Tag Archives: #facts

Ancient Bone Artefact Found (Archeology)

Archaeologists describe rare Lower Murray find

The discovery of a rare bone artefact near the Lower Murray River casts more light on the rich archaeological record on Ngarrindjeri country in southern Australia.

Details of the Murrawong bone point, dated between c. 5,300-3,800 years old, has have been described by Flinders University, Griffith University and other experts in a new paper in Australian Archaeology.

Probably made from a macropod (kangaroo or wallaby) bone, the point was likely used for piercing soft materials – for example, used as a pin on a cloak made of possum furs – or possibly as a projectile point, say the research leaders Dr Christopher Wilson and Professor Amy Roberts from Flinders University Archaeology.

Figure 1. Map showing the location of Murrawong in the Lower Murray River Gorge region of South Australia. © Flinders University

While stone artefacts and shell middens are commonly found on the surface, bone objects are mostly uncovered during excavations. The last similar one was uncovered in the Lower Murray River Gorge was in the 1970s.

Dr Wilson, a Ngarrindjeri man, says that “even one find of this kind provides us with opportunities to understand the use of bone technologies in the region and how such artefacts were adapted to a riverine environment.”

“Bone artefacts have lacked the same amount of study in comparison to artefacts made of stone, so every discovery reminds us of the diverse material culture used by Aboriginal peoples in this country,” adds Professor Roberts.

Archaeology dig at the Murrawong excavation (2008). From left to right: Duncan Wright, Christopher Wilson, Roger Luebbers and Kelly Wiltshire. © Flinders University

The artefact was found during recent excavation work. The project was undertaken in collaboration with the Ngarrindjeri community.

This research forms part of a larger project that Dr Wilson is leading to investigate the rich archaeological record on Ngarrindjeri country.

The paper, ‘Analysis and contextualisation of a Holocene bone point from Murrawong (Glen Lossie), Lower Murray River Gorge, South Australia’ (2021) by C Wilson, AL Roberts, M Langley, L Wallis, R Luebbers, C Westell, C Morton and the Ngarrindjeri Aboriginal Corporation has been published in Australian Archaeology DOI: 10.1080/03122417.2021.1886893

Featured image: (a) The Murrawong bone point; (b) superior view; (c) inferior view; and (d) distal edge featuring userelated damage. © Flinders University


Provided by Flinders University

Why Massive Stars are More Prone to Form Massive Planets? (Planetary Science)

Summary:

○ According to Flor-Torres and colleagues, massive stars rotating faster than low-mass stars, had more massive protoplanetary disks (PPDs) with higher angular momentum, explaining why they formed more massive planets rotating faster around their stars.

○ They also found that most stars and planets lost their angular momentum due to the fact that there are interactions of the planets with their PPDs and that massive PPDs dissipates more angular momentum than lower mass PPD.

○ Thus, high mass exoplanets (HMEs) to have higher orbital angular momentum than the LMEs and to have lost more angular momentum through migration.


The discovery of gas giant planets rotating very close to theirs stars (hot Jupiter, or HJs) has forced Flor-Torres and colleagues to reconsider their model for the formation of planets around low mass stars by including in an ad hoc way large scale migration. Since this did not happen in the solar system, it brings the natural question of understanding under what conditions large scale migration could be triggered in a proto-planetary disk (PPD). By stating such question, they adopted the simplest view that there is only one universal process for the formation of planets, following the collapse of dense regions in a molecuar cloud.


This reduces the problem to a more specific one which is: how do we include migration in a well developed model like the core collapse scenario (the standard model), which explains in details how the solar system formed

— said Flor-Torres, lead author of the study.

In the literature, two migration mechanisms are favored for HJs. The first is disk migration, which proposes that a planet looses its orbit angular momentum by tidal interactions with the PPD, while the second, high-eccentricity migration, suggests a planet interacting with other planets gains a higher eccentricity, which brings it close to its star where it reaches equilibrium by tidal interactions (a process known as circularization). In terms of migration, these two mechanisms might suggest massive disks somehow amplified the level of migration compared to what happened in the solar system, because more massive PPDs either increase the intensity of interactions of the planets with their disks or favor the formation of a higher number of planets. Within the standard model this would suggest that what counts is whether the PPD follows the minimum mass model, with a mass between 0.01 to 0.02 M⊙, or the maximum mass model with a mass above 0.5 M⊙. There are few clues which could help determining which path the PPD of the solar system followed (and strong difficulties compared to direct observations of PPD). One is the total mass of the planets, which represents only 0.1% the mass of the Sun. This implies the solar system PPD have lost an important amount of its mass after the formation of the planets. Another clue is that 99% of the angular momentum of the solar system is located in the planets, suggesting that the initial angular momentum of the PPD might have been conserved in the planets. However, this is obviously not the case when large scale migration occurs, so what was the difference?

Fig. 1. Star rotational velocity vs. temperature, distinguishing between stars hosting HMEs and LMEs. The position of the Sun is included as well as the star with a BD as companion. © Flor-Torres et al.

If the initial angular momentum of the PPD passes to the planets, then one could use the orbital rotation momentum in exoplanetary systems to test different scenarios connecting the formation of the planets to the formation of their stars. For example, how is the angular momentum of the PPD coupled to the angular momentum of the stars? Since large scale migration represents a loss of angular momentum of the planets (at least by a factor 10), what was the initial angular momentum of the PPD when it formed and how does this compared to the initial mass of the PPD? Does this influence the masses of the planets and their migration? The answers are not trivial, considering that the physics involved is still not fully understood.


