astrobites 2017

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Re: A Contracting White Dwarf?

Postby Ann » Sat Nov 18, 2017 6:25 pm

bystander wrote:A Contracting White Dwarf?
astrobites | 2017 Nov 17
Matthew Green wrote:
Today’s paper takes another look at a binary system, HD 49798, which has been puzzling scientists for some time. HD 49798 is an X-ray binary, a type of binary in which matter is transferred onto a central, compact star (a white dwarf, neutron star or black hole) from a donor star. The authors suggest that many of the unusual attributes of the system could be explained if one of the stars is a young, half-formed white dwarf which is still in the process of contracting. ...

A Young Contracting White Dwarf in the Peculiar Binary HD 49798/RX J0648.0–4418 ? - S.B. Popov et al

viewtopic.php?t=30985


Very interesting. I note that the donor star is an O6 star and very blue, with a -0.27 Johnson B-V index, which is blue indeed, not least given the distance to the binary of about 2,700 light-years.

If the compact star is a contracting white dwarf, some two million years old, then the progenitor must have been an O-type star too, and massive enough to die after a few million years. And yet, this massive star didn't turn into a neutron star, much less into a black hole, but into a humble white dwarf, albeit a massive one as white dwarfs go.

It seems strange to me that an O6-type star would be the surviving member of a binary system whose more-massive star has already died, and yet it hasn't turned into a neutron star. Admittedly though, the O6-type star just might be a blue straggler, which picked up mass from its swollen, dying sibling. Maybe, in fact, the progenitor of the compact star dumped most of its mass on its companion, Algol style. So maybe the progenitor of the compact star wasn't quite as massive as we might think it was, at least not when it died.

I guess it hasn't been proved beyond a doubt that the compact object is in fact a white dwarf. But this is hugely interesting, all the same.

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Planet Frequencies in the Galactic Bulge

Postby bystander » Wed Nov 22, 2017 3:01 pm

Planet Frequencies in the Galactic Bulge
astrobites | 2017 Nov 20
Elisabeth Matthews wrote:
I don’t know if you’ve heard, but astronomers have found quite a few exoplanets in the last couple of decades. However, most of these are clustered in our tiny corner of the galaxy. For the 2043 planets with stellar distance listed on exoplanets.org today (yes, I know this article will be out of date in a week…) the average distance of the host star is 624pc. The center of the galaxy, meanwhile, is ~8000pc away. That’s further than even the furthest known exoplanet, OGLE-05-390L b, which is 6500pc from us.

And we’d really like to have a better understanding of the exoplanets in the galactic bulge, because their presence – or lack thereof – helps us to understand planet formation. Planet formation is believed to be affected by several external factors such as the host star’s metallicity, the stellar mass, the stellar multiplicity, and the stellar environment. That final category is what we’re going to consider today: does the presence of a large number of nearby stars interrupt the formation of planets? The galactic bulge, as the part of the galaxy with the highest number density of stars, is an ideal place to test this – if only we could detect enough planets out there…

Toward a Galactic Distribution of Planets. I. Methodology and Planet
Sensitivities of the 2015 High-cadence Spitzer Microlens Sample
- Wei Zhu et al
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What were globular clusters doing during reionization?

Postby bystander » Wed Nov 22, 2017 3:08 pm

What were globular clusters doing during reionization?
astrobites | 2017 Nov 21
Joshua Kerrigan wrote:
In the past we’ve covered a few potential sources for the reionization of the universe, such as AGN or supernovae. It is believed that the primary contributor of UV radiation during reionization was from the earliest formed galaxies (think redshift z ~ 12). Therefore it can be really informative to understand how these galaxies are producing their UV flux. So for today’s astrobite we look into what ancient globular clusters were doing during the epoch of reionization (z ~ 6-10). ...

The Little Engines That Could? Globular Clusters Contribute
Significantly to Reionization-era Star Formation
- Michael Boylan-Kolchin
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Re: A Contracting White Dwarf?

