It’s been over 100 years since the first solution for a black hole was discovered in General Relativity. For generations, scientists argued over whether these objects were physical, existing all throughout our Universe, or whether they were mere mathematical artifacts. In the 1960s, Roger Penrose’s Nobel-winning work demonstrated how black holes could realistically form in our Universe, and shortly thereafter, the first black hole — Cygnus X-1 — was discovered.
Black holes are now known to range from just a few times the mass of our Sun up to many billions of solar masses, with most galaxies housing supermassive black holes at their centers. In 2017, a tremendous observing campaign was coordinated between a large number of radio telescopes around the world in an attempt to directly image a black hole’s event horizon for the first time. That first image was released in 2019, revealing a donut-like shape surrounding the interior void. Now, a new series of papers has improved upon that image, and we can see it’s not a donut, but rather a cruller, with sweeping magnetic “lines” tracing out the hot plasma. Here’s the new science behind this epic image, and why black holes are crullers, not donuts.
This animation shows the event horizon, singularity, and other features for rotating black holes. In … [+] the vicinity of a black hole, space flows like either a moving walkway or a waterfall, depending on how you want to visualize it. At the event horizon, even if you ran (or swam) at the speed of light, there would be no overcoming the flow of spacetime, which drags you into the singularity at the center. Outside the event horizon, though, other forces (like electromagnetism) can frequently overcome the pull of gravity, causing even infalling matter to escape.
Andrew Hamilton / JILA / University of Colorado
In our Universe, black holes aren’t merely clumps of mass that have collapsed under their own gravity to a single point. In space, all forms of matter exert gravitational forces on one another, and whenever objects interact in this way, they attract the “closer” parts of the object by a greater amount than the “farther” parts of it. This type of force — known as a tidal force — isn’t just responsible for tides, but also for causing a torque: a change in the angular momentum of an object. As a result, everything that exists in the Universe rotates, or spins, rather than remaining stationary.
This means that the black holes that we form aren’t stationary and non-rotating, but rather spin about some axis. Indirect measurements had previously indicated that black holes spin relativistically: close to the speed of light. However, the major idea of the Event Horizon Telescope is that, regardless of how this spinning black hole is oriented, there will be light emitted from the surrounding matter that just “grazes” the event horizon, and goes off in a straight line, creating a photon ring for us to observe that encircles the dark center, from where no light can escape. (For reasons related to the curvature of space, the size of this dark center is actually more like ~250% the diameter of the physical event horizon.)
This artist’s impression depicts the paths of photons in the vicinity of a black hole. The … [+] gravitational bending and capture of light by the event horizon is the cause of the shadow captured by the Event Horizon Telescope. The photons that aren’t captured create a characteristic sphere, and that helps us confirm General Relativity’s validity in this newly-tested regime.
Nicolle R. Fuller/NSF
The way we went about imaging this was a tremendous technological achievement. We needed to take an array of radio images (at millimeter-submillimeter wavelengths) from all around the globe at once. This gave us the light-gathering power of all the telescopes that were part of the array, combined, but gave us the resolution of the maximum separation between the various telescopes, which was roughly the diameter of Earth.
In order to see anything, then, we had to look for black holes that were simultaneously very large, with a large angular diameter as seen from our perspective on Earth, and were also active: emitting copious amounts of radiation at radio wavelengths. There are only two that fit the bill:
Sagittarius A*, the four million solar mass black hole at the center of our galaxy, just ~27,000 light-years away.
And the black hole at the center of the massive elliptical galaxy M87, which comes in at 6.5 billion solar masses (some 1500 times the mass of Sagittarius A*), but some 50-60 million light-years distant (about 2000 times as far).
In April of 2019, after two years of analysis, the first images were released: a map of the radio light that traced out the emitted photons from around the black hole in the distant galaxy M87.
The Event Horizon Telescope’s first released image achieved resolutions of 22.5 microarcseconds, … [+] enabling the array to resolve the event horizon of the black hole at the center of M87. A single-dish telescope would have to be 12,000 km in diameter to achieve this same sharpness. Note the differing appearances between the April 5/6 images and the April 10/11 images, which show that the features around the black hole are changing over time. This helps demonstrate the importance of syncing the different observations, rather than just time-averaging them.
Event Horizon Telescope Collaboration
Even though this is usually depicted as a single image — where the four images from the four different days are added and averaged together — it’s important to recognize what’s actually happening here. Light from a very distant source is striking our telescopes at many different locations on Earth. In order to make sure we’re adding the data from the same exact times together, we have to sync up the various observatories with atomic clocks, and then account for the light-travel time to each unique point on Earth’s surface. In other words, we need to make sure that the telescopes are properly synchronized: a tremendously difficult task.
