astrobites: Daily Paper Summaries 2019

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The Secret to a Steady Relationship in the Kuiper Belt

Post by bystander » Sun Jul 14, 2019 11:12 pm

The Secret to a Steady Relationship in the Kuiper Belt
astrobites | Daily Paper Summaries | 2019 Jul 01
Will Saunders wrote:
Every object in the Kuiper Belt is a survivor. Some survived collisions that nearly smashed them apart and others survived nearby encounters with planets that could have sent them out of the Solar System forever. The luckiest accreted dust from their smashed neighbors or used a nearby passage of Neptune to fling them into a stable orbit. Of the many that survived, most survived alone.

A small number of known Kuiper Belt Objects (KBOs), however, contain companions that orbit around the mutual center of mass of the binary system. These KBO binaries can vary from equal mass binaries to a pebble orbiting a monolith. Astronomers study KBOs in part because their survival patterns give clues to the conditions in the early Solar System; the same is true about survival of KBO binaries. Today’s authors recently published work on a binary asteroid, (617) Patroclus-Menoetius, that survived unprobable transportation from the outer Solar System to an orbit near Jupiter. ...

The goal of the research presented in this paper is to simulate the history of KBO binaries to determine how each population evolved. As more binaries are discovered, better population statistics can then be used to estimate the conditions in the early Solar System that created them. ...

Binary Survival in the Outer Solar System ~ David Nesvorny, David Vokrouhlicky
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The Sun vs. Your Uncle: Chromosphere Edition

Post by bystander » Sun Jul 14, 2019 11:18 pm

The Sun vs. Your Uncle: Chromosphere Edition
astrobites | Daily Paper Summaries | 2019 Jul 02
Stephanie Hamilton wrote:
We’ve all been there. You’re enjoying a nice float in the pool on a hot summer’s day when suddenly you hear those dreaded words… “CANNONBALL!” The next thing you know, your uncle soars overhead and you brace yourself for the ensuing tsunami. But you might not have known that as your uncle was cannonballing, an analogous process may also have been happening on the surface of the sun. Today’s paper reports the discovery of a phenomenon in the Sun’s atmosphere that the authors name “cannonballs” due to their circular appearance and arc-like trajectory, much like your uncle and his pooltime performance. ...

Chromospheric Cannonballs on the Sun ~ Shuhong Yang et al
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Morpheus, God of Dreams and Morphological Galaxy Classification

Post by bystander » Sun Jul 14, 2019 11:40 pm

Morpheus, God of Dreams and Morphological Galaxy Classification
astrobites | Daily Paper Summaries | 2019 Jul 03
Kate Storey-Fisher wrote:
In Greek mythology, Morpheus is the God of Dreams, who shaped and formed the dreams of mortals. It is fitting, then, that Morpheus is now dabbling in classifying galaxies based on their shape, to help us mortals with our astronomy. Born of Tensorflow and Python 3, the 21st-century Morpheus is a new neural network dreamed up by the authors of today’s paper to perform galaxy classification.

The shape, or morphology, of galaxies is critical to understanding their formation and evolution. As it is such an important characteristic, astronomers must have found a robust algorithm or quantitative model that determines morphology, right? Not quite—it turns out that the most accurate way to classify galaxies morphologically is to round up a pack of trained astronomers and have them look through pictures of galaxies by eye.

Unfortunately, galaxies far outnumber astronomers. The most well-known method that overcomes this is Galaxy Zoo, which enlists interested internet users to classify galaxies. While very successful, this is still limited by accuracy and scalability. To address these issues, researchers have begun to use machine learning techniques to push morphological classification forward.

Today’s paper introduces Morpheus, a new deep learning network to classify astronomical images. The network determines the morphological type of each pixel in an astronomical image, increasing its capabilities beyond existing methods. ...

Morpheus: A Deep Learning Framework for Pixel-Level Analysis
of Astronomical Image Data
~ Ryan Hausen, Brant Robertson
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Twins for the Win!

Post by bystander » Mon Jul 15, 2019 2:01 am

Twins for the Win!
astrobites | Daily Paper Summaries | 2019 Jul 04
Tomer Yavetz wrote: ...
Like humans, the stars in our night sky are also typically born into large extended families. Star formation occurs in dense molecular clouds, in which many stars are typically born around the same time. If two stars are born close enough together to be gravitationally bound to each other, they form a binary system (or a triple system if there are three, etc.). These systems are so common that roughly half of the stars in our galaxy have companions, or siblings. ...

Two of the most important parameters for studying binaries are their separation and the ratio of the two stars’ masses. Studying the statistics of these two quantities is central to every single one of the topics mentioned above. One particularly intriguing feature is a surprisingly large excess of equal-mass binaries, sometimes referred to as “twin systems.”

An abrupt excess of binaries with mass ratios between 0.95 and 1 was first noticed many decades ago, but it has frequently been tagged as an artifact of observational biases. In other words, equal mass binaries are easier to observe than binary systems with two stars of different masses, and it was believed that correcting for this selection bias might remove the excess altogether. Today’s paper makes use of data from the Gaia mission to provide a conclusive answer to this. ...