Postby BDanielMayfield » Wed Nov 22, 2017 3:29 pm

Ann wrote:
bystander wrote:A Contracting White Dwarf?
astrobites | 2017 Nov 17
Matthew Green wrote:
Today’s paper takes another look at a binary system, HD 49798, which has been puzzling scientists for some time. HD 49798 is an X-ray binary, a type of binary in which matter is transferred onto a central, compact star (a white dwarf, neutron star or black hole) from a donor star. The authors suggest that many of the unusual attributes of the system could be explained if one of the stars is a young, half-formed white dwarf which is still in the process of contracting. ...

A Young Contracting White Dwarf in the Peculiar Binary HD 49798/RX J0648.0–4418 ? - S.B. Popov et al

viewtopic.php?t=30985


Very interesting. I note that the donor star is an O6 star and very blue, with a -0.27 Johnson B-V index, which is blue indeed, not least given the distance to the binary of about 2,700 light-years.

If the compact star is a contracting white dwarf, some two million years old, then the progenitor must have been an O-type star too, and massive enough to die after a few million years. And yet, this massive star didn't turn into a neutron star, much less into a black hole, but into a humble white dwarf, albeit a massive one as white dwarfs go.

It seems strange to me that an O6-type star would be the surviving member of a binary system whose more-massive star has already died, and yet it hasn't turned into a neutron star. Admittedly though, the O6-type star just might be a blue straggler, which picked up mass from its swollen, dying sibling. Maybe, in fact, the progenitor of the compact star dumped most of its mass on its companion, Algol style. So maybe the progenitor of the compact star wasn't quite as massive as we might think it was, at least not when it died.

I guess it hasn't been proved beyond a doubt that the compact object is in fact a white dwarf. But this is hugely interesting, all the same.

Ann


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No Missing Satellites?

Postby bystander » Sun Nov 26, 2017 4:17 pm

No Missing Satellites?
astrobites | 2017 Nov 22
Gourav Khullar wrote:
It can be said with tremendous confidence that the Lambda Cold Dark Matter (LCDM) model of the universe is doing a fantastic job so far as THE model of the universe that explains most of its phenomena – the cosmic microwave background, the formation and evolution of objects in the universe, cosmic accelerated expansion, the evolution of various particle species, and even gravitational waves! Both simulations and observations that incorporate LCDM to make predictions have been consistent with each other. That being said, there are a few areas in the field of astrophysics where LCDM is falling a little short of convincing; this is a cause for worry.

Structure formation has been an exciting field for the past few decades, keeping astrophysicists busy with the mysteries of how objects like galaxies and galaxy clusters evolve from the primordial perturbations in the universe. Simulations of large-scale structure from the early universe to now (e.g. Bolshoi, Millenium, Illustris), and large sky surveys that observe billions of objects (e.g. SDSS, DES), indicate the presence of massive dark matter halos whose gravitational potential wells attract matter to form galaxies and eventually galaxy clusters. Moreover, natural product of this is the presence of low mass and low brightness dwarf galaxies on the peripheries of larger galaxies, known as satellites. These are galaxies that are influenced by the gravitational potential of their host galaxies, but are stable astrophysical entities in themselves. The above described paradigm and its products are the centerpiece of an ongoing debate (one of the major LCDM issues), called the ‘Missing Satellites Problem’. ...

There is No Missing Satellites Problem - Stacy Y. Kim, Annika H. G. Peter, Jonathan R. Hargis
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How many stars have companions?

Postby bystander » Sun Nov 26, 2017 4:26 pm

How many stars have companions?
astrobites | 2017 Nov 23
Ingrid Pelisoli wrote:
Have you ever tried to count the stars in the sky? I remember doing that as a kid, and always giving up even before I got to a hundred. Little did I know that I would never get the right number. As we’ve talked before here on Astrobites, one plus one is not always two when it comes to stars. The process of stellar formation occurs in dense molecular clouds, where many stars form at the same time. As a result, many of them end up in multiple systems (binaries, ternary, etc.). But how many?

