astrobites: Daily Paper Summaries 2019

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Are AGN Quiescent Adolescents?

Post by bystander » Tue Aug 13, 2019 5:36 pm

Are AGN Quiescent Adolescents?
astrobites | Daily Paper Summaries | 2019 Aug 07
Keir Birchall wrote:
It has long been understood that a connection exists between galaxies and the supermassive black holes (SMBHs) that exist at their centres. Gas from the host galaxy finds its way into the centre where it is consumed by the black hole. The sated black hole then bathes the host galaxy in huge amounts of radiation that can be detected across the electromagnetic spectrum, a phenomenon known as an active galactic nucleus (AGN). The difficult question is: how does the gas find its way into the centre and what effects might this have on the host galaxy? The well-cited Alexander & Hickox (2012) paper suggests that these AGN are fuelled mainly by mergers between galaxies and is outlined in figure 1. ...

Today’s authors studied a sample of obscured quasars in this so-called ‘adolescent’ phase (figure 1; stage 3) to investigate whether AGN and their host galaxies will always follow this evolutionary path. To accomplish this the authors identified and imaged a sample of 10 FeLoBAL quasars at the lowest possible redshifts (0.6 < z < 1.1) using the Hubble Space Telescope (HST). FeLoBAL quasars are active galaxies described by broad absorption lines in their spectrum, particularly iron, indicating powerful outflows of material. A sample of 20 blue, unobscured quasars from the author’s previous work were used as a control sample. The aim was to characterise and compare the shapes of both samples of galaxies. Assuming this merger-driven theory is correct, the authors would expect an enhancement of merger signatures in the FeLoBAL quasar sample when compared to their unobscured counterparts as FeLoBAL quasars more recently experienced the initial merger event. ...

The host galaxies of FeLoBAL quasars at z ∼ 0.9
are not dominated by recent major mergers
~ C. Villforth et al
viewtopic.php?t=39684
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Moonetesimals likely form relatively quickly

Post by bystander » Tue Aug 13, 2019 5:51 pm

Moonetesimals likely form relatively quickly
astrobites | Daily Paper Summaries | 2019 Aug 08
Samuel Factor wrote:
Disks of gas and dust around young stars are fairly common; they are the birthplaces of planetary systems, hence the term protoplanetary disk. In the past few years, astronomers have used the Atacama Large Millimeter/Submillimeter Array (ALMA) to image these circumstellar disks and even catch planets forming within them. But the giant planets in our solar system also have systems of moons. How do they form? Most likely in a similar process by which the planets themselves formed, though in a circumplanetary disk (or protolunar) rather than a circumstellar disk (or protoplanetary). Today’s paper combines new and old observations of young giant planets that looked for, but failed to detect, these circumplanetary disks in order to constrain the timescale of moon formation. ...

Upper limits on protolunar disc masses using ALMA
observations of directly imaged exoplanets
~ Sebastián Pérez et al
viewtopic.php?t=39492#p293669
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A Proposed Moon Formation Theory: The Multiple-Impact Hypothesis

Post by bystander » Tue Aug 13, 2019 6:26 pm

A Proposed Moon Formation Theory: The Multiple-Impact Hypothesis
astrobites | Daily Paper Summaries | 2019 Aug 12
Jacob Azoulay wrote:
It’s been with us since before humans laid foot on Earth. Any person you have ever known or heard of has seen it shine bright in the night sky. Yet, researchers can only speculate about its creation.

The Moon is estimated to have formed 4.53 billion years ago, when a Mars-sized celestial body collided with Earth, spewing out debris that eventually clumped together. But what if this “giant-impact hypothesis” is not, in fact, how the Moon formed? Luckily, by using computer simulations, Robert I. Citron, Hagai B. Perets, and Oded Aharonson — the authors of today’s paper — can help us better understand our Moon’s origins. ...

The Role of Multiple Giant Impacts in the Formation of the Earth–Moon System ~ Robert I. Citron, Hagai B. Perets, Oded Aharonson
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When stretching stars with black holes gets unstable

Post by bystander » Tue Aug 13, 2019 6:40 pm

When stretching stars with black holes gets unstable
astrobites | Daily Paper Summaries | 2019 Aug 13
Elen Golightly wrote:
When a star wanders too close to a supermassive black hole at the centre of a galaxy, it can get stretched and pulled apart in what astronomers refer to as a ‘tidal disruption event’ or ‘TDE’. For this to occur the star must pass within tidal radius, the distance at which the tidal force from the black hole can overcome the self-gravity that keeps the star intact and spherical. Passing stars are not always disrupted however—those that plunge too deep within the tidal radius may be swallowed whole, while others may only be partially disrupted or miss the tidal field altogether, avoiding disruption completely.