Discovery of an equal-mass "twin'' binary population reaching 1000+ AU separations ~ Kareem El-Badry et al
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Re: Twins for the Win!

Post by Ann » Mon Jul 15, 2019 6:38 am

bystander wrote:
Mon Jul 15, 2019 2:01 am
Twins for the Win!
astrobites | Daily Paper Summaries | 2019 Jul 04
Tomer Yavetz wrote: ...
Like humans, the stars in our night sky are also typically born into large extended families. Star formation occurs in dense molecular clouds, in which many stars are typically born around the same time. If two stars are born close enough together to be gravitationally bound to each other, they form a binary system (or a triple system if there are three, etc.). These systems are so common that roughly half of the stars in our galaxy have companions, or siblings. ...

Two of the most important parameters for studying binaries are their separation and the ratio of the two stars’ masses. Studying the statistics of these two quantities is central to every single one of the topics mentioned above. One particularly intriguing feature is a surprisingly large excess of equal-mass binaries, sometimes referred to as “twin systems.”

An abrupt excess of binaries with mass ratios between 0.95 and 1 was first noticed many decades ago, but it has frequently been tagged as an artifact of observational biases. In other words, equal mass binaries are easier to observe than binary systems with two stars of different masses, and it was believed that correcting for this selection bias might remove the excess altogether. Today’s paper makes use of data from the Gaia mission to provide a conclusive answer to this. ...

Discovery of an equal-mass "twin'' binary population reaching 1000+ AU separations ~ Kareem El-Badry et al
Surely Alpha Centauri is a twin system? The masses of the two main components are 1.10 and 0.92 solar, according to Jim Kaler. They orbit one another in 79.9 years, with an average separation slightly larger than the orbit of Uranus.

The third component, tiny Proxima Centauri, is ridiculously far away, with an orbit (if indeed it is in orbit) of at least three-quarters of a million years, according to Jim Kaler. So Alpha Centari may be all about the twins, and Proxima might be like a little piece of space fluff that had its path around the Milky Way disturbed by the twins, but we can't be sure that it managed to become a real hitch-hiker of spaceship Alpha Centauri in the Universe.

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Re: Twins for the Win!

Post by BDanielMayfield » Mon Jul 15, 2019 6:25 pm

Ann wrote:
Mon Jul 15, 2019 6:38 am
Surely Alpha Centauri is a twin system? The masses of the two main components are 1.10 and 0.92 solar, according to Jim Kaler. They orbit one another in 79.9 years, with an average separation slightly larger than the orbit of Uranus.
I think the two main stars of the Alpha Cen system would almost qualify as twins, as their A to B mass ratio is about 1 : 0.84.
The third component, tiny Proxima Centauri, is ridiculously far away, with an orbit (if indeed it is in orbit) of at least three-quarters of a million years, according to Jim Kaler. So Alpha Centari may be all about the twins, and Proxima might be like a little piece of space fluff that had its path around the Milky Way disturbed by the twins, but we can't be sure that it managed to become a real hitch-hiker of spaceship Alpha Centauri in the Universe.

Ann
Proxima is now known with a high degree of confidence to actually be a gravitationally bound member of the Alpha Cen system. From wikipedia's article on Proxima:
Proxima Centauri forms a third member of the Alpha Centauri system, being identified as component Alpha Centauri C, and is 2.18° to the southwest of the Alpha Centauri AB pair.[17] Currently it has a physical separation of about 12,950 AU (1.94 trillion km) from AB and an orbital period of 550,000 years.
...
Ever since the discovery of Proxima, it has been suspected to be a true companion of the Alpha Centauri binary star system. Data from the Hipparcos satellite, combined with ground-based observations, were consistent with the hypothesis that the three stars are a bound system. For this reason, Proxima is sometimes referred to as Alpha Centauri C. Kervella et al. (2017) used high-precision radial velocity measurements to determine with a high degree of confidence that Proxima and Alpha Centauri are gravitationally bound.[8] Proxima's orbital period around the Alpha Centauri AB barycenter is 547000+6600−4000 years with an eccentricity of 0.5±0.08; it approaches Alpha Centauri to 4300+1100−900 AU at periastron and retreats to 13000+300−100 AU at apastron.[8] At present, Proxima is 12,947 ± 260 AU (1.94 ± 0.04 trillion km) from the Alpha Centauri AB barycenter, nearly to the farthest point in its orbit.[8]
So the almost twins have a distant tag along sibling.

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A Lunar Time Machine

Post by bystander » Mon Jul 15, 2019 7:21 pm

A Lunar Time Machine: Secrets to our Sun’s Active Past
astrobites | Daily Paper Summaries | 2019 Jul 08
Ellis Avallone wrote:
Throughout the solar system’s history, the frequency of flares and eruptive events from the Sun have had a strong effect on the development of the inner planets, from the top of their atmospheres right down to their surfaces. The amount of eruptive events the Sun produces just so happens to be closely related to the rate at which it rotates. Therefore, to understand how planets like the Earth came to be, it is incredibly important to understand the Sun’s rotation during the early stages of the solar system’s development. Previous studies have attempted to do so by considering other sun-like stars. However, today’s authors have found answers by looking much closer to home.

