Disinfection of public drinking water is one of the great public health success stories of the 20th century. In 1900, outbreaks of cholera and typhoid, both caused by waterborne bacteria, were common in American cities. In 1908, Jersey City, N.J., became the first U.S. city to routinely disinfect community water. Other cities and towns quickly followed, and by 1920, the typhoid rate in the United States had dropped by 66 percent.
But that battle isn’t over. Around the world, more than 2 billion people lack reliable access to safe water (SN: 8/18/18, p. 14), and half a million people die each year from diarrhea caused by contaminated water, according to the World Health Organization. And in the United States, challenges remain. The management failures that caused the 2014 lead contamination crisis in Flint, Mich., were a wake-up call (SN: 3/19/16, p. 8), but Flint is hardly alone. Systems in other big cities are also falling short. In October, officials in Newark, N.J., scrambled to hand out home water filters after it became clear that efforts to prevent lead from leaching into drinking water were not getting the job done. In the first six months of 2017, more than 22 percent of water samples in that city exceeded federal limits for lead, according to news reports.
If big cities are struggling, small towns with skimpy budgets as well as the many people who get their water from private wells often have it harder, lacking access to the infrastructure or technology to make water reliably safe. But science can help.
In this issue, Science News staff writer Laurel Hamers digs into the latest research on water treatment technology and finds a focus on efforts to invent affordable, scalable solutions. There’s a lot of engineering and chemistry involved, not surprisingly, and also physics — it’s hard to move water efficiently through a filter while also catching the bad stuff. Her story is a testament to researcher ingenuity, and a helpful primer on how a typical municipal water treatment plant works.
As I read Hamers’ story, I realized that I didn’t know how our water is treated here in Washington, D.C., even though I live barely a mile from one of the city’s two treatment plants. (I at least get credit for knowing the water comes from the Potomac River.) So I Googled it and found a description of how that process works. Plus I found data on potential contaminants such as Giardia and Cryptosporidium, as well as information on how residents can get their water tested for lead, which can leach from pipes or fixtures. I also learned that each spring, the Washington Aqueduct briefly switches disinfectants from chloramine to chlorine while the agency cleans the water pipes. That might explain the short-lived swimming pool smell in the tap water.
For me, this became a double win; I learned a lot about advances in water treatment technology from Hamers’ reporting, and I was motivated to seek out information about my local water supply.
If other readers feel inspired by our work to learn more, count me as a happy journalist.
Devices that eavesdrop on neural activity can help paralyzed people command computer tablets to stream music, text friends, check the weather or surf the internet.
Three people with paralysis below the neck were able to navigate off-the-shelf computer tablets using an electrode array system called BrainGate2. The results, published November 21 in PLOS One, are the latest to show that neural signals can be harnessed to directly allow movement (SN: 6/16/12, p. 5).
The two men and one woman had electrode grids implanted over part of the motor cortex, an area of the brain that helps control movement. The brain implants picked up neural activity indicating that the participants were thinking about moving a cursor. Those patterns were then sent to a virtual mouse that was wirelessly paired to the tablet. Using nothing more than their intentions to move a cursor, the three participants performed seven common digital tasks, including web browsing and sending e-mail. One participant looked up orchid care, ordered groceries online and played a digital piano. “The tablet became second nature to me, very intuitive,” she told the researchers when asked about her experience, according to the study.
Another participant enjoyed texting friends, “especially because I could interject some humor,” he told the scientists. The system even allowed two of the participants to chat with each other in real time.
For the study, the researchers used tablets with standard settings, without installing any shortcuts or features to make typing or navigation easier.
SAN DIEGO — Getting goose bumps doesn’t just make hairs stand on end; it may also help hair grow.
Nerves and muscles that raise goose bumps also stimulate stem cells in the skin to make hair follicles and grow hair. Ya-Chieh Hsu, a stem cell researcher at Harvard University, reported the unpublished findings December 9 at the joint meeting of the American Society for Cell Biology and the European Molecular Biology Organization. Getting goose bumps when it’s cold may encourage animals’ fur to grow thicker, Hsu said. Nerves that are part of the sympathetic nervous system — which controls pupil dilation, heart rate and other automatic processes — nestle next to stem cells that will create hair follicles, Hsu and her colleagues found. Usually nerves are wrapped in a protective coating called myelin, like electrical wire sheathed in plastic. But Hsu’s group found that the nerves’ ends were naked where they meet hair follicle stem cells, like wires stripped at the tips to make contacts with electrical nodes.
