astrobites 2018

Find out the latest thinking about our universe.
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A Delicate Binary Dance

Post by bystander » Thu Nov 08, 2018 6:43 pm

A Delicate Binary Dance
Astrobites | 2018 Nov 06
Stephanie Hamilton wrote:
Sometimes the little things in life are the most important.

In the case of the Solar System’s life, those little things are asteroids, comets, and Kuiper Belt objects — the leftover debris that didn’t conglomerate into planets. The giant planets (Jupiter, Saturn, Uranus, and Neptune) have tugged these smaller objects around during the Solar System’s 4.5 billion year lifetime, often ejecting them completely. Astronomers can deduce the past behavior of the giant planets by studying the small bodies of the Solar System and how they are distributed. In other words, the Solar System’s smallest members are an important key to unlocking its dynamical past.

With several hundred thousand known asteroids and a few thousand known Kuiper Belt objects, astronomers are just starting to understand the Solar System’s complex history. However, the early days of our Solar System largely remain a mystery (and by early days, I actually mean the first several hundred million years). Various ideas have been proposed to explain how the planets formed and arrived at their current orbits. Each theory predicts variations in observable features of the Solar System, such as how small bodies are distributed. All generally agree that the giant planets underwent some degree of migration, yet none satisfactorily explain what we observe. Today’s bite throws another wrench into the story. The subject? A peculiar binary asteroid named (617) Patroclus-Menoetius. ...

Evidence for Very Early Migration of the Solar System Planets
from the Patroclus-Menoetius Binary Jupiter Trojan
~ David Nesvorný et al
viewtopic.php?t=38681
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Re: astrobites 2018

Post by bystander » Thu Nov 08, 2018 7:01 pm

No, astronomers did not just claim that ‘Oumuamua is an extraterrestrial probe
Astrobites | 2018 Nov 07
Samuel Factor wrote:
If you have been paying attention to space news recently you may have seen stories suggesting that the interstellar object ‘Oumuamua, which passed through our solar system just over a year ago, could have been an extraterrestrial probe. Some headlines are a bit sensational (e.g. Scientists say mysterious ‘Oumuamua’ object could be an alien spacecraft (NBC News), Mysterious interstellar object floating in space might be alien, say Harvard researchers (USA Today), or An Alien Spacecraft May Have Passed Through Our Solar System Last Year, Claim Scientists (IFL Science!)) while other articles are a little more doubtful (e.g. Interstellar object may have been alien probe, Harvard paper argues, but experts are skeptical (CNN)). Today’s paper is the source of these articles and, while the premise is a little less far-fetched than you might think, the conclusion lacks transparency. ...
Could Solar Radiation Pressure Explain 'Oumuamua's Peculiar Acceleration? ~ Shmuel Bialy, Abraham Loeb
viewtopic.php?t=37698
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Black Holes During the Cosmic Dawn

Post by bystander » Thu Nov 08, 2018 7:20 pm

Black Holes During the Cosmic Dawn
Astrobites | 2018 Nov 08
Joshua Kerrigan wrote:
Cosmologically important phenomena are typically discussed on the scales of gigaparsecs (Gpc); to give you some idea of the sizes involved, one Gpc could fit approximately 33 thousand Milky Way galaxies end-to-end. That’s a pretty crazy scale and with that in mind today we’ll gain an understanding for how astrophysical events beginning on the order of parsecs can have far-reaching affects cosmologically.

The cosmological period prior to the reionization of the Universe’s hydrogen is typically described as being the cosmic dawn. This stage in the history of the Universe is marked by the formation of the first stars and galaxies. But it doesn’t end there, connecting these large structures throughout the Universe is the Intergalactic Medium (IGM). The IGM during the cosmic dawn consists of mostly neutral hydrogen, and compared to galaxies, is much less dense (10-27 kg/m3 compared to the density of our Milky Way which is ~10-19 kg/m3). The UV radiation from these early stars and galaxies are what most astronomers and cosmologists believe led to reionization. Put simply, this ionizing radiation extended symmetrically from these sources and over time these regions of reionized IGM began to overlap leading to complete reionization. While this is our current `best guess’, cosmologists typically wonder: ‘What roles do other structures play during this period?’ One type of galaxy of interest are those containing Active Galactic Nuclei (AGN), which are galaxies with a very dense core with a supermassive black hole (SMBH) at its center that is accreting matter. These AGN are extremely luminous and can produce a lot of X-ray and UV emissions. What we’ll be exploring today is how these SMBH influence the surrounding regions. ...