The Moon, Earth’s only natural satellite, is a surprisingly ideal place to look for clues about the history of solar activity. The lack of a thick atmosphere causes solar eruptions that reach the Moon to strip material from its surface, leaving behind an imprint that can be used to understand the Sun’s tumultuous past ...

Was the Sun a Slow Rotator? Sodium and Potassium Constraints from the Lunar Regolith ~ Prabal Saxena et al
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Potential Comets & Water Vapor Around Beta Pic

Post by bystander » Mon Jul 15, 2019 7:34 pm

Potential Comets & Water Vapor Around Beta Pic
astrobites | Daily Paper Summaries | 2019 Jul 09
Lauren Sgro wrote:
If you keep up with your astronomy news, the name Beta Pictoris (affectionately known as “Beta Pic”) may ring a bell. This star is quite popular because of its easily observed debris disk and confirmed exoplanet. Beta Pic’s debris disk is similar to others, containing second-generation dusty debris left over from planet formation. But this debris disk is part of a special few that contain gas along with the dust. Something interesting may be going on to cause a clump of CO (carbon monoxide) gas within the disk – and where there is CO, there is often water. ...

Today’s authors commence this hunt for water in the Beta Pic disk by gathering archival data from the Herschel HIFI instrument. HIFI observed the rotational 110-101 transition of ortho-H20 (‘ortho’ just refers to the spins of the H atoms being parallel, while the “110-101” refers to the jump from the molecule’s lowest rotational level to the second lowest) on July 19, 2010, which actually resulted in a non-detection. But even a non-detection provides illuminating information as it provides us with an upper limit, which is like saying “this is the highest value that could be happening in order to still get the non-detection that we observe.” ...

Upper Limits on the Water Vapour Content of the Beta Pictoris Debris Disk ~ M. Cavallius et al
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A new site for the s-process?

Post by bystander » Mon Jul 15, 2019 8:10 pm

A new site for the s-process?
astrobites | Daily Paper Summaries | 2019 Jul 10
Sanjana Curtis wrote:
One of the main goals of nuclear astrophysics is to understand and explain the composition of the universe. Starting out with Hydrogen, Helium and a teeny bit of Lithium, the universe evolved to have an entire periodic table worth of chemical elements. How did this happen? We know that stars and supernovae played a key role in this chemical enrichment. However, exactly how and where different elements are produced, and in what quantities, remains a topic of vigorous ongoing research. Heavy element nucleosynthesis is a key piece of this puzzle and has received a lot of attention recently in the context of neutron star mergers.

Heavy elements, i.e. elements heavier than iron, are mainly formed through the s-process and the r-process. The s-process involves slow neutron capture and the r-process involves rapid neutron capture with respect to the decay time of the isotopes involved. Typical s- and r-process paths in the chart of nuclides are shown in Figure 1. The main thing to note here is that the s-process stays fairly close to the black dots indicating stable nuclei whereas the r-process proceeds far away from stability.

Although both these processes make roughly equal overall contribution to the total abundance of heavy elements, the s-process does not get the same hype as it’s cool twin, the r-process. This is partly due to the fact that the site of the r-process was a huge mystery until very recently, when neutron star mergers were identified as one of the sites where the process occurs. It still remains to be seen whether they are the only site of the r-process.

The s-process, on the other hand, is known to occur inside asymptotic giant branch (AGB) stars. This is the final stage of evolution for long-lived, low-mass stars between 1-3 solar masses. The AGB stars can produce elements up to 209Bi, forming what’s called the “main” component of the s-process. However, a weaker version of the s-process also happens in massive stars (>10 solar masses), producing elements up to atomic mass number (A) ~ 90. Today’s paper shakes things up by introducing a new site for the main s-process – in rotating metal-poor massive stars! ...

New s-process Site in Rapidly-Rotating Massive Pop II Stars ~ Projjwal Banerjee, Alexander Heger, Yong-Zhong Qian
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H0ly Cow! A New Measurement of the Hubble Constant

Post by bystander » Mon Jul 15, 2019 8:33 pm

H0ly Cow! A New Measurement of the Hubble Constant
astrobites | Daily Paper Summaries | 2019 Jul 12
Kaitlyn Shin wrote:
The rate of expansion of the universe is governed by a parameter called the Hubble constant (H0), measured in units km/s/Mpc (the “clunky-looking” units are explained well in this astrobite). H0 is one of the most important cosmological parameters––it can constrain models of the evolution of our universe––but there are two sets of observationally measured H0 values that significantly disagree with each other. The first type of measurement comes from astronomers who look at the “early” universe by studying the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO), which give snapshots of the universe at only a few hundred thousand years old. A recent measurement of H0 from using this method was made by the Planck satellite, with a value of H0 = 67.27 +/- 0.6 km/s/Mpc. However, astronomers who look at the “late” universe, when the universe is billions of years old, are studying Type-Ia supernovae and Cepheid variables (relying on the cosmic distance ladder), with a recently measured value of H0 = 74.03 +/- 1.42 km/s/Mpc. These objects were formed long after the CMB and BAO made their mark on the universe, which means that these two H0 values are independently measured and thus do not have a shared source of error.

