Researchers led by Göttingen University examine the long-term results of an experiment from more than 40 years ago
The fairy circles of the Namib are one of nature’s greatest mysteries. Millions of these circular barren patches extend over vast areas along the margins of the desert in Namibia. In 1979, G.K. Theron published the first research about their origin. His hypothesis was that poisonous substances from Euphorbia damarana leaves induced fairy circles. As part of a new study, scientists from the University of Göttingen and the Gobabeb Namib Research Institute located the original euphorbia plants that were part of Theron’s study. Four decades later, the researchers are now able to conclusively disprove Theron’s original hypothesis. Their results were published in the journal BMC Ecology and Evolution.
In the late 1970s, South African botanist Theron noticed several dying and decomposing shrubs of euphorbia in the Giribes area of north-western Namibia. He therefore proposed that poisonous substances from the leaves of this plant could kill the grasses and induce fairy circles and his hypothesis was published in 1979. As part of the current study, scientists went back to this same area and managed to locate the original metal pins that marked the plants. In 2020, the research team documented these remote sites in detail for the first time, using ground-based photography as well as high-resolution drone imagery and historic satellite images.
The researchers show that none of the marked euphorbia locations developed into a fairy circle. Instead, long-lived grass tussocks were growing around all the metal pins. This runs contrary to the hypothesis that poisons from euphorbia inhibited the growth of other plants because these grasses survived. Given that the euphorbia hypothesis proposes that only dead and decaying shrubs would induce a barren patch, the researchers also measured the sizes of the dying euphorbias and compared them to the sizes of fairy circles in the same study plots. As well as in Giribes, this second part of the study was also carried out at Brandberg. In both regions, the diameters of decaying euphorbias could not explain the sizes of the much smaller or the larger fairy circles. In a third part of the study, the spatial patterns of the fairy circles were directly compared to the patterns of euphorbias within the same areas to investigate a potential link between both distributions in the regions Giribes, Brandberg and Garub. However, the patterns of shrubs and circles did not match: in four out of five plots the patterns differed significantly, with the circles being regularly distributed while the euphorbias were predominantly clustered. Hence the process that creates the pattern of fairy circles is different from the process that creates the pattern of the euphorbias.
Dr Stephan Getzin, Department of Ecosystem Modelling at the University of Göttingen, summarizes, “When Theron published his original euphorbia hypothesis more than four decades ago, he was a pioneer in fairy-circle research: almost nothing was known about them at that time. Today, however, we see the long-term outcome of his early experiment and – based on our detailed field observations – we have to reject the euphorbia hypothesis.” Getzin explains, “Disproving hypotheses about the origin of fairy circles is an important step in solving their mystery because it helps advance our scientific understanding. It enables us to identify more probable mechanisms which explain these stunning formations as well as other fascinating biological phenomena.”
This project was possible thanks to funding from the German Research Foundation (DFG).
Original publication: Getzin, S., Nambwandja, A., Holch, S. & Wiegand, K. (2021) Revisiting Theron’s hypothesis on the origin of fairy circles after four decades: Euphorbias are not the cause. BMC Ecology and Evolution, 21, 102. DoI: 10.1186/s12862-021-01834-5
A University of Oklahoma doctoral student, graduate and undergraduate research assistants, and an associate professor in the Homer L. Dodge Department of Physics and Astronomy in the University of Oklahoma College of Arts and Sciences are lead authors on a paper describing a “changing-look” blazar – a powerful active galactic nucleus powered by supermassive blackhole at the center of a galaxy. The paper is published in The Astrophysical Journal.
Hora D. Mishra, a Ph.D. student, and faculty member Xinyu Dai are lead authors of the paper, along with Christopher Kochanek and Kris Stanek at the Ohio State University and Ben Shappee at the University of Hawaii. The paper represents the findings of researchers from 12 different institutions who participated in a two-year collaborative project involving the collection of spectra or imaging data in different electromagnetic bands. The OU team led the effort in analyzing all the data collected from the collaboration and contributed primarily on the interpretation of the analysis results, assisted by OU graduate student Saloni Bhatiani and undergraduate students Cora DeFrancesco and John Cox who performed ancillary analyses to the project.
Blazars, explains Mishra, who also serves as president of Lunar Sooners, appear as parallel rays of light or particles, or jets, pointing to observers and radiating across all wavelengths of the electromagnetic spectrum. These jets span distances on the million light-year scales and are known to impact the evolution of the galaxy and galaxy cluster in which they reside via the radiation. These features make blazars ideal environments in which to study the physics of jets and their role in galaxy evolution.