This may seem like a naive question, but it has implications in different fields of astronomy. Multiple systems host many interesting astronomical sources, such as X-ray binaries and cataclysmic variables. Interacting binaries are progenitors of Type Ia supernovae, which ultimately led us to infer that the Universe was expanding at an increasing rate. Moreover, they are sources of gravitational waves. Therefore we have plenty of reasons to ask how many stars have companions, and that’s exactly what the authors of today’s paper did. ...

Stellar Multiplicity Meets Stellar Evolution and Metallicity: The APOGEE View - Carles Badenes et al
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Extinction Events from Giant Space Explosions

Postby bystander » Thu Nov 30, 2017 5:46 pm

Extinction Events from Giant Space Explosions: A Cosmological Perspective
astrobites | 2017 Nov 27
Christopher Lovell wrote:
We’re still unsure how life began, but we have plenty of ideas for how to snuff it out completely. From global warming to an asteroid collision, rogue AI to a supervolcano explosion, we have a morbid ability to imagine our own demise (and dramatic rescue, if you have a Bruce Willis with a thermonuclear weapon). But the cosmos has far more powerful means of sterilising planets beyond the solar system, and depending on how common they are, the chances of life lasting elsewhere in the cosmos could be slim indeed.

Massive stars end their lives in massive explosions known as a supernovae (SNe), and if they are rotating rapidly enough can lead to gamma ray bursts (GRBs). GRBs can also occur during the collision of two neutron stars. Both SNe and GRBs release massive amounts of hard, ionising radiation that can dissociate complex molecules, or strip the atmosphere of a planet completely, killing any complex life on the surface. Such extinction events are not purely hypothetical – at least one mass extinction event in the history of life on Earth, in the late Ordivician period, has been attributed to a GRB. The supermassive black holes at the center of every galaxy can also release huge amounts of radiation when they’re accreting matter (hence the name, Active Galactic Nuclei, or AGN), which can irradiate any nearby stellar system in a similar way to a SNe or GRB.

In today’s paper, the authors use a cosmological simulation combined with a stellar evolution model (that takes into account the effects of metallicity) to study how such extinction events affect the habitability of stars in a galaxy. This type of cosmological simulation follows many thousands of galaxies that can interact and merge together, processes that can have a profound effect on star formation and, in turn, how many SNe and GRB events occur in a galaxy over time. ...

Exploring the Cosmic Evolution of Habitability with Galaxy Merger Trees - E. R. Stanway et al
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All-sky spectroscopy with SDSS-V

Postby bystander » Thu Nov 30, 2017 6:07 pm

All-sky spectroscopy with SDSS-V
astrobites | 2017 Nov 28
Suk Sien Tie wrote:
“Our human eyes are the tools that peek at the secrets of the night sky”, so said the ancient Chinese astronomers who witnessed the supernova of the Crab Nebula in 1054 AD. But the heavens only truly light up through the lenses of telescopes, allowing us not only to peer into, but also to peel away, the mysteries of our Universe. We started out in 1609 with Galileo’s 37 mm refracting telescope, proceeded to Newton’s 150 mm reflecting telescope in 1668, and leapfrogged to William Herschel’s 49 inch (125 cm) reflector in 1789, which held the record as the world’s largest telescope for the next 50 years. Two hundred years later, not only do we have artificial eyes in space constantly staring deeper into the infancy of the Universe, we also have all sky maps in various wavelengths of light and larger telescopes from the ground, with bigger and more ambitious programs already lined up for the next five to ten years. As an astronomer in training, I never fail to be amazed by the giant leaps we have made over the course of human history.

Even so, we are still only scratching the surface.