Observing the Influence of Growing Black Holes on the Pre-reionization IGM ~ Evgenii O. Vasiliev, Shiv K. Sethi, Yuri A. Shchekinov
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Feeding black holes, up close and personal

Post by bystander » Tue Nov 13, 2018 4:31 pm

Feeding black holes, up close and personal
Astrobites | 2018 Nov 12
Joanna Ramasawmy wrote:
Supermassive black holes — the phenomenal engines that power the brightest objects in the universe, quasars — are observed only moments (ok, a few hundred million years) after the Big Bang. These observations present a major problem for astrophysics: how can these supermassive objects grow so large in such a short space of time?

There are a few competing scenarios for the formation of supermassive black holes, or SMBHs. ... A critical factor in working out which of these scenarios is most likely is our understanding of how black holes grow. And it’s complicated. The main ingredient is gas, but funnelling that gas into a black hole depends on processes spanning orders of magnitude in distance, from the megaparsecs-wide large scale structure of the cosmic web down to the relatively miniscule intricacies of gas falling into the event horizon of a black hole as small as our own solar system. Creating a simulation that can explore this detail as well as taking the largest structures in the universe into account is, as the authors of today’s astrobite put it, a “tremendous computational challenge”. ...

Zooming in on Supermassive Black Holes: How Resolving Their Gas Cloud Host
Renders Their Accretion Episodic
~ Ricarda S. Beckmann, Julien Devriendt, Adrianne Slyz
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A hidden reservoir of multi-planet systems?

Post by bystander » Tue Nov 13, 2018 4:44 pm

A hidden reservoir of multi-planet systems?
Astrobites | 2018 Nov 13
Eckhart Spalding wrote:
Kepler is dead, long live Kepler! It would be an understatement to say that the Kepler spacecraft transformed our understanding of exoplanets, and it’s sad to see it go. Kepler made an especially big impact on our understanding of exoplanet systems with Neptune- or Earth-sized planets, especially those close in to their stars, and with periods of fewer than ~100 days. In combination with ground-based transit and radial velocity (RV) surveys, the thousands of planets we now know of make it possible to actually do population syntheses and start to understand the demographics of exoplanet systems.

For example, we have learned that there is a pretty solid correlation between host star metallicity and the presence of hot Jupiter planets, which may be evidence for core-accretion models of planet formation. Strangely, systems of multiple, rocky planets appear around stars with a wide range of metallicities. Could it be that there just isn’t enough material in protoplanetary disks around metal-poor stars to feed Jovian-mass planets? Or are there severe observational biases in play? RV surveys have tended to avoid metal-poor stars, because they have fewer absorption lines to measure; maybe metal-poor stars haven’t been sampled enough? Even more curiously, systems with hot Jupiters appear to be very distinct from compact multi-planet systems: they tend not to overlap. To try to resolve some of these conundrums, the authors of today’s paper shed new light on the relation of exoplanet system type to host star metallicity. ...

Compact Multi-planet Systems are more Common around Metal-poor Hosts ~ John M. Brewer et al
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Old but gold: a huge primordial proto-cluster

Post by bystander » Thu Nov 15, 2018 5:00 pm

Old but gold: a huge primordial proto-cluster
Astrobites | 2018 Nov 14
Natalia Del Coco wrote:
The biggest structures know in the Universe are galaxy clusters (GC): they are made of hundreds or even thousands of galaxies, lots of gas and a huge amount of dark matter. But a long time ago, these giants were actually babies. Right after the Big Bang, when no galaxies, stars or even molecules were formed yet, the Universe was extremely homogeneous, although it had density fluctuations with relative amplitude of ~ 10-5. During the cosmos’ expansion, the regions that initially were slightly heavier became increasingly heavier, because mass attracts mass. Then, clumps of gas turned into stars. Due to their mutual gravitational attraction force, they gradually got closer to each other, growing into galaxies, which congregated further – also because of the gravity – into today’s GC (for a deeper understanding, read this).

