astrobites 2017

Find out the latest thinking about our universe.
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A black hole with kick

Postby bystander » Fri Sep 15, 2017 7:08 pm

A black hole with kick
astrobites | 2017 Sep 11
Eckhart Spalding wrote:
... The authors finish by offering up an interesting possible formation mechanism. This black hole is far too massive to have been generated upon the death of a massive star, but it may have formed from stellar mergers. If that’s the case, then it should take an entire dwarf galaxy to produce a black hole so massive. Given the dozens of dwarf galaxies drifting around the Milky Way in various stages of cannibalization, the authors suggest that we may be seeing the black hole remnant of a long-lost dwarf galaxy.

This means that IMBHs could represent signatures of the Milky Way’s galactic merger history which has already been erased in the kinematics of stars, and further discoveries could also indicate the likelihood that Sgr A* is itself the product of stellar mergers.

Millimetre-Wave Emission from an Intermediate-Mass Black Hole Candidate in the Milky Way - Tomoharu Oka et al

viewtopic.php?t=37548
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Can gas giant planets form through pebble accretion?

Postby bystander » Fri Sep 15, 2017 7:43 pm

Can gas giant planets form through pebble accretion?
astrobites | 2017 Sep 13
Michael Hammer wrote:
Do you know how gas giant planets form in a protoplanetary disk? It all starts with a bunch of planetesimals (km-sized and above) that collide together one-by-one until they grow into an object that is the largest in the neighborhood. As the biggest object in its vicinity, this protoplanet core will naturally continue to collect and accrete more planetesimals until it consumes everything nearby. Eventually, the core will grow large enough to build up a significant atmosphere from the gas that makes up the disk. Once its atmosphere becomes more massive than the core itself, it will become unstable and devour a ton more gas — thereby growing to roughly Jupiter’s size.

If anyone tells you they know how gas giants form and provides an explanation of the process (like I did above), it might be a good idea to ask them: How long does that process take? Protoplanetary disks – a gas giant’s source of gas – only live about 3 million years on average. Yet, the original model (a classic paper by Pollack et al. from 1996) for this process (called core accretion) suggested it should take 8 million years. While recent improvements to the model have proposed ways to accelerate this process, it is still an open question as to how to speed up core accretion so that it can create Jupiter-mass planets before the disk fades away ...

How cores grow by pebble accretion - M.G. Brouwers, A. Vazan, C.W. Ormel
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WFIRST: Exploring the Solar System

Postby bystander » Fri Sep 15, 2017 7:50 pm

WFIRST: Exploring the Solar System
astrobites | 2017 Sep 14
Elisabeth Matthews wrote:
WFIRST is one of NASA’s key missions for the next decade. The mission is a 2.4m space telescope that will operate in the infrared, and include coronagraphic, spectroscopic, and wide field imaging functionalities, and will be launching in 2025 or 2026, for a 6-year nominal mission. That means the telescope should be functional for at least 6 years, and may well be extended if there is sufficient demand from the community. The key goals of the mission are to (a) answer fundamental questions about dark energy, (b) carry out a microlensing survey to assess exoplanet frequency across a wide stretch of parameter space and (c) directly image Earth-sized exoplanets around nearby stars.

However, in today’s post we’re going to take a slightly different angle: we’ll be looking at a white paper that’s recently been published, discussing the potential of the instrument for Solar System science. There are a huge range of solar system applications for the instrument, and today’s bite will be by no means exhaustive. We’ll be going on a whistle-stop tour of some possible science projects and just begin to whet your appetite for the exciting Solar System science WFIRST might carry out. ...

Solar System Science with the Wide-Field InfraRed Survey Telescope (WFIRST) - B.J. Holler et al

viewtopic.php?t=35659
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The First Pulsar

Postby bystander » Fri Sep 15, 2017 7:57 pm

The First Pulsar
astrobites | 2017 Sep 15
Joshua Kerrigan wrote:
Today’s summary of a classical and significant paper highlights an important event in radio astronomy. This event results in two astronomers receiving the Nobel Prize while creating some much deserved controversy. It primarily involves three astronomers, Antony Hewish, Jocelyn Bell, and Martin Ryle. Both Hewish and Ryle were the eventual awardees of the 1974 Nobel Prize in Physics for the combined discovery of the first pulsar and development of aperture synthesis for radio telescopes which is described below. ...

