Every few years, for a handful of minutes or so, science shines while the sun goes dark.

A total eclipse of the sun is, for those who witness it, something like a religious experience. For those who understand it, it is symbolic of science’s triumph over mythology as a way to understand the heavens.

In ancient Greece, the pioneer philosophers realized that eclipses illustrate how fantastic phenomena do not require phantasmagoric explanation. An eclipse was not magic or illusion; it happened naturally when one celestial body got in the way of another one. In the fourth century B.C., Aristotle argued that lunar eclipses provided strong evidence that the Earth was itself a sphere (not flat as some primitive philosophers had believed). As the eclipsed moon darkened, the edge of the advancing shadow was a curved line, demonstrating the curvature of the Earth’s surface intervening between the moon and sun.

Oft-repeated legend proclaims that the first famous Greek natural philosopher, Thales of Miletus, even predicted a solar eclipse that occurred in Turkey in 585 B.C. But the only account of that prediction comes from the historian Herodotus, writing more than a century later. He claimed that during a fierce battle “day suddenly became night,” just as Thales had forecast would happen sometime during that year.

There was an eclipse in 585 B.C., but it’s unlikely that Thales could have predicted it. He might have known that the moon blocks the sun in an eclipse. But no mathematical methods then available would have allowed him to say when — except, perhaps, a lucky coincidence based on the possibility that solar eclipses occurred at some regular cycle after lunar eclipses. Yet even that seems unlikely, a new analysis posted online last month finds.

“Some scholars … have flatly denied the prediction, while others have struggled to find a numerical cycle by means of which the prediction could have been carried out,” writes astronomer Miguel Querejeta. Many such cycles have already been ruled out, he notes. And his assessment of two other cycles concludes “that none of those conjectures can be regarded as serious explanations of the problematic prediction of Thales: in addition to requiring the existence of long and precise eclipse records … both cycles that have been examined overlook a number of eclipses which match the visibility criteria and, consequently, the patterns suggested seem to disappear.”

It’s true that the ancient Babylonians worked out methods for predicting lunar eclipses based on patterns in the intervals between them. And the famous Greek Antikythera mechanism from the second century B.C. seems to have used such cycle data to predict some eclipses.

Ancient Greek astronomers, such as Hipparchus (c. 190–120 B.C.), studied eclipses and the geometrical relationships of the Earth, moon and sun that made them possible. Understanding those relationships well enough to make reasonably accurate predictions became possible, though, only with the elaborate mathematical description of the cosmos developed (drawing on Hipparchus’ work) by Claudius Ptolemy. In the second century A.D., he worked out the math for explaining the movements of heavenly bodies, assuming the Earth sat motionless in the center of the universe.

His system specified the basic requirements for a solar eclipse: It must be the time of the new moon — when moon and sun are on the same side of the Earth — and the positions of their orbits must also be crossing the ecliptic, the plane of the sun’s apparent orbital path through the sky. (The moon orbits the Earth at a slight angle, crossing the plane of the ecliptic twice a month.) Only precise calculations of the movements of the sun and moon in their orbits could make it possible to predict the dates for eclipsing alignments.

Predicting when an eclipse will occur is not quite the same as forecasting exactly where it will occur. To be accurate, eclipse predictions need to take subtle gravitational interactions into account. Maps showing precisely accurate paths of totality (such as for the Great American Eclipse of 2017) became possible only with Isaac Newton’s 17th century law of gravity (and the further development of mathematical tools to exploit it). Nevertheless Ptolemy had developed a system that, in principle, showed how to anticipate when eclipses would happen. Curiously, though, this success was based on a seriously wrong blueprint for the architecture of the cosmos.

As Copernicus persuasively demonstrated in the 16th century, the Earth orbits the sun, not vice versa. Ptolemy’s geometry may have been sound, but his physics was backwards. While demonstrating that mathematics is essential to describing nature and predicting physical phenomena, he inadvertently showed that math can be successful without being right.

It’s wrong to blame him for that, though. In ancient times math and science were separate enterprises (science was then “natural philosophy”). Astronomy was regarded as math, not philosophy. An astronomer’s goal was to “save the phenomena” — to describe nature correctly with math that corresponded with observations, but not to seek the underlying physical causes of those observations. Ptolemy’s mathematical treatise, the Almagest, was about math, not physics.