The reason we have an image of the black hole at the center of M87 and not one of the black hole in our own galaxy’s center is because of its remarkable size. At 6.5 billion solar masses, its diameter is approximately one light-day, meaning that the features in the photon ring take about ~1 day to change appreciably. At just 0.15% of that black hole’s mass, our black hole’s features change by that same amount every single minute, making the image much more difficult to construct.
However, while the Event Horizon Telescope team is still working on our black hole’s first image, the one at the center of M87 has just gotten a far more detailed image thanks to a special set of measurements that were also taken: polarization measurements.
Light is nothing more than an electromagnetic wave, with in-phase oscillating electric and magnetic … [+] fields perpendicular to the direction of light’s propagation. The shorter the wavelength, the more energetic the photon, but the more susceptible it is to changes in the speed of light through a medium. The direction of the electric and magnetic fields defines light’s polarization.
And1mu / Wikimedia Commons
Whether you view them in a quantum way (as photons) or in a classical way (as waves), the phenomenon of light behaves with intrinsic electromagnetic properties. As an electromagnetic wave, light is made of oscillating, in-phase, mutually perpendicular electric and magnetic fields. Whenever light either, passes through a magnetized plasma or reflects off of a material, it can become partially or completely polarized: where instead of having the electric and magnetic fields oriented randomly, they’re preferentially oriented in a particular direction.
Around pulsars — radio-emitting neutron stars with very strong magnetic fields — light can be almost 100% polarized. We’d never measured the polarization of photons from around a black hole before, but in addition to simply measuring the flux and density of photons, the Event Horizon Telescope also measured the information required to reconstruct the polarization data for the black hole at the center of M87.
Just as we were able to reconstruct images of the black hole’s photon ring that evolved with time, so too could we reconstruct polarization data on that individual, day-by-day basis.
These lines trace out the polarization of the hot plasma surrounding M87’s black hole. The … [+] polarization is strongest along the southern and western limbs of the black hole, and clearly migrate over time. Only about 15% of the light is polarized, which is significant but not as large as it is for other extreme objects, such as pulsars.
EHT Collaboration, ApJL, Vol. 910, L13, 24 March 2021
The polarization data is completely complementary to the direct light received, as it gives information that’s independent of the shape and density of the light emitted from around the black hole. Instead, polarization data is useful for teaching us about the matter that surrounds the black hole, including what the strength of the magnetic field is in that region, the number density of free electrons, the temperature of that hot plasma, and how much mass the black hole is consuming over time.
What we learn is fascinating, and perhaps not what many expected.
The magnetic field strength in the vicinity of the black hole is between 1 and 30 Gauss, where ~1 Gauss is the strength of Earth’s magnetic field at the surface. Compared to neutron stars, where fields can reach more than 1015 Gauss, this is minuscule, but on much larger scales.
There are between ten thousand and ten million free electrons in every cubic centimeter around this black hole.
The temperature of the plasma that has accreted around this black hole is enormous: between 10 and 120 billion K, or more than 1000 times the temperature at the center of the Sun.
And finally, this black hole is consuming mass at a rate that’s between 100 and 700 Earth masses every single year.
Still, as exciting as this is, the greatest sight of all was the new image of the radiation around the black hole, with the magnetic fields (traced out by the polarization data) included.
Polarized view of the black hole in M87. The lines mark the orientation of polarization, which is … [+] related to the magnetic field around the shadow of the black hole. Note how much swirlier this image appears than the original, which was more blob-like.
The first thing you’ll notice — and you might even worry about it — is that these swirling features appear so much sharper than the original image, which looked more like a blurry ring than anything else. Why would this polarization data, which was taken with the same instruments as the regular light data, have such a high resolution?
The answer is: surprisingly, it doesn’t. The polarization data has the same resolution as the regular data, meaning it can resolve features down to about ~20 micro-arc-seconds. There are 360 degrees in a full circle, 60 arc-minutes in each degree, 60 arc-seconds in each arc-minute, and one million micro-arc-seconds in each arc-second. If you were able to view the Apollo mission manual that was left on the Moon from Earth, 20 micro-arc-seconds would span roughly the “Ap” from the word Apollo.
What the polarization data tells us, however, is how much the light twists and in which direction, which basically traces out the magnetic field around the black hole. Just as we see the light and the polarization data evolving over time, we can put those results together, and determine how the photon ring around the black hole’s event horizon has changed and evolved during the course of our observations.
This 8-panel image shows the inferred polarization (top) and the reconstructed photons (bottom) for … [+] the black hole at the center of the galaxy M87. Note how the polarization evolves over time, and how, along with the light data, the structure of the photon ring (or photon sphere, if you prefer) changes over the period of the observations.
EHT Collaboration, ApJL, Vol. 910, L12, 24 March 2021
One of the big surprises is how small the photon polarization is. If you have a magnetized plasma surrounding this black hole — and we’re pretty certain that we do — you’d naively expect that the light would arrive almost completely polarized: with polarization fractions of 80-90% or even more. And yet, what we see is that the polarization fraction is tiny: about ~15-20% at its peak, with the actual value being even smaller in most locations.
