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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