One of the great accomplishments of Copernicus was to merge the math with the physical realty of his system. He argued that the sun occupied the center of the cosmos, and that the Earth was a planet, like the others previously supposed to have orbited the Earth. Copernicus worked out the math for a sun-centered planetary system. It was a simpler system than Ptolemy’s. And it was just as good for predicting eclipses.

As it turned out, though, even Copernicus didn’t have it quite right. He insisted that planetary orbits were circular (modified by secondary circles, the epicycles). In fact, the orbits are ellipses. It’s a recurring story in science that mathematically successful theories sometimes are just approximately correct because they are based on faulty understanding of the underlying physics. Even Newton’s law of gravity turned out to be just a good mathematical explanation; the absolute space and invariable flow of time he believed in just aren’t an accurate representation of the universe we live in. It took Einstein to see that and develop the view of gravity as the curvature of spacetime induced by the presence of mass.
Of course, proving Einstein right required the careful measurement by Arthur Eddington and colleagues of starlight bending near the sun during a solar eclipse in 1919. It’s a good thing they knew when and where to go to see it.

Scientists have created the largest map of dark matter yet, part of a slew of new measurements that help pin down the universe’s dark contents. Covering about a thirtieth of the sky, the map (above) charts the density of both normal matter — the stuff that’s visible — and dark matter, an unidentified but far more abundant substance that pervades the cosmos.

Matter of both types is gravitationally attracted to other matter. That coupling organizes the universe into more empty regions of space (No. 1 below and blue in the map above) surrounded by dense cosmic neighborhoods (No. 2 below and red in the map above).
Researchers from the Dark Energy Survey used the Victor Blanco telescope in Chile to survey 26 million galaxies in a section of the southern sky for subtle distortions caused by the gravitational heft of both dark and normal matter. Scientists unveiled the new results August 3 at Fermilab in Batavia, Ill., during a meeting of the American Physical Society.

Dark matter is also accompanied by a stealthy companion, dark energy, an unseen force that is driving the universe to expand at an increasing clip. According to the new inventory, the universe is about 21 percent dark matter and 5 percent ordinary matter. The remainder, 74 percent, is dark energy.

The new measurements differ slightly from previous estimates based on the cosmic microwave background, light that dates back to 380,000 years after the Big Bang (SN: 3/21/15, p. 7). But the figures are consistent when measurement errors are taken into account, the researchers say.
“The fact that it’s really close, we think is pretty remarkable,” says cosmologist Josh Frieman of Fermilab, who directs the Dark Energy Survey. But if the estimates don’t continue to align as the survey collects more data, something might be missing in cosmologists’ theories of the universe.

A new genetics study adds fuel to the debate about muscle aches that have been reported by many people taking popular cholesterol-lowering drugs called statins.

About 60 percent of people of European descent carry a genetic variant that may make them more susceptible to muscle aches in general. But counterintuitively, these people had a lower risk of muscle pain when they took statins compared with placebos, researchers report August 29 in the European Heart Journal.
Millions of people take statins to lower cholesterol and fend off the hardening of arteries. But up to 78 percent of patients stop taking the medicine. One common reason for ceasing the drugs’ use is side effects, especially muscle pain, says John Guyton, a clinical lipidologist at Duke University School of Medicine.

It has been unclear, however, whether statins are to blame for the pain. In one study, 43 percent of patients who had muscle aches while taking at least one type of statin were also pained by other types of statin (SN: 5/13/17, p. 22). But 37 percent of muscle-ache sufferers in that study had pain not related to statin use. Other clinical trials have found no difference in muscle aches between people taking statins and those not taking the drugs.

The new study hints that genetic factors, especially ones involved in the immune system’s maintenance and repair of muscles, may affect people’s reactions to statins. “This is a major advance in our understanding about myalgia,” or muscle pain, says Guyton, who was not involved in the study.

People with two copies of the common form of the gene LILRB5 tend to have higher-than-usual blood levels of two proteins released by injured muscles, creatine phosphokinase and lactate dehydrogenase. Higher levels of those proteins may predispose people to more aches and pains. In an examination of data from several studies involving white Europeans, people with dual copies of the common variant were nearly twice as likely to have achy muscles while taking statins as people with a less common variant, Moneeza Siddiqui of the University of Dundee School of Medicine in Scotland and colleagues discovered.

