astrobites: Daily Paper Summaries 2019

Find out the latest thinking about our universe.
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It’s Getting Hot, Hot, Hot With Coronal Loops

Post by bystander » Tue Apr 30, 2019 1:38 pm

It’s Getting Hot, Hot, Hot With Coronal Loops
astrobites | Daily Paper Summaries | 2019 Apr 29
Ellis Avallone wrote:
The coronal heating problem is one of the biggest unsolved mysteries in solar physics. The solar corona is the region of the Sun’s atmosphere that extends past the surface – or photosphere – of the Sun. It is a diffuse cloud of plasma that is heated to temperatures several hundred times that of the photosphere, which isn’t what you’d expect as you move further away from a hot object. The coronal heating problem has been hotly debated since the 1940s and is thought to be related to the Sun’s magnetic field. However, no theory has yet been able to explain why the corona is so much hotter than the photosphere, and the possibility remains that multiple processes may be at work.

To study coronal heating, solar physicists use various structures that operate on smaller scales. The authors of today’s paper focus on the heating processes of coronal loops, which occur when plasma in the corona flows along the solar magnetic field (Figure 2). Coronal loops are rooted in strong concentrations of magnetic field such as sunspots – dark patches in the solar photosphere. Sunspots are composed of two regions, a dark umbra and a surrounding penumbra (Figure 3), that are surrounded by a bright region called a plage. Understanding how coronal loops are linked to their sunspot footprints and the surrounding magnetic field is critical to determining the heating mechanisms at work. ...

New Evidence that Magnetoconvection Drives Solar–Stellar Coronal Heating ~ Sanjiv K. Tiwari et al
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Start of a New Era: The One of Cold Dark Matter

Post by bystander » Tue Apr 30, 2019 2:10 pm

Start of a New Era: The One of Cold Dark Matter
astrobites | Daily Paper Summaries | 2019 Apr 30
Islam Kahn wrote:
Thanks to Vera Rubin, the “missing” baryonic matter, now known as Dark Matter (DM), was discovered in the late 1970s by observing rotation curves of galaxies. These rotation velocities did not decrease as rapidly with increasing radius of the galaxies as predicted based on the light coming from them. DM was proposed to make up for the missing mass that is responsible for these flat rotation curves. While it is still unknown what DM is, we now know it accounts for about 24% of the universe and it played a big part in the formation of structures in the universe such as stars, galaxies, galaxy clusters, and superclusters. By 1984, it was already evident that the dark matter in our universe has at least ten times more mass compared to that of baryonic (visible) matter. Dark matter was hypothesized to be hot, cold or warm. Temperature of particles is directly correlated to their speed, and as the names suggest, the hotter the DM, the faster these particles are moving. Why do we mostly hear about cold dark matter (CDM) and not the other types? You’ve guessed it! It’s because CDM prevailed and today’s paper goes to great lengths to convince you that the universe is dominated by CDM. ...

Formation of Galaxies and Large-Scale Structure with Cold Dark Matter ~ George R. Blumenthal et al
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On the verge of revealing a singularity

Post by bystander » Fri May 03, 2019 3:06 pm

On the verge of revealing a singularity
astrobites | Daily Paper Summaries | 2019 May 01
Jatan Mehta wrote:
Black holes are regions of space-time exhibiting gravitational effects so strong that not even light, the fastest thing in the Universe, can escape from inside them. Typical black holes are formed when a giant star collapses under its own gravity, crushing its entire mass to a single point called the singularity. A singularity cannot be seen directly because light cannot escape from the region around it, resulting in a black hole.

For all their mysteriousness, all black holes can in fact be described using just three values: mass, spin, and charge. The masses of many black holes have been inferred by observing how objects orbit them. The most popular example is Sagittarius A*, the supermassive black hole at the Milky Way’s center. Using the orbits of stars around a point in space, the black hole has been measured to weigh about four million solar masses. A black hole’s spin is however more difficult to infer. So far, only six black holes have had their spins measured, including the subject black hole of an earlier Astrobite post and the new result we’ll talk about today. ...

