hard surface would definitely be visible, they figured.

“We estimated the rate of stars falling onto supermassive black holes,” Lu said. “Nearly every galaxy has one. We only considered the most massive ones, which weigh about 100 million solar masses or more. There are about a million of them within a few billion light-years of Earth.”

So they looked up. Using the Pan-STARRS 1.8-meter telescope in Hawaii, looking for things that glow a bit and then fade, as you’d expect would be the case here. They found nothing.

This artist’s impression shows a star crossing the event horizon of a supermassive black hole located in the center of a galaxy. In this case, the star is swallowed whole. Image credits: Mark A. Garlick/CfA.

Of course, it’s extremely difficult to prove a negative. This doesn’t necessarily mean that no black holes have solid horizons, but if the theory holds true, at least 10 such events should have been detected, and none has. So it does seem to indicate that this is not really the case, and General Relativity passes yet another test.

Researchers now want to survey an even larger portion of the sky, to see if they get similar results.

Journal Reference: “Stellar disruption events support the existence of the black hole event horizon”  by Wenbin Lu, Pawan Kumar, and Naresh Narayan in the June 2017 issue of Monthly Notices of the Royal Astronomical Society here: https://doi.org/10.1093/mnras/stx542

Image: The Guardian

Black holes store information as holograms at the event horizon, says Stephen Hawking

Nothing can escape a black hole, not even light, any scientists schooled in modern physics will tell you. Eminent British physicists, Stephen Hawking, suggests however that information is still retained at the boundary of black holes, known as the event horizon — an amazing new black hole fact!

Image: The Guardian

Image: The Guardian

Quantum mechanics dictates that anything – that is, matter and energy – can be broken down into information, strings of 1s and 0s for instance. A consequence of this rule is that information should never disappear, not even if the matter or energy it’s linked to is being sucked by a black hole. This hypothesis, however, contradicts Einstein’s theory of general relativity which suggests the information should be destroyed by a black hole. This is the information paradox, as physicists call it.

Hawking says that the information isn’t destroyed by a black hole because it never makes through inside. Instead, it’s trapped at the event horizon – the boundary in spacetime through which matter and light can only pass inward towards the mass of the black hole. At this boundary layer, the information is stored as a 2D hologram or super translation. A hologram is a 2D description of a 3D object.

“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.”

Some physicists believe we’re actually living in a holographic universe. Not that everything you see and touch isn’t real, like say in the Matrix. Rather, what we’re currently registering is a projection of a 2D Universe. Imagine watching TV – what seems like 3D objects projected on the screen are actually flat. It might sound crazy (because it’s counter-intuitive to our innate sensing abilities), but when physicists do their work assuming a 2D universe, the laws of physics make more sense. For instance, paradoxes like the information loss problem or entropy problem can be solved.

It’s not clear even that matter is being sucked by the black hole, either. The matter might also be transformed into a hologram, though there’s no consensus on this.

“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,” Prof Marika Taylor, a theoretical physicist at the University of Southampton, told BBC News.

If the information can be stored, can it be read? Theoretically, if you could tap this information somehow you would be able to reconstruct all the events that caused matter to plunge into the black hole. Think of a black hole as a paper shredder; documents are ripped to pieces and become unreadable, but if put all the paper strings together it’ll make sense. In the 1970s, the same Hawking introduced the concept of Hawking radiation – photons emitted by the black hole itself due to quantum fluctuations. Initially, Hawking thought the photons carried no meaningful information but has since changed his mind. This Hawking radiation might be a means for information to escape the black hole. The downside is that it’s in a “chaotic, useless form,” says Hawking, adding: “for all practical purposes the information is lost.”

For now, details are sketchy. Hawking and collaborators will publish a paper at the end of the month expanding on the subject.

“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,” Hawking said during a public lecture on Monday held in Stockholm. “Things can get out of a black hole both on the outside and possibly come out in another universe.”

Scientists claim incredibly small stars emerge from black holes

Via Universe Today.

Black holes have fascinated both researchers and laymen for decades. Without a doubt, they are the point of maximum interest in terms of astrophysical research – objects with an incredibly large mass – so large that even light itself can’t escape it… what secrets do these objects still hold?

According to Carlo Rovelli at the University of Toulon in France, and Francesca Vidotto at Radboud University in the Netherlands, one of those secrets is the fact that every black hole still holds the ghastly remnants of its former star (black holes are formed when object’s internal pressure is insufficient to resist the object’s own gravity – which typically means it was a large star). According to their work, these quantum stars can later emerge as the black hole evaporates.