But when researchers examined who had pain when taking statins versus placebos, those with two copies of the common variant seemed to be protected from getting statin-associated muscle pain. Why is not clear.
People with double copies of the common form of the gene who experience muscle pain may stop taking statins because they erroneously think the drugs are causing the pain, study coauthor Colin Palmer of the University of Dundee said in a news release.

The less common version of the gene is linked to reduced levels of the muscle-damage proteins, and should protect against myalgia. Yet people with this version of the gene were the ones more likely to develop muscle pain specifically linked to taking statins during the trials.

The finding suggests that when people with the less common variant develop muscle pain while taking statins, the effect really is from the drugs, the researchers say.

But researchers still don’t know the nitty-gritty details of how the genetic variants promote or protect against myalgia while on statins. Neither version of the gene guarantees that a patient will develop side effects — or that they won’t. The team proposes further clinical trials to unravel interactions between the gene and the drugs.

More study is needed before doctors can add the gene to the list of tests patients get, Guyton says. “I don’t think we’re ready to put this genetic screen into clinical practice at all,” he says. For now, “it’s much easier just to give the patient the statin” and see what happens.

Patience is a virtue in the hunt for dark matter. Experiment after experiment has come up empty in the search — and the newest crop is no exception.

Observations hint at the presence of an unknown kind of matter sprinkled throughout the cosmos. Several experiments are focused on the search for one likely dark matter candidate: weakly interacting massive particles, or WIMPs (SN: 11/12/16, p. 14). But those particles have yet to be spotted.

Recent results, posted at arXiv.org, continue the trend. The PandaX-II experiment, based in China, found no hint of the particles, scientists reported August 23. The XENON1T experiment in Italy also came up WIMPless according to a May 18 paper. Scientists with the DEAP-3600 experiment in Sudbury, Canada, reported their first results on July 25. Signs of dark matter? Nada. And the SuperCDMS experiment in the Soudan mine in Minnesota likewise found no hints of WIMPs, scientists reported August 29.

Another experiment, PICO-60, also located in Sudbury, reported its contribution to the smorgasbord of negative results June 23 in Physical Review Letters.

Scientists haven’t given up hope. Researchers are building ever-larger detectors, retooling their experiments and continuing to expand the search beyond WIMPs.

A single genetic mutation made the Zika virus far more dangerous by enhancing its ability to kill nerve cells in developing brains, a new study suggests.

The small change — which tweaks just one amino acid in a protein that helps Zika exit cells — may cause microcephaly, researchers report September 28 in Science. The mutation arose around May 2013, shortly before a Zika outbreak in French Polynesia, the researchers calculate.

Zika virus was discovered decades ago but wasn’t associated with microcephaly — a birth defect characterized by a small head and brain — until the 2015–2016 outbreak in Brazil. Women who had contracted the virus while pregnant started giving birth to babies with the condition at higher-than-usual rates (SN: 4/2/16, p. 26).
Researchers weren’t sure why microcephaly suddenly became a complication of Zika infections, says Pei-Yong Shi, a virologist at the University of Texas Medical Branch at Galveston. Maybe the virus did cause microcephaly before, scientists suggested, but at such low rates that no one noticed. Or people in South America might be more vulnerable to the virus. Perhaps their immune systems don’t know how to fight it, they have a genetic susceptibility or prior infections with dengue made Zika worse (SN: 4/29/17, p. 14). But Shi and colleagues in China thought the problem might be linked to changes in the virus itself.
The researchers compared a strain of Zika isolated from a patient in Cambodia in 2010 with three Zika strains collected from patients who contracted the virus in Venezuela, Samoa and Martinique during the epidemic of 2015–2016. The team found seven differences between the Cambodian virus and the three epidemic strains.

Researchers engineered seven versions of the Cambodian virus, each with one of the epidemic strains’ mutations, and injected the viruses into fetal mouse brains. Viruses with one of these mutations, dubbed S139N, killed brain cells in fetal mice and destroyed human brain cells grown in lab dishes more aggressively than the Cambodian strain from 2010 did, the researchers found.
“That’s pretty convincing evidence that it at least plays some role in what we’re seeing now,” says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

The mutation changes an amino acid in a Zika protein called prM. That protein helps the virus mature within infected cells and get out of the cells to infect others. Shi and colleagues don’t yet know why tweaking the protein makes the virus kill brain cells more readily.

