Using Game-theory To Look For Extraterrestrial Intelligence (Astronomy)

Astronomer Eamonn Kerins with the University of Manchester has developed an approach to looking for intelligent extraterrestrial beings on other planets that involves using game theory. He has written a paper describing his ideas and has uploaded it to the arXiv preprint server.

Credit: Unsplash/CC0 Public Domain

The current approach to looking for intelligent life on other planets is basically two-pronged. One approach involves scanning the skies looking for signals from space that could be created by intelligent beings. The other involves scanning the sky for evidence of exoplanets that appear to be habitable. Kerins suggests that a way to meld the two approaches into a logical systematic search for extraterrestrial intelligence is to use some of the logic inherent in game theory.

Kerins starts by noting that it seems possible that the reason scientists on Earth have not discovered signals from beings on other planets is because they are not sending any, fearing that doing so might draw the attention of unfriendly adversaries. He further suggests that if others are out there, they might be listening just as intently as we are. This leads to the SETI paradox, in which everyone is listening but no one is sending. And it also leads to the question of how such a paradox could be resolved. He notes that game theory suggests that both parties should agree that the party with more access to information should be the one that transmits first to the other.

Kerins also suggests that both parties in such a situation try to use what he describes as “common-denominator information” to decide whether to send a target a signal. Such information, he notes, should be in a form that either party could recognize. He further notes that such signaling should begin with something very basic, like transit signal strength (the amount of starlight that is blocked by a planet as it moves in front of its star). Such a signal, he notes, is easy to measure and is also independent of any life forms that might be residing on a given planet. This approach would also narrow the search to only those planets that lie in a plane relative to their star compared to ours, and vice versa.

He concludes that following such an approach based on data currently available would narrow the search to just one exoplanet: K2-155d. He suggests that because it is more visible to us than the other way around, that we be the first to send a signal—and then to watch and listen for any reply.

References: Eamonn Kerins. Mutual detectability: a targeted SETI strategy that avoids the SETI Paradox, arXiv:2010.04089 [astro-ph.EP] , arxiv.org/abs/2010.04089 https://arxiv.org/abs/2010.04089

This article is republished here from phys.org under common creative licenses

To Survive Asteroid Impact, Algae Learned To Hunt (Botany)

Tiny, seemingly harmless ocean plants survived the darkness of the asteroid strike that killed the dinosaurs by learning a ghoulish behavior—eating other living creatures.

K/Pg, or Cretaceous-Paleogene extinction event, refers to the aftermath of the asteroid hitting Earth 66 million years ago. Credit: Odysseus Archontikis/University of Oxford.

Vast amounts of debris, soot, and aerosols shot into the atmosphere when an asteroid slammed into Earth 66 million years ago, plunging the planet into darkness, cooling the climate, and acidifying the oceans. Along with the dinosaurs on the land and giant reptiles in the ocean, the dominant species of marine algae were instantly wiped out—except for one rare type.

A team of scientists, including researchers at UC Riverside, wanted to understand how these algae managed to thrive while the mass extinction rippled throughout the rest of the global food chain.

“This event came closest to wiping out all multicellular life on this planet, at least in the ocean,” said UCR geologist and study co-author Andrew Ridgwell. “If you remove algae, which form the base of the food chain, everything else should die. We wanted to know how Earth’s oceans avoided that fate, and how our modern marine ecosystem re-evolved after such a catastrophe.”

To answer their questions, the team examined well-preserved fossils of the surviving algae and created detailed computer models to simulate the likely evolution of the algae’s feeding habits over time. Their findings are now published in the journal Science Advances.

According to Ridgwell, scientists were a bit lucky to find the nano-sized fossils in the first place. They were located in fast accumulating and high-clay-content sediments, which helped preserved them in the same way the La Brea tar pits provide a special environment to help preserve mammoths.

High-resolution scanning electron microscope images of fossil cell coverings of nannoplankton highlighting holes that would have allowed flagella and haptonema to emerge from the cell and draw in food particles. Credit: Paul Brown/University College London

Most of the fossils had shields made of calcium carbonate, as well as holes in their shields. The holes indicate the presence of flagella—thin, tail-like structures that allow tiny organisms to swim.

“The only reason you need to move is to get your prey,” Ridgwell explained.

Modern relatives of the ancient algae also have chloroplasts, which enable them to use sunlight to make food from carbon dioxide and water. This ability to survive both by feeding on other organisms and through photosynthesis is called mixotrophy. Examples of the few land plants with this ability include Venus flytraps and sundews.

Researchers found that once the post-asteroid darkness cleared, these mixotrophic algae expanded from coastal shelf areas into the open ocean where they became a dominant life form for the next million years, helping to quickly rebuild the food chain. It also helped that larger creatures who would normally feed on these algae were initially absent in the post-extinction oceans.

“The results illustrate both the extreme adaptability of ocean plankton and their capacity to rapidly evolve, yet also, for plants with a generation time of just a single day, that you are always only a year of darkness away from extinction,” Ridgwell said.