What do you mean ‘as the black hole evaporates’?

Stephen Hawking showed (though there is still some doubt among other physicists) that black holes all emit black-body radiation – a type of electromagnetic radiation emitted by a black body (an opaque and non-reflective body) held at constant, uniform temperature. When particles escape, the black hole loses a small amount of its energy and therefore some of its mass.

Rovelli and Vidotto believe that as a black hole evaporates, the star remains can pop up, in what they call “Planck stars” – which they claim can solve some of the most important questions in astrophysics.

Among the biggest mysteries of the Universe, the so ‘information paradox’ is definitely up with the best. Basically, black holes suck things; they have an incredibly large mass and they attract things – that’s what they do, we know that. But if a black hole slowly evaporates, then what happens to its information? From a physics stand point, the information that describes an object must fully determine its future and be fully derivable from its past, at least in principle. In other words, you can’t really destroy information. But if black holes disappear, what happens to this information? This is the information paradox, and there isn’t any good solution for it; or at least, there wasn’t.

Rethinking the Big Crunch

To get around this problem, they reanalyzed what we know about the theoretical end of the Universe – the big crunch, the reverse of the big bang, in which everything collapses to a infinitesimal dot of infinite mass; pretty hard to wrap your mind around that one, but what they came up with was even more challenging. They believe that quantum gravitational effects prevent the universe from collapsing to infinite density. Instead, the universe ”bounces” when the energy density of matter reaches the Planck scale, the smallest possible size in physics.

“The bounce does not happen when the universe is of planckian size, as was previously expected; it happens when the matter energy density reaches the Planck density,” they say. In other words, quantum gravity could become relevant when the volume of the universe is some 75 orders of magnitude larger than the Planck volume.

They explain that if this is indeed the case, then the same would happen to a black hole – of forming a singularity, the collapse of a star is eventually stopped by the same quantum pressure, a similar force to the one which prevents electrons from crashing on the nucleus of atoms.

“We call a star in this phase a “Planck star”,” they say.

Planck stars would be incredibly small – some 1.000.000.000 smaller than a millimeter. They would exist for a very short time, but due to the fact that time becomes dilated at very high densities, to an outside observer, they would appear to carry on for much longer. For such an observer , a Planck star would last just as long as its parent black hole. This also solves the information paradox.

As the black hole shrinks more and more, it would eventually reach the size of its core star.

“At this point there is no horizon any more and all information trapped inside can escape,” they say.

Information isn’t lost, and it is sent back to the Universe; and they believe that this theory can be tested fairly easily. Due to its very small size, such a Planck star would emit radiation with a very small wavelength – in other words, gamma radiation. The universe is filled with a foggy background of gamma rays that astrophysicists have already observed in considerable detail with orbiting telescopes – could it be that they are in fact observing the gamma signals emitted by the Planck stars? I’m pretty sure time will tell.

Scientific Reference.

Astronomers find star orbiting a black hole in the center of our galaxy

Einstein’s theory, as well as other theories about the fundamental space-time fabric around a black hole may be strongly tested, after astronomers report the finding of a a star that orbits an enormous black hole at the center of the Milky Way galaxy.

Scientists explain it takes the star 11 and a half years to orbit the black hole, making it the object closest to any black hole that we know of. They hope they can use this data to figure out if Einstein was right in his prediction of how objects such as black holes can distort space and time. The faint star, called S0-102 has a stable and possibly changing orbit.

“The fact that we are finding stars this close to the supermassive black hole—a hundred times closer to its event horizon than ever identified before—shows just how fast this field is developing,” said study co-author Andrea Ghez, an astrophysicist at the University of California, Los Angeles. An event horizon is a boundary beyond which nothing, not evenlight, can escape from a black hole. “Our first goal has been to make the discoveries. But the next layer of science is the fundamental physics because this is an unparalleled laboratory for testing the general theory of relativity.”

If Einstein was correct in his theory, then the star’s orbit, although stable, will change slightly with every cycle, never returning to the same spot, creating a sort of daisy-like pattern. In order to figure this out, the most important thing is to study the star when it is closest to the black hole — the point known as the periapse.

“This is such an important discovery, because for stars located closer to the black hole, the gravitational field to study gets stronger and the effects more pronounced,” said Avi Loeb, a Harvard theoretical astrophysicist not involved with the new finding.

The findings were reported in the journal Science.