A star that finds itself within the tidal radius begins to stretch into a stream, getting longer as it continues its orbit around the black hole. Approximately half of the elongated stream of stellar debris is then gravitationally bound to the black hole, while the other half remains unbound and escapes out into the galaxy at high velocities. The bound debris begins to fall back towards the black hole and forms an accretion disc that feeds it (see Figure 1). This accretion process can power a highly luminous and detectable flare from the disc.

The authors of this paper have modelled these TDEs computationally and were the first to simulate the full evolution of the events with realistic parameters. They simulated these events using PHANTOM, a 3D hydrodynamical code. Their system used a solar mass (1M) star, modelled as an adiabatic sphere of gas made up of one million particles, and a 106M black hole (a black hole mass between 105−108M is a reasonable choice). The authors started the star outside of the black hole’s tidal influence and ran the simulation until 90% of the disrupted material had returned to the disc, which was about 10 years after disruption started. ...

Variability in Tidal Disruption Events: Gravitationally Unstable Streams ~ Eric R. Coughlin, Chris Nixon
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The Imprint of an Invisible Giant

Post by bystander » Fri Aug 16, 2019 11:28 pm

The Imprint of an Invisible Giant
astrobites | Daily Paper Summaries | 2019 Aug 14
Spencer Wallace wrote:
Without Jupiter, the solar system might be a vastly different place. Our largest planetary companion is thought to be responsible for everything from clearing out planet-building material near the sun to throwing Neptune and Uranus to the outer solar system to delivering water to the Earth. Given the crucial role that this behemoth played in shaping our solar system, a natural question to ask is how important gas giants are for building planets around other stars.

Unfortunately, we can’t just look at stars with terrestrial planets and then determine which of those also have something resembling Jupiter. With the exception of a rather exotic and unexpected subclass of close-in giant planets known as hot Jupiters, most gas giants take far too long to orbit their host stars to be easily detectable. To illustrate this point, consider how an observer from outside the solar system would detect Jupiter. There are two ways to do this. The first involves gradually watching the sun redshift and blueshift as Jupiter’s gravity tugs on it over the course of an orbit. Alternatively, if you are extremely lucky, Jupiter might pass between you and the sun, producing a momentary dimming of the sun’s light. Both of these methods require you to potentially wait for Jupiter to complete nearly an entire orbit around the sun. This would take 12 years! Unless you’re continuously watching the sun for over a decade, you probably wouldn’t ever detect this giant.

Although extrasolar terrestrial planets are found using these same methods, the problem mentioned above is not quite so severe because these types of worlds tend to lie close to their star. This means that they complete an orbit fairly quickly and so you don’t have to wait long for them to alter the star’s light. For this reason, any large-scale exoplanet survey such as Kepler or TESS will tend to detect mostly close-in planets, while missing most of the longer period ones. This brings us to the goal of today’s paper, which is to determine how the presence of a gas giant, many of which lie on wide, long period orbits, affects the distribution of inner terrestrial worlds during the planet formation process. With a better understanding of this connection, it might be possible to use the measured properties of the more easily detectable terrestrial planets to figure out where the gas giants actually are (or aren’t). ...

Giant Planet Effects on Terrestrial Planet Formation and System Architecture ~ Anna C. Childs et al
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A Historical Nova and the First Radioactive Molecule

Post by bystander » Fri Aug 16, 2019 11:44 pm

A Historical Nova and the First Radioactive Molecule in Space
astrobites | Daily Paper Summaries | 2019 Aug 15
Charles Law wrote:
Nearly 350 years ago, two Sun-like stars collided in a spectacular explosion and formed a new type of star. The source, known as CK Vulpeculae (or more simply, CK Vul), was first seen in 1670 when observers reported the appearance of a new bright, red star. Initially visible with the naked eye, Nova CK Vul quickly faded and astronomers now need large telescopes to study the remnants left behind: a dim central star and surrounding hot, glowing gas (Figure 1). This gaseous debris, cast out into space during the violent stellar merger that created CK Vul, affords astronomers a unique opportunity to study the dense inner layers of a star, where heavy elements and radioactive isotopes are produced. In today’s astrobite, we take a look at the detection of a radioactive version of aluminum in this gaseous debris around CK Vul, which represents the first definitive detection of an unstable radioactive molecule outside of our Solar System. ...