In particular, we know that the angular momentum is not conserved during the formation of stars. This is obvious when one compares how fast the Sun rotates with how fast its rotation should have been assuming the angular momentum of the collapsing molecular cloud where it formed was conserved.

— said Jack, co-author of the study.

Actually, working the math (a basic problem, but quite instructive; see course notes by Alexander 2017), the Sun effective angular momentum, j⊙ = J⊙/M⊙, is ∼ 10^6 times lower than expected. Intriguingly, j⊙ is also 10³ lower than the angular momentum of its breaking point, jb, the point where the centripetal force becomes stronger than gravity. If that was not true, then no stars whatever massive would be able to form. In fact, observations revealed that, in general, the angular momentum of stars with spectral type O5 to A5 trace a power law, J ∝ Mα, with α ∼ 2, with typical J∗ values that are exactly ten times lower than their breaking point. How universal is this “law”and how stars with different masses get to it, however, is unexplained. To complicate the matter, it is clear now that lower mass stars, later than A5, do not follow this law, their spin going down exponentially (cf. Fig.6 in Paper I). For low-mass stars, McNally, Kraft and Kawaler suggested a steeper power law, J ∝ M5.7, which suggests they loose an extra amount of angular momentum as their mass goes down. What is interesting is that low-mass stars are also those that form PPDs and planets, which had led some researchers to speculate there could be a link between the two.

To explain how low-mass stars loose their angular momentum, different mechanisms are considered. The most probable is stellar wind, which is related to the convective envelopes of these stars. This is how low-mass stars would differ from massive ones. However, whether this mechanism is sufficient to explain the break in the J – M relation is not obvious, because it ignores the possible influence of the PPD (the formation of a PPD seems crucial). This is what the magnetic braking model takes into account. Being bombarded by cosmic rays and UV radiation from ambient stars, the matter in a molecular cloud is not neutral, and thus permeable to magnetic fields. This allows ambipolar diffusion (the separation of negative and positive charges) to reduce the magnetic flux, allowing the cloud to collapse. Consequently, a diluted field follows the matter through the accretion disk to the star forming its magnetic field. This also implies that the accretion disk (or PPD) stays connected to the star through its magnetic field as long as it exists, that is, a period that although brief includes the complete phase of planet formation and migration. According to the model of disk-locking, a gap opens between the star and the disk at a distance Rt from the star, and matter falling between Rt and the radius of corotation, Rco (where the Keplerian angular rotation rate of the PPD equals that of the star), follow the magnetic field to the poles of the star creating a jet that transports the angular momentum out. In particular, this mechanism was shown to explain why the classic T-Tauri rotates more slowly than the weak T-Tauri. How this magnetic coupling could influence the planets and their migrations, on the other hand, is still an open question.

To investigate further these problems, Flor-Torres and colleagues started a new observational project to observe host stars of exoplanets using the 1.2 m robotic telescope TIGRE, which is installed near their department at the LA Luz Observatory (in central Mexico). In paper I, they explained how they succeeded in determining in an effective and homogeneous manner the physical characteristics ( Teff , log g, [M/H], [Fe/H], and V sin i) of a initial sample of 46 bright stars using iSpec. In this study, they explored the possible links between the physical characteristics of these 46 stars and the physical characteristics of their planets, in order to gain new insight about a connection between the formation of stars and their planets.


Our main goal is to check is there could be a coupling between the angular momentum of the planets and their host stars.

— said Flor-Torres, lead author of the study.

Table 1: Physical parameters of the High Mass Exoplanets (HME) & Low Mass Exoplanets (LME) in their samples. © For-Torres et al.

Separating our sample in two, stars hosting high-mass exoplanets (HMEs) and low-mass exoplanets (LMEs), we found the former to be more massive and to rotate faster than the latter.

– said Schmitt, co-author of the study.

They found that there is a connection between the stars and their exoplanets, which passes by their protoplanetary disks (PPDs). Massive stars rotating faster than low-mass stars, had more massive PPDs with higher angular momentum, explaining why they formed more massive planets rotating faster around their stars. However, in terms of stellar spins & planets orbit angular momentum, they found that both the stars and their planets have lost a huge amount of angular momentum (by more than 80% in the case of the planets), a phenomenon which could have possibly erased any correlations expected between the two. The fact that all the planets in their sample stop their migration at the same distance from their stars irrespective of their masses, might favor the views that the process of migration is due to the interactions of the planets with their PPDs and that massive PPDs dissipates more angular momentum than lower mass PPD. Consistent with this last conclusion, authors proposed that HMEs might have different structures than LMEs which made them more resilient to circularization.

We also found the HMEs to have higher orbital angular momentum than the LMEs and to have lost more angular momentum through migration. These results are consistent with the view that the more massive the star and higher its rotation, the more massive was its protoplanetarys disk and rotation, and the more efficient the extraction of angular momentum from the planets.

— concluded authors of the study.

Reference: (1) L. M. Flor-Torres, R. Coziol, K.-P. Schröder, D. Jack, J. H. M. M. Schmitt, S. Blanco-Cuaresma, “Connecting the formation of stars and planets. I — Spectroscopic characterization of host stars with Tigre”, ArXiv, 27 Jan 2021. https://arxiv.org/abs/2101.11666v1 (2) L. M. Flor-Torres, R. Coziol, K.-P. Schröder, D. Jack, J. H. M. M. Schmitt, “Connecting the formation of stars and planets. II: coupling the angular momentum of stars with the angular momentum of planets”, ArXiv, 27 Jan 2021. https://arxiv.org/abs/2101.11676v1


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Defensive Activation Theory Can Answer Why We Dream (Neuroscience)

Eagleman and colleagues hypothesized that the circuitry underlying dreaming serves to amplify the visual system’s activity periodically throughout the night, allowing it to defend its territory against takeover from other senses.