Since looking at distant astronomical objects means to look into the past, we may be able to see the progenitors of the GC, the proto-clusters. They should be far from us (at high redshifts, z), comprised by dozens of galaxies forming lots of stars, therefore containing a huge amount of dust and gas (the stars’ ingredients). In other words, we should see these proto-clusters as distant aggregations of galaxies that are very bright and very red, and therefore visible only in the submillimeter/millimeter from Earth (which are the color and wavelength detected in earth frame from the gas and dust radiation of distant galaxies when heated by its stars). To observe these systems may teach us about how the Universe and its structures evolve through the cosmic time. In today’s paper, the authors report the discovery of a proto-cluster core with extreme characteristics: super dense, super massive and super old. ...

An Extreme Protocluster of Luminous Dusty Starbursts in the Early Universe - I. Oteo et al
viewtopic.php?t=38233
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How can you tell if a young planet is migrating?

Post by bystander » Thu Nov 15, 2018 5:08 pm

How can you tell if a young planet is migrating?
Astrobites | 2018 Nov 15
Michael Hammer wrote:
Imagine if we could watch planetary systems take shape. We would point our telescopes at the nearest and brightest newly-formed stars that are still surrounded by some of the leftover material from the cloud in which they formed. We would then see this leftover material mold itself into a disk around the star, a so-called “proto-planetary disk” made up of mostly gaseous molecules and a small, but sufficient amount of dust for building planets. Every day, we could observe each disk and watch each system evolve.

With a series of snapshots, we would see things like the first planetesimals coalescing from what started out as microscopic micron-sized dust. We would see the gas in the disk slowly spill onto the star. We would see the dust in the disk drift through the gas and fall towards the star as well. And eventually, we would see the planetesimals grow large enough to form planets the size of the Earth or even Jupiter. Once these planets form, we would also see whether each one stays where it formed or if they migrate and move either towards or away from their stars.

Unfortunately, many of these processes last not days, but thousands of years, or even the entire lifetime of the disk itself (3 to 10 million years). To make matters worse, planets that have just formed are often extremely difficult to spot as they are typically too small, too dim, and also enshrouded by the disks in which they formed. Both of these factors make it difficult to study the processes that sculpt planetary systems.

In particular, we cannot wait millennia to see if planets migrate away from where they formed or if they just stay where they are. This issue is of paramount importance since we cannot develop good models of how specific planets formed if we do not even know where they formed. In today’s paper, Farzana Meru et al. propose a solution to that problem by developing a new way to probe whether a planet is migrating through the disk, just from looking at observations of dust at a single point in time. ...

Is the Ring Inside or Outside the Planet?
The Effect of Planet Migration on Dust Rings
~ Farzana Meru et al
viewtopic.php?t=38808
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Re: Old but gold: a huge primordial proto-cluster

Post by Ann » Thu Nov 15, 2018 5:35 pm

bystander wrote:
Thu Nov 15, 2018 5:00 pm
Old but gold: a huge primordial proto-cluster
Astrobites | 2018 Nov 14
Natalia Del Coco wrote:
The biggest structures know in the Universe are galaxy clusters (GC): they are made of hundreds or even thousands of galaxies, lots of gas and a huge amount of dark matter. But a long time ago, these giants were actually babies. Right after the Big Bang, when no galaxies, stars or even molecules were formed yet, the Universe was extremely homogeneous, although it had density fluctuations with relative amplitude of ~ 10-5. During the cosmos’ expansion, the regions that initially were slightly heavier became increasingly heavier, because mass attracts mass. Then, clumps of gas turned into stars. Due to their mutual gravitational attraction force, they gradually got closer to each other, growing into galaxies, which congregated further – also because of the gravity – into today’s GC (for a deeper understanding, read this). ...

An Extreme Protocluster of Luminous Dusty Starbursts in the Early Universe - I. Oteo et al
viewtopic.php?t=38233
Natalia del Coco wrote:

The lower limit value obtained was solar masses per year, being the highest found until now.
...
For the primer, they utilized the CI emission lines, achieving a minimal value of times the solar mass.

The second one was calculated in three different manners, reaching up to times the solar mass (for comparison, the estimated mass of the Local Group is times the solar mass).
I don't get it.

Ann
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Re: Old but gold: a huge primordial proto-cluster

Post by BDanielMayfield » Fri Nov 16, 2018 5:59 am

Ann wrote:
Thu Nov 15, 2018 5:35 pm
Natalia del Coco wrote:

The lower limit value obtained was _____ solar masses per year, being the highest found until now.
...
For the primer, they utilized the CI emission lines, achieving a minimal value of ______ times the solar mass.

