Researchers found that the white dwarf is 56 percent the mass of our Sun. This agrees with earlier theoretical predictions of the white dwarf’s mass and corroborates current theories of how white dwarfs evolve as the end product of a typical star’s evolution. The unique observation yields insights into theories of the structure and composition of white dwarfs.

Until now, previous white dwarf mass measurements have been gleaned from observing white dwarfs in binary star systems. By watching the motion of two co-orbiting stars, straightforward Newtonian physics can be used to measure their masses. However, these measurements can be uncertain if the white dwarf’s companion star is in a long-period orbit of hundreds or thousands of years. Orbital motion can be measured by telescopes only over a brief slice of the dwarf’s orbital motion.

For this companion-less white dwarf, researchers had to employ a trick of nature, called gravitational microlensing. The light from a background star was slightly deflected by the gravitational warping of space by the foreground dwarf star. As the white dwarf passed in front of the background star, microlensing caused the star to appear temporarily offset from its actual position on the sky.

The results are reported in the Monthly Notices of the Royal Astronomical Society. The lead author is Peter McGill, formerly of the University of Cambridge (now based at the University of California, Santa Cruz).

McGill used Hubble to precisely measure how light from a distant star bent around the white dwarf, known as LAWD 37, causing the background star to temporarily change its apparent position in the sky.

Kailash Sahu of the Space Telescope Science Institute in Baltimore, Maryland, the principal Hubble investigator on this latest observation, first used microlensing in 2017 to measure the mass of another white dwarf, Stein 2051 B. But that dwarf is in a widely separated binary system. “Our latest observation provides a new benchmark because LAWD 37 is all by itself,” Sahu said.

The collapsed remains of a star that burned out 1 billion years ago, LAWD 37 has been extensively studied because it is only 15 light-years away in the constellation Musca. “Because this white dwarf is relatively close to us, we’ve got lots of data on it — we’ve got information about its spectrum of light, but the missing piece of the puzzle has been a measurement of its mass,” said McGill.

The team zeroed in on the white dwarf thanks to ESA’s Gaia space observatory, which makes extraordinarily precise measurements of nearly 2 billion star positions. Multiple Gaia observations can be used to track a star’s motion. Based on this data, astronomers were able to predict that LAWD 37 would briefly pass in front of a background star in November 2019.

Once this was known, Hubble was used to precisely measure over several years how the background star’s apparent position in the sky was temporarily deflected during the white dwarf’s passage.

“These events are rare, and the effects are tiny,” said McGill. “For instance, the size of our measured offset is like measuring the length of a car on the Moon as seen from Earth.”

Since the light from the background star was so faint, the main challenge for astronomers was extracting its image from the glare of the white dwarf, which is 400 times brighter than the background star. Only Hubble can make these kinds of high-contrast observations in visible light.

“The precision of LAWD 37’s mass measurement allows us to test the mass-radius relationship for white dwarfs,” said McGill. “This means testing the theory of degenerate matter (a gas so super-compressed under gravity it behaves more like solid matter) under the extreme conditions inside this dead star,” he added.

The researchers say their results open the door for future event predictions with Gaia data. In addition to Hubble, these alignments can now be detected with NASA’s James Webb Space Telescope. Because Webb works at infrared wavelengths, the blue glow of a foreground white dwarf looks dimmer in infrared light, and the background star looks brighter.

Based on Gaia’s predictive powers, Sahu is observing another white dwarf, LAWD 66, with NASA’s James Webb Space Telescope. The first observation was done in 2022. More observations will be taken as the deflection peaks in 2024 and then subsides.

“Gaia has really changed the game — it’s exciting to be able to use Gaia data to predict when events will happen, and then observe them happening,” said McGill. “We want to continue measuring the gravitational microlensing effect and obtain mass measurements for many more types of stars.”

In his 1915 theory of general relativity, Einstein predicted that when a massive compact object passes in front of a background star, the light from the star would bend around the foreground object due to the warping of space by its gravitational field.

Exactly a century before this latest Hubble observation, in 1919, two British-organized expeditions to the southern hemisphere first detected this lensing effect during a solar eclipse on May 19th. It was hailed as the first experimental proof of general relativity — that gravity warps space. However, Einstein was pessimistic that the effect could ever be detected for stars outside our solar system because of the precision involved. “Our measurement is 625 times smaller than the effect measured at the 1919 solar eclipse,” said McGill.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

Decades of research has shown that we can transplant individual human and rodent neurons into rodent brains, and, more recently, it has been demonstrated that human brain organoids can integrate with developing rodent brains. However, whether these organoid grafts can functionally integrate with the visual system of injured adult brains has yet to be explored.

