Casting light on mystery of a star that vanished after 14 days
News and notes about science
Nearly six centuries ago, Korean astronomers scanning the night sky for omens of the future spotted a new star in the cluster of stars they called Wei, and what today’s star watchers consider the tail of the Scorpius constellation.
Fourteen nights later, it vanished.
Astronomers have now identified the source of that brief brightening — a binary star system a couple of thousand lightyears away.
Michael Shara, an astrophysicist at the American Museum of Natural History in New York, has been seeking to understand what happens following explosions in violent star systems known as “cataclysmic variables.” He has searched for the remnants of this particular event for a long time.
“Now, about 25 years later, we’ve finally come up with it,” Shara said. The researchers reported their findings Aug. 30 in the journal Nature.
In these systems, one of the stars is a white dwarf, the burned out but still hot remnant of a star. The powerful gravity of the white dwarf pulls hydrogen away from its companion star and onto its surface. “You accumulate about a Pacific Ocean’s worth of hydrogen,” Shara said.
With more and more hydrogen, the pressure builds until it sets off a thermonuclear explosion, a burst of light known as a nova that is up 1 million times as bright as the sun.
“You get a giant fusion bomb, a hydrogen bomb going off on top of this white dwarf star,” he said.
That is what the Koreans saw on March 11, 1437.
As powerful as nova explosions are, they do not destroy either star (unlike much larger supernovas). The white dwarf fades, and the cycle repeats until the next explosion, which could be up to 100,000 years later.
In recent decades, astronomers have observed the fading of novas over decades. They have also spotted similar binary star systems that appear quite stable, calmly orbiting each other, and others that are belching only small eruptions known as dwarf novas.
— Kenneth Chang
Hints of trigonometry on Babylonian tablet
Two Australian mathematicians assert that an ancient clay tablet was a tool for working out trigonometry problems, possibly adding to the many techniques that Babylonian mathematicians had mastered.
“It’s a trigonometric table, which is 3,000 years ahead of its time,” said Daniel F. Mansfield of the University of New South Wales. Mansfield and his colleague Norman J. Wildberger reported their findings Aug. 24 in the journal Historia Mathematica.the tablet, known as Plimpton 322, was discovered in the early 1900s in southern Iraq and has long been of interest to scholars. It contains 60 numbers organized into 15 rows and four columns inscribed on a piece of clay about 5 inches wide and 3.5 inches tall. It eventually entered the collection of George Arthur Plimpton, an American publisher, who later donated his collection to Columbia University.
Based on the style of cuneiform script used for the numbers, Plimpton 322 has been dated to between 1822 and 1762 B.C.
One of the columns on Plimpton 322 is just a numbering of the rows from 1 to 15.
The other three columns are much more intriguing. In the 1940s, mathematics historians Otto Neugebauer and Abraham Sachs pointed out that the other three columns were essentially Pythagorean triples — sets of integers, or whole numbers, that satisfy the equation a2 + b2 = c2.
This equation also represents a fundamental property of right triangles — that the square of the longest side, or hypotenuse, is the sum of the squares of the other two shorter sides.
That by itself was remarkable given that the Greek mathematician Pythagoras, for whom the triples were named, would not be born for another 1,000 years.
Mansfield, who was searching for examples of ancient mathematics to intrigue his students, came across Plimpton 322 and found the previous explanations unsatisfying. “None of them really seemed to nail it,” he said.
But what is conspicuously missing is the notion of angle, the central concept impressed upon students learning trigonometry today. Wildberger had a decade earlier proposed teaching trigonometry in terms of ratios rather than angles, and the two wondered that Babylonians took a similar angle-less approach to trigonometry.
“I think the interpretation is possible,” said Alexander R. Jones, director of the Institute for the Study of the Ancient World at New York University, who was not involved with the research, “but we don’t have much in the way of contexts of use from any Babylonian tablets that would confirm such an intention, so it remains rather speculative.”
