astrobites 2018

Find out the latest thinking about our universe.
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astrobites 2018

Post by bystander » Tue Jan 02, 2018 4:14 pm

astrobites

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.

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No Escape from the Milky Way

Post by bystander » Tue Jan 02, 2018 4:24 pm

No Escape from the Milky Way
astrobites | 2018 Jan 01
Amber Hornsby wrote:
Back in 2002, an apparent overdensity of stars was uncovered by the Sloan Digital Sky Survey (SDSS). This so-called Monoceros ring is a long filament of stars which has wrapped itself around the Milky Way several times. In the first bite of the year, we look at the simulations undertaken by astronomers to explore one of many scenarios proposed to explain its much disputed origin.

The Milky Way, like many other galaxies in the universe, is surrounded by several streams of stars. For example, the impressive Sagittarius stream, shown in Figure 1, is composed of stars it stole from the Sagittarius dwarf elliptical galaxy during its merger with the Milky Way. From its shared stellar properties to the dwarf galaxy and the stream’s structure, astronomers were able to deduce its origin. ...

On the Origin of the Monoceros Ring - I: Kinematics, Proper Motions, and the Nature of the Progenitor - Magda Guglielmo et al
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A Recipe for Mini-Neptunes

Post by bystander » Tue Jan 02, 2018 4:38 pm

A Recipe for Mini-Neptunes
astrobites | 2018 Jan 02
Michael Hammer wrote:
To be a master chef, one must have an incredible amount of culinary expertise and creativity to create a wide variety of dishes. To be a computational astrophysicist building planets in simulations, it feels a lot more like going to the store and buying a box of pancake mix. Instead of buying all the ingredients, you start with a pre-made mixture. From there, all you have to do is just add water! ...

In today’s paper, Julia Venturini and Ravit Helled explore which planet and disk conditions are best for building planets that have just the right-sized atmosphere to be classified as Mini-Neptunes – the most common type of exoplanet (see Figure 2), even though there are none in our solar system. ...

The Formation of Mini-Neptunes - Julia Venturini, Ravit Helled
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Sensing a Pulsar’s Sense of Rotation

Post by bystander » Mon Jan 08, 2018 8:58 pm

Sensing a Pulsar’s Sense of Rotation
astrobites | 2018 Jan 03
Thankful Cromartie wrote:
In 2017, the field of pulsar astrophysics turned 50 years old. In those 50 years, we’ve learned a lot about these rapidly rotating neutron stars — and they’ve facilitated some of the most exciting scientific discoveries of the last century. It’s easy to assume that in the years since 1967 we’ve confirmed most of the basic assumptions we make about these compact objects (like their evolutionary history, motion, and composition). However, today’s astrobite reveals that we still have a lot to learn.

We use pulsars to do unfathomably cool science, from testing general relativity and detecting gravitational waves to enabling spacecraft navigation. With such an advanced understanding of these objects, you might expect us to be able to determine a property as basic as what direction a pulsar is rotating. Remarkably, we haven’t been able to — at least not with much certainty. This study from Pol et al. presents the first direct determination of a pulsar’s sense of rotation (i.e. if it’s rotating prograde or retrograde with respect to its orbit). It also provides support for the widely accepted rotating lighthouse model of pulsars, which describes pulsars as rotating neutron stars with radiation emitted from their magnetic poles. Their beams sweep across our line of sight, creating the rapid pulsing signals we detect.

The authors of this work exploited a one-of-a-kind system, called PSR J0737–3039 (the Double Pulsar). It is the only known binary that consists of two detectable radio pulsars, and its fast orbital period (~2.5 hours) makes it the most relativistic pulsar binary we know of. More subtle features (detailed below) make this system ideal for the determination of a pulsar’s sense of rotation. ...