“Blazars are a unique kind of AGN with very powerful jets,” she said. “Jets are a radio mode of feedback and because of their scales, they penetrate the galaxy into their large-scale environment. The origin of these jets and processes driving the radiation are not well-known. Thus, studying blazars allows us to understand these jets better and how they are connected to other components of the AGN, like the accretion disk. These jets can heat up and displace gas in their environment affecting, for example, the star formation in the galaxy.”
The team’s paper highlights the results of a campaign to investigate the evolution of a blazar known as B2 1420+32. At the end of 2017, this blazar exhibited a huge optical flare, a phenomenon captured by the All Sky Automated Survey for SuperNovae telescope network.
“We followed this up by observing the evolution of its spectrum and light curve over the next two years and also retrieved archival data available for this object,” Mishra said. “The campaign, with data spanning over a decade, has yielded some most exciting results. We see dramatic variability in the spectrum and multiple transformations between the two blazar sub-classes for the first time for a blazar, thus giving it the name ‘changing-look’ blazar.”
The team concluded that this behavior is caused by the dramatic continuum flux changes, which confirm a long-proposed theory that separates blazars into two major categories.
“In addition, we see several very large multiband flares in the optical and gamma-ray bands on different timescales and new spectral features,” Mishra said. “Such extreme variability and the spectral features demand dedicated searches for more such blazars, which will allow us to utilize the dramatic spectral changes observed to reveal AGN/jet physics, including how dust particles around supermassive black holes are destructed by the tremendous radiation from the central engine and how energy from a relativistic jet is transferred into the dust clouds, providing a new channel linking the evolution of the supermassive black hole with its host galaxy.”
“We are very excited by the results of discovering a changing-look blazar that transforms itself not once, but three times, between its two sub-classes, from the dramatic changes in its continuum emission,” she added. “In addition, we see new spectral features and optical variability that is unprecedented. These results open the door to more such studies of highly variable blazars and their importance in understanding AGN physics.”
“It is really interesting to see the emergence of a forest of Iron emission lines, suggesting that nearby dust particles were evaporated by the strong radiation from the jet and released free Iron ions into the emitting clouds, a phenomenon predicted by theoretical models and confirmed in this blazar outburst,” Dai said.
Researchers at Vanderbilt University Medical Center (VUMC) have identified a common mechanism underlying a spectrum of epilepsy syndromes and neurodevelopmental disorders, including autism, that are caused by variations in a gene encoding a vital transporter protein in the brain.
Their findings, reported last month in the journal Brain, suggest that boosting transporter function via genetic or pharmacological means could be beneficial in treating brain disorders linked to these genetic variations.
“This points (to) a clear direction of treating a wide spectrum of neurodevelopmental disorders, from various epilepsy syndromes (and) autism to neurodevelopmental delay and intellectual disabilities, caused by the pathological variants in this gene,” said Jing-Qiong (Katty) Kang, MD, PhD, associate professor of Neurology and Pharmacology, and the paper/s corresponding author.
“The disorders associated with the gene mutations are rare and there is no effective treatment available,” Kang said. “If … the clinical syndromes we see are the tip of an iceberg, we now know what is going on underneath, and we start to know how to correct the problems.”
The gene, SLC6A1, encodes the GABA transporter 1 (GAT-1) at the axonal termini (ends) of neurons (nerve cells) and astrocytes (star-shaped glial cells that support and protect neurons). GAT-1 removes or “reuptakes” GABA, the major inhibitory neurotransmitter, from the synaptic cleft between two neurons.
GABA regulates nerve signals throughout the brain and plays a key role in normal brain development. Reuptake enables the brain to precisely regulate the supply of the neurotransmitter in concert with GABAA receptors, ion channels that bind it.
Kang and her colleagues have extensively studied GABAA receptors and are world leaders in determining how disrupted GABA signaling can affect brain function and development.
SLC641 variants previously have been associated with a spectrum of epilepsy syndromes, autism and impaired cognition. But until now scientists did not know how these variants could cause such a broad range of brain disorders.
Using high-throughput assays such as flow cytometry and a radioactive labeling technique for measuring GABA reuptake by neurons and astrocytes, the VUMC researchers determined the impact of 22 different variants of SLC6A1 on GAT-1 function in several types of nerve cells derived from patients with neurodevelopmental disorders, epilepsy and autism.
The work was validated in patient-induced pluripotent stem cells that were “reprogrammed” to form neurons and astrocytes.
