astrobites: Daily Paper Summaries 2020

Find out the latest thinking about our universe.
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astrobites: Daily Paper Summaries 2020

Post by bystander » Mon Jan 06, 2020 8:18 pm

astrobites: Daily Paper Summaries

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy since 2010. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.

<< astrobites 2019
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Missing the Fireworks in Massive Dusty Galaxies

Post by bystander » Mon Jan 06, 2020 8:32 pm

Missing the Fireworks in Massive Dusty Galaxies
astrobites | Daily Paper Summaries | 2020 Jan 01
John Weaver wrote:
The results of the first extragalactic surveys undertaken in the submillimeter wavelength regime in the early 2000s were dramatic and astonishing. Images acquired from staring blindly at the sky with the James Clerk Maxwell Telescope demonstrated that there exists a population of galaxies that shine with phenomenal luminosity at these long wavelengths.

After much debate, it was hypothesized that the reason for these “submillimeter galaxies” is massive reservoirs of dust. Generally, infrared emission is due to absorption and re-emission of light from star-formation. The amount of dust seen in these galaxies implies star-formation rates in excess of 1000 M*/yr! Their extreme dust emission even allows us to detect submillimeter galaxies in the early universe.

Fast-forward to 2020. Multitudes of focused observations of these submillimeter galaxies in other wavelength regimes (x-ray, ultraviolet, optical, and near-infrared) have bolstered our standing hypothesis of a population of dust-obscured, infrared-bright, and extremely star-forming galaxies. We have dubbed them “Dusty Star-Forming Galaxies”, or DSFGs. However, their existence continues to challenge traditional galaxy formation models and the cause of their immense dust content is unknown. Despite these open questions, they provide a valuable lens through which we can study the first two billion years of the universe.

Today’s Astrobite proposes that like viewing a fireworks display through the smoke, we might be missing some of the action. ...

The Star Formation Rate of Massive Dusty Galaxies
at Early Cosmic Times
~ Zacharias E. Escalante, Shardha Jogee, Sydney Sherman
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Never underestimate a droid: deep learning for turbulence

Post by bystander » Mon Jan 06, 2020 8:47 pm

Never underestimate a droid: deep learning for turbulence
astrobites | Daily Paper Summaries | 2020 Jan 02
Sanjana Curtis wrote:
Turbulence is a fact of life and of physics. You can see it in action when you turn on a faucet, pour cream into your coffee, or simply look up at the clouds. Most of us have an intuitive understanding of what turbulence means: random, chaotic fluid motion that leads to mixing. However, it’s arguably one of the most important unsolved problems of classical physics. A complete description of turbulence is much sought after and accurately simulating turbulence, especially when magnetic fields are involved, is a notoriously difficult problem. Today’s paper explores the use of deep learning techniques to capture the physics of magnetized turbulence in astrophysical simulations.

The onset of turbulence is linked with the Reynolds number of the fluid flow, which is the ratio of inertial forces (associated with the fluid’s momentum) to the fluid viscosity. Viscosity inhibits turbulence. When the Reynolds number is low, viscous forces dominate and the flow is laminar, or smooth. The particles in a laminar flow move more or less in the same direction with the same speed. When the Reynolds number is high, inertial forces dominate and produce eddies, vortices, and other instabilities. This is the turbulent regime, where fluid particles move in different directions with different speeds. ...

Artificial neural network subgrid models of 2-D compressible
magnetohydrodynamic turbulence
~ Shawn G. Rosofsky, E. A. Huerta
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Oh, the Places You—Came From?

Post by bystander » Mon Jan 06, 2020 8:59 pm

Oh, the Places You—Came From?
astrobites | Daily Paper Summaries | 2020 Jan 03
Tarini Konchady wrote:
To our knowledge, 2I/Borisov is the second interstellar object to pass through our solar system (its discovery is highlighted in this Astrobite). Unlike the first visitor, 1I/‘Oumuamua, 2I/Borisov is very distinctly a comet. It was discovered by amateur astronomer Gennady Borisov (who had discovered seven comets prior to this one) at the end of August 2019.

The tell-tale of a passing interstellar object is its extreme orbit — it will likely never swing by the Sun again. The nature of 2I/Borisov became evident within a few weeks following its discovery, and astronomers were able to pick it out in older observations going all the way back to December 2018.

In the paper discussed in this Astrobite, astronomers try to determine which star system 2I/Borisov was ejected from, using archival observations and the second release of Gaia data (Gaia DR2) to retrace its journey. ...

