Solar Wind: And The Blobs Just Keep On Coming

When Simone Di Matteo first saw the patterns in his data, it seemed too good to be true. “It’s too perfect!” Di Matteo, a space physics Ph.D. student at the University of L’Aquila in Italy, recalled thinking. “It can’t be real.” And it wasn’t, he’d soon find out.

Di Matteo was looking for long trains of massive blobs — like a lava lamp’s otherworldly bubbles, but anywhere from 50 to 500 times the size of Earth — in the solar wind. The solar wind, whose origins aren’t yet fully understood, is the stream of charged particles that blows constantly from the Sun. Earth’s magnetic field, called the magnetosphere, shields our planet from the brunt of its radiation. But when giant blobs of solar wind collide with the magnetosphere, they can trigger disturbances there that interfere with satellites and everyday communications signals.

In his search, Di Matteo was re-examining archival data from the two German-NASA Helios spacecraft, which launched in 1974 and 1976 to study the Sun. But this was 45-year-old data he’d never worked with before. The flawless, wave-like patterns he initially found hinted that something was leading him astray.

It wasn’t until uncovering and removing those false patterns that Di Matteo found exactly what he was looking for: dotted trails of blobs that oozed from the Sun every 90 minutes or so. The scientists published their findings in JGR Space Physics on Feb. 21, 2019. They think the blobs could shed light on the solar wind’s beginnings. Whatever process sends the solar wind out from the Sun must leave signatures on the blobs themselves.

Making Way for New Science

Di Matteo’s research was the start of a project NASA scientists undertook in anticipation of the first data from NASA’s Parker Solar Probe mission, which launched in 2018. Over the next seven years, Parker will fly through unexplored territory, soaring as close as 4 million miles from the Sun. Before Parker, the Helios 2 satellite held the record for the closest approach to the Sun at 27 million miles, and scientists thought it might give them an idea of what to expect. “When a mission like Parker is going to see things no one has seen before, just a hint of what could be observed is really helpful,” Di Matteo said.

The problem with studying the solar wind from Earth is distance. In the time it takes the solar wind to race across the 93 million miles between us and the Sun, important clues to the wind’s origins — like temperature and density — fade. “You’re constantly asking yourself, ‘How much of what I’m seeing here is because of evolution over four days in transit, and how much came straight from the Sun?'” said solar scientist Nicholeen Viall, who advised Di Matteo during his research at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Helios data — some of which was collected at just one-third the distance between the Sun and Earth — could help them begin to answer these questions.

Modeling Blobs

The first step was tracing Helios’ measurements of the blobs to their source on the Sun. “You can look at spacecraft data all you want, but if you can connect it back to where it came from on the Sun, it tells a more complete story,” said Samantha Wallace, one of the study collaborators and a physics Ph.D. student at the University of New Mexico in Albuquerque.

Wallace used an advanced solar wind model to link magnetic maps of the solar surface to Helios’ observations, a tricky task since computer languages and data conventions have changed greatly since Helios’ days. Now, the researchers could see what sorts of regions on the Sun were likely to bud into blobs of solar wind.

Sifting the Evidence

Then, Di Matteo searched the data for specific wave patterns. They expected conditions to alternate — hot and dense, then cold and tenuous — as individual blobs engulfed the spacecraft and moved on, in a long line.

The picture-perfect patterns Di Matteo first found worried him. “That was a red flag,” Viall said. “The actual solar wind doesn’t have such precise, clean periodicities. Usually when you get such a precise frequency, it means some instrument effect is going on.” Maybe there was some element of the instrument design they weren’t considering, and it was imparting effects that had to be separated from true solar wind patterns.

Di Matteo needed more information on the Helios instruments. But most researchers who worked on the mission have long since retired. He did what anyone else would do, and turned to the internet.

Many Google searches and a weekend of online translators later, Di Matteo unearthed a German instruction manual that describes the instruments dedicated to the mission’s solar wind experiment. Decades ago, when Helios was merely a blueprint and before anyone ever launched a spacecraft to the Sun, scientists didn’t know how best to measure the solar wind. To prepare themselves for different scenarios, Di Matteo learned, they equipped the probes with two different instruments that would each measure certain solar wind properties in their own way. This was the culprit responsible for Di Matteo’s perfect waves: the spacecraft itself, as it alternated between two instruments.

After they removed segments of data taken during routine instrument-switching, the researchers looked again for the blobs. This time, they found them. The team describes five instances that Helios happened to catch trains of blobs. While scientists have spotted these blobs from Earth before, this is the first time they’ve studied them this close to the Sun, and with this level of detail. They outline the first conclusive evidence that the blobs are hotter and denser than the typical solar wind.