The second one was calculated in three different manners, reaching up to _______ times the solar mass (for comparison, the estimated mass of the Local Group is ______ times the solar mass).
I don't get it.

Ann
Nor could anyone else Ann. She must have left filling in the numbers as an exercise for the reader :?:
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Re: Old but gold: a huge primordial proto-cluster

Post by Ann » Fri Nov 16, 2018 6:12 am

BDanielMayfield wrote:
Fri Nov 16, 2018 5:59 am
Ann wrote:
Thu Nov 15, 2018 5:35 pm
Natalia del Coco wrote:

The lower limit value obtained was _____ solar masses per year, being the highest found until now.
...
For the primer, they utilized the CI emission lines, achieving a minimal value of ______ times the solar mass.

The second one was calculated in three different manners, reaching up to _______ times the solar mass (for comparison, the estimated mass of the Local Group is ______ times the solar mass).
I don't get it.

Ann
Nor could anyone else Ann. She must have left filling in the numbers as an exercise for the reader :?:
Obviously. :wink:

The task she has given us, filling in the missing numbers, is a bit hard for the average amateur astro nerd. :P

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Re: Old but gold: a huge primordial proto-cluster

Post by bystander » Fri Nov 16, 2018 2:19 pm

Ann wrote:
Thu Nov 15, 2018 5:35 pm
Natalia del Coco wrote:
The lower limit value obtained was 6500 solar masses per year, being the highest found until now.
...
For the primer, they utilized the CI emission lines, achieving a minimal value of 6.6×1011 times the solar mass.

The second one was calculated in three different manners, reaching up to 4.4×1013 times the solar mass

(for comparison, the estimated mass of the Local Group is 4.2×1012 times the solar mass).
The first three values are from the abstract of the referenced paper (DOI: 10.3847/1538-4357/aaa1f1).
The mass for the Local Group I took from the abstract of arXiv:1312.2587.
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Re: Old but gold: a huge primordial proto-cluster

Post by Ann » Fri Nov 16, 2018 3:47 pm

bystander wrote:
Fri Nov 16, 2018 2:19 pm
Ann wrote:
Thu Nov 15, 2018 5:35 pm
Natalia del Coco wrote:
The lower limit value obtained was 6500 solar masses per year, being the highest found until now.
...
For the primer, they utilized the CI emission lines, achieving a minimal value of 6.6×1011 times the solar mass.

The second one was calculated in three different manners, reaching up to 4.4×1013 times the solar mass

(for comparison, the estimated mass of the Local Group is 4.2×1012 times the solar mass).
The first three values are from the abstract of the referenced paper (DOI: 10.3847/1538-4357/aaa1f1).
The mass for the Local Group I took from the abstract of arXiv:1312.2587.
Thanks, bystander! :D

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Re: astrobites 2018

Post by BDanielMayfield » Fri Nov 16, 2018 4:38 pm

Ann is by no means an "average amateur astro nerd."

Come to think of it, none of us are. Especially bystander. Well done sir.
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Why don’t they just break up?

Post by bystander » Sat Nov 17, 2018 3:41 am

Why don’t they just break up?
Astrobites | 2018 Nov 16
Thankful Cromartie wrote:
Known for their extreme density and unfathomably rapid rotation rates, millisecond pulsars (MSPs) are among the Universe’s most exotic treasures. Here at astrobites, however, one rotation every few milliseconds isn’t good enough — we need to know why they won’t spin faster. ...

The authors of today’s featured article conducted simulations to explore the spin period distribution in low-mass X-ray binary (LMXB) neutron stars, which are actively accreting matter from their low-mass stellar companions. They investigated what spin period distributions would result from three different GW emission mechanisms. Observations have suggested that the population of rapidly rotating, accreting pulsars is bimodal in spin frequency (see Figure 1), with an excess of MSPs in the 550-600 Hz range. If their GW emission simulations could reproduce such a distribution, it might aid in understanding the mysterious lack of ultra-fast MSPs. ...

Population Synthesis of Accreting Neutron Stars Emitting Gravitational Waves ~ Fabian Gittins, Nils Andersson
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What does a neutron star actually look like?

Post by bystander » Thu Nov 22, 2018 3:59 pm

What does a neutron star actually look like?
Astrobites | 2018 Nov 19
Lisa Drummond wrote:
Today we will look at two papers which attempt to answer the question posed in the title – what does a neutron star look like up-close? In the process, they illustrate (1) a cool feature of relativity which means we can see the far-side of a neutron star from a single vantage point and (2) that this feature is relevant for understanding astrophysical observations. ...