The alteration in that protein probably isn’t the entire reason epidemic strains cause microcephaly, Shi says. The Cambodian strain also led to the death of a few brain cells, but perhaps not enough to cause microcephaly. “We believe there are other changes in the virus that collectively enhance its virulence,” he says. In May in Nature, Shi and colleagues described a different mutation that allows the virus to infect mosquitoes more effectively.

Brain cells from different people vary in their susceptibility to Zika infections, says infectious disease researcher Scott Weaver, also at the University of Texas Medical Branch but not involved in the study. He says more work on human cells and in nonhuman primates is needed to confirm whether this mutation is really the culprit in microcephaly.

Immigrants, they get the job done — eventually. Among dwarf mongooses, it takes newcomers a bit to settle into a pack. But once these immigrants become established residents, everyone in the pack profits, researchers from the University of Bristol in England report online December 4 in Current Biology.

Dwarf mongooses (Helogale parvula) live in groups of around 10, with a pecking order. The alphas — a top male and female — get breeding priority, while the others help with such group activities as babysitting and guard duty. But the road to the top of the social hierarchy is linear and sometimes crowded. So some individuals skip out on the group they were born into to find one with fewer members of their sex with which to compete —“effectively ‘skipping the queue,’” says ecologist Julie Kern.
Kern and her colleague Andrew Radford tracked mongoose immigration among nine packs at Sorabi Rock Lodge Reserve in Limpopo, South Africa. The researchers focused on guard duty, in which sentinels watch for predators and warn foragers digging for food.

Dwarf mongoose packs gain about one member a year. Among pack animals, higher group numbers are thought to come with the benefit of better access to shared social information like the approach of prowling predators. But upon arrival, new individuals are less likely to pitch in and serve as sentinels, Kern and Radford found. One possible reason: Immigrants lose weight during their transition from one pack to another and may not have the energy required for guard duty.
Pack residents don’t exactly put out a welcome mat for strangers, either. On the rare occasions when newcomers take a guard shift, residents tend to ignore their warning calls. Newbies may be seen as less reliable guards, or packs may have signature alarm calls that immigrants must learn. But after five months, these immigrants have come far. “Given time to recuperate following dispersal and a period of integration,” Kern says, “they contribute equally to their new group.”

Science came out of the lab and touched people’s lives in some awe-inspiring and alarming ways in 2017. Science enthusiasts gathered to celebrate a total solar eclipse, but also to march on behalf of evidence-based policy making. Meanwhile, deadly natural disasters revealed the strengths and limitations of science. Here’s a closer look at some of the top science events of the year.

Great American Eclipse
On August 21, many Americans witnessed their first total solar eclipse, dubbed the “Great American Eclipse.” Its path of totality stretched across the United States, passing through 14 states — with other states seeing a partial eclipse. This was the first total solar eclipse visible from the mainland United States since 1979, and the first to pass from coast to coast since 1918 (SN: 8/20/16, p. 14).
As people donned protective glasses to watch, scientists used telescopes, spectrometers, radio receivers and even cameras aboard balloons and research jets in hopes of answering lingering questions about the sun, Earth’s atmosphere and the solar system. One of the biggest: Why is the solar atmosphere so much hotter than the sun’s surface (SN Online: 8/20/17)? Data collected during the event may soon provide new insights.

March for Science
On April 22, Earth Day, more than 1 million people in over 600 cities around the world marched to defend science’s role in society. Called the first-ever March for Science, the main event was in Washington, D.C. Featured speakers included Denis Hayes, coordinator of the first Earth Day in 1970, and science advocate Bill Nye (SN Online: 4/22/17). Attendees advocated for government funding for scientific research and acceptance of the scientific evidence on climate change.

The march came on the heels of the Trump administration’s first budget proposal, released in March, which called for cutting federal science spending in fiscal year 2018 (SN: 4/15/17, p. 15). Some scientists worried that being involved with the march painted science in a partisan light, but others said science has always been political since scientists are people with their own values and opinions (SN Online: 4/19/17).