The nerves secrete the hormone norepinephrine. That hormone is necessary for hair growth, the researchers found. Those findings might help explain why hair loss is a side effect of drugs known as beta-blockers, which interfere with norepinephrine’s action.
Sympathetic nerves next to hair follicles are also wrapped around tiny arrector pili muscles, which contract to make hair cells stand on end, causing goose bumps. Mice with mutations that prevented the muscles from growing also lacked the sympathetic nerves and didn’t grow hair normally. Men with male pattern baldness also lack arrector pili muscles in their scalps, Hsu said, suggesting that sympathetic nerves and goose bump–raising muscles may also be important in that type of baldness. Restoring the nerves and muscles may lead to new hair growth, she said.
An orbital oopsie has led to new proof of Albert Einstein’s physics prowess.
In 2014, two satellites intended for Europe’s Galileo network, the equivalent of the United States’ GPS network, were placed into orbit incorrectly, causing them to travel around Earth in ellipses rather than circles. That wasn’t ideal for the satellites’ originally intended navigational use, but scientists realized the wayward satellites were perfect for another purpose: testing Einstein’s theory of gravity, the general theory of relativity.
According to general relativity, gravity affects not just space, but also time. The deeper within a gravitational field you are, the slower time passes (SN: 10/17/15, p. 16). So a clock at a higher altitude will tick faster than one closer to Earth’s surface, where Earth’s gravity is stronger. The satellites’ orbital mishap allowed the most precise test yet of this effect, known as gravitational redshift, two teams of scientists report in a pair of papers in the Dec. 7 Physical Review Letters.
As the two misplaced satellites move in their elliptical orbits, their distance from Earth periodically increases and decreases by about 8,500 kilometers. Using the precise atomic clocks on the satellites, the scientists studied how that altitude change affected the flow of time. The clocks sped up and slowed down by tiny fractions of a second as expected, agreeing with the predictions of general relativity within a few thousandths of a percent, the teams report.
SEATTLE — The next generation exoplanet hunter is coming into its own. NASA’s Transiting Exoplanet Survey Satellite, or TESS, has already found eight confirmed planets in its first four months of observing — and some are unlike anything astronomers have seen before.
“The torrent of data is starting to flow already,” TESS principal investigator George Ricker of MIT said January 7 in a news conference at a meeting of the American Astronomical Society.
TESS launched in April and began science observations in July (SN: 5/12/18, p. 7). It was designed to be a follow-up to the prolific Kepler space telescope, which went dark in October after almost a decade of observing (SN Online: 10/30/18). Like Kepler, TESS searches for planets by watching for dips in starlight as planets cross, or transit, in front of their stars. Unlike Kepler, which stared unblinkingly at a single patch of sky for years, TESS scans a new segment of sky every month. Over two years, TESS will cover the entire 360 degrees of sky visible from Earth’s orbit.
In the first four segments, TESS has already spotted eight confirmed planets and more than 320 unconfirmed candidates, said Xu Chelsea Huang of MIT. And several of them are downright strange. Take the third-found planet, HD 21749b. Only 52 light-years away, it has the lowest temperature known for a planet orbiting a bright, nearby star, astronomers reported at the meeting and in a paper posted at arXiv.org on January 1. That makes it a great candidate for follow-up observations with future telescopes like the James Webb Space Telescope, scheduled to launch in 2021. Webb will use starlight filtering through the atmospheres of planets like this one to measure those atmospheres’ properties and search for signs of life (SN: 4/30/16, p. 32).
“If we want to study atmospheres of cool planets, this is the one to start with,” Huang said.
“Cool” is a relative term. This particular planet is still probably too hot and gassy to host life. Its orbit takes 36 Earth days, the longest known orbital period for planets transiting bright stars within 100 light-years of the sun.
That leaves it at a distance from the star that should heat the planet’s surface to about 150° Celsius, too hot for liquid water. And at 2.84 times Earth’s size and 23.2 times Earth’s mass, its density suggests it must have a thick atmosphere, unlike Earth’s life-friendly one.
But it’s still worth checking out, says astronomer Diana Dragomir of MIT, a member of the TESS team. Despite its heat, this planet is “tepid” compared with most of the scorched worlds whose atmospheres astronomers can probe right now, she says, so closer to an Earthlike system. Smaller, cooler, more Earthlike worlds are few and far between, and may not orbit such bright stars.