The Relativistic “Looks” of a Neutron Star ~ H.P. Nollert et al, 1989, Astronomy & Astrophysics
Light Deflection Near Neutron Stars ~ U. Krauss, 1998, Relativistic Astrophysics
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Chance the IMF

Post by bystander » Thu Nov 22, 2018 4:22 pm

Chance the IMF: How small fluctuations can have big effects on dwarf galaxies
Astrobites | 2018 Nov 20
Mia de los Reyes wrote:
Dwarf galaxies are little, but they pack a big punch—they’re among the most extreme and diverse environments in the universe. Also, our current understanding of structure formation in the universe (called ΛCDM) suggests that these low-mass galaxies formed first and built up into larger structures like our own Milky Way. This means that understanding the formation of dwarf galaxies can tell us a lot about how overall structures form in the universe.

Computational models of dwarf galaxies have become realistic enough to be able to match most theoretical predictions. The highest-resolution models are now pushing to smaller and smaller galaxy masses—into the regime of the “ultra-faint dwarf galaxies” (UFDs, which we’ll define as galaxies with stellar masses <10^{5} solar masses). But because UFDs are such extreme environments, some of the standard assumptions about typical galaxy formation break down.

Today’s paper by Applebaum et al. focuses on one of these assumptions, arguably the most ubiquitous of all: the stellar initial mass function (IMF). This function describes the relative numbers of stars that are born at different masses. Why does this matter? It turns out that assumptions about the IMF underpin nearly all of our observations of galaxy properties and our theoretical models of galaxy evolution. So questions about the IMF—its exact shape, whether or not it’s the same in all galaxies, etc.–are actually incredibly important areas of active research. And as the authors of today’s paper discover, the IMF can have huge consequences in UFDs. ...

Roll of the Dice: A Stochastically Sampled IMF Alters
the Stellar Content of Simulated Dwarf Galaxies
~ Elaad Applebaum et al
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NOW that’s what I call a moon!

Post by bystander » Thu Nov 22, 2018 4:33 pm

NOW that’s what I call a moon!
Astrobites | 2018 Nov 21
Amber Hornsby wrote:
With over 100 moons between them, most of the Solar System satellites can be found around our gas giants – Saturn and Jupiter. Similar to planet formation, moons are thought to form in gaseous circumplanetary disks (CPDs) which surround giant planets during their later stages of formation.

But, what about smaller planets like Neptune and Uranus? Today’s bite delves into the world of radiative hydrodynamical simulations to see whether CPDs, and thus moons, could also form around our ice giants. ...

In Situ Formation of Icy Moons of Uranus and Neptune ~ J. Szulágyi, M. Cilibrasi, L. Mayer
Encouraging Prospects for Moon Hunters
National Centre of Competence in Research: PlanetS | 2018 Nov 19
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Mirach’s Ghost and Mirach’s Goblin

Post by bystander » Sat Nov 24, 2018 3:53 pm

Mirach’s Ghost and Mirach’s Goblin:
A New Galaxy Found Near the Local Group

Astrobites | 2018 Nov 22
Daniel Berke wrote:
Despite the title this isn’t a Halloween post accidentally scheduled for Thanksgiving, but a full explanation will take a little while so bear with me: the brightest star in the constellation of Andromeda is known as Mirach, a brilliant 2nd-magnitude red giant star. Located a mere seven arc-minutes away on the sky (the full Moon is about thirty arc-minutes across for reference) sits NGC 404, the closest-known lenticular galaxy. NGC 404 is about ten million light-years away, just beyond the Local Group of galaxies which contains our own Milky Way, the Andromeda Galaxy (Messier 31), the Large and Small Magellanic Clouds, and several dozen dwarf satellite galaxies. Due to NGC 404’s proximity to such a bright star it was historically very difficult to see or photograph it, especially for observers with early telescopes. Its diffuse, nebulous look could easily be mistaken for a blurry internal reflection of Mirach in those early telescopes, which led to its common nickname of “Mirach’s Ghost.” (This fact, combined with its NGC number, meant I really couldn’t help myself making the extremely obvious joke seen in Figure 1.)

