When it comes to the dimensions of spacetime, what you see may be what you get.
Using observations from the collision of two neutron stars that made headlines in 2017 (SN: 11/11/17, p. 6), scientists found no evidence of gravity leaking into hidden dimensions. The number of observed large spatial dimensions — kilometer-scale or bigger — is still limited to the three we know and love, the researchers report January 24 at arXiv.org.
Just as insects floating on a pond may be unaware of what’s above or below the water’s surface, our 3-D world might be part of a higher-dimensional universe that we can’t directly observe. However, says astrophysicist David Spergel of Princeton University, a coauthor of the new study, “gravity might be able to explore those other dimensions.” Such extra dimensions might explain some conundrums in physics, such as the existence of dark matter (an as-yet-unidentified source of mass in the universe) and dark energy (which causes the universe’s expansion rate to accelerate), says coauthor Daniel Holz, an astrophysicist at the University of Chicago. “That’s why people get excited about these modifications.”
To look for any hint of leaking gravity, scientists turned to the light and gravitational waves emitted in the neutron star smashup detected on August 17, 2017. The light allowed scientists to find the galaxy where the neutron stars merged. Spergel, Holz and colleagues showed that, given the galaxy’s distance from Earth, the strength of the gravitational waves was as expected. Extra dimensions weren’t stealing, and thus weakening, the observed ripples.
A variety of theories predict extra dimensions of spacetime into which gravity could leak, but the new result applies only to large extra dimensions, Spergel says. That’s because the gravitational waves detected from the neutron star collision have wavelengths of thousands of kilometers. Tiny extra dimensions, smaller than a fraction of a millimeter across, have also been proposed, but they wouldn’t affect such extended ripples. One theory, proposed in 2000 by a group of theoretical physicists including Georgi Dvali, predicts a type of large extra dimension. The effects of gravity leaking into such dimensions would be visible only over long distances — explaining why gravity on smaller scales, such as the size of the solar system, behaves as if there are three spatial dimensions.
Because the gravitational waves don’t seem to weaken on their trek to Earth, they must travel more than about 65 million light-years before leaking into any potential additional dimension, the researchers concluded in the new study.
But other theories of extra dimensions are unaffected by the result. String theory, which posits that particles are made up of infinitesimal vibrating strings, predicts tiny extra dimensions that are curled up on themselves. “We’re not in any way ruling out string theory,” Spergel says. Another variety of extra spacetime dimension, of potentially infinite size, was proposed by physicists Lisa Randall and Raman Sundrum in 1999 (SN: 9/26/09, p. 22). But such theories also would not be ruled out, because gravity can’t penetrate very far into that type of extra dimension.
Neutron star mergers are “a completely new laboratory of testing gravity,” says Dvali, of Ludwig-Maximilians-Universität in Munich, who was not involved with the research. “This is absolutely fascinating and fantastic.” But, Dvali notes, the type of extra dimension he proposed back in 2000 already seems unlikely on these scales. “I would say there is already an extremely strong constraint on leakage coming from cosmology.” No matter how far we peer out into space, the universe seems to follow the normal laws of gravity in three dimensions.
For now, the dimensions of space remain as simple as 1, 2, 3.
Human activities are driving phosphorus levels in the world’s lakes, rivers and other freshwater bodies to a critical point. The freshwater bodies on 38 percent of Earth’s land area (not including Antarctica) are overly enriched with phosphorus, leading to potentially toxic algal blooms and less available drinking water, researchers report January 24 in Water Resources Research.
Sewage, agriculture and other human sources add about 1.5 teragrams of phosphorus to freshwaters each year, the study estimates. That’s roughly equivalent to about four times the weight of the Empire State Building. The scientists tracked human phosphorus inputs from 2002 to 2010 from domestic, industrial and agricultural sources. Phosphorus in human waste was responsible for about 54 percent of the global load, while agricultural fertilizer use contributed about 38 percent. By country, China contributed 30 percent of the global total, India 8 percent and the United States 7 percent.
High-energy particle beams can reveal how 2-D thin sheets behave when the heat is cranked up.
Researchers have devised a way to track how these materials, such as the supermaterial graphene, expand or contract as temperatures rise (SN: 10/3/15, p. 7). This technique, described in the Feb. 2 Physical Review Letters, showed that 2-D semiconductors arranged in single-atom-thick sheets expand more like plastics than metals when heated. Better understanding the high-temp behaviors of these and other 2-D materials could help engineers design sturdy nano-sized electronics. Commonly used silicon-based electronics are “hitting a brick wall,” regarding how much smaller they can get, says Zlatan Aksamija, an electrical engineer at the University of Massachusetts Amherst not involved in the work. Materials made of ultrathin, 2-D films could be ideal for building the next generation of tinier devices.