A Direct Measurement of Sense of Rotation of PSR J0737-3039A - Nihan Pol et al
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Hot Jupiters are not really like layer-cakes

Post by bystander » Mon Jan 08, 2018 9:10 pm

Hot Jupiters are not really like layer-cakes
astrobites | 2018 Jan 04
Shang-Min Tsai wrote:
The phase curves of transit planets reveal the longitudinal (from day to night) variation. When observing with multiple-wavelengths, they further tell us the information in the radial direction. Different wavebands in principle probe different pressure depths in the atmosphere, since different wavelengths have different opacities (the ability to absorb and scatter photons). However, the opacity is determined by the local temperature, pressure, and gaseous composition, and there is no reason for the opacity to hold constant across the planet, as we will see later. In today’s paper, the authors address this important yet challenging issue when it comes to interpreting the multi-band phase curves. ...

Wavelength Does Not Equal Pressure: Vertical Contribution Functions and
Their Implications for Mapping Hot Jupiters
- Ian Dobbs-Dixon, Nicolas B. Cowan
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A new kind of animal in the exoplanet zoo

Post by bystander » Mon Jan 08, 2018 9:17 pm

A new kind of animal in the exoplanet zoo
astrobites | 2018 Jan 05
Kerrin Hensley wrote:
By now, exoplanet enthusiasts will be familiar with hot Jupiters, super-Earths, mini Neptunes, and even exo-Venuses, to name just a few. As the search continues, astronomers are finding colder and smaller planets, making possible the discovery of more Solar System analogs. In today’s paper, Lora et al. consider exoplanets similar to one of the most tantalizingly Earth-like yet alien bodies in the Solar System: Titan. ...

In today’s paper, Lora et al. use theoretical models to investigate the atmospheres of Titan-like exoplanets orbiting Sun-like stars as well as K and M dwarfs, which are smaller and redder than the Sun. Thanks to Cassini, we already have an idea of what Titan might look like masquerading as an exoplanet around a Sun-like star, but Titan takes about 30 years to orbit the Sun; that’s a long time to wait to detect and confirm an exoplanet! Around an M dwarf, a planet with the same effective temperature as Titan (~80 K) takes only about 2 years to complete an orbit—much easier and quicker to detect. Titan-like exoplanets don’t need to crowd M dwarfs as closely as Earth-like planets do, so they are less susceptible to the notoriously nasty space weather of cool stars and they are less likely to be tidally locked. Though neither issue immediately disqualifies M dwarf planets from the habitability contest, considering a cooler planet appears to solve both problems at once. ...

Atmospheric circulation, chemistry, and infrared spectra of Titan-like
exoplanets around different stellar types
- Juan M. Lora, Tiffany Kataria, Peter Gao
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Where’s the flux? Dust? Discuss.

Post by bystander » Fri Jan 19, 2018 3:26 pm

Where’s the flux? Dust? Discuss.
astrobites | 2018 Jan 15
Emily Sandford wrote:
We’ve posted before about Boyajian’s Star, one of the great unsolved mysteries of the Kepler mission. Discovered by citizen scientists in 2015, this star has everything: deeply bizarre (and bizarrely deep) dips in flux, a hundred-year fade, intermittent brightening spells. Since Kepler, investigations of this star have been hampered by the lack of new data–it’s hard to tell, for example, whether the crazy flux dips repeat if you don’t stare at the star continuously, because you might have just missed them.

All of that changed in 2016, when Dr. Boyajian began monitoring her namesake star with the Las Cumbres Observatory Global Telescope Network (LCOGT). LCOGT has two completely independent telescopes in the northern hemisphere–one in Hawaii and one in the Canary Islands–so on May 18, 2017, when both telescopes reported that Boyajian’s Star was dimming anew, Dr. Boyajian could immediately rule out instrumental effects as the cause.

That dimming turned out to be the first night of a very interesting summer for Boyajian’s Star. Since May, the star has dimmed four separate times. In today’s paper, Dr. Boyajian presents the new data, and offers, for the first time, a hint at a solution to the mystery. ...

The First Post-Kepler Brightness Dips of KIC 8462852 - Tabetha S. Boyajian et al
http://asterisk.apod.com/viewtopic.php?t=35401#p278501
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How habitable is your galaxy?