“We focused on not just transplanting individual cells, but actually transplanting tissue,” says senior author H. Isaac Chen, a physician and Assistant Professor of Neurosurgery at the University of Pennsylvania. “Brain organoids have architecture; they have structure that resembles the brain. We were able to look at individual neurons within this structure to gain a deeper understanding of the integration of transplanted organoids.”

The researchers cultivated human stem cell-derived neurons in the lab for around 80 days before grafting them into the brains of adult rats that had sustained injuries to their visual cortex. Within three months, the grafted organoids had integrated with their host’s brain: becoming vascularized, growing in size and number, sending out neuronal projections, and forming synapses with the host’s neurons.

The team made use of fluorescent-tagged viruses that hop along synapses, from neuron to neuron, to detect and trace physical connections between the organoid and brain cells of the host rat. “By injecting one of these viral tracers into the eye of the animal, we were able to trace the neuronal connections downstream from the retina,” says Chen. “The tracer got all the way to the organoid.”

Next, the researchers used electrode probes to measure the activity of individual neurons within the organoid when the animals were exposed to flashing lights and alternating white and black bars. “We saw that a good number of neurons within the organoid responded to specific orientations of light, which gives us evidence that these organoid neurons were able to not just integrate with the visual system, but they were able to adopt very specific functions of the visual cortex.”

The team was surprised by the degree to which the organoids were able to integrate within only three months. “We were not expecting to see this degree of functional integration so early,” says Chen. “There have been other studies looking at transplantation of individual cells that show that even 9 or 10 months after you transplant human neurons into a rodent, they’re still not completely mature.”

“Neural tissues have the potential to rebuild areas of the injured brain,” says Chen. “We haven’t worked everything out, but this is a very solid first step. Now, we want to understand how organoids could be used in other areas of the cortex, not just the visual cortex, and we want to understand the rules that guide how organoid neurons integrate with the brain so that we can better control that process and make it happen faster.”

Researchers at Baylor College of Medicine, the University of Michigan and collaborating institutions working with animal models of GVHD report today in the journal Immunity that alterations in the gut microbiome are connected to an increase in oxygen levels in the intestine that follows immune-mediated intestinal damage. Pharmacologically reducing intestinal oxygen levels alleviated the microbial imbalance and reduced the severity of the intestinal disease.

“There is a lot of data showing that microbes change in many diseases, but we do not understand how that happens,” said leading author Dr. Pavan Reddy, professor and director of Baylor’s Dan L Duncan Comprehensive Cancer Center, who was at the University of Michigan during the development of this project. “This study is one of the first to provide an explanation and a potential solution for the imbalance in the gut microbiome that exacerbates GVHD and possibly other inflammatory intestinal conditions.”

GVHD is a potentially life-threatening complication of bone marrow transplantation. “It is the complication that can prevent us from using this therapy that has proven to be effective to treat many blood cancers and inherited blood diseases,” Reddy said. “The idea is to understand what makes GVHD worse so we can effectively control it. The study also is relevant to more common inflammatory bowel diseases, including Crohn’s disease and ulcerative colitis.”

Reddy and his colleagues discovered that the damage immune cells cause to intestinal cells prevents these cells from fully using oxygen to conduct their normal functions. Consequently, all the oxygen that is not being used by intestinal cells oozes into the intestine, changing the environment for the resident microbes.

“Most of the ‘good microbes’ we have in the intestine grow in oxygen-poor environments — oxygen is toxic to them. They are called anaerobic (without oxygen) bacteria,” Reddy said. “When oxygen levels in the intestine increase, these microbes tend to disappear, and oxygen-loving microbes tend to grow. An increase in oxygen level provides an explanation for the microbiome changes in the context of these inflammatory diseases.”

The findings suggested that restoring the normal environment by reducing the oxygen level in the intestine could help reestablish the balance of the microbial community and lead to attenuation of GVHD.

“Indeed, we discovered that reducing the intestinal oxygen level actually made a difference in the progression of GVHD in the animal models,” Reddy said. “We found that a commonly used drug to reduce iron overload, an iron chelator, mitigated the microbial imbalance and reduced the severity of GVHD.”

Iron chelators have been used for many years to treat conditions in which excess iron causes tissue damage, such as hemochromatosis. Iron chelators are compounds that bind to iron, pulling it out and removing it from the body. “We discovered that iron chelators also can act as oxygen sinks,” Reddy said. “In our animal models, iron chelators removed iron from the intestine and that facilitated the restoration of an oxygen-poor environment that gave anaerobic bacteria an opportunity to bloom. Importantly, this reduced the severity of GVHD.”