But electronics warm up as electric current courses through them. If 2-D materials in a nanodevice expand or shrink at different rates from each other when heated, that could change the device’s electronic properties — such as how well it conducts electricity, says Antoine Reserbat-Plantey, a physicist at the Institute of Photonic Sciences in Barcelona not involved in the research. It’s crucial to know how the thin films react to higher temps.
The new method uses a scanning transmission electron microscope to bombard a film with a beam of high-energy particles. That particle beam stirs up electrons in the 2-D sheet, making the electrons swish back and forth through the material. The collective oscillation, called a plasmon, occurs at a frequency that depends on the material’s density, explains Matthew Mecklenburg, a physicist at the University of Southern California in Los Angeles who was not involved in the work.
The plasmon frequency affects how much energy the particles of the microscope beam lose as they streak through the 2-D material: the higher the frequency, the denser the material, and the more energy that is sapped from the beam. By using another instrument to measure the energies of beam particles after they’ve passed through the 2-D material, researchers can discern the material’s density — and track how that density changes as they turn up the heat. Robert Klie, a physicist at the University of Illinois at Chicago, and colleagues used this technique on samples of graphene, which is made of carbon atoms, and four 2-D semiconductors made of transition metal and chalcogen atoms. (Chalcogen elements are found in group 16 on the periodic table and include sulfur and selenium). These materials were arranged in sheets from a single atom to a few atoms thick. The team measured the density of each sample at eight temperatures between about 100° and 450° Celsius. That allowed the scientists to calculate how much each material expanded or contracted per degree of temperature increase.
These measurements revealed that the thinnest structures undergo more significant size changes than thicker sheets: A single layer of graphene, which contracts when heated, shrinks more than materials composed of a few graphene layers. The 2-D semiconductors expand at higher temps, but those made of one-atom-thick sheets swell more than semiconductors a few atoms thick. In fact, the heat response of the single-atom-thick semiconductors is “more like [that] of a plastic than a metal,” Mecklenburg says.
This finding may indicate that, like plastics, some 2-D semiconductors have low melting temperatures, which could affect how or whether they’re used in future electronics.
Harbor porpoises are frequently exposed to sounds from shipping vessels that register at around 100 decibels, about as loud as a lawnmower, scientists report February 14 in Proceedings of the Royal Society B. Sounds this loud can cause porpoises to stop echolocation, which they use to catch food.
While high-frequency submarine sonar has been found to harm whales (SN: 4/23/11, p. 16), low-frequency noise from shipping vessels is responsible for most human-made noise in the ocean, the researchers say. Porpoises have poor hearing in lower frequencies, so it was unclear if they were affected.
In the first study to assess the effects of shipping vessel noise on porpoises, researchers tagged seven harbor porpoises off the coast of Denmark with sensors that tracked the animals’ movement and echolocation usage in response to underwater noise over about 20 hours.
One ship created a 130 decibel noise — twice as loud as a chainsaw — that caused a porpoise to flee at top speed. These initial results indicate that ship noise could affect how much food porpoises hunt and consume.
In a white lab coat and blue latex gloves, Neda Vishlaghi peers through a light microscope at six milky-white blobs. Each is about the size of a couscous grain, bathed in the pale orange broth of a petri dish. With tweezers in one hand and surgical scissors in the other, she deftly snips one tiny clump in half.
When growing human brains, sometimes you need to do some pruning.
The blobs are 8-week-old bits of brainlike tissue. While they wouldn’t be mistaken for Lilliputian-sized brains, some of their fine-grained features bear a remarkable resemblance to the human cerebral cortex, home to our memories, decision making and other high-level cognitive powers.
Vishlaghi created these “minibrains” at the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA, where she’s a research assistant. First she immersed batches of human pluripotent stem cells — which can morph into any cell type in the body — in a special mix of chemicals. The free-floating cells multiplied and coalesced into itty-bitty balls of neural tissue. Nurtured with meticulously timed doses of growth-supporting ingredients, the cell clumps were eventually transferred to petri dishes of broth laced with Matrigel, a gelatin-like matrix of proteins.
On day 56, the blobs display shadowy clusters of neural “rosettes.” Under a laser scanning microscope, razor-thin slices of those rosettes reveal loose-knit layers of a variety of dividing neural stem cells and the nerve cells, or neurons, they give rise to. The layered structures look similar to the architecture of a human fetal brain at 14 weeks of gestation. Across the globe, labs such as this one, led by UCLA developmental biologist and neuroscientist Bennett Novitch, are cultivating thousands of these brainy clumps for research. Less than five years ago, a team of biologists in Austria and the United Kingdom and one in Japan wowed the world when they announced they had made rudimentary bits of 3-D human cerebral cortex in a dish. Since then, researchers have been eagerly tinkering with techniques for producing these miniature brain models, like chefs obsessively refining their favorite recipes.