Post by bystander » Fri Jan 19, 2018 3:36 pm

How habitable is your galaxy?
astrobites | 2018 Jan 16
Matthew Green wrote:
When we talk about the habitability of a planet, astronomers are normally referring to one thing: whether a planet’s temperature is right for life. This comes down to a planet’s relationship to its host star — how hot the star is, and how far away the planet is from the star. Of course, there are a whole host of other factors at play regarding whether life could evolve on a planet or not — some that we know about and undoubtedly many that we don’t. As our understanding increases, the conversation is widening to include some of these other factors (for instance, what impact X-rays or flares from the host star will have). Today’s paper takes a broader view, by looking at habitability not on the level of stars and planets, but on the level of galaxies. It turns out that both the nature of the galaxy you’re in and where you are within it are important questions for any aspiring life-forms. ...

Exploring the Cosmic Evolution of Habitability with Galaxy Merger Trees - E. R. Stanway et al
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Capturing neutrons in the thin disk

Post by bystander » Fri Jan 19, 2018 3:50 pm

Capturing neutrons in the thin disk
astrobites | 2018 Jan 17
Eckhart Spalding wrote:
The evolution of the Milky Way holds a place of special importance for us, because many aspects of it are easier to study than in other galaxies, and, after all, we live in it. From our vantage point, we can observe up-close the nitty-gritty of the galactic assembly process, and come to understand how the formation of our own solar system is intimately tied to the Galaxy’s long and storied dynamicaland chemical history. In today’s bite, let’s focus on an aspect of the Milky Way’s chemical story. ...

In today’s paper, which was published before the observations of GW170817, the authors assemble a homogeneous data set to infer the spatial distribution of r- and s-process elements in the Galaxy. What’s a good way to map the distribution of elements in the Galaxy? Well, by measuring abundances in stars that are good distance indicators! ...

Neutron-capture elements across the Galactic thin disk using Cepheids - R. da Silva et al
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New Directly Imaged Planet Challenges Planet Formation Theories

Post by bystander » Fri Jan 19, 2018 4:19 pm

New Directly Imaged Planet Challenges Planet Formation Theories
astrobites | 2018 Jan 18
Samuel Factor wrote:
Taking a picture of an extremely faint planet next to a bright star is exceptionally challenging, both due to the difficulty of the observations and the rarity of planets at wide separations. So, when a new planet is imaged, it makes waves in the community. HIP 65426 b is the first planet discovered with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on the Very Large Telescope (VLT) at Paranal Observatory in Chile. You may remember a paper published last year about a planet in a triple system discovered by SPHERE. Unfortunately that object is most likely a background star (paper), making HIP 65426 b the first planet discovered by SPHERE. Figure 1 shows the discovery image. ...

Discovery of a Warm, Dusty Giant Planet around HIP65426 - G. Chauvin et al
http://asterisk.apod.com/viewtopic.php?t=37369
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Good vs. Evil: A Cosmic Challenge

Post by bystander » Fri Jan 26, 2018 4:47 pm

Good vs. Evil: A Cosmic Challenge
astrobites | 2018 Jan 22
Stephanie Hamilton wrote:
It’s not every day that the astronomical community gets an outright competition-style challenge to produce a result. But that’s exactly what today’s paper outlines. The goal? To promote the development of the best method the astronomical community can come up with to measure the local expansion rate of the universe, also known as the Hubble constant, H0. ...

A perhaps lesser-known (or maybe just less publicized) effect of strong lensing is the notion of “time delay.” Time delay refers to the differing arrival times of light that follows different trajectories on the way from the background source galaxy, around the lensing mass, and to our telescopes. We observe this effect as multiple images of the same object at different times. ...

It is relatively straightforward to obtain precise time delay measurements for a strongly-lensed system, if the quality of the light curve data is good. Fortunately, good-quality light curve data will not be hard to obtain with the immense quantity of data sure to come from the Large Synoptic Survey Telescope (LSST). The question now becomes whether current methods that use this time delay data to map the gravitational potential of the lensing mass are good enough to produce precision cosmology measurements. Specifically, we are now in an era where a difference in the measurement of H0 of only a few km/s is significant, and the attainable precision in the measurement is affected by nuances in the strong lens models. That is, systematic errors are starting to dominate our measurements, which is certainly not desirable. This is exactly the motivation behind the challenge outlined in today’s paper. ...