The researchers found that disease-causing variants were associated with misfoldings of the GAT-1 protein that led to its degradation and which reduced its expression on cell surfaces. Less GAT-1, in turn, lowered GABA reuptake by nerve cells and astrocytes and disrupted neurotransmitter function.
“This is the first large-scale study on SLC6A1 pathological variants,” Kang said. “Our work indicates that SLC6A1-mediated disorders are good candidates for pharmacological as well as gene therapy that restore the functional transporter at the cell surface.”
A compound identified at VUMC that corrects GAT-1 function in mouse models and cells from patients with urea cycle disorder is now being tested in a clinical trial. The inherited disease causes a buildup of ammonia in the bloodstream that can damage the brain and may be fatal.
Another potential approach is the use of antisense oligonucleotides, short, synthetic pieces of genetic material that may increase expression of the normal, “wild-type” GAT-1 protein.
Kang said the research could not have been done without the help of two “hero” mothers of children with rare genetic disorders: Amber Freed, founder and CEO of the Denver-based advocacy group SLC6A1 Connect; and Terry Jo Bichell, PhD, founder and director of Nashville-based COMBINEDBrain, which supports brain research.
“I have been very lucky and privileged to work with them,” Kang said. “They have taught me so much along the way and inspired me to do meaningful research.”
“She loves kids with SLC6A1 as her own and selflessly works to improve their lives with the urgency of a mother,” Freed responded. “Throughout this journey, Katty has been a loving person, inquisitive scientist and pillar of strength.”
“That empathy kept her discoveries progressing through the pandemic,” Bichell added. “She would ride her bicycle to the lab and care for the mouse and cell models at night, on weekends and even holidays … Dr. Kang is doing basic science that will translate to real treatments for real children she has met–and hugged.”
Felicia Mermer and Sarah Poliquin are the paper’s first authors. Other VUMC co-authors are Kathryn Rigsby, Anuj Rastogi, Wangzhen Shen, MD, Alejandra Romero-Morales, Gerald Nwosu and Vivian Gama, PhD.
The research was supported by SLC6A1 Connect, Taysha Gene Therapies, the Charles C. Gates Center Director’s Innovation Fund, the Stoddard family, and by National Institutes of Health grants NS082635, GM128915, CA227483 and MH116901.
Reference: Felicia Mermer, Sarah Poliquin, Kathryn Rigsby, Anuj Rastogi, Wangzhen Shen, Alejandra Romero-Morales, Gerald Nwosu, Patrick McGrath, Scott Demerast, Jason Aoto, Ganna Bilousova, Dennis Lal, Vivian Gama, Jing-Qiong Kang, Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons, Brain, 2021;, awab207, https://doi.org/10.1093/brain/awab207
At the heart of almost every sufficiently massive galaxy there is a black hole whose gravitational field, although very intense, affects only a small region around the centre of the galaxy. Even though these objects are thousands of millions of times smaller than their host galaxies our current view is that the Universe can be understood only if the evolution of galaxies is regulated by the activity of these black holes, because without them the observed properties of the galaxies cannot be explained.
Theoretical predictions suggest that as these black holes grow they generate sufficient energy to heat up and drive out the gas within galaxies to great distances. Observing and describing the mechanism by which this energy interacts with galaxies and modifies their evolution is therefore a basic question in present day Astrophysics.
With this aim in mind, a study led by Ignacio Martín Navarro, a researcher at the Instituto de Astrofísica de Canarias (IAC), has gone a step further and has tried to see whether the matter and energy emitted from around these black holes can alter the evolution, not only of the host galaxy, but also of the satellite galaxies around it, at even greater distances. To do this, the team has used the Sloan Digital Sky Survey, which allowed them to analyse the properties of the galaxies in thousands of groups and clusters. The conclusions of this study, started during Ignacio’s stay at the Max Planck Institute for Astrophysics, are published today in Nature magazine.
“Surprisingly we found that the satellite galaxies formed more or fewer stars depending on their orientation with respect to the central galaxy”, explains Annalisa Pillepich, researcher at the Max Planck Institute for Astronomy (MPIA, Germany) and co-author of the article. To try to explain this geometrical effect on the properties of the satellite galaxies the researchers used a cosmological simulation of the Universe called Illustris-TNG whose code contains a specific way of handling the interaction between central black holes and their host galaxies. “Just as with the observations, the Illustris-TNG simulation shows a clear modulation of the star formation rate in satellite galaxies depending on their position with respect to the central galaxy”, she adds.