AstroSat and Chandra View of the High Soft State of 4U 1630–47 (4U 1630–472):
Evidence of the Disk Wind and a Rapidly Spinning Black Hole
~ Mayukh Pahari et al
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Cepheid yourself – confirming tensions in the Hubble expansion

Post by bystander » Fri May 03, 2019 3:31 pm

Cepheid yourself – confirming tensions in the Hubble expansion
astrobites | Daily Paper Summaries | 2019 May 02
Sunayana Bhargava wrote:
Hubble’s law tells us that all galaxies, stars and planets are moving away from each other, and the more distant the object, the faster it is moving away. We quantify this expansion as a speed per distance, which gives us a unit like km/s (speed) per megaparsec (distance). This value is known as the Hubble constant, or H0.

The Hubble constant has been determined using various methods. However, two of these titan measurements disagree with each other in a way that astronomers deem significant. ...

Today’s authors stir the Hubble cauldron a bit more with 70 space-based observations of Cepheid variables in the Large Magellanic Cloud (LMC) from the Hubble Space Telescope. ...

Large Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination
of the Hubble Constant and Stronger Evidence for Physics Beyond ΛCDM
~ Adam G. Riess et al
viewtopic.php?t=39378
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Thats no exomoon… or is it?

Post by bystander » Tue May 07, 2019 9:23 pm

Thats no exomoon… or is it? A careful evaluation of evidence for Kepler-1625b-i
astrobites | Daily Paper Summaries | 2019 May 06
Oliver Hall wrote:
If we’ve found so many planets, why haven’t we found any moons? It is now widely accepted that there are more planets than stars. In our own solar system moons outnumber planets 12 to 1 (and thats only the moons we know of!). By extension, it would make sense for moons to exist around exoplanets. However it is hard enough to find exoplanets at all. Finding an exomoon, then, is even more difficult, and requires the most precise measurements available.

A first candidate for an exomoon was put forth back in a 2018 paper (hereafter T18) by today’s authors. The moon-like signal was first noticed in Kepler space telescope data of the gas-giant Kepler-1625b, which itself orbits in the habitable zone of its sun-like parent star. When observing the planetary transit of Kepler-1625b, the authors noticed a second, fainter transit trailing the planetary transit, as if it was being followed by a smaller object, such as an exomoon! The authors followed up with observations from the Hubble Space Telescope (HST), which is four times more precise than Kepler. Using HST, they found a clearer moon-like transit signal, and also noticed that the planetary transit occured 77.8 minutes earlier than expected. This change in transit time is called a ‘Transit Timing Variation‘ (TTV), and is indicative of another mass in the system, be it a planet or an exomoon, ‘tugging’ on the transiting planet.

Because the candidate signal was so faint, the original research was treated with a great deal of caution, and has drawn a lot of attention to its methods. Today’s paper aims to address some of the possible reasons the detection could be a false-positive, as well as a recent paper by Kreidberg et al. (hereafter K19) re-evaluating the signal from the HST and drawing the conclusion that there is no moon signal at all. ...

Loose Ends for the Exomoon Candidate Host Kepler-1625b ~ Alex Teachey et al
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Planets May Form Faster Than Expected

Post by bystander » Tue May 07, 2019 9:33 pm

Planets May Form Faster Than Expected
astrobites | Daily Paper Summaries | 2019 May 07
Lauren Sgro wrote:
If you were watching the astronomical news back in 2017, you may have heard of ‘Oumuamua. That’s the weird interstellar object (ISO) that was found floating around in our solar system and is the first intruder we have ever seen. It was initially identified as a comet, then an asteroid, then neither, and then according to the media, an alien ship. Potential alien spacecraft or innocent space boulder, this was a big discovery.

‘Oumuamua sparked interesting theories in the minds of today’s authors, and ultimately lead to, you guessed it, a new hypothesis for the rapid formation of planets. How could ISOs have anything to do with planet formation? Well, that’s what Susanne Pfalzner and Michele Bannister set out to tell us. ...

A Hypothesis for the Rapid Formation of Planets ~ Susanne Pfalzner, Michele T. Bannister
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STROOPWAFEL: An astrophysical algorithm

Post by bystander » Thu May 09, 2019 7:33 pm

STROOPWAFEL: An astrophysical algorithm, not a Dutch cookie
astrobites | Daily Paper Summaries | 2019 May 08
Bryanne McDonough wrote:
Modern astronomy relies heavily on computational resources. This is especially true when it comes to the budding field of gravitational waves. While only a handful of detections have been made to date, this number will likely grow significantly in the coming years. By comparing the observed properties and frequency of gravitational wave events with simulations, astronomers can test their theories about the origin of certain objects. However, getting good results from simulations requires a lot of computational time. The authors of today’s paper came up with a way to speed up the computational efficiency and increase the accuracy of simulations using an algorithm called STROOPWAFEL (Simulating The Rare Outcomes Of Populations With AIS For Efficient Learning).