Why would this be the case?
Unlike pulsars, where the magnetic field can be coherent on scales comparable to the size of the neutron star (about ~10 kilometers), this black hole is absolutely enormous. At about 1 light-day in diameter (about 0.003 light-years) for the black hole, there’s almost certainly a complicated magnetic structure on smaller scales than that. When light passes through a magnetic field, its polarization direction rotates, and rotates proportionally to the strength of the field. (This is known as Faraday rotation.)
However, if that magnetic field is non-uniform, the rotating polarization should “scramble” the signal, reducing its magnitude significantly. If we want to accurately map out the magnetic field, we’d need to leave Earth: building a similar telescope array that was larger than the diameter of our planet.
This composite image shows three views of the central region of the Messier 87 (M87) galaxy in … [+] polarised light, namely, from top to bottom, with the Chile-based 5 Atacama Large Millimeter/submillimeter Array (ALMA), the National Radio Astronomy Observatory’s Very Long Baseline Array (VLBA) in the US, and with the Earth-sized telescope synthesized by the Event Horizon Telescope.
EHT Collaboration; ALMA (ESO/NAOJ/NRAO), Goddi et al.; VLBA (NRAO), Kravchenko et al.; J.C. Algaba, I. Martí-Vidal
Still, none of this should diminish just how remarkable an achievement this is. By combining the effects of the light we directly observed with the polarization data, we can more accurately map out the behavior of the light emitted from this supermassive black hole: quite possibly the most massive supermassive black hole within ~100 million light-years of Earth.
When the data from the black hole at our own galaxy’s center is finally put together properly, we should have an incredibly interesting comparison to make. Right now, there are a slew of open questions, including:
will the same parts of the black hole remain “bright” and “dark” over time, or will the accretion flows migrate to all directions in space?
how large is the magnetic substructure around the black hole compared to the event horizon, and is it consistent between supermassive and ultra-mega-supermassive black holes?
will we observe a larger polarization fraction for smaller mass black holes, and will that teach us anything about Faraday rotation?
will there be comparable temperatures, magnetic field strengths, and electron densities between these two black holes, or will they be different?
Perhaps most importantly, will our theoretical calculations, borne out through simulations that incorporate all the relevant physics, match the reconstructed data to the extraordinary degree that they aligned for the black hole at the center of M87?
The April 11, 2017 reconstructed image (left) and a modeled EHT image (right) line up remarkably … [+] well. This is an excellent indication that the model library the Event Horizon Telescope (EHT) collaboration put together can, in fact, model the physics of the matter surrounding these supermassive, rotating, plasma-rich black holes quite successfully.
Huib Jan van Langevelde (EHT Director) on behalf of the EHT Collaboration
Just a few years ago, we didn’t even know whether it was a certainty that black holes had an event horizon, as we’d never observed one directly. In 2017, a series of observations were finally taken that could settle the issue. After a wait of two years, the first direct image of a black hole was released, and it showed us that the event horizon was, in fact, real as predicted, and that its properties agreed with Einstein’s predictions.
Now, another two years later, the polarization data has been added into the fold, and we can now reconstruct the magnetic properties of the plasma surrounding the black hole, along with how those features are imprinted onto the emitted photons. We still only have the one black hole that’s been directly imaged, but we can see how the light, the polarization, and the magnetic properties of the plasma surrounding the event horizon all change over time.
From over 50 million light-years away, we’re finally beginning to understand how the most massive, active black holes in the Universe work: powered by over 100 Earth masses per year and driven by the combination of Einstein’s gravity and electromagnetism. With a little bit of luck, we’ll have a second black hole that’s very different to compare it to in only a few months.
More than 40 trillion gallons of rain drenched the Southeast United States in the last week from Hurricane Helene and a run-of-the-mill rainstorm that sloshed in ahead of it — an unheard of amount of water that has stunned experts.
That’s enough to fill the Dallas Cowboys’ stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina that much water would be 3.5 feet deep (more than 1 meter). It’s enough to fill more than 60 million Olympic-size swimming pools.
“That’s an astronomical amount of precipitation,” said Ed Clark, head of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. “I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky.”
The flood damage from the rain is apocalyptic, meteorologists said. More than 100 people are dead, according to officials.
Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated the amount of rain, using precipitation measurements made in 2.5-mile-by-2.5 mile grids as measured by satellites and ground observations. He came up with 40 trillion gallons through Sunday for the eastern United States, with 20 trillion gallons of that hitting just Georgia, Tennessee, the Carolinas and Florida from Hurricane Helene.