The researchers’ next steps include conducting studies to determine whether iron chelation can help control the severity of GVHD in patients who have received a bone marrow transplant.

Another advantage of iron chelation would be that it may reduce or avoid the use of immune suppressor medications that are usually used to control GVHD. Suppressing the immune system may control GVHD, but also favors infections, which can be life-threatening. “If iron chelation helps control the condition in patients, it would be a novel non-immunosuppressive approach to treat GVHD with seemingly little side effects,” Reddy said.

Other contributors to this work include Keisuke Seike, Anders Kiledal, Hideaki Fujiwara, Israel Henig, Marina Burgos da Silva, Marcel R.M. van den Brink, Robert Hein, Matthew Hoostal, Chen Liu, Katherine Oravecz-Wilson, Emma Lauder, Lu Li, Yaping Sun, Thomas M. Schmidt, Yatrik M. Shah, Robert R. Jenq and Gregory Dick. The authors are affiliated with one or more of the following institutions: Baylor College of Medicine, University of Michigan, Okayama University Hospital, Rambam Health Care Campus-Israel, Memorial Sloan Kettering Cancer Center, Yale University School of Medicine and MD Anderson Cancer Center.

This work was supported by the US National Institutes of Health grants P01HL149633, HL152605, CA217156, R01CA148828, 4 R01CA245546 and R01DK095201. Further support was provided by National Cancer Institute award numbers R01-CA228358, R01-CA228308, P30 CA008748 MSK Cancer Center Support Grant/Core Grant and P01-CA023766; National Heart, Lung, Blood Institute award number R01-HL123340 and R01- 8 HL147584; Tri-Institutional Stem Cell Initiative and NIH grant CA46592.

“How the thalamus communicates with the cortex in a fundamental feature of how the brain interprets the world,” said Elly Nedivi, William R. and Linda R. Young Professor in The Picower Institute for Learning and Memory at MIT. Despite the importance of thalamic input to the cortex, neuroscientists have struggled to understand how it works so well given the relative paucity of observed connections, or “synapses,” between the two regions.

To help close this knowledge gap, Nedivi assembled a collaboration within and beyond MIT to apply several innovative methods. In a new study in Nature Neuroscience, the team reports that thalamic inputs into superficial layers of the cortex are not only rare, but also surprisingly weak, and quite diverse in their distribution patterns. Despite this, they are reliable and efficient representatives of information in the aggregate, and their diversity is what underlies these advantages.

Essentially, by meticulously mapping every thalamic synapse on 15 neurons in layer 2/3 of the visual cortex in mice and then modeling how that input affected each neuron’s processing of visual information, the team found that wide variations in the number and arrangement of thalamic synapses made them differentially sensitive to visual stimulus features. While individual neurons therefore couldn’t reliably interpret all aspects of the stimulus, a small population of them could together reliably and efficiently assemble the overall picture.

“It seems this heterogeneity is not a bug, it’s a feature that provides not only a cost benefit, but also confers flexibility and robustness to perturbation” said Nedivi, corresponding author of the study and a member of MIT’s faculty in the Departments of Biology and Brain and Cognitive Sciences.

Aygul Balcioglu, the research scientist in Nedivi’s lab who led the work, added that the research has created a way for neuroscientists to track all the many individual inputs a cell receives as that input is happening.

“Thousands of information inputs pour into a single brain cell. The brain cell then interprets all that information before it communicates its own response to the next brain cell,” Balcioglu said. “What is new and we feel exciting is we can now reliably describe the identity and the characteristics of those inputs, as different inputs and characteristics convey different information to a given brain cell. Our techniques give us the ability to describe in living animals where in the structure of the single cell what kind of information gets incorporated. This was not possible until now.”

‘MAP’ping and modeling

Nedivi and Balcioglu’s team chose layer 2/3 of the cortex because tthis layer is where there is relatively high flexibility or “plasticity,” even in the adult brain. Yet, thalamic innervation there has rarely been characterized. Moreover, Nedivi said, even though the model organism for the study was mice, those layers are the ones that have thickened the most over the course of evolution, and therefore play especially important roles in the human cortex.

Precisely mapping all the thalamic innervation onto entire neurons in living, perceiving mice is so daunting it’s never been done.

To get started the team used a technique established in Nedivi’s lab that enables observing whole cortical neurons under a two-photon microscope using three different color tags in the same cell simultaneously, except in this case, they used one of the colors to label thalamic inputs contacting the labeled cortical neurons. Whereever the color of those thalamic inputs overlapped with the color labeling excitatory synapses on the cortical neurons that revealed the location of putative thalamic inputs onto the cortical neurons.