The Return of the Blobs

Whether blob trains bubble in 90-minute intervals continuously or in spurts, and how much they vary between themselves, is still a mystery. “This is one of those studies that brought up more questions than we answered, but that’s perfect for Parker Solar Probe,” Viall said.

Parker Solar Probe aims to study the Sun up close, seeking answers to basic questions about the solar wind. “This is going to be very helpful,” said Aleida Higginson, the mission’s deputy project scientist at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “If you want to even begin to understand things you’ve never seen before, you need to know what we’ve measured before and have a solid scientific interpretation for it.”

Parker Solar Probe performs its second solar flyby on April 4, which brings it 15 million miles from the Sun — already cutting Helios 2’s record distance in half. The researchers are eager to see if blobs show up in Parker’s observations. Eventually, the spacecraft will get so close it could catch blobs right after they’ve formed, fresh out of the Sun.

Heavy Metal Planet Fragment Survives Destruction From Dead Star

A fragment of a planet that has survived the death of its star has been discovered by University of Warwick astronomers in a disc of debris formed from destroyed planets, which the star ultimately consumes.

The iron and nickel rich planetesimal survived a system-wide cataclysm that followed the death of its host star, SDSS J122859.93+104032.9. Believed to have once been part of a larger planet, its survival is all the more astonishing as it orbits closer to its star than previously thought possible, going around it once every two hours.

The discovery, reported in the journal Science, is the first time that scientists have used spectroscopy to discover a solid body in orbit around a white dwarf, using subtle variations in the emitted light to identify additional gas that the planetesimal is generating.

Using the Gran Telescopio Canarias in La Palma, the scientists studied a debris disc orbiting a white dwarf 410 light years away, formed by the disruption of rocky bodies composed of elements such as iron, magnesium, silicon, and oxygen — the four key building blocks of the Earth and most rocky bodies. Within that disc they discovered a ring of gas streaming from a solid body, like a comet’s tail. This gas could either be generated by the body itself or by evaporating dust as it collides with small debris within the disc.

The astronomers estimate that this body has to be at least a kilometre in size, but could be as large as a few hundred kilometres in diameter, comparable to the largest asteroids known in our Solar System.

White dwarfs are the remains of stars like our sun that have burnt all their fuel and shed their outer layers, leaving behind a dense core which slowly cools over time. This particular star has shrunk so dramatically that the planetesimal orbits within its sun’s original radius. Evidence suggests that it was once part of a larger body further out in its solar system and is likely to have been a planet torn apart as the star began its cooling process.

Lead author Dr Christopher Manser, a Research Fellow in the Department of Physics, said: “The star would have originally been about two solar masses, but now the white dwarf is only 70% of the mass of our Sun. It is also very small — roughly the size of the Earth — and this makes the star, and in general all white dwarfs, extremely dense.

“The white dwarf’s gravity is so strong — about 100,000 times that of the Earth’s — that a typical asteroid will be ripped apart by gravitational forces if it passes too close to the white dwarf.”

Professor Boris Gaensicke, co-author from the Department of Physics, adds: “The planetesimal we have discovered is deep into the gravitational well of the white dwarf, much closer to it than we would expect to find anything still alive. That is only possible because it must be very dense and/or very likely to have internal strength that holds it together, so we propose that it is composed largely of iron and nickel.

“If it was pure iron it could survive where it lives now, but equally it could be a body that is rich in iron but with internal strength to hold it together, which is consistent with the planetesimal being a fairly massive fragment of a planet core. If correct, the original body was at least hundreds of kilometres in diameter because it is only at that point planets begin to differentiate — like oil on water — and have heavier elements sink to form a metallic core.”

The discovery offers a hint as to what planets may reside in other solar systems, and a glimpse into the future of our own.

Dr Christopher Manser said: “As stars age they grow into red giants, which ‘clean out’ much of the inner part of their planetary system. In our Solar System, the Sun will expand up to where the Earth currently orbits, and will wipe out Earth, Mercury, and Venus. Mars and beyond will survive and will move further out.

“The general consensus is that 5-6 billion years from now, our Solar System will be a white dwarf in place of the Sun, orbited by Mars, Jupiter, Saturn, the outer planets, as well as asteroids and comets. Gravitational interactions are likely to happen in such remnants of planetary systems, meaning the bigger planets can easily nudge the smaller bodies onto an orbit that takes them close to the white dwarf, where they get shredded by its enormous gravity.

“Learning about the masses of asteroids, or planetary fragments that can reach a white dwarf can tell us something about the planets that we know must be further out in this system, but we currently have no way to detect.