Finding more longer-period planets “helps you explore the diversity of planets that are out there,” says astronomer Paul Dalba of the University of California, Riverside, who studies exoplanet atmospheres but was not involved in the TESS discovery. Because TESS spends such a short stretch of time looking at each segment of the sky, astronomers expect most of its planets to have shorter years than an Earth month. “The fact that we’re already getting one that’s longer period I think is just really exciting, showing that TESS isn’t just for the shortest-period exoplanets.” The other planets in TESS’s first haul are equally exotic. TESS’s first find, Pi Mensae c, was reported in September ( SN Online: 9/18/18 ). The planet orbits its star every 6.27 days, and is about 2.14 times Earth’s size and 4.8 times Earth’s mass, giving it a density similar to pure water. The weirdest thing about that super-Earth is the company it keeps, Huang said. Previous observations showed that the star Pi Mensae also has a planet 10 times the mass of Jupiter that orbits every 5.7 years. That planet, Pi Mensae b, revolves on a wildly eccentric orbit, swinging between the distance of Earth and the distance of Jupiter from its star.
“This is the most extreme system we know of that has this type of architecture,” Huang said.
Theories of how planets develop such wonky orbits suggest that this super-Jupiter should have booted Pi Mensae c out of the system (SN: 5/12/18, p. 28). “We are really surprised that the inner super-Earth actually survived that disruptive event,” Huang said. “It’s a mystery we really want to understand.”
The second planet found by TESS, LHS 3844b, has a radius just 1.3 times Earth’s. But it swings around its star every 11 hours, giving it a surface temperature of about 540° C, Huang said. “It’s likely a lava world.”
TESS has completed about one-twelfth of its first sky survey, but Ricker is already writing proposals to extend its initial two-year mission. TESS’s orbit is held stable by the moon’s gravity, so it doesn’t need to spend any fuel to stay put. The fuel on board, used to change the direction the telescope points, is enough to last for 300 years.
“The orbit itself was designed to be extremely stable on timescales of decades to centuries,” Ricker said. “TESS is really going to be an important part of our astronomical efforts for the next decade and for more to come.”
Editor’s note: This story was updated January 29, 2019, to correct the description of the planet LHS 3844b’s orbit. It orbits a star, not a planet.
SEATTLE — Astronomers have spotted a second repeating fast radio burst, and it looks a lot like the first. The existence of a second repeating burst suggests there could be many more of the mysterious signals in the cosmos.
The burst, called FRB 180814.J0422+73, is one of 13 newly discovered fast radio bursts, or FRBs — brief, bright signals of radio energy that come from distant galaxies. The FRBs were detected over a few weeks last year by the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, in British Columbia. Astronomers reported the discoveries at a meeting of the American Astronomical Society on January 7 and in the Jan. 9 Nature. Most such bursts erupt once, last for a few milliseconds, and are never seen again. So astronomers have puzzled over what causes them for years (SN: 8/9/14, p. 22).
“If you have something that flashes for a millisecond in the sky, and there’s nothing that happens for many years, it’s really hard to study,” says astronomer Shriharsh Tendulkar of McGill University in Montreal, a member of the CHIME team.
But then in 2016, astronomers discovered the first repeating FRB when they realized that a series of bursts all came from a single source, called FRB 121102 (SN: 4/2/16, p. 12). Astronomers tracked the signal to its host galaxy (SN: 2/4/17, p. 10) and determined it was coming from an extremely magnetic environment, such as the region surrounding a black hole (SN: 2/3/18, p. 6). Researchers didn’t know if FRB 121102’s repeating signal was unique. Of the more than 60 FRBs detected, no other was known to repeat — until now. Having spotted a second one, scientists are searching for more.
“Imagine you saw a unicorn,” Tendulkar says. “Then suddenly you discover another one. You know now there is a population of these. There is hope for discovering a lot more.” The CHIME team detected the first of the repeating FRB signals on August 14, with four more coming over the next two months from the same spot on the sky. It wasn’t until the third burst, on September 17, that the team realized they might have a repeater, Tendulkar says.
“Somebody pointed out, hey look, these three bursts seem to have the same properties,” he says. “Everybody got really excited.”
Calculations show that the new repeater is about 1.6 billion light-years away. The CHIME team also saw an odd similarity between the two known repeating bursts. Most FRBs are just a sharp blip, akin to a single note being played on a trumpet. But some of the individual bursts in both repeaters were made up of multiple sub-bursts that descended in frequency, like the “wah wah wah wah” of a sad trombone.