This result is doubly important because it gives observational support for the idea that central black holes play an important role in regulating the evolution of galaxies, which is a basic feature of our current understanding of the Universe. Nevertheless, this hypothesis is continually questioned, given the difficulty of measuring the possible effect of the black holes in real galaxies, rather than considering only theoretical implications.
These results suggest, then, that there is a particular coupling between the black holes and their galaxies, by which they can expel matter to great distances from the galactic centres, and can even affect the evolution of other nearby galaxies. “So not only can we observe the effects of central black holes on the evolution of galaxies, but our analysis opens the way to understand the details of the interaction”, explains Ignacio Martín Navarro, who is the first author of the article.
“This work has been possible due to collaboration between two communities: the observers and the theorists which, in the field of extragalactic Astrophysics, are finding that cosmological simulations are a useful tool to understand how the Universe behaves”, he concludes.
Featured image: Artistic composition of a supermassive black hole regulating the evolution of its environment. Credit: Gabriel Pérez Díaz, SMM (IAC) and Dylan Nelson (Illustris-TNG).
Article: Ignacio Martín Navarro, Annalisa Pillepich, et al. “Anisotropic satellite quenching modulated by black hole activity”. Nature, June 10, 2021. DOI: 10.1038/s41586-021-03545-9
In a major scientific leap, University of Queensland researchers have created a quantum microscope that can reveal biological structures that would otherwise be impossible to see.
This paves the way for applications in biotechnology, and could extend far beyond this into areas ranging from navigation to medical imaging.
The microscope is powered by the science of quantum entanglement, an effect Einstein described as “spooky interactions at a distance”.
Professor Warwick Bowen, from UQ’s Quantum Optics Lab and the ARC Centre of Excellence for Engineered Quantum Systems (EQUS), said it was the first entanglement-based sensor with performance beyond the best possible existing technology.
“This breakthrough will spark all sorts of new technologies – from better navigation systems to better MRI machines, you name it,” Professor Bowen said.
“Entanglement is thought to lie at the heart of a quantum revolution.
“We’ve finally demonstrated that sensors that use it can supersede existing, non-quantum technology.
“This is exciting – it’s the first proof of the paradigm-changing potential of entanglement for sensing.”
Australia’s Quantum Technologies Roadmap sees quantum sensors spurring a new wave of technological innovation in healthcare, engineering, transport and resources.
A major success of the team’s quantum microscope was its ability to catapult over a ‘hard barrier’ in traditional light-based microscopy.
UQ team researchers (counter-clockwise from bottom-left) Caxtere Casacio, Warwick Bowen, Lars Madsen and Waleed Muhammad aligning the quantum microscope.
“The best light microscopes use bright lasers that are billions of times brighter than the sun,” Professor Bowen said.
“Fragile biological systems like a human cell can only survive a short time in them and this is a major roadblock.
“The quantum entanglement in our microscope provides 35 per cent improved clarity without destroying the cell, allowing us to see minute biological structures that would otherwise be invisible.
“The benefits are obvious – from a better understanding of living systems, to improved diagnostic technologies.”
Professor Bowen said there were potentially boundless opportunities for quantum entanglement in technology.
“Entanglement is set to revolutionise computing, communication and sensing,” he said.
“Absolutely secure communication was demonstrated some decades ago as the first demonstration of absolute quantum advantage over conventional technologies.
“Computing faster than any possible conventional computer was demonstrated by Google two years ago, as the first demonstration of absolute advantage in computing.
“The last piece in the puzzle was sensing, and we’ve now closed that gap.
“This opens the door for some wide-ranging technological revolutions.”
The research was supported by the United States Air Force Office of Scientific Research and the Australian Research Council. It is published in Nature (DOI: 10.1038/s41586-021-03528-w).
Researchers investigating a group of microscopic cells have discovered they can put the brakes on the rapid development of melanoma lesions.
A team at the University of Queensland and collaborators from WEHI and Peter MacCallum Cancer Centre have taken a close look at the Group 2 innate lymphoid cells (ILC2) which are crucial for initiating and orchestrating immune responses.
UQ Diamantina Institute’s Professor Gabrielle Belz said their aim was to understand more about the function of these relatively recently identified cells, and their roles in melanoma.
“We wanted to investigate how ILC2 contribute to melanoma formation, because we already knew these cells harboured functions that could either suppress or stimulate production of cancerous tumours,” Professor Belz said.
“The exact outcome depends on the setting, and it wasn’t known if ILC2 could positively influence the behaviour of tumour cells.
“Previously, we understood very little about the underlying mechanisms of these intriguing cells, and whether they could be clinically relevant or targeted to apply the brakes on melanoma development.