Astronomers looking at the early universe have H0 measurements in excellent agreement with each other, and H0 measurements of the late universe have agreement and have ruled out multiple possible sources of systematic errors as well. The disagreement has reached a 4.4σ tension: the error bars on each type of measurement easily rule the other type of measurement out! As a result, there is a strong need for different, independent measurements of H0, to explore both unknown sources of systematic error and possible new physics. Today’s paper provides one such independent approach. ...

A SHARP view of H0LiCOW: H0 from three time-delay gravitational
lens systems with adaptive optics imaging
~ Geoff C.-F. Chen et al
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Peas in a Pod?

Post by bystander » Mon Jul 15, 2019 8:50 pm

Peas in a Pod?
astrobites | Daily Paper Summaries | 2019 Jul 15
Spencer Wallace wrote:
If it weren’t for stars, we would know almost nothing about planets outside of the solar system. Nearly every trick that astronomers use for finding exoplanets involves carefully examining the way a distant planet alters the light from its host star. The 4000th exoplanet was discovered recently and, like the majority of known exoplanets, was found by watching the slight dimming of the host star’s light as the planet passed between us and it.

Unfortunately, this technique (known as the transit method) is biased. When you measure the amount of light blocked by a planet passing in front of a star, you can’t immediately determine the size of the planet. Instead, the temporary dimming of the star tells you the ratio between the size of the star and the size of the planet. Stars come in many different sizes, so a small planet orbiting a small star will produce the same transit signal as a large planet orbiting a large star. To make things even more complicated, starspots, flares and even inherent limitations of the instrument prevent you from seeing the dimming produced by the smallest planets.

These limitations become most apparent when astronomers search for trends and patterns between exoplanetary systems all across the sky. One of the more recently discovered trends has been dubbed ‘peas in a pod’. Adjacent planets that are orbiting the same host star seem to have similar sizes. This pattern has been observed across hundreds of planetary systems and is thought to be an important clue for understanding how planets form. The author of today’s paper argues that this apparent trend is nothing more than an artifact of our observational bias. In other words, if there were a magic telescope that could see and detect every single exoplanet, the ‘peas in a pod’ correlation would vanish. ...

On the Patterns Observed in Kepler Multi-Planet Systems ~ Wei Zhu
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Re: A new site for the s-process?

Post by BDanielMayfield » Tue Jul 16, 2019 1:39 am

bystander wrote:
Mon Jul 15, 2019 8:10 pm
A new site for the s-process?
astrobites | Daily Paper Summaries | 2019 Jul 10
Sanjana Curtis wrote:
One of the main goals of nuclear astrophysics is to understand and explain the composition of the universe. Starting out with Hydrogen, Helium and a teeny bit of Lithium, the universe evolved to have an entire periodic table worth of chemical elements. How did this happen? We know that stars and supernovae played a key role in this chemical enrichment. However, exactly how and where different elements are produced, and in what quantities, remains a topic of vigorous ongoing research. Heavy element nucleosynthesis is a key piece of this puzzle and has received a lot of attention recently in the context of neutron star mergers.

Heavy elements, i.e. elements heavier than iron, are mainly formed through the s-process and the r-process. The s-process involves slow neutron capture and the r-process involves rapid neutron capture with respect to the decay time of the isotopes involved. Typical s- and r-process paths in the chart of nuclides are shown in Figure 1. The main thing to note here is that the s-process stays fairly close to the black dots indicating stable nuclei whereas the r-process proceeds far away from stability.

Although both these processes make roughly equal overall contribution to the total abundance of heavy elements, the s-process does not get the same hype as it’s cool twin, the r-process. This is partly due to the fact that the site of the r-process was a huge mystery until very recently, when neutron star mergers were identified as one of the sites where the process occurs. It still remains to be seen whether they are the only site of the r-process.

The s-process, on the other hand, is known to occur inside asymptotic giant branch (AGB) stars. This is the final stage of evolution for long-lived, low-mass stars between 1-3 solar masses. The AGB stars can produce elements up to 209Bi, forming what’s called the “main” component of the s-process. However, a weaker version of the s-process also happens in massive stars (>10 solar masses), producing elements up to atomic mass number (A) ~ 90. Today’s paper shakes things up by introducing a new site for the main s-process – in rotating metal-poor massive stars! ...