“Our discovery is only the second solid planetesimal found in a tight orbit around a white dwarf, with the previous one found because debris passing in front of the star blocked some of its light — that is the “transit method” widely used to discover exoplanets around Sun-like stars. To find such transits, the geometry under which we view them has to be very finely tuned, which means that each system observed for several hours mostly leads to nothing. The spectroscopic method we developed in this research can detect close-in planetesimals without the need for a specific alignment. We already know of several other systems with debris discs very similar to SDSS J122859.93+104032.9, which we will study next. We are confident that we will discover additional planetesimals orbiting white dwarfs, which will then allow us to learn more about their general properties.”

Unexpected Coronal Rain On Sun Links Two Solar Mysteries

For five months in mid 2017, Emily Mason did the same thing every day. Arriving to her office at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, she sat at her desk, opened up her computer, and stared at images of the Sun — all day, every day. “I probably looked through three or five years’ worth of data,” Mason estimated. Then, in October 2017, she stopped. She realized she had been looking at the wrong thing all along.

Mason, a graduate student at The Catholic University of America in Washington, D.C., was searching for coronal rain: giant globs of plasma, or electrified gas, that drip from the Sun’s outer atmosphere back to its surface. But she expected to find it in helmet streamers, the million-mile tall magnetic loops — named for their resemblance to a knight’s pointy helmet — that can be seen protruding from the Sun during a solar eclipse. Computer simulations predicted the coronal rain could be found there. Observations of the solar wind, the gas escaping from the Sun and out into space, hinted that the rain might be happening. And if she could just find it, the underlying rain-making physics would have major implications for the 70-year-old mystery of why the Sun’s outer atmosphere, known as the corona, is so much hotter than its surface. But after nearly half a year of searching, Mason just couldn’t find it. “It was a lot of looking,” Mason said, “for something that never ultimately happened.”

The problem, it turned out, wasn’t what she was looking for, but where. In a paper published today in the Astrophysical Journal Letters, Mason and her coauthors describe the first observations of coronal rain in a smaller, previously overlooked kind of magnetic loop on the Sun. After a long, winding search in the wrong direction, the findings forge a new link between the anomalous heating of the corona and the source of the slow solar wind — two of the biggest mysteries facing solar science today.

How It Rains on the Sun

Observed through the high-resolution telescopes mounted on NASA’s SDO spacecraft, the Sun — a hot ball of plasma, teeming with magnetic field lines traced by giant, fiery loops — seems to have few physical similarities with Earth. But our home planet provides a few useful guides in parsing the Sun’s chaotic tumult: among them, rain.

On Earth, rain is just one part of the larger water cycle, an endless tug-of-war between the push of heat and pull of gravity. It begins when liquid water, pooled on the planet’s surface in oceans, lakes, or streams, is heated by the Sun. Some of it evaporates and rises into the atmosphere, where it cools and condenses into clouds. Eventually, those clouds become heavy enough that gravity’s pull becomes irresistible and the water falls back to Earth as rain, before the process starts anew.

On the Sun, Mason said, coronal rain works similarly, “but instead of 60-degree water you’re dealing with a million-degree plasma.” Plasma, an electrically-charged gas, doesn’t pool like water, but instead traces the magnetic loops that emerge from the Sun’s surface like a rollercoaster on tracks. At the loop’s foot points, where it attaches to the Sun’s surface, the plasma is superheated from a few thousand to over 1.8 million degrees Fahrenheit. It then expands up the loop and gathers at its peak, far from the heat source. As the plasma cools, it condenses and gravity lures it down the loop’s legs as coronal rain.

Mason was looking for coronal rain in helmet streamers, but her motivation for looking there had more to do with this underlying heating and cooling cycle than the rain itself. Since at least the mid-1990s, scientists have known that helmet streamers are one source of the slow solar wind, a comparatively slow, dense stream of gas that escapes the Sun separately from its fast-moving counterpart. But measurements of the slow solar wind gas revealed that it had once been heated to an extreme degree before cooling and escaping the Sun. The cyclical process of heating and cooling behind coronal rain, if it was happening inside the helmet streamers, would be one piece of the puzzle.

The other reason connects to the coronal heating problem — the mystery of how and why the Sun’s outer atmosphere is some 300 times hotter than its surface. Strikingly, simulations have shown that coronal rain only forms when heat is applied to the very bottom of the loop. “If a loop has coronal rain on it, that means that the bottom 10% of it, or less, is where coronal heating is happening,” said Mason. Raining loops provide a measuring rod, a cutoff point to determine where the corona gets heated. Starting their search in the largest loops they could find — giant helmet streamers — seemed like a modest goal, and one that would maximize their chances of success.

