For stem cells, bigger doesn’t mean better

MIT biologists have answered an important biological question: Why do cells control their size?

Cells of the same type are strikingly uniform in size, while cell size differs between different cell types. This raises the question of whether cell size is important for cellular physiology.

The new study suggests that cellular enlargement drives a decline in function of stem cells. The researchers found that blood stem cells, which are among the smallest cells in the body, lose their ability to perform their normal function -- replenishing the body's blood cells -- as they grow larger. However, when the cells were restored to their usual size, they behaved normally again.

The researchers also found that blood stem cells tend to enlarge as they age. Their study shows that this enlargement contributes to stem cell decline during aging.

"We have discovered cellular enlargement as a new aging factor in vivo, and now we can explore if we can treat cellular enlargement to delay aging and aging-related diseases," says Jette Lengefeld, a former MIT postdoc, who is now a principal investigator at the University of Helsinki.

Lengefeld is the lead author of the study, which appears today in Science Advances. The late Angelika Amon, an MIT professor of biology and member of the Koch Institute for Integrative Cancer Research, is the senior author of the study.

Outsized effects

It has been known since the 1960s that human cells grown in a lab dish enlarge as they become senescent -- a nondividing cellular state

that is associated with aging. Every time a cell divides, it can encounter DNA damage. When this happens, division is halted to repair the damage. During each of these delays, the cell grows slightly larger. Many scientists believed that this enlargement was simply a side effect of aging, but the Amon lab began to investigate the possibility that large cell size drives age-related losses of function.

Lengefeld studied the effects of size on stem cells -- specifically, blood stem cells, which give rise to the blood cells of our body throughout life. To study how size affects these stem cells, the researchers damaged their DNA, leading to an increase in their size. They then compared these enlarged cells to other cells that also experienced DNA damage but were prevented from increasing in size using a drug called rapamycin.

After the treatment, the researchers measured the functionality of these two groups of stem cells by injecting them into mice that had their own blood stem cells eliminated. This allowed the researchers to determine whether the transplanted stem cells were able to repopulate the mouse's blood cells.

They found that the DNA-damaged and enlarged stem cells were unable to produce new blood cells. However, the DNA-damaged stem cells that were kept small were still able to produce new blood cells.

In another experiment, the researchers used a genetic mutation to reduce the size of naturally occurring large stem cells that they found in older mice. They showed that if they induced those large stem cells to become small again, the cells regained their regenerative potential and behaved like younger stem cells.

"This is striking evidence supporting the model that size is important for functionality of stem cells," Lengefeld says. "When we damage the stem cells' DNA but keep them small during the damage, they retain their functionality. And if we reduce the size of large stem cells, we can restore their function."

Keeping cells small

When the researchers treated mice with rapamycin, beginning at a young age, they were able to prevent blood stem cells from enlarging as the mice got older. Blood stem cells from those mice remained small and were able to build blood cells like young stem cells even in mice 3 years of age -- an old age for a mouse.

Rapamycin, a drug that can inhibit cell growth, is now used to treat some cancers and to prevent organ transplant rejection, and has raised interest for its ability to extend lifespan in mice and other organisms. It may be useful in slowing down the enlargement of stem cells and therefore could have beneficial effects in humans, Lengefeld says.

"If we find drugs that are specific in making large blood stem cells smaller again, we can test whether this improves the health of people who suffer from problems with their blood system -- like anemia and a reduced immune system -- or maybe even help people with leukemia," she says.

The researchers also demonstrated the importance of size in another type of stem cells -- intestinal stem cells. They found that larger stem cells were less able to generate intestinal organoids, which mimic the structure of the intestinal lining.

"That suggested that this relationship between cell size and function is conserved in stem cells, and that cellular size is a marker of stem cell function," Lengefeld says.

Read more at Science Daily

Illuminating dark matter in human DNA

Researchers at University of California San Diego have produced a single-cell chromatin atlas for the human genome. Chromatin is a complex of DNA and protein found in eukaryotic cells; regions of chromatin at key gene regulatory elements appear in open configurations within certain cell nuclei. Precisely delineating these accessible chromatin regions in cells of different human tissue types would be a major step toward understanding the role of gene regulatory elements (non-coding DNA) in human health or disease.

The findings are published online in the November 12, 2021, issue of Cell.