Computer simulation of superheated plasma swirling around the black hole at the center of our galaxy. (Image by Scott Noble/RIT)

Achieving the unbelievable: taking a picture of a black hole

Black Holes are the least understood entities, so far, in the Universe. However, if there’s one thing scientists know for sure about them, it’s that they’re the most extreme environment in cosmos. Black Holes have such a powerful, relentless gravity pull that it swallows absolutely everything in its vicinity, even light gets absorbed with zero reflection. This makes it practically invisible, which is why they’re very difficult to study. Scientists  are now set to embark on one of the most ambitious astrophysical ventures in history – taking a picture of a black hole. No, by no means is this a mad science stunt. The greatest minds of the scientific community have pledged their aid for the project and firmly believe this is possible, in an unprecedented worldwide combined effort, which only a few years ago would’ve been considered ludicrous.

“Nobody has ever taken a picture of a black hole,” said Dimitrios Psaltis, an associate professor of astrophysics at the University of Arizona’s Steward Observatory, who along with Daniel Marrone, an assistant professor of astronomy at Steward Observatory, organized a conference in Tucson, Ariz. where the endeavor was announced “We are going to do just that.”

“Even five years ago, such a proposal would not have seemed credible,” added Sheperd Doeleman, assistant director of the Haystack Observatory at Massachusetts Institute of Technology (MIT), who is the principal investigator of the Event Horizon Telescope, as the project is dubbed. “Now we have the technological means to take a stab at it.”

Computer simulation of superheated plasma swirling around the black hole at the center of our galaxy. (Image by Scott Noble/RIT)

Computer simulation of superheated plasma swirling around the black hole at the center of our galaxy. (Image by Scott Noble/RIT)

Einstein’s Theory of Relativity laid the foundation for the postulation of black holes, proving gravity does indeed influence light’s motion. Based on Einstein’s theory, fellow German physicist Karl Schwarzschild found a solution which described the gravitational field of a point mass and a spherical mass. Since then, scientists have observed, measured and conducted experiments for decades with significant breakthroughs, however it was never possible for them to directly observe or image a black hole. But if black holes don’t emit light, how is it possible to image them? Professor Doeleman explains this extremely ingenious project in a masterful way.

“As dust and gas swirls around the black hole before it is drawn inside, a kind of cosmic traffic jam ensues,” Doeleman explained. “Swirling around the black hole like water circling the drain in a bathtub, the matter compresses and the resulting friction turns it into plasma heated to a billion degrees or more, causing it to ‘glow’ – and radiate energy that we can detect here on Earth.”

Capturing the Milky Way’s supermassive black hole halo

Very clever, right? Once light passes the point of no return, or Event Horizon, it is lost forever, however its outline can be studied – this is called the black hole’s shadow.

Scientists have well founded reasons to believe that at the center of the Milky Way, like in most galaxies, if not all actually, lies a supermassive black hole (one to four million times the mass of the sun). Estimated at 26,000 light years away, to have a chance at seeing it scientists say you’d need a very big telescope – a telescope the size of the entire Earth to be more exact.

Of course, there’s a solution around this – connecting the biggest and most powerful radio telescopes in the world together. As such, 50 radio telescopes scattered around the globe have joined the effort, including the Submillimeter Telescope (SMT) on Mt. Graham in Arizona, telescopes on Mauna Kea in Hawaii and the Combined Array for Research in Millimeter-wave Astronomy (CARMA) in California. The astronomers hope once the biggest telescope in the world, the Atacama Large Millimeter Array (ALMA) in Chile, is finished it will provide the necessary power to provide the project, the Event Horizon Telescope as it was dubbed, with a great chance of success.

“In essence, we are making a virtual telescope with a mirror that is as big as the Earth,” Doeleman said. “Each radio telescope we use can be thought of as a small silvered portion of a large mirror. With enough such silvered spots, one can start to make an image.”

“The Event Horizon Telescope is not a first-light project, where we flip a switch and go from no data to a lot of data,” he added. “Every year, we increase its capabilities by adding more telescopes, gradually sharpening the image we see of the black hole.”

General Relativity predicts that the bright outline defining the black hole’s shadow must be a perfect circle. If this shape will be found to be deviated in any manner, than it would prove that the Theory of Relativity is wrong. On the contrary, if it is indeed a circle, little doubt would be left to cast.

Bringing together radio telescopes around the globe requires an extraordinary global team effort, and I can only salute this initiative. What a milestone for science would it be if the researchers will manage to capture a black hole’s shadow.

“This is not only the usual international conference where people come from all over the world because they are interested in sharing their research,” Psaltis said. “For the Event Horizon Telescope, we need the entire world to come together to build this instrument because it is as big as the planet. People are coming from all over the world because they have to work on it.”

source

What’s a black hole?