She had the best data for the job: Images taken by NASA’s Solar Dynamics Observatory, or SDO, a spacecraft that has photographed the Sun every twelve seconds since its launch in 2010. But nearly half a year into the search, Mason still hadn’t observed a single drop of rain in a helmet streamer. She had, however, noticed a slew of tiny magnetic structures, ones she wasn’t familiar with. “They were really bright and they kept drawing my eye,” said Mason. “When I finally took a look at them, sure enough they had tens of hours of rain at a time.”

At first, Mason was so focused on her helmet streamer quest that she made nothing of the observations. “She came to group meeting and said, ‘I never found it — I see it all the time in these other structures, but they’re not helmet streamers,'” said Nicholeen Viall, a solar scientist at Goddard, and a coauthor of the paper. “And I said, ‘Wait…hold on. Where do you see it? I don’t think anybody’s ever seen that before!'”

A Measuring Rod for Heating

These structures differed from helmet streamers in several ways. But the most striking thing about them was their size.

“These loops were much smaller than what we were looking for,” said Spiro Antiochos, who is also a solar physicist at Goddard and a coauthor of the paper. “So that tells you that the heating of the corona is much more localized than we were thinking.”

While the findings don’t say exactly how the corona is heated, “they do push down the floor of where coronal heating could happen,” said Mason. She had found raining loops that were some 30,000 miles high, a mere two percent the height of some of the helmet streamers she was originally looking for. And the rain condenses the region where the key coronal heating can be happening. “We still don’t know exactly what’s heating the corona, but we know it has to happen in this layer,” said Mason.

A New Source for the Slow Solar Wind

But one part of the observations didn’t jibe with previous theories. According to the current understanding, coronal rain only forms on closed loops, where the plasma can gather and cool without any means of escape. But as Mason sifted through the data, she found cases where rain was forming on open magnetic field lines. Anchored to the Sun at only one end, the other end of these open field lines fed out into space, and plasma there could escape into the solar wind. To explain the anomaly, Mason and the team developed an alternative explanation — one that connected rain on these tiny magnetic structures to the origins of the slow solar wind.

In the new explanation, the raining plasma begins its journey on a closed loop, but switches — through a process known as magnetic reconnection — to an open one. The phenomenon happens frequently on the Sun, when a closed loop bumps into an open field line and the system rewires itself. Suddenly, the superheated plasma on the closed loop finds itself on an open field line, like a train that has switched tracks. Some of that plasma will rapidly expand, cool down, and fall back to the Sun as coronal rain. But other parts of it will escape — forming, they suspect, one part of the slow solar wind.

Mason is currently working on a computer simulation of the new explanation, but she also hopes that soon-to-come observational evidence may confirm it. Now that Parker Solar Probe, launched in 2018, is traveling closer to the Sun than any spacecraft before it, it can fly through bursts of slow solar wind that can be traced back to the Sun — potentially, to one of Mason’s coronal rain events. After observing coronal rain on an open field line, the outgoing plasma, escaping to the solar wind, would normally be lost to posterity. But no longer. “Potentially we can make that connection with Parker Solar Probe and say, that was it,” said Viall.

Digging Through the Data

As for finding coronal rain in helmet streamers? The search continues. The simulations are clear: the rain should be there. “Maybe it’s so small you can’t see it?” said Antiochos. “We really don’t know.”

But then again, if Mason had found what she was looking for she might not have made the discovery — or have spent all that time learning the ins and outs of solar data.

“It sounds like a slog, but honestly it’s my favorite thing,” said Mason. “I mean that’s why we built something that takes that many images of the Sun: So we can look at them and figure it out.”

Astronomers Find Evidence Of A Planet With A Mass Almost 13 Times That Of Jupiter

In the past three decades, almost 4,000 planet-like objects have been discovered orbiting isolated stars outside the Solar System (exoplanets). Beginning in 2011, it was possible to use NASA’s Kepler Space Telescope to observe the first exoplanets in orbit around young binary systems of two live stars with hydrogen still burning in their core.

Brazilian astronomers have now found the first evidence of the existence of an exoplanet orbiting an older or more evolved binary in which one of the two stars is dead.

The study resulted from a postdoctoral research project and a research internship abroad, both with scholarships from São Paulo Research Foundation — FAPESP. Its findings have just been published in the Astronomical Journal.

Leonardo Andrade de Almeida, first author of the article, told as follow: “We succeeded in obtaining pretty solid evidence of the existence of a giant exoplanet with a mass almost 13 times that of Jupiter [the largest planet in the Solar System] in an evolved binary system. This is the first confirmation of an exoplanet in a system of this kind.”

Almeida is currently a postdoctoral fellow of the Federal University of Rio Grande do Norte (UFRN), having conducted postdoctoral research at the University of São Paulo’s Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG-USP), where he was supervised by Professor Augusto Damineli, a coauthor of the study.