Astronomical Detection of a Radioactive Molecule 26AlF in a Remnant of an Ancient Explosion - Tomasz Kamiński et al
viewtopic.php?t=38561
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Subgiant in the Spotlight

Post by bystander » Fri Aug 16, 2019 11:57 pm

Subgiant in the Spotlight: Characterising a New Benchmark Star
astrobites | Daily Paper Summaries | 2019 Aug 16
Oliver Hall wrote:
We are currently living in the era of big data astronomy; and especially so in the field of asteroseismology – the study of stellar properties through measuring their pulsations. Between the recent Kepler, K2 and TESS missions, as well as supplementary data from Gaia, ensemble studies are often the norm, studying population effects of many stars in tandem. However in this era of large data sets it is important to continue to calibrate our methods, and this is where detailed studies of single, ‘benchmark’ stars are still very important.

The authors of today’s paper set out to study such a benchmark star, HR 7322 in great detail, using multiple complementary methods, with the intention of using the measured parameters of this star to identify problems with asteroseismic theory. The star they picked was a subgiant — a star that has burned through all the hydrogen in its core and is on its way to become a red giant. Recent results have shown a disagreement between radii of subgiant stars calculated from Gaia mission data and those calculated using asteroseismology. The authors study this subgiant to great precision in order to identify the source of this disagreement. ...

The Subgiant HR 7322 as an Asteroseismic Benchmark Star ~ Amalie Stokholm et al
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Guide to finding planets around ultracool dwarfs

Post by bystander » Thu Aug 22, 2019 3:32 pm

A step by step guide to finding planets around ultracool dwarfs
astrobites | Daily Paper Summaries | 2019 Aug 19
Emma Foxell wrote:
Over the last 20 or so years, over 3000 exoplanets have been detected, most around stars like our Sun. Recently, many exoplanet hunters have been focusing on M dwarfs, as Earth-sized planets at habitable temperatures are easier to detect. But could we go even cooler? L and T dwarfs (LTs) are a mixed bunch. While all have radii about 1 RJup and temperatures 500-2200 K, their masses vary wildly from stellar main sequence (0.08MSun) through brown dwarfs to planetary mass objects. Earth around a L0 star would produce transits blocking 1% of their host star’s light and receive the same amount of flux orbiting in just 1.65 days, making the habitable zone even more accessible. The habitable zone may actually be further out due to tidal heating, as happens to Jupiter’s moon Io.

But can these planets exist? Theory and observations suggest so. Circumstellar disks, from which planets form, have been observed around M-type brown dwarfs and 3 MJup objects have been detected around brown dwarfs at large separation by direct imaging. While slightly higher mass, TRAPPIST-1 is the prime example of an ultracool M8 dwarf with 7 Earth-sized planets. Theory suggests that brown dwarfs may be able to form planets up to 5 Earth masses, and considering planets are very common around M dwarfs, perhaps it is reasonable to expect planets around LTs.

Discovering planets around LTs would inform our general theory on satellite formation and help us understand how planet occurrence rates vary compared to higher mass stars and within the wide range of LTs. Astronomers are also interested whether planets around LTs are predominately terrestrial. So what is the best way to search for them? ...

Design Considerations for a Ground-Based Search for Transiting
Planets around L and T Dwarfs
~ Patrick Tamburo, Philip S. Muirhead
  • arXiv.org > astro-ph > arXiv:1908.03593 > 09 Aug 2019 (v1), 21 Aug 2019 (v2)
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UV Won’t Stop Exoplanets from Becoming Habitable

Post by bystander » Thu Aug 22, 2019 3:44 pm

Let’s Not Make Assumptions: UV Radiation
Won’t Stop Exoplanets from Becoming Habitable

astrobites | Daily Paper Summaries | 2019 Aug 20
Yesenia Ruano wrote:
Astrophysicists have been investigating the habitability of exoplanets—planets that orbit around stars other than the Sun—as well as the factors which contribute to a planet’s habitability, like UV radiation.

What’s UV radiation? It’s the part of the electromagnetic spectrum that we fight off while using sunblock at the beach. UV radiation emitted from stars is harmful to the surfaces of planets, including the Earth’s. Radiation of this kind can cause the erosion of a planet’s atmosphere and hinder the formation of organic life, making the planet less habitable. As organic molecules absorb UV radiation, the efficiency of nucleic acids (a substance that makes up all of our DNA) can be damaged. By now, you might think that there is no way in which exoplanets near a radiating star can sustain life, but surprisingly they still have a chance.