STROOPWAFEL: Simulating rare outcomes from astrophysical populations,
with application to gravitational-wave sources
~ Floor S. Broekgaarden et al
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Feeling gassy?

Post by bystander » Fri May 10, 2019 5:33 pm

Feeling gassy?
astrobites | Daily Paper Summaries | 2019 May 09
Stephanie Hamilton wrote:
Astronomers often compare exoplanets to the planets in our own Solar System — Jupiters, Neptunes, super-Earths, etc. — because they are familiar. But the distinction can be made even simpler: planets that are gas-rich, and those that are not. Where does the boundary between the two fall, and how does it arise? Today’s paper addresses that very question. ...

The Boundary Between Gas-rich and Gas-poor Planets ~ Eve J. Lee
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How to Find Exoplanet Oceans

Post by bystander » Fri May 10, 2019 5:44 pm

How to Find Exoplanet Oceans
astrobites | Daily Paper Summaries | 2019 May 10
Briley Lewis wrote:
In the coming decades, there are plentiful opportunities and ideas for space-based missions that may be able to detect life on other planets – the James Webb Space Telescope (JWST), LUVOIR, the Origins Space Telescope, HabEx, and more. But, what would those signs of life look like, and what do we need to actually detect these biosignatures with confidence? These are two of the key questions astronomers face as they prepare to choose the next big space telescopes.

Given that we only have one example of life in the universe (as of today), an exoplanet must mirror the thermal and chemical properties of Earth to be deemed habitable. One of the main ways to judge if a planet is habitable is to look at its atmosphere, finding out more about its temperature and what it’s made of. We can glean lots of information about a planet’s atmosphere through spectroscopy, such as what molecules may be present, if there are clouds or hazes, what its temperature may be, and more. In particular, modern surveys are concerned with finding water, oxygen, and other compounds that signal habitability in the atmospheres of these exoplanets. However, transmission spectroscopy (what JWST will be capable of) only allows us to see the very upper layers of an atmosphere. This isn’t very interesting for finding water, considering that, on Earth, all our water vapor is concentrated in the very bottom layers of our atmosphere. Today’s paper focuses on a different avenue for finding water on exoplanets: oceans. ...

Detecting Ocean Glint on Exoplanets Using Multiphase Mapping ~ Jacob Lustig-Yaeger et al
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Zombie Star Went Supernova Twice?

Post by bystander » Sat May 18, 2019 4:26 pm

Zombie Star Went Supernova Twice?
astrobites | Daily Paper Summaries | 2019 May 13
Eda Vurgun wrote:
Astronomers recorded a supernova explosion in 1954. After many years, at the same location, iPTF14hls was discovered in September 2014 by intermediate Palomar Transient Factory (iPTF) and classified as a supernova event again. And yes, this is a bit confusing because supernova events happen once in a lifetime of a star. Long-term monitoring of the source revealed some bizarre and unique characteristics such as constant temperature and multiple outburst peaks which cannot be fully explained with the current understanding of typical supernovae.

iPTF14hls has hydrogen-dominated spectra. This type of spectrum is generally identified as a core-collapse supernova, but its characteristics also differ from known core-collapse supernovae. The light curve of iPTF14hls has five peaks and has remained bright for more than 600 days compared to the known supernova that usually show a single peak and descent of 100 days. In addition, the temperature of iPTF14hls remains constant instead of cooling. The total energy emitted in light during the first 600 days was about 2.2 × 10^50 ergs, making iPTF14hls a luminous, but not a particularly “superluminous” supernova. In a normal core-collapse supernova, the released energy is typically about 10^53 ergs. iPTF14hls requires larger energy to maintain the long duration.

In this study, there are several varieties of models to explain this unusual event. They are based upon circumstellar medium interaction in an ordinary supernova, pulsational supernovae, and magnetar formation. Each is able to explain the enduring emission and brightness of iPTF14hls, but has shortcomings when confronted with other observed characteristics. ...