Climate deal announcement
On June 1, President Donald Trump announced that the United States would pull out of the Paris climate accord (SN Online: 6/1/17) — an agreement the United States and nearly 200 other countries signed in 2015 pledging to curb greenhouse gas emissions to combat global warming. With the announcement, Trump made good on one of his campaign promises. He said during a news conference that the agreement “is less about the climate and more about other countries gaining a financial advantage over the United States.”

Nicaragua and Syria signed on to the agreement in late 2017. A withdrawal from the United States would leave it as the only United Nations–recognized country to reject the global pact. President Trump left the door open for the United States to stay in the climate deal under revised terms. A U.S. climate assessment released in November by 13 federal agencies said it is “extremely likely” that humans are driving warming on Earth (SN Online: 11/3/17). Whether that report — the final version of which is due to be released in 2018 — will have an impact on U.S. involvement in the global accord remains to be seen.

North Korea nuclear test
On September 3, North Korea reported testing a hydrogen bomb, its sixth confirmed nuclear detonation, within a mountain at Punggye-ri. That test, along with the launch of intercontinental ballistic missiles this year, increased hostilities between North Korea and other nations, raising fears of nuclear war. As a result of these tests, the United Nations Security Council passed a resolution strengthening sanctions against North Korea to discourage the country from more nuclear testing.

As the international community waits to see what’s next, scientists continue to study the seismic waves that result from underground explosions in North Korea. These studies can help reveal the location, depth and strength of a blast (SN: 8/5/17, p. 18).

Natural disasters
The 2017 Atlantic hurricane season saw hurricanes Harvey, Irma and Maria devastate areas of Texas, Florida and the Caribbean. More than 200 people died from these three massive storms, and preliminary estimates of damage are as high as hundreds of billions of dollars. The National Oceanic and Atmospheric Administration had predicted that the 2017 season could be extreme, thanks to above-normal sea surface temperatures. The storms offered scientists an opportunity to test new technologies that might save lives by improving forecasting (SN Online: 9/21/17) and by determining the severity of flooding in affected regions (SN Online: 9/12/17).

In addition to these deadly storms, two major earthquakes rocked Mexico in September, killing more than 400 people. More than 500 died when a magnitude 7.3 earthquake shook Iran and Iraq in November. And wildfires raged across the western United States in late summer and fall. In California, fires spread quickly thanks to record summer heat and high winds. At least 40 people died and many more were hospitalized in California’s October fires. Rising global temperatures and worsening droughts are making wildfire seasons worldwide last longer on average than in the past, researchers have found (SN Online: 7/15/15).

Not so long ago, the lives of sea turtles were largely a mystery. From the time that hatchlings left the beaches where they were born to waddle into the ocean until females returned to lay their eggs, no one really knew where the turtles went or what they did.

Then researchers started attaching satellite trackers to young turtles. And that’s when scientists discovered that the turtles aren’t just passive ocean drifters; they actively swim at least some of the time.
Now scientists have used tracking technology to get some clues about where South Atlantic loggerhead turtles go. And it turns out that those turtles are traveling to some unexpected places.

Katherine Mansfield, a marine scientist and turtle biologist at the University of Central Florida in Orlando, and colleagues put 19 solar-powered satellite tags on young (less than a year old), lab-reared loggerhead sea turtles. The turtles were then let loose into the ocean off the coast of Brazil at various times during the hatching season, between November 2011 and April 2012.

The tags get applied to the turtles in several steps. Turtle shells are made of keratin, like your fingernails, and this flakes off and changes shape as a turtle grows. Mansfield’s team had figured out, thanks to a handy tip from a manicurist, that a base layer of manicure acrylic deals with the flaking. And then some strips of neoprene along with aquarium silicone attach the tag to the shell. With all that prep, the tag can stay on for months. The tags transmit while a turtle is at the water’s surface. A loss of the signal indicates that either the tag has fallen off and sunken into the water, “or something ate the turtle,” Mansfield says.
The trackers revealed that not all Brazilian loggerhead sea turtles stay in the South Atlantic. Turtles released in the early- to mid-hatching season stay in southern waters. But then the off-coast currents change direction, which brings later-season turtles north, across the equator. Their trajectories could take them as far as the Caribbean, the Gulf of Mexico or even farther north, which would explain genetic evidence of mixing between southern and northern loggerhead populations. And it may help to make the species, which is endangered, more resilient in the face of environmental and human threats, the researchers conclude December 6 in the Proceedings of the Royal Society B.