A search for the origin of the interstellar comet 2I/Borisov ~ Coryn A.L. Bailer-Jones et al
viewtopic.php?t=39796
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TESS’s First Earth-Like Planet Found in Interesting Trio

Post by bystander » Sat Jan 11, 2020 4:33 pm

The TESS Mission’s First Earth-Like Planet Found in an Interesting Trio
astrobites | Daily Paper Summaries | 2020 Jan 09
Haley Wahl wrote:
Since the discovery of the first planet outside of our solar system in 1992, the field of exoplanets has been booming with interesting finds. From the diamond planet orbiting a neutron star to the giant pink planet orbiting a star in the constellation of Virgo, telescopes all over the world have been racing to find the latest gem. Of particular interest are Earth-like planets. A team led by a graduate student at the University of Chicago report the first Earth-sized planet in the habitable zone found by the TESS mission, and its surroundings were quite a surprise to astronomers. ...

The First Habitable Zone Earth-sized Planet from TESS.
I: Validation of the TOI-700 System
~ Emily A. Gilbert et al
viewtopic.php?p=298584#p298584
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Re: TESS’s First Earth-Like Planet Found in Interesting Trio

Post by Ann » Sun Jan 12, 2020 9:46 am

bystander wrote:
Sat Jan 11, 2020 4:33 pm
The TESS Mission’s First Earth-Like Planet Found in an Interesting Trio
astrobites | Daily Paper Summaries | 2020 Jan 09
Haley Wahl wrote:
Since the discovery of the first planet outside of our solar system in 1992, the field of exoplanets has been booming with interesting finds. From the diamond planet orbiting a neutron star to the giant pink planet orbiting a star in the constellation of Virgo, telescopes all over the world have been racing to find the latest gem. Of particular interest are Earth-like planets. A team led by a graduate student at the University of Chicago report the first Earth-sized planet in the habitable zone found by the TESS mission, and its surroundings were quite a surprise to astronomers. ...

The First Habitable Zone Earth-sized Planet from TESS.
I: Validation of the TOI-700 System
~ Emily A. Gilbert et al
viewtopic.php?p=298584#p298584
I thank Haley Wahl for reporting on the properties of the host star. With an effective temperature of 3480 K, and a mass and radius that is about half that of our Sun, TOI-700 is likely an M0V or an M1V star. That clearly puts it in the higher temperature range of M-type stars, and my guess is that it could well be more stable than some of the cooler, flaring M-type stars. Or, in other words, TOI-700 could well be a little more friendly as a host for potential life-bearing planets than many other M-type stars.

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Hot planets hiding under a shroud of dust and gas

Post by bystander » Fri Jan 17, 2020 5:25 pm

Hot planets hiding under a shroud of dust and gas
astrobites | Daily Paper Summaries | 2020 Jan 12
Vatsal Panwar wrote:
Giant exoplanets in tight orbits around their host stars were one of the first ones to be discovered using the radial velocity (RV) technique until the Kepler Space telescope found a flurry of short period low mass planets using the transit technique. While transit photometry tells you about the radius of the planet, RV measurements can be used to determine their mass. Both mass and radius measurements of planets are important for understanding the bulk properties of the exoplanets and their atmosphere. Using RVs for conducting a search for low mass short-period planets and measuring their mass can be rather challenging though, even more so if the host star is faint. However, there could already be a smoking gun for the presence of these planets! Close-in low mass exoplanets suffer ablation of dust and gas from their surface and atmosphere due to high levels of stellar irradiation and tidal stretching from their close-in orbits and this can have a noticeable effect on the spectra of their host star on which can provide some hints of their presence. Authors of today’s paper test this hypothesis in their Dispersed Matter Planet Project (DMPP) and present a very effective way of conducting a search for planets in compact configuration around nearby bright stars. ...

Dispersed Matter Planet Project Discoveries of Ablating
Planets Orbiting Nearby Bright Stars
~ Carole A. Haswell et al
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Iterative Emulation is the Sincerest Form of Parameter Estimation

Post by bystander » Fri Jan 17, 2020 5:33 pm

Iterative Emulation is the Sincerest Form of Parameter Estimation
astrobites | Daily Paper Summaries | 2020 Jan 13
Kate Storey-Fisher wrote:
Say you want to make the perfect soufflé. You know how fluffy it should be, but you don’t know how many eggs and sticks of butter you need. You could try a whole bunch of different combinations, but this would take forever (and waste a lot of ingredients on bad soufflés). Your sous-chef decides to help you out: you tell them about some of your previous attempts and how the souffle turned out, and they build you a predictor. You can now tell the predictor any amount of eggs and butter, and it estimates how fluffy the soufflé will be!