Two-photon microscopes offer deep looks into living tissues, but their resolution is not sufficient to confirm that the overlapping labels are indeed synaptic contacts. To confirm their first indications of thalamic inputs, the team turned to a technique called MAP invented in The Picower Institute lab of MIT Chemical Engineering Associate Professor Kwanghun Chung. MAP physically enlarges tissue in the lab, effectively increasing the resolution of standard microscopes. Rebecca Gillani, a postdoc in the Nedivi lab, with help from Taeyun Ku, a Chung Lab postdoc, was able to combine the new labeling and MAP to definitely resolve, count, map, and even measure the size of all thalamic-cortical synapses onto entire neurons.

The analysis revealed that the thalamic inputs were rather small (typically presumed to also be weak and maybe temporary), and accounted for between 2 and 10 percent of the excitatory synapses on individual visual cortex neurons. The variance in thalamic synapse numbers was not just at a cellular level, but also across different “dendrite” branches of individual cells, accounting for anywhere between zero and nearly half the synapses on a given branch.

“Wisdom of the crowd”

These facts presented Nedivi’s team with a conundrum. If the thalamic inputs were weak, sparse and widely varying, not only across neurons but even across each neuron’s dendrites, then how good could they be for reliable information transfer?

To help solve the riddle, Nedivi turned to colleague Idan Segev, a professor at Hebrew University in Jerusalem specializing in computational neuroscience. Segev and his student Michael Doron used the Nedivi lab’s detailed anatomical measurements and physiological information from the Allen Brain Atlas to create a biophysically faithful model of the cortical neurons.

Segev’s model showed that when the cells were fed visual information (the simulated signals of watching a grating go past the eyes) their electrical responses varied based on how their thalamic input varied. Some cells perked up more than others in response to different aspects of the visual information, such ascontrast or shape, but no single cell revealed much about the overall picture. But with about 20 cells together, the whole visual input could be decoded from their combined activity — a so-called “wisdom of the crowd.”

Notably, Segev compared the performance of cells with the weak, sparse and varying input akin to what Nedivi’s lab measured, to the performance of a group of cells that all acted like the best single cell of the lot. Up to about 5,000 total synapses, the “best” cell group delivered more informative results but after that level, the small, weak and diverse group actually performed better. In the race to represent the total visual input with at least 90 percent accuracy, the small weak and diverse group reached that level with about 6,700 synapses while the “best” cell group needed more than 7,900.

“Thus heterogeneity imparts a cost reduction in terms of the number of synapses required for accurate readout of visual features,” the authors wrote.

Nedivi said the study raises tantalizing implications regarding how thalamic input into the cortex works. One, she said, is that given the small size of thalamic synapses they are likely to exhibit significant “plasticity.” Another is that the surprising benefit of diversity may be a general feature, not just a special case for visual input in layer 2/ 3. Further studies, however, are needed to know for sure.

In addition to Nedivi, Balcioglu, Gillani, Ku, Chung, Segev and Doron, other authors are Kendyll Burnell and Alev Erisir.

The National Eye Institute of the National Institutes of Health, the Office of Naval Research, and the JPB Foundation funded the study.

The researchers, from the University of Cambridge, along with colleagues from the US, Israel and Austria, developed a theory describing a new state of light, which has controllable quantum properties over a broad range of frequencies, up as high as X-ray frequencies. Their results are reported in the journal Nature Physics.

The world we observe around us can be described according to the laws of classical physics, but once we observe things at an atomic scale, the strange world of quantum physics takes over. Imagine a basketball: observing it with the naked eye, the basketball behaves according to the laws of classical physics. But the atoms that make up the basketball behave according to quantum physics instead.

“Light is no exception: from sunlight to radio waves, it can mostly be described using classical physics,” said lead author Dr Andrea Pizzi, who carried out the research while based at Cambridge’s Cavendish Laboratory. “But at the micro and nanoscale so-called quantum fluctuations start playing a role and classical physics cannot account for them.”

Pizzi, who is currently based at Harvard University, worked with Ido Kaminer’s group at the Technion-Israel Institute of Technology and colleagues at MIT and the University of Vienna to develop a theory that predicts a new way of controlling the quantum nature of light.

“Quantum fluctuations make quantum light harder to study, but also more interesting: if correctly engineered, quantum fluctuations can be a resource,” said Pizzi. “Controlling the state of quantum light could enable new techniques in microscopy and quantum computation.”