Astronomers are not strangers to sky surveys. Among the tens of sky surveys, the Sloan Digital Sky Survey (SDSS) is probably the king of them all (see this bite for a historical overview), having been in operation since 2000, with WISE and ROSAT chasing its tail for being truly all-sky. However, all surveys to date, both full- and partial-sky, have been imaging surveys. There is no yet a full-sky spectroscopic survey — at least not until SDSS-V. ...

SDSS-V: Pioneering Panoptic Spectroscopy - Juna A. Kollmeier et al

viewtopic.php?t=37767
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Hunting for the faintest galaxies

Postby bystander » Thu Nov 30, 2017 6:14 pm

Hunting for the faintest galaxies
astrobites | 2017 Nov 29
Stacy Kim wrote:
One marvelous fact about our universe is that at the largest scales, it is fractal. Unlike true fractals, which exhibit exact self-similarity, the universe is only statistically self-similar. If you looked at the most massive objects in the universe, a record held by the gargantuan, invisible dark matter blobs holding clusters of galaxies together, which clock in with masses upwards of 10^15 times the mass of the Sun, you’d find that they’re rife with smaller blobs, or “halos” of dark matter. Many of these smaller dark matter halos are inhabited by a galaxy, including giant bright elliptical galaxies, the smaller and fainter spiral galaxies, and hordes of yet smaller, fainter galaxies. Peering closer at, say, one of the dark matter halos of a Milky Way-like spiral galaxy, which clocks in at about 10^12 times the mass of the Sun, you’d find that it in turn is surrounded by a similar but down-sized army of even smaller dark matter halos, which may contain even fainter “dwarf” galaxies. And the halos of each of these dwarf galaxies in turn can host their own army of even tinier dark matter halos. If you just looked at the dark matter of a galaxy cluster, a single spiral galaxy, or a dwarf galaxy, it would be hard to tell which was which—they would roughly look like scaled up (or down) versions of each other. ...

Hunting Faint Dwarf Galaxies in the Field Using Integrated Light Surveys - Shany Danieli, Pieter van Dokkum, Charlie Conroy
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Gaia and the Red Clump

Postby bystander » Thu Nov 30, 2017 6:29 pm

Gaia and the Red Clump
astrobites | 2017 Nov 30
Philipp Plewa wrote:
Red clump (RC) stars are common stars, once similar to the sun, that have evolved into red giants now supported by helium fusion in their cores. Independent of their exact age or composition, all RC stars end up having about the same absolute luminosity. This is why they tend to “clump” in a particular spot in a color-magnitude or Hertzsprung–Russell diagram (Figure 1), and what makes them standard candles: The apparent brightness of RC stars is directly related to their distance.

As standard candles, RC stars have been used to measure distances to stellar associations in the Milky Way, as well as nearby galaxies. However, such measurements require a prior calibration, for which the reference brightness of known RC stars with known distances needs to be determined in the wavelength band used, and corrected for interstellar extinction. The authors of today’s paper carry out this calibration for a number of widely used bands, carefully taking into account the involved measurement uncertainties, and quantify just how useful RC stars are as standard candles. ...

Red Clump Stars and Gaia: Calibration of the Standard Candle using a Hierarchical Probabilistic Model - Keith Hawkins et al
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Charging Forward to Alpha Centauri!

Postby bystander » Thu Dec 07, 2017 3:04 pm

Charging Forward to Alpha Centauri!
astrobites | 2017 Dec 01
Amber Hornsby wrote:
Space travel is difficult. We’ve had to learn this lesson the hard way through some pretty spectacular failures (see the Mars Climate Orbiter), but we persevere and are rewarded with a lot of science and so many stunning images (see Juno). However, this is just our own Solar System, which is a tiny grain of sand in our Universe’s beach. Interstellar travel, that is, travelling to another star, is impossible with our current chemical-fuelled rocket technology. To reach our nearest neighbour, Proxima Centauri, will take current probes, travelling around 10 km per second, hundreds of thousands of years. Thus, the Breakthrough Starshot project was born.