— Kenneth Chang
How horses got their hooves
All four-limbed, land-based vertebrates came from a common ancestor with legs that ended in five toes. Over time, many animals lost some of their digits: Hippos, rhinos and camels have four, three and two toes on each leg. But only one living group of animals ended up with a single toe per foot: the group containing modern horses.
A comprehensive new study, published Aug. 23 in Proceedings of the Royal Society B, lends support to existing hypotheses about the dramatic transformation in horses’ hooves through history. Namely, as horses evolved and got larger from their ancestral, dogsized form, it was better to have one very robust toe than several smaller ones to support their increased body mass. Furthermore, having just one toe reduced the weight horses had to carry at the end of each leg, making it easier for them to run and maneuver.
The study is a careful examination of “a story everyone had taken for granted and hadn’t really tested thoroughly,” said Christine Janis, a professor emerita of evolutionary biology at Brown University who was not involved in the research.
As told in textbooks and evolutionary biology classes, the earliest horses were small, dwelled in forests and had four toes on their front legs and three on their back legs. Then, more than 20 million years ago, their habitat in North America started to shift from forest to grassland. In these new grasslands, ancient horses needed to move at faster speeds to evade predators and cover more ground for grazing. It made sense that a larger body and longer, more slender legs with fewer toes would help horses achieve that.
Brianna Mchorse, a PH.D. candidate at Harvard University, wanted to see if this narrative checked out. In the new study, she and colleagues scanned leg fossils from 12 kinds of horses, ranging from the oldest ones that lived 55 million years ago to species in the same group as modern-day horses.
Mchorse’s team created a model to estimate the forces acting on the lower legs, including the toes, of different horses over evolutionary history.
Early on, when horses were smaller and had more evenly-sized toes, their side digits were essential for carrying some body weight, the scientists showed. However, over time, as horses evolved larger bodies and their side toes started to shrink, their center toes became larger and more robust, compensating for the extra load, until they were the only digits left.
— Steph Yin
The secret ingredient that stops honeybees from becoming queens
“You are what you eat” is a common adage among humans, but a new study explains why it might be more apt for honeybees.
In a paper published Aug. 31 in PLOS Genetics, researchers found specific molecules in the pollen and honey mixture that honeybee larvae feed on cause physical changes that determine whether females develop into long-living, reproductive queens or the mostly sterile workers that nourish larvae and collect food.
Researchers have long known that these differences are not determined at birth but rather are a product of diet. Larvae that eat royal jelly, a substance secreted by the glands of nurse bees, develop into queens, while those that feed on a combination of pollen and honey called bee bread become workers.
Previous research focused on the role of the protein and sugar-rich royal jelly in caste development, but this study found a new mechanism: small molecules in plants called microrna. These molecules can affect the size and colorfulness of plants, and also play a crucial role in bee development. Transferred to a bee through bee bread, the microrna can affect genes in ways that delay physical development and keep the bees sterile.
“Neither substance is sufficient alone,” said Chen-yu Zhang, co-author of the study and a professor of biochemistry at Nanjing University in China. “The royal jelly and plant microrna work together to affect caste formation.”
Researchers raised honeybees in the lab to study the effects of the plant microrna in bee bread. They found that larvae raised on diets supplemented with the plant material had smaller bodies and smaller ovaries than those raised without the supplement. Further experiments showed that one of the most common types of plant microrna found in bee bread targets a gene in honeybees, TOR, which helps determine caste.
“They did a nice job documenting the specific role of microrNA that has a very profound impact on this development,” said Xiangdong Fu, a professor of cellular and molecular medicine at the University of California, San Diego, who was not involved with the study. “It’s fascinating. Depending on what you eat, you can end up a different way.”
This information could provide insight into the mysterious trend of rising honeybee deaths in the past decade, which could have a large impact on agriculture.
— Aneri Pattani
How plesiosaurs swam through the oceans
Millions of years ago, when dinosaurs dominated the land, leviathans known as plesiosaurs prowled the oceans. With their long necks and barreled bodies, these marine reptiles — which were not dinosaurs — resembled the mythical Loch Ness monster.