One of neuroscience’s unsolved mysteries is why brains dream. Do our bizarre nighttime hallucinations carry meaning, or are they simply random neural activity in search of a coherent narrative? And why are dreams so richly visual, activating the occipital cortex so strongly? Eagleman and colleagues in their recent paper, leverage recent findings on neural plasticity to propose a novel hypothesis.

Just as sharp teeth and fast legs are useful for survival, so is neural plasticity: the brain’s ability to adjust its parameters (e.g., the strength of synaptic connections) enables learning, memory, and behavioral flexibility.

On the scale of brain regions, neuroplasticity allows areas associated with different sensory modalities to gain or lose neural territory when inputs slow, stop, or shift. For example, in the congenitally blind, the occipital cortex is taken over by other senses such as audition and somatosensation. Similarly, when human adults who recently lost their sight listen to sounds while undergoing functional magnetic resonance imaging (fMRI), the auditory stimulation causes activity not only in the auditory cortex, but also in the occipital cortex. Such findings illustrate that the brain undergoes changes rapidly when visual input stops.

Rapid neural reorganization happens not only in the newly blind, but also among sighted participants with temporary blindness. In one study, sighted participants were blindfolded for five days and put through an intensive Braille-training paradigm. At the end of five days, the participants could distinguish subtle differences between Braille characters much better than a control group of sighted participants who received the same training without a blindfold. The difference in neural activity was especially striking: in response to touch and sound, blindfolded participants showed activation in the occipital cortex as well as in the somatosensory cortex and auditory cortex, respectively. When the new occipital lobe activity was intentionally disrupted by magnetic pulses, the Braille-reading advantage of the blindfolded subjects went away. This finding indicates that the recruitment of this brain area was not an accidental side effect—it was critical for the improved performance. After the blindfold was removed, the response of the occipital cortex to touch and sound disappeared within a day.

Of particular interest here is the unprecedented speed of the changes. When sighted participants were asked to perform a touching task that required fine discrimination, investigators detected touch-related activity emerging in the primary visual cortex after only 40 to 60 minutes of blindfolding. The rapidity of the change may be explained not by the growth of new axons, but by the unmasking of pre-existing non-visual connections in the occipital cortex.

It is advantageous to redistribute neural territory when a sense is permanently lost, but the rapid conquest of territory may be disadvantageous when input to a sense is diminished only temporarily, as in the blindfold experiment. This consideration leads Eagleman and colleagues to propose a new hypothesis for the brain’s activity at night. In the ceaseless competition for brain territory, the visual system in particular has a unique problem: due to the planet’s rotation, we are cast into darkness for an average of 12 hours every cycle. (This of course refers to the vast majority of evolutionary time, not to our present electrified world). Given that sensory deprivation triggers takeover by neighboring territories, how does the visual system compensate for its cyclical loss of input?

Eagleman and colleagues suggested that the brain combats neuroplastic incursions into the visual system by keeping the occipital cortex active at night. They term this the Defensive Activation theory. In this view, dream sleep exists to keep the visual cortex from being taken over by neighboring cortical areas. After all, the rotation of the planet does not diminish touch, hearing, taste, or smell. Only visual input is occluded by darkness.

“We suggest that the brain preserves the territory of the visual cortex by keeping it active at night. In our “defensive activation theory,” dream sleep exists to keep neurons in the visual cortex active, thereby combating a takeover by the neighboring senses. In this view, dreams are primarily visual precisely because this is the only sense that is disadvantaged by darkness. Thus, only the visual cortex is vulnerable in a way that warrants internally-generated activity to preserve its territory.”, said Eagleman.

In humans, sleep is punctuated by REM (rapid eye movement) sleep about every 90 minutes. This is when most dreaming occurs. Although some forms of dreaming can occur during non-REM sleep, such dreams are quite different from REM dreams; non-REM dreams usually are related to plans or thoughts, and they lack the visual vividness and hallucinatory and delusory components of REM dreams.

REM sleep is triggered by a specialized set of neurons in the pons, Increased activity in this neuronal population has two consequences. First, elaborate neural circuitry keeps the body immobile during REM sleep by paralyzing major muscle groups. The muscle shut-down allows the brain to simulate a visual experience without moving the body at the same time. Second, they experience vision when waves of activity travel from the pons to the lateral geniculate nucleus and then to the occipital cortex (these are known as ponto-geniculo-occipital waves or PGO waves). When the spikes of activity arrive at the occipital pole, they felt as though they were seeing even though our eyes are closed. They found that the visual cortical activity is presumably why dreams are pictorial and filmic instead of conceptual or abstract.

Fig. 1. PGO waves. As a prelude to REM sleep, waves of activity move from the brainstem into the occipital cortex. We suggest that this infusion of activity is necessitated by the rotation of the planet into darkness: the visual system needs extra cyclic activation to keep its territory intact.

These nighttime volleys of activity are anatomically precise. The pontine circuitry connects specifically to the lateral geniculate nucleus, which passes the activity on to the occipital cortex, only. The high specificity of this circuitry supports the biological importance of dream sleep: putatively, this circuitry would be unlikely to evolve without an important function behind it.

“As predicted, we found that species with more flexible brains spend more time in REM sleep each night. Although these two measures—brain flexibility and REM sleep—would seem at first to be unrelated, they are in fact linked.”, said Eagleman.