Today’s paper covers the discovery of another galaxy a bit further away from Mirach on the sky (about one degree), but so small and diffuse that it was only discovered a few years ago. In September 2016 an amateur astronomer named Giuseppe Donatiello (who’s listed as one of the authors on the paper) was taking long exposures of the area around the Andromeda Galaxy, when he noticed a faint smudge in one of his images that didn’t match any known features, as seen in Figure 2. ...

Mirach's Goblin: Discovery of a dwarf spheroidal galaxy behind the Andromeda galaxy ~ David Martinez-Delgado et al
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Cluster Creation in a Cosmological Context

Post by bystander » Mon Dec 03, 2018 5:50 pm

Cluster Creation in a Cosmological Context
Astrobites | 2018 Nov 27
Heitor Ernandes wrote:
Globular clusters consist of around 10,000 to 10,000,000 (Omega Cen) stars, which are tightly bound by gravity. Their structure makes us expect that they were born in a single star formation event (not entirely true though, they can show multiple stellar populations). This means that a globular cluster would have formed from a single gas cloud at the same time in the early Universe in the highest density peaks.

Globular clusters can be generally separated in two groups—the blue and the red clusters—with regard to their color and metallicity. ... It is proposed that the blue clusters form in galaxies in the early Universe at high redshifts (z) while the red clusters are formed in situ through merging mechanisms. ... In this paper the RAMSES code is used, which is a zoom-in cosmological simulation. A set of parameters and constants are used as input, including the evolution in time and space for a system with a particular resolution. ...

The Origin of the Milky Way Globular Clusters ~ Florent Renaud, Oscar Agertz, Mark Gieles
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The Milky Way’s Ghostly Neighbor

Post by bystander » Mon Dec 03, 2018 5:58 pm

The Milky Way’s Ghostly Neighbor
Astrobites | 2018 Nov 29
Nora Shipp wrote:
An international team of scientists has discovered a curious new galactic neighbor. Antlia 2 (or Ant 2 for short) is a dwarf galaxy unlike any previously detected. Its area is similar to that of the Large Magellanic Cloud (LMC; the largest satellite of the Milky Way) and about a third the size of the Milky Way itself, but it contains about 10,000 times fewer stars than the LMC. This relatively small number of stars spread across this large area causes Ant 2 to appear almost ghostly – a faint, diffuse shadow of a galaxy (Figure 1). For this reason, along with the fact that Ant 2 is partially hidden behind the bright disk of the Milky Way, Ant 2 was much more difficult to detect than similarly-sized galaxies like the LMC. Furthermore, this hard-to-find, unusual galaxy does not fit neatly into commonly accepted theories; its discovery opens up exciting new questions about dark matter and galaxy formation. ...

The Hidden Giant: Discovery of an Enormous Galactic Dwarf Satellite in Gaia DR2 ~ G. Torrealba et al
viewtopic.php?t=38883
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A change in the tides

Post by bystander » Mon Dec 03, 2018 6:08 pm

A change in the tides
Astrobites | 2018 Dec 01
Katie Harris wrote:
In May 2016, the world was struck with sudden excitement over the discovery of the Trappist-1 system. At just 12 parsecs away, the system is host to several Earth-sized planets inside the habitable zone, which makes said planets prime candidates for harbouring life (see this bite and this one for more). The discovery of this neighbouring exoplanet system ignited the curiosity not only of astronomers and exoplanet scientists who had a new system to study but the general public who were excited to follow the search for possible signs of extraterrestrial beings.

However, as we peer more deeply into the dynamics of the system, the once idyllic scene of Trappist-1 is rapidly becoming more complex. The system is unique in that all the planets are very tightly packed, with the furthest out only having an orbital period of 12 days. While the questions of excess radiation and water loss have been well parsed, today’s paper calls attention to the role of planet-planet tides in the system. ...

Planet-Planet Tides in the TRAPPIST-1 System ~ Jason T. Wright
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The Stuff of Stars

Post by bystander » Thu Dec 06, 2018 4:12 pm

The Stuff of Stars
Astrobites | 2018 Dec 03
Mia de los Reyes wrote:
“The universe is mostly hydrogen and ignorance,” goes a version of one of my favorite quotes. It’s true: we’re pretty ignorant about dark energy (~70% of the universe) and dark matter (~26% of the universe). Of the matter that we do know about (the “baryonic matter”), about 3/4 is hydrogen!