A SEM view of a seafloor after the extinction showing the abundance of these cells with flagellar openings. These cells are around 7 microns in diameter (7/1000ths of a millimetre) with the scale bars next to each image showing the size of a micron (1/1000th mm). Credit: Paul Bown

Only much later did the algae evolve, losing the ability to eat other creatures and re-establishing themselves to become one of the dominant species of algae in today’s ocean.

“Mixotrophy was both the means of initial survival and then an advantage after the post-asteroid darkness lifted because of the abundant small pretty cells, likely survivor cyanobacteria,” Ridgwell said. “It is the ultimate Halloween story—when the lights go out, everyone starts eating each other.”

References: Samantha J. Gibbs, Paul R. Bown, Ben A. Ward et al., “Algal plankton turn to hunting to survive and recover from end-Cretaceous impact darkness”, Science Advances 30 Oct 2020: Vol. 6, no. 44, eabc9123 DOI: 10.1126/sciadv.abc9123 https://advances.sciencemag.org/content/6/44/eabc9123

Provided by University of California – Riverside

Is Your Brain Stuck? (Neuroscience)

Do you ever wonder what your brain is doing?  Perhaps you unexpectedly lost your temper and responded in a way that left you feeling embarrassed and ashamed?  Or maybe, despite your good intentions to eat a healthy lunch, you found yourself munching on a sweet treat instead.  The truth is, we all experience moments when what we want our brains to do and what they actually do feels completely out of alignment.

Source: iStock:HbrH.

So, how can our brains help us to show up more often in the ways that are good for us and others?

“Studies have found that the best predictor of our happiness and health, both mental and physical, is how integrated our brains are,” explained Dr. Dan Siegel, a Clinical Professor of Psychiatry at the UCLA School of Medicine and author of the new book Aware: The Science and Practice of Presence, when Michelle McQuaid interviewed him recently. “Integration links different parts of our body, such as the right and left sides of the brain, or the higher and lower parts of the nervous system to promote a flexible and adaptive way of being that is characterized by harmony, vitality, and creativity.”

Dan explained her that when our brain lacks integration, the result is either rigidity or chaos; stuck and dull on the one hand, or explosive and unpredictable on the other, as we try to navigate the world around us.  Without integration, we can become imprisoned in behavioral ruts – anxiety, depression, greed, obsession, and addiction.

On the other hand, neurological integration enables us to be flexible and free.  It makes it easier for us to consistently show up in ways that are good for us and others when we have optimal integration because our brains have five qualities: flexibility, adaptivity, coherence, energy, and stability (FACES).  With the connecting freedom of integration comes a sense of vitality and the ease of well-being.

“We can think of the FACES as a river that in the middle is an ever-changing flow of integration and harmony,” explained Dan.  “On one riverbank, there is chaos, and on the other is rigidity.  Sometimes we might move towards the bank of rigidity and can feel stuck, and other times we might lean towards the bank of chaos where life feels erratic and uncontrollable.  But there are practical steps we can take to create more internal and relational integration in our lives.”

Dan suggests the following:

  • Understand your brain – Try this simple hand model.  Start by putting your thumb in the middle of your palm and put your fingers over the top.  The fingers represent the most evolved cortex part of your brain, which helps focus attention and gives you insight and empathy.  Then lift open your fingers to see the thumb folded in the middle of your palm.  That represents the sub-cortical areas below the cortex and includes the limbic and brainstem areas.  These areas create our basic drives and emotions.  The lower brainstem areas at our wrist affect the regulation of our body.  Integration of your brain involves linking the cortex, limbic and brainstem areas, and your body together.  If they are not, you’re likely to experience chaos and rigidity.  The linking fibers grow with the three pillar practices.  Not only can this lead to a reduction in stress, but it can also improve your immune function, reduce inflammation, slow the aging process, and connect your heart with your brain in a more balanced way.
  • Develop a three-pillar practice – A combination of mindfulness and compassionate training involves three pillars: focusing attention, increasing awareness to be open, and building kind intentions.  You can develop all three of these in a single practice called The Wheel of Awareness.  Studies have found that practicing these three pillars helps the different structures and functions of the brain to become more integrated.  And this integration in the brain helps our regulation and executive functioning, so we can live a life with positive emotions and not be taken over, in a non-regulated way, by painful, chaotic, or rigid states of mind.
  • Cultivate interconnectedness – As well as an internal integrative healing process that helps us resolve trauma, we also need a relational integrative process that allows us to be differentiated.  This enables us to feel that our own internal experience is heard, respected, and empathized with.  And then we need to be linked to other others, so we can become connected as a part of a larger whole.  Many social injustices and environmental injustices lack acknowledgment of the reality of interconnection; that we each have a responsibility to support others – either individuals or collectives – experiencing these traumas.  For example, awareness of the importance of Black Lives Matter, of respecting women, and of respecting the environment is about interconnection.  And if we can use the disruption of the COVID-19 pandemic to ask, “How can we live a more interconnected life?” then we may be able to turn this painful time into a moment of discovering more integrative ways of living.

What can you do to cultivate more focus, awareness, and kind intentions to help integrate your brain?