Clues followed by the researchers to discover the exoplanet in the evolved binary called KIC 10544976, located in the Cygnus constellation in the northern celestial hemisphere, included variations in eclipse timing (the time taken for each of the two stars to eclipse the other) and orbital period.

“Variations in the orbital period of a binary are due to gravitational attraction among the three objects, which orbit around a common center of mass,” Almeida said.

Orbital period variations are not enough to prove the existence of a planet in the case of binaries, however, because binary stars’ magnetic activity fluctuates periodically, just as the Sun’s magnetic field changes polarity every 11 years, with turbulence and the number and size of sunspots peaking and then declining.

“Variations in the Sun’s magnetic activity eventually cause a change in its magnetic field. The same is true of all isolated stars. In binaries, these variations also cause a change in orbital period due to what we call the Applegate mechanism,” Almeida explained.

To refute the hypothesis that variations in the orbital period of KIC 10544976 were due only to magnetic activity, the researchers analyzed the effect of eclipse timing variation and the magnetic activity cycle of the binary’s live star.

KIC 10544976 consists of a white dwarf, a dead low-mass star with a high surface temperature, and a red dwarf, a live (magnetically active) star with a small mass compared to that of our Sun and scant luminosity due to low energy output. The two stars were monitored by ground-based telescopes between 2005 and 2017 and by Kepler between 2009 and 2013, producing data minute by minute.

“The system is unique,” Almeida said. “No similar system has enough data to let us calculate orbital period variation and magnetic cycle activity for the live star.”

Using the Kepler data, they were able to estimate the magnetic cycle of the live star (red dwarf) based on the rate and energy of flares (large eruptions of electromagnetic radiation) and variability due to spots (regions of cooler surface temperature and hence darkness caused by different concentrations of magnetic field flux).

Analysis of the data showed that the red dwarf’s magnetic activity cycle lasted 600 days, which is consistent with the magnetic cycles estimated for low-mass isolated stars. The binary’s orbital period was estimated at 17 years.

“This completely refutes the hypothesis that orbital period variation is due to magnetic activity. The most plausible explanation is the presence of a giant planet orbiting the binary, with a mass approximately 13 times that of Jupiter,” Almeida said.

Formation hypotheses

How the planet orbiting the binary was formed is unknown. One hypothesis is that it developed at the same time as the two stars billions of years ago. If so, it is a first-generation planet. Another hypothesis is that it formed out of the gas ejected during the death of the white dwarf, making it a second-generation planet.

Confirmation of its status as either a first- or second-generation planet and its direct detection as it orbits the binary could be obtained using the new generation of ground-based telescopes with primary mirrors exceeding 20 meters, including the Giant Magellan Telescope (GMT) installed in Chile’s Atacama Desert. The GMT is expected to see first light in 2024.

FAPESP will invest US$40 million in the GMT, or approximately 4% of the telescope’s estimated total cost. This investment will guarantee 4% of the telescope’s operating time for studies by researchers from São Paulo State.

“We’re probing 20 systems in which external bodies could show gravitational effects, such as KIC 10544976, and most are only observable from the southern hemisphere. The GMT will enable us to detect these objects directly and obtain important answers on the formation and evolution of these exotic environments, as well as the possibility of life there,” Almeida said.

Working Together As A ‘Virtual Telescope,’ Observatories Around The World Produce First Direct Images Of A Black Hole

An international team of over 200 astronomers, including scientists from MIT’s Haystack Observatory, has captured the first direct images of a black hole. They accomplished this remarkable feat by coordinating the power of eight major radio observatories on four continents, to work together as a virtual, Earth-sized telescope.

In a series of papers published today in a special issue of Astrophysical Journal Letters (https://iopscience.iop.org/issue/2041-8205/875/1), the team has revealed four images of the supermassive black hole at the heart of Messier 87, or M87, a galaxy within the Virgo galaxy cluster, 55 million light years from Earth.

All four images show a central dark region surrounded by a ring of light that appears lopsided — brighter on one side than the other.

Albert Einstein, in his theory of general relativity, predicted the existence of black holes, in the form of infinitely dense, compact regions in space, where gravity is so extreme that nothing, not even light, can escape from within. By definition, black holes are invisible. But if a black hole is surrounded by light-emitting material such as plasma, Einstein’s equations predict that some of this material should create a “shadow,” or an outline of the black hole and its boundary, also known as its event horizon.

Based on the new images of M87, the scientists believe they are seeing a black hole’s shadow for the first time, in the form of the dark region at the center of each image.