But, Mansfield cautions, “these are just a handful of satellite tracks for a handful of turtles off the coast of Brazil.” She and other scientists “are just starting to build a story” about what happens to these turtles out in the ocean. “There’s still so much we don’t know,” she says.

Mansfield hopes the tracking data will help researchers figure out where the young turtles can be found out in the open ocean so scientists can catch, tag and track wild turtles. And there’s a need for even tinier tags that can be attached to newly hatched turtles to see exactly where they go and how many actually survive those first vulnerable weeks and months at sea. Eventually, Mansfield would like to have enough data to make comparisons between sea turtle species.

“The more we’re tracking, the more we’re studying them, we’re starting to realize [the turtles] behave differently than we’ve historically assumed,” Mansfield says.

It’s like having “an elephant stand on your thumb.”

That’s how deep-sea physiologist and ecologist Mackenzie Gerringer describes the pressure squeezing down on the deepest known living fish, some 8 kilometers down. What may help these small, pale Mariana snailfish survive elephantine squashing, says Gerringer of the University of Washington’s Friday Harbor Labs, is a body bulked up, especially at the rump, with a watery goo.

The snailfish family gets its nickname from the way some shallow-water species in thundering tides grip a rock with a little suction cup on the belly and curl up. “Quite cute,” Gerringer says, and maybe, if you squint, somewhat like a snail.
She and colleagues discovered the deepest fish in 2014 in the western Pacific Ocean’s Mariana Trench and described the newly named Psuedoliparis swirei November 28 in Zootaxa. To catch specimens, Gerringer and colleagues turned to extreme trapping. They weighted a boxy, mesh-sided trap with steel plates to sink it. It took about four hours to fall to the bottom.

The scientists baited traps with mackerel, which snailfish don’t eat. But the fish do eat the underwater amphipods that mob a mackerel feast. Remotely related to harmless garden pill bugs, trench amphipods clean mackerel to the bones, Gerringer says. “I certainly wouldn’t swallow a live amphipod after seeing what they can do.” A snailfish, however, has a second set of jaws at the back of its throat that render crustaceans safe to swallow.

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For animals that live in such extreme pressures and temperatures (1° or 2° Celsius), snailfish don’t “look very robust … or very armored,” she says. “You can actually see the brain through the skull.”

Skimping on dense muscles and bones may improve snailfish buoyancy and save energy. These fish also lack air pockets that give a little lift to some other fishes, but that would get squashed to nothing so far down. Instead, the snailfish have inner deposits of a watery goo, more buoyant than muscles and bones and less compressible than air.

The goo also may aid swimming efficiency by offering a cheap shape improvement, Gerringer and colleagues proposed December 6 in Royal Society Open Science. To test the idea, she 3-D printed and motorized a robo-snailfish. Easier than catching a real one, Gerringer says.

A latex sleeve around the robot tail let her add or subtract water as an approximation of the gelatinous tissue. With an empty sleeve, the wide fish body pinches in to a thin tail, inviting vortices that cause drag. With this abrupt narrowing, robo-swimming proved a struggle. Filling the tail-sleeve to create a tapering rear let the robo-snailfish swim faster.

This goo is cheap tissue to grow, Gerringer says. It’s mostly water, one thing a fish living underneath eight kilometers of ocean has in abundance.

OXON HILL, Md. — Fast radio bursts could come from a turbulent home. At least one source of these bright, brief blasts of radio energy may be a young neutron star assisted by a nearby massive black hole, new research suggests.

“The biggest mystery around fast radio bursts is how such powerful and short-duration bursts are emitted,” says astronomer Daniele Michilli of the University of Amsterdam. The latest observations, reported online January 10 in Nature and at a meeting of the American Astronomical Society, suggest the bursts are coming from an environment with an unusually strong magnetic field. That field leaves a signature mark on the radio waves, twisting them into spirals, Michilli and his colleagues report.
Only a few fast radio bursts have ever been detected, and most appear as one-off events. Few known processes in the universe can explain them. But one burst, FRB 121102, has been seen repeating over the past decade or so (SN Online: 12/21/16). That repetition let astronomers follow up on the burst, and track it to a dwarf galaxy some 2.5 billion light-years away (SN: 2/4/17, p. 10).