This is the principle behind an emulator, which has become popular for estimating cosmological quantities. Today’s paper presents a new way of using emulators iteratively to perform this estimation even faster. This will get fairly technical, so put your apron on and prepare to get your hands dirty. ...

Cosmological parameter estimation via iterative emulation of likelihoods ~ Marcos Pellejero-Ibañez et al
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More metals, more planets?

Post by bystander » Fri Jan 17, 2020 5:41 pm

More metals, more planets?
astrobites | Daily Paper Summaries | 2020 Jan 14
Spencer Wallace wrote:
A complete, start-to-finish picture of planet formation process continues to elude astronomers. We know that dust grains around young stars collide to form pebble (roughly centimeter) sized bodies. This stage has been observationally confirmed by examining the infrared and radio emission from protoplanetary disks. Beyond this stage, however, the details get less clear. Simple theoretical models predict that bodies larger than pebbles should quickly spiral in and fall onto the host star, due to the aerodynamic drag from the surrounding gas. Even if growing planet-building material can somehow avert this fate, laboratory experiments suggest that it is extremely difficult for any larger bodies to grow further by sticking together. To further complicate matters, bodies larger than pebbles do not emit or reflect very much light, making later stages of planet formation nearly impossible to directly observe.

Nevertheless, there is much that can be learned about this complex process by matching observed properties of planets with their host star. One clue that narrows down the possible formation pathways is the fact that gas giant planets are more common around metal-rich stars. This suggests that these planets form by first growing a metal-rich core, which accumulates a gaseous envelope after passing a certain threshold mass. A more metal-rich star generally implies that the protoplanetary disk was also metal-rich. This should therefore allow the core of the planet to form more quickly and efficiently.

Although this trend is broadly true, the details introduce further complications. In particular, the giant planets in the solar system are slightly more metal-rich than the Sun. This suggests that planet-building material might grow in locally concentrated pockets throughout the protoplanetary disk. This explanation conveniently solves some of the problems with the radial drift and growth barriers mentioned above. To shed more light on this process, the authors of today’s paper examine the relation between the metallicity of a number of gas giant exoplanets and their host stars. In doing so, they hope to uncover some additional clues into how these worlds came to be and how these growth barriers are overcome. ...
Do Metal-rich Stars Make Metal-rich Planets? New Insights on Giant
Planet Formation from Host Star Abundances
~ Johanna K. Teske et al
viewtopic.php?t=40086
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Uncovering the Invisible: Imaging the Sun with Helioseismology

Post by bystander » Fri Jan 17, 2020 5:53 pm

Uncovering the Invisible: Imaging the Sun with Helioseismology
astrobites | Daily Paper Summaries | 2020 Jan 15
Ellis Avallone wrote:
The Sun is the most well-observed star in the Universe. But even with this abundance of observations, part of the solar surface still remains mysterious.

The side of the Sun pointing away from us, the far side, remains invisible to observers at Earth until it rotates into view (see Figure 1). However, there is one way we can image the far side of the Sun indirectly. Helioseismology utilizes acoustic waves on the solar surface to study the solar interior. However, these waves also carry information about the far side of the Sun to the near side. Using helioseismology, solar astronomers can create global maps of the solar surface without directly imaging the entire star.

Solar astronomers use this technique to observe the ever-evolving solar magnetic field. Traditional methods involve creating a synoptic map, which show the solar surface at several points in time. While these can provide a tool to understand the global solar magnetic field, synoptic maps fail to capture critical information about how the global field evolves. By using helioseismology, we can create global maps for a single point in time. This is an incredibly powerful tool for modeling the global solar field from the Sun to the edge of the solar system and for predicting space weather events.

The authors of today’s paper focus on imaging solar active regions, which are strong concentrations of magnetic field in the solar surface. Active regions are a major source of space weather events that can negatively affect Earth and understanding them is essential to accurately predicting space weather. If an active region forms on the far side of the Sun, space weather forecasters want to know when it forms and have some idea of its magnetic structure. ...

Imaging the Sun's Far-side Active Regions by Applying Multiple
Measurement Schemes on Multiskip Acoustic Waves
~ Junwei Zhao et al
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How to Classify Your Favorite Ring-Satellite System

Post by bystander » Fri Jan 17, 2020 6:07 pm

Boomerang, Slingshot, or Torque-Dependent?
How to Classify Your Favorite Ring-Satellite System

astrobites | Daily Paper Summaries | 2020 Jan 16
Will Saunders wrote:
The number of known ring-bearing objects in the solar system continues to expand. Once limited to Saturn, the list added all four giant planets in the 1970s and 80s. More recently, stellar occultation observations have found rings around minor planets Chariklo, Chiron, and Haumea.