For scientists, the human genome, popularly called the "book of life," is mostly unwritten. Or at least unread. While science has famously put an (approximate) number to all of the protein-coding genes required to build a human being, approximately 20,000+, that estimation does not really begin to explain how exactly the construction process works or, in the case of disease, it might go awry.

"The human genome was sequenced 20 years ago, but interpreting the meaning of this book of life continues to be challenging," said Bing Ren, PhD, director of the Center for Epigenomics, professor of cellular and molecular medicine at UC San Diego School of Medicine and a member of the Ludwig Institute for Cancer Research at UC San Diego.

"A major reason is that the majority of the human DNA sequence, more than 98 percent, is non-protein-coding, and we do not yet have a genetic code book to unlock the information embedded in these sequences."

Put another way, it's a bit like knowing chapter titles but with the rest of the pages still blank.

Efforts to fill in the blanks are broadly captured in an ongoing international effort called the Encyclopedia of DNA Elements (ENCODE), and include the work of Ren and colleagues. In particular, they have investigated the role and function of chromatin, a complex of DNA and proteins that form chromosomes within the nuclei of eukaryotic cells.

DNA carries the cell's genetic instructions. The major proteins in chromatin, called histones, help tightly package the DNA in a compact form that fits within the cell nucleus. (There are roughly six feet of DNA tucked into each cell nucleus and approximately 10 billion miles in each human body.) Changes in how chromatin bundles up DNA are associated with DNA replication and gene expression.

After working with mice, Ren and collaborators turned their attention to a single-cell atlas of chromatin in the human genome.

They applied assays to more than 600,000 human cells sampled from 30 adult human tissue types from multiple donors, then integrated that information with similar data from 15 fetal tissue types to reveal the status of chromatin at approximately 1.2 million candidate cis-regulatory elements in 222 distinct cell types.

"One of the initial challenges was identifying the best experimental conditions for such a diverse set of sample types, particularly given each tissue's unique makeup and sensitivity to homogenization," said study co-author Sebastian Preissl, PhD, associate director for Single Cell Genomics at UC San Diego Center for Epigenomics, a collaborative research center that carried out the assays.

Cis-regulatory elements are regions of non-coding DNA that regulate transcription (copying a segment of DNA into RNA) of neighboring genes. Transcription is the essential process that converts genetic information into action.

"Studies in the last decade have established that sequence variations in non-coding DNA are a key driver in multi-genic traits and diseases in human populations, such as diabetes, Alzheimer's' disease and autoimmune diseases," said study co-author Kyle J. Gaulton, PhD, assistant professor in the Department of Pediatrics at UC San Diego School of Medicine.

"A new paradigm that helps explain how these noncoding variants contribute to diseases posits that these sequence alterations disrupt function of transcriptional regulatory elements and lead to dysregulation of gene expression in disease-relevant cell types, such as neurons, immune cells or epithelial cells," said co-first author Kai Zhang, PhD, a postdoctoral fellow in the Department of Cellular and Molecular Medicine. "A major barrier to unlocking the function of noncoding risk variants, however, is the lack of cell-type-specific maps of transcriptional regulatory elements in the human genome."

Ren said the new findings identify disease-trait-relevant cell types for 240 multi-genic traits and diseases, and annotate the risk of noncoding variants.

"We believe that this resource will greatly facilitate the study of mechanism across a broad spectrum of human diseases for many years to come."

Read more at Science Daily

Tread lightly: ‘Eggshell planets’ possible around other stars

Strange 'eggshell planets' are among the rich variety of exoplanets possible, according to a study from Washington University in St. Louis. These rocky worlds have an ultra-thin outer brittle layer and little to no topography. Such worlds are unlikely to have plate tectonics, raising questions as to their habitability.

Only a small subset of extrasolar planets are likely eggshell planets. Planetary geologist Paul Byrne, first author of the new modeling study in the Journal of Geophysical Research: Planets, said at least three such worlds found during previous astronomical surveys may already be known. Scientists could use planned and future space telescopes to examine these exoplanets in greater detail and confirm their geological characteristics.

"Understanding whether you've got the possibility of plate tectonics is a really important thing to know about a world, because plate tectonics may be required for a large rocky planet to be habitable," said Byrne, associate professor in the Department of Earth and Planetary Sciences in Arts & Sciences and a faculty fellow of the university's McDonnell Center for the Space Sciences. "It's therefore especially important when we're talking about looking for Earth-like worlds around other stars and when we're characterizing planetary habitability generally."