Relativity predicts that the immense gravitational field will cause light to bend around the black hole, forming a bright ring around its silhouette, and will also cause the surrounding material to orbit around the object at close to light speed. The bright, lopsided ring in the new images offers visual confirmation of these effects: The material headed toward our vantage point as it rotates around appears brighter than the other side.

From these images, theorists and modelers on the team have determined that the black hole is about 6.5 billion times as massive as our sun. Slight differences between each of the four images suggest that material is zipping around the black hole at lightning speed.

“This black hole is much bigger than the orbit of Neptune, and Neptune takes 200 years to go around the sun,” says Geoffrey Crew, a research scientist at Haystack Observatory. “With the M87 black hole being so massive, an orbiting planet would go around it within a week and be traveling at close to the speed of light.”

“People tend to view the sky as something static, that things don’t change in the heavens, or if they do, it’s on timescales that are longer than a human lifetime,” says Vincent Fish, a research scientist at Haystack Observatory. “But what we find for M87 is, at the very fine detail we have, objects change on the timescale of days. In the future, we can perhaps produce movies of these sources. Today we’re seeing the starting frames.”

“These remarkable new images of the M87 black hole prove that Einstein was right yet again,” says Maria Zuber, MIT’s vice president for research and the E.A. Griswold Professor of Geophysics in the Department of Earth, Atmospheric and Planetary Sciences. “The discovery was enabled by advances in digital systems at which Haystack engineers have long excelled.”

“Nature was kind”

The images were taken by the Event Horizon Telescope, or EHT, a planet-scale array comprising eight radio telescopes, each in a remote, high-altitude environment, including the mountaintops of Hawaii, Spain’s Sierra Nevada, the Chilean desert, and the Antarctic ice sheet.

On any given day, each telescope operates independently, observing astrophysical objects that emit faint radio waves. However, a black hole is infinitely smaller and darker than any other radio source in the sky. To see it clearly, astronomers need to use very short wavelengths — in this case, 1.3 millimeters — that can cut through the clouds of material between a black hole and the Earth.

Making a picture of a black hole also requires a magnification, or “angular resolution,” equivalent to reading a text on a phone in New York from a sidewalk café in Paris. A telescope’s angular resolution increases with the size of its receiving dish. However, even the largest radio telescopes on Earth are nowhere near big enough to see a black hole.

But when multiple radio telescopes, separated by very large distances, are synchronized and focused on a single source in the sky, they can operate as one very large radio dish, through a technique known as very long baseline interferometry, or VLBI. Their combined angular resolution as a result can be vastly improved.

For EHT, the eight participating telescopes summed up to a virtual radio dish as big as the Earth, with the ability to resolve an object down to 20 micro-arcseconds — about 3 million times sharper than 20/20 vision. By a happy coincidence, that’s about the precision required to view a black hole, according to Einstein’s equations.

“Nature was kind to us, and gave us something just big enough to see by using state-of-the-art equipment and techniques,” says Crew, co-leader of the EHT correlation working group and the ALMA Observatory VLBI team.

“Gobs of data”

On April 5, 2017, the EHT began observing M87. After consulting numerous weather forecasts, astronomers identified four nights that would produce clear conditions for all eight observatories — a rare opportunity, during which they could work as one collective dish to observe the black hole.

In radio astronomy, telescopes detect radio waves, at frequencies that register incoming photons as a wave, with an amplitude and phase that’s measured as a voltage. As they observed M87, every telescope took in streams of data in the form of voltages, represented as digital numbers.

“We’re recording gobs of data — petabytes of data for each station,” Crew says.

In total, each telescope took in about one petabyte of data, equal to 1 million gigabytes. Each station recorded this enormous influx that onto several Mark6 units — ultrafast data recorders that were originally developed at Haystack Observatory.

After the observing run ended, researchers at each station packed up the stack of hard drives and flew them via FedEx to Haystack Observatory, in Massachusetts, and Max Planck Institute for Radio Astronomy, in Germany. (Air transport was much faster than transmitting the data electronically.) At both locations, the data were played back into a highly specialized supercomputer called a correlator, which processed the data two streams at a time.

As each telescope occupies a different location on the EHT’s virtual radio dish, it has a slightly different view of the object of interest — in this case, M87. The data received by two separate telescopes may encode a similar signal of the black hole but also contain noise that’s specific to the respective telescopes.

The correlator lines up data from every possible pair of the EHT’s eight telescopes. From these comparisons, it mathematically weeds out the noise and picks out the black hole’s signal. High-precision atomic clocks installed at every telescope time-stamp incoming data, enabling analysts to match up data streams after the fact.

“Precisely lining up the data streams and accounting for all kinds of subtle perturbations to the timing is one of the things that Haystack specializes in,” says Colin Lonsdale, Haystack director and vice chair of the EHT directing board.