Models for the Unusual Supernova iPTF14hls ~ S. E. Woosley
viewtopic.php?t=37741
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Young, massive, and mysterious

Post by bystander » Sat May 18, 2019 4:45 pm

Young, massive, and mysterious
astrobites | Daily Paper Summaries | 2019 May 14
Hannah Dalgleish wrote:
Star clusters are all around us, from ancient globular clusters, to younger open clusters, and even nuclear star clusters – but what is a young massive cluster (YMC)? Like other star clusters, YMCs are gravitationally bound stellar systems. What makes them unique is that they are young (~100 million years old) and massive (typical solar masses greater than 104). To make things even more confusing, YMCs in other galaxies are called super star clusters [there’s an astrobites post about them here].

But why are these clusters interesting? A puzzle which astronomers have long been trying to solve is how do clusters, like globulars, form? One idea is that YMCs are the progenitors to globular clusters. Therefore, through studies of the stellar kinematics of YMCs and making comparisons to other clusters, astronomers hope to shed some light on the problem. ...

It is only until very recently that we have been able to look at regions like this in such detail, made possible by instruments like MUSE (Multi Object Spectroscopic Explorer). In 2017, MUSE received a makeover when it gained adaptive optics capabilities and can now make even better observations than Hubble! By pointing MUSE at Westerlund 2 we can derive the velocity dispersion (how stellar velocity differs from the average cluster motion) of the cluster at a high accuracy. We can discover if the cluster is massive enough to be long-lived, and help us answer if this YMC is in fact a globular cluster progenitor. ...

With the MUSE observations, the team used special software called PampelMuse [German for grapefruit!] to extract the stellar spectra from the datacube. In total, they extracted 72 stars from the whole observed region of Westerlund 2 for which they derived radial velocities. They then plotted a colour-magnitude diagram to determine which of the stars were actually cluster members of the cluster, and which were field stars: 44 out of 72 stars are actually cluster members. ...

The Young Massive Star Cluster Westerlund 2 Observed with MUSE.
I. First Results on the Cluster Internal Motion from Stellar Radial Velocities
~ Peter Zeidler et al
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Speed check on the ‘fastest’ star in Gaia

Post by bystander » Sat May 18, 2019 5:02 pm

Speed check on the ‘fastest’ star in Gaia
astrobites | Daily Paper Summaries | 2019 May 15
Emma Foxell wrote:
‘Hypervelocity’ stars move fast. So fast they can escape from the gravitational pull of the Milky Way. A few tens of hypervelocity stars are known but the Gaia space telescope is expected to find hundreds more as it maps the positions and velocities of stars in the sky. A star’s velocity is split into its tangential velocity (how fast it moves across the sky, a.k.a. proper motion) and radial velocity (how fast it moves towards or away from us). Combining them together using trigonometry gives the star’s total velocity.

As the Gaia pipelines are still being improved to combine these velocities, only stars with radial velocity greater than the escape velocity of the Milky Way (600 km s-1) are guaranteed hypervelocity stars. Currently one star meets this criteria: Gaia DR2 5932173855446728064 (which we’ll call Gaia ‘064 for short). Gaia ‘064 has an incredible radial velocity of -614 +-2 km s-1, calculated as the median of seven individual measurements. Figure 1 shows Gaia ‘064 is in a very crowded field on the sky. It has nine neighbouring stars within 8 arcsec, far more than other hypervelocity stars tested.

As Gaia ‘064 is in an abnormally crowded field, the authors took follow up spectra to verify the Gaia DR2 radial velocity. Using eight spectra from the SOAR telescope taken between 5th May and 16th September 2018, they calculated a median radial velocity of -56.5 +-5.3 km s-1. ...

Lessons from the curious case of the ‘fastest’ star in Gaia DR2 ~ Douglas Boubert et al
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Using a Neural Network to Find Exoplanets in K2 Data

Post by bystander » Sat May 18, 2019 5:28 pm

Using a Neural Network to Find Exoplanets in K2 Data
astrobites | Daily Paper Summaries | 2019 May 16
Jenny Calahan wrote:
In today’s astrobite, we explore how to discover exoplanets using a neural network. ...

One way to find exoplanets is by looking at the light emitted from stars for long periods of time to see if the light dims periodically due to an exoplanet passing in front of the star (see figure 1). If the light curve (a plot of light emitted vs time) looks anything like this, the dips in brightness could correspond to an exoplanet crossing in front of the star.