Time Delay Lens Modeling Challenge: I. Experimental Design - Xuheng Ding et al
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Accidentally Finding a Solar Twin

Post by bystander » Fri Jan 26, 2018 5:09 pm

Accidentally Finding a Solar Twin
astrobites | 2018 Jan 23
Daniel Berke wrote:
What role does chance play in scientific discoveries? The exact amount is up for debate, but what’s undeniable is that many discoveries in the history of science have involved a degree of chance. From Archimedes and his “Eureka!” moment to Newton observing an apple falling from a tree, plenty of scientific discoveries have involved someone investigating something random or accidental that happened.

Today’s paper involves a case of astronomers observing the wrong object but getting a paper out of it anyway. While observing with the HIRES spectrograph on the Keck I telescope the authors of the paper attempted to observe the carbon star BPS CS 22949-0037. After finishing a 20-minute exposure they discovered that they had actually observed a different star nearby, only 49.16 arcseconds away (as shown in Figure 1). Instead of discarding the mistaken observation they investigated the spectrum from the star they’d observed and realized that it was extremely close to that of the Sun, making it a so-called solar twin. The authors named this new star Inti 1 after the Quechua word for the Sun. ...

Serendipitous discovery of the faint solar twin Inti 1 - Jhon Yana Galarza, Jorge Meléndez, Judith G. Cohen
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Hunting for new physics in a black hole’s shadow

Post by bystander » Fri Jan 26, 2018 5:29 pm

Hunting for new physics in a black hole’s shadow
astrobites | 2018 Jan 24
Aaron Tohuvavohu wrote:
For 5 days in April of 2017, 8 radio telescopes on 4 continents all pointed in concert at Sagittarius A*, the supermassive black hole at the center of our galaxy. During this observing campaign these 8 telescopes effectively became one Earth-sized radio telescope, the Event Horizon Telescope (EHT). Using hydrogen maser atomic clocks to track the difference in the arrival times of the radio signal at the various telescopes, the far-flung array can emulate a single telescope with an effective diameter equal to that of our planet, a technique called very long baseline interferometry (VLBI). ...

Alongside the recent successes of gravitational wave astronomy, the EHT is another way to probe the ‘strong-field’ gravitational regime and provide long-awaited answers to questions about general relativity. Specifically, the EHT uses mm-wavelength radio astronomy to trace the extremely hot gas that is believed to inhabit the area directly outside the event horizon of the black hole. General relativity predicts that a silhouette, or ‘shadow’, will be seen imprinted onto the image of the hot gas, the distinct signature of the black hole’s event horizon (See Fig. 2). Today’s paper looks at ways to test general relativity, alternative theories of gravity, and the quantum structure of space-time by studying the size and shape of this shadow. ...

Event Horizon Telescope Observations as Probes for Quantum Structure of Astrophysical Black Holes - Steven B. Giddings, Dimitrios Psaltis
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Diagnosing the Amnesia of Exoplanetary Systems

Post by bystander » Fri Jan 26, 2018 5:38 pm

Diagnosing the Amnesia of Exoplanetary Systems
astrobites | 2018 Jan 25
Vatsal Panwar wrote:
The abundance of discoveries of exoplanetary systems over the last two decades, especially from the Kepler Mission, have revealed an immense diversity in terms of planetary masses, sizes, atmospheric properties, and potential formation histories. The marked differences in the architectures of these systems with respect to that of our solar system have pushed astronomers to revise their planet formation models, that were earlier based solely on the solar system. In this game of exoplanetary systems archaeology, two of the most important pieces of information that can be used to understand the formation pathways and evolution history of exoplanetary systems are the planet sizes and their respective orbital periods (both together representing the size-ordering of planets in the system). ...

By invoking an information theoretic approach of quantifying information, employing counting methods from combinatorics, and leveraging the large sample of multiplanet systems observed by Kepler, today’s paper tries to put forward a quantitative argument to determine if the observed size-ordering of planetary systems contains any residual information about their past. ...