“We’ve seen this in 121102, and we can’t explain it,” says astronomer Emily Petroff of ASTRON, the Netherlands Institute of Radio Astronomy, who was not involved in the new work. “Up until now we’ve only had the one repeater, and it’s given us more questions than answers.” But the fact that both repeaters behave similarly could suggest they have similar origins, she says.
Astronomers may have already caught a third repeating burst, too. FRB 110523, discovered in 2015, has some similar features to the first known repeating FRB, so it was worth checking to see if it also repeats, said astronomer Allison McCarthy of the University of Alabama in Tuscaloosa.
Together with Andrew Seymour of the Green Bank Observatory in West Virginia, McCarthy analyzed more than 41 hours of observations of FRB 110523 taken at the Arecibo Observatory in Puerto Rico. They found one potential repeat burst, McCarthy reported January 9 in a poster at the AAS meeting, but they’re not declaring victory just yet. “It wasn’t strong enough for us to be very sure we had detected one,” McCarthy said, adding that they’re about 60 percent certain. “But it’s still a promising candidate.”
Astronomers’ theories for what causes FRBs are almost as numerous as known FRBs themselves. At one point, astronomers even considered the idea that FRBs could be signals from intelligent aliens. But it’s unclear if the repeating bursts and single bursts both come from the same kinds of sources, or even if one-offs might also repeat if watched for long enough.
“It’s the wild, wild west out there,” Tendulkar says. “We have tantalizing clues, but it’s hard to make definitive conclusions.”
CHIME is likely to catch a lot more of these fast radio bursts. The telescope was still being tested when it caught the 13 new ones, so was not operating at peak performance. “They just barely turned on the telescope,” Petroff says, “and they’re already finding things.”
SAN FRANCISCO — Seizures during sleep can scramble memories — a preliminary finding that may help explain why people with epilepsy sometimes have trouble remembering.
The sleeping brain normally rehashes newly learned material, a nocturnal rehearsal that strengthens those memories. Neuroscientist Jessica Creery and her colleagues forced this rehearsal by playing certain sounds while nine people with epilepsy learned where on a screen certain pictures of common objects were located. Then, while the subjects later slept, the researchers played the sounds to call up some of the associated memories.
This sneaky method of strengthening memories, called targeted memory reactivation, worked as expected for five people who didn’t have seizures during the process. When these people woke up, they remembered the picture locations reactivated by a tone better than those that weren’t reactivated during sleep, said Creery, of Northwestern University in Evanston, Ill. She presented the research March 25 at the annual meeting of the Cognitive Neuroscience Society.
The opposite was true, however, for four people who had mild seizures, detected only by electrodes implanted deep in the brain, while they slept. For these people, memory reactivation during sleep actually worsened memories, making the reactivated memories weaker than the memories that weren’t reactivated during sleep. The combination of seizures and memory reactivation “seems like it’s actually scrambling the memory,” Creery says, a finding that suggests that seizures somehow accelerate forgetting.
Robot revolution? Educational robots could help students learn new skills and good study habits. But researchers still have a lot to learn about the potential risks involved when young kids keep close company with such robots, Maria Temming reported in “Robots are becoming classroom tutors. But will they make the grade?” (SN: 2/16/19, p. 16).The story reminded reader A. Bogart of Isaac Asimov’s novel The Naked Sun, in which robots and humans live side by side. Asimov “raised the specter of some of the same issues with which scientists are now grappling,” Bogart wrote. Although Asimov had a positive view of science and innovation, all inventions are force multipliers, Bogart noted. “That means they can be used to multiply the effects of good and evil,” Bogart wrote. “Even at this early stage, it is well to think about negative impacts as well as positive ones.” Dogged questions Bone fragments of dogs and other animals unearthed from Shubayqa 6, the site of an ancient settlement in Jordan, suggest that dogs may have helped humans devise new ways of hunting small game around 11,500 years ago, Bruce Bower reported in “Dogs may have helped ancient Middle Easterners hunt small game” (SN: 2/16/19, p. 13).
Reader Eric Hobday took issue with the researchers’ conclusion that dogs assisted with hunting. “I will accept as fact that the bones in Shubayqa show signs of having passed through a dog’s digestive system. However, this in no way indicates that the dog in Shubayqa was any more involved in hunting the animal than my dog was,” Hobday wrote. He suggested that the dogs could have been feral and scavenged villagers’ leftovers. “No evidence of domestication was presented, yet the article says the findings offer new insights into domestication,” Hobday wrote. “Really?”