If we can get computers to look for transit patterns, they may be able to find exoplanets better than humans. Or at least find exoplanets a lot faster than individual people. The first step to building a neural network is to create a training set of light curves. In order to do that, a human needs to go through and identify light curves as exoplanet or no exoplanet. The authors of today’s paper used data from the K2 mission. ...

Identifying Exoplanets with Deep Learning. II. Two New
Super-Earths Uncovered by a Neural Network in K2 Data
~ Anne Dattilo et al
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Radio Pulsars: How Slow Do They Go?

Post by bystander » Wed May 22, 2019 4:40 pm

Radio Pulsars: How Slow Do They Go?
astrobites | Daily Paper Summaries | 2019 May 20
Aaron Pearlman wrote:
Neutron stars are formed from massive stars that undergo violent supernova explosions after they run out of nuclear fuel and collapse under their own gravity. Radio pulsars are highly magnetized, rotating neutron stars that emit beams of radiation from their magnetic poles. When these beams of radio emission sweep across our line of sight, they generate radio pulses that can be detected with radio telescopes on Earth. The surface magnetic field strength, age, and internal structure of these objects can be studied through measurements of their rotational rates. Astronomers have now discovered more than 2,700 pulsars in the Galaxy, and they’re constantly on the look out for rare breeds. In today’s astrobite, we cover the discovery of the slowest known spinning radio pulsar, PSR J0250+5854, which has a rotational period of 23.5 s. This exciting finding demonstrates that radio pulsars can rotate much slower than expected and still produce radio pulsations. ...

LOFAR Discovery of a 23.5 s Radio Pulsar ~ C. M. Tan et al
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Can a planet change the measured age of its parent star?

Post by bystander » Wed May 22, 2019 4:57 pm

Can a planet change the measured age of its parent star?
astrobites | Daily Paper Summaries | 2019 May 21
Oliver Hall wrote:
Stars, like their Hollywood namesakes, like to be elusive about their age. Finding ways to reliably determine how old stars are is therefore a large part of current research. One such technique is gyrochronology, the study of the relation between a star’s rotation, colour, and age. Stars of a given colour on the Main Sequence stage of their lifetime will spin more slowly (or ‘spin down’) as they evolve at a relatively reliable rate. This means if you know a star’s colour and rotation you can derive a reliable age estimate, which is especially useful in cases where other methods don’t work as well.

But what happens when a star doesn’t get to spin down in isolation; what if it is disrupted somehow? If the star was caused to spin more quickly (or ‘spun up’) (for example, by stealing material from a stellar companion), using gyrochronology to determine its age would make it look younger than it actually is. One way to change a star’s spin down rate could be due to tidal interactions with a nearby planet, creating tides on the star much like the moon creates tides on earth. Today’s authors ask the question: how close and how big does a planet need to be before it starts seriously disrupting the stellar spin and our use of gyrochronology? ...

Star-planet tidal interaction and the limits of gyrochronology ~ Florian Gallet, Philippe Delorme
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TESS Spies, with its Little Eye, Something Multi-planetary

Post by bystander » Wed May 22, 2019 5:11 pm

TESS Spies, with its Little Eye, Something Multi-planetary
astrobites | Daily Paper Summaries | 2019 May 22
Tarini Konchady wrote:
The Transiting Exoplanet Survey Satellite (TESS) has been operating for over a year now. It is nearly halfway through its survey of the sky, currently observing Sector 11 of 26 (see Figure 1). TESS has already revealed new planets (including an Earth-sized one) and even caught some supernovae as they were getting brighter.

The paper discussed in this Astrobite announces another new and exciting TESS detection—not one, not two, but three super-Earths orbiting a bright, nearby star. The host, HR 858, is located in the constellation of Fornax the Furnace and as a sixth magnitude star, it is just at the edge of what can be seen with the naked eye. ...

TESS Spots a Compact System of Super-Earths around the Naked-Eye Star HR 858 ~ Andrew Vanderburg et al
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Journey to the centre of a galaxy cluster

Post by bystander » Fri May 24, 2019 3:19 pm

Journey to the centre of a galaxy cluster
astrobites | Daily Paper Summaries | 2019 May 23
Joanna Ramasawmy wrote:
Why do galaxies come in different shapes, sizes and colours? What are the physical processes that determine a galaxy’s observable properties? These questions drive extragalactic astrophysics. One factor in a galaxy’s evolution that is under scrutiny is the environment it is found in. Depending on whether a galaxy is located in a dense cluster or is relatively isolated in the field, the physical processes that shape it will differ. There is an observable difference in colour and morphology of galaxies depending on their environments: in the densest environments, galaxies tend to be red and elliptical, whereas in low-density environments we find many more blue spirals. Why?

