astrobites 2017

Find out the latest thinking about our universe.
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astrobites 2017

Postby bystander » Mon Jan 16, 2017 5:56 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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And along came a Neptune-sized planet

Postby bystander » Mon Jan 16, 2017 6:00 pm

And along came a Neptune-sized planet
astrobites | 2017 Jan 09

At the end of its extended 4 year campaign in space, Kepler scientists were left with a telescope that despite certain limitations, could still do good science. Thus the K2 mission was born and has so far found an additional 520 candidate exoplanets, including K2:105 b: a “Hot-Neptune” orbiting around a Sun-like G2 star. In this astrobite we will be discussing the K2 mission, confirming candidate planets using ground based telescopes and the importance of objects like K2-105 b if we are ever going to understand our own Solar system. ...

The K2-ESPRINT Project VI: K2-105 b, a Hot-Neptune around a Metal-rich G-dwarf - Norio Narita et al
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A Too-Hot Pulsar Speeding Through the Galaxy

Postby bystander » Mon Jan 16, 2017 6:16 pm

A Too-Hot Pulsar Speeding Through the Galaxy
astrobites | 2017 Jan 10

Pulsars — the rapidly rotating, highly magnetized neutron stars that beam radiation from their magnetic axes — are as mysterious as they are exotic. They’re most often observed at radio frequencies using single-dish telescopes, and are sometimes glimpsed in X-ray and gamma-ray bands. Far rarer are pulsar observations at “in-between” frequencies, such as ultraviolet (UV), optical, and infrared (IR) (collectively, UVOIR); in fact, only about a dozen pulsars have been detected this way. However, their study in this frequency range has proved enlightening, as we will see in today’s post. ...

Hubble Space Telescope detection of the millisecond pulsar J2124-3358
and its far-ultraviolet bow shock nebula
- B. Rangelov et al
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Your Jewelry and the Mysterious Tilt of the Moon

Postby bystander » Mon Jan 16, 2017 6:22 pm

Your Jewelry and the Mysterious Tilt of the Moon
astrobites | 2017 Jan 11
...
Whether it was expected or coincidental, we know not, but the formation of the Moon is definitely good news for all life residing on our planet. While it’s comforting to gaze at it through the window on most nights, the true understanding of the Moon’s formation remains elusive to its admirers. ...

Collisionless Encounters and the Origin of the Lunar Inclination - Kaveh Pahlevan, Alessandro Morbidelli
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Auroral Displays at Brown Dwarfs

Postby bystander » Mon Jan 16, 2017 6:30 pm

Auroral Displays at Brown Dwarfs
astrobites | 2017 Jan 12

Auroras are the spectacular light shows visible in the polar regions at Earth and other planets. In 2015 they were detected for the first time outside of the solar system. Brown dwarfs are objects often described as “failed stars”, meaning they are insufficiently massive to ignite hydrogen fusion in their cores. Today’s paper reports on the remarkable discovery that a particular brown dwarf plays host to auroral displays far more powerful than those found anywhere in the solar system. ...

Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence - G. Hallinan et al
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When Planets Won’t Stay Put

Postby bystander » Mon Jan 16, 2017 6:38 pm

When Planets Won’t Stay Put
astrobites | 2017 Jan 13

If you fill your house with rocks and go away for a while, you may reasonably expect that the rocks will be there, in their original configuration, when you return. This is in the Constitution.

If you instead choose to decorate with lizards (which are bound not by the Constitution, but by lizard law), you will find your house much changed when you come back. No matter how you arranged them originally, several will have escaped, and the rest will be under your furniture (whence they will need to be chased if you want to salvage your decor).

Haters may say that planets are more like rocks than like lizards, which is true in the narrow sense that many planets are large rocks with gaseous envelopes, not reptiles with feet and external ears. But get a whole bunch of planets together, and they behave more like a house full of lizards than a house full of rocks. ...

Dynamical Origin of Extrasolar Planet Eccentricity Distribution - M. Juric, S. Tremaine
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Re: When Planets Won’t Stay Put

Postby Chris Peterson » Mon Jan 16, 2017 6:54 pm

bystander wrote:

But get a whole bunch of planets together, and they behave more like a house full of lizards than a house full of rocks. ...

Well, that's certainly a colorful way of describing the inherent chaos of multiple body systems!
Chris

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Re: When Planets Won’t Stay Put

Postby geckzilla » Mon Jan 16, 2017 7:50 pm

Can confirm that lizards like to hide under furniture.
Just call me "geck" because "zilla" is like a last name.