“It’s like making a cake: You have many different ways in which you can do it,” says Novitch, who prefers using the Japanese method with a few tweaks. “There are all sorts of little tricks that people have come up with to overcome some of the common challenges.”
For instance, because the brain blobs lack a built-in blood supply, they must absorb enough oxygen and nutrients from the tissue-culture broth to remain healthy. To help, some labs circulate the broth around the tissue clumps. The UCLA researchers choose instead to grow theirs at higher oxygen levels and chop the blobs at the 35-day mark, when they are as wide as three millimeters, and then about every two weeks after. Sounds radical, but the slicing gives cells on the inside — some of which start dying — exposure to much-needed oxygen and nutrients. Those divided bits then continue growing separately. But cutting can be done only so many times before the expanding rosette structures inside are damaged.
With all the experimenting, researchers have cooked up a lot of innovations, including some nifty progress reported in just the last year. Scientists have concocted tiny versions of several brain regions ranging from the hypothalamus, which regulates body temperature, thirst and hunger, to the movement-controlling basal ganglia. Electrical chatter among neurons, reflecting active brain circuits, has been detected. And research groups have recently begun linking bits of specific regions like Legos. Scientists have even observed some early developmental processes as they happen within the human brain blobs. Stem cell payoff The work is part of a broader scientific bonanza that comes from coaxing human stem cells to self-assemble into balls of organlike tissue, known as organoids, that are usually no bigger than a lentil. Although the organoids don’t grow enough to replicate entire human organs, these mini-versions can mimic the 3-D cellular infrastructure of everything from our guts to our lungs. That’s something you can’t get from studies of rodents, which have different biology than humans do.
Mini-organ models promise enormous advantages for understanding basic human biology, teasing apart human disease processes, and offering an accurate testing ground for finding or vetting drug therapies. And by creating personalized organoids from the reprogrammed cells of patients, scientists could study disease in a very individualized way — or maybe even use organoid structures to replace certain damaged tissues, such as in the liver or spinal cord.
“Organoids offer an unprecedented level of access into the inner workings of the human brain,” Novitch says, noting that our brains are largely off-limits to poking and cutting into for research. If scientists can study accurate models of working neural circuits in these brain bits, he and others say, researchers might finally get a handle on uniquely human neurological conditions. Such disorders, which include epilepsy and, experts theorize, schizophrenia and autism (SN Online: 7/17/15), can arise when the brain’s communication networks develop off-kilter. But the research is still in its early days. Although there’s been exciting headway, studies sometimes overstate the extent to which human brain organoids reproduce features of actual developing brain tissue, says stem cell biologist Arnold Kriegstein of the University of California, San Francisco. The minimodels still lack many basic components, including certain cell types, a blood-vessel network and inputs from other neural regions.
Another stumbling block is that brain organoids can vary a lot from protocol to protocol, or even batch to batch within the same lab. “The major focus now needs to be on reproducibility, and being able to get an approach that you can rely on to give you the same outcome each time,” Kriegstein says.
DIY organs For decades, biology research has relied on cell lines grown in flat sheets in petri dishes, but those sheets lack the structural complexity of living tissue. Then came pioneering work that unveiled the do-it-yourself magic of stem cells raised free-floating in broth.
Organlike tissue bits can be generated from pluripotent stem cells that are either plucked from embryos or created by taking a person’s adult skin or blood cells and chemically inducing them to revert to an embryonic-like state. Starting in the mid-2000s, Yoshiki Sasai’s team at the RIKEN Center for Developmental Biology in Kobe, Japan, demonstrated how to grow brainlike structures using embryonic stem cells, first from mice and then humans. In their groundbreaking study in 2013 in Proceedings of the National Academy of Sciences, the researchers used chemical cues to direct human embryonic stem cells to form a specific region of the human cortex. (Tragically, Sasai committed suicide the next year, after two stem cell studies that he coauthored were retracted amid scientific misconduct charges against a research colleague [SN: 12/27/14, p. 25]. Before his death, Sasai was cleared of any direct involvement. The discredited studies were not related to the organoid research.)
A few months before the 2013 Sasai team paper, Madeline Lancaster and Juergen Knoblich of the Institute of Molecular Biotechnology in Vienna and U.K. colleagues demonstrated their more freewheeling, landmark approach to growing brain organoids (SN: 9/21/13, p. 5). The recipe, described in Nature, allows human pluripotent stem cells to spontaneously attempt to assemble into a tiny approximation of a whole brain by making whatever brain structures the stem cells choose.
Meanwhile, biologists elsewhere were whipping up other types of organoids, starting instead with adult stem cells. These rare, damage-repairing cells are found in many organs (including the brain), but the cells can transform into only a limited range of cell types. In 2009, Hans Clevers of the Hubrecht Institute in Utrecht, the Netherlands, announced that his lab unexpectedly created a miniature version of a gut while cultivating adult stem cells that the team had discovered in mouse intestinal tissue. Grown in a drop of Matrigel with a trio of growth-inducing factors, these cells coalesced into little spheres containing tiny projections that resembled the fingerlike villi that absorb nutrients in the gut.