Today, it’s an accepted fact that nearly all stars are predominantly made of hydrogen. But how do we know this? Enter Cecilia Payne, whose PhD thesis in 1925 changed the way we understand the composition of the universe. Her thesis tied together two seemingly disparate elements—a theory by Indian physicist Meghnad Saha, and the system used to classify stars by Annie Jump Cannon and other women astronomers—into one beautiful work that explained the stuff of stars.

Payne’s thesis was written as a book with three parts, which we’ll go through here. ...

Stellar Atmospheres, A Contribution to the Observational
Study of High Temperature in the Reversing Layers of Stars
~ Cecilia Payne
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Potential Planets in the Bulge

Post by bystander » Thu Dec 06, 2018 4:21 pm

Potential Planets in the Bulge
Astrobites | 2018 Dec 04
Lauren Sgro wrote:
Everyone loves exoplanets. And luckily for us (everyone), astronomers have discovered thousands of new alien worlds in the last decade using data from the Kepler mission. Two campaigns (9 and 11) of the extended Kepler mission, dubbed K2, set sights on the galactic bulge. Today’s authors supplement data from these K2 campaigns with VVV survey data, an ongoing mission to survey the galactic bulge in near-infrared wavelengths, in order to hunt for exoplanets.

The authors analyze just shy of 900 light curves from K2 for their exoplanetary treasure hunt. Specifically, they are interested in transiting exoplanets, which are easy to detect from light curves alone. Light curves show how the light we receive from a star changes over time — if a significant dimming occurs periodically, it could be a sign that an exoplanet is passing in front of its host star, blocking a portion of the star’s light from reaching us.

The next step is to analyze the aforementioned light curves for periodic signals. The authors fit the signals they find, discard bad photometry, and use any available VVV survey data to throw out false positives like nearby stars, which can disrupt the light curve (VVV has a much higher resolution than K2, making it easy to double check for contaminants not resolved in the K2 images). From their analysis, they find five real-life transits that likely belong to exoplanets. ...

Search for Exoplanetary Transits in the Galactic Bulge ~ C.C.Cortes, D. Minniti, S. Villanova
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What Are Starspots Like on Sun-like Stars?

Post by bystander » Sat Dec 08, 2018 3:41 pm

What Are Starspots Like on Sun-like Stars?
Astrobites | 2018 Dec 06
Kerrin Hensley wrote:
We refer to stars with approximately the same spectral type as the Sun as “Sun-like,” but how similar are they really? One way to gauge this is by studying the stars’ magnetic activity, like their starspots (relatively cool areas of the stellar photosphere where magnetic flux bubbles out of the surface) or stellar flares (sudden releases of energy in the form of lots and lots of photons — all the way from X-ray to radio). ...

However, our telescopes don’t have the resolution necessary to directly image starspots on other stars. How do we study activity on distant stars? ...

Lifetimes and Emergence/Decay Rates of Star Spots on Solar-type Stars Estimated
by Kepler Data in Comparison with Those of Sunspots
~ Kosuke Namekata et al
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Mixing up a Batch of Stars

Post by bystander » Sat Dec 08, 2018 3:51 pm

Mixing up a Batch of Stars
Astrobites | 2018 Dec 07
Jamila Pegues wrote:
Though the Big Bang and the birth of the universe as we know it – or, at least, *think* we know it – all happened way before any of us were born, we can still piece together the universe’s history from the starlight we observe today. ...

In today’s astrobite, we consider the story told by a special class of second-generation star: the carbon-enhanced, metal-poor (CEMP) stars. CEMP stars are metal-poor but have relatively high carbonicity, which means they have enhanced amounts of carbon compared to their iron content. Specifically, we look at CEMP-no stars, which are CEMP stars that also have relatively little barium with respect to iron. These CEMP-no stars are believed to directly represent the chemical composition of the environment they formed in. ...

Today’s authors consider a different perspective. They question if the carbon enhancements observed for these CEMP-no stars might be explained in part by inhomogeneous metal mixing – aka, an uneven distribution of metals in the environment where they formed. So far, not much research has been done on the effects of inhomogeneous mixing of elements in the early universe. So today’s authors used theory and modeling to test their scenario, in which inhomogeneous metal mixing leads to the formation of a CEMP-no star. ...

Formation of carbon-enhanced metal-poor stars as a consequence of inhomogeneous metal mixing ~ Tilman Hartwig, Naoki Yoshida
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