This article is republished here from psychology today under common creative licenses

Why Does Autism Affect More Boys Than Girls? (Psychiatry)

Males are three times more likely than females to have autism. Although autism is strongly heritable, the male prevalence of autism must be due to more than just genes since autistic girls carry a much higher mutational load than autistic boys. Thus, having genes for autism alone does not explain why more boys are diagnosed with autism than girls.

The latest evidence suggests that the neurobiological mechanisms of sexual differentiation predispose males to the development of autism. There are numerous reasons to support this conclusion: Autistic women have atypical brain structure in sexually dimorphic regions; the brain of males with autism shows both hypermasculine and hyperfeminine patterns of connectivity; autistics show masculinized scores on sexually dimorphic psychological traits; autistic women have elevated androstenedione levels, the precursor to testosterone; and finally, autistic children have hypermasculine facial features.

While prenatal androgens are responsible for masculinization in humans, prenatal estrogens contribute significantly more to fetal and neonatal brain development. Prenatal estrogens are also critical for the development of one particularly important neurotransmitter system in the cortex, GABA. GABA is one of the brain’s most prevalent neurotransmitter and plays a critical role in neuroplasticity. Estrogens support the normal development of the cortex by influencing GABA activity, while inducing synapse formation and neuronal differentiation; these functions are all atypical in the autistic brain.

This latest study measured prenatal levels of estriol, estradiol, estrone, and estrone sulphate in amniotic fluid of boys with and without autism. They provide the first evidence that elevated levels of prenatal amniotic estradiol, estriol, and estrone are each associated with autism, with estradiol levels being the most significant predictor of autism in males.

The authors speculated that these hormonal changes in the uterine environment could potentially be attributed to changes within the placenta. This is a reasonable hypothesis given that the placenta acts as an endocrine regulator at the maternal-fetal interface. The placenta is also the main source of estrogen production for the fetus. This suggestion is consistent with other lines of evidence that suggest a causal role for the placenta in the etiology of autism. First of all, there is increased placental inflammation in autism. Studies from my lab have previously demonstrated that the brains of autistics also have elevated levels of inflammatory proteins. Second, the morphology of the placenta is atypical and of increased size. Third, complications related to placenta hypertensive disorders are more frequent in pregnancies that result in autism. Previous studies have shown that placental dysfunction disproportionately affects males more than females.

The results of this novel study demonstrate for the first time that prenatal estrogens contribute to the probability of developing autism and offer the best current explanation for the prevalence of autism in males. The elevated prenatal steroidogenic activity likely further affects sexual differentiation, brain development, and function that are characteristic of this disorder.

References: Baron-Cohen S, et al (2020) Foetal oestrogens and autism. Molecular Psychiatry Vol 25:2970–2978. https://doi.org/10.1038/s41380-019-0454-9

This article is republished here from psychology today under common creative licenses

Why Some People Dig In Instead of Admit They’re Wrong (Psychology)

The practice of staunchly defending one’s point of view or position, despite a great deal of information and evidence that would totally disconfirm it, has become much more obvious in recent years.

Here are a few explanations for why people stubbornly refuse to change their minds, regardless of the facts.

©gettyimages.

Cognitive Dissonance

Cognitive dissonance is the mental discomfort experienced by a person who simultaneously holds two or more contradictory beliefs, ideas, or values. To reduce the psychological discomfort, the person will have to change either their mind or their behavior so that the inconsistency or contradiction is resolved, thus restoring mental balance and emotional harmony. That is, cognitive consonance.

People continually reduce their cognitive dissonance to align their beliefs with their actions, thereby maintaining psychological consistency and less mental stress. Fundamentally, there are two ways a person can reduce cognitive dissonance. One is to change or discard one of the beliefs. The other is to change one’s behavior so that it is consistent with one or the other belief.

A helpful example of this phenomenon is smoking cigarettes. Clearly, when people smoke cigarettes (their behavior) they are aware that they are imperiling their health (their cognition). This creates a strong mental tension that can be reduced by either changing their thinking about smoking or changing their smoking behavior (i.e., stop smoking). That is, changing their cognition that smoking is dangerous — through mental gymnastics like denial — or changing their behavior so that it’s consonant with the rational belief that smoking is hazardous would both reduce cognitive dissonance.

Unfortunately, when there is a clash of ideas and information, leading to a conflict between our attitudes and our behavior, we tend to change our attitudes to make them consistent with our maladaptive behavior rather than change our behavior to make it consistent with our adaptive attitudes.

Confirmation Bias

This is the tendency to interpret new information as confirmation of one’s existing beliefs or ideas. In essence, this involves filtering out evidence that would contradict pre-existing beliefs and focusing instead only on things that would seem to support the established ideas. For example, if a person with low self-esteem doesn’t receive a response to a text in a timely fashion, they would be prone to interpret it as confirmation that they are not valued by the text’s recipient––even though a much more likely explanation is the recipient was indisposed and couldn’t reply promptly. Most concerning is the fact that this psychological phenomenon is at the root of most stereotyping, bigotry, and racism.

The Dunning-Kruger Effect

This is a cognitive bias in which people with very low ability grossly overestimate their competence. It is a type of illusory superiority in which people see themselves as much more capable of a task than they actually are. Hence, instead of recognizing and accepting that they are in over their heads, people reflecting the DKE will stubbornly refuse to acknowledge their limitations and ineptitude.