By comparing bones of modern Afghan hounds, greyhounds, gray wolves and golden jackals, researchers have determined that the Shubayqa 6 bones likely came from domesticated dogs, Bower says. “As pointed out in the story, the presence of numerous dogs at the site fits with observations of modern foragers who use dogs to locate small prey during hunts,” he says. “Reconstructions of ancient behavior are always provisional.” Soil science High demand for sparkling wine may be depleting 400 million kilograms of soil every year from northeastern Italy’s vineyards, Cassie Martin reported in “Prosecco production takes a toll on northeast Italy’s environment” (SN: 2/16/19, p. 5).
“The best wine grows in poor soil conditions,” reader Jonathan Quint wrote. “Is erosion even a concern for a vineyard?”
Soil erosion isn’t necessarily a bad thing. It can help generate new soils to keep an ecosystem healthy. But such a high rate of soil erosion in Italy is a big concern, says Jesús Rodrigo Comino, a geographer at the University of Málaga’s Institute of Geomorphology and Soils in Spain. The current rate is unsustainable and could actually harm vineyards there. A few simple changes, like leaving grass between rows of vines as well as planting hedges around vineyards and vegetation along rivers and streams, might help prosecco vineyards reduce their soil loss, scientists suggest.
On the rise Deaths involving a type of antianxiety medication rose 830 percent from 1999 to 2017 in U.S. women ages 30 to 64, Aimee Cunningham reported in “Overdose deaths tied to antianxiety drugs like Xanax continue to rise” (SN: 2/16/19, p. 12).
Reader Dan Furtado asked if benzodiazepines alone cause overdose deaths. He thought that the drugs, such as Xanax and Valium, could cause an overdose only if a person had additional medical issues or combined the drugs with opioids or similar substances.
“An overdose of benzodiazepines alone can cause death,” Cunningham says. “The drugs depress the central nervous system, so a person who overdoses can stop breathing. But overdose deaths are more likely to happen when benzodiazepines are taken with opioids or alcohol,” she says.
Just beyond the tip of the Antarctic Peninsula lies an iceberg graveyard.
There, in the Scotia Sea, many of the icebergs escaping from Antarctica begin to melt, depositing sediment from the continent that had been trapped in the ice onto the seafloor. Now, a team of researchers has embarked on a two-month expedition to excavate the deposited debris, hoping to discover secrets from the southernmost continent’s climatic past.
That hitchhiking sediment, the researchers say, can help piece together how Antarctica’s vast ice sheet has waxed and waned over millennia. And knowing how much the ice melted in some of those warmest periods, such as the Pliocene Epoch about 3 million years ago, may provide clues to the ice sheet’s future. That includes how quickly the ice may melt in today’s warming world and by how much, says paleoclimatologist Michael Weber of the University of Bonn in Germany. Weber and Maureen Raymo, a paleoclimatologist at Lamont-Doherty Earth Observatory in Palisades, N.Y., are leading the expedition, which set sail on March 25.
“By looking at material carried by icebergs that calved off of the continent, we should be able to infer which sectors of the ice sheet were most unstable in the past,” Raymo says. “We can correlate the age and mineralogy of the ice-rafted debris to the bedrock in the section of Antarctica from which the bergs originated.” Icebergs breaking off from the edges of Antarctica’s ice sheet tend to stay close to the continent, floating counterclockwise around the continent. But when the bergs reach the Weddell Sea, on the eastern side of the peninsula, they are shunted northward through a region known as Iceberg Alley toward warmer waters in the Scotia Sea.
Because so many icebergs from all around the continent converge in one region, it is the ideal place to collect sediment cores and take stock of the debris that the bergs have dropped over millions of years.
“That area in the Scotia Sea is so exciting, because it’s a focus point between South America and the Antarctic Peninsula where the currents flow through, and there are a lot of icebergs,” says Gerhard Kuhn, a marine geologist at the Alfred Wegener Institute in Bremerhaven, Germany. “You get a picture of more or less [all of] Antarctica in that area,” says Kuhn, who has studied the region but is not aboard the current cruise. The expedition, known as leg 382 of the International Ocean Discovery Program, plans to drill at six different sites in the Scotia Sea. At three sites, the team plans to penetrate about 600 meters into the seafloor. “That would likely bring us back to the mid-Miocene, which could translate into 12 million to 18 million years back in time,” Weber says.