Unlike moons, most ring systems are never alone. The existence of satellites and rings alongside one another creates complex dynamics that shape the course of evolution for both objects. Beyond that, there are outside influences, such as close encounters with scattered Kuiper Belt objects (which happened to Neptune) or giant impacts (which happened to Earth) that vastly increase the number of possible evolution tracks.

The authors of this paper designed a generalized model of ring and satellite co-evolution designed to be simple to comprehend and applicable to the solar system. ...

Three Dynamical Evolution Regimes for Coupled Ring-Satellite Systems and Implications for
the Formation of the Uranian Satellite Miranda
~ Andrew J. Hesselbrock, David A. Minton
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Titan’s icy alley: An elusive surface revealed

Post by bystander » Thu Jan 23, 2020 4:23 pm

Titan’s icy alley: An elusive surface revealed
astrobites | Daily Paper Summaries | 2020 Jan 20
Anthony Maue wrote:
Although Saturn’s largest moon, Titan, is expected to have an icy composition, unambiguous detection of H2O ice on its surface has been less than straightforward. Titan inspires great intrigue given its Earth-like landforms, including lakes, rivers, sand dunes, mountains, and possibly volcanoes. However, these features occur at frigid temperatures (~94 K) and have very different compositions than their terrestrial counterparts. Whereas Earth has water flowing over a silicate rock surface, Titan has liquid methane and ethane flowing over a surface that likely includes both ice and carbon-bearing organic compounds.

So where is the H2O? Based on Titan’s low density (1.88 g/cm3), it is thought to be made up of H2O around a wet, rocky core. In a popular model of its interior, Titan has differentiated, or organized into layers, such that the H2O layer includes an upper crust of “normal” H2O ice (like you have in your freezer) and a lower layer of totally weird, higher-density H2O ice (like you have in your ultra-pressurized freezer) with a liquid water ocean sandwiched between the two (see Figure 1). Titan is thus among the many outer solar system moons considered “ocean worlds.” Despite this likely water-rich composition, innovative methods have been necessary to definitively detect H2O ice on its surface via spectral measurements.

Understanding Titan’s surface has been a unique challenge for a few reasons. Titan is somewhat unusual compared to other icy worlds in that it bears an atmosphere more massive than even the Earth’s. Hydrocarbons like methane condense in this atmosphere and rain across the surface, transporting sediment and supplying lakes at the poles. In the upper atmosphere, methane is zapped by solar radiation and reassembled into complex organic molecules that can then “snow” upon the surface, potentially burying and obscuring water ice-rich materials. In addition to this complication, surface compositions have generally been difficult to identify since the thick atmosphere provides “windows” only at specific and narrow wavelength bands (see Figure 2). As a consequence, the prevalence of H2O ice and its relationship to diverse organic compositions has been difficult to assess. ...

A corridor of exposed ice-rich bedrock across Titan’s tropical region ~ Caitlin A. Griffith et al
viewtopic.php?t=39387
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A Super Runner in the Milky Way

Post by bystander » Thu Jan 23, 2020 4:38 pm

A Super Runner in the Milky Way
astrobites | Daily Paper Summaries | 2020 Jan 21
Wei Vivyan Yan wrote:
Look at that unique runner! Just like our Sun, most stars spend their entire lives in the Milky Way (MW). They follow certain trajectories orbiting the central supermassive blackhole (SMBH) in the galactic center. Coincidentally, humans are not the only ones with dreams of leaving home to see the world — so does a whole group of young and massive (O- and B-type) stars! These travelers are called hypervelocity stars (HVSs, Figure 1). Their velocities are on the order of 1000 km/s! Many HVSs are rebelliously running away from the gravitational influence of the SMBH towards the outside world, living out their short but extraordinary lives.

One particular runner, LAMOST-HVS1, stands out with its “super speed” as determined by its spectra. LAMOST-HVS1 is a subgiant star with a mass of 8.3 solar-masses and is currently running away at a total speed of 553 km/s, five times higher than the fastest rocket (NASA’s Juno spacecraft)! In today’s paper, the authors used Gaia data (Gaia Collaboration et al. 2018) to explore the origin of this special runaway star’s “super speed”. ...