Pathological Narcissism

This is a pervasive pattern of grandiosity, a constant need for admiration, an utter lack of empathy, and a deceitful tendency to manipulate others for one’s personal gain. In addition, pathological narcissists have trouble handling anything they perceive as criticism. They always have to be right, proclaim they know more than they actually do, never take any responsibility for their wrongful acts, and always blame others for their mistakes.

The Stockholm Syndrome

This is a particularly fascinating psychological phenomenon in which hostages or victims of a kidnapping develop feelings of trust and affection for their captor. The term was coined in 1973 when four hostages were taken during a botched bank robbery in Stockholm Sweden. After being released, the hostages defended their captors and refused to testify against them in court. Plainly said, this is a type of “brainwashing.“ And while considered to be generally rare, the Stockholm Syndrome’s parallel to cultism is obvious and can theoretically occur to any extent (see “groupthink” below).

Groupthink

The desire for conformity or harmony within a group can result in people failing to think critically or independently and consequently make dysfunctional decisions. This “agree at all costs” attitude creates a sense of cohesiveness in a group but often leads group members to exercise poor judgment. Examples of groupthink are peer pressure, acting in a “go-along-to-get-along” manner, fear of “rocking the boat” and being a “yes person.”

Pride and Ego

Not to be confused with pathological narcissism, simple pride and ego can compel people to stand their ground even when they are clearly wrong. Whether people see being wrong as a sign of weakness, or their stubbornness is due to compensation for a massive inferiority complex, this is a very common, often self-defeating, human tendency. And, indeed, I spend a fair amount of time during therapy with people trying to encourage them to pick happiness over pride and ego. Because in most instances, I believe, it is better to be happy than right.

Ignorance

I have blogged several times about ignorance and various kinds of illiteracy. Especially, scientific illiteracy. The above explanations for intransigence have all involved a basic refusal to acknowledge or accept the facts. But when people are ignorant of the facts or have a very limited understanding of them, they can dig in simply because they just don’t know any better.

Simple Stupidity

This explanation requires no further elaboration.

Remember: Think well, act well, feel well, be well!

Copyright of this article totally belongs to author of this article, ‘Clifford N. Lazarus’, Ph.D. which was originally published on psychology today.

New Evidence Our Neighborhood in Space Is Stuffed With Hydrogen (Astronomy)

Only the two Voyager spacecraft have ever been there, and it took than more than 30 years of supersonic travel. It lies well past the orbit of Pluto, through the rocky Kuiper belt, and on for four times that distance. This realm, marked only by an invisible magnetic boundary, is where Sun-dominated space ends: the closest reaches of interstellar space.

©NASA

In this stellar no-man’s land, particles and light shed by our galaxy’s 100 billion stars jostle with ancient remnants of the big bang. This mixture, the stuff between the stars, is known as the interstellar medium. Its contents record our solar system’s distant past and may foretell hints of its future. 

Measurements from NASA’s New Horizons spacecraft are revising our estimates of one key property of the interstellar medium: how thick it is. Findings published today in the Astrophysical Journal share new observations that the local interstellar medium contains approximately 40% more hydrogen atoms than some prior studies suggested. The results unify a number of otherwise disparate measurements and shed new light on our neighborhood in space.

Slogging through interstellar fog

Just as Earth moves around the Sun, so our entire solar system hurtles through the Milky Way, at speeds exceeding 50,000 miles per hour. As we cruise through a fog of interstellar particles, we’re shielded by the magnetic bubble around our Sun known as the heliosphere. Many interstellar gases flow around this bubble, but not all.

Our heliosphere repels charged particles, which are guided by magnetic fields. But more than half of local interstellar gases are neutral, meaning they have a balanced number of protons and electrons. As we plow into them the interstellar neutrals seep right through, adding bulk to the solar wind.

“It’s like you’re running through a heavy mist, picking up water,” said Eric Christian, space physicist at NASA’s Goddard Space Flight Center in Greenbelt, MD. “As you run, you’re getting your clothes all soggy and it’s slowing you down.” 

Soon after those interstellar atoms drift into our heliosphere, they are zapped by sunlight and slammed by solar wind particles. Many lose their electrons in the tumult, becoming positively-charged “pickup ions.” This new population of particles, though changed, carry with them secrets of the fog beyond.

“We don’t have direct observations of interstellar atoms from New Horizons, but we can observe these pickup ions,” said Pawel Swaczyna, postdoctoral researcher at Princeton University and lead author of the study. “They are stripped of an electron, but we know they came to us as neutrals atoms from outside the heliosphere.”

NASA’s New Horizons spacecraft, launched in January 2006, is the one best suited to measure them. Now five years past its rendezvous with Pluto, where it captured the first up-close images of the dwarf planet, today it ventures through the Kuiper belt at the edge of our solar system where pickup ions are the freshest. The spacecraft’s Solar Wind Around Pluto, or SWAP instrument, can detect these pickup ions, distinguishing them from the normal solar wind by their much higher energy. 