Breakthrough Starshot intends to use lasers to accelerate tiny spacecrafts with huge sails, which they call sailcrafts, towards the Alpha Centauri system. Today’s paper contends with one of many concerns for the sailcraft as it traverses the interstellar medium (ISM) — magnetic fields. We have previously considered how the gravitational pull and radiation pressure from stars can be used to slow down a sailcraft upon reaching the Alpha Centauri system, enabling the spacecraft the time required to undertake good observations. In this bite, however, we will focus on the addition of a third force, the magnetic force, and how having an electrically-charged sail can dramatically impact a sailcraft’s trajectory. ...

Photogravimagnetic Assists of Light Sails: A Mixed Blessing for Breakthrough Starshot? - Duncan H. Forgan, René Heller, Michael Hippke
viewtopic.php?t=35830
viewtopic.php?p=270690#p270690
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Ancient Trees: A New Kind of Cherenkov Telescope

Postby bystander » Thu Dec 07, 2017 3:15 pm

Ancient Trees: A New Kind of Cherenkov Telescope
astrobites | 2017 Dec 04
Thankful Cromartie wrote:
Naturally, astronomers spend a lot of time looking up into the vastness of the cosmos. What if astronomy research could be conducted by looking down instead? Today’s astrobite demonstrates that something as common and lovely as trees can help us learn about the universe. ...

A rapid cosmic-ray increase in BC 3372-3371 from ancient buried tree rings in China - F. Y. Wang et al
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Surviving the Ice Age

Postby bystander » Thu Dec 07, 2017 3:23 pm

Surviving the Ice Age
astrobites | 2017 Dec 05
Shang-Min Tsai wrote:
Like most of the main sequence stars, the Sun brightened as it aged due to the gravitational contrast from hydrogen fusion. About 4 billion years ago, the Sun shined only about 70 percent as bright as today. Astronomers Carl Sagan and George Mullen raised the issue that according to the irradiation from the fainter young Sun, Earth should have been in a fully frozen state about 4 billion years ago, the so-called snowball Earth. However, if the Earth was truly in a snowball state, it would have been very difficult to escape the global glaciation, as we will discuss later in the article. The geological evidence, such as sedimentary rocks, also tells us that the Earth had liquid oceans over its evolution history. Carl Sagan and George Mullen proposed that a different atmospheric composition with more greenhouse gases, like ammonia or carbon-dioxide, would help to warm up the early Earth, preventing it from being locked in a global glaciation state.

An interesting complication is that the climate is not always the only stable state. Keeping all the conditions unchanged, a close to current climate can be tipped into a snowball state when the solar insolation slightly decreases. This may be easily understood by simply considering the albedo (reflectivity) of the ice. Ice has a much higher albedo (about 0.6) than seawater (about 0.2), so a snowball Earth is able to reflect much more radiation and maintain the temperature below the freezing point. There is a tipping point as the solar insolation decreases, the climate suddenly transitions to global glaciation, referred as the snowball bifurcation. In today’s paper, the authors investigate the snowball bifurcation on habitable tidally-locked planets compared to Earth. ...

No Snowball on Habitable Tidally Locked Planets - Jade Checlair, Kristen Menou, Dorian S. Abbot
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What is the Most Massive Object in the Universe?

Postby bystander » Thu Dec 07, 2017 3:39 pm

What is the Most Massive Object in the Universe?
astrobites | 2017 Dec 06
Gourav Khullar wrote:
There are many things to like about astrophysics. What I personally find fascinating is the range of sizes over which astrophysicists try to understand objects and phenomena. Having a grasp of micro-phenomena (like atomic transitions in spectra from stars) is as important as getting the hang of macrophysics (like merging of gigantic galaxies, and radiation from the big bang. My liking for objects like galaxy clusters stems from the above rationale too; various physical phenomena occur within these structures at all distance scales!