At another site, the team plans to drill even deeper, 900 meters, to go further back in time, in hopes of finding sediments that date to the opening of the Drake Passage about 41 million years ago. That passage, a body of water that now lies between South America and Antarctica, opened a link between the Atlantic and Pacific oceans and may have played a role in building up Antarctica’s ice sheets at different times in its history.
A graveyard turned crystal ball How much a melting Antarctica might have contributed to global sea-level rise following the last great ice age, which ended about 19,000 years ago, has been a subject of debate. Seas rose by about 130 meters from 19,000 to 8,000 years ago, Weber says, and much of the melting happened in the northern hemisphere.
But Antarctica may have played a larger role than once thought. In a study published in Nature in 2014, Kuhn, Weber and other colleagues reported that ice-rafted debris from that time period, as recorded in relatively short sediment cores from Iceberg Alley, often occurred in large pulses lasting a few centuries to millennia. Those data suggested that the southernmost continent was shedding lots of bergs much more quickly during those times than once thought.
Now, the researchers want to see even further into the past, to understand how quickly Antarctica’s ice sheet might have melted during even warmer periods, and how much it may have contributed to episodes of past sea-level rise.
The new drilling expedition targets several periods when the climate is thought to have warmed dramatically. One is a warm period in the middle Pliocene about 3.3 million to 3 million years ago, when average global temperatures were 2 to 3 degrees warmer than today; another is the ending of an older ice age about 130,000 years ago, when sea levels rose by about 5 to 9 meters.
Such periods may serve as analogs to the continent’s future behavior due to anthropogenic global warming. Currently, global average temperatures on Earth are projected to increase by between about 1.5 degrees and 4 degrees Celsius relative to preindustrial times, depending on greenhouse gas emissions to the atmosphere over the next few decades (SN: 10/22/18, p. 18).
“The existing [ice core] record from Iceberg Alley taught us Antarctica lost ice through a threshold reaction,” Weber says. That means that when the continent reached a certain transition point, there was sudden and massive ice loss rather than just a slow, gradual melt.
“We have rather firm evidence that this threshold is passed once the ice sheet loses contact with the underlying ocean floor,” he says, adding that at that point, the shedding of ice becomes self-sustaining, and can go on for centuries. “With mounting evidence of recent ice-mass loss in many sectors of West Antarctica of a similar fashion, we need to be concerned that a new ice-mass loss event is already underway, and there is no stopping it.”
A world-spanning network of telescopes called the Event Horizon Telescope zoomed in on the supermassive monster in the galaxy M87 to create this first-ever picture of a black hole.
“We have seen what we thought was unseeable. We have seen and taken a picture of a black hole,” Sheperd Doeleman, EHT Director and astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., said April 10 in Washington, D.C., at one of seven concurrent news conferences. The results were also published in six papers in the Astrophysical Journal Letters.
“We’ve been studying black holes so long, sometimes it’s easy to forget that none of us have actually seen one,” France Córdova, director of the National Science Foundation, said in the Washington, D.C., news conference. Seeing one “is a Herculean task,” she said. That’s because black holes are notoriously hard to see. Their gravity is so extreme that nothing, not even light, can escape across the boundary at a black hole’s edge, known as the event horizon. But some black holes, especially supermassive ones dwelling in galaxies’ centers, stand out by voraciously accreting bright disks of gas and other material. The EHT image reveals the shadow of M87’s black hole on its accretion disk. Appearing as a fuzzy, asymmetrical ring, it unveils for the first time a dark abyss of one of the universe’s most mysterious objects.
“It’s been such a buildup,” Doeleman said. “It was just astonishment and wonder… to know that you’ve uncovered a part of the universe that was off limits to us.”
The much-anticipated big reveal of the image “lives up to the hype, that’s for sure,” says Yale University astrophysicist Priyamvada Natarajan, who is not on the EHT team. “It really brings home how fortunate we are as a species at this particular time, with the capacity of the human mind to comprehend the universe, to have built all the science and technology to make it happen.” (SN Online: 4/10/19)
The image aligns with expectations of what a black hole should look like based on Einstein’s general theory of relativity, which predicts how spacetime is warped by the extreme mass of a black hole. The picture is “one more strong piece of evidence supporting the existence of black holes. And that, of course, helps verify general relativity,” says physicist Clifford Will of the University of Florida in Gainesville who is not on the EHT team. “Being able to actually see this shadow and to detect it is a tremendous first step.”