“We discovered these cells can halt the rapid development of full-blown melanoma lesions and can potentially be harnessed to drive protective functions with potential immunotherapy applications.”
Approximately two thirds of Australians will be diagnosed with a form of skin cancer before they are 70 years of age, and Australia and New Zealand have the highest rates of melanoma in the world.
Dr Nicolas Jacquelot, who helped lead the study at WEHI and is now at the Princess Margaret Cancer Centre in Canada, said the findings were promising.
“This shows our capacity to further increase immune responses against melanoma and the possibility to develop new immunotherapy strategies to boost the ILC2-eosinophil axis to fight tumour cells,” Dr Jacquelot said.
“This gives us real hope for improving outcomes for patients.
“Our results identified that ILC2s have a critical function in melanoma immunity, and that there was a potentially coordinated approach to harness ILC2 function for anti-tumour immunotherapies.
“This opens a new pathway to explore targets not previously used as part of the immunotherapy regime, to both prevent development of metastasis and prevent resistance to therapy.”
Associate Professor Paul Neeson said the team at Peter MacCallum Cancer Centre and the collaborative Centre for Cancer Immunotherapy was able to clinically validate the findings in human skin and, in particular, cases of melanoma.
“Our team showed these rare immune cells (ILC2) were present in human melanoma samples – both when patients were first diagnosed, and in patients with advanced disease,” Dr Neeson said.
The research, supported by the National Health and Medical Research Council, was published in the journal Nature Immunology(DOI: 10.1038/s41590-021-00943-z).
Monotremes are among the world’s strangest animals, mixing mammalian and reptilian characteristics in the one creature.
When British scientists in the 18th Century first saw a platypus they dismissed it as a hoax. Eventually, a new group of mammals had to be created to account for the platypus and its fellow monotremes—the four different species of echidnas.
Even today, they remain the least understood group of living mammals.
Monotremes are the only egg-laying mammals, but they also have a number of other unique reproductive characteristics.
For the males, their testes never descend, they have no scrotum, when not in use, their penis is stored internally and their ejaculate contains bundles of up to 100 sperm that swim cooperatively until they reach the egg.
In most other species, sperm swim individually and it’s every sperm for themselves.
Unlike other mammals, the monotreme penis is used only for mating and never carries urine.
Among echidna females, in addition to laying an egg, the pouch where they nurse their young is only a temporary structure and develops by the thickening of the lateral margins around the abdominal region that surrounds the mammary glands.
But perhaps what is most bizarre about the echidna penis is that it has four heads, which are actually rosette-like glans at the end. Only two of these four glans ever become functional during erection and which glans are functional appears to alternate between subsequent erections.
Exactly how echidnas do this has always been a mystery. But for the first time we have untangled what is going on anatomically, with the results now published in the journal Sexual Development.
Our research is a collaborative project involving scientists from the University of Melbourne, University of Queensland and Monash University, but most crucial to the work has been the Currumbin Wildlife Sanctuary on the Gold Coast, which has established a small breeding colony of echidnas.
Around 50 injured echidnas are brought to the wildlife hospital at Currumbin every year, the majority from road accidents. Unfortunately, many of these echidnas are hurt beyond recovery and have to be euthanised. It’s these animals we used for the study, but we were also able to observe a tame echidna.
To understand the mechanisms at work we used microCT (Computer Tomography) scanning in combination with microscopy techniques. A normal CT scan, which uses computer technology to make 3D images from X-rays, only picks up mineralised (hard) tissue, but by staining the penis with iodine we could pick up the soft tissue details.
This meant we could create a 3D model of the whole echidna penis and its important internal structures in order to see how it operates.
Most mammals have a single urethral tube which carries the semen to the penis tip. The echidna urethra starts as a single tube, but toward the end of the penis it splits into two and each of these then splits again—resulting in each of the four branches ending up at one of the four glans.
Initially, we thought we’d find some sort of valve mechanism on the urethra when it first started branching to control the one-sided action seen in our tame echidna. Instead, we found that the erectile tissues that make up the echidna’s penis are a very unusual.
All mammalian penises consist of two erectile tissues, the corpus cavernosum and the corpus spongiosum. The main role of the corpus cavernosum is to fill up with blood and maintain an erection. The corpus spongiosum also fills up with blood, but its main role is to ensure that the urethral tube remains open at erection so that semen can pass through.
In most other mammals, both the corpus cavernosum and the corpus spongiosum start off as two separate tissues at the base of the penis but then the corpora spongiosa merge into one.
In the echidna, the corpora cavernosoa merge into one structure and the corpora spongiosa remains as two separate structures.