Origin of a Massive Hyper-runaway Subgiant Star LAMOST-HVS1:
Implication from Gaia and Follow-up Spectroscopy
~ Kohei Hattori et al
viewtopic.php?t=39257
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Probing the Secrets of Gravity

Post by bystander » Thu Jan 23, 2020 4:52 pm

Probing the Secrets of Gravity
astrobites | Daily Paper Summaries | 2020 Jan 22
Mitchell Cavanagh wrote:
Humans have long dreamed of conquering the stars. Yet, even with the best of today’s technological capabilities, such an endeavour could take centuries. Since Newton’s incident with an apple, his theories of motion and universal gravitation have remained largely accepted save Einstein’s 1915 overhaul. Still, there remains observations that Newtonian dynamics cannot fully describe. One such observation is that of a galaxy’s rotation curve. We would expect a galaxy to rotate more slowly the further we move away from its center. It turns out that the rotation remains the same, and in some cases increases. The common solution to this problem is to invoke dark matter. This invisible matter accounts for the “missing mass” that enables galaxies to spin more than they otherwise should. MOdified Newtonian Dynamics (MOND) is an alternative theory of gravity that also attempts to account for these rotation curves. Instead of invoking dark matter, MOND alters the gravitational acceleration. This paper shows how this modified acceleration can alter the trajectory of interstellar probes. ...

Testing gravity with interstellar precursor missions ~ Indranil Banik, Pavel Kroupa
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Compton-Thick or Thin? Classifying NGC 5347

Post by bystander » Thu Jan 23, 2020 5:06 pm

Compton-Thick or Thin? Classifying NGC 5347
astrobites | Daily Paper Summaries | 2020 Jan 23
Gloria Fonseca Alvarez wrote:
Black holes are some of the most interesting and extreme objects in the universe. Fortunately, we think that almost every galaxy in the universe has a supermassive black hole (SMBH) at its center, giving many opportunities to study their environments. As matter falls towards a black hole, it forms an accretion disk — a flattened disk of gas and other debris — outside of its event horizon. This accretion disk is hot and emits radiation, even though we can’t see any light from the black hole itself. When SMBHs at the centers (or nuclei) of galaxies are actively accreting mass and emitting a huge amount of energy, we call them Active Galactic Nuclei (AGN). The different structural components of AGN, shown in Figure 1, emit radiation in a wide range of wavelengths, from low-energy radio to high-energy X-rays and gamma-rays. ...

NGC 5347 is an AGN that has been classified as both Compton-thick and Compton-thin by different methods, with an estimated hydrogen content differing by a factor of 10 between measurements. Today’s paper re-opens this question by analyzing new high-sensitivity observations of NGC 5347, as well as incorporating more physical models. This investigation could solidify the classification of NGC 5347, as well as help explain the “missing” fraction of CT AGN. ...

A Hard Look at NGC 5347: Revealing a Nearby Compton-thick AGN ~ E. S. Kammoun et al
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Searching for Black Holes in Globular Clusters with Pulsars

Post by bystander » Fri Jan 24, 2020 7:08 pm

Pulling on Pulsars: Searching for Black Holes in Globular Clusters with Pulsars
astrobites | Daily Paper Summaries | 2020 Jan 24
Brent Shapiro-Albert wrote:
Globular clusters, dense groups of hundreds of thousands of stars bound together by their own gravity, are home to some of the most exotic objects in the universe. Among these are pulsars, highly magnetized neutron stars that beam radio emission out as they rotate. Some pulsars complete a full rotation in just a few milliseconds, and are aptly called millisecond pulsars. Globular clusters are also known to host black holes, some of the most elusive astronomical bodies known.

Just four years ago, observations with the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected black holes with masses of 7 to 80 times the mass of the sun (stellar mass black holes) for the first time. This past year, the Event Horizon Telescope imaged a supermassive black hole, which have masses of a million to a billion times that of our sun, at the center of the galaxy M87. Yet, there remains a population of black holes that has thus far eluded us: intermediate mass black holes (IMBHs), which have masses between a hundred to a hundred thousand times the mass of the sun. IMBH’s could be the “missing link” between stellar mass black holes and supermassive black holes and help us learn how supermassive black holes form. But despite searches spanning several years, we have yet to detect them.

The best place to search for IMBHs has long been thought to be in the centers of globular clusters. This paper uses the millisecond pulsars in globular clusters to search for IMBHs. ...

Intermediate mass black holes in globular clusters:
Effects on jerks and jounces of millisecond pulsars
~ Federico Abbate, Mario Spera, Monica Colpi
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Bosons in the Sky with Black Holes

Post by bystander » Mon Jan 27, 2020 7:42 pm

Bosons in the Sky with Black Holes
astrobites | Daily Paper Summaries | 2020 Jan 25
Luna Zagorac wrote:
The success of the LIGO/VIRGO collaboration has opened a window into many previously gravitationally unprobed phenomena, from tiny dark matter candidates to supermassive black holes. One such example is black hole superradiance: when a wave is scattered off a rotating black hole, it can exit with a larger amplitude than it had before, carrying with it some of the angular momentum of the black hole. This effect is particularly interesting in the case of bosonic waves, whose quantum numbers are not suppressed by Pauli’s Exclusion Principle. This interaction leads to the formation of high occupation bound states around the black hole – creating, in essence, a gravitational atom, with the black hole as its nucleus.