Enhanced color global view of Pluto, taken when NASA’s New Horizons spacecraft was 280,000 miles (450,000 kilometers) away. Credits: NASA/JHUAPL/SwRI

The amount of pickup ions New Horizons detects reveals the thickness of the fog we’re passing through. Just as a jogger gets wetter running through thicker fog, the more pickup ions New Horizons observes, the denser the interstellar fog must be outside. 

Diverging measurements

Swaczyna used SWAP’s measurements to derive the density of neutral hydrogen at the termination shock, where the solar wind butts up against the interstellar medium and abruptly slows down. After months of careful checks and tests, the number they found was 0.127 particles per cubic centimeter, or about 120 hydrogen atoms in a space the size of a quart of milk. 

This result confirmed a 2001 study which used Voyager 2 – about 4 billion miles away – to measure how much the solar wind had slowed by the time it arrived at the spacecraft. The slowdown, largely due to intervening interstellar medium particles, suggested a matching interstellar hydrogen density, about 120 hydrogen atoms in a quart-sized space.

But newer studies converged around a different number. Scientists using data from NASA’s Ulysses mission, from a distance slightly closer to the Sun than Jupiter, measured pickup ions and estimated a density of about 85 hydrogen atoms in a quart of space. A few years later, a different study combining Ulysses and Voyager data found a similar result.

“You know, if you discover that something different than previous work, the natural tendency is to start looking for your errors,” said Swaczyna.

But after a little digging, the new number began to look like the right one. The New Horizons measurements fit better with observations based on faraway stars. The Ulysses measurements, on the other hand, had a shortcoming: they were made much closer to the Sun, where pickup ions are rarer and measurements more uncertain.

“The inner heliosphere pickup ions observations go through billions of miles of filtering,” Christian said. “Being most of the way out there, where New Horizons is, makes a huge difference.”

As for the combined Ulysses/Voyager results, Swaczyna noticed that one of the numbers in the calculation was outdated, 35% lower than the current consensus value. Recalculating with the currently accepted value gave them an approximate match with the New Horizons measurements and the 2001 study.

“This confirmation of our old, almost forgotten result comes as a surprise,” said Arik Posner, author of the 2001 study at NASA Headquarters in Washington, D.C. “We thought our rather simple methodology for measuring the slowdown of the solar wind had been overcome by more sophisticated studies conducted since, but not so.”

A new lay of the land

Going from 85 atoms in a quart of milk to 120 may not seem like much. Yet in a model-based science like heliophysics, a tweak to one number affects every other. 

The new estimate may help explain one of the biggest mysteries in heliophysics of the last few years. Not long after NASA’s Interstellar Boundary Explorer or IBEX mission returned its first complete dataset, scientists noticed a strange stripe of energetic particles coming from the forward edge of our heliosphere. They called it the “IBEX ribbon.” 

“The IBEX ribbon was a big surprise – this structure at the edge of our solar system a billion miles wide, 10 billion miles long, that no one knew was there,” Christian said. “But even as we developed the models for why it was there, all of the models were showing that it shouldn’t be as bright as it is.”

The ribbon remains one of IBEX’s biggest discoveries. It refers to a vast, diagonal swath of energetic neutrals, painted across the front of the heliosphere. Credits: NASA/IBEX

“The 40% higher interstellar density observed in this study is absolutely critical” said David McComas, professor of astrophysical sciences at Princeton University, principal investigator for NASA’s IBEX mission and coauthor of the study. “Not only does this show that our Sun is embedded in a much denser part of interstellar space, it also may explain a significant error in our simulation results compared to the actual observations from IBEX.”

Most of all, though, the result gives an improved picture of our local stellar neighborhood.

“It’s the first time we’ve had instruments observe pickup ions this far away, and our picture of the local interstellar medium is matching those from other astronomical observations,” said Swaczyna. “It’s a good sign.”

Provided by NASA

Einstein’s Zoo: LIGO And Virgo Confirm Gravitational Waves From 50 Cosmic Collisions (Astronomy)

The LIGO and Virgo Collaborations, which includes researchers from the University of Birmingham, have announced a further 39 gravitational-wave events, bringing the total number of confident detections to 50.

These 50 events include the mergers of binary black hole, binary neutron stars and, possibly, neutron star-black holes. ©University of Birmingham.

These 50 events include the mergers of binary black hole, binary neutron stars and, possibly, neutron star-black holes. The 39 events announced [today], in the release of the Collaboration’s second Gravitational-Wave Transient Catalogue (GWTC-2) also span a wide range of masses and contain a wealth of information on the history and formation of black holes and neutron stars throughout the universe. The events were detected during the first half of the third observing run, between 1 April and 1 October 2019.

The University of Birmingham has been a key member of the Advanced LIGO project since its inception. Researchers from the Institute for Gravitational Wave Astronomy have contributed to the design and construction of the LIGO detectors, have developed accurate models for the gravitational radiation emitted by binary systems and have pioneered the techniques used to mine astrophysical information from the gravitational-wave data. This work allows us to study the physics of binary systems, their astrophysical evolution and perform precision tests of Einstein’s theory with gravitational-wave observations. Members of the Institute for Gravitational Wave Astronomy have played a leading role in the analysis and interpretation of the data collected throughout the three observing runs.