Earlier studies have tested general relativity by looking at the motions of stars (SN: 8/18/18, p. 12) or gas clouds (SN: 11/24/18, p. 16) near a black hole, but never at its edge. “It’s as good as it gets,” Will says. Tiptoe any closer and you’d be inside the black hole — unable to report back on the results of any experiments. “Black hole environments are a likely place where general relativity would break down,” says EHT team member Feryal Özel, an astrophysicist at the University of Arizona in Tucson. So testing general relativity in such extreme conditions could reveal deviations from Einstein’s predictions.
Just because this first image upholds general relativity “doesn’t mean general relativity is completely fine,” she says. Many physicists think that general relativity won’t be the last word on gravity because it’s incompatible with another essential physics theory, quantum mechanics, which describes physics on very small scales. The image also provides a new measurement of the black hole’s size and heft. “Our mass determination by just directly looking at the shadow has helped resolve a longstanding controversy,” Sera Markoff, a theoretical astrophysicist at the University of Amsterdam, said in the Washington, D.C., news conference. Estimates made using different techniques have ranged between 3.5 billion and 7.22 billion times the mass of the sun. But the new EHT measurements show that its mass is about 6.5 billion solar masses.
The team has also determined the behemoth’s size — its diameter stretches 38 billion kilometers — and that the black hole spins clockwise. “M87 is a monster even by supermassive black hole standards,” Markoff said.
EHT trained its sights on both M87’s black hole and Sagittarius A, the supermassive black hole at the center of the Milky Way. But, it turns out, it was easier to image M87’s monster. That black hole is 55 million light-years from Earth in the constellation Virgo, about 2,000 times as far as Sgr A. But it’s also about 1,000 times as massive as the Milky Way’s giant, which weighs the equivalent of roughly 4 million suns. That extra heft nearly balances out M87’s distance. “The size in the sky is pretty darn similar,” says EHT team member Feryal Özel. Due to its gravitational oomph, gases swirling around M87’s black hole move and vary in brightness more slowly than they do around the Milky Way’s. “During a single observation, Sgr A* doesn’t sit still, whereas M87 does,” says Özel, an astrophysicist at the University of Arizona in Tucson. “Just based on this ‘Does the black hole sit still and pose for me?’ point of view, we knew M87 would cooperate more.”
After more data analysis, the team hopes to solve some long-standing mysteries about black holes, such as how M87’s behemoth spews a bright jet of charged particles thousands of light-years into space.
This first image is like the “shot heard round the world” that kicked off the American Revolutionary War, says Harvard University astrophysicist Avi Loeb who isn’t on the EHT team. “It’s very significant; it gives a glimpse of what the future might hold, but it doesn’t give us all the information that we want.” Hopes are still high for a much-anticipated glimpse of Sgr A*. The EHT team was able to collect some data on the Milky Way’s behemoth and are continuing to analyze that data, in the hopes of adding its image to the new black hole portrait gallery.
Since the appearance of that black hole changes so quickly, the team is having to develop new techniques to analyze the data. “We’re very excited to work on Sgr A*,” Daniel Marrone, an astrophysicist at the University of Arizona in Tucson, said in the Washington, D.C., news conference. “We’re doing that shortly. We’re not promising anything but we hope to get that very soon.”
Studying such different environments could reveal more details of how black holes behave, Loeb says. “The Milky Way is a very different galaxy from M87.” The next look at the M87 and Milky Way behemoths will have to wait.
Scientists got a lucky stretch of good weather at all eight sites that made up the Event Horizon Telescope in 2017. Then bad weather in 2018 and technical difficulties, which cancelled the 2019 observing run, stymied the team.
The good news is that by 2020, there will be more observatories to work with. The Greenland Telescope joined the consortium in 2018, and the Kitt Peak National Observatory outside Tucson, Ariz., and the NOrthern Extended Millimeter Array (NOEMA) in the French Alps will join EHT in 2020.
Adding more telescopes could allow the team to extend the image, to better capture the jets that spew from the black hole. The researchers also plan to make observations using light of slightly higher frequency, which can further sharpen the image. And even bigger plans are on the horizon: “World domination is not enough for us; we also want to go to space,” Doeleman said.
These extra eyes may be just what’s needed to bring black holes into even greater focus.