Another interesting scale is that of mass. Clusters are the most massive objects in the universe (typical mass of clusters is ~ 10^14 solar masses and above). They spawn from initial dark matter density perturbations in the very early universe, grow by adding nearby perturbations, convert into stable structures, and then go on a mass-accreting spree for billions of years into the evolved structures – made up of a dark matter halo, hot plasma, old galaxies and chaos – that we see today. Naturally, being able to predict or detect what would be the most massive galaxy cluster ever is a challenging task, but fruitful nonetheless. Because of the finite volume of the universe that can be observed, there must be ‘an object’ (likely a galaxy cluster) that can be called the most massive. ...

The Most Massive Objects in the Universe - Daniel E. Holz, Saul Perlmutter
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DAMPE cosmic ray spectrum may shed light on dark matter

Postby bystander » Thu Dec 07, 2017 3:53 pm

DAMPE cosmic ray spectrum may shed light on dark matter
astrobites | 2017 Dec 07
Kelly Malone wrote:
The DArk Matter Particle Explorer (DAMPE) is China’s first ever dedicated space observatory, and it made a splash last month with some interesting insights into the cosmic-ray spectrum of electrons and positrons. ...

Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons - DAMPE Collaboration
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A Map of Astronomy

Postby bystander » Fri Dec 15, 2017 4:53 pm

A Map of Astronomy
astrobites | 2017 Dec 08
Emily Sandford wrote: ...
Today’s bite is for those of you who, like me, like to see everything all in one place. It’s not a paper this time–rather, it’s a map of papers, everything written and published on the arXiv since its founding in 1991. Behold: physics. ...
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Flux Tube Bundles in Neutron Star Super-Mixture

Postby bystander » Fri Dec 15, 2017 5:00 pm

Flux Tube Bundles in Neutron Star Super-Mixture
astrobites | 2017 Dec 11
Lisa Drummond wrote:
Physicists are fascinated by neutron stars because their dense interior acts as a laboratory for exotic materials beyond what we find on Earth. Today’s paper suggests that flux tubes, which are quantum objects that exist in superconductors, could form bundles inside a neutron star – this unusual behaviour challenges the standard picture we have of terrestrial superconductors. ...

Flux tubes and the type-I/type-II transition in a superconductor coupled to a superfluid - Mark G. Alford, Gerald Good
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Exploding stars and sleight of hand: A case of magnetic misdirection

Postby bystander » Fri Dec 15, 2017 5:13 pm

Exploding stars and sleight of hand: A case of magnetic misdirection
astrobites | 2017 Dec 12
Kerrin Hensley wrote:
In the roiling outer layers of exploding stars, electrons are accelerated to near light speed. These relativistic electrons have a habit of causing glitches in orbiting spacecraft and sparking showers of secondary particles. Striking the retinae of in-orbit astronauts, they generate flashes of phantom light.

How do these electrons reach their enormously high velocities? The exact mechanism isn’t known, but it’s thought to depend upon the magnetic fields threaded throughout the expanding shells of young supernova remnants. Curiously, as shown in Figure 1, many young supernova remnants appear to have well-ordered radial magnetic fields, pointing neatly away from or toward the center of the explosion. While it’s not impossible for the magnetic field to be orderly, it’s reasonable to expect that the explosion of a dying star, which creates swirling knots and curlicues of hot plasma, would impart some turbulence and randomness to its magnetic field. Could the neat, radial pattern that we observe belie the true, messy magnetic field? If so, how can we tell? ...

When Disorder Looks Like Order: A New Model to Explain Radial Magnetic Fields in Young Supernova Remnants - J. L. West et al
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How fast is dark matter?