Observation of a Rapidly Pulsating Radio Source - A. Hewish et al
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Re: The First Pulsar

Postby MargaritaMc » Sat Sep 16, 2017 6:04 pm

bystander wrote:The First Pulsar
astrobites | 2017 Sep 15
Joshua Kerrigan wrote:
Today’s summary of a classical and significant paper highlights an important event in radio astronomy. This event results in two astronomers receiving the Nobel Prize while creating some much deserved controversy. It primarily involves three astronomers, Antony Hewish, Jocelyn Bell, and Martin Ryle. Both Hewish and Ryle were the eventual awardees of the 1974 Nobel Prize in Physics for the combined discovery of the first pulsar and development of aperture synthesis for radio telescopes which is described below. ...

Observation of a Rapidly Pulsating Radio Source - A. Hewish et al


https://youtu.be/DCPereT6XxU ( sorry - I can't get the video to embed)
Published on 22 Jun 2015
Jocelyn Bell Burnell in Conversation at the 2015 Edinburgh International Science Festival
Today Prof Jocelyn Bell Burnell is known as one of the most influential scientists in the UK. But getting there was not easy. From girls not being taught science at her secondary school to being greeted to university by rooms full of howling men, her journey is one fraught with resistance. Her discovery of radio pulsars in 1967, as a young researcher at Cambridge, pays testament to her dogged pursuit of the truth and remains one of the most significant astronomical discoveries of the last 100 years.

Here she discusses her incredible career, as well as her thoughts on the future of science and its place in society in conversation with Andrew Cohen, Head of Science at the BBC.

"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
— Dr Debra M. Elmegreen, Fellow of the AAAS

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Biography of a Galaxy

Postby bystander » Fri Sep 22, 2017 2:58 pm

Biography of a Galaxy: Uncovering Star Formation Histories
astrobites | 2017 Sep 18
Christopher Lovell wrote:
Every galaxy has a story to tell. And every story has a few common plot devices: violent supernovae from dying young stars, bursts of activity from central supermassive black holes, mergers with other galaxies, and other dramatic astrophysical events that can change the course of a galaxies evolution. One galaxy property in particular can be severely impacted by these events, and that’s how many stars it is forming at a given time. The Star Formation Rate (SFR) throughout the lifetime of a galaxy is known as its Star Formation History (SFH), and is of interest to physicists trying to understand the lives of all galaxies.

Unfortunately, we can only see the stars that are in the galaxy at any given time; to infer the past history of star formation we must look for evidence of previous star forming events. For nearby galaxies, we can see them in enough detail to see separate populations of stars, and determine their individual ages. But for galaxies further away we can only observe the combined light of all the stars mixed together, and then have to disentangle each component in order to get the underlying history of star formation.

However, in simulations of galaxies we can explicitly see the SFH in high resolution (see these ‘bites for previous examples). The authors of today’s paper looked at galaxies in the state-of-the-art Illustris simulation. They found that, whilst SFHs tend to be noisy, on average they show similar shapes over time. This shape is known as the log-normal distribution, and it typically exhibits a sharp rise to a peak, then a gradual fall. ...

Log-normal Star Formation Histories in Simulated and Observed Galaxies - Benedikt Diemer et al
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Checking up on Circumstellar CO

Postby bystander » Fri Sep 22, 2017 3:15 pm

Checking up on Circumstellar CO
astrobites | 2017 Sep 19
Jamila Pegues wrote:
We can all acknowledge that stars are some of the coolest objects (figuratively speaking) in the Milky Way galaxy. But today we consider something even cooler (literally speaking): the envelopes of certain stars.

Today’s astrobite looks at modeling carbon monoxide (aka, CO) in the envelopes, or layers of shells of gas, around evolved stars (hence the name circumstellar envelopes; check out this astrobite for some more discussion!). CO is pretty infamous enough here on Earth, but it’s also famous in space for an entirely different reason: it’s actually the second-most abundant known molecule (after molecular hydrogen, H2). CO plays a crucial role in the envelopes surrounding evolved stars – and so understanding how CO is distributed in these circumstellar envelopes can help us understand the chemistry of these systems overall. ...