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So what does a molecular cloud produce, anyway?

Postby bystander » Thu Jan 19, 2017 4:29 pm

So what does a molecular cloud produce, anyway?
astrobites | 2017 Jan 16

Collapsing regions of molecular clouds produce objects with a range of masses, from teeny planets to stars that are a hundred times the mass of the Sun. The ‘initial mass function’ plots the relative number of bodies as a function of mass. What does the initial mass function look like? And how much does it depend on the local environment? The distribution is determined by the poorly-constrained processes of star formation, which involve physics of the evolution of structure, chemistry, and star formation rates of galaxies, as well as the formation and evolution of stellar and exoplanetary systems. If we can determine the initial mass function exactly, we can help make some headway in these disparate fields.

There are two alternative theories for how the initial mass function may be formed: the parent core masses in collapsing molecular clouds map directly to the initial mass function, or gravitational interactions affect accretion onto protostars and fling members out of multiple-object systems. It is difficult to tell which effect is most important because, well, it is difficult to measure the initial mass function precisely. Low-mass objects are very dim, and some fade away into complete invisibility as they cool. High-mass stars are easy to detect, but they burn faster and quickly blow away their atmospheres or explode as supernovae. ...

The bimodal initial mass function in the Orion Nebula Cloud - H. Drass et al
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Gaia: The Stars in Motion

Postby bystander » Thu Jan 19, 2017 4:38 pm

Gaia: The Stars in Motion
astrobites | 2017 Jan 17

Although the night sky seems unchanging, it is in constant motion. Stars are not stationary objects but move through space, just like the Sun is moving along an orbit around the center of the Milky Way. A consequence is that all of today’s well-known constellations will eventually become unrecognizable (after a few hundred thousand years).

The apparent motions of individual stars on the sky are called proper motions and the study of such motions is part of a field called astrometry. A revolutionary satellite dedicated to precision astrometry, Hipparcos, was launched in 1989 and provided a comprehensive catalog of the motions of stars in the backyard of the Solar System, which grew to include 2.5 million stars. Its modern successor, Gaia, was launched in 2013 and will reveal the motions of about a billion stars in total. ...

First Gaia Local Group Dynamics: Magellanic Clouds Proper Motion and Rotation - Roeland P. van der Marel, Johannes Sahlmann
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Detecting Cosmic Sound using the Square Kilometer Array

Postby bystander » Thu Jan 19, 2017 4:44 pm

Detecting Cosmic Sound using the Square Kilometer Array
astrobites | 2017 Jan 18

You may be familiar with the tagline from the movie Alien, “In space, no one can hear you scream”, but what if I told you on cosmological scales there is somewhat of an exception? During the earliest periods of the universe, cosmic forces led to a phenomenon that would be analogous to sound. In today’s bite, we will see how astronomers plan to detect these oscillations. ...

Baryonic acoustic oscillations from 21cm intensity mapping:
the Square Kilometre Array case
- Francisco Villaescusa-Navarro, David Alonso, Matteo Viel
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The Milky Way – Tearing Apart Friendships for Billions of Years

Postby bystander » Thu Jan 19, 2017 4:50 pm

The Milky Way – Tearing Apart Friendships for Billions of Years
astrobites | 2017 Jan 19

Joining the Milky Way galactic system comes at a cost – groups of galaxies that have been “friends” for billions of years may be torn apart. On large scales, small galaxies joining the Milky Way system seems like a peaceful process, leaving the Milky Way unfazed, but when you zoom in, you see that these small galaxies are struggling to survive the fall and that groups of galactic friends are broken up. (Learn more about galaxy collisions in this astrobite!) Today’s paper examines whether these groups of friends are able to hang onto each other throughout the tumultuous journey of falling into a galaxy. ...

Satellites of LMC-Mass Dwarfs: Close Friendships Ruined by Milky Way Mass Halos - Alis J. Deason et al
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Re: So what does a molecular cloud produce, anyway?