"What we've laid out here is essentially a how-to guide, or handy manual," he said. "If you have a planet of a given size, at a given distance from its star and of a given mass, then with our results you can make some estimates for a variety of other features -- including whether it may have plate tectonics."

A new way to think about exoplanets

To date, exoplanets have largely been the domain of astronomers, because space scientists rely on astronomical techniques and instruments to detect exoplanets. More than 4,000 exoplanets have been discovered and are considered "confirmed." Byrne's study offers new and concrete ways that other scientists could identify eggshell planets, as well as other types of exoplanets that could be interesting because of their particular combinations of size, age and distance to their host star.

"We have imaged a few exoplanets, but they are splotches of light orbiting a star. We have no technical ability to actually see the surface of exoplanets yet," Byrne said. "This paper is one of a small but growing number of studies taking a geological or geophysical perspective to try and understand the worlds that we cannot directly measure right now."

Planets have certain qualities that are inherent to the planets themselves, like their size, interior temperature and the materials that they are made of. Other properties are more of a function of the planet's environment, like how far it is from the sun. The planets that humans know best are those in our own solar system -- but these truths are not necessarily universal for planets that orbit other stars.

"We know from published work that there are exoplanets that experience conditions in a more extreme way than what we see in our solar system," Byrne said. "They might be closer to their star, or they might be much larger, or have hotter surfaces, than the planets we see in our own system."

Byrne and his collaborators wanted to see which planetary and stellar parameters play the most important role in determining the thickness of a planet's outer brittle layer, which is known as the lithosphere.

This thickness helps determine whether, for example, a planet can support high topography such as mountains, or has the right balance between rigidity and flexibility for one part of the surface to dive down, or subduct, beneath another -- the hallmark of plate tectonics. It is this process that helps Earth regulate its temperature over geological timescales, and the reason why plate tectonics is thought to be an important component of planetary habitability.

For their modeling effort, the scientists chose a generic rocky world as a starting point. ("It was kind of Earth sized -- although we did consider size in there, too," he said).

"And then we spun the dials," Byrne said. "We literally ran thousands of models."

Perhaps similar to parts of Venus

They discovered that surface temperature is the primary control on the thickness of brittle exoplanet lithospheres, although planetary mass, distance to its star and even age all play a role. The new models predict that worlds that are small, old or far from their star likely have thick, rigid layers, but, in some circumstances, planets might have an outer brittle layer only a few kilometers thick -- these so-called eggshell planets.

Although we are a long way from directly imaging the surfaces of these eggshell planets, they might resemble the lowlands on Venus, Byrne noted. Those lowlands contain vast expanses of lavas but have little high-standing terrain, because the lithosphere there is thin as a result of searing surface temperatures.

"Our overall goal is more than just understanding the vagaries of exoplanets," Byrne said. "Ultimately we want to help contribute to identifying the properties that make a world habitable. And not just temporarily, but habitable for a long time, because we think life probably needs a while to get going and become sustainable."

Read more at Science Daily

Crushed resistance: Tectonic plate sinking into a subduction zone

The Earth's surface consists of a few large plates and numerous smaller ones that are continuously moving either away from or towards each other at an extremely slow pace. At the boundaries of two plates, the heavier oceanic plate sinks below the lighter continental plate in a process that experts call subduction. For a long time, though, those experts have been puzzling over what happens to the plate margin that dives into the Earth's mantle, known as the subducting slab. Some scientists assumed that the slab remains as rigid and strong as the plate itself and simply bends due to the gravity force and mechanical interaction with the Earth's mantle.

Heavily deformed plate margin

However, models of the Earth's interior constructed by scientists using seismic tomography revealed contradictory results: in the western United States, for example, the researchers observed anomalies at different depths on their tomographic images. These indicated that the slabs submerged beneath the Americas may be segmented. The scientists therefore concluded that the slabs in the mantle must be strongly deformed and are by no means rigid and immobile.

With the aid of computer models, other researchers, including ETH Professor Paul Tackley, confirmed that subducted slabs are indeed weak and deformable. And they formulated the subduction dichotomy hypothesis that can be expressed in simple terms: plates on the surface are rigid and strong (read: non-deformable), while the slabs in the mantle are soft and weak.

Seeking a plausible mechanism

"Until now, however, research has lacked a plausible mechanism to explain how this bending occurs and why sinking plate margins (slabs) become soft and weak," says Taras Gerya, Professor of Geophysics at ETH Zurich.