The Photodissociation of CO in Circumstellar Envelopes - M.A.T. Groenewegen
The Photodissociation of CO in Circumstellar Envelopes - G. A. Mamon, A. E. Glassgold, P. J. Huggins
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Taking the training wheels off

Postby bystander » Fri Sep 22, 2017 3:57 pm

Taking the training wheels off
astrobites | 2017 Sep 21
Mia de los Reyes wrote:
In 2007, astronomers realized that they had a bit of a problem. The Sloan Digital Sky Survey had observed over a quarter of the sky, obtaining images of a million galaxies. This enormous dataset showed immense promise, especially in helping scientists understand the incredible diversity of galaxy populations… except for the fact that the galaxies first needed to be classified into different morphologies (e.g., spiral vs elliptical galaxies). ...

Is there a way to fully automate galaxy morphology, without requiring any sort of human input? The authors of today’s paper, headed by a computer scientist, present such an “unsupervised machine learning” method that identifies and classifies galaxies from survey images. ...

An automatic taxonomy of galaxy morphology using unsupervised machine learning - Alex Hocking et al
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Detecting hot gas in the cosmic web

Postby bystander » Fri Sep 22, 2017 4:08 pm

Detecting hot gas in the cosmic web
astrobites | 2017 Sep 22
Suk Sien Tie wrote:
Baryons or normal matter comprise only a tiny fraction (~5%) of the total density of the Universe. However, this does not stop them from playing hide-and-seek with astronomers. Even after subtracting off the baryons locked up in stars, the interstellar medium, and hot gas in galaxy clusters, we are still missing 50% of the baryons. Simulations suggest that most of the “missing baryons” could be in the form of low-density warm-hot gas that threads the cosmic web between galaxy clusters, known as the warm-hot intergalactic medium (WHIM). The cosmic web is an invisible network of dark matter filaments that form the backbone of the large scale structures of the Universe, as illustrated on the front page of today’s article by The Millennium Simulation Project (see this Astrobites post for a detection of a dark matter filament). The low-density of the WHIM makes them very difficult to detect, with only a handful of non-definitive detections in the UV and X-rays. Since we cannot directly observe the WHIM with current telescopes, we need to infer their existence through indirect means. ...

A Search for Warm/Hot Gas Filaments between Pairs of SDSS Luminous Red Galaxies - Hideki Tanimura et al
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Counting the Dwarf Galaxies of the Milky Way

Postby bystander » Fri Sep 29, 2017 5:31 pm

Counting the Dwarf Galaxies of the Milky Way
astrobites | 2017 Sep 25
Stacy Kim wrote:
Our home galaxy, the Milky Way, is surrounded by small, “dwarf” galaxies. Astronomers are obsessed with counting how many exist. Why? In the 1990s, we realized that the prevailing view of the universe as one primarily composed of dark energy and dark matter, called LCDM for short, predicts that the Milky Way should be surrounded by a vast horde of at least a hundred. But perplexingly, we saw only 11 dwarf galaxies. This stark discrepancy has fueled much consternation and many papers, and has been dubbed the “missing satellites problem.” ...

To determine the true number of dwarfs in the Milky Way, the authors of today’s paper attempted to correct for the number we can’t see. This is called a “completeness correction.”

To do this, the authors turned to the Aquarius Project, a simulation suite with six realizations of the Milky Way, each run with dark matter only and thus without the bright disk of stars and gas that make up the familiar, visible portion of the galaxy (which only makes up about a fifth of the mass of the galaxy, anyway). ...

And what did they find? The Milky Way should host about 108-195 total dwarfs. It thus looks like the missing satellites problem might not be so bad after all. ...

The Total Satellite Population of the Milky Way - Oliver Newton et al
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Is S0-2 a Binary Star?

Postby bystander » Fri Sep 29, 2017 5:41 pm

Is S0-2 a Binary Star?
astrobites | 2017 Sep 26
Philipp Plewa wrote:
The most exciting discoveries in astronomy all have something in common: They let us marvel at the fact that nature obeys laws of physics. The discovery of S0-2 is one of them. S0-2 (also known as S2) is a fast-moving star that has been observed to follow a full elliptical, 16-year orbit around the Milky Way’s central supermassive black hole, precisely according to Kepler’s laws of planetary motion. Serving as a test particle probe of the gravitational potential, S0-2 provides some of the best constraints on the black hole’s mass and distance yet, being the brightest of the S-stars, which are a group of young main-sequence stars concentrated within the inner 1” (0.13 ly) of the nuclear star cluster.