Postby Ann » Thu Jan 19, 2017 11:17 pm

bystander wrote:So what does a molecular cloud produce, anyway?
astrobites | 2017 Jan 16

Collapsing regions of molecular clouds produce objects with a range of masses, from teeny planets to stars that are a hundred times the mass of the Sun. The ‘initial mass function’ plots the relative number of bodies as a function of mass. What does the initial mass function look like? And how much does it depend on the local environment? The distribution is determined by the poorly-constrained processes of star formation, which involve physics of the evolution of structure, chemistry, and star formation rates of galaxies, as well as the formation and evolution of stellar and exoplanetary systems. If we can determine the initial mass function exactly, we can help make some headway in these disparate fields.

There are two alternative theories for how the initial mass function may be formed: the parent core masses in collapsing molecular clouds map directly to the initial mass function, or gravitational interactions affect accretion onto protostars and fling members out of multiple-object systems. It is difficult to tell which effect is most important because, well, it is difficult to measure the initial mass function precisely. Low-mass objects are very dim, and some fade away into complete invisibility as they cool. High-mass stars are easy to detect, but they burn faster and quickly blow away their atmospheres or explode as supernovae. ...

The bimodal initial mass function in the Orion Nebula Cloud - H. Drass et al


Fascinating! (Putting on Spock ears.)

Eckhart Spalding wrote:

Surprisingly, the mass function corresponding to an age of 2-5 million years has two distinct peaks (Fig. 2)! If the Orion Nebula is indeed that old (some think it might actually be younger) and if the isochrones are accurate (isochrones are debatable at the lowest masses), then the Orion Nebular Cloud seems to be preferentially producing objects at around 0.25 and 0.025 solar masses. These correspond to low-mass stars and brown dwarfs. There are also, the authors note, some free-floating planets below the brown dwarf range.


The Orion Nebular Cloud seems to preferentially produce objects at around 0.25 and 0.025 solar masses! I knew it! (Well, no, I didn't, but I'm not surprised - not at the 0.25 solar mass peak, at least!)

So we can make the following conclusions:

1) The Sun is a massive star, not average at all. At least, it is most certainly not a low-mass star!

2) M-type dwarfs are the most common stars.

3) Tiny Proxima Centauri, at about 12% the mass of the Sun, is really small fry even among M-type dwarfs.

4) Wow, brown dwarfs are that common?

5) There are free-floating planets in the Orion Nebular Cloud. Yes, double, double toil and trouble in the Orion Nebular Cloud! Where fires burning and cauldrons bubbling tear planets from the suns whose protoplanetary disks hatched them! Good thing the Earth escaped its formative years (and all the years after that) without being torn from our own dear Sun!

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Re: astrobites 2017

Postby Ann » Fri Jan 20, 2017 12:17 am

By the way, I want to thank bystander for posting these astrobites. They are such fun reading!

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Why I won’t change my mind

Postby bystander » Sat Jan 28, 2017 6:07 pm

Why I won’t change my mind
astrobites | 2017 Jan 21
Zephyr Penoyre wrote:
We hope you’re enjoying our beyond posts, going beyond astronomical research and beyond published papers to talk about issues facing astronomers and astronomy in general.

I’m going to go a step further, and talk about an issue that directly affects not only anyone in astronomy, but also anyone who consumes any form of science media. Heck, it concerns anyone who consumes oxygen.

I’m going to talk about a paper that shows us how intractable our opinions can become, and how taking in more information may not actually free us from our biases. ...

Climate-Science Communication and the Measurement Problem - Dan M. Kahan
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The Curious Case of Planetary Nebulae in Globular Clusters

Postby bystander » Sat Jan 28, 2017 6:24 pm

The Curious Case of Planetary Nebulae in Globular Clusters
astrobites | 2017 Jan 23
Kerrin Hensley wrote:
Have you ever looked at something and wondered, “How did that get there?!” Has that something ever been a planetary nebula? Astronomers are scratching their heads over four planetary nebulae that have turned up in the unlikeliest of locations: globular clusters. ...

Masses of the Planetary-Nebula Central Stars in the Galactic Globular-Cluster
System from HST Imaging and Spectroscopy
- George H. Jacoby et al
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Bulges are red, disks are blue…

Postby bystander » Sat Jan 28, 2017 6:33 pm

Bulges are red, disks are blue…
astrobites | 2017 Jan 24
Mia de los Reyes wrote:
In astronomy, the relationship between the color and the brightness of objects has been used as a basic classification tool for decades. For stars, color is a measure of temperature; the bluer a star, the hotter it is. Measuring the relationship between observed colors and brightnesses of stars helps astronomers figure out the evolutionary sequences of stars.