Fig. 2. Representation of the Defensive Activation theory. With the onset of sleep, visual synaptic connections are weakened by encroachment from other sensory areas. When a threshold is reached (dotted line), PGO waves are initiated and drive activity into the occipital lobe. This process repeats cyclically throughout the sleep cycle.

Their Defensive Activation theory makes a strong prediction: the higher an organism’s neural plasticity, the higher its ratio of REM to non-REM sleep. This relationship should be observable across species as well as within a given species across the lifespan. They thus set out to test their hypothesis by comparing 25 species of primates on behavioral measures of plasticity and the fraction of sleep time they spend in REM and found that measures of plasticity across 25 species of primates correlate positively with the proportion of rapid eye movement (REM) sleep.

They further found that plasticity and REM sleep increase in lockstep with evolutionary recency to humans. Finally, they concluded that their hypothesis is consistent with the decrease in REM sleep and parallel decrease in neuroplasticity with aging.

Reference: David M. Eagleman, Don A. Vaughn, “The Defensive Activation theory: dreaming as a mechanism to prevent takeover of the visual cortex”, bioRxiv, 2020. doi: https://doi.org/10.1101/2020.07.24.219089 https://www.biorxiv.org/content/10.1101/2020.07.24.219089v1

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Do You Know The Mass Of Milky Way Within 100 Kpc? (Astronomy)

Astronomers using a large sample of halo stars estimated the mass of the Milky Way out to 100 kpc and found that it is 6.31 ± 0.32(stat.) ± 1.26(sys.) × 10¹¹ M

The total mass of the Milky Way has been an historically difficult parameter to pin down. Despite decades of measurements, there remains an undercurrent of elusiveness surrounding “the mass of the Milky Way”. However, the continued eagerness to provide an accurate measure is perhaps unsurprising — the mass of a halo is arguably its most important characteristic. For example, almost every property of a galaxy is dependent on its halo mass, and thus this key property is essential to place our “benchmark” Milky Way galaxy in context within the general galaxy population. In addition, the host halo mass is inherently linked to its subhalo population, so most of the apparent small scale discrepancies with the ΛCDM model are strongly dependent on the Milky Way mass. Moreover, tests of alternative dark matter candidates critically depend on the total mass of the Milky Way, particularly for astrophysical tests.

Milky way © wallpaper cave

The uncertainty has stemmed from two major shortcomings:
(1) a lack of luminous tracers with full 6D phase-space information out to the viral radius of the Galaxy, and (2) an underestimated, or unquantified, systematic uncertainty in the mass estimate.

However, there has been significant progress since the first astrometric data release from the Gaia satellite. This game-changing mission for Milky Way science provided the much needed tangential velocity components for significant numbers of halo stars, globular clusters and satellite galaxies. Indeed, there are encouraging signs that we are converging to a total mass of just over 1×10¹²M. However, mass estimates at very large distances (i.e. beyond 50 kpc), are dominated by measures using the kinematics of satellite galaxies, which probe out to the virial radius of the Galaxy. It is well-known that the dwarf satellites of the Milky Way have a peculiar planar alignment, and, without independent measures at these large distances, there remains uncertainty over whether or not the satellites are biased kinematic tracers of the halo.

Arguably the most promising tracers at large radii are the halo stars. They are significantly more numerous than the satellite galaxies and globular clusters, and are predicted to reach out to the virial radius of the Galaxy. There currently exist thousands of halo stars with 6D phase-space measurements, thanks to the exquisite Gaia astrometry and wide-field spectroscopic surveys such as the Sloan Digital Sky Survey (SDSS) and the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) survey. Moreover, with future Gaia data releases and the next generation of wide-field spectroscopic surveys from facilities such as the Dark Energy Spectroscopic Instrument, the WHT Enhanced Area Velocity Explorer, and the 4-metre Multi-Object Spectroscopic Telescope, there will be hundreds of thousands of halo stars with 6D measurements. The magnitude limit of Gaia and the complementary spectroscopic surveys will likely limit the samples of halo stars to within ∼100 kpc, but this is still an appreciable fraction of the virial radius (∼0.5𝑟200c), and will probe relatively unchartered territory beyond 50 kpc.

As we enter a regime of more precise mass measures, and significantly reduced statistical uncertainties, it is vital to be mindful of any systematic influences in our mass estimates. Although many mass-modelling techniques assume dynamical equilibrium, it is well-documented that “realistic” stellar haloes can be a mash-up of several coherent streams and substructures. Thus, comparisons with cosmologically motivated models of stellar haloes are crucial. However, while cosmological simulations can provide much needed context, the unique assembly history of the Milky Way is most relevant for Galactic mass measurements. For example, the influence of the Sagittarius (Sgr) stream, which contributes a significant fraction to the total stellar halo mass, needs to be considered. Furthermore, and perhaps more importantly, it has recently been recognised that the recent infall of the massive Large Magellanic Cloud (LMC) can imprint significant velocity gradients in the Milky Way halo. Indeed, Erkal et al. (2020) showed that these velocity gradients can bias equilibrium based mass modelling, and is thus an effect that can no longer ignore.

In this work, researchers compile a sample of distant (𝑟 > 50 kpc) halo stars from the literature with 6D phase-space measurements, and use a distribution function analysis to measure the total mass within 100 kpc. They pay particular attention to systematic influences, such as the Sagittarius (Sgr) stream and the LMC, and, where possible, correct for these perturbative effects.

The resulting circular velocity (left panel) and mass (right panel) profiles as a function of galactocentric radius. The results when no velocity offset is applied (dashed lines) and when Sgr stars are included (purple lines) are also shown. The shaded regions indicate the 1- 𝜎 uncertainty. © deason et al.