New s-process Site in Rapidly-Rotating Massive Pop II Stars ~ Projjwal Banerjee, Alexander Heger, Yong-Zhong Qian
Interesting that AGB stars can produce elements up to bismuth. Bi-209 has this claim to fame, among others:
Bismuth was long considered the element with the highest atomic mass that is stable, but in 2003 it was discovered to be extremely weakly radioactive: its only primordial isotope, bismuth-209, decays via alpha decay with a half-life more than a billion times the estimated age of the universe.[4][5] Because of its tremendously long half-life, bismuth may still be considered stable for almost all purposes.
Also without Bi we'd have no Pepto Bismo for our gut distresses. :p:

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Does an AGN help or hurt star formation?

Post by bystander » Thu Jul 18, 2019 3:04 pm

Does an AGN help or hurt star formation?
astrobites | Daily Paper Summaries | 2019 Jul 16
Caitlin Doughty wrote:
One of the many mysteries of galaxy evolution is how the formation of stars is affected by a process called feedback. Unlike comments coming from a teacher on an essay, in the galactic context, feedback is coming from powerful sources of energy such as an active galactic nuclei (AGN). Star formation in galaxies requires a lot of dense gas (also called the interstellar medium, or ISM), so any feedback processes that disrupt the presence or the denseness of said gas can affect the ability of a galaxy to form stars. Simulations have shown that AGN are theoretically capable of providing negative feedback by heating up the ISM or blowing it away. However, they might also provide positive feedback by compressing the ISM with their winds, making it denser and triggering bursts of star formation.

Each of these options have theoretical merit and are observed in simulations, but it can be hard to observe the effects in the wild. Today’s paper takes advantage of a particularly well-situated Seyfert 2 galaxy, NGC 5728, to enhance our understanding of AGN feedback processes. The Seyfert 2 designation is used to describe galaxies containing AGN that are similar to quasars, but that have visible host galaxies while most quasars do not. ...

Positive and Negative Feedback of AGN Outflows in NGC 5728 ~ Jaejin Shin et al
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In the Heart of a Trainwreck Galaxy

Post by bystander » Thu Jul 18, 2019 3:25 pm

In the Heart of a Trainwreck Galaxy:
Potential for Future Gravitational Waves

astrobites | Daily Paper Summaries | 2019 Jul 17
John Weaver wrote:
With the announcement of the experimental confirmation of gravitational waves by LIGO in 2016 in tandem with additional electromagnetic follow-up of a neutron star merger, astronomy was quickly ushered into an era of truly multi-messenger science. Although the number of gravitational wave events since observed by LIGO is already substantial, the sheer number of black holes (and neutron stars) predicted to exist within our Universe vastly outweighs this cumulative yield. One reason why LIGO is not constantly finding strong gravitational waves from all of these black holes (the gravitational wave background or GWB) is that not every black hole exists in a pair, which is a necessary condition to spiral inwards, merge, and set off a gravitational wave event. Predictions suggest that the timescales required for some of these events to occur are a sizable fraction of the age of our Universe!

LIGO has however shown direct evidence for the merging of solar mass black holes with atypically large masses between 10 – 40 M⊙︎, and although easier to observe due to their strong gravitational signal, their existence has continued to challenge theoretical explanations. Scaling up to even greater masses does not reduce the pressure on theory either, as the predicted dominant mass contribution to the yet undetected GWB is from super-massive black holes (SMBHs) on the order of 10^8 – 10^9 M⊙︎.

It has long been hypothesized that SMBHs inhabit the central-most regions of almost all galaxies, and accumulative mass through the slow accretion of gas and stellar material. When galaxies undergo the often violent processes of a wholesale merger, these SMBHs are predicted to collect within the central region of a galaxy and become gravitationally bound on short Myr timescales, accelerated by dynamical friction. However, the black hole pair can only bleed off so much energy through interacting with nearby material and at some point within the final parsec the merger is predicted to stall out. This so-called “final parsec problem” has yet to be resolved. For the sample of intermediate-mass black hole mergers suggested by the LIGO observations, it appears that nature has ways around this problem. Whether this is true for SMBH mergers has yet to be seen.

Putting the final parsec problem aside, the authors of today’s astrobite provide definitive evidence for a precursor system which may one day produce a low-frequency gravitational wave event consistent with a strong contribution to the GWB. ...

Discovery of a Close-separation Binary Quasar at the Heart of a z ~ 0.2 Merging Galaxy
and Its Implications for Low-frequency Gravitational Waves
~ Andy D. Goulding et al
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Learning about galaxy evolution with naked red nuggets

Post by bystander » Sun Jul 21, 2019 3:15 pm

Learning about galaxy evolution with naked red nuggets
astrobites | Daily Paper Summaries | 2019 Jul 18
Bryanne McDonough wrote:
The evolution of galaxies as they age is a tricky thing to study. Even if we had observed a galaxy over the entire course of human history it would only have been a small fraction of that galaxy’s lifetime. Because of this, studying galaxies involves looking at an ensemble of galaxies from far away (where we see light emitted when the galaxy was young) to nearby (where we see galaxies roughly as they are today). The problem with this is that we can’t see how a single galaxy evolves, only snapshots of different galaxies over time. Imagine seeing a collection of photographs of different people at different ages, you could get some understanding of the general aging process but you would still be missing some key information.