The next time S0-2 will reach its closest approach to the black hole, in 2018, there will exist a unique opportunity to detect a deviation from Keplerian motion, namely the relativistic redshift of S0-2’s radial (line-of-sight) velocity, in a direct measurement. In anticipation of this event, the authors of today’s paper investigate possible consequences of S0-2 not being a single star, but a spectroscopic binary, which would complicate this measurement. ...

Investigating the Binarity of S0-2: Implications for its Origins and Robustness
as a Probe of the Laws of Gravity around a Supermassive Black Hole
- Devin S. Chu et al

viewtopic.php?t=29693
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Looking beyond the James Webb Space Telescope

Postby bystander » Fri Sep 29, 2017 6:04 pm

Looking beyond the James Webb Space Telescope
astrobites | 2017 Sep 27
Amber Hornsby wrote:
One of the best things about being a scientist today is being part of a huge, supportive community. Through the sharing of ideas at conferences all over the world and through the publication of scientific papers on sites like arXiv, unlikely collaborations are formed. This often results in a better scientific output. Moreover, in an age where the costs of cutting-edge facilities and ground-breaking space missions have crept over into the billions, global cooperation and collaboration are vital if we are going to keep pushing the frontier of what we know about our pale blue dot and the universe which engulfs it. Today’s bite focuses on a recent workshop, hosted by the International Astronomical Union (IAU), held to discuss the future of space-based Ultraviolet-Optical-Infrared (UVOIR) telescopes, more specifically the main scientific motivation for such a telescope and how it fits into the long-term plans for space missions. ...

Report of the Kavli IAU Workshop on Global Coordination:
Future Space-Based Ultraviolet-Optical-Infrared Telescopes
- Debra Elmegreen et al

Recommendations from IAU Workshop on Future Space-Based Telescopes
International Astronomical Union | 2017 Sep 21
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An Answer to LIGO’s Low-Mass Black Hole Woes

Postby bystander » Fri Sep 29, 2017 6:30 pm

An Answer to LIGO’s Low-Mass Black Hole Woes
astrobites | 2017 Sep 28
Thankful Cromartie wrote:
As our readers likely know, the LIGO Scientific Collaboration made history in September 2015 with the first direct detection of gravitational waves. Since the historic initial detection, there have been several more measurements of binary black hole (BBH) mergers (including one announced yesterday!). Today’s astrobite explores a strange question arising from the initial LIGO results: why were the BBH sources much less massive than LIGO’s sensitivity suggests they could be? Though four detections aren’t necessarily representative of an entire BBH population, it turns out that some statistically significant information can still be gleaned from just a few sources.

For its two most recent observing runs, LIGO was technically capable of detecting BBH mergers with individual BH masses up to 100 times the mass of the sun (M); however, the largest component masses measured were only 36 and 29 M (fortuitously coming from the first detection — GW150914). As it turns out, binaries with one component of at least 40 M comprise more than 90% of the volume of theoretical detections available to LIGO during that time. How is it possible that we didn’t see any massive BBH coalescence events? The authors of today’s paper (succinctly titled, “Where are LIGO’s Big Black Holes?”) suggest the presence of a gap in the expected distribution of BH masses. ...

Where are LIGO's Big Black Holes? - Maya Fishbach, Daniel E. Holz
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A long hunt for titanium oxide in hot Jupiters

Postby bystander » Fri Sep 29, 2017 6:48 pm

A long hunt for titanium oxide in hot Jupiters
astrobites | 2017 Sep 29
Shang-Min Tsai wrote:
Hot Jupiters are the earliest discovered and the most studied class of exoplanets. They have a comparable size to that of Jupiter and orbit very close to their stars (typically < 0.1 AU). Many studies have been attributed to understanding the dynamics and the composition of their atmospheres, with some mysteries still unsolved, such as the inflated size (e.g. bite1, bite2). The authors of today’s paper announced the exciting news of finding titanium oxide (TiO) in the atmosphere of a hot Jupiter, WASP-19b. ...