It turns out that you can do almost the exact same thing for galaxies. Except this time, the color of a galaxy is a measure of how quickly it produces stars, called its star formation rate. This is because hot (and therefore blue) stars are extremely bright, despite being relatively rare, so they can make a whole galaxy appear blue. And such hot stars don’t live for long, so if a galaxy has these stars it must have formed them very recently. On the other hand, the brightness of a galaxy is roughly correlated with its mass, since a more massive galaxy will generally have more stars and therefore be brighter than a less-massive galaxy. ...

Morphology and the Color-Mass Diagram as Clues to Galaxy Evolution at z~1 - Meredith C. Powell et al
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Black Hole Orbits: Zoom-Whirls and Four-Leaf Clovers

Postby bystander » Sat Jan 28, 2017 6:40 pm

Black Hole Orbits: Zoom-Whirls and Four-Leaf Clovers
astrobites | 2017 Jan 25
Lisa Drummond wrote:
Orbits around a black hole can be fascinatingly intricate. Surprisingly, the simple precessing ellipse we observe in planetary motion is not what we see close to a black hole. Rather these orbits exhibit something called “zoom-whirl” behaviour, tracing out patterns that look like four-leaf clovers. The authors concentrate especially on periodic orbits and catalogue these orbits into a “periodic table” according to their main features. ...

A Periodic Table for Black Hole Orbits - Janna Levin, Gabe Perez-Giz
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Supermassive Black Holes Tango in a Distant Quasar

Postby bystander » Sat Jan 28, 2017 6:51 pm

Supermassive Black Holes Tango in a Distant Quasar
astrobites | 2017 Jan 26
Maria Charisi wrote:
In the center of almost every galaxy lives a Supermassive Black Hole (SMBH), i.e. a BH with mass a million to a billion times the mass of our Sun. Throughout the history of the universe, galaxies collide with each other and form new, bigger galaxies. Naturally, the newly formed galaxy will contain two SMBHs in its center, orbiting around each other, i.e. a Supermassive Black Hole Binary (SMBHB) is formed.

Such systems should be fairly common in galactic nuclei as a result of frequent galaxy mergers. However, we rarely observe them and there is a good reason for this. SMBHBs may spend a large fraction of their lifetime (about ten million years) in very close proximity, with orbital separation less than 1 pc (parsec is a typical distance unit in astronomy, equivalent to 3.26 lightyears). Currently, our telescopes do not have the resolution to detect the individual BHs.

Despite this limitation, we can infer the existence of a SMBHB by identifying the effects of a binary in its environment. One such (indirect) method is to detect periodic changes in the brightness/variability of quasars. ...

Relativistic boost as the cause of periodicity in a massive black-hole binary candidate - Daniel J. D'Orazio et al
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Lensed Substructures

Postby bystander » Sat Jan 28, 2017 6:59 pm

Lensed Substructures
astrobites | 2017 Jan 27
Stacy Kim wrote:
Our best model of our universe, Lambda cold dark matter (LCDM for short) predicts that the universe should be bristling with little galaxies. Milky Way, for instance, should be surrounded by hundreds of galaxies at least a thousand times less massive than itself. But we’ve seen only a perplexing few tens of small galaxies around our home galaxy, a conundrum that’s been given its own name, the missing satellites problem. It turns out that dwarf galaxies—those at least a thousand times less massive than the Milky Way—are finicky when it comes to producing stars, as they don’t have much star-forming gas to work with. If you lined up a series of small galaxies identical in mass, you’d find that some teem with stars, shining like beacons in the dark, while others have but a handful, preferring to be veiled in murky darkness. And to make matters more complicated, the least massive galaxies tend to fizzle more often than flare. There may be legions of small, dark galaxies hiding in the universe. ...

Probing dark matter substructure in the gravitational lens HE0435-1223 with the WFC3 grism - A. M. Nierenberg et al
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Larger accretion disks for quasars

Postby bystander » Mon Feb 06, 2017 6:45 pm

Larger accretion disks for quasars
astrobites | 2017 Jan 30
Suk Sien Tie wrote:
Active supermassive black holes, also known as quasars, are “active” because they continuously feed on materials that spiral into them, forming accretion disks. These accretion disks light up the surrounding of the black holes and make them visible ... Intuitively then, how luminous and massive a quasar grows to be must somehow depend on the size and structure of its disk. The properties of the quasar are then believed to affect the evolution of its host galaxy, as suggested by various black hole and host galaxy relations such as the MBH and MBH-Mbulge relations.