Black holes are some of the most interesting and puzzling phenomena we have encountered so far; everybody has heard of them, from movies or books or whatever, but there are many misconceptions or just things most people don’t know about them, so we’re going to take a journey to the “bowels” of a black hole. I won’t get into the hardcore physics here, just explain how a black hole is formed, what it is, and other black hole facts you might find interesting.

The idea of such a thing goes from before the 1800s when geologist John Michell wrote a letter to Henry Cavendish in 1783, but it wasn’t until Albert Einstein developed his theory of general relativity that it could be (at least somewhat) understood. Black holes are the final point of the evolution of some stars; stars that are generally 10-15 times bigger than the Sun sometimes undergo a supernova explosion, which will leave behind fairly massive stellar “leftovers” that have already been burned out. Without any force to work against the gravitational pull, the remnant material will collapse on itself and the star will collapse to the point of zero volume and infinite density called singularity (since density is mass/volume) and it will create an undetectable surface which marks the event horizon or the point of no return. If something goes past that point, no matter what it is, it won’t be able to escape the gravitational pull. It is so strong, that even light cannot escape it – hence the term black hole.

This property makes it invisible to the eye, but it can be studied by analyzing the way it interacts with other matter, especially from a gravitational point of view – which requires a quick word about gravity. From the classic or Newtonian point of view, gravity is a force in which two bodies with mass attract each other. However, from Einstein’s modern relativistic point of view, gravitation is described as an effect of the spacetime curvature instead of a force, a curvature caused by the mass of the bodies. So gravity and time are bound together – if we were to measure time closer to a black hole, we would find that time would pass much slower, and if you were to measure time in the center of the black hole, you would find it would not pass at all.

As I explained above, in the center of the black hole there lies a gravitational singularity, a region where the spacetime curvature becomes infinite. That region can be thought of as zero volume and infinite density. Anything that falls into the singularity will be ripped apart and its mass will be added to that of the black hole. But a black hole isn’t a demonic vacuum cleaner that slowly sucks anything and everything, no matter the distance. If for example, we were to replace the Sun with a black hole of exactly the same mass, the Earth, as well as the whole Solar System would move exactly the same; for an outside observer, this would be pretty funny, seeing a whole solar system revolve around… nothing (nothing visible, that is). If we were to speak about temperatures, it would be an entirely different problem, but the gravitational effect would be the same, despite the black hole having a radius of only a few tens of kilometers.

The closest black hole from us is no less than 1.000 years away, so we probably don’t have anything to worry about, but then again, at the center of our galaxy, the Milky Way, there is a supermassive black hole with a mass of 4,000,000 times bigger than the Sun. There is good reason to believe that these supermassive black holes are at the center of most, if not all, galaxies, and it’s estimated that they can have a mass a few billion times bigger than that of the Sun. Also, black holes do grow, basically sucking anything they can around them, and making things they cannot suck revolve around them.

In 1970, British researchers Stephen Hawking and Roger Penrose realized that black holes and the Big Bang have very much in common. Inside the black hole, there is a point of infinite curvature, which is presumably what the Universe looked like before the Big Bang, so the process of a star collapsing into a black hole is just like the Big Bang in reverse. The details surrounding this matter, however, become quite fuzzy. General relativity does explain how things work when space is curved but doesn’t explain how it works when infinitely curved. Since we are talking about an indefinitely small space, the laws of quantum mechanics should be considered too, but our current understanding of quantum mechanics doesn’t work in space that is curved, let alone space that is infinitely curved. So from this point of view, quantum mechanics and general relativity are inconsistent with each other, which is just one of the reasons why studying black holes is important. Both theories predict something different will happen, given a set of conditions, so if we were to somehow find what would happen, this will show us the correct theory to apply. If we were to put it this way, quantum mechanics and general relativity are the key players in a team. But sometimes they just don’t work together at all, so there is a need for another theory to reconcile the two and smoothen things up – for example, string theory.

To make things even harder to study, black holes may also be rotating, and/or electrically charged. There are only three properties that can characterize a black hole:

  • mass, the most important parameter
  • angular momentum
  • electric charge

An interesting fact is that mathematically speaking, any general relativity equation solution is symmetric in time, basically, take any solution and imagine another solution that works as the first one, but with time in reverse. If you apply this to black holes, you will get what is a white hole, and object you can not enter, and that can only spit things out. This is a good example of why mathematical solutions cannot exist in nature; if we define a white hole as the temporal opposite of a black hole, then the process of creating a white hole is the same as the process of destroying a black hole – which is impossible.

Picture sources: 1 2 3 4