Detection of Titanium Oxide in the Atmosphere of a Hot Jupiter - Elyar Sedaghati et al

viewtopic.php?t=37558
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The Science of the Next Generation

Postby bystander » Sat Oct 07, 2017 3:28 pm

The Science of the Next Generation
astrobites | 2017 Oct 02
Kelly Malone wrote:
Today’s document shows the far-reaching goals of the next-generation gamma-ray experiment, the Cherenkov Telescope Array (CTA). Gamma rays are important probes of cosmic rays, charged particles of which the origins and acceleration mechanisms are still unknown. Over the course of a hefty 211 pages and representing years of work, the authors explain the science goals of this experiment, which will greatly enhance our knowledge of the universe when it comes online in a few years. ...

CTA Releases its Updated Science Case
Cherenkov Telescope Array Press Release | 2017 Sep 27

Science with the Cherenkov Telescope Array - Cherenkov Telescope Array Consortium
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Future Gamma-ray Telescopes and the Search for Dark Matter

Postby bystander » Sat Oct 07, 2017 3:41 pm

Future Gamma-ray Telescopes and the Search for Dark Matter
astrobites | 2017 Oct 03
Nora Shipp wrote:
We are surrounded by undetected dark matter. In fact, our entire Galaxy is enveloped in a large halo of it, but because dark matter does not emit or reflect light, the halo is completely invisible. Inside this halo, orbiting our galaxy, are hundreds of smaller, equally invisible dark matter halos (Figure 1). The larger ones contain their own dwarf galaxies, but the smallest halos are so tiny that they contain no stars at all. However, if the leading theory of WIMP (Weakly Interacting Massive Particle) dark matter is correct, there is one way that we could actually see these dark matter halos without the help of any stars. If dark matter particles are their own antiparticle, they would annihilate when they come into contact with each other, producing various particles, including highly energetic photons known as gamma-rays. ...

Two sources of gamma-rays fit all the requirements – they are in the right part of the sky, do not emit any other kind of light (as you’d expect from a halo containing only dark matter), and appear to extend wider across the sky than the single point of a far away star. However, it’s impossible to tell whether these sources are really extended like a dark matter halo or whether they are just two star-like points so close to each other that they blur together, appearing to Fermi as a single blob. Today’s paper considers whether a proposed successor to Fermi called e-ASTROGAM will be able to resolve the mystery of these gamma-ray blobs. Are they in fact dark matter halos (in which case this would be the first confirmed detection of dark matter annihilation!) or are they simply two points blurred into one? ...

Resolving Dark Matter Subhalos With Future Sub-GeV Gamma-Ray Telescopes - Ti-Lin Chou, Dimitrios Tanoglidis, Dan Hooper
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How Plural are Singularities?

Postby bystander » Sat Oct 07, 2017 3:47 pm

How Plural are Singularities?
astrobites | 2017 Oct 04
Bhawna Motwani wrote:
Only a short while ago, in September 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) made its maiden detection of the ripples travelling in spacetime, known as gravitational waves. The detection of these waves, a key prediction made by the Einstein’s Theory of General Relativity, has since revolutionalised the field of astronomy by presenting a novel avenue for us to understand the workings of the ever-so-elusive-and-vast cosmos.

In the discovery that LIGO made, it sensed the gravitational waves created by the merger of two distant black holes, each about as massive as 30 Suns. For scientists specializing in black hole physics, as well as others with a keen excitement about the field, this event immediately triggered the question: how many more events will we see, and how often?

Motivated by this curiosity, the authors of today’s paper have analyzed the gravitational wave signals from the first three binary black hole mergers detected by LIGO, and developed an understanding of their characteristics in the context of our current knowledge about galaxy formation. Based on what we know about the formation of stars, the relationship between their ages/metallicities and the mass of their host galaxy, as well the overall number density of galaxies in our universe, the authors infer the age and mass distribution of black holes in different types of galaxies. In their study, however, they assume that the extant population of black holes is attained solely from the death of massive stars, and does not feature any primordial black holes, allowing them to make confident estimates from reasonably well quantified galaxy observables. ...

Counting Black Holes: The Cosmic Stellar Remnant Population
and Implications for LIGO
- Oliver D. Elbert, James S. Bullock, Manoj Kaplinghat

viewtopic.php?t=37464
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Nuclear Pasta in Neutron Stars

Postby bystander » Sat Oct 07, 2017 3:59 pm

Nuclear Pasta in Neutron Stars
astrobites | 2017 Oct 05
Lisa Drummond wrote:
Neutron stars are the densest objects in the universe. Naturally, the matter inside of them is exotic and unlike anything on Earth — imagine squashing the mass of our Sun into a star only 10 km across! As one might guess from their name, neutron stars are comprised of mostly neutrons, with a small fraction of electrons and protons also contributing to their mass. A neutron star can be thought of as analogous to a giant atomic nucleus, bound by gravitational forces rather than the strong force. Under the pressure exerted by gravity, matter is compressed to the same density as the nuclei of atoms; properties of the high density matter in neutron stars are discussed in this bite. ...