Scientists soon were concocting tiny facsimiles of human stomachs, livers, kidneys, lungs and more (SN: 12/28/13, p. 20). “We essentially are discovering the vitality of what the stem cells actually do,” says Clevers, who is president of the International Society for Stem Cell Research. “We give [the cells] a little push, and they do whatever they’re good at.”
The trick is knowing exactly which ingredients to use to make different organs. For pluripotent stem cells, that means exposing them to just the right growth factors or inhibitors at just the right times, over about a month, says James Wells of the Center for Stem Cell and Organoid Medicine at Cincinnati Children’s Hospital Medical Center. Some of those essential instructions are well-known from decades of research on embryo development in fish, chickens and rodents; the same chemical cues generally work for all animals with spinal cords, including people. However, for many body parts, organoid makers must suss out recipe instructions from scratch. Working with Jorge Múnera and other colleagues, Wells recently produced a minimodel of a human colon using human induced pluripotent stem cells. But first, the team conducted months of experiments on frog and mouse embryos to identify the signals for forming a colon. “It took a while to figure out what the special sauce was,” Wells says.
Some scientists have distant dreams of using organoid methods to grow full-size livers or kidneys in the lab for transplantation. A more attainable goal may be regenerative tissue transplants, for example, replacing dying liver cells in someone with early-stage liver disease with chunks of healthy stem cells from a personalized liver organoid. Or, in patients who’ve had part of the small intestine removed, tiny pieces of gut organoid tissue could be implanted and, after growing larger, connected to the intestine.
Head games The human brain, meanwhile, is vastly more complicated than any other organ. It’s unlikely that scientists will ever be able to build a full replica. While the initial brain-making recipes were stunning for what they could achieve, they left much room for improvement. In the years since the 2013 debut of human brain organoids, research groups have worked to grow bigger brain tissue clumps and more uniform structures.
The Austrian method for making whole-brain organoids, in particular, produced a random mix of neural regions laid out in a topsy-turvy manner. But bioengineering tricks may help. In a study last year, Lancaster, now at the MRC Laboratory of Molecular Biology in Cambridge, England, and Knoblich got more consistent results by adding polymer filaments as scaffolding to guide the organization of the minibrain models. Other scientists, following the Japanese approach, which generally gives more predictable results, have concentrated on coaxing out specific cell types or structural features of the real brain. For instance, one constraint is that the organoids form slowly, more or less sticking to the same timeline of development as does a human brain during gestation. But without a blood supply, growth is limited; the brain bits reach only a few millimeters in size. That means organoid models are often short on cell types from later development stages, such as cells called astrocytes. These star-shaped cells are crucial for creating and curating the connections between neurons, and also may help with forming memories (SN Online: 11/15/17).
Astrocytes don’t fully mature in a baby’s brain until after birth. But Stanford University neuroscientist Sergiu Paşca has crafted a method for making and maintaining 4-millimeter-wide balls of human cortex–like tissue (he calls them spheroids) in 3-D culture for an extended time. Last August in Neuron, his team described organoids that survived for more than 20 months — long enough, analyses showed, for astrocytes to mature and function in ways that mimic their real-brain counterparts.
Of great interest, also, are the outer radial glial (oRG) cells, neural stem cells that are pivotal for constructing the unusually big cortex that’s unique to humans; oRG cells are scarce in mouse brains. When Novitch’s lab group at UCLA tried the original Japanese and Austrian organoid-making recipes, the output of oRG cells was underwhelming. So Novitch worked with Vishlaghi and postdoctoral researcher Momoko Watanabe to refine the protocol to pump up the cells’ production and reliably generate better cerebral blobs.
Among other tweaks, Novitch’s team added a dash of a molecule dubbed LIF, which recent studies by others had suggested can spur the oRGs to multiply. It worked, leading to a threefold increase in the oRG populations and enhanced growth of upper neuron layers. The researchers shared their revised protocol last October in Cell Reports. On a different front, labs have begun assembling more complex minibrain models, like playing with self-directed Legos. For two months, Paşca’s team at Stanford grew spheroids in separate sets of dishes that mimicked either cortex tissue or an adjacent underlying region known as the subpallium. Then the researchers put the different bits side-by-side and left them overnight in a culture tube. Similar to how the two regions normally connect in the developing brain, the little pieces knew what to do. “By the next day they are essentially fused to each other,” says Paşca, who announced the results in May in Nature.
During the fusion process, the researchers took time-lapse videos of long, spaghetti-like cells called interneurons migrating from a spheroid of the subpallium into a cortexlike spheroid.
“They don’t crawl, they actually jump,” Paşca says. The images capture aspects of a hallmark phenomenon that normally unfolds during the second and third trimester of fetal gestation.