Do planets remember how they formed? - David Kipping
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Hunting for Gravitational Waves from Spinning Neutron Stars

Post by bystander » Sat Feb 03, 2018 5:50 pm

Hunting for Gravitational Waves from Spinning Neutron Stars
astrobites | 2018 Jan 29
Lisa Drummond wrote:
Astrobites has reported extensively on gravitational waves from compact binary coalescences (CBCs) – see here, here and here. CBCs involve pairs of massive, compact objects such as neutron stars and black holes encircling each other and colliding. However, these cataclysmic collisions are not the only events that can produce gravitational waves! Last year, LIGO published a paper reporting on searches for another type of gravitational radiation – continuous gravitational waves. Continuous waves are likely to be produced by spinning neutron stars with some kind of rotational asymmetry. An investigation using four different approaches was conducted in order to carefully comb through the data from LIGO’s first observing run (O1). ...

All-sky Search for Periodic Gravitational Waves in the O1 LIGO Data - LIGO Scientific Collaboration, Virgo Collaboration
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Blowing the wrong way round? Westward winds on CoRoT-2b

Post by bystander » Sat Feb 03, 2018 6:05 pm

Blowing the wrong way round? Westward winds on CoRoT-2b
astrobites | 2018 Jan 30
Emma Foxell wrote:
Hot Jupiters should be tidally locked as they orbit so close to their stars. Just as we always see the same side of our orbiting Moon, a hot Jupiter would continually have the same ‘dayside’ subject to its star’s blistering heat. The part of the planet directly below and closest to the star’s furnace (the substellar point) should therefore be the hottest region.

However, observations show the substellar point is not always the hottest part. Astronomers theorise strong winds caused by large differences in temperature between the hot Jupiter’s superheated dayside and cool nightside can shift the hottest region of the atmosphere.

Simple planetary atmospheric models, which assume there are no strong external forces, agree these strong winds will blow in the direction the tidally locked planet rotates, so the hottest point comes into full view before the substellar point occurs at secondary eclipse. Astronomers call this an eastward shift. This eastward shift is observed on HD 209458b, and the authors expected the same for CoRoT-2b as it has a similar temperature due to stellar irradiation. ...

Detection of a Westward Hotspot Offset in the Atmosphere of a Hot Gas Giant CoRoT-2b - Lisa Dang et al
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Shooting the Breeze with Mars

Post by bystander » Sat Feb 03, 2018 6:16 pm

Shooting the Breeze with Mars
astrobites | 2018 Jan 31
Jamila Pegues wrote:
Even though we’re pretty close (relatively speaking), there’s still a lot that we don’t know about our next-door-neighbor, Mars. Today we often think of Mars as a cold desert-wasteland of craters, dunes, and lots and lots of rocks. This is certainly how we’ve seen it in sci-fi of all kinds (like this one and this other one). But, as the authors of today’s paper show, there’s more going on for the surface of Mars than just Martian rocks. By performing laboratory experiments under Martian environmental conditions, today’s authors took steps towards understanding more about our dusty neighbor’s climate and related surface morphology.

The authors used wind tunnel experiments to gain insight into how atmosphere-soil interactions occur on Mars. Wind tunnel experiments are quite aptly named; they consist of tunnels through which scientists blow air around solid objects (like airplanes), to learn more about things like pressure and velocity on and for the objects. The authors put Mars-like soil into their wind tunnel to study its wind-based transport, particularly through saltation. Saltation is a neat word that refers to when the wind makes a grain of soil ‘bounce’ on the surface: when the wind picks up a grain of soil, carries it away at a height a little bit above the soil bed, and then drops it again somewhere else. ...

Saltation under Martian Gravity and its Influence on the Global Dust Distribution - Grzegorz Musiolik et al
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Post-starburst galaxies: the missing link in galaxy evolution?