Under the extreme, high-density conditions inside a neutron star, the competition between nuclear attraction and Coulomb repulsion yields exotic structures called nuclear pasta. Ravenhall, Pethick, and Wilson were the first to investigate these unusual configurations of nuclear matter. Nuclear pasta is characterised by complex, non-spherical patterns such as tubes, sheets and bubbles; these configurations minimize their energy (see Figure 2). The name “nuclear pasta” arose due to a resemblance to different varieties of pasta — such as lasagna, gnocchi and spaghetti! ...

In this paper, the authors conduct semi-classical molecular dynamics simulations of nuclear pasta. The semi-classical approach is justified because the relevant behaviours involve clusters of thousands of nucleons and these heavy clusters can be treated classically. The quantum effects present at smaller scales are put in by hand through the parameters in the semi-classical model. ...

Astromaterial Science and Nuclear Pasta - M. E. Caplan, C. J. Horowitz
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First detection of an equatorial jet on Venus

Postby bystander » Sat Oct 07, 2017 4:13 pm

First detection of an equatorial jet on Venus
astrobites | 2017 Oct 06
Kerrin Hensley wrote:
Venus’ thick atmosphere is full of surprises. Our nearest planetary neighbor (between 0.28 and 1.72 astronomical units away, depending on the time of year), Venus has been visited by over a dozen spacecraft. The fleet of past and present Venusian spacecraft have revealed sulfuric acid clouds, a surprising lack of a global magnetic field, and a young surface studded with sprawling mountains but devoid of any Earthly plate tectonics. Chief among the oddities discovered at Venus is its ferociously fast atmosphere; though Venus rotates sluggishly, just once per 243 Earth days, its atmosphere whips around much more quickly—the speediest layer, at an altitude of about 70 km, takes only a few days to circle the planet. This phenomenon is called superrotation. Although Venus’ atmospheric superrotation was discovered in the 1960s, the cause is still debated. What, then, makes Venus’ atmosphere go ‘round?

The newest of the Venusian spacecraft, Japan’s Akatsuki orbiter, is equipped to study the atmosphere of Venus and may help to answer this question. Slated to arrive at Venus in 2010, Akatsuki initially missed its target and spent a few years orbiting the Sun before achieving orbital insertion at Venus in 2015. In its brief time at Venus, Akatsuki has observed the dynamics of Venus’ atmosphere, including a planet-wide gravity wave (not to be confused with a gravitational wave!) shortly after arrival.

In today’s paper, the authors study atmospheric dynamics on Venus using near-infrared images from the Akatsuki orbiter. Specifically, they observe the silhouettes of clouds against the background of thermal radiation from the planet’s night-side surface. They then use an automated cloud-tracking method to determine the wind speeds in the lower and middle cloud layers. ...

Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki - Takeshi Horinouchi et al
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Training Deep Neural Networks

Postby bystander » Fri Oct 13, 2017 6:40 pm

Training Deep Neural Networks, or the Unexpected Virtue of Ignorance
astrobites | 2017 Oct 09
Emily Sandford wrote:...
Today’s authors, who are computer scientists and neuroscientists, offer a new insight into what’s going on under the hood while a neural network trains to do a task like recognize images. This training seems to proceed in two phases: a fast first stage when the network connects every possible detail of the input data to the output, and then a slower second stage where it forgets some of those connections. ...

Opening the Black Box of Deep Neural Networks via Information - Ravid Shwartz-Ziv, Naftali Tishby
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A Neptune in the Nearby Hyades

Postby bystander » Fri Oct 13, 2017 6:49 pm

A Neptune in the Nearby Hyades
astrobites | 2017 Oct 10
Mara Zimmerman wrote:
The authors of today’s paper report the discovery of a Neptune-sized planet in the nearby Hyades Cluster around a binary star. A binary is just two stars mutually orbiting their center of gravity; the larger star is called the primary and the smaller is the secondary. In a close binary where the stars are separated only by a short distance, the two stars affect the evolution and size of each other. Planets in binaries have to survive in an extreme environment for an incredibly long time. This binary system is referred to as EPIC 247589423 (also called LP 358-348), but the primary and secondary stars within this system are called K2-NnnA and K2-NnnB, respectively. Since this planet was discovered orbiting just the primary star, the authors of this paper have decided to refer to it as K2-NnnA b: exoplanets are generally named after their host star and then have another letter added to the end. However, this planet does not yet officially have a name, so there is hope that it will be called something that rolls off the tongue a bit more easily. ...