Furthermore, we found that the major blood vessel of the penis also splits into four branches following the branching of the urethra.
In effect, this means that the end of the echidna penis acts like two separate glans penises. Blood flow can be directed down one side of the corpus spongiosum or the other to control which half becomes erect and which branch of the urethra remains open.
We’re not sure exactly why they only use two glans at any one time. It’s possible that it’s to do with male competition for females. By alternating the use of each side our tame echidna can ejaculate 10 times without significant pause, potentially allowing him to out-mate less efficient males.
Superficially, the platypus penis looks very different—not only does it have only two heads (or glans), but, the entire penis is covered with distinct keratinous spines. However, the internal structures appear very similar to those in the echidna.
Currently, we don’t have any data on what an erect platypus penis looks like so we don’t know if they use both at the same time.
The echidna penis is very unusual amongst mammals.
Some marsupials like the bilby also have a split urethra, but these split into two branches only and, in these species, it’s the corpora cavernosum that separates into two structures when the urethra splits.
Previous studies had suggested that the echidna resembled some snakes and lizards which have hemipenes (split penises). However, we found that the echidna penis had some similarities to those of crocodiles and turtles. For example, some turtles have a five glans penis, which appears to have a similar internal anatomy.
There’s some evidence that the penis in all amniotes (reptiles, birds and mammals) has the same evolutionary origin. Our study shows that while the echidna penis is mammalian in origin—it has some evolutionary innovations all of its own.
This is probably because they don’t need to use their penis for urine, so they didn’t have the evolutionary constraints of other mammals to stick to the standard penis design.
Regardless, the echidna penis functions efficiently to transfer sperm directly to the female reproductive tract.
References: (1) Jane C. Fenelon et al, The Unique Penile Morphology of the Short-Beaked Echidna, Tachyglossus aculeatus, Sexual Development (2021). DOI: 10.1159/000515145 (2) S. D. Johnston et al, One‐Sided Ejaculation of Echidna Sperm Bundles, The American Naturalist (2007). DOI: 10.1086/522847
A new study indicates that supermassive black holes at the center of active galaxies do not behave too differently than their stellar mass analogues in X-ray binaries, at least in terms of how surrounding matter accretes and the emission that it follows. We interviewed one of the two co-authors, Juan Fernández Ontiveros of INAF from Rome
The known black holes in the universe occur mainly in two classes, with masses extremely different from each other. On the one hand there are the “featherweights”, or black holes of stellar mass – we are talking about several times the mass of the Sun. Some of these are found in binary systems , in which the black hole orbits together with a star which regularly gases to grow their mass, which are called ‘binary X-rays’ as this process results in a strong emission in the X-rays.
On the other hand we find the heavyweights, supermassive black holes , with masses equal to millions or even billions of times that of the Sun. These giants live in the center of large galaxies, they are generally in a dormant state but when they “activate” they begin to devour the surrounding gas at a sustained rate and consequently emit radiation over the entire electromagnetic spectrum, giving rise to what astronomers call active galactic nuclei (Agn).
While the accretion processes of stellar-mass black holes are well known, those of their supermassive counterparts are less so, making a comparative analysis of the physical mechanisms at work in the two types of systems difficult. A new approach to the problem comes from the collaboration between Teo Muñoz Darias of the Canary Institute of Astrophysics (Iac), which deals with binaries X, and Juan A. Fernández Ontiveros of INAF, expert in active galaxies and supermassive black holes, the whose results recently appeared in the Monthly Notices of the Royal Astronomical Society .
In this study, the two Spanish researchers surveyed 167 active galaxies, looking for similarities between the accretion modes of supermassive black holes at their center and those of their stellar mass analogues in binary X. To learn more, Media Inaf interviewed Juan A. Fernández Ontiveros. Originally from Granada, he studied physics at the University of Granada and astrophysics at the University of La Laguna in Tenerife, Canary Islands, where he earned a doctorate on the subject of Agn, followed by post-doc at the Max Planck Institute of Radio Astronomy in Bonn , at the IAC, at the University of Athens and at the INAF Iaps in Rome.
Dr. Fernández Ontiveros, how did this study come about?
“It’s a collaboration with a longtime friend, Teo Muñoz Darias. We did the doctorate together in La Laguna: he works on X-ray binaries, which are systems that have a stellar-mass black hole , therefore small, with a companion star that transfers material onto the compact object. Instead, I work on supermassive black holes at the center of galaxies ».
What are these two types of systems different?