In this paper, the authors argue that exoplanets that are exposed to high levels of UV radiation can still harbor life. They use M star systems—systems that consist of exoplanets orbiting a dim long-lasting star called a red dwarf—to test this. ...

Lessons from early Earth: UV surface radiation should not limit the
habitability of active M star systems
~ Jack T. O'Malley-James, Lisa Kaltenegger
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Why are Jupiter and Saturn Spinning so Slowly??

Post by bystander » Thu Aug 22, 2019 4:00 pm

Why are Jupiter and Saturn Spinning so Slowly??
astrobites | Daily Paper Summaries | 2019 Aug 21
Jenny Calahan wrote:
The rotation periods of Jupiter and Saturn are 9.93 hours and 10.7 hours, respectively. Now, compared to our tiny Earth that lazes around on a 24-hour rotational period, you might think, “wow, those are some zoomy-bois.” However, our best theories of planet formation tell us that, based on how massive they were when they formed, they should really be doin’ a faster spin. ...

Today’s paper attempts to lay the groundwork for solving this angular momentum problem in Jovian-planet formation using magnetohydrodynamics. Big (scary) word, yes, but put more simply, this paper creates a semi-analytic model of a newly forming Jovian planet with a strong magnetic field, and explores how this might slow the planet down. ...

On the Terminal Rotation Rates of Giant Planets ~ Konstantin Batygin
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Is the Fault in their Stars?

Post by bystander » Thu Aug 22, 2019 4:10 pm

Is the Fault in their Stars?
astrobites | Daily Paper Summaries | 2019 Aug 22
Keir Birchall wrote:
At the centre of almost every massive galaxy lies a supermassive black hole (SMBH) into which gas and dust occasionally fall. When this happens, the central region is bathed in huge amounts of light and an active galactic nucleus (AGN) is born. They are a diverse phenomenon, emitting light in different wavelengths, with different intensities and for different lengths of time. Such variation in observed properties makes AGN very difficult to study. What factors or processes can trigger an AGN? What role does the host galaxy play? And, more specifically, how does star formation rate affect likelihood of triggering?

Previous observations of AGN have shown that galaxies with similar properties (stellar mass, star formation rate, etc.) are observed to have a wide range of luminosities. Thus, trying to understand the underlying connections between AGN activity and the properties of its host galaxy using only the observed AGN luminosity is extremely challenging. For example, two galaxies with the same mass could host AGN with hugely different observed luminosities, from which you could then conclude that the host galaxy mass played very little in role in triggering AGN. However, this approach fails to take into account that the varying AGN luminosities could be explained by the central SMBH accreting material at different rates. Today’s paper attempts to take into account these varying rates of accretion of material, and connect a galaxy’s star formation rate (SFR) to the likelihood that it will host an AGN. ...

X-rays across the galaxy population - III. The incidence of AGN as a
function of star formation rate
~ James Aird, Alison L. Coil, Antonis Georgakakis
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Fluorescent Worlds: Searching for Life’s Glow

Post by bystander » Fri Aug 30, 2019 5:55 pm

Fluorescent Worlds: Searching for Life’s Glow
astrobites | Daily Paper Summaries | 2019 Aug 27
Jamie Wilson wrote:
Are we alone? It is perhaps one of the most profound questions we humans have ever thought to ask ourselves. An even more astonishing aspect of this question is that we may well be living in the first period of history where it might be possible to obtain the answer. Recent research has shown that our galaxy appears to be teeming with new worlds to discover and a growing number of the already known worlds orbit within their host star’s habitable zone, the region where water can exist in liquid form on a planet’s surface. The nearest potentially habitable planet orbits the star Proxima Centauri at just over four light years away. However, whilst the presence of water might indicate that a planet could be habitable, it’s not the same as saying that a planet is inhabited. Since we have little hope of visiting these new worlds in the near future, the best we can do is search remotely for atmospheric biosignatures – chemicals present in a planet’s atmosphere that suggest the existence of past or present life, for example oxygen, which exists in large proportions in the Earth’s atmosphere because it is continually produced by vegetation. Now a team of researchers, led by Jack O’Malley-James at Cornell’s Carl Sagan Institute, have discovered a previously unknown way to search for life in the Universe – observing the protective glow of biofluorescent organisms triggered by ultraviolet flares from red dwarf stars. ...