Testing ground Once on the other side, interneurons form a circuit with — and quell the activity of — excitatory neurons in the cortexlike tissue, electrophysiological tests suggest. If not quieted, excitatory neurons will trigger neighboring cells to fire. In the real brain, maintaining a proper balance in neural network activity is important; disruptions in it appear to foster disorders such as epilepsy, and perhaps schizophrenia and autism.
Indeed, in the same paper, the Stanford team reported new discoveries using personalized brain spheroids derived from induced pluripotent stem cells of patients with Timothy syndrome — a rare condition caused by an overactive calcium channel found mainly in the brain and heart. Patients with the disorder have epilepsy, autism and heart problems. In the patients’ spheroids, interneurons migrated inefficiently but, by adding drugs that blocked the dysfunctional calcium channel, the researchers could reverse the problem. The brain organoids made these intriguing observations possible, Paşca says. “We couldn’t have done this in any other way.” Organoid experiments by others have, meanwhile, helped confirm that the Zika virus targets and kills oRG cells and other neural precursor cells, contributing to small brain size in infected infants.
In a 2016 study, Johns Hopkins University neuroscientists Guo-li Ming and Hongjun Song reported on their own techniques for creating brain bits that have a well-defined zone of oRG cells. After infecting these organoids with the Zika virus, the researchers observed a collapse of cortexlike tissue that may partly explain the stunted brain growth (SN: 4/2/16, p. 26). 2-D cell-culture and mouse experiments also provided key evidence of the virus’s modus operandi; although the rodent brain doesn’t harbor the full contingent of human neural stem cells, it has blood vessels and immune-system components that organoids lack.
In search of Zika-fighting treatments, Ming and Song, both now at University of Pennsylvania, and their colleagues have been screening thousands of compounds in 2-D cell cultures, and then validating the most promising candidates with tests in 3-D brain organoids. The team has found several potential antiviral and neuron-protecting agents to pursue. Novitch’s UCLA lab group has likewise used its brain organoids to pinpoint additional receptors by which the virus may gain entry into neural stem cells, and identified a few other drug leads for blocking infection.
Organoids may also prove valuable for tailoring treatments for patients, says David Panchision, chief of the developmental neurobiology program at the National Institute of Mental Health in Bethesda, Md. Researchers might generate personalized brain organoids from the reprogrammed skin cells of individuals with, say, schizophrenia and test which medications work best for patients with particular genetic profiles of the illness.
In the Netherlands, based on research reported in 2016 in Science Translational Medicine, Clevers and colleagues are already using personalized gut organoids, derived from rectal biopsies, to test whether cystic fibrosis patients will benefit from available drugs. Tailored regenerative therapies with 3-D substructures of neural tissue may also be possible, Panchision adds, for conditions like Parkinson’s disease or spinal cord injury. Growing pains For now, though, scientists have hefty challenges to overcome. Much work remains in optimizing how faithfully the bits of tissue reproduce normal brain function and architecture, Panchision says. For one thing, the organoids are developmentally young and don’t reflect a mature brain. And researchers must figure out how to build in some core features: the necessary blood vessels, immune-system cells called microglia and connections from other brain regions, such as the thalamus and cerebellum. Not to mention steroid and thyroid hormones, which also shape brain growth.
However, scientists don’t necessarily need or want to create a comprehensive replica of the human brain in a dish, Panchision and others point out. Rather, the goal is to build robust and reliable models for studying specific aspects of brain function.
Thus the pressing need for standardized, reproducible organoid-making recipes. Novitch’s group and many other labs are still trying to figure out why the brain bits can vary so much in size, composition and structure. Part of the trouble is the ingredients: Subtle variations in tissue-culture chemicals and Matrigel, or in different stem cell lines and how they are grown first in 2-D culture, can have a big impact on how the organoids turn out, Novitch says.
At the same time, researchers need to do a more thorough job of analyzing brain organoids to know what’s actually in them at different developmental time points, compared with actual human fetal brain tissue, says UCSF’s Kriegstein. It’s otherwise hard to say whether a brain blob truly recapitulates the neural tissue that scientists claim it does. Labs have started tackling the problem with a tool called single-cell transcriptome analysis, which gives readouts of all the genes that are active in individual cells.
“Greater rigor is needed,” Kriegstein says. “And I am sure we will eventually get there.”
When you’re pregnant, you spend a lot of time on scales. Every doctor appointment begins with hopping (or waddling) up for a weigh-in. Health care workers then plot those numbers into a (usually) ascending curve as the weeks go by.
A morbid curiosity about exactly how enormous you’re getting isn’t what’s behind the scrutiny. Rather, the pounds put on during pregnancy can give clues about how the pregnancy is progressing.