Galaxies can be broken up into two different categories: blue and red. Bluer galaxies appear that way because they have younger stars; they have a high star formation rate where the young stars dominate. Redder galaxies have stopped forming stars at a high rate and appear red because they are dominated by the red old stars. There are very few galaxies in between these categories, so it can be assumed that there is some process that is relatively quick that quenches star formation. Figure 1 shows an illustration of the evolution process with two trends that represent pre- and post- quenching.

A big question in galaxy evolution is what, exactly, that process is. Studying red (quenched) galaxies could help uncover that process, but the information is often contaminated by material that was added to the galaxy through mergers that occurred after the quenching. However, there are a few red galaxies that have remained “naked” by not undergoing any major merging episodes. These galaxies have compact cores, hence why they are called “naked red nuggets.” Using information from these galaxies, the authors of today’s paper were able to learn more about galaxies after they undergo quenching. ...

Star formation quenching imprinted on the internal structure of naked
red nuggets
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Heating up the guts of gas giants

Post by bystander » Tue Aug 06, 2019 5:37 pm

Heating up the guts of gas giants
astrobites | Daily Paper Summaries | 2019 Jul 22
Vatsal Panwar wrote:
Jupiter sized gas giant exoplanets in close orbits around their stars, commonly referred to as hot Jupiters, have been the prime targets for probing planetary atmospheres beyond our solar system. One of the many mystifying features of hot Jupiters, which ironically also makes them easier to detect and characterize, is their inflated radii. A good fraction of known hot Jupiters have sizes larger than that predicted by evolutionary models that take into account the properties of the system like temperature, age, and metallicity of the system. What could be causing these hot Jupiters to puff up?

A proposed mechanism to explain hot Jupiter inflation is deposition of energy from stellar irradiation deep into the interiors of the planet. However, in addition to inflating the planet, energy from stellar flux heating up the planetary interiors can also radically alter the thermal structure (temperature variation with altitude) of its atmosphere which has direct consequences on its inferred atmospheric properties. Today’s paper attempts to draw a connection between the stellar irradiation of hot Jupiters and their intrinsic temperature, and how that ultimately affects the observations and our understanding of the atmospheres of these gas giants. ...

The Intrinsic Temperature and Radiative-Convective Boundary Depth
in the Atmospheres of Hot Jupiters
~ Daniel P. Thorngren, Peter Gao, Jonathan J. Fortney
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Ghosts of Spiral Arms Past

Post by bystander » Tue Aug 06, 2019 5:43 pm

Ghosts of Spiral Arms Past
astrobites | Daily Paper Summaries | 2019 Jul 23
Caitlin Doughty wrote:
Despite our home planet being embedded in it, the Milky Way and its immediate environment remain an enigma to astronomy. Once thought to have few satellite neighbors, The Milky Way has been found to have many dwarf galaxies orbiting it. New stellar streams are being uncovered as well, likely remnants of past gravitational interactions with dwarf galaxies, in which the Milky Way pulled rivers of stars from its now-dissipated partners. This burst of discoveries of new nearby and entangled structures are thanks to advancements in technology allowing astronomers to observe dimmer objects and to track stars with greater precision.

Today’s paper utilizes one of these advancements, the much lauded Gaia, in tandem with machine learning methods to identify new substructures within the Milky Way and, in so doing, learn about its murky past. ...

Untangling the Galaxy I: Local Structure and Star Formation History of the Milky Way ~ Marina Kounkel, Kevin Covey
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Making it Rain in the Circumgalactic Medium

Post by bystander » Tue Aug 06, 2019 5:55 pm

Making it Rain in the Circumgalactic Medium
astrobites | Daily Paper Summaries | 2019 Jul 24
Michael Foley wrote:
It can be easy to think of galaxies as islands in the universe, floating around in isolation. However, a galaxy is actually surrounded by a huge sea of low-density gas that extends out to its virial radius and beyond. This gas is known as the circumgalactic medium (CGM), and more and more research is showing that the CGM has a crucial role to play in galaxy evolution. Observing the CGM has proven difficult due to its extremely low density, though, so simulations have played a large role in understanding the physics of this region. In today’s paper, the authors detail the effects of running a CGM simulation with significantly increased resolution, capable of resolving cool gas that precipitates in the CGM and rains down on the galaxy. ...

The Impact of Enhanced Halo Resolution on the Simulated Circumgalactic Medium ~ Cameron B. Hummels et al
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TLDR: the TRGB gives us another H0tTake!

Post by bystander » Tue Aug 06, 2019 6:10 pm

TLDR: the TRGB gives us another H0tTake!
astrobites | Daily Paper Summaries | 2019 Jul 25
Tarini Konchady wrote:
The value of the Hubble Constant (H0) is a beast to pin down. However, it’s integral to our understanding of how the Universe evolved and will continue to evolve. H0 relates the speed with which distant objects are moving away from us—due to the Universe’s expansion—to how far away they are (see this Astrobite for a detailed explanation of how H0 assumed its place of importance). Measurements of H0 can be made using the early Universe, from the cosmic microwave background (CMB), and the late Universe, from distance measurements for stars, galaxies and other objects.