Biofluorescent Worlds – II. Biological Fluorescence Induced by Stellar UV
Flares, a New Temporal Biosignature
~ Jack T. O'Malley-James, Lisa Kaltenegger
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Looking at Stars but Seeing the Kuiper Belt

Post by bystander » Fri Aug 30, 2019 6:07 pm

Looking at Stars but Seeing the Kuiper Belt
astrobites | Daily Paper Summaries | 2019 Aug 29
Will Saunders wrote:
Detecting small Kuiper Belt Objects (KBOs) is challenging even with state-of-the-art telescopes and massive collaboration surveys. A tiny dot on a CCD could be a KBO, cosmic ray, asteroid, or anything else. Distinguishing a KBO from the alternatives requires many nights of successive imaging of the same objects. And astronomical instruments are expensive, costing upwards of tens of millions of dollars.

However, the paper in this Astrobite details how two amateur telescopes costing only $32,000 discovered the first KBO roughly 2 km in diameter. The goal of the work is not to directly compete with massive astronomical surveys, but rather to demonstrate the groundbreaking research can be done at significantly lower cost. ...

A kilometre-sized Kuiper belt object discovered by stellar occultation using amateur telescopes ~ K. Arimatsu et al
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Explaining Ancient Stellar Populations

Post by bystander » Fri Aug 30, 2019 6:24 pm

Explaining Ancient Stellar Populations
astrobites | Daily Paper Summaries | 2019 Aug 30
Caitlin Doughty wrote:
Of the multitude of galaxies in the universe, none are so close to us and so numerous as the dwarf galaxies. With 59 little galaxies whirling around the Milky Way, one might think that astronomers would understand them perfectly by now; they are, after all, relatively accessible. However, mysteries abound surrounding their origins and evolutionary history, and they have introduced all kinds of problems into our understanding of astronomy. There doesn’t appear to be enough of them, occasionally they appear to be missing their dark matter and, most pertinent to today’s paper (although perhaps less exciting-sounding), some of them have peculiarly old stellar populations. A few of these galaxies contain stars that, the youngest of which appear to have formed when the universe was less than one billion years old, a mere 7% of its current age. What could cause these particular dwarf galaxies to host only incredibly ancient stars?

One explanation that has been put forward is that an event from early in the universe’s history, called reionization, could have played a hand in this. During this time period, the amount of radiation coming from stars and galaxies ramped up and ionized almost all of the hydrogen in the universe, deconstructing hydrogen atoms into their component nuclei and electrons (this is where the name “reionization” comes from). But even as this radiation was splitting apart hydrogen atoms, it was simultaneously heating up all of the gaseous elements, including the hydrogen, as well as helium and the other less abundant elements. It is theorized that this heating effect on the gas may have somehow either (1) prevented dwarf galaxies from collecting new gas or (2) caused them to lose what gas they already had, as it photoevaporated away. It is also believed to be more significant for smaller galaxies.

The investigators behind today’s paper have used cosmological simulations—which model dark matter and baryonic matter (i.e. the kind that both stars and your coffee cup are made of) from very early times to form galaxies, the cosmic web, and any other large-scale object in the universe that you can think of—to examine how including a simulated reionization event may have affected dwarf galaxies’ ability to accrete and retain the gas necessary for forming stars. These simulations in particular, called SPHINX, incorporate radiative transfer, allowing the researchers to create a more realistic representation of reionization than a simulation that excludes these calculations. ...

How to Quench a Dwarf Galaxy: The Impact of Inhomogeneous
Reionization on Dwarf Galaxies and Cosmic Filaments
~ Harley Katz et al
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With Age Comes Wisdom

Post by bystander » Wed Sep 04, 2019 5:19 pm

With Age Comes Wisdom
astrobites | Daily Paper Summaries | 2019 Sep 02
Jessica Roberts wrote:
The age of something seems like such a simple, easy to obtain, and fundamental property in science. But it is a critical measurement for helping us better understand the history and evolution of most everything in the Universe. For instance, you might want to know how old a tree is so you can trace back its history and understand why it grew a certain way. We know that our Solar System is about 4.5 billion years (Gyrs) old. From this knowledge we can look back in history and explain how the Sun and its planets must have evolved into what we see today. We believe the Universe is around 13.7 billion years old, and based on the ages of other galaxies, we conclude that galaxies must have formed shortly after the Big Bang (in cosmological terms). But determining the age of something in astronomy is extremely difficult. Stars in our own galaxy, the Milky Way, pose an interesting challenge. It might surprise you that we know the age of the Universe more precisely than we do most stars nearby. Why this discrepancy? You would think that stars closer to us should be easier to date than the entire Universe! However to know the age of a star, we need to know how bright or luminous it actually is. With this information, stellar evolution models can trace back the star’s origin and age. Sounds easy enough, but in order to know how bright a star truly is we need to know how far away the star is. After all, a flashlight can outshine a spotlight if we move close enough to it. The same principle applies to stars. However, accurate distance measurements to these stars have for decades been difficult to obtain. Then Gaia came along and provided precise distance measurements to millions of stars in the Milky Way. Equipped with this new powerful information, the authors of today’s paper determine the ages of many of these stars and begin to piece together the most detailed history of our Milky Way. ...