Post by bystander » Sat Feb 03, 2018 6:28 pm

Post-starburst galaxies: the missing link in galaxy evolution?
astrobites | 2018 Feb 01
Joanna Ramasawmy wrote:
Surveys of the nearby universe show that we can divide galaxies into two types if we look at their colours — we find a “blue cloud” of star-forming galaxies, and “red sequence” of passive ellipticals without active star formation. Besides their colours, there is another important difference between these two types of galaxies: their shape, or morphology. It turns out that most blue galaxies have a disc shape, while red galaxies are spheroidal. The majority of massive galaxies we see around us are spheroidal passive galaxies. But how and when do galaxies evolve from star-forming discs to red-and-dead spheroids?

In this paper, the authors investigate post-starburst galaxies (PSBs, or E+A galaxies as described in the astrobites galaxy classification guide), which are galaxies that have only recently stopped forming stars. One narrative of galaxy evolution suggests that galaxies move from the blue cloud to the red sequence following a rapid quenching of star formation. By shutting down star formation, the hot blue stars rapidly die out and the galaxy is left with an old red stellar population, explaining the transition in colour. However, this doesn’t explain the additional structural transformation that changes galaxies from a disc to a spheroid morphology. PSBs, rare galaxies caught in this transition phase, might hold the key. ...

Massive post-starburst galaxies at z > 1 are compact proto-spheroids - Omar Almaini et al
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Biodiversity or Bust

Post by bystander » Sun Feb 11, 2018 6:04 pm

Biodiversity or Bust
astrobites | 2018 Feb 05
Lauren Sgro wrote:
Are we alone in the universe? This question still baffles astronomers (along with the rest of humanity) today, despite the confirmed discovery of thousands of exoplanets. Sure, there may be a plethora of other space pebbles out there, but do any of them actually host life? And if they do, could it ever compare to the variety of species we see on Earth, from human beings to tardigrades?

Unfortunately, we don’t have the answers to these questions yet, but today’s authors take a step in the right direction. By creating a model to measure potential biodiversity, they explore which stars are most likely to host planets capable of supporting complex life. These findings may help future exoplanet habitability studies point in the right direction. ...

Reduced Diversity of Life around Proxima Centauri and TRAPPIST-1 - Manasvi Lingam, Abraham Loeb
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GW170817: The X-ray Emission Did What?

Post by bystander » Sun Feb 11, 2018 6:15 pm

GW170817: The X-ray Emission Did What?
astrobites | 2018 Feb 06
Sanjana Curtis wrote:
In August 2017, gravitational waves from a binary neutron star merger (GW170817) were detected for the first time ever, by LIGO and Virgo. Also detected were (deep breath recommended) – gamma-rays, X-rays, ultraviolet rays, optical, infrared and radio waves – all from the same source. The era of multi-messenger astronomy was thus kicked off in spectacular fashion. The coincident short gamma-ray burst (GRB 170817A) confirmed that merging neutron stars are indeed one of the progenitors of short GRBs. Read this astrobite for more details about these observations.

Today’s bite further illustrates why multimessengers are so very important and exciting. It is not entirely clear what happened after the merger, and complementary information from different channels can help construct an accurate picture. The optical signal or ‘’messenger’’, for example, may carry slightly different information about the source than the radio waves do. So, if we manage to detect both, we end up with an additional clue about whatever produced them! Here, we will discuss the X-ray observations of GW170817/GRB 170817A. ...

Brightening X-Ray Emission from GW170817/GRB 170817A: Further Evidence for an Outflow - John J. Ruan et al
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The Deepest Rumblings of the Sun

Post by bystander » Sun Feb 11, 2018 6:22 pm

The Deepest Rumblings of the Sun
astrobites | 2018 Feb 07
Avery Schiff wrote:
Far below its surface, the Sun slowly breaths with invisible pulses. Blobs of plasma are launched upwards by buoyant forces, only to reach the peak of their trajectories and plunge back to the depths below. This motion is known as a g-mode oscillation, and until recently it was unseen by solar scientists. In today’s paper, Fossat et al. describe one of the most promising detections of the g-modes to date and the implications for the Sun’s deepest layers. ...

Asymptotic g modes: Evidence for a rapid rotation of the solar core - E. Fossat et al
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How much does the Milky… weigh?