Observations revealed that numerous faults are found on the upper surface of a sinking plate where it meets the other plate. Seawater penetrates the plate through these faults and is in fact literally sucked in by suction forces. This weakens the plate on its upper side.

Yet this alone is not sufficient to explain the segmentation of the slab -- the anomalies observed on tomographic images. Another mechanism must also be at work to weaken the underside of the margin enough for segmentation to occur.

Gerya and his American colleagues David Bercovici and Thorsten Becker therefore suspected that compression of the underside of the plate at the point where it bends downward was "crushing" large and strong, millimetres size olivine crystals in the plate by forcing them to recrystallise into much weaker, micrometres size granular aggregate -- thereby reducing the plate's resistance and allowing it to bend.

Sinking plate margin divided into segments

Using a new two-dimensional computer model that integrated this grain reduction as a central mechanism, the three researchers then studied the process in silico. Their study was recently published in the journal Nature.

And indeed, the simulations revealed that sinking plates deform due to the massive reduction of olivine grains on their undersides, splitting into individual segments over time. These segments are rigid and stiff, but remain connected to each other by weak hinges made of ground grains.

In the simulations, parallel cracks appear at the segment boundaries on the plate's upper surface. Below these cracks are the zones with "crushed" mineral grains.

"Just imagine you're breaking a bar of chocolate," Gerya says with a grin. A bar of chocolate, too, can be divided into segments only along the specified weak points. The squares of chocolate are rigid, but the connecting pieces between them are weak. "That's why a sinking plate isn't uniformly bent or deformed, but segmented."

And here's how it might play out in reality: The heavier plate sinks under the lighter one. A weak spot with smaller mineral grains within the sinking plate allows it to bend. The bending stress causes the minerals to crumble in more places on the underside. The resulting weakness leads to a fracture, and a segment forms. As the plate margin sinks deeper and deeper into the mantle, it causes further segments to form at the bend. As a result, the slab eventually resembles a chain with rigid links and bendable connectors. At a depth of about 600 kilometres, the segmented plate margin slides onto what is known as the 670 km discontinuity in the Earth's mantle, from which point it moves horizontally.

Clues from nature support simulation

"The results of our simulations are consistent with observations in nature," Gerya explains. A great deal of research has been done on the natural situation along the Japan Trench, where the Pacific plate sinks below the Okhotsk plate. The pattern of faults found here is an exact match for the pattern produced in the simulations.

Researchers have also studied the seismic velocity structure of subducting Japan slab thoroughly using its recently produced high-resolution seismic tomography model. They found that the velocity of the seismic waves sent out by earthquakes was reduced at some nodes inside the slab. The pattern with which these nodes occur in reality coincides with that of the segment boundaries from the simulations. And both in nature and in the computer model, it is zones with very small crystals only micrometres across that are responsible for reducing the velocity of the seismic waves.

Read more at Science Daily

‘Dancing molecules’ successfully repair severe spinal cord injuries

Northwestern University researchers have developed a new injectable therapy that harnesses "dancing molecules" to reverse paralysis and repair tissue after severe spinal cord injuries.

In a new study, researchers administered a single injection to tissues surrounding the spinal cords of paralyzed mice. Just four weeks later, the animals regained the ability to walk.

The research will be published in the Nov. 12 issue of the journal Science.

By sending bioactive signals to trigger cells to repair and regenerate, the breakthrough therapy dramatically improved severely injured spinal cords in five key ways: (1) The severed extensions of neurons, called axons, regenerated; (2) scar tissue, which can create a physical barrier to regeneration and repair, significantly diminished; (3) myelin, the insulating layer of axons that is important in transmitting electrical signals efficiently, reformed around cells; (4) functional blood vessels formed to deliver nutrients to cells at the injury site; and (5) more motor neurons survived.

After the therapy performs its function, the materials biodegrade into nutrients for the cells within 12 weeks and then completely disappear from the body without noticeable side effects. This is the first study in which researchers controlled the collective motion of molecules through changes in chemical structure to increase a therapeutic's efficacy.

"Our research aims to find a therapy that can prevent individuals from becoming paralyzed after major trauma or disease," said Northwestern's Samuel I. Stupp, who led the study. "For decades, this has remained a major challenge for scientists because our body's central nervous system, which includes the brain and spinal cord, does not have any significant capacity to repair itself after injury or after the onset of a degenerative disease. We are going straight to the FDA to start the process of getting this new therapy approved for use in human patients, who currently have very few treatment options."