Now, Michilli and his colleagues have used the Arecibo radio telescope in Puerto Rico to show that the burst’s source is embedded in an extremely strong magnetic field, 200 times stronger than the average magnetic field in the Milky Way.

The team measured the radio waves from 16 distinct bursts over three two-hour observational runs spanning several months. The bursts were exceptionally brief, the shortest lasting just 30 microseconds. That means that whatever emitted it must be just 10 kilometers wide, Michilli says.

“To emit a short burst you need a small region,” he says. “Therefore compact objects such as neutron stars are strongly favored by this result.”
The team also analyzed the radio waves in a new way, revealing that what looked like individual bursts were actually composed of many smaller sub-bursts, says astronomer Andrew Seymour of the Universities Space Research Association at Arecibo. That complicates the picture even further. The sub-bursts might be intrinsic to the object that creates them, or they might be the result of the waves passing through blobs of plasma, he says.

Finally, the observations showed that the waves were polarized, all oriented in the same direction. But something had twisted the waves, forcing them to rotate in corkscrews on their way from the dwarf galaxy to Earth. Follow-up observations with the Green Bank Telescope in West Virginia confirmed the twists were really there.

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The only phenomenon that is known to create such a rotation is a strong magnetic field, Michilli says. There are two main hypotheses for the bursts’ behavior. One is that they are from a young, energetic neutron star called a magnetar that’s sitting inside a shell of magnetized gas, which the magnetar itself expelled in a supernova explosion. The magnetar emits radio waves, and the shell makes them rotate.

“If you have young magnetars that have just been born in supernova explosions, only a few decades old, they could be very bursty objects, have very violent youths, and that could give rise to repeating fast radio bursts,” says astronomer Brian Metzger of Columbia University, who was not involved in the new study.

But Michilli points out that in order to drive such strong magnetic fields, the supernova remnant would have to be a million times brighter than even the brightest remnant in the Milky Way, the Crab nebula (SN: 1/1/11, p. 11). Instead, the bursts could come from a young neutron star orbiting the dwarf galaxy’s dominant black hole, which probably has between 10,000 and 1 million times the mass of the sun, he says.

Such large black holes are already known to have strong magnetic fields and to make polarized light rotate. And a neutron star nestling up next to a black hole is a plausible setup: There’s one orbiting the supermassive black hole at the center of the Milky Way. Although this neutron star’s radio waves don’t come in brief bright bursts, they are also twisted, the researchers say.

If not for that neutron star, “this would seem very contrived to me,” Metzger says. “That combines two unlikely things.”

More exotic explanations remain possible, too, Michilli’s team says.

“The joke is there are far more theories than there are observed bursts,” said coauthor Jason Hessels of the University of Amsterdam in a news conference January 10. “In the coming weeks we expect that very creative theorists will come up with explanations for our observations we haven’t thought of yet.”

Questions remain about whether all fast radio bursts, including the ones that don’t repeat, come from such exciting neighborhoods. “We cannot say yet if there are two classes with different properties, or if it’s one class of fast radio bursts and they just happen to be seen in different configurations,” Michilli says.

It’s also still unknown whether any other bursts have twisted waves at high frequencies — the smoking gun for strong magnetic fields. Measuring the rotation of the waves in FRB 121102 required hacking Arecibo with new hardware that let it detect higher frequencies than before. “We weren’t able to do that until recently,” Seymour says. “I stayed up on Christmas evening [2016] and made these observations, and luckily it paid off.” Maybe other fast radio bursts that Arecibo observed didn’t show the same rotation signature because the telescope wasn’t ready to measure it yet.

Hessels thinks “the prospects are quite good” for figuring out what fast radio bursts are in the near future. Several new radio observatories around the world are due to come online in the next few years. “These are going to be FRB factories,” Hessels said. He expects to find other repeating bursts, if they exist. “Then we can see if this repeating source is really a complete oddball, or part of a distribution of sources.”