K2-nnnA~b: A Binary System in the Hyades Cluster Hosting a Neptune-Sized Planet - David R. Ciardi et al
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A Helium-Powered Supernova

Postby bystander » Fri Oct 13, 2017 6:57 pm

A Helium-Powered Supernova
astrobites | 2017 Oct 11
Matthew Green wrote:...
Today’s paper is about a supernova called MUSSES1604D, which was first detected in April 2016. It was discovered by a survey using the impressively named Hyper Suprime-Cam instrument (a camera which is larger than a person and heavier than the average car). This survey is optimised towards finding supernovae in the first few days after they start, while their brightness is still shooting up. While the team were watching MUSSES1604D it did several interesting things. Firstly it showed signs of what they call an ‘early flash’: an initial period in which the supernova was growing brighter, after which it seemed to either stall or fade in brightness for several days before continuing to brighten. Secondly, during this early flash the supernova turned very red, before becoming blue again during the main explosion. ...

A hybrid type Ia supernova with an early flash triggered by helium-shell detonation - Ji-an Jiang et al

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Illusion and Reality

Postby bystander » Fri Oct 13, 2017 7:12 pm

Illusion and Reality
astrobites | 2017 Oct 12
Eckhart Spalding wrote:
In discussions of exoplanet atmospheres, variations of the word “illusion” come up a lot. They pop up 27 times in today’s sobering article, which takes stock of the current state of knowledge and observational techniques. The fact is, real science is much messier than the popular image of science as a streamlined and systematic process of establishing truths. Despite scientists’ best efforts, published results sometimes turn out to be illusions.

This has certainly been the case in the field of exoplanet atmospheres, where the observational signals are extremely small, often measured in hundreds of parts-per-million or less. They are usually made using detectors that were never built with exoplanets in mind, and faint signals have to be sieved painfully from the fuzz of detector noise. Furthermore, sources of systematic error have been poorly understood, as one might expect in any new field. This has led to a litany of published results which have later vanished like a mirage. ...

Illusion and Reality in the Atmospheres of Exoplanets - Drake Deming, Sara Seager
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The Hubble Constant(s)

Postby bystander » Fri Oct 13, 2017 8:34 pm

The Hubble Constant(s)
astrobites | 2017 Oct 13
Emily Sandford wrote:...
Until about 2010, it looked like the CMB and galaxy estimates of H0 were both going to converge to the same answer. But as both types of experiment became more precise, their uncertainty bands overlapped less and less. Today’s paper is a commentary–Wendy Freedman, a cosmologist who has made major contributions to the galaxy-side measurement of H0, raising her eyebrow at this situation. ...

Cosmology at at Crossroads: Tension with the Hubble Constant - Wendy L. Freedman
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Re: The Hubble Constant(s)

Postby Ann » Sat Oct 14, 2017 4:50 am

bystander wrote:The Hubble Constant(s)
astrobites | 2017 Oct 13
Emily Sandford wrote:...
Until about 2010, it looked like the CMB and galaxy estimates of H0 were both going to converge to the same answer. But as both types of experiment became more precise, their uncertainty bands overlapped less and less. Today’s paper is a commentary–Wendy Freedman, a cosmologist who has made major contributions to the galaxy-side measurement of H0, raising her eyebrow at this situation. ...

Cosmology at at Crossroads: Tension with the Hubble Constant - Wendy L. Freedman


This is indeed incredibly interesting.

I note that an overall tendency of both the CMB and the galaxy estimates is that the Hubble constant has been decreasing somewhat, though a lot more in the CMB measurements than in the galaxy estimates.

Could a non-constant dark energy "constant" explain the disagreements? Or is it possible that the more we learn about the Universe, the lesser the need for a mysterious dark energy contributor becomes? Or is that, too, wishful thinking?

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