Thus, black hole superradiance can be used to detect signals of bosonic fields which cannot be observed in a detector. In this paper, Arvanitaki et al. consider in particular the QCD axion, a robust bosonic dark matter candidate, and the signatures it might produce through black hole superradiance. They estimate its gravitational signatures, both from transitions between “orbitals” of the gravitational atom and from annihilation, as well as its bounds from black hole spin measurements. Both of these criteria are measurable by advanced LIGO (aLIGO), and future observations will serve to constrain axion masses in the event of no detection.

Discovering the QCD Axion with Black Holes and Gravitational Waves ~ Asimina Arvanitaki, Masha Baryakhtar, Xinlu Huang
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Baryonification – Dark matter N-body simulations

Post by bystander » Mon Jan 27, 2020 8:03 pm

Baryonification – Dark matter N-body simulations and the impact of gas-trophysics
astrobites | Daily Paper Summaries | 2020 Jan 27
Jamie Sullivan wrote:
The standard model of cosmology (ΛCDM) tells us the matter content of the universe with exquisite precision. Matter can be broken up into two chunks: normal, visible, matter including galaxies, stars, and gas that we know and love in the night sky, and the other much larger piece – invisible dark matter. The visible matter is referred to as “baryonic” (as in, made of baryons), and comes along with all the rich physics of fluids, thermodynamics, and radiation. In contrast, dark matter (at least, the cold kind) is extremely simple. Dark matter only interacts gravitationally, and this simple fact allows for very accurate simulation of dark matter dynamics using Newtonian gravity N-body simulations.

Dark-matter-only N-body simulations are excellent for describing the formation of dense dark matter halos, where galaxy formation takes place, but do not tell us anything about galaxy formation or its effects, where normal baryonic matter plays a large role. To accurately capture the full physics at play, hydrodynamic cosmological simulations are required to include gas, stars, and radiation (see Figure 1). However, even these “full-hydro” simulations are fundamentally limited by the smallest length scales that can be resolved in the simulation (often of order 1 kpc – for reference, the closest star to the solar system is roughly 1 pc away). As a result, they cannot capture the full details of small-scale effects that drive gas outflows (or “feedback“) via supernovae explosions or Active Galactic Nuclei (AGN). The modern solution to this is to use so-called sub-grid models, which approximately capture the effect of the small-scale physics that cannot be resolved.

Today’s paper is concerned with the effect of baryons – and particularly feedback – on the distribution of dark matter. You may have heard that we live in the age of precision cosmology, and amazingly, cosmologists now need to worry about percent-level effects in their models of the dark matter density distribution at relatively small length scales. To reach this level of accuracy, models and simulations need to account for the impact of baryons on the dark matter distribution, which can be gravitationally disturbed by something like an AGN jet. Such disturbances are not accounted for in the dark-matter-only simulations widely used in cosmological analyses, usually because hydro simulations are astronomically more computationally costly than dark-matter-only ones. This difference in cost is so enormous that using only hydro simulations in cosmological analyses would be impossible. Faced with this dilemma, what do we do? ...

A new method to quantify the effects of baryons on the matter power spectrum ~ Aurel Schneider, Romain Teyssier
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An iced cosmic-ray macchiato

Post by bystander » Wed Jan 29, 2020 7:54 pm

An iced cosmic-ray macchiato
astrobites | Daily Paper Summaries | 2020 Jan 28
Alex Pizzuto wrote:
Our Universe is littered with particles of unbelievably high energy, called cosmic rays. The most extreme of these particles carry the same amount of energy as a professional tennis serve, like the Oh-My-God Particle detected nearly 30 years ago. The catch: we don’t know exactly what processes can pack so much energy into a single particle. The authors of today’s article discuss how these particles might gain their energy in a way analogous to your morning trip to Dunkin’™. ...

Bottom-up Acceleration of Ultra-high-energy Cosmic Rays
in the Jets of Active Galactic Nuclei
~ Rostom Mbarek, Damiano Caprioli
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Do we need to expand the cosmological standard model?