They used a rigid Milky Way-LMC model to constrain the systematic reflex motion effect of the massive LMC on their halo mass estimate. And found that, simple velocity offset correction in 𝑣los and 𝑣𝑏 can minimize the overestimate caused by the reflex motion induced by the LMC, and, assuming a rigid LMC mass of 1.5 × 10¹¹ M, they can recover the true mass within 1-𝜎.

Phase-space diagrams (𝑣𝑟 vs. 𝑟) for four example Auriga haloes, and the Milky Way data (bottom
panels). The top two panels show Auriga haloes with shell-type structures in the radial range 50-100 kpc. The middle two panels show cases with no obvious shells. Typically, the presence of shells causes the mass estimates to be underestimated. In the bottom two panels they show the 𝑣los vs. 𝑟 diagram for the observational sample in the distance range 50 < 𝑟/kpc < 100. In the bottom left panel they show each individual star and the associated 𝑣los errors. The red points indicate the stars that likely belong to the Sgr stream. The bottom right panel shows a 2D histogram in the 𝑣los-𝑟 space. Here, they have taken into account uncertainties in the distance and velocity of each star. Note that Sgr stars are excluded in the right-hand panel. ©deason et al.

Then by applying their method to a sample of Milky Way-mass haloes from the Auriga simulation they found that the halo masses are typically underestimated by 10%. However, this bias is reduced to ∼ 5% if we only consider haloes with relatively quiescent recent accretion histories. The residual bias is due to the presence of long-lived shell-like structures in the outer halo. The halo-to-halo scatter is ∼20% for the quiescent haloes, and represents the dominant source of error in the mass estimate of the Milky Way.

They also found that the mass of milky way within 100 kpc is 6.31 ± 0.32(stat.) ± 1.26(sys.) × 10¹¹ M. A systematic bias correction (+5%), and additional uncertainty (20%), are included based on their results from the Auriga simulations and found that the mass estimates are slightly higher when they do not include a velocity offset to correct for the reflex motion induced by the LMC, or slightly lower when Sgr stars are included in their analysis.

Their mass estimate within 100 kpc is in good agreement with recent, independent measures in the same radial range. If they assume the predicted mass-concentration relation for Navarro-Frenk-White haloes, their measurement favours a total (pre-LMC infall) Milky Way mass of 𝑀200c = 1.05 ± 0.25 × 10¹²M, or (post-LMC infall) mass 𝑀200c = 1.20 ± 0.25 × 10¹²M when a rigid 1.5 × 10¹¹M LMC is included.

References: Alis J. Deason, Denis Erkal, Vasily Belokurov, Azadeh Fattahi, Facundo A. Gómez, Robert J. J. Grand, Rüdiger Pakmor, Xiang-Xiang Xue, Chao Liu, Chengqun Yang, Lan Zhang, Gang Zhao, “The mass of the Milky Way out to 100 kpc using halo stars”, ArXiv, 2020. https://arxiv.org/abs/2010.13801

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Improved Model Shows Gamma Rays And Gold At Merging Neutron Stars (Astromomy)

An international team of astrophysicists under Dutch leadership has demonstrated with an improved model that colliding neutron stars can emit gamma rays. Old models did not predict this and faltered since the merging of two neutron stars in 2017 that released gamma rays. The researchers publish their findings in the The Astrophysical Journal.

A snapshot of the simulation of two merged neutron stars. Gamma radiation is created in the grey strand running through the red ring. In the blue hourglass form, gold may be formed. Credit: Philipp Mösta et al.

The researchers, led by Philipp Mösta (University of Amsterdam), provided their model of colliding neutron stars with more variables than ever before. They considered, among other things, the theory of relativity, gas laws, magnetic fields, nuclear physics and the effects of neutrinos. The researchers ran their simulations on the Blue Waters supercomputer at the University of Illinois in Urbana-Champaign (United States) and on the Frontera supercomputer at the University of Texas, Austin (United States).

In the simulation, a ring is created around the merged neutron stars from which a thin strand of gamma radiation shoots up and down. This radiation then finds its way out like a whirlwind along the magnetic field lines of the merged stars. Furthermore, an hourglass-like cone moves up and down from the ring. This is where heavier elements such as gold possibly form. Gold is, like gamma rays, observed in the merging neutron stars in 2017 where a kilonova was formed.

Philipp Mösta (University of Amsterdam) led the new simulations: “The gamma radiation is really new for these kind of simulations. That radiation had not appeared in the old simulations. The production of heavy elements, such as gold, had already been simulated. However, our simulation shows that these heavy elements move much faster than previously predicted. Our simulation is therefore more in line with what astronomers observed in the merging neutron stars in 2017”.

The simulations are not only meant to explain the observed phenomena around merging neutron stars. They also serve to predict new phenomena. For example, the researchers want to further refine and expand their model so that it can also deal with large stars that explode as supernova at the end of their lives and with a collision of a neutron star with a black hole.

Movie of the simulation of two merged. Credit: Philipp Mösta et al.

References: Philipp Mösta et al. A Magnetar Engine for Short GRBs and Kilonovae, The Astrophysical Journal (2020). DOI: 10.3847/2041-8213/abb6ef

Provided by Netherlands Research School for Astronomy

Scientists Proposed, “There Might Be Massive Black Holes Than SMBH”, And They Call It SLAB’s (Astronomy)

Bernard Carr and colleagues recently considered the observational constraints on stupendously large black holes (SLABs) in the mass range M≳10¹¹ M, i.e. about the size of 100 billion suns or more. Discovering such gargantuan black holes may shed light on the nature of a significant fraction of the mysterious dark matter that makes up four-fifths of the matter in the universe.