Weight gain during pregnancy is tied to the birth weight of the new baby: On average, the more weight that mothers gain, the bigger the babes. If a mother gains a very small amount of weight, her baby is more likely to be born too early and too small. And if a mother gains too much weight, her baby is at risk of being born large, which can cause trouble during delivery and future health problems for babies. But staying within the recommended weight range is hard. Very hard. A 2017 review of studies that, all told, looked at over a million pregnancies around the world showed that the vast majority of women fell outside the weight gain sweet spot. Twenty-three percent of those women didn’t gain enough, and 47 percent gained too much, the review, published in JAMA, shows.
But here’s the tricky part. Many studies on weight gain during pregnancy and babies’ outcomes start monitoring women who are already pregnant. That means that these studies rely on women to remember, and report correctly, their prepregnancy weight. And that might not always be accurate.
A new study offers a more nuanced look at pregnancy weight gain. The results, taken from the pregnancies of more than 1,000 Chinese women, suggest that when it comes to babies’ birth weights, the timing of maternal weight gain matters, a lot. Overall, a woman’s weight gain during pregnancy was clearly linked to baby’s weight at birth, the researchers found. But within those 40 weeks, there were big differences. Prepregnancy weight and weight gain during the first half of pregnancy are the measurements that matter, researchers suggested in the February JAMA Pediatrics. Weight gain after 18 weeks wasn’t linked to babies’ birth weight, researchers note.
Similar results, described in PLOS ONE, come from a 2017 study of Vietnamese women: Weight gain during the first half of pregnancy had two to three times the influence on infant birth outcomes than weight gain in the second half of pregnancy. It’s worth mentioning that nearly three-quarters of the Vietnamese women gained too little weight during pregnancy. And on the whole, the Chinese women were lean before they got pregnant, scenarios that make it hard to translate those findings to women who began pregnancy overweight.
Still, the point remains that weight gain during the first half of pregnancy (and even before it) may have outsized influence on the baby’s growth. Pregnancy — and the growing baby — change so much from week 0 to week 40. It makes sense that all pregnancy weight gain isn’t all one and the same.
It’s nice to see these complexities emerge as scientists get more fine-grained data. There’s still so much we don’t know about how weight gain during pregnancy, as well as other aspects of the in utero environment, can shape babies’ future health.
For the first time, scientists may have detected hints of the universe’s primordial sunrise, when the first twinkles of starlight appeared in the cosmos.
Stars began illuminating the heavens by about 180 million years after the universe was born, researchers report in the March 1 Nature. This “cosmic dawn” left its mark on the hydrogen gas that surrounded the stars (SN: 6/8/02, p. 362). Now, a radio antenna has reportedly picked up that resulting signature. “It’s a tremendously exciting result. It’s the first time we’ve possibly had a glimpse of this era of cosmic history,” says observational cosmologist H. Cynthia Chiang of the University of KwaZulu-Natal in Durban, South Africa, who was not involved in the research.
The oldest galaxies seen directly with telescopes sent their starlight from significantly later: several hundreds of millions of years after the Big Bang, which occurred about 13.8 billion years ago. The new observation used a technique, over a decade in the making, that relies on probing the hydrogen gas that filled the early universe. That approach holds promise for the future of cosmology: More advanced measurements may eventually reveal details of the early universe throughout its most difficult-to-observe eras.
But experts say the result needs additional confirmation, in particular because the signature doesn’t fully agree with theoretical predictions. The signal — a dip in the intensity of radio waves across certain frequencies — was more than twice as strong as expected.
The unexpectedly large observed signal suggests that the hydrogen gas was colder than predicted. If confirmed, this observation might hint at a new phenomenon taking place in the early universe. One possibility, suggested in a companion paper in Nature by theoretical astrophysicist Rennan Barkana of Tel Aviv University, is that the hydrogen was cooled due to new types of interactions between the hydrogen and particles of dark matter, a mysterious substance that makes up most of the matter in the universe. If the interpretation is correct, “it’s quite possible that this is worth two Nobel Prizes,” says theoretical astrophysicist Avi Loeb of Harvard University, who was not involved with the work. One prize could be given for detecting the signature of the cosmic dawn, and another for the dark matter implications. But Loeb expresses reservations about the result: “What makes me a bit nervous is the fact that the [signal] that they see doesn’t look like what we expected.”
To increase scientists’ confidence, the result must be verified by other experiments and additional tests, says theoretical cosmologist Matias Zaldarriaga of the Institute for Advanced Study in Princeton, N.J. Several other efforts to detect the signal are already under way.