Post by bystander » Sun Feb 11, 2018 6:36 pm

How much does the Milky… weigh?
astrobites | 2018 Feb 08
Tomer Yavetz wrote:
Picture this: you’re at your local clinic for an annual physical, and your doctor asks to measure your weight. Simple, right? But now, imagine your doctor doesn’t have a scale, nor the ability to lift you, nor any understanding of what your body is made of. Oh, and you’re invisible, too. Not so simple anymore…

This is (more or less) the challenge astrophysicists face when trying the measure the mass of the Milky Way, our humble galactic home. And even though this has been an active area of research for nearly 60 years, today’s best estimates still vary widely from one another (see figure 1 for a few recent examples). Back at your annual physical, it’s as if your doctor tells you, “I think you weigh about 150 lbs, give or take 80 lbs.” ...

What galaxy masses perturb the local cosmic expansion? - Jorge Peñarrubia, Azadeh Fattahi
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Ghostly Hosts: Looking for the Sources of Enrichment

Post by bystander » Sun Feb 11, 2018 6:47 pm

Ghostly Hosts: Looking for the Sources of Enrichment
astrobites | 2018 Feb 09
Caitlin Doughty wrote:
Astronomers often find themselves studying objects that aren’t visible. To understand the behaviors of supermassive black holes or exoplanets, for example, astronomers need to be clever and devise indirect methods for observing them. For objects like Sgr A*, our own galaxy’s supermassive black hole, one observational proxy might be watching the frantic orbits of stars in the very center of the Milky Way. For an exoplanet, the proxy might be a transit visible in a light curve or a wobble in the radial velocity measurements of its host star. But what can we look for when trying to study some of the first galaxies, dwarfs with low stellar masses that are not bright enough to be directly imaged? ...

Theoretical study of an LAE-CIV absorption pair at z = 5.7 - L. A. García et al
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A Hitchhiker’s Guide to TRAPPIST-1

Post by bystander » Fri Feb 16, 2018 4:56 pm

A Hitchhiker’s Guide to TRAPPIST-1
astrobites | 2018 Feb 12
Tarini Konchady wrote:
In 1975, Viking 1 and Viking 2 were sent to explore Mars. Before they were launched, both probes were baked at 112 degrees Celsius for about 30 hours. This was not a test of their hardiness; NASA was guarding against Mars being invaded by terrestrial lifeforms. Over forty years later, the risks of contamination by space exploration are still being debated. One argument against excessive precaution is that if life from Earth could infest other planets or moons, it would have already done so by piggybacking on interplanetary debris.

Last February, astronomers confirmed a system of seven Earth-like planets orbiting the star TRAPPIST-1 (see this astrobite for details). Besides the number of planets it hosts, TRAPPIST-1 is especially interesting because it’s awfully close (12 parsecs away to be specific) and because three of its planets — TRAPPIST-1e, f, and g — lie in the star’s habitable zone (HZ).

The TRAPPIST-1 HZ planets are much closer to each other than the Earth is to Mars, prompting the authors of this paper to wonder — if life could survive in the TRAPPIST-1 system, what’s the likelihood of life spreading from one planet to the next? ...

Enhanced Interplanetary Panspermia in the TRAPPIST-1 System - Manasvi Lingam, Abraham Loeb
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Primordial black holes

Post by bystander » Fri Feb 16, 2018 5:08 pm

(Just can’t get enough) primordial black holes
astrobites | 2018 Feb 13
Philippa Cole wrote:
The recent gravitational wave detections by LIGO/VIRGO of black hole mergers have brought primordial black holes (PBHs) right back into the fray as a potential candidate for dark matter. This is because the black holes detected by LIGO that were a few dozen times the mass of the Sun could well have been PBHs.

However, even more intriguingly, there is another window of opportunity for primordial black holes with much lower masses to make up all of dark matter. In today’s paper, Inomata et al. show that it’s possible to produce enough PBHs with masses of around 1020g (the mass of the asteroid Ida) to make them a viable dark matter candidate, without violating the new and very stringent constraints on the number of allowed PBHs from the Subaru Hyper Suprime-Cam (see the results here). ...

Inflationary Primordial Black Holes as All Dark Matter - Keisuke Inomata et al
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