Stupp is Board of Trustees Professor of Materials Science and Engineering, Chemistry, Medicine and Biomedical Engineering at Northwestern, where he is founding director of the Simpson Querrey Institute for BioNanotechnology (SQI) and its affiliated research center, the Center for Regenerative Nanomedicine. He has appointments in the McCormick School of Engineering, Weinberg College of Arts and Sciences and Feinberg School of Medicine.

Life expectancy has not improved since the 1980s

According to the National Spinal Cord Injury Statistical Center, nearly 300,000 people are currently living with a spinal cord injury in the United States. Life for these patients can be extraordinarily difficult. Less than 3% of people with complete injury ever recover basic physical functions. And approximately 30% are re-hospitalized at least once during any given year after the initial injury, costing millions of dollars in average lifetime health care costs per patient. Life expectancy for people with spinal cord injuries is significantly lower than people without spinal cord injuries and has not improved since the 1980s.

"Currently, there are no therapeutics that trigger spinal cord regeneration," said Stupp, an expert in regenerative medicine. "I wanted to make a difference on the outcomes of spinal cord injury and to tackle this problem, given the tremendous impact it could have on the lives of patients. Also, new science to address spinal cord injury could have impact on strategies for neurodegenerative diseases and stroke."

'Dancing molecules' hit moving targets

The secret behind Stupp's new breakthrough therapeutic is tuning the motion of molecules, so they can find and properly engage constantly moving cellular receptors. Injected as a liquid, the therapy immediately gels into a complex network of nanofibers that mimic the extracellular matrix of the spinal cord. By matching the matrix's structure, mimicking the motion of biological molecules and incorporating signals for receptors, the synthetic materials are able to communicate with cells.

"Receptors in neurons and other cells constantly move around," Stupp said. "The key innovation in our research, which has never been done before, is to control the collective motion of more than 100,000 molecules within our nanofibers. By making the molecules move, 'dance' or even leap temporarily out of these structures, known as supramolecular polymers, they are able to connect more effectively with receptors."

Stupp and his team found that fine-tuning the molecules' motion within the nanofiber network to make them more agile resulted in greater therapeutic efficacy in paralyzed mice. They also confirmed that formulations of their therapy with enhanced molecular motion performed better during in vitro tests with human cells, indicating increased bioactivity and cellular signaling.

"Given that cells themselves and their receptors are in constant motion, you can imagine that molecules moving more rapidly would encounter these receptors more often," Stupp said. "If the molecules are sluggish and not as 'social,' they may never come into contact with the cells."

One injection, two signals

Once connected to the receptors, the moving molecules trigger two cascading signals, both of which are critical to spinal cord repair. One signal prompts the long tails of neurons in the spinal cord, called axons, to regenerate. Similar to electrical cables, axons send signals between the brain and the rest of the body. Severing or damaging axons can result in the loss of feeling in the body or even paralysis. Repairing axons, on the other hand, increases communication between the body and brain.

The second signal helps neurons survive after injury because it causes other cell types to proliferate, promoting the regrowth of lost blood vessels that feed neurons and critical cells for tissue repair. The therapy also induces myelin to rebuild around axons and reduces glial scarring, which acts as a physical barrier that prevents the spinal cord from healing.

"The signals used in the study mimic the natural proteins that are needed to induce the desired biological responses. However, proteins have extremely short half-lives and are expensive to produce," said Zaida Álvarez, the study's first author and former research assistant professor in Stupp's laboratory. "Our synthetic signals are short, modified peptides that -- when bonded together by the thousands -- will survive for weeks to deliver bioactivity. The end result is a therapy that is less expensive to produce and lasts much longer."

Read more at Science Daily

Using mechanical tools improves our language skills, study finds

Our ability to understand the syntax of complex sentences is one of the most difficult language skills to acquire. In 2019, research had revealed a correlation between being particularly proficient in tool use and having good syntactic ability. A new study, by researchers from Inserm, CNRS, Université Claude Bernard Lyon 1 and Université Lumière Lyon 2 in collaboration with Karolinska Institutet in Sweden, has now shown that both skills rely on the same neurological resources, which are located in the same brain region. Furthermore, motor training using a tool improves our ability to understand the syntax of complex sentences and -- vice-versa -- syntactic training improves our proficiency in using tools. These findings could be applied clinically to support the rehabilitation of patients having lost some of their language skills.