Dr Patricia Schmidt, lecturer at the Institute for Gravitational Wave Astronomy, says: “Only five years after the very first detection of gravitational waves, we already have 50 events. Gravitational-wave astronomy is rapidly becoming an indispensable tool for studying some of the most fascinating objects such as black holes and neutron stars as well as the universe as a whole.”

These new observations are a treasure chest to peek into the evolutionary paths of black holes and neutron stars in binary systems. GWTC-2 contains a population of binary black holes that span a much wider mass range than previously observed, from approximately 5 to 85 times the mass of the Sun. The lower end of the range is where theorists expect the lightest black holes to be formed in Nature, a prediction that can now be tested observationally. The higher end of the mass spectrum is too high for standard stellar evolution models to produce a black hole as the end state of massive stars. To find out how and where in the Universe the systems found by LIGO-Virgo were formed, will keep astrophysicists busy for quite some time.

For the first time, this sample also provides a clear indication that at least some black holes spin and tumble in their death-dance around each other. A small fraction of them, around 20 per cent, seem to like to dance upside-down. Measuring the masses and spins of the binary companions is of extreme importance towards connecting the compact objects to their stellar progenitors, allowing us to solve the puzzle of their formation and evolution which can take many different paths and crucially depends on them.

Riccardo Buscicchio, a PhD student at the University of Birmingham School of Physics and Astronomy and member of the LIGO-Virgo Collaboration says: “It’s like reconstructing the entire history of primates, their origin and migration across the continents only by looking at Neanderthals and Homo Sapiens. Except that black holes progenitors are much older, 200 times further in the past than primates’ history on Earth.”

These new gravitational-wave detections provide yet another stress-test of Einstein’s General Theory of Relativity. By comparing the observed gravitational-wave signals to our best theoretical predictions we can search for small deviations from General Relativity: once more Einstein’s theory passes every test unscathed.

Dr Geraint Pratten, a researcher at the University of Birmingham, who played a leading role in the confirmation of Einstein’s theory, says: “Gravitational-wave observations provide us with a unique arena in which we can perform novel tests of fundamental physics. The wealth of observed binary black holes allow us to scrutinise Einstein’s theory of relativity in unprecedented detail, gaining remarkable insights into the astrophysical and fundamental nature of black holes.”

The future of gravitational-wave astronomy seems to be as bright as ever. The analysis of the second half of O3 is currently in progress and will further expand the growing gravitational-wave transient catalog. Following O3, detectors will undergo additional engineering improvements to further increase their astrophysical reach in time for the fourth observing run, currently scheduled to start in 2022. While scientists await instrumental improvements and the construction of even more ambitious detectors, GWTC-2 offers unprecedented opportunities to explore the nature of black holes and neutron stars throughout the universe.

Professor Alberto Vecchio, director of the Institute for Gravitational Wave Astronomy says: “I remember when over 20 years ago I started to devote most of my time to gravitational wave science many of my former PhD colleagues thought I was mad: I would spend my scientific career just staring at terabytes of noise. I am so glad I was foolish enough not to pay much attention to their remarks. Now it’s surprise after surprise in an exhilarating journey across the Universe, and this is just the very beginning.”

A Highlight of Exceptional Events in GWTC-2:

  • GW190412: a BBH with asymmetric component masses that shows evidence for higher harmonics.
  • GW190425: the second gravitational-wave event consistent with a BNS, following GW170817.
  • GW190426_152155: a low-mass event consistent with either an NSBH or BBH.
  • GW190514_065416: a BBH with the smallest effective aligned spin of all O3a events.
  • GW190517_055101: a BBH with the largest effective aligned spin of all O3a events.
  • GW190521: a BBH with total mass over 150 times the mass of the Sun.
  • GW190814: a highly asymmetric system of ambiguous nature, corresponding to the merger of a 23 solar mass black hole with a 2.6 solar mass compact object, making the latter either the lightest black hole or heaviest neutron star observed in a compact binary.
  • GW190924_021846: likely the lowest-mass BBH, with both black holes exceeding 3 solar masses.

Publication details

GWTC-2: https://arxiv.org/abs/2010.14527

Tests of General Relativity: https://arxiv.org/abs/2010.14529

Population properties of compact objects: https://arxiv.org/abs/2010.14533

Provided by Birmingham University

Can Supernova Shells Feed Supermassive Black Holes In Galactic Nuclei? (Astronomy)

The mechanisms leading to the formation and growth of SMBHs in the centers of their host galaxies is an open unsolved problem in astrophysics. The mass of the SMBH is correlated with the mass of the bulge & some extraordinary starburst activities of active galactic nuclei (AGN) may be connected to accreting SMBHs. However, this starburst activity usually occurs in regions enshrouded by dust, hiding completely their emission in optical wave bands. The energy is radiated away usually at infrared wavelengths and galaxies with abundant accretion onto a central SMBH appear as ultra luminous infrared galaxies (ULIRG). Interstellar matter can be funneled into central regions of galaxies by mergers and interactions of gas-rich galaxies that trigger the starburst activity. The feedback driven by young and massive stars leads to outflows, thereby reducing the interstellar matter (ISM) supply to the central SMBH, limited also by the conservation of angular momentum.