Currently the largest known black hole, powering the quasar TON 618, has a mass of 66 billion solar masses. TON 618’s enormous bulk led scientists to speculate whether or not even larger black holes exist, and if there is any upper limit to their sizes.

In the new study, the researchers dubbed black holes 100 billion solar masses in size or larger — bigger than any currently seen — “stupendously large black holes,” or SLABs. Although they noted there is currently no evidence that stupendously large black holes are real, they noted that supermassive black holes almost that size do exist.

A key question when it comes to stupendously large black holes is whether they could form in the first place. However, much remains uncertain about how even regular supermassive black holes are born.

The conventional assumption is that the supermassive black holes at the hearts of galaxies formed as smaller black holes merged and gobbled up matter around them. However, previous research found this model faced challenges when it comes to explaining how black holes could have reached supermassive sizes when the universe was only a few billion years old.

Another way to explain how both regular supermassive black holes and possibly stupendously large black holes formed hinges on so-called primordial black holes. Prior work speculated that within a second after the Big Bang, random fluctuations of density in the hot, rapidly expanding newborn universe might have concentrated pockets of matter enough for them to collapse into black holes. These primordial black holes could have served as seeds for larger black holes to form later on.

If primordial black holes do exist, they might help explain what dark matter is. Although dark matter is thought to make up most of the matter in the universe, scientists don’t know what this strange stuff is made of, as researchers still have not seen it; it can currently be studied only through its gravitational effects on normal matter. The nature of dark matter is currently one of the greatest mysteries in science.

One way to detect stupendously large black holes is through gravitational lensing.

Another way to detect stupendously large black holes is through the effects they would have on their environment, such as gravitationally distorting galaxies. These black holes could also generate heat, light and other radiation as they consume matter that astronomers could detect.

Aside from primordial black holes, another potential candidate for dark matter are so-called weakly interacting massive particles (WIMPs). If WIMPs exist, they would be invisible and largely intangible, but previous research suggested that if two WIMPs ever collided, they would annihilate one another and generate gamma rays, providing a way for scientists to spot them indirectly. The powerful gravitational pulls of stupendously large black holes would gather a halo of WIMPs around them, and the high-energy gamma rays that could result from WIMP annihilation might help scientists discover stupendously large black holes.

They also commented on the constraints on the mass of ultra-light bosons from future measurements of the mass and spin of SLABs.

References: Bernard Carr, Florian Kuhnel, Luca Visinelli, “Constraints on Stupendously Large Black Holes”, ArXiv, 2020. Doi: arXiv:2008.08077v2 link: https://arxiv.org/abs/2008.08077

There’s A Strange Reason Why So Many People Regain Weight After Dieting (Biology)

Anyone who has tried to lose weight and keep it off knows how difficult the task can be. It seems like it should be simple: Just exercise to burn more calories and reduce your calorie intake. But many studies have shown that this simple strategy doesn’t work very well for the vast majority of people.

A dramatic example of the challenges of maintaining weight loss comes from a recent National Institutes of Health study. The researchers followed 14 contestants who had participated in the “World’s Biggest Loser” reality show. During the 30 weeks of the show, the contestants lost an average of over 125 pounds per person. But in the six years after the show, all but one gained back most of their lost weight, despite continuing to diet and exercise.

Why is it so hard to lose weight and keep it off? Weight loss often leads to declines in our resting metabolic rate — how many calories we burn at rest, which makes it hard to keep the weight off. So why does weight loss make resting metabolism go down, and is there a way to maintain a normal resting metabolic rate after weight loss? As someone who studies musculo-skeletal physiology, I will try to answer these questions.

Activating muscles deep in the leg that help keep blood and fluid moving through our bodies is essential to maintaining resting metabolic rate when we are sitting or standing quietly. The function of these muscles, called soleus muscles, is a major research focus for us in the Clinical Science and Engineering Research Center at Binghamton University. Commonly called “secondary hearts,” these muscles pump blood back to our heart, allowing us to maintain our normal rate of metabolic activity during sedentary activities.

Resting metabolic rate (RMR) refers to all of the biochemical activity going on in your body when you are not physically active. It is this metabolic activity that keeps you alive and breathing, and very importantly, warm.

Quiet sitting at room temperature is the standard RMR reference point; this is referred to as one metabolic equivalent, or MET. A slow walk is about two MET, bicycling four MET, and jogging seven MET. While we need to move around a bit to complete the tasks of daily living, in modern life we tend not to move very much. Thus, for most people, 80 percent of the calories we expend each day are due to RMR.

When you lose weight, your RMR should fall a small amount, as you are losing some muscle tissue. But when most of the weight loss is fat, we would expect to see only a small drop in RMR, as fat is not metabolically very active. What is surprising is that relatively large drops in RMR are quite common among individuals who lose body fat through diet or exercise.

The “World’s Biggest Loser” contestants, for example, experienced a drop in their resting metabolic rate of almost 30 percent even though 80 percent of their weight loss was due to fat loss. A simple calculation shows that making up for such a large drop in RMR would require almost two hours a day of brisk walking, seven days a week, on top of a person’s normal daily activities. Most people cannot fit this activity level into their lifestyle.

There’s no question that eating a balanced diet and regular exercise are good for you, but from a weight management perspective, increasing your resting metabolic rate may be the more effective strategy for losing weight and maintaining that lost weight.