In this paper, the authors investigate what happens in and around galaxy clusters, the largest gravitationally-bound structures in the universe. Such structures grow over time as galaxies fall into their gravitational potential, and during this infall a galaxy can be transformed. In the space between galaxies, a cluster isn’t empty — it’s filled with hot gas (the “intra-cluster medium”), which exerts a pressure on a galaxy falling through it. The resulting wind can blow gas out of the galaxy in a process known as ram pressure stripping. In fact, this process is observed spectacularly in jellyfish galaxies, with tentacles of gas trailing behind the galactic disk. Stripping a galaxy of its gas prevents it from forming stars, thus changing the colour from the blue of young stellar populations to the red of older stars — and so ram pressure stripping is a favoured mechanism behind the blue galaxies in the field vs. red galaxies in clusters problem.

To study how and when this happens, the authors of this paper use a suite of over three hundred simulations of galaxy clusters (figure 1 shows an example). These simulations deal with haloes — clumps of gravitationally-bound matter — rather than galaxies themselves, but halo properties tell us about what would happen to galaxies residing in them. ...

The Three Hundred Project: Ram pressure and gas content
of haloes and subhaloes in the phase-space plane
~ Jake Arthur et al
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Mysteries of the Orion Nebula Cluster

Post by bystander » Sat May 25, 2019 5:09 pm

Three Stellar Populations? Unresolved Binaries?
Mysteries of the Orion Nebula Cluster

astrobites | Daily Paper Summaries | 2019 May 24
Tomer Yavetz wrote:
The Orion Nebula has been a top target for astronomers and their fancy cameras for over a century. In fact, a photo of the Orion Nebula by the amateur astronomer and astrophotographer Andrew Ainslie Common from 1883 was the first demonstration that a long exposure photograph could reveal stars that were too dim to be seen by eye. Thanks to modern-day telescopes, we now know the Orion Nebula to be a large cloud of gas and dust that is actively forming new stars. The newly formed stars in and around the nebula are collectively referred to as the Orion Nebula Cluster (ONC).

One of the assumptions made about star clusters is that all of the stars are born at more or less the same time, within approximately one million years. Not so for the ONC! Two years ago, observations made using the OmegaCAM instrument in the VLT Survey Telescope were able to pick out not one, not two, but three distinct populations of stars living in the ONC, suggesting that star formation may not have happened all at once but rather in three separate bursts.

To arrive at this conclusion, the authors created a Color-Magnitude Diagram (CMD), on which newly formed stars of the same age appear to form a line called the Pre-Main Sequence. By making a CMD of the stars seen in the ONC, the authors were able to pick out three distinct sequences indicating that these three groups of stars all formed at different times. ...

When the Tale Comes True: Multiple Populations and Wide Binaries in the Orion Nebula Cluster ~ Tereza Jerabkova et al Evidence for Feedback and Stellar-Dynamically Regulated Bursty Star
Cluster Formation: The Case of the Orion Nebula Cluster
~ Pavel Kroupa et al
viewtopic.php?t=37420
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Order from Chaos

Post by bystander » Tue May 28, 2019 4:00 pm

Order from Chaos: Machine Learning
Helps Classify Interstellar Turbulence

astrobites | Daily Paper Summaries | 2019 May 27
Michael Foley wrote:
Machine learning has quickly become a crucial tool for many sectors of society, from small businesses looking to maximize customer engagement to national security teams trying to identify the latest threat. These algorithms ask computers to “learn” how to best predict the desired outcome. For this, the size of the input dataset and the computational time of running the model are important considerations in employing machine learning for a specific goal. And who has loads of data and a love for computers? Astronomers!

Today’s paper applies a specific machine learning algorithm – a Convolutional Neural Network (CNN) – to simulated images of the interstellar medium (ISM) in order to distinguish between sub-Alfvénic and super-Alfvénic turbulence. ...