Postby bystander » Fri Dec 15, 2017 5:23 pm

How fast is dark matter?
astrobites | 2017 Dec 13
Nora Shipp wrote:
Our galaxy is embedded in a cloud of dark matter, thought to consist of tiny particles traveling along orbits through the halo. These dark matter particles permeate all regions of the galaxy, extending far beyond the edge of the bright central spiral, but also orbiting through our solar system, and even passing right through the Earth. This is why scientists build giant detectors, hoping to trap some of these dark matter particles as they pass by. So far, these experiments have not detected dark matter, but that lack of detection is actually quite interesting. Finding out what dark matter is not, thereby narrowing down the possibilities, is an important step towards revealing the true nature of these mysterious particles.

In order to really understand what it means when a detecter does not see dark matter, it is important to have a clear prediction for how much dark matter should be detected. For example, if we expect very few dark matter particles to pass through the Earth in a given amount of time, then maybe the lack of detections over a few years doesn’t actually mean those particles don’t exist. One essential piece of information in this prediction is the velocity of dark matter particles as they orbit past our solar system. ...

Empirical Determination of Dark Matter Velocities using Metal-Poor Stars - Jonah Herzog-Arbeitman et al
The Metal-Poor Stellar Halo in RAVE-TGAS and its Implications for
the Velocity Distribution of Dark Matter
- Jonah Herzog-Arbeitman et al
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Rogue One: Measurements of A Free-Floating Planet

Postby bystander » Fri Dec 15, 2017 5:34 pm

Rogue One: The First Einstein Ring Measurements of A Free-Floating Planet
astrobites | 2017 Dec 14
Mara Zimmerman wrote:
A free-floating, or rogue, planet is simply a planet that is not gravitationally bound to any star. Given that current planetary detection methods, such as the transiting method and radial velocity measurements, highly depend on the properties of the host star, planets without accompanying stars have proven more difficult to detect. However, there still have been detections of these objects, mainly due to microlensing surveys. The microlensing effect is shown in detail below in Figure 1. These kinds of events are rare, but when they are detected they reveal a lot of information about the planet creating the lens.

In today’s paper, the authors present microlensing event OGLE-2016-BLG-1540, which they attribute to the detection of a rogue planet candidate. In addition to detection, today’s paper presents the first measurement of the Einstein ring for this planet. ...

A Free-Floating Planet Candidate from the OGLE and KMTNET Surveys - Przemek Mroz et al
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Where do globular clusters (maybe) come from?

Postby bystander » Sun Dec 17, 2017 5:51 pm

Where do globular clusters (maybe) come from?
astrobites | 2017 Dec 15
Mia de los Reyes wrote:
In recent years, large galaxy surveys have given us an unprecedented look at galaxies at a wide range of redshifts. This has led to the discovery of a bewildering number of new galaxy types—a Galaxy Zoo, if you will. These galaxy subpopulations are important to study because they can provide direct links between the high-redshift universe and the galaxies we see today. (Just to refresh your memory, redshift is both a measure of distance and age, so high redshift means far away, when the universe was older.)

For example, the “Green Pea” galaxies were discovered by citizen scientists, who noticed that these galaxies don’t look much like traditional early-type (elliptical) or late-type (spiral) galaxies. (See this page for a quick primer on the differences between some galaxy classifications.) Instead, these Green Peas look… well, small and green (Figure 1). ...

But Green Peas aren’t the only weird galaxies out there. More recently, even lower-mass galaxies have been discovered. These galaxies, called “blueberries,” are similar to the Green Pea galaxies but fainter and with more intense star formation. (I personally think this is a poor choice of name because actual blueberries are more massive than actual peas, but they do look like blueberries (Figure 2). And maybe the people who named them were just really hungry?)

Today’s paper reports the discovery of even lower-mass galaxies, which the authors (somewhat more sensibly) call “Little Blue Dots,” or LBDs (Figure 3).

The Little Blue Dots were found in the Hubble Frontier Fields, patches of sky that the Hubble Space Telescope stared at for a really long time.

Little Blue Dots in the Hubble Space Telescope Frontier Fields:
Precursors to Globular Clusters?
- Debra Meloy Elmegreen, Bruce G. Elmegreen
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