Teams at both Haystack and Max Planck then began the painstaking process of “correlating” the data, identifying a range of problems at the different telescopes, fixing them, and rerunning the correlation, until the data could be rigorously verified. Only then were the data released to four separate teams around the world, each tasked with generating an image from the data using independent techniques.

“It was the second week of June, and I remember I didn’t sleep the night before the data was released, to be sure I was prepared,” says Kazunori Akiyama, co-leader of the EHT imaging group and a postdoc working at Haystack.

All four imaging teams previously tested their algorithms on other astrophysical objects, making sure that their techniques would produce an accurate visual representation of the radio data. When the files were released, Akiyama and his colleagues immediately ran the data through their respective algorithms. Importantly, each team did so independently of the others, to avoid any group bias in the results.

“The first image our group produced was slightly messy, but we saw this ring-like emission, and I was so excited at that moment,” Akiyama remembers. “But simultaneously I was worried that maybe I was the only person getting that black hole image.”

His concern was short-lived. Soon afterward all four teams met at the Black Hole Initiative at Harvard University to compare images, and found, with some relief, and much cheering and applause, that they all produced the same, lopsided, ring-like structure — the first direct images of a black hole.

“There have been ways to find signatures of black holes in astronomy, but this is the first time anyone’s ever taken a picture of one,” Crew says. “This is a watershed moment.”

“A new era”

The idea for the EHT was conceived in the early 2000s by Sheperd Doeleman, who was leading a pioneering VLBI program at Haystack Observatory and now directs the EHT project as an astronomer at the Harvard-Smithsonian Center for Astrophysics. At the time, Haystack engineers were developing the digital back-ends, recorders, and correlator that could process the enormous datastreams that an array of disparate telescopes would receive.

“The concept of imaging a black hole has been around for decades,” Lonsdale says. “But it was really the development of modern digital systems that got people thinking about radio astronomy as a way of actually doing it. More telescopes on mountaintops were being built, and the realization gradually came along that, hey, [imaging a black hole] isn’t absolutely crazy.”

In 2007, Doeleman’s team put the EHT concept to the test, installing Haystack’s recorders on three widely scattered radio telescopes and aiming them together at Sagittarius A*, the black hole at the center of our own galaxy.

“We didn’t have enough dishes to make an image,” recalls Fish, co-leader of the EHT science operations working group. “But we could see there was something there that’s about the right size.”

Today, the EHT has grown to an array of 11 observatories: ALMA, APEX, the Greenland Telescope, the IRAM 30-meter Telescope, the IRAM NOEMA Observatory, the Kitt Peak Telescope, the James Clerk Maxwell Telescope, the Large Millimeter Telescope Alfonso Serrano, the Submillimeter Array, the Submillimeter Telescope, and the South Pole Telescope.

Coordinating observations and analysis has involved over 200 scientists from around the world who make up the EHT collaboration, with 13 main institutions, including Haystack Observatory. Key funding was provided by the National Science Foundation, the European Research Council, and funding agencies in East Asia, including the Japan Society for the Promotion of Science. The telescopes contributing to this result were ALMA, APEX, the IRAM 30-meter telescope, the James Clerk Maxwell Telescope, the Large Millimeter Telescope Alfonso Serrano, the Submillimeter Array, the Submillimeter Telescope, and the South Pole Telescope.

More observatories are scheduled to join the EHT array, to sharpen the image of M87 as well as attempt to see through the dense material that lies between Earth and the center of our own galaxy, to the heart of Sagittarius A*.

“We’ve demonstrated that the EHT is the observatory to see a black hole on an event horizon scale,” Akiyama says. “This is the dawn of a new era of black hole astrophysics.”

The Haystack EHT team includes John Barrett, Roger Cappallo, Joseph Crowley, Mark Derome, Kevin Dudevoir, Michael Hecht, Lynn Matthews, Kotaro Moriyama, Michael Poirier, Alan Rogers, Chester Ruszczyk, Jason SooHoo, Don Sousa, Michael Titus, and Alan Whitney. Additional contributors were MIT alumni Daniel Palumbo, Katie Bouman, Lindy Blackburn, and Bill Freeman, a professor in MIT’s Department of Electrical Engineering and Computer Science.

Massive Storm Sparks Blizzard Warnings From Colorado To Minnesota

A potentially record-breaking storm is squeezing the warmth from spring as it brings snow and howling winds across the U.S. Great Plains and threatens to flood rivers from Canada to the Gulf of Mexico.