Do Androids Dream of Magnetic Fields? Using Neural Networks
to Interpret the Turbulent Interstellar Medium
~ J.E.G. Peek, Blakesley Burkhart
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Weighing a Galaxy by Counting Its Globular Clusters

Post by bystander » Tue May 28, 2019 4:14 pm

Weighing a Galaxy by Counting Its Globular Clusters
astrobites | Daily Paper Summaries | 2019 May 28
Jenny Calahan wrote:
Measuring the mass of an entire galaxy is difficult. Not only are they far far away from us, so we can’t always easily resolve its different components, but the majority of the mass in a galaxy is made up of dark matter, which cannot be observed directly. Having a precise mass measurement of an individual galaxy or a cluster of galaxies is very important to our understanding of dark matter and its role in galaxy formation and evolution. So how do we begin to measure the mass of a galaxy when the majority of that mass is invisible to us?

There are a few ways to indirectly measure the mass of a galaxy. One method is with rotation curves. To make a rotation curve, you look at the stars and clusters of stars in a galaxy and see how fast they are orbiting around the center of the galaxy. Their velocities should fall off according to the inverse square nature of gravitation. However, if clusters far from the center are moving just as fast as clusters closer in, this is an apparent violation of gravitation and in order for it to make sense, there needs to be a large amount of ‘invisible’ mass in the galaxy halo. This is what we call dark matter. Another method is micro-lensing; like gravitational lensing, but micro. With this method, you can observe the tiiiinnnyy effect a galaxy has on the space-time around it and, from that, you can determine a mass. Both of these methods have major assumptions that need to be made, and sometimes they don’t agree, or they lead to imprecise mass values. This paper suggests a more robust way of measuring a galaxy’s mass: counting the number of globular clusters.

Globular clusters are cumulations of old stars, with ages on the order of 12 billion years (compared to the age of our universe at 13.7 billion years old). They are relatively common, our Milky Way hosts ~150, and are associated with all sorts of galaxies. Specifically, they are located in the dark matter halo of a galaxy. The authors find that the number of globular clusters around a galaxy of any kind (spirals and ellipticals) correlates very well with the host galaxy’s virial mass (which is one way of characterizing the total mass of the galaxy). ...

High-Precision Dark Halo Virial Masses from Globular Cluster Numbers:
Implications for Globular Cluster Formation and Galaxy Assembly
~ Andreas Burkert, Duncan Forbes
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How old are you really, Psc-Eri?

Post by bystander » Fri May 31, 2019 3:34 pm

How old are you really, Psc-Eri?
astrobites | Daily Paper Summaries | 2019 May 29
Sanjana Curtis wrote:
Earlier this year, Meingast et al. conducted a study using the Gaia mission’s second data release (DR2) and made an exciting discovery. They found a nearby stellar stream that stretches across ≈120º of the sky and spans ≈400 pc in space. You may wonder how such an object was hidden for so long in the first place. The reason is that the stars in the stream are quite spread out. Without the sort of precise motion measurements made available by Gaia, it would be very difficult (if not impossible) to say that these stars are moving in the same direction.

To make things even more intriguing, the discovery paper estimated that the stream, which lies only ≈129+/-32 pc away from the Earth, is around 1 Gyr old! Groups of stars that are this old are rare and tend to be much more distant, making this an incredibly unusual discovery. This age estimate was based on comparing the observational Hertzsprung-Russel diagram of the stream to a set of stellar isochrones. If the stream really is 1 Gyr old, its proximity makes it a very valuable target for understanding stars and their evolution. Its stellar population could serve as a benchmark for old stars. However, this also means we need to examine its age very (very!) carefully, and that brings us to today’s paper. The paper we will discuss uses two different methods to test the age of the Pisces–Eridanus stream (Psc–Eri), as the authors call it, with some help from TESS! ...