But alas, most quasars are simply too far away and their accretion disks far too small for our current telescopes to resolve (i.e. take sharp images of). The handful of size measurements of quasar disks we currently have come mostly from gravitational microlensing, which requires years of monitoring and significant amount of (good) modeling. An alternative and more direct approach to probe the quasar disks is by extracting information from the quasar variability in luminosity. ...

Detection of Time Lags Between Quasar Continuum Emission Bands based on Pan-STARRS Light-curves - Yan-Fei Jiang et al
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Making Discoveries in Your Idle Time

Postby bystander » Mon Feb 06, 2017 6:54 pm

Making Discoveries in Your Idle Time
astrobites | 2017 Jan 31
Michael Zevin wrote:
What is your computer doing right now? Your tablet? Your smartphone? Unless you’re reading this astrobite concurrently on all of your devices, chances are at least one of them is idle – it’s cores yearning for computational endeavors. What if all that processor downtime could instead be utilized to make scientific discoveries? As you may have guessed by my leading questions, it can and it has. ...

Einstein@Home Discovery of a Double-Neutron Star Binary in the PALFA Survey - P. Lazarus et al

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Discovery of Water on 51 Peg b

Postby bystander » Mon Feb 06, 2017 7:01 pm

Discovery of Water on 51 Peg b
astrobites | 2017 Feb 01
Joseph Schmitt wrote:
51 Peg b was the first exoplanet ever discovered orbiting another main sequence star (51 Peg). This Jupiter-sized planet, found orbiting in a 4 day orbit, revolutionized astronomy and upended our understanding of planet formation. It was discovered by measuring the star’s spectrum and seeing periodic shifts in the star’s radial velocity. This radial velocity shift was caused by the planet gravitationally pulling on the star, which indirectly proves the existence of the planet. However, even early on, it was realized that astronomers should be able to see a similar radial velocity shift in the light reflected by the planet. Critically, this method could used to determine the planet’s inclination, mass, and atmospheric composition, properties that would otherwise be near impossible to measure. First used in 2010, it has now been used on several hot Jupiters. ...

Discovery of water at high spectral resolution in the atmosphere of 51 Peg b - J. L. Birkby et al
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Anisotropies in our galaxy

Postby bystander » Mon Feb 06, 2017 7:07 pm

Anisotropies in our galaxy
astrobites | 2017 Feb 02
Kelly Malone wrote:
One of the big unsolved mysteries in particle astrophysics is the origins and acceleration mechanisms of cosmic rays, or charged particles that are constantly bombarding the Earth. It is impossible to tell which astronomical source is the origin of any one particular cosmic ray. Because cosmic rays are charged particles, they are deflected on their way to Earth by the Galactic magnetic field. Due to this effect, one might expect cosmic rays to arrive isotropically (in equal numbers in every direction), with slight anisotropy because of diffusion effects. However, that is not what is observed. Instead, there is a large-scale anisotropy with an energy-dependent amplitude. This causes problems for traditional diffusion models. Studying this anisotropy is important in learning more about cosmic rays.

Today’s bite uses roughly five years of data from the Tibet Air Shower experiment, located at 4300 meters above sea level in Tibet, to provide an update in the study of the cosmic ray anisotropy. ...

Northern sky Galactic Cosmic Ray anisotropy between 10-1000 TeV
with the Tibet Air Shower Array
- Tibet AS-gamma Collaboration, M. Amenomori
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The Sloan Digital Sky Survey: A Legacy

Postby bystander » Mon Feb 06, 2017 7:18 pm

The Sloan Digital Sky Survey: A Legacy
astrobites | 2017 Feb 03
Gourav Khullar wrote:
The story today begins with the Princeton astronomer James Gunn, who in the 1980s was well aware of the advancements in optical detector technologies and processing power in computers that could analyse gigabytes of data. Gunn, who was famous for predicting the Gunn-Peterson trough in the spectra of distant quasars, dreamt of a next generation telescope that would point to the sky and look at the ensemble of objects that adorn it – the cosmic web of galaxies! This dream would bring together physicists, engineers, computer scientists and astrophysicists in a rapidly changing community to create a legacy that was going to change the field as we knew it.

The product? The Sloan Digital Sky Survey. ...

The Sloan Digital Sky Survey: Technical Summary - D. G. York et al (SDSS Collaboration)
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