The giant system, set to strengthen Wednesday, has sparked blizzard warnings from Colorado to Minnesota and could drop more than 2 feet of snow in South Dakota and as much as 8 inches in Minneapolis, the National Weather Service said. Severe thunderstorms will hit Texas and the Mississippi Valley. The system threatens to delay wheat and corn planting.

“It is pretty extensive,” David Roth, a senior branch forecaster at the U.S. Weather Prediction Center, said by telephone.

The storm, which will pack near-record low pressure, could be on par with the massive system that triggered flooding across Nebraska and Iowa last month. Snow and rain area already falling across the Great Plains and Midwest. The storm will build over Wyoming on Wednesday, cross Nebraska on Thursday and then hit Minneapolis, said Rob Carolan, owner of Hometown Forecast Services.

Farther south, the storm will push dry winds across Kansas, Oklahoma, New Mexico and Texas — raising the risk of wildfires.

The Mississippi River is already at moderate-to-major flood stage in Wisconsin, Illinois and Iowa. The Red River is at major flood stage in Fargo, N.D.

“Because the Mississippi is flooding — none of this is welcome,” Roth said.

Nonetheless, the Mississippi should be able to handle this week’s storm, because water levels are currently falling, said Matt Roe, spokesman for the Army Corps of Engineers in New Orleans. The Corps has begun to close the Bonnet Carre spillway upstream from New Orleans, designed to prevent flooding.

High water has restricted Mississippi barge traffic to daylight and has limited the amount of freight that can be hauled, said Austin Golding, president of Golding Barge Line in Vicksburg, Miss. Right now, the river is entirely navigable, but the hardest parts to traverse are the bridges in Vicksburg and Baton Rouge.

“May will be nasty if it gets hot up north and the snow melt accelerates after this winter system they are encountering now,” Golding said.

This system’s icy reach won’t extend to Chicago, which will get rain and have a low of 39 degrees Wednesday before temperatures rebound into the 60s by Thursday. Detroit and Toronto will also be spared, Carolan said.

As the storm passes, weather will whiplash between extremes in many places. On Tuesday, Denver’s temperature reached 78 degrees. Wednesday, however, the city is under a blizzard warning with readings set to plunge to 21, the weather service said. Cheyenne, Wyo., will go from 71 on Tuesday to 18 degrees late Wednesday.

While the storm bulldozes across the central U.S., mild air on the East Coast will keep temperatures in New York in the high 50s and low 60s through the rest of the week, the weather service said.

The snow and rain across the northern Midwest will delay corn and wheat planting, said Dan Hicks, a meteorologist with Freese-Notis Weather Services in Des Moines, Iowa. Farther south, from Kansas to Southern Illinois, planting is unlikely to be interrupted.

These Rocks Look Like They Could Topple at Any Moment. They Hold 1,000 Years of Earthquake Secrets.

Studying PBRs as a proxy for earthquake magnitude is hardly a new concept. “This methodology has been proven as effective in evaluating the maximal magnitude on faults and fault systems around the world,” the researchers wrote in the abstract. This information is critical for understanding the seismic rumblings in southern Israel, a region that’s home to several fault lines, villages and valuable infrastructure, including hazardous-material disposal sites and nuclear research facilities, according to EOS, the news site of the American Geophysical Union, which first covered the research.

But finding PBRs takes time, so study lead researcher Yaron Finzi, a geophysicist at the Arava Institute and the Arava Dead-Sea Science Center, and his team collaborated with citizen scientists to find these picturesque rock pillars.

“I could not have completed the field work without the help of the tour guides and hikers,” Finzi told Live Science. These citizen scientists were so enthusiastic, they drew him maps so he could find the rock formations. Many times, he would bump into people at the grocery store who would ask him how the project was going.

After looking at the photos of these PBRs, the researchers identified the best ones that could help with their research. Then, study lead author Noam Ganz, who just earned a master’s degree in geology from Ben Gurion University and now works as a research assistant at the Dead Sea and Arava Science Center, spent about 80 days visiting each of these formations. In all, the team located about 80 limestone PBRs and rock pillars between 2015 and 2018, the tallest measuring more than 130 feet (40 meters) high.

Next, the researchers examined digitized images of each PBR to determine each formation’s stability. Then, they estimated the ground motion each PBR could withstand, as well as its distance from different rupture points, so they could see how much shaking these rock stacks could take before toppling, EOS reported.

In addition, the researchers dated the rocks by analyzing the dust trapped between the cliffs and the pillars with a technique called optically stimulated luminescence. This method allows researchers to determine how long ago quartz crystals in the dust were exposed to the sun.

“I was relieved that most of the pillars were older than 1,000 years and older than 1,300 years,” Finzi told Live Science. “So, they actually give us a bulk of significant and new knowledge about long term seismicity.”