TESS reveals that the nearby Pisces-Eridanus stellar stream is only 120 Myr old ~ Jason Lee Curtis et al
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Re: astrobites: Daily Paper Summaries 2019

Post by bystander » Tue Jun 11, 2019 3:45 pm

astrobites must have suffered a catastrophic failure. They were offline for over a week and everything back to 2019 Jan 03 is missing. There is a new post for 2019 Jun 07, but nothing between May 29 and Jun 07 and nothing since.
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Is That a Supernova? Classifying Transients in Real-Time

Post by bystander » Tue Jun 11, 2019 4:06 pm

Is That a Supernova? Classifying Transients in Real-Time with Machine Learning
astrobites | Daily Paper Summaries | 2019 Jun 07
Michael Foley wrote:
Humanity is overwhelmed with data. It is estimated that 2.5 quintillion bytes (or 2.5 million terabytes) of data are now created every day. Astronomers have kept up with this pace, designing new observatories and facilities that will produce incredible quantities of data. A prime example of this is the Large Synoptic Survey Telescope (LSST), expected to see first light in 2020. This observatory alone is projected to produce over 15 terabytes of data every night!

There simply aren’t enough people to process and analyze data production at this level, so scientists and engineers must come up with increasingly creative ways to handle this deluge of information. This is where machine learning comes in. By designing algorithms that allow computers to “learn” how to analyze it themselves, this intangible mountain of data can become an informative molehill used to inform government policies, business decisions, or scientific studies. One of the most promising algorithms for this work is a neural network. See this bite for an explanation of neural networks and an example of using machine learning to study the interstellar medium.

Today’s paper uses a neural network to classify astronomical transients, phenomena that are only visible for a short time. Some examples of transients include supernovae or tidal disruption events (TDEs), where a star is stripped apart as it falls into a black hole. The authors of this work develop a tool called RAPID (Real-time Automated Photometric IDentification), which tries to classify transients while they are being observed! For surveys like LSST, which will image the entire visible sky from Chile every few nights, real-time classification would provide a major advantage to astronomers: the ability to obtain as much information as possible about a transient while it is still occurring. ...

RAPID: Early Classification of Explosive Transients using Deep Learning ~ Daniel Muthukrishna et al
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Unraveling the Formation History of Hot Jupiters

Post by bystander » Sun Jul 14, 2019 10:55 pm

Unraveling the Formation History of Hot Jupiters
astrobites | Daily Paper Summaries | 2019 Jun 27
Spencer Wallace wrote:
To fully understand how and where planets can form, astronomers must look to the extremes. One of the most exotic discoveries in exoplanet research has been of a class of planets known as hot Jupiters. These are gaseous worlds, hundreds of times the mass of the Earth, that orbit their host stars in mere days. Given the major role that Jupiter had in shaping the solar system, it is crucial to understand how gas giant planets form in a variety of environments.

The formation of a Jupiter-sized world is thought to be a two-step process. First, material in the protoplanetary disk conglomerates to form a solid core. If this core grows larger than about 10x the mass of the Earth, its gravitational pull becomes strong enough for the planet to accumulate a gaseous envelope. As this envelope grows, the gravitational pull gets stronger, allowing the planet to attain a huge mass fairly quickly. Eventually, the gaseous envelope becomes too hot for material to continue to condense and the growth is throttled.

For intermediate-sized worlds, radiation from the star can blast away the atmosphere if the planet is too close. This results in a dearth of close-in planets around 1/10 the mass of Jupiter. For larger worlds, however, this evaporation is ineffective. Even very highly irradiated Jupiter-sized planets only ever lose about 1% of their mass. There appears to be a very sharp cutoff, below which hot Jupiters that are too small and close to their host stars simply don’t exist. The authors of today’s paper explain this cutoff with a wonderfully simple and succinct model and use it to argue that most hot Jupiters formed at their current location, rather than having been built further out and subsequently migrating inwards. ...

The Hot Jupiter Period–Mass Distribution as a Signature of in situ Formation ~ Elizabeth Bailey, Konstantin Batygin
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Localization of a Single Fast Radio Burst

Post by bystander » Sun Jul 14, 2019 11:00 pm

Localization of a Single Fast Radio Burst to a Massive Early-Type Spiral Galaxy
astrobites | Daily Paper Summaries | 2019 Jun 27
Haley Wahl wrote:
Fast radio bursts (FRBs) are one of the most fast-paced fields of astronomy at the moment and continue to captivate and puzzle scientists all over the world. Powerful new telescopes equipped with advanced technology are coming online, which will enable astronomers to understand the inner workings of these mysterious objects. The first major breakthrough in the field was the discovery and localization of a repeating FRB. Now a team of astronomers has made a new discovery that could turn the theories of why and how FRBs happen on their heads. ...

A Single Fast Radio Burst Localized to a Massive Galaxy at Cosmological Distance ~ K.W. Bannister et al
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