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Nuclear star clusters (NSCs) are found nestled in the cores of galaxies with SMBHs at the bottom of the galaxy’s potential wells. Their typical half-mass radii are (2 – 5) pc, with the full extent going out to (5 – 50) pc and estimated masses are in the range (10^5- 10^9 M). NSC masses appear to be related to masses of their host galaxies sharing a relationship similar to that between SMBH masses and galactic bulge masses. The formation of a NSC follows two possible scenarios. The first assumes that globular clusters formed in the galaxy outside of the galactic center and then spiralled down into the galaxy’s core because of dynamical friction before merging there to form the NSC. However, it appears that there are not enough RR Lyrae stars in the NSC of our Galaxy to be consistent with this first scenario: if the NSC were formed from globular clusters, the expected number of RR Lyrae stars would be almost an order of magnitude higher compared to numbers identified by the Hubble space telescope observations of the center of the Milky Way. The alternative scenario proposes in situ formation of the NSC developing from gas migrating into the galactic center due to internal processes in the galactic disc or as a result of interactions with other galaxies.

Now in this current paper, Morris and colleagues investigated the evolution of shells expanding into the interstellar medium surrounding the SMBH in the centers of galaxies inside of NSCs. The expanding shells are the result of energy and momentum inserted by young and massive stars of the NSC in the form of winds, radiation, and supernova explosions. The evolution of shells expanding into the interstellar medium resulting from either supernovae or stellar winds has been described in many papers and books. Here they summarize very briefly how the blast wave resulting from a supernova explosion evolves. The first stage is the phase of free expansion followed by the so-called Sedov-Taylor phase characterized by constant thermal energy inside the blast wave driving the expansion. When the radiative losses in the shell of the swept-up gas become important and the heat energy created by the compression of interstellar gas is radiated away, the dense wall of the shell behind the shock shrinks to a thin layer and the structure enters the pressure-driven, thin-shell phase. Later, when the pressure inside the shell drops, the wave is no longer driven by the interior pressure and it only keeps its momentum. This is the so-called snowplow phase. Even later, when the expansion velocity decreases below the local sound speed, the mass accumulation ceases and the thin shell dissolves.

Their main intention was to investigate whether supernovae (SNe) occurring in NSCs can deliver mass into the central region inside of the circumnuclear disk surrounding the SMBHs in the centers of galaxies. They explore the importance of the SN position relative to the SMBH and analyze how the inserted energy, mass, and the density of the interstellar medium influence the mass delivery to the SMBH. Here, they assume that the gas inside the expanding SN remnant is non-relativistic (gas velocity is below a few thousand km s-¹), and that shells are able to survive encounters with random density fluctuations and stay coherent when they are deformed by the tidal forces of the SMBH and of the NSC. To find suitable energies and positions of SNe for mass delivery near the central SMBH, in this paper they performed simulations with the simplified hydrodynamical code RING.

In the 3D code RING they assume that the wall of the shell is infinitesimally thin, meaning that its thickness is much smaller than its diameter. In this and future papers, simulations with the fast code RING will map the expanding shell properties for different SNe energies, positions relative to the SMBH and NSC,
and densities of the ISM.

In their model, the homogeneously distributed ISM rotates following the rotation curve,

where, rGC = √R² + z² is the galactocentric distance and (R,z) are the galactocentric cylindrical coordinates with the rotational axis perpendicular to the z = 0 plane.

which partially balances the gravitational attraction of the NSC and SMBH. They tested three different ISM densities, nout = 10³, 10⁴, and 10^5 cm-³, and identified the delivery region from where the SN expanding shells deliver mass into the central 1 pc. It is a region of small angular momentum with a low value of RL centered around the rotational axis,

Their simulations showed that supernovae occurring within a conical region around the rotational axis of the galaxy can feed the central accretion disk surrounding the SMBH. For ambient densities between 10³ and 10^5 cm³, the average mass deposited into the central parsec by individual supernovae varies between 10 to 1000 solar masses depending on the ambient density and the spatial distribution of supernova events. Supernovae occurring in the aftermath of a starburst event near a galactic center can supply two to three orders of magnitude more mass into the central parsec, depending on the magnitude of the starburst. The deposited mass typically encounters and joins an accretion disk. The fate of that mass is then divided between the growth of the SMBH and an energetically driven outflow from the disk.

Three-dimensional simulations with the code RING. The color bar gives the projected density in units of cm-². The meshed region shows the central region with a radius of 1 pc. The dashed line shows the reference circle with a radius of 5 pc and the cross gives the original position of the SN explosion. J. Palous et al.

References: J. Palouš, S. Ehlerová, R. Wünsch, and M. R. Morris, “Can supernova shells feed supermassive black holes in galactic nuclei?”, ArXiv, pp. 1-12, 2020. Link: https://arxiv.org/abs/2010.15412

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New Survey Finds That Single Burst Of Star Formation Created Milky Way’s “Central Bulge” (Astronomy)

Result contradicts previous studies suggesting two or more episodes of star formation.