“X-ray binaries were discovered as explosions in X-rays, and from the point of view of accretion they are the systems we know best because they evolve on human time scales. They spend most of their lives in a ‘quiet’ state in which the companion star transfers material that accumulates in the accretion disk around the black hole. At some point the disc becomes unstable and a period of activity lasting months or years begins, during which these systems become very bright in X-rays, and eventually fade back to their initial state. Supermassive black holes at the center of galaxies, on the other hand, have much longer evolution times, of the order of millions of years, so we cannot follow their evolution on an individual level “.
These are very different timelines… how did you get around this problem?
‘We took a fairly large sample of data statistically, nearly 170 galaxies observed with infrared spectroscopy, and with this statistic we identified several accretion states in supermassive black holes. We cannot follow one during its evolution, but we can identify several that are in different states ”.
How do you practically observe gas falling on black holes?
«The accretion disk [through which the gas falls on the black hole, ed] in binary X-rays emits in X-rays and therefore we can measure this emission directly. In the case of Agn, the disc’s emission is mainly in the ultraviolet but it is absorbed a lot by the hydrogen in the Agn host galaxy – and also in our own galaxy, the Milky Way – so we cannot recover it in most cases. The technique we used, however, allows us to do this: the gas around the black hole absorbs ultraviolet radiation and processes it into emission lines [an emission line corresponds to light emitted by atoms, ions or molecules in a precise frequency, ed.] and we have measured these lines ».
What lines have you observed?
«The lines associated with the different chemical elements and their ions are excited by radiation coming from different parts of the electromagnetic spectrum: if you look at some of these lines you can reconstruct the shape of the original spectrum before it was absorbed. We used the oxygen and neon lines in the mid-infrared frequencies, using data from the Spitzer satellite . ‘
And what did you find?
“We used the lines to identify the presence or absence of the accretion disk in the various Agn, and we built a diagram to identify the different states of accretion.”
Can you explain what we see in the diagram?
«The diagram we built is called Led: luminosity-excitation diagram . Shows the brightness of the system relative to the brightness of the disc. The horizontal axis tells us the importance of the disk, the vertical axis the total brightness of the active nucleus; the latter, normalized with respect to the mass of the black hole, is linked to the system’s accretion state. There are two main accretion states: one bright, top left, dominated by the disk, and the other right, in which the disk is weak and dominates the emission from the jet and the corona around the black hole. The first is called soft state and the second hard state respectively , the names come from the shape of the X-ray spectrum in binaries X ».
Were you surprised by this result?
«Traditionally the physics of accretion has been developed to explain the behavior of binaries X, which are well known because they change frequently and their evolution can be studied. In Agn, the accretion disk could have different physical properties, it should be much colder than that of X binaries, and this means that it may not be dominated by the pressure of the gas but by the pressure of radiation and the magnetic field. Despite the differences, this diagram tells theorists that there appear to be very similar states in black holes throughout the mass interval: surely there are specific features, but the general evolution seems very similar.
Is it the first time that the different growth states in Agn have been identified?
«It is not the very first time but in our opinion this is the clearest result because we have solved some systematics present in previous attempts. Our diagram is the one that most closely resembles that of X binaries, where the systems describe a trajectory in the shape of a ‘q’. In 2006, for example, Körding and co-workers had done similar work but without normalizing the system’s brightness for the black hole’s mass, because they didn’t have these mass estimates. So in their study there was a dispersion of a factor of 100-1000 in the vertical axis. With this noise, the shape a ‘q’ cannot be clearly seen, which instead is perceived in our diagram ».
What did you deduce about the physics of these systems from this analysis?
“The fact that the jet dominates the radio emission during the hard state is seen very well in the X binaries. Seeing the same phenomenon in the Agn – in the diagram it is the region with the black dots, where the emission of the jet is strong – reinforces much parallelism “.
There are differently colored regions in the diagram. What do they represent?
«The regions colored in red, green and blue indicate the different types of active galaxies according to the classical classification, based on the properties of their optical spectrum. The difference between Seyfert 1 (in red) and Seyfert 2 (in green) has traditionally been interpreted as a difference in the orientation of the system relative to us. Liners (in blue) are typically fainter active nuclei usually found in older galaxies. But there is a relatively recently discovered class of active galaxies that are the ‘ changing-look Agn‘: they are active galaxies that change from one type to another, and their brightness can also change a lot. They could be systems in transition, and it would be very interesting to understand how they move in the diagram when the properties of the spectrum change, because they are systems that could be in transition between one accretion state and another ».
What is special about these Agn changing looks ?