Clark did the calculations independently and said the 40 trillion gallon figure (151 trillion liters) is about right and, if anything, conservative. Maue said maybe 1 to 2 trillion more gallons of rain had fallen, much if it in Virginia, since his calculations.
Clark, who spends much of his work on issues of shrinking western water supplies, said to put the amount of rain in perspective, it’s more than twice the combined amount of water stored by two key Colorado River basin reservoirs: Lake Powell and Lake Mead.
Several meteorologists said this was a combination of two, maybe three storm systems. Before Helene struck, rain had fallen heavily for days because a low pressure system had “cut off” from the jet stream — which moves weather systems along west to east — and stalled over the Southeast. That funneled plenty of warm water from the Gulf of Mexico. And a storm that fell just short of named status parked along North Carolina’s Atlantic coast, dumping as much as 20 inches of rain, said North Carolina state climatologist Kathie Dello.
Then add Helene, one of the largest storms in the last couple decades and one that held plenty of rain because it was young and moved fast before it hit the Appalachians, said University of Albany hurricane expert Kristen Corbosiero.
“It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain,” Maue said. “That collected at high elevation, we’re talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down.”
The fact that these storms hit the mountains made everything worse, and not just because of runoff. The interaction between the mountains and the storm systems wrings more moisture out of the air, Clark, Maue and Corbosiero said.
North Carolina weather officials said their top measurement total was 31.33 inches in the tiny town of Busick. Mount Mitchell also got more than 2 feet of rainfall.
Before 2017’s Hurricane Harvey, “I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,” Clark said. “And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We’re seeing events year in and year out where we are measuring rainfall in feet.”
Storms are getting wetter as the climate change s, said Corbosiero and Dello. A basic law of physics says the air holds nearly 4% more moisture for every degree Fahrenheit warmer (7% for every degree Celsius) and the world has warmed more than 2 degrees (1.2 degrees Celsius) since pre-industrial times.
Corbosiero said meteorologists are vigorously debating how much of Helene is due to worsening climate change and how much is random.
For Dello, the “fingerprints of climate change” were clear.
“We’ve seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction. ”
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It’s a dinosaur that roamed Alberta’s badlands more than 70 million years ago, sporting a big, bumpy, bony head the size of a baby elephant.
On Wednesday, paleontologists near Grande Prairie pulled its 272-kilogram skull from the ground.
They call it “Big Sam.”
The adult Pachyrhinosaurus is the second plant-eating dinosaur to be unearthed from a dense bonebed belonging to a herd that died together on the edge of a valley that now sits 450 kilometres northwest of Edmonton.
It didn’t die alone.
“We have hundreds of juvenile bones in the bonebed, so we know that there are many babies and some adults among all of the big adults,” Emily Bamforth, a paleontologist with the nearby Philip J. Currie Dinosaur Museum, said in an interview on the way to the dig site.
She described the horned Pachyrhinosaurus as “the smaller, older cousin of the triceratops.”
“This species of dinosaur is endemic to the Grand Prairie area, so it’s found here and nowhere else in the world. They are … kind of about the size of an Indian elephant and a rhino,” she added.
The head alone, she said, is about the size of a baby elephant.
The discovery was a long time coming.
The bonebed was first discovered by a high school teacher out for a walk about 50 years ago. It took the teacher a decade to get anyone from southern Alberta to come to take a look.
“At the time, sort of in the ’70s and ’80s, paleontology in northern Alberta was virtually unknown,” said Bamforth.
When paleontogists eventually got to the site, Bamforth said, they learned “it’s actually one of the densest dinosaur bonebeds in North America.”
“It contains about 100 to 300 bones per square metre,” she said.
Paleontologists have been at the site sporadically ever since, combing through bones belonging to turtles, dinosaurs and lizards. Sixteen years ago, they discovered a large skull of an approximately 30-year-old Pachyrhinosaurus, which is now at the museum.
About a year ago, they found the second adult: Big Sam.
Bamforth said both dinosaurs are believed to have been the elders in the herd.
“Their distinguishing feature is that, instead of having a horn on their nose like a triceratops, they had this big, bony bump called a boss. And they have big, bony bumps over their eyes as well,” she said.
“It makes them look a little strange. It’s the one dinosaur that if you find it, it’s the only possible thing it can be.”
The genders of the two adults are unknown.
Bamforth said the extraction was difficult because Big Sam was intertwined in a cluster of about 300 other bones.
The skull was found upside down, “as if the animal was lying on its back,” but was well preserved, she said.
She said the excavation process involved putting plaster on the skull and wooden planks around if for stability. From there, it was lifted out — very carefully — with a crane, and was to be shipped on a trolley to the museum for study.
“I have extracted skulls in the past. This is probably the biggest one I’ve ever done though,” said Bamforth.
“It’s pretty exciting.”
This report by The Canadian Press was first published Sept. 25, 2024.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