Uncovering the Birth of the Milky Way through Accurate Stellar Ages with Gaia ~ Carme Gallart et al
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Cloudy with a chance of wind

Post by bystander » Tue Sep 10, 2019 3:58 pm

Cloudy with a chance of wind
astrobites | Daily Paper Summaries | 2019 Sep 04
Stephanie Hamilton wrote:
Jupiter’s horizontal banding is arguably one of the most iconic features in our Solar System, alongside Saturn’s rings. But did you know that Saturn also has similar horizontal banding? The two largest planets in our Solar System appear quite different, but they also share similarities. Today’s paper looks at data from two different spacecraft, Juno and Cassini, to compare and contrast the winds of both planets. ...

Comparison of the deep atmospheric dynamics of Jupiter and Saturn
in light of the Juno and Cassini gravity measurements
~ Yohai Kaspi et al
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What do galaxy clusters and Russian dolls have in common?

Post by bystander » Tue Sep 10, 2019 4:12 pm

What do galaxy clusters and Russian dolls have in common?
astrobites | Daily Paper Summaries | 2019 Sep 05
Sunayana Bhargava wrote:
Astronomers have observed that clusters of galaxies have a peculiar property: they all look roughly the same regardless of their mass or distance. Unlike individual galaxies, which are distinguishable by their distinct shapes or “morphologies,” galaxy clusters are intriguingly similar looking.

This peculiarity of galaxy clusters is referred to as self-similarity. When we say galaxy clusters are self-similar, we mean they have an identical appearance at different masses or distances from us. Strong self-similarity states that a smaller cluster is an identical, scaled version of a massive one.

Weak self-similarity is a bit subtler. When we look at distant clusters, we are looking back in time at a younger universe which had a higher overall density. However, if we consider the changing density in the universe, a distant cluster is identical to a nearby cluster of the same mass. ...

In a recent paper, a team of authors showed that 25 massive galaxy clusters generated from a “dark-matter only” simulation are astonishingly self-similar at redshifts (z) greater than 1. While this is an interesting result, the authors of today’s paper take self-similarity to task with a different approach to measuring the evolution of cluster halos. ...

The Three Hundred Project: The evolution of galaxy cluster density profiles ~ Robert Mostoghiu et al
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Dust Accretion & Double Suns

Post by bystander » Tue Sep 10, 2019 4:25 pm

Dust Accretion & Double Suns
astrobites | Daily Paper Summaries | 2019 Sep 09
Lauren Sgro wrote:
Imagine walking out your front door tomorrow morning and gazing up at the sky. What if, instead being lit up by the light of one sun, your world was illuminated by two suns.

This isn’t as crazy as it sounds. Astronomers have found plenty of planets whose potential alien life forms would witness such a double sunrise. However, there are many unanswered questions about these planets that form around binary stars, such as how they end up living so close to their host stars, just outside the dynamical stability limit (the point past which planets/satellites can survive in a stable orbit).

Today’s authors seek to find out if these planets are more likely to form where they are observed (in situ formation), or if they form farther out and migrate inward (ex situ formation). Previous studies have shown that the dynamics of the circumbinary disk may have a lot to do with which of these two formation options is most viable. Using Smoothed Particle Hydrodynamics (SPH), the authors model their binary systems with various eccentricities (a measure of how circular or extended an orbit is), mass ratios (q = the ratio of the primary mass to the secondary mass), and dust properties to determine how dust and gas accrete onto the companion stars and their individual (circumstellar) or shared (circumbinary) disks. Their results shed light on where planets form most easily in binary systems, and whether or not in situ formation can actually take place where astronomers have observed such planets. ...

Dust accretion in binary systems: Implications for planets and transition discs ~ Yayaati Chachan et al
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