Post by bystander » Wed Jan 29, 2020 8:25 pm

Do we need to expand the cosmological standard
model? New cepheid observations suggest yes

astrobites | Daily Paper Summaries | 2020 Jan 29
Laila Linke wrote:
The Hubble constant H0 describes the rate at which the universe expands today. It is a fundamental parameter of the standard model of cosmology, the ΛCDM-model, which is well supported by a range of observations. However, in recent years there has been a controversy surrounding H0, called “Hubble Trouble” by popular media and “H0 Tension” by scientists. It comprises the discrepancy between measurements of the Hubble parameter by the Planck satellite (67.4 ± 0.5 km/s/Mpc ) and in the local universe (72.04 ± 2.67 km/s/Mpc). Up to now, this discrepancy was less than 3σ and could still be explained by a statistical fluke. In today’s paper, however, Adam Riess and his co-authors reduced the error bars on their measurement of H0 in the local universe and found that the discrepancy to the Planck measurement increases to what they call “beyond a plausible level of chance”. This could imply that the standard model is wrong and needs to be extended! ...

Large Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination
of the Hubble Constant and Stronger Evidence for Physics Beyond ΛCDM
~ Adam G. Riess et al
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Using a Random Forest to Classify ASAS-SN Variable Stars

Post by bystander » Fri Jan 31, 2020 6:29 pm

Using a Random Forest to Classify ASAS-SN Variable Stars
astrobites | Daily Paper Summaries | 2020 Jan 30
Huei Sears wrote:
Since its creation in 2014, the All-Sky Automated Survey for Supernovae (ASAS-SN) has monitored the whole sky every 2-3 days down to ~17th magnitude. As this survey searches for supernovae, it often finds other variable stars too who are not exploding — yet their brightness, in general, varies with time! The authors of today’s paper attempt to classify ~90,000 variable star candidates found by ASAS-SN and present a catalogue of 66,179 previously unknown variable stars. ...

The ASAS-SN Catalog of Variable Stars I: The Serendipitous Survey ~ T. Jayasinghe et al
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It Takes Two to Tango: Eclipsing White Dwarfs

Post by bystander » Fri Jan 31, 2020 6:47 pm

It Takes Two to Tango: Eclipsing White Dwarfs Push General Relativity to its Limit
astrobites | Daily Paper Summaries | 2020 Jan 31
Wynn Jacobson-Galan wrote:
50% of all stars form with a friend. However, within the multitude of stellar relationships in the universe, eclipsing white dwarf binaries are one of the most intensely dynamic (Figure 1). Each star in this configuration is the remnant of a sun-like star that has violently shed its outer hydrogen/helium layers to leave behind a compact stellar core. The white dwarf star that is created is approximately the mass of our sun, yet squeezed down to the size of Earth in diameter! Fascinating in their singularity, these stellar structures, when orbiting each other at an increasing rate, create some of the most extreme physics in the universe. Unlike studies of stable white dwarf systems, these eclipsing binaries provide a rare, yet highly precise, test of white dwarf structure including the uncertain relationship between their mass and radius. Observing these rapidly revolving binary systems lets us probe uncharted territory in orbital dynamics, binary star evolution and gravitational wave physics.

We know that binary white dwarfs can orbit each other in less than ten minutes — it takes more time to scroll to the bottom of our social media of choice, recap the weekend with a friend or enjoy a bag of chips. So, amongst the billions of twinkling stars in the Milky Way, how can we find an elusive binary system whose brightness changes on such a fleeting timescale? Well, you need a powerful telescope that scans the sky all night, every night. And such a survey exists! The Zwicky Transient Factory (ZTF) observes the entire northern sky and collects data on as many stars as possible. Combing through the light curves of 20 million stars with periodic changes in brightness, the authors of today’s paper found a hidden gem called ZTF J1539+5027, an eclipsing white dwarf binary with an orbital period of only 6.91 minutes. ...

General Relativistic Orbital Decay in a Seven-Minute-Orbital-Period Eclipsing Binary System ~ Kevin B. Burdge et al
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FRB 121102 CHIMEs in Again

Post by bystander » Wed Feb 05, 2020 6:54 pm

FRB 121102 CHIMEs in Again
astrobites | Daily Paper Summaries | 2020 Feb 01
Ali Crisp wrote:
Fast radio bursts, or FRBs, are a newer and somewhat mysterious phenomenon in radio astronomy. This paper details how the authors used a new instrument called CHIME/FRB to observe and put new constraints on FRB 121102, one of the few FRBs known to repeatedly send signals.

FRBs were first discovered in 2007 in archival data from the Parkes Observatory in Australia. FRBs are characterized by very short—on the order of milliseconds—but very strong signals emitted in radio wavelengths. As of late January 2020, there have only been 110 verified FRBs. Of these 110, only 9 FRBs have been found to repeat, so it’s hard to pinpoint what their sources might be, or if they’re even all caused by the same mechanism (your microwave oven has been ruled out, but aliens have not). It is difficult to localize such short signals from just one detection since A) astronomers don’t have much time to work with and B) there can be multiple stars, galaxies, etc. in the same general direction, which makes it hard to determine exactly which object is the source. So far, only two FRBs have been well-localized: the non-repeating FRB 180924 and the hero of this story—besides the researchers, of course—FRB 121102.