Under our current understanding of the Universe, these two sorts of measurements ought to yield similar values of H0. Instead, we’ve witnessed a growing divergence between them that’s only gotten worse (or more interesting?) with time (see Figure 4, though it does come with a spoiler). Currently, early Universe measurements of H0 rely on CMB observations made by the Planck satellite while late Universe measurements rely on Cepheid variables and Type Ia supernovae (Sne Ia). The discrepancy between these early and late measurements of H0 could be chalked up to new physics in the early Universe that is outside our current models. But before claiming that, we’d want to rule out any hidden issues in how these measurements are being made.

On the side of the late Universe, this requires using other astronomical objects to make measurements of H0 and to calibrate the distances to standard candles (objects whose brightness we understand very well), like Sne Ia. Very recently, a new measurement of H0 was announced, which used strong gravitational lens systems for distance calibration (see this Astrobite for a good summary). The paper being discussed in this Astrobite comes out of the Carnegie-Chicago Hubble Program, which was established to calibrate Sne Ia through alternate methods. Here, the authors use something called the Tip of the Red Giant Branch (TRGB). ...

The Carnegie-Chicago Hubble Program. VIII. An Independent Determination of the
Hubble Constant Based on the Tip of the Red Giant Branch
~ Wendy L. Freedman et al
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First Photos of a Baby Planet

Post by bystander » Tue Aug 06, 2019 7:11 pm

First Photos of a Baby Planet
astrobites | Daily Paper Summaries | 2019 Jul 26
Briley Lewis wrote:
Planet formation begins with a cloud of gas and dust collapsing into a disk. At the center of this collapse is a protostar, not yet hot enough in its center to fuse hydrogen into helium, but on its way to becoming a fully formed main sequence star, like our Sun. The remainder of the material in the disk, swirling around the central protostar, is what will eventually coagulate into planets. Dust grains stick together into pebbles, and then accrete more material onto them until they grow into planetesimals. We’ve seen how complex these disks can be, as planets carve gaps out of the material around them, leading to stunning images such as those from ALMA (shown in Figure 1). Eventually, the planets clear the remaining material out of the disk, corralling it into asteroid belts or ejecting it out to the outer solar system (or out of the system entirely). This leaves a neat arrangement of orbits around the central star, like what we see in our own solar system today.

Although we know these broad strokes of planet formation, a lot of questions still remain about the details. We don’t totally understand how long each step of the process takes, when the process starts, where planets form (compared to where we observe them later in life), or the physical properties a forming planet. The key to answering some of these lingering questions is observing a baby planet in its early formation stages—and that’s exactly what’s done in today’s paper. The authors, part of the European Southern Observatory consortium, present observations of PDS 70b, the first detected young, forming planet around a protostar at this stage of development. ...

Orbital and Atmospheric Characterization of the Planet
within the Gap of the PDS 70 Transition Disk
- A. Müller et al
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An interplanetary collision — in a distant planetary system

Post by bystander » Tue Aug 06, 2019 7:24 pm

An interplanetary collision — in a distant planetary system
astrobites | Daily Paper Summaries | 2019 Jul 29
Joanna Ramasawmy wrote:
In the search for exoplanets, we’re discovering an increasing number of planetary systems around distant stars that are very different from our own Solar System: Jupiter-mass planets so close to their star that they reach temperatures over 2000 Kelvin, circumbinary planets which, like Luke Skywalker’s home Tatooine, have two suns, or systems with giant planets larger than Jupiter at incredible distances from their central star. This study focuses on one of these unusual systems, for the first time finding evidence that an interplanetary collision took place while the system was still forming. This is Kepler-107. ...

A giant impact as the likely origin of different twins in the Kepler-107 exoplanet system ~ Aldo S. Bonomo et al
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The First Molecule in the Universe

Post by bystander » Tue Aug 06, 2019 7:38 pm

The First Molecule in the Universe
astrobites | Daily Paper Summaries | 2019 Jul 30
Charles Law wrote:
Have you ever wondered what the first molecule that formed in the universe was? As the temperature of the young universe cooled to below 4000 K (or about 7000 °F / 3700 °C), light elements produced during Big Bang nucleosynthesis began to combine together to form electrically neutral atoms – a process, somewhat confusingly, referred to as recombination. The helium ions He2+ and He+ were the first to combine with free electrons to form neutral atoms, with hydrogen following shortly thereafter. In this metal-free and low-density environment, the stage was set for the formation of the first molecular bond in the universe: the helium hydride ion HeH+. As recombination progressed, the eventual destruction of HeH+ created a path to the formation of molecular hydrogen, the most abundant molecule in the present universe. Despite its importance in models of the chemical evolution of the early universe, the HeH+ ion had never before been detected in interstellar space. In today’s astrobite, we take a look at how astronomers found the first molecule ever created in the universe and the implications for the origins of chemical complexity in the present universe. ...