This study is published in November 2021 in the journal Science.

Language has long been considered a very complex skill, mobilizing specific brain networks. However, in recent years, scientists have revisited this idea.

Research suggests that brain areas, which control certain linguistic functions, such as the processing of word meanings, are also involved in controlling fine motor skills. However, brain imaging had not provided evidence of such links between language and the use of tools. Paleo-neurobiology has also shown that the brain regions associated with language had increased in our ancestors during periods of technological boom, when the use of tools became more widespread.

When considering this data, research teams couldn't help wondering: what if the use of certain tools, which involves complex movements, relies on the same brain resources as those mobilized in complex linguistic functions such as syntax?

Syntax exercises and use of tongs

In 2019, Inserm researcher Claudio Brozzoli in collaboration with CNRS researcher Alice C. Roy and their team had shown that individuals who are particularly proficient in the use of tools were also generally better at handling the finer points of Swedish syntax.

In order to explore the subject in greater depth, the same team, in collaboration with CNRS researcher Véronique Boulenger, developed a series of experiments that relied on brain imaging techniques (functional magnetic resonance imaging or MRI) and behavioral measurements. The participants were asked to complete several tests consisting of motor training using 30 cm-long pliers and syntax exercises in French. This enabled the scientists to identify the brain networks specific to each task, but also common to both tasks.

They discovered for the first time that the handling of the tool and the syntax exercises produced brain activations in common areas, with the same spatial distribution, in a region called the "basal ganglia."

Cognitive training

Given that these two skill types use the same brain resources, is it possible to train one in order to improve the other? Does motor training with the mechanical tongs improve the understanding of complex phrases? In the second part of their study, the scientists looked at these issues and showed that this is indeed the case.

This time, the participants were asked to perform a syntactic comprehension task before and after 30 minutes of motor training with the pliers (see box for details of the experiment). With this, the researchers demonstrated that motor training with the tool leads to improved performance in syntactic comprehension exercises.

In addition, the findings show that the reverse is also true: training of language faculties, with exercises to understand sentences with complex structure, improved motor performance with the tool.

The scientists are now thinking about how to best apply these findings in the clinical setting."We are currently devising protocols that could be put in place to support the rehabilitation and recovery of language skills of patients with relatively preserved motor faculties, such as young people with developmental language disorders. Beyond these innovative applications, these findings also give us an insight into how language has evolved throughout history. When our ancestors began to develop and use tools, this proficiency profoundly changed the brain and imposed cognitive demands that may have led to the emergence of certain functions such as syntax," concludes Brozzoli.

Motor training and syntax exercises

The motor training involved using the pliers to insert small pegs into holes that matched their shape but with differing orientations.

The syntax exercises which were completed before and after this training consisted of reading sentences with a simple syntax, such as "The scientist who admires the poet writes an article" or with a more complex syntax, such as "The scientist whom the poet admires writes an article." Then the participants had to decide whether statements such as "The poet admires the scientist" were true or false. Sentences with the French object relative pronoun "que" are more difficult to process and therefore performance was generally poorer.

Read more at Science Daily

Black hole found hiding in star cluster outside our galaxy

Using the European Southern Observatory's Very Large Telescope (ESO's VLT), astronomers have discovered a small black hole outside the Milky Way by looking at how it influences the motion of a star in its close vicinity. This is the first time this detection method has been used to reveal the presence of a black hole outside of our galaxy. The method could be key to unveiling hidden black holes in the Milky Way and nearby galaxies, and to help shed light on how these mysterious objects form and evolve.

The newly found black hole was spotted lurking in NGC 1850, a cluster of thousands of stars roughly 160,000 light-years away in the Large Magellanic Cloud, a neighbour galaxy of the Milky Way.

"Similar to Sherlock Holmes tracking down a criminal gang from their missteps, we are looking at every single star in this cluster with a magnifying glass in one hand trying to find some evidence for the presence of black holes but without seeing them directly," says Sara Saracino from the Astrophysics Research Institute of Liverpool John Moores University in the UK, who led the research now accepted for publication in Monthly Notices of the Royal Astronomical Society. "The result shown here represents just one of the wanted criminals, but when you have found one, you are well on your way to discovering many others, in different clusters."

This first "criminal" tracked down by the team turned out to be roughly 11 times as massive as our Sun. The smoking gun that put the astronomers on the trail of this black hole was its gravitational influence on the five-solar-mass star orbiting it.

Astronomers have previously spotted such small, "stellar-mass" black holes in other galaxies by picking up the X-ray glow emitted as they swallow matter, or from the gravitational waves generated as black holes collide with one another or with neutron stars.

However, most stellar-mass black holes don't give away their presence through X-rays or gravitational waves. "The vast majority can only be unveiled dynamically," says Stefan Dreizler, a team member based at the University of Göttingen in Germany. "When they form a system with a star, they will affect its motion in a subtle but detectable way, so we can find them with sophisticated instruments."

This dynamical method used by Saracino and her team could allow astronomers to find many more black holes and help unlock their mysteries. "Every single detection we make will be important for our future understanding of stellar clusters and the black holes in them," says study co-author Mark Gieles from the University of Barcelona, Spain.

The detection in NGC 1850 marks the first time a black hole has been found in a young cluster of stars (the cluster is only around 100 million years old, a blink of an eye on astronomical scales). Using their dynamical method in similar star clusters could unveil even more young black holes and shed new light on how they evolve. By comparing them with larger, more mature black holes in older clusters, astronomers would be able to understand how these objects grow by feeding on stars or merging with other black holes. Furthermore, charting the demographics of black holes in star clusters improves our understanding of the origin of gravitational wave sources.

To carry out their search, the team used data collected over two years with the Multi Unit Spectroscopic Explorer (MUSE) mounted at ESO's VLT, located in the Chilean Atacama Desert. "MUSE allowed us to observe very crowded areas, like the innermost regions of stellar clusters, analysing the light of every single star in the vicinity. The net result is information about thousands of stars in one shot, at least 10 times more than with any other instrument," says co-author Sebastian Kamann, a long-time MUSE expert based at Liverpool's Astrophysics Research Institute. This allowed the team to spot the odd star out whose peculiar motion signalled the presence of the black hole. Data from the University of Warsaw's Optical Gravitational Lensing Experiment and from the NASA/ESA Hubble Space Telescope enabled them to measure the mass of the black hole and confirm their findings.

Read more at Science Daily

Near-earth asteroid might be a lost fragment of the moon

A near-Earth asteroid named Kamo`oalewa could be a fragment of our moon, according to a new paper published in Nature Communications Earth and Environment by a team of astronomers led by the University of Arizona.

Kamo`oalewa is a quasi-satellite -- a subcategory of near-Earth asteroids that orbit the sun but remain relatively close to Earth. Little is known about these objects because they are faint and difficult to observe. Kamo`oalewa was discovered by the PanSTARRS telescope in Hawaii in 2016, and the name -- found in a Hawaiian creation chant -- alludes to an offspring that travels on its own. The asteroid is roughly the size of a Ferris wheel -- between 150 and 190 feet in diameter -- and gets as close as about 9 million miles from Earth.

Due to its orbit, Kamo`oalewa can only be observed from Earth for a few weeks every April. Its relatively small size means that it can only be seen with one of the largest telescopes on Earth. Using the UArizona-managed Large Binocular Telescope on Mount Graham in southern Arizona, a team of astronomers led by planetary sciences graduate student Ben Sharkey found that Kamo`oalewa's pattern of reflected light, called a spectrum, matches lunar rocks from NASA's Apollo missions, suggesting it originated from the moon.

The team can't yet be sure how it may have broken loose. The reason, in part, is because there are no other known asteroids with lunar origins.

"I looked through every near-Earth asteroid spectrum we had access to, and nothing matched," said Sharkey, the paper's lead author.

The debate over Kamo`oalewa's origins between Sharkey and his adviser, UArizona associate professor Vishnu Reddy, led to another three years of hunting for a plausible explanation.

"We doubted ourselves to death," said Reddy, a co-author who started the project in 2016. After missing the chance to observe it in April 2020 due to a COVID-19 shutdown of the telescope, the team found the final piece of the puzzle in 2021.

"This spring, we got much needed follow-up observations and went, 'Wow it is real,'" Sharkey said. "It's easier to explain with the moon than other ideas."

Kamo`oalewa's orbit is another clue to its lunar origins. Its orbit is similar to the Earth's, but with the slightest tilt. Its orbit is also not typical of near-Earth asteroids, according to study co-author Renu Malhotra, a UArizona planetary sciences professor who led the orbit analysis portion of the study.