In this paper, the authors discuss how they used the new CHIME/FRB detector and data pipeline to capture data for FRB 121102 CHIME, the Canadian Hydrogen Intensity Mapping Experiment, is capable of taking highly sensitive radio data covering half the night sky, which is perfect for trying to detect large numbers of FRBs. ...

CHIME/FRB Detection of the Original Repeating Fast Radio Burst Source FRB 121102 ~ A. Josephy et al
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Uncovering a Cosmic Matter Reservoir

Post by bystander » Wed Feb 05, 2020 7:15 pm

Uncovering a Cosmic Matter Reservoir
astrobites | Daily Paper Summaries | 2020 Feb 03
James Negus wrote:
When you gaze up at the night sky on a clear evening, all of the matter you observe is “baryonic”. This class of matter is primarily composed of neutrons and protons, the fundamental building blocks of atoms. In fact, all of the visible matter in the universe, including the matter the makes up you and I, is classified as baryonic matter. Surprisingly, though, this type of “normal” matter only accounts for 5% of the mass-energy in the universe; the remaining exists in the form of dark matter (25%) and dark energy (70%), which are not visible in the electromagnetic spectrum.

Ground and space-based instrumentation should be able to effectively trace the spatial distribution of this visible baryonic matter. However, the number of baryons that have been optically observed within the universe’s large scale structures (i.e. nebulae, globular clusters, and galaxies) falls 30-40% short of what existing models predict!

To account for this discrepancy, several numerical simulations suggest that the missing baryons may be masked within hot tendrils of filamentary gas that form the cosmic web (Figure 1). Here, characteristic gas temperatures fluctuate between 100 thousand to 10 million Kelvin, which results in the ionization of hydrogen, the most abundant element within these structures. Once ionized, the hydrogen atoms cannot produce the spectral features necessary for detection in visible wavelengths since they have been stripped of their sole electron. Coupled with the inherently low density of these regions, the baryons are effectively invisible.

To address this challenge the authors of today’s paper worked to uncover the location of the elusive reservoir of baryonic matter. They used X-ray observations, which are ideally suited to study highly energetic environments due to their short wavelength sensitivity (0.01 – 10 nanometers). Utilizing the European Space Agency’s XMM-Newton X-ray Space Telescope, they conducted nearly 20 days of observations of a blazar. These supermassive black holes generate energetic jets of ionized matter that are oriented towards Earth and can approach the speed of light. The observation of this object (1ES 1553+113) was the longest ever performed on a single target using the telescope’s spectrometer, allowing the researchers to achieve unrivaled high-resolution measurements. ...

Observations of the Missing Baryons in the Warm-Hot Intergalactic Medium - F. Nicastro et al
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Disturbed Naps and Black Hole Mass Gaps

Post by bystander » Wed Feb 05, 2020 7:40 pm

Disturbed Naps and Black Hole Mass Gaps
astrobites | Daily Paper Summaries | 2020 Feb 04
Sumeet Kulkarni wrote:
The Laser Interferometer Gravitational-wave Observatory (LIGO) and its European counterpart, Virgo, have started issuing joint open public alerts to those who sign up whenever they pick up a cosmic whisper of these ripples in spacetime. In the wee hours of September 24, 2019, many cosmic enthusiasts who had subscribed, including me, were woken up by a new gravitational wave detection.

I’m someone who enjoys a sound sleep more than anything else, but I never complain when the universe calls—and this particular alert was especially worth waking up for. Not only had LIGO-Virgo made a new detection, but I could immediately see what kind of event had triggered this blast of gravitational waves. It was almost certainly a collision between two objects in a mysterious gray area known as the “mass gap.” (Figure 1)

I could know all of this because, in addition to sending notices within minutes of a detection, LIGO-Virgo release the probability of whether the source is astrophysical in origin or caused due to terrestrial noise. If astrophysical, they indicate if it’s likely to be a collision between a pair of Binary Black Holes (BBH), a pair of Binary Neutron stars (BNS), or between a neutron star and a black hole (NSBH). However, the recent signal showed a greater than 99% probability of falling in the apparent void between the three categories: the mass gap.

Neutron Stars Versus Black Holes: Probing the Mass Gap with LIGO/VIRGO ~ Tyson B. Littenberg et al
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