Metabolic activity is dependent on oxygen delivery to the tissues of the body. This occurs through blood flow. As a result, cardiac output is a primary determinant of metabolic activity.

The adult body contains about four to five liters of blood, and all of this blood should circulate throughout the body every minute or so. However, the amount of blood the heart can pump out with each beat is dependent on how much blood is returned to the heart between beats.

If the “plumbing” of our body, our veins in particular, was made of rigid pipes, and the skin of our legs was tough like that of bird legs, cardiac outflow would always equal cardiac inflow, but this is not the case. The veins in our body are are quite flexible and can expand many times their resting size, and our soft skin also allows lower body volume expansion.

As a result, when we are sitting quietly, blood and interstitial fluid (the fluid which surrounds all the cells in our body) pools in the lower parts of the body. This pooling significantly reduces the amount of fluid returning to the heart, and correspondingly, reduces how much fluid the heart can pump out during each contraction. This reduces cardiac output, which dictates a reduced RMR.

Our research has shown that for typical middle-aged women, cardiac output will drop about 20 percent when sitting quietly. For individuals who have recently lost weight, the fluid pooling situation can be greater because their skin is now much looser, providing much more space for fluids to pool. This is especially the case for people experiencing rapid weight loss, as their skin has not had time to contract.

For young, healthy individuals, this pooling of fluid when sitting is limited because specialized muscles in the calves of the legs — the soleus muscles — pump blood and interstitial fluid back up to heart. This is why soleus muscles are often referred to as our “secondary hearts.” However, our modern, sedentary lifestyles mean that our secondary hearts tend to weaken, which permits excessive fluid pooling into the lower body. This situation is now commonly referred to as “sitting disease.”

Moreover, excessive fluid pooling can create a vicious cycle. Fluid pooling reduces RMR, and reduced RMR means less body heat generation, which results in a further drop in body temperature; people with low RMR often have persistently cold hands and feet. As metabolic activity is strongly dependent on tissue temperature, RMR will therefore fall even more. Just a 1 degree Fahrenheit drop in body temperature can produce a 7 percent drop in RMR.

One logical, though expensive, approach to reduce fluid pooling after weight loss would be to undergo cosmetic surgery to remove excess skin to eliminate the fluid pooling space created by the weight loss. Indeed, a recent study has confirmed that people who had body contouring surgery after losing large amounts of weight due to gastric banding surgery had better long-term control of their body mass index than people who did not have body contouring surgery.

A much more convenient approach to maintaining RMR during and after weight loss is to train up your secondary hearts, or soleus muscles. The soleus muscles are deep postural muscles and so require training of long duration and low intensity.

Tai chi, for instance, is an effective approach to accomplish this. However, we’ve observed that many people find the exercises onerous.

Over the last several years, investigators in the Clinical Science and Engineering Research Lab at Binghamton University have worked to develop a more practical approach for retraining the soleus muscles. We have created a device, which is now commercially available through a university spin-off company, that uses a specific mechanical vibration to activate receptors on the sole of the foot, which in turn makes the soleus muscles undergo a reflex contraction.

In a study of 54 women between the ages of 18 and 65 years, we found that 24 had secondary heart insufficiency leading to excessive fluid pooling in the legs, and for those women, soleus muscle stimulation led to a reversal of this fluid pooling. The ability to prevent or reverse fluid pooling, allowing individuals to maintain cardiac output, should, in theory, help these individuals maintain RMR while performing sedentary activities.

This premise has been confirmed, in part, by recent studies undertaken by our spin-off venture. These unpublished studies show that by reversing fluid pooling, cardiac output can be raised back to normal levels. Study results also indicate that by raising cardiac output back to normal resting levels, RMR returns to normal levels while individuals are sitting quietly. While these data are preliminary, a larger clinical trial is currently underway.

Could There Be A Life On Stars?? (Republish) (Astronomy)

You may be very well familiar of carbon life, and have heard of nitrogen life, where methane plays an important role and yes even, silicon life too which we already discussed on our Instagram page.. But, what if I say, there could be a life on stars? Yeah there are writers of science fiction who have explored who have explored even wilder ideas for life. One of them is, Robert L. Forward who proposed a form of life, not based on atoms, but atomic nuclei in his 1980’s book, “Dragon egg”..

Cheela. Img credit: the sea lemon

In Dragon’s Egg, he described a species known as the cheela (shown above), who lived on the surface of a neutron star.. Because nuclear interactions occur at a much faster rate than atomic chemistry, the cheela civilization moves from simple tools to advanced technology in the span of a month.. Native to the neutron star Dragon’s Egg, cheela are vastly different from any kind of Earth life. “Chemistry” on their world is based around compounds made of nuclei and held together by the strong force. This results in chemical reactions that are a million times faster than those on Earth. A day on Dragon’s Egg lasts 0.2 seconds, and a cheela will live for about 40 minutes. 

Each cheela is roughly the size of a sesame seed but, thanks to the super dense neutron star material they are made out of, weigh about as much as an adult human. They have fairly amorphous bodies, from which they can extend pseudopods at will. These appendages can be articulated if the need arises, as cheela can consciously form crystalline “bones” anywhere in their bodies. All cheela have twelve stalked eyes on top of their bodies, which can be reinforced with crystal to be stretched higher if needed. With these they can see in the ultraviolet and X-ray spectrum. They can also detect magnetic field, which aids them in navigation. Cheela communicate by vibrating their foot against the ground, which allows them to talk over both long and short distances. Under extreme stress, cheela are able to modify their bodies into a plant-like form. This allows them to weather dangerous circumstances. After the “plant” has acquired enough resources, the cheela will revert to its mobile form.