Experimental cosmologist Judd Bowman of Arizona State University in Tempe and colleagues teased out their evidence for the first stars from the impact the light had on hydrogen gas. “We don’t see the starlight itself. We see indirectly the effect that the starlight would have had” on the cosmic environment, says Bowman, a collaborator on the Experiment to Detect the Global Epoch of Reionization Signature, EDGES, which detected the stars’ traces. Collapsing out of dense pockets of hydrogen gas early in the universe’s history, the first stars flickered on, emitting ultraviolet light that interacted with the surrounding hydrogen. The starlight altered the proportion of hydrogen atoms found in different energy levels. That change caused the gas to absorb light of a particular wavelength, about 21 centimeters, from the cosmic microwave background — the glow left over from around 380,000 years after the Big Bang (SN: 3/21/15, p. 7). A distinctive dip in the intensity of the light at that wavelength appeared as a result.
Over time, that light’s wavelength was stretched to several meters by the expansion of the universe, before being detected on Earth as radio waves. Observing the amount of stretching that had taken place in the light allowed the researchers to pinpoint how long after the Big Bang the light was absorbed, revealing when the first stars turned on.
Still, detecting the faint dip was a challenge: Other cosmic sources, such as the Milky Way, emit radio waves at much higher levels, which must be accounted for. And to avoid interference from sources on Earth — like FM radio stations — Bowman and colleagues set up their table-sized antenna far from civilization, at the Murchison Radio-astronomy Observatory in the western Australian outback.
Scientists hope to use similar techniques with future, more advanced instruments to map out where in the sky stars first started forming, and to reveal other periods early in the universe’s history. “This is really the first step in what’s going to become a new and exciting field,” Bowman says.
A new molecule that reveals active tuberculosis bacteria in coughed-up mucus and saliva could simplify TB diagnoses and speed up tests for detecting strains of the disease that are resistant to drugs.
This synthetic molecule is a modified version of a sugar that TB bacteria consume to help build their cell walls. The sugar is tagged with a dye that lights up under a fluorescent microscope — but only if the dye isn’t surrounded by water. Dubbed DMN-Tre, the hybrid molecule stays dark until it enters a fatty, water-repellant layer in a TB bacterium’s cell wall, where it starts to glow, researchers report online February 28 in Science Translational Medicine. Standard tests use dyes that stain a bunch of different bacteria, so technicians have to bleach the dye off everything except the TB cells, says Sumona Datta, a tuberculosis researcher at Imperial College London not involved in the work. But that chemical washing is time-consuming and prone to error. Since DMN-Tre only glows when it’s gobbled up by TB or one of its close relatives, the molecule could offer a simpler, more reliable diagnosis, she says. Tuberculosis killed 1.7 million people worldwide in 2016, according to the World Health Organization. And rampant resistance to drugs is making the disease harder to fight. Chemical biologist Carolyn Bertozzi, a Howard Hughes Medical Institute investigator at Stanford University, and colleagues tested the new molecule on mucus-saliva mixtures hacked up by 16 people with tuberculosis. The molecule flagged TB microbes in the samples after a couple of hours, and it revealed similar amounts of bacteria as the standard staining technique — without the hassle of post-dye chemical washing.
“That’s pretty impressive,” says Jianghong Rao, a chemist and radiologist at Stanford not involved in the work. But DMN-Tre needs to be tested in a larger clinical trial before being ready for prime time, he says.
The new TB screening technique may also have an edge in checking whether patients respond to treatment, says Eric Rubin, a microbiologist at Harvard University. Because the molecule only lights up when eaten by healthy, hungry TB bacteria, it won’t flag microbes that have been crippled or killed by antibiotics as typical tests do. So if there are still lots of glowing microbes in phlegm from patients treated with an antibiotic, a doctor knows to try a different drug.
While current drug-resistance tests can take weeks or months, DMN-Tre reveals how drug-treated bacteria are faring within a few hours. “That’s tremendously exciting,” says Carlton Evans, also a tuberculosis researcher at Imperial College London not involved in the study. Speedy drug-resistance tests (SN Online: 12/7/14) could help researchers predict sooner which antibiotics stand the best chance of taking down TB bacteria.
LOS ANGELES — In the search for new superconductors, scientists are leaving no stone — and no meteorite — unturned. A team of physicists has now found the unusual materials, famous for their ability to conduct electricity without resistance, within two space rocks.
The discovery implies that small amounts of superconducting materials might be relatively common in meteorites, James Wampler of the University of California, San Diego, said March 6 at a meeting of the American Physical Society. While the superconducting materials found weren’t new to science, additional interplanetary interlopers might harbor new, more technologically appealing varieties of superconductors, the researchers suggest. Superconductors could potentially beget new, energy-saving technologies, but they have one fatal flaw: They require very cold temperatures to function, making them impractical for most uses. So scientists are on the hunt for new types of superconductors that work at room temperature (SN: 12/26/15, p. 25). If found, such a substance could lead to dramatic improvements in power transmission, computing and high-speed magnetically levitated trains, among other things.
Space rocks are a good avenue to explore in the search for new, exotic materials, says Wampler. “Meteorites are formed under these really unique, really extreme conditions,” such as high temperatures and pressures.