Like most spiral galaxies, the Milky Way has a roughly spherical collection of stars at its center called the bulge. How the bulge formed has been a long-standing mystery, with many studies suggesting that it built up over time through multiple bursts of star formation.

New research finds that the majority of stars in our galaxy’s central bulge formed in a single burst of star formation more than 10 billion years ago. To reach this conclusion, astronomers surveyed millions of stars across 200 square degrees of sky—an area equivalent to 1,000 full Moons. The resulting wealth of data is expected to fuel many more scientific inquiries.

Our Milky Way galaxy is shaped like two fried eggs glued back-to-back. A central bulge of stars sits in the middle of a sprawling disk of stars. Though this is a common feature among myriad spiral galaxies, astronomers have spent decades puzzling out how and when the Milky Way’s central bulge might have formed. Were the stars within the bulge born early in our galaxy’s history, 10 to 12 billion years ago? Or did the bulge build up over time through multiple episodes of star formation?

Some studies have found evidence for at least two star-forming bursts, leading to stellar populations as old as 10 billion years or as young as 3 billion. Now, a comprehensive new survey of millions of stars instead finds that most stars in the central 1,000 light-years of the Milky Way’s hub formed when it was engorged with infalling gas more than 10 billion years ago. This process might have been triggered by simple accretion of primordial material, or something more dramatic like merging with another young galaxy.

“Many other spiral galaxies look like the Milky Way and have similar bulges, so if we can understand how the Milky Way formed its bulge then we’ll have a good idea for how the other galaxies did too,” said co-principal investigator Christian Johnson of the Space Telescope Science Institute in Baltimore, Maryland.

“This survey gives us a big picture view of the bulge in a way that many previous surveys have not been able to do,” added co-author Caty Pilachowski of Indiana University in Bloomington, Indiana.

Looking Younger than their Age

To reach their conclusion, the team studied the stars’ chemical compositions. Like many Hollywood stars, stars in the galactic bulge look like they’ve undergone a cosmic Botox treatment – they appear younger than they are. That’s because they contain about the same amount of heavy elements (heavier than hydrogen and helium) as the Sun – what astronomers call metals. That’s surprising because metals take time to accumulate. They must be created by earlier generations of stars, ejected through stellar winds or supernovas, and then incorporated into later generations.

Our Sun, at 4.5 billion years old, is a relative newcomer, so it makes sense that it would be replete in metals. In contrast, most old stars within our galaxy are lacking in heavy elements. And yet bulge stars are metal-enriched despite their advanced age.

“Something different happened in the bulge. The metals there built up very, very quickly, possibly in the first 500 million years of its existence,” said co-principal investigator Michael Rich of the University of California, Los Angeles.

The team used the measured brightness of stars at different wavelengths of light, particularly in the ultraviolet, to determine their metal content. Stars forming at different times would be expected to have different metallicities on average. Instead, they found that stars within 1,000 light-years of the galactic center showed a distribution of metals clustered around a single average. If stars were students and metallicities were U.S. grades, bulge stars would all have a solid ‘C’ average, rather than a group of ‘A’ students and a group of ‘D’ students. This suggests that those stars formed in a brief firestorm of star birth.

Big Pictures, Big Data

The team surveyed a portion of the sky covering more than 200 square degrees – an area approximately equivalent to 1,000 full Moons. They used the Dark Energy Camera (DECam) on the Victor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory in Chile, a Program of NSF’s NOIRLab. This wide-field camera is capable of capturing 3 square degrees of sky in a single exposure.

The team collected more than 450,000 individual photographs that allowed them to accurately determine chemical compositions for millions of stars. A subsample of 70,000 stars were analyzed for this study.

“Our survey is unique because we were able to scan a continuous section of the bulge at wavelengths of light from ultraviolet to visible to near-infrared. That allows us to get a clear understanding of what the various components of the bulge are and how they fit together,” said Johnson.

The wealth of data collected by this survey will fuel additional scientific inquiries. For example, the researchers are looking into the possibility of measuring stellar distances to make a more accurate 3D map of the bulge. They also plan to seek correlations between their metallicity measurements and stellar orbits. That investigation could locate “flocks” of stars with similar orbits, which could be the remains of disrupted dwarf galaxies, or identify signs of accretion like stars orbiting opposite the galaxy’s rotation.

Is the Milky Way’s bulge-formation history unique or common in galaxy evolution? To answer that question, astronomers will have to look at galaxy assembly in the distant, young universe – a task for which NASA’s James Webb Space Telescope was specifically designed. “With Webb, we’ll have a front-row seat to watching galaxies like our Milky Way forming,” said Rich.

The Blanco DECam Bulge Survey is named in honor of Victor and Betty Blanco. Victor Blanco was the first Director of the Cerro-Tololo Inter-American Observatory; he and Betty Blanco also pioneered study of the galactic bulge and Magellanic Clouds using the observatory’s 4-meter telescope.

The scientific publications discussing these findings are available online at Monthly Notices of the Royal Astronomical Society in two papers here and here.

Provided by University of California, Los Angeles