Anatomy of cheela

Cheela life on Dragon’s Egg is governed by the star’s immense magnetic field. Though they can use it to navigate, moving can be very difficult for a cheela depending on the direction they pick. Moving against the magnetic field is so difficult for cheela that it is considered impractical unless circumstances like famine or predators make it necessary. Because of this, cheela call moving with the magnetic field moving in the “easy direction”. Moving against it is considered moving in the “hard direction”. Extreme magnetic and gravitational forces on Dragon’s Egg also warp the cheela’s bodies themselves, with their bodies being stretched parallel to the direction of the magnetic field. Since their eyes are stretched as well, cheela are generally unaware of this. 

While it makes for a great tale, the idea doesn’t help much in searching for life. In the novel, the cheela are only discovered when humans visit their neutron star. Cheela civilization couldn’t be detected from light-years away. There is also a great deal of handwaving done by Forward to advance the story. While nuclear chemistry can be complicated, we don’t know that it could give rise to some DNA-like structure that could allow for evolution.

The mapped surface of a neutron star. Credit: NASA, NICER, GSFC’s CI Lab

While it makes for a great tale, the idea doesn’t help much in searching for life. In the novel, the cheela are only discovered when humans visit their neutron star. Cheela civilization couldn’t be detected from light-years away. There is also a great deal of handwaving done by Forward to advance the story. While nuclear chemistry can be complicated, we don’t know that it could give rise to some DNA-like structure that could allow for evolution.

Recently, however, a team looked at this idea in more detail. Rather than relying on pure nuclear interactions to play the role of DNA, the team focuses on cosmic strings and magnetic monopoles. Cosmic strings are hypothetical fissures that might have formed when the early universe underwent a phase transition during the creation of matter. Magnetic monopoles are particles that have only one magnetic pole (north or south) rather than all known magnetic particles that have both. While there is no evidence that either of these exists, theoretical work suggests they might.

In the paper, the team proposes that monopoles would cluster along cosmic strings, and the gravity of stars could capture these strings. Given the turbulent motion of nuclei within the cores of stars, these beaded strings could entangle so that they encode and replicate information. And if all that is true, then maybe it could be the seed for nuclear life.

It’s all very speculative and mostly unprovable. However, the team proposes that if such life does arise in the core of a star, it would need to consume some of the core’s energy to survive. As a result, their star might cool faster than predicted by stellar models. Some stars do have excess cooling, but you don’t need cosmic strings, monopoles, and nuclear life to explain it.

Right now, there’s no evidence to support nuclear life, but studies like this can help us think outside the box of terrestrial life. The universe is often stranger than we can imagine, and life out there might be far more alien than we expect.

References: Anchordoqui, L., & Chudnovsky, E. M. (2020, June 25). Can Self-Replicating Species Flourish in the Interior of a Star?. https://doi.org/10.31219/osf.io/j6gux pdf: http://journals.andromedapublisher.com/index.php/LHEP/article/download/166/85/

Quantum Light Enables Measurement Of Signals Otherwise Buried By Noise (Quantum)

ORNL researchers developed a quantum, or squeezed, light approach for atomic force microscopy that enables measurement of signals otherwise buried by noise.

Unlike today’s classical microscopes, Pooser’s team quantum microscope requires quantum theory to describe its sensitivity. The nonlinear amplifiers in ORNL’s microscope generate a special quantum light source known as squeezed light.

Credit: Raphael Pooser, ORNL, U.S. Dept. of Energy

They demonstrated the first practical application of nonlinear interferometry by measuring the displacement of an atomic force microscope microcantilever with 50% better sensitivity than is classically possible. For one-second long measurements, the quantum-enhanced sensitivity was 1.7 femtometers—about twice the diameter of a carbon nucleus. Further, they minimize photon backaction noise while taking advantage of quantum noise reduction (up to 3 dB below the standard quantum limit) by transducing the cantilever displacement signal with a weak squeezed state while using dual homodyne detection with a higher power local oscillator.

Their approach to quantum microscopy relies on control of waves of light. When waves combine, they can interfere constructively, meaning the amplitudes of peaks add to make the resulting wave bigger. Or they can interfere destructively, meaning trough amplitudes subtract from peak amplitudes to make the resulting wave smaller. This effect can be seen in waves in a pond or in an electromagnetic wave of light like a laser.

A well-known aspect of quantum mechanics, the Heisenberg uncertainty principle, makes it impossible to define both the position and momentum of a particle with absolute certainty. A similar uncertainty relationship exists for the amplitude and phase of light.

That fact creates a problem for sensors that rely on classical light sources like lasers: The highest sensitivity they can achieve minimizes the Heisenberg uncertainty relationship with equal uncertainty in each variable. Squeezed light sources reduce the uncertainty in one variable while increasing the uncertainty in the other variable, thus “squeezing” the uncertainty distribution. For that reason, the scientific community has used squeezing to study phenomena both great and small.

The sensitivity in such quantum sensors is typically limited by optical losses. Entanglement means independent objects behaving as one. Einstein called it “spooky action at a distance.” In this case, the intensities of the light beams are correlated with each other at the quantum level. ORNL’s approach to quantum microscopy is broadly relevant to any optimized sensor that conventionally uses lasers for signal readout.


References: R. C. Pooser, N. Savino, E. Batson, J. L. Beckey, J. Garcia, and B. J. Lawrie, “Truncated Nonlinear Interferometry for Quantum-Enhanced Atomic Force Microscopy”, Physical Review Letters 124 (2020). DOI: 10.1103/PhysRevLett.124.230504 link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.230504