What makes the meteorite superconductors special, the researchers say, is that they occurred naturally, instead of being fabricated in a lab, as most known superconductors are. In fact, says physicist Ivan Schuller, also of University of California, San Diego, these are the highest temperature naturally occurring superconductors known — although they still have to be superchilled to about 5 kelvins (–268.15° C) to work. They are also the first known to have formed extraterrestrially.
“At this point, it’s a novelty,” says chemist Robert Cava of Princeton University. Although Cava is skeptical that scrutinizing meteorites will lead to new, useful superconductors, he says, it’s “kinda cool” that superconductors show up in meteorites. Wampler, Schuller and colleagues bombarded bits of powdered meteorite with microwaves and looked for changes in how those waves were absorbed as the temperature changed. The sensitive technique can pick out minute traces of superconducting material within a sample.
Analysis of powdered scrapings from more than a dozen meteorites showed that two meteorites contained superconducting material. However, the superconductors found within the meteorites were run-of-the-mill varieties, made from alloys of metals including indium, tin and lead, which are already known to superconduct.
“The idea is, try to look for something that is very unusual,” such as a room temperature superconductor, says Schuller, who led the research. So far, that hope hasn’t been realized — but that hasn’t deterred the search for something more exotic. For a previous study, Wampler, Schuller and colleagues scanned 65 tiny micrometeorites, but found no superconductors at all.
Since parts of space are colder than 5 kelvins, some meteorites may even contain materials that were once superconducting in their chilly natural habitat. That’s an interesting idea, Wampler says, although it’s too early to say whether that possibility might have any astronomical implications for how the objects behave out in space.
Bit by bit, Jupiter is revealing its deepest, darkest secrets.
The latest findings are in from the Juno spacecraft. And they unveil the roots of the planet’s storms, what lies beneath the opaque atmosphere and a striking geometric layout of cyclones parked around the gas giant’s north and south poles.
“We’re at the beginning of dissecting Jupiter,” says Juno mission leader Scott Bolton of the Southwest Research Institute in San Antonio. And the picture that’s emerging — still just a sketch — topples many preconceived notions. The results appear in four papers in the March 8 Nature. Juno has been orbiting Jupiter since July 4, 2016, on a mission to map the planet’s interior (SN: 6/25/16, p. 16). The probe loops around once every 53 days, traveling on an elongated orbit that takes the spacecraft from pole to pole and as close as about 4,000 kilometers above the cloud tops.
As it plows through Jupiter’s gravity field, Juno speeds up and slows down in response to shifting masses inside the planet. By measuring these minute accelerations and decelerations, scientists can calculate subtle variations in Jupiter’s gravity and deduce how its mass is distributed. That lets researchers build up a three-dimensional map of the planet’s internal structure. At the same time, Juno snaps pictures in visible and infrared light. While other probes have extensively photographed much of the planet, Juno is the first to get an intimate look at the north and south poles.
“The whole thing is really intriguing, especially when you compare [Jupiter] to other giant planets,” says Imke de Pater, a planetary scientist at the University of California, Berkeley. “They are all unique, it looks like.” Check out these four surprising new things we’ve learned that make Jupiter one of a kind:
Rings of cyclones Parked at each pole is a cyclone several thousand kilometers wide. That part isn’t surprising. But each of those cyclones is encircled by a polygonal arrangement of similarly sized storms — eight in the north and five in the south. The patterns have persisted throughout Juno’s visit.
“We don’t really understand why that would happen, and why they would collect up there in such a geometric fashion,” Bolton says. “That’s pretty amazing that nature is capable of something like that.”
More than skin deep Researchers have long debated whether the photogenic bands of clouds that wrap around Jupiter have deep roots or just skim the top of the atmosphere. Juno’s new look shows that the bands penetrate roughly 3,000 kilometers below the cloud tops. That’s 30 times as thick as the bulk of Earth’s atmosphere. While just a tiny fraction of Jupiter’s diameter, that’s deeper than previously thought, Bolton says.
Weighty weather Within those 3,000 kilometers lies what passes for an atmosphere on Jupiter. It’s the stage on which Jupiter’s turbulent weather plays out. The atmosphere alone is about three times as massive as our planet, or 1 percent of Jupiter’s entire mass, researchers estimate.
Stuck together Below the atmosphere, Jupiter is fluid. But unlike most fluids, the planet rotates as if it’s a solid mass. Like kids playing crack-the-whip, atoms of hydrogen and helium figuratively link arms and spin around the planet in unison, scientists report. Earlier results from Juno also indicate there’s no solid core lurking beneath this fluid (SN: 6/24/17, p. 14), so anyone dropped into the planet can expect a terribly long fall.
Many of these results are preliminary, and it’s unclear what it all means for how Jupiter operates. But what’s been learned so far, Bolton says, “is quite different than anybody anticipated.”