«They are very rare, you have to look at many to find one, while in binaries the variability in brightness is a common feature. They are galaxies where changes are seen that could indicate changes in the disk, in the central region. There is certainly a lot of physics to learn in these systems. Before, many of them were not known because they are rare events, but now there are surveys that map the sky every day and we are discovering that these Agn changing looks are a more frequent phenomenon than previously thought ».
How will your study continue?
“The data comes from Spitzer, who is no longer operational now. The next telescope to be able to observe the same lines in the infrared will be James Webb space telescope (Jwst). Part of this work began to prepare the science of the Spica mission , together with Prof. Luigi Spinoglio here at Iaps, which was then very drastically canceled by ESA. Even our recently accepted observation proposal for Jwst derives from the work done for Spica which therefore did not die at all, it gave rise to a lot of science ».
What exactly do you plan to do with Jwst?
“Jwst will see the lines we use to build this diagram with a much higher resolution. So we expect that when Jwst departs and begins measuring a statistically representative amount of these active galaxies, we can use these and other even fainter lines to better understand where the Agn are in this diagram. Another possibility is to use Euclid to do a similar thing, but from the perspective ».
Why Euclid precisely?
“The diagram we have made now is for the galaxies of the local universe. Euclid will be able to do this for the time when galaxies were in formation, 10 billion years ago. It is certainly not a difficult thing to do, you have to identify the lines that Euclid will see in those galaxies. If we can adapt our methodology to use the optician’s lines, we will have many more. And there is not only Euclid but also the Sloan Digital Sky Survey from the ground and then there will be the Roman space telescope : many of the future missions will map galaxies all over the sky, this amount of information is extremely useful for us ».
What can be learned new with a larger sample of galaxies?
“The current sample has 167 galaxies. If the statistic increases, the regions can be better defined. For now we have divided the Agn into 4 types, but if you have a statistic of hundreds of thousands of galaxies you can study the dependencies on other parameters such as the mass of the black hole, the type of galaxy, etc. In the family of active galaxies there is a gigantic taxonomy, and so it will be possible to highlight some classes with special properties to understand what happens differently ».
Featured image: Artist’s impression of the stellar-mass black hole Cygnus X-1. Credits: Nasa
Researchers from Tokyo Medical and Dental University (TMDU) find that eating a soft diet during development changes the way in which the brain controls chewing in rats
Incoming sensory information can affect the brain’s structure, which may in turn affect the body’s motor output. However, the specifics of this process are not always well understood. In a recent study published in Scientific Reports, researchers from Tokyo Medical and Dental University (TMDU) found that when young rats were fed a diet of either soft or regular food, these different sensory inputs led to differences in muscle control and electrical activity of the jaw when a specific chewing-related brain region was stimulated.
Chewing is mainly controlled by the brainstem, a brain region that controls many automatic activities such as breathing and swallowing. For chewing, the brainstem is also influenced by signaling that comes from higher brain regions, including the cortical masticatory area (CMA), which can be split into the front (anterior) and back (posterior) parts. When the anterior CMA is stimulated, signals travel through the brainstem and reach the jaw muscles, causing chewing to occur. However, it remains unknown whether incoming sensory information affects chewing under the control of the anterior CMA, something researchers at Tokyo Medical and Dental University decided to address.
“In the developing brain, changes in sensory information can greatly affect the brain’s structure,” says senior author of the study Takashi Ono. “We fed 2-week-old rats either a soft diet or a regular diet, and then investigated a range of different neuromuscular outcomes in response to stimulation of the anterior CMA.”
After rats had been fed the soft or regular diet for 3 to 9 weeks, electrodes were used to stimulate the anterior CMA while the rats’ jaw movements were measured, along with the electrical activity of the jaw muscles. In response to anterior CMA stimulation, rats in the soft diet group had altered movement and electrical activity in the jaw muscles compared with the regular diet group.
“Our findings suggest that the anterior CMA strongly influences the regulation of chewing, and is affected by sensory inputs during development. As such, reduced chewing function during growth should be corrected as soon as possible to avoid any potential adverse effects on jaw muscle development and chewing ability,” says Ono.
Given the importance of chewing for obtaining nutrients, the results of this study could be vital for monitoring and improving chewing ability in young children with chewing difficulties, as well as in adults after trauma or disease. The results of this study suggest that the brain’s control of chewing may be influenced by simply increasing chewing difficulty.
The article, “Effects of low occlusal loading on the neuromuscular behavioral development of cortically-elicited jaw movements in growing rats,” was published in Scientific Reports at DOI: 10.1038/s41598-021-86581-9