Though not every plesiosaur had a neck like “Nessie,” they all had four long flippers. Since the first fossils of this prehistoric sea creature were found about two centuries ago, the two nearly identical pairs of aquatic limbs have puzzled paleontologists.
“Having four big flippers like that is rather strange,” said Luke Muscutt, a biomechanist and postdoctoral researcher at the University of Southampton in England. Muscutt spent his thesis decoding how the plesiosaur paddled, which he said is unlike any other living vertebrate that swims in the ocean. Fish and sharks swim by swinging their tails side to side, and whales and dolphins swing theirs up and down. Even other animals with flippers like sea lions and sea turtles do not swim with all four flippers, he said.
A study he published Aug. 30 in the journal Proceedings of the Royal Society B provides further evidence that the hind flippers were key to the plesiosaur’s underwater moves, and were not just limbs used for steering.
“Plesiosaurs definitely used all four flippers for propulsion and that made them more efficient and effective swimmers,” said Muscutt. The findings, he said, could help settle the long-running debate on how the plesiosaur swam. They could also contribute to future designs for underwater drones or submersibles.
Muscutt used a 3-D printer to create two faux flippers to represent one side of a plesiosaur and attached them to a mechanical device that aimed to mimic how the creature moved. He crafted the foot-long robotic flippers using photographs of plesiosaur fossil specimens as well as from geometric data collected from today’s flippered-creatures like penguins, turtles and sea lions.
He put the flippers into a large water tank, and using different colored dyes, ran several simulations to determine under what conditions the flippers acted most efficiently. The system performed best when the front and back flippers both flapped.
Every flap from the front flipper generated a vortex, or whirlpool, as it went up and as it went down. When the back flippers wove between the whirlpools made by the front flippers, they could use that excess energy to move more efficiently.
“There’s no other animal apart from a dragonfly which utilizes its own wake in this way,” said Muscutt.
— Nicholas St. Fleur
Hunting moose to save caribou from wolves
You like caribou. You like wolves. How do you preserve one without killing the other? Research supporting an unusual conservation approach suggests that it may have something to do with hunting moose, at least in one region of North America.
Scientists spent a decade monitoring wolf, moose and endangered mountain caribou populations in the remote rain forests of southern British Columbia. In a study published Aug. 29 in the journal Peerj, they found that if you let people hunt more moose, you get fewer wolves and more caribou. While this approach may only be part of the solution for preserving the caribou, it illustrates the complexity of conservation in natural environments.
“The Band-aid solution is killing wolves, but that’s been treating the symptom,” said Robert Serrouya, a biologist at The University of Alberta who led the study. “We’re trying to deal with the cause.”
And that cause is part of a counterintuitive narrative that goes like this: When a non-native species wanders into a new place, its predators follow. The non-native species knows how to fight or avoid its predators, and is good at reproducing. But for native species that evolved without worrying about the new predators, and are less fecund, it’s a big problem.
That’s what happened in the Channel Islands off California when pigs brought by humans attracted eagles that started preying on native foxes. The Canadian caribou tale is more indirect: Climate change, extensive wolf control in other areas and logging in British Columbian rain forests — which left decades worth of shrubby moose food in place of ancient trees — encouraged the moose to expand its territory. They traveled from their flat boreal forests homes to the rugged rain forests in southern British Columbia and Idaho where mountain caribou live. Wolves followed and started preying on the native caribou.
Over 10 years of monitoring the movements, survival and reproduction of moose, the scientists found that extra moose hunting, even in this remote area, was enough to reduce the moose from around 1,700 to just 300 or 400. It also reduced the wolves, which dispersed from the area and had fewer babies. The survival rate of the largest caribou subpopulation increased enough to stabilize in the hunting area but continued to plummet in the area where hunting was not allowed to increase.
—Joannaklein