"It is very unlikely that a garden-variety near-Earth asteroid would spontaneously move into a quasi-satellite orbit like Kamo`oalewa's," she said. "It will not remain in this particular orbit for very long, only about 300 years in the future, and we estimate that it arrived in this orbit about 500 years ago," Malhotra said. Her lab is working on a paper to further investigate the asteroid's origins.

Kamo`oalewa is about 4 million times fainter than the faintest star the human eye can see in a dark sky.

"These challenging observations were enabled by the immense light gathering power, of the twin 8.4-meter telescopes of the Large Binocular Telescope," said study co-author Al Conrad, a staff scientist with the telescope.

Read more at Science Daily

Humans hastened the extinction of the woolly mammoth

New research shows that humans had a significant role in the extinction of woolly mammoths in Eurasia, occurring thousands of years later than previously thought.

An international team of scientists led by researchers from the University of Adelaide and University of Copenhagen, has revealed a 20,000-year pathway to extinction for the woolly mammoth.

"Our research shows that humans were a crucial and chronic driver of population declines of woolly mammoths, having an essential role in the timing and location of their extinction," said lead author Associate Professor Damien Fordham from the University of Adelaide's Environment Institute.

"Using computer models, fossils and ancient DNA we have identified the very mechanisms and threats that were integral in the initial decline and later extinction of the woolly mammoth."

Signatures of past changes in the distribution and demography of woolly mammoths identified from fossils and ancient DNA show that people hastened the extinction of woolly mammoths by up to 4,000 years in some regions.

"We know that humans exploited woolly mammoths for meat, skins, bones and ivory. However, until now it has been difficult to disentangle the exact roles that climate warming and human hunting had on its extinction," said Associate Professor Fordham.

The study also shows that woolly mammoths are likely to have survived in the Arctic for thousands of years longer than previously thought, existing in small areas of habitat with suitable climatic conditions and low densities of humans.

"Our finding of long-term persistence in Eurasia independently confirms recently published environmental DNA evidence that shows that woolly mammoths were roaming around Siberia 5,000 years ago," said Associate Professor Jeremey Austin from the University of Adelaide's Australian Centre for Ancient DNA.

Associate Professor David Nogues-Bravo from the University of Copenhagen was a co-author of the study which is published in the journal Ecology Letters.

"Our analyses strengthens and better resolves the case for human impacts as a driver of population declines and range collapses of megafauna in Eurasia during the late Pleistocene," he said.

"It also refutes a prevalent theory that climate change alone decimated woolly mammoth populations and that the role of humans was limited to hunters delivering the coup de grâce".

"And shows that species extinctions are usually the result of complex interactions between threatening processes."

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Domestic cats drive spread of Toxoplasma parasite to wildlife

New UBC research suggests free-roaming cats are likely to blame in the spread of the potentially deadly Toxoplasma gondii parasite to wildlife in densely populated urban areas.

The study -- the first to analyze so many wildlife species over a global scale -- also highlights how healthy ecosystems can protect against these types of pathogens.

The researchers, led by UBC faculty of forestry adjunct professor Dr. Amy Wilson, examined 45,079 cases of toxoplasmosis in wild mammals -- a disease that has been linked to nervous system disorders, cancers and other debilitating chronic conditions -- using data from 202 global studies.

They found wildlife living near dense urban areas were more likely to be infected.

"As increasing human densities are associated with increased densities of domestic cats, our study suggests that free-roaming domestic cats -- whether pets or feral cats -- are the most likely cause of these infections," says Dr. Wilson.

"This finding is significant because by simply limiting free roaming of cats, we can reduce the impact of Toxoplasma on wildlife."

One infected cat can excrete as many as 500 million Toxoplasma oocysts (or eggs) in just two weeks. The oocysts can then live for years in soil and water with the potential to infect any bird or mammal, including humans. Toxoplasmosis is particularly dangerous for pregnant people.

If an animal is healthy, the parasite remains dormant and rarely causes direct harm. However, if an animal's immune system is compromised, the parasite can trigger illness and potentially death.

The study also highlights the way healthy forests, streams and other ecosystems can filter out dangerous pathogens like Toxoplasma, notes Dr. Wilson.

"We know that when wetlands are destroyed or streams are restricted, we are more likely to experience runoff that carries more pathogens into the waters where wild animals drink or live," she says. "And when their habitats are healthy, wildlife thrives and tends to be more disease-resistant."

Research results like these remind us that all ecosystems, forested or other, are intrinsically linked.

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