Astrophysical Detection of the Helium Hydride Ion HeH+ ~ Rolf Güsten et al
viewtopic.php?t=39361
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Discovery of a star yeeted out of the Milky Way

Post by bystander » Tue Aug 06, 2019 7:47 pm

Discovery of a star yeeted out of the Milky Way
astrobites | Daily Paper Summaries | 2019 Jul 31
Bryanne McDonough wrote:
While targeting stars in stellar streams, the Southern Stellar Stream Spectroscopic Survey (S5) scientists stumbled upon a serendipitous sighting of a super fast Main Sequence star. That is an alliterative way to say that the authors of today’s paper have found the fastest Main Sequence star yet. There are few mechanisms that can accelerate a star to that velocity, and the authors concluded that this one, named S5-HVS1, must have come from the Galactic Center. ...

The Great Escape: Discovery of a Nearby 1700 km/s Star
Ejected from the Milky Way by Sgr A*
~ Sergey E. Koposov et al
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Big and Fuzzy or Small and Rocky?

Post by bystander » Tue Aug 06, 2019 7:57 pm

Big and Fuzzy or Small and Rocky?
A Close-In Sub-Neptune with Near-Solar Metallicity

astrobites | Daily Paper Summaries | 2019 Aug 01
Jamie Wilson wrote:
During the nine and a half years in which NASA’s Kepler Space Telescope was operational, it discovered thousands of new extrasolar planets which show an astonishing diversity of physical properties. Many of these newly discovered systems are unlike anything found in our own Solar system, with its familiar inner terrestrial planets and outer gas giants. These include the discovery of highly irradiated hot-Jupiters; gas giants with masses similar to Jupiter orbiting extremely close to their host stars, and planets with masses and radii intermediate between Earth and Neptune, often described as super-Earths and sub-Neptunes. Although not found in the Solar system, these latter planet types are surprisingly common around other stars and it’s possible that up to 80% of planets in the Galaxy might lie within this range.

An important long-term aim of exoplanetary science is the discovery of habitable planets like the Earth but the majority of observations so far have been for hot, giant planets with extended atmospheres and large scale heights. The atmospheric characterisation of small, rocky planets like the Earth is, at present, largely unfeasible due to the tiny size of these planets relative to their host stars. If we are willing to consider the habitability of larger, intermediate-mass planets, such as super-Earths, orbiting close to small host stars, then the chances of successful atmospheric detections improve. The drawback to this method is that presently the bulk composition and atmospheric properties of these planet types remains uncertain, in particular, it isn’t clear what proportion of these planets resemble scaled-down versions of gas giants or perhaps larger versions of rocky, terrestrial planets with extended atmospheres, or maybe even a combination of the two. The authors of today’s paper bring us a step closer to understanding the atmospheric properties of these intermediate-mass planets. ...

A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted
Atmosphere and Mie-Scattering Clouds
~ Björn Benneke et al
viewtopic.php?t=39601
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Adventure to an Asteroid: Hayabusa2 visits Ryugu

Post by bystander » Tue Aug 13, 2019 5:15 pm

Adventure to an Asteroid: JAXA’s Hayabusa2 visits Ryugu
astrobites | Daily Paper Summaries | 2019 Aug 05
Briley Lewis wrote:
Sometimes, humans do pretty ridiculously cool things. In 2010, we landed a spacecraft on a hunk of rock hurtling through space, millions of miles away, so that we could bring a piece of it back to Earth. This was the purpose of Japan’s Hayabusa spacecraft: to visit the asteroid Itokawa, observe it, and return a sample to Earth for further study. Hayabusa was the first time we had attempted (and successfully completed!) a sample return from an asteroid. To follow up on this accomplishment, JAXA (the Japan Aerospace Exploration Agency) is now piloting another mission, Hayabusa2, to visit another asteroid. This time, though, they’re learning from past mistakes—Hayabusa’s surface rover failed to deploy correctly—and learning about a different type of asteroid, one which can help unveil the secrets of life on Earth. ...

In Summer 2018, Hayabusa2 reached its target, orbiting at only 20 km above its surface (keep in mind, that’s only ⅕ the distance spanned by the English Channel or Southern California’s notorious 405 freeway). It successfully deployed its first rover in Fall 2018, around the same time NASA’s OSIRIS-REx mission reached the asteroid Bennu. Earlier this year, it landed to collect its first sample (which you can watch a video of!) and very recently (July 2019) it collected another sample after it sent an explosive to impact the surface. This impact revealed the subsurface layers, which haven’t been affected as much by space weathering and thus can tell us more about the asteroid’s composition. All this time, the orbiter part of Hayabusa2 has been collecting remote sensing information, taking images and other data to characterize Ryugu’s orbit, shape, size, and more. Today’s paper takes a look at that first year of remote sensing data, reporting on what we’ve figured out about Ryugu and its interesting history. ...

Hayabusa2 arrives at the carbonaceous asteroid
162173 Ryugu—A spinning top–shaped rubble pile
~ S. Watanabe et al
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