One of the main techniques for generating light uses strong lasers. When a strong enough laser is pointed at a collection of emitters, it can rip some electrons away from the emitters and energise them. Eventually, some of these electrons recombine with the emitters they were extracted from, and the excess energy they absorbed is released as light. This process turns the low-frequency input light into a high-frequency output radiation.

“The assumption has been that all these emitters are independent from one another, resulting in output light in which quantum fluctuations are pretty featureless,” said Pizzi. “We wanted to study a system where the emitters are not independent, but correlated: the state of one particle tells you something about the state of another. In this case, the output light starts behaving very differently, and its quantum fluctuations become highly structured, and potentially more useful.”

To solve this type of problem, known as a many body problem, the researchers used a combination of theoretical analysis and computer simulations, where the output light from a group of correlated emitters could be described using quantum physics.

The theory, whose development was led by Pizzi and Alexey Gorlach from the Technion, demonstrates that controllable quantum light can be generated by correlated emitters with a strong laser. The method generates high-energy output light, and could be used to engineer the quantum-optical structure of X-rays.

“We worked for months to get the equations cleaner and cleaner, until we got to the point where we could describe the connection between the output light and the input correlations with just one compact equation. As a physicist, I find this beautiful,” said Pizzi. “Looking forward, we would like to collaborate with experimentalists to provide a validation of our predictions. On the theory side of things, our work suggests many-body systems as a resource for generating quantum light, a concept that we want to investigate more broadly, beyond the setup considered in this work.”

The research was supported in part by the Royal Society. Andrea Pizzi is a Junior Research Fellow at Trinity College, Cambridge.

Pathogens are disease-causing organisms. By natural selection, they develop evading mechanisms to outsmart the host’s immune system and to get the upper hand. One way to support the immune system and fight back is medical intervention. However, this can lead to unwanted adaptions of pathogens as seen in antibiotic-resistant bacteria. Another strategy is social intervention. Some social groups like ants are trying to fight infection with “social immunity,” the collective hygiene and health care measures to avoid spreading throughout the community. If and how pathogens can respond to this kind of group behavior, is still unknown.

The latest study by Professor Sylvia Cremer and her research team at the Institute of Science and Technology Austria (ISTA) shows the extraordinary effects of these kinds of host-parasite interactions. Together, with chemical ecologists at the University of Würzburg in Germany, the scientists took a close look at social ants, to see how pathogenic fungi respond to their hosts’ social care intervention during infection. The results reveal that fungi reduce their chemical detection signals to outplay social immunity. The study is published today in Nature Ecology & Evolution.

More spores but less grooming

“Fungi infect the ants from the body surface and grow inside, but nestmates groom off many of the spores before they can even cause internal infection,” explains Barbara Milutinović, one of the lead authors, former postdoc in the Cremer Group and now Marie Curie Sklodowska Fellow at Ruđer Bošković Institute in Croatia. The scientists set up an experiment where Argentine ants (Linepithemahumile) were infected with pathogenic Metarhizium fungi either in the absence or presence of caregiving colony members. “We found that the fungi fundamentally changed in response to the ant workers’ caregiving,” Milutinović continues. Over ten infection cycles, fungi which experienced grooming nestmate ants boosted their spore production compared to fungi accompanied by only individual ants. “Producing more spores will help the fungus counteract the spore-removal by helping nestmates. Yet, we were surprised to see that the ants showed less grooming against the spores,” Sylvia Cremer adds. “This suggests, that the spores have become more difficult to detect by the ants.”

Fungi lose their typical chemical profile

To check why ant workers had difficulties sensing fungi and to analyze possible fungal detection cues, the scientists teamed up with a chemical ecologist from the University of Würzburg. Local Professor Thomas Schmitt explains: “The fungi, that adapted to social hosts were perceived less strongly, due to a strong reduction of a fungi-specific compound called ergosterol.” Ergosterol is an essential membrane compound, that all fungi have. By exposing the ants to pure fungal ergosterol or the slightly different non-fungal vertebrate equivalent, the researchers showed, that only the fungal compound induced intense grooming. Milutinović summarizes: “This demonstrates that fungal pathogens react to the presence of caregiving ants by reducing their characteristic fungal signals. They are no longer recognized as a disease threat and can escape the social immunity of the colony.”

The findings highlight the impact that social hosts have on their pathogens by group behaviors. “It’s fascinating how collective hygiene measures trigger evasion strategies in the pathogen. It would be interesting to see how the ant colony will react in turn. Maybe they become more sensitive in detecting lower and lower fungal cues,” Cremer concludes.