astrobites: Daily Paper Summaries 2020

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The Formation of Massive Stars

Post by bystander » Sat Jul 11, 2020 2:56 pm

The Formation of Massive Stars
astrobites | Daily Paper Summaries | 2020 Jul 06
Mitchell Cavanagh wrote:
Stellar physics is a broad field that touches on a range of phenomena from magnetic fields to radiative processes and thermonuclear fusion to plasmas. Stars form through the gravitational collapse of cold, dense, dusty proto-stellar cores, themselves embedded in thick molecular clouds or filaments. Massive stars, defined as those with a mass greater than 8 solar masses, are of key interest in star formation. Although they are extremely rare, comprising less than 1% of the total stellar population, they make their presence known by dominating the surrounding interstellar medium (ISM) with their powerful stellar winds as well as shocks from their eventual supernovae. Their formation is known to be impeded by several feedback mechanisms, including outflows, radiation pressure and magnetic fields. Today’s paper uses a series of radiative magnetohydrodynamic (RMHD) simulations to understand the overall impact that these combined mechanisms have on star formation. ...

The Role of Outflows, Radiation Pressure, and Magnetic Fields
in Massive Star Formation
~ Anna L. Rosen, Mark R. Krumholz
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How to Grow a Massive Black Hole through TDEs

Post by bystander » Sat Jul 11, 2020 3:14 pm

Stellar Snacks or: How to Grow a Massive Black Hole through TDEs
astrobites | Daily Paper Summaries | 2020 Jul 07
Jason Hinkle wrote:
Massive black holes (MBHs) are known to live in the centers of most galaxies, including Sagittarius A* in our own Milky Way. These MBHs are intimately linked to the evolution and growth of their host galaxies (and vice versa), as evidenced by the M–σ relationship. However, the details of how MBHs are born and quickly grow to such gargantuan masses are still largely unknown.

There are two main channels for MBHs to grow throughout cosmic time, accretion and mergers. While it is thought that the majority of black hole growth is through accretion of gas, infalling gas is subject to heating processes called feedback. Considering this, gas accretion alone cannot fully explain the existence of extremely massive (more than a billion solar mass) black holes within the first billion years after the Big Bang. However, the accretion of stars is independent of feedback, thereby providing a way for MBHs to grow largely unimpeded in their early lives.

When a star passes too close to a MBH, the intense tidal forces of the black hole become stronger than the gravity holding the star together, and the star is ripped apart. This is known as a tidal disruption event (TDE), and in many cases produces a luminous flare of light. This allows us to observationally measure the rate of stars getting close enough to MBHs that they are eventually eaten up. ...

In this paper, the authors set up a simulation to study the growth of MBHs and evolution of the TDE rate during the early universe. Their setup includes detailed physics on cosmology, gas cooling and heating, star formation, feedback from AGN and supernovae, black hole physics, and galactic dynamics. While these details are beyond the scope of this bite, the results of the simulations give clear insight into the growth of MBHs. ...

Tidal Disruption Events in the First Billion Years of a Galaxy ~ Hugo Pfister et al
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Hot Zombie Stars in Your Area

Post by bystander » Sat Jul 11, 2020 3:41 pm

Hot Zombie Stars in Your Area
astrobites | Daily Paper Summaries | 2020 Jul 09
Wynn Jacobson-Galan wrote:
Almost a decade ago, amongst the heap of exotic transients observed every day in our Universe, a new class of stellar explosion was identified and labeled Type Iax supernovae (SNe Iax). Similar to the infamous Type Ia supernovae (SNe Ia) that are commonly used to measure the expansion rate of the universe, SNe Iax are also thought to arise from the destruction of a white dwarf star as it approaches the Chandrasekhar mass limit. However, these supernovae are physically distinct explosions from SNe Ia given their low observed luminosities and kinetic energies, combined with the slow velocities at which the obliterated white dwarf blasts through interstellar space i.e., the ejecta velocity.

After their identification, theorists were tasked with explaining how the destruction of a white dwarf could produce such a “weak” explosion rather than the typical characteristics seen in SNe Ia. Many now agree that in order to create a SN Iax, the white dwarf needs to explode via a deflagration rather than a detonation: the shock wave that initially ripples through the white dwarf will travel sub-sonically instead of super-sonically. As the weakened shock wave attempts to explode the white dwarf, it will not be strong enough to overcome the pull of gravity and completely unbind the star. Instead, only some of the white dwarf’s stellar structure will be released in the explosion to produce a SN Iax, leaving behind a remnant stellar core. And thus, a zombie star is born!

Of the ~100 SNe Iax known presently, all have occurred in galaxies far from the Milky Way. However, for every 10 SN Ia identified, which make up ~20% of all explosions in the universe, 2-5 SNe Iax are also discovered, making them relatively common explosions. Nevertheless, none of the remnant supernovae that exploded in the Milky Way in the past have been identified as a SN Iax despite the identification of many SNe Ia remnants, as well as those from the collapse of massive stars. And so, since the inception of the SN Iax class, a pressing question has eluded astronomers: where are all the galactic Type Iax supernova remnants?

The authors of today’s paper attempt to answer this burning question by offering up what may be the first confirmed SN Iax remnant in the Milky Way. Using archival data from the Chandra X-ray Observatory, the authors study the X-ray emission from supernova remnant Sgr A East (i.e., G0.0+0.0, shown in Figure 1) that is thought to have exploded at least 2000 years ago near the galactic center. Even after thousands of years, shock waves within the synthesized supernova material will continue to accelerate subatomic particles, which in turn created prominent X-ray emission that can be observed in supernova remnants throughout our own galaxy. Consequently, the strength of this X-ray emission from different elements in the remnant is directly linked to the type of explosion that may have produced the G0.0+0.0 remnant. ...

Chemical Abundances in Sgr A East: Evidence for a Type Iax Supernova Remnant ~ Ping Zhou et al
viewtopic.php?t=35339
viewtopic.php?t=33733
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The Faint Young Sun (is not a) Problem

Post by bystander » Sat Jul 18, 2020 4:13 pm

The Faint Young Sun (is not a) Problem
astrobites | Daily Paper Summaries | 2020 Jul 11
Anthony Maue wrote:
Like other stars, our Sun has likely evolved and changed during its life—born of a molecular cloud, coalesced in a disk, and currently burning through its supply of hydrogen as a rather typical main sequence star. We infer this history by studying other stars at different stages of their life cycle and by creating models to help us simulate our own star’s evolution. An early realization of these studies was that the young Sun would have been 20–25% less luminous, resulting in a much colder Earth. However, our geologic record contradicts this lower solar luminosity with clear evidence that liquid water was abundant during the Archean (an early geologic eon stretching 3.8–2.5 billion years ago, AKA 3.8–2.5 Ga). This apparent discrepancy, known as the faint young Sun problem, has plagued researchers for decades. Greenhouse gases like carbon dioxide (CO2) could have kept the early Earth warm despite a less luminous Sun, but geochemical studies indicate there likely wasn’t enough present on early Earth. Today’s paper reviews the many possible solutions to this infamous problem and suggests that recent advances in modelling may be able to finally close the book on this so-called paradox. ...

Is the Faint Young Sun Problem for Earth Solved? ~ Benjamin Charnay et al
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Is it a Black Hole? Is it a Neutron Star?

Post by bystander » Sat Jul 18, 2020 4:35 pm

Look, Up in the Sky! Is it a Black Hole?
Is it a Neutron Star? Good Question.

astrobites | Daily Paper Summaries | 2020 Jul 13
Brent Shapiro-Albert wrote:
Over the last five years the Laser Interferometer Gravitational-Wave Observatory, or LIGO, has been reporting detections of gravitational waves from the mergers of binary black hole and binary neutron star systems. In their third observing run, O3, which ran from April 1 – September 30, 2019, LIGO, in conjunction with VIRGO, have already reported two new and exciting detections: the merger of two black holes with the largest mass differential (GW190412) ever observed and a second binary neutron star merger (GW190425). The focus of today’s paper is on their latest announcement, GW190814 (shown in Figure 1), which may give us new insights into the formation of lopsided binary systems and what matter is like inside of a neutron star.

GW190814 is similar to GW190412 in that the difference in the masses of the merging objects is large. The heavier object is conclusively a black hole with a mass 23 times the mass of the Sun (solar masses, or M), and the smaller one is only 2.6 M, as shown in Figure 2. However, it is unclear whether the 2.6 M object is a black hole or a neutron star. Either way, it is record-breaking! It is either the least massive black hole, or the most massive neutron star, ever observed in a binary system with another compact object. ...

GW190814: Gravitational Waves from the Coalescence of a 23 M Black Hole
with a 2.6 M Compact Object
~ LIGO Scientific Collaboration, Virgo Collaboration: R. Abbott et al
viewtopic.php?t=40706
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Re: Is it a Black Hole? Is it a Neutron Star?

Post by BDanielMayfield » Sat Jul 18, 2020 4:57 pm

bystander wrote:
Sat Jul 18, 2020 4:35 pm
Look, Up in the Sky! Is it a Black Hole?
Is it a Neutron Star? Good Question.

astrobites | Daily Paper Summaries | 2020 Jul 13
Brent Shapiro-Albert wrote:
Over the last five years the Laser Interferometer Gravitational-Wave Observatory, or LIGO, has been reporting detections of gravitational waves from the mergers of binary black hole and binary neutron star systems. In their third observing run, O3, which ran from April 1 – September 30, 2019, LIGO, in conjunction with VIRGO, have already reported two new and exciting detections: the merger of two black holes with the largest mass differential (GW190412) ever observed and a second binary neutron star merger (GW190425). The focus of today’s paper is on their latest announcement, GW190814 (shown in Figure 1), which may give us new insights into the formation of lopsided binary systems and what matter is like inside of a neutron star.

GW190814 is similar to GW190412 in that the difference in the masses of the merging objects is large. The heavier object is conclusively a black hole with a mass 23 times the mass of the Sun (solar masses, or M), and the smaller one is only 2.6 M, as shown in Figure 2. However, it is unclear whether the 2.6 M object is a black hole or a neutron star. Either way, it is record-breaking! It is either the least massive black hole, or the most massive neutron star, ever observed in a binary system with another compact object. ...

GW190814: Gravitational Waves from the Coalescence of a 23 M Black Hole
with a 2.6 M Compact Object
~ LIGO Scientific Collaboration, Virgo Collaboration: R. Abbott et al
viewtopic.php?t=40706
This astrobite totally ignores other interesting possibilities, such as quark stars, that might populate the observed mass gap between 2.5 and 5 solar masses.
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Re: Is it a Black Hole? Is it a Neutron Star?

Post by Chris Peterson » Sat Jul 18, 2020 5:24 pm

BDanielMayfield wrote:
Sat Jul 18, 2020 4:57 pm
bystander wrote:
Sat Jul 18, 2020 4:35 pm
Look, Up in the Sky! Is it a Black Hole?
Is it a Neutron Star? Good Question.

astrobites | Daily Paper Summaries | 2020 Jul 13
Brent Shapiro-Albert wrote:
Over the last five years the Laser Interferometer Gravitational-Wave Observatory, or LIGO, has been reporting detections of gravitational waves from the mergers of binary black hole and binary neutron star systems. In their third observing run, O3, which ran from April 1 – September 30, 2019, LIGO, in conjunction with VIRGO, have already reported two new and exciting detections: the merger of two black holes with the largest mass differential (GW190412) ever observed and a second binary neutron star merger (GW190425). The focus of today’s paper is on their latest announcement, GW190814 (shown in Figure 1), which may give us new insights into the formation of lopsided binary systems and what matter is like inside of a neutron star.

GW190814 is similar to GW190412 in that the difference in the masses of the merging objects is large. The heavier object is conclusively a black hole with a mass 23 times the mass of the Sun (solar masses, or M), and the smaller one is only 2.6 M, as shown in Figure 2. However, it is unclear whether the 2.6 M object is a black hole or a neutron star. Either way, it is record-breaking! It is either the least massive black hole, or the most massive neutron star, ever observed in a binary system with another compact object. ...

GW190814: Gravitational Waves from the Coalescence of a 23 M Black Hole
with a 2.6 M Compact Object
~ LIGO Scientific Collaboration, Virgo Collaboration: R. Abbott et al
viewtopic.php?t=40706
This astrobite totally ignores other interesting possibilities, such as quark stars, that might populate the observed mass gap between 2.5 and 5 solar masses.
To be fair, we know that black holes exist. We know that neutron stars exist. We have no evidence at all that quark stars exist.
Chris

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Salt and Hot Water around Massive Protostars

Post by bystander » Sat Jul 18, 2020 5:25 pm

Salt and Hot Water around Massive Protostars
astrobites | Daily Paper Summaries | 2020 Jul 14
Charles Law wrote:
Massive stars have an outsized impact on their local environments and throughout entire galaxies, as they are important sources of UV radiation, turbulent energy, and heavy elements. While the formation of their low-mass counterparts is largely understood, the process of forming high-mass stars is still unclear. It is unknown whether massive protostars accrete through disks – a scaled-up version of low-mass star formation – or form through an otherwise distinct mechanism.

While recent theoretical work and simulations support this disk accretion model, detecting the presence of such disks is not free from observationally difficulties. To do so, observers seek to identify the signatures of rotating gas within these disks by using molecular emission lines at millimeter wavelengths. But high spatial resolutions are required to correctly disentangle emission from molecules in the inner disk versus those associated with surrounding gas structures, such as protostellar envelopes and outflows. The advent of interferometers, such as the Atacama Large Millimeter/Submillimeter Array (ALMA), provided the necessary angular resolutions and have led to the detections of an increasing number of disk-like structures around massive protostars. But, despite this, there is no consensus as to which molecular lines uniquely trace these massive circumstellar disks. Moreover, few studies have been conducted at sufficiently small spatial scales to directly probe the structure of these disks.

In today’s astrobite, we take a look at new high spatial resolution observations of massive protostellar object IRAS 16547-4247, which reveal the presence of two rotating massive disks and identify a potentially-universal “hot-disk” chemistry found in the innermost disks around massive protostars. ...

Salt, Hot Water, and Silicon Compounds Tracing Massive Twin Disks ~ Kei E. I. Tanaka et al
viewtopic.php?t=34614
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One Dark Matter Profile Please, Hold the Subhaloes

Post by bystander » Sat Jul 18, 2020 5:34 pm

One Dark Matter Profile Please, Hold the Subhaloes
astrobites | Daily Paper Summaries | 2020 Jul 15
Luna Zagorac wrote:
Each of the galaxies inhabiting our universe lives in the center of a halo of dark matter. What that means is that a whole lot of matter we can see (including planets, stars, globular clusters, and light bulbs) all globbed together to make up a galaxy is surrounded by a whole lot of stuff we can’t see, called dark matter (DM). Despite its invisibility, the dark matter produces a gravitational pull both on other dark matter and “normal” matter. Consequently, the shape and structure of the dark matter in the galaxy’s halo are incredibly important to understand; they tell us not just how the halo interacts gravitationally, but also give us clues on how the galaxy got there in the first place.

In fact, the dark matter halo forms first—there happens to be a little more dark matter in this particular corner of the universe, so it decides to get the band together and form a halo. Because there’s so much mass present, the halo is extremely gravitationally attractive, and it ends up bringing in a bunch of “normal” matter into the center of its gravitational potential well, where a galaxy forms. If this were the only thing to ever happen to a halo, most of them would look the same (except for a difference in total mass). Instead, we live in a much more interesting universe, where galaxy haloes are constantly going bump in the night and merging with other haloes to create one bigger halo. This can happen in several iterations, creating truly massive haloes with a bunch of subhaloes floating around inside (see Figure 1). This is called hierarchical halo formation, and it makes for some interesting halo shapes.

Because massive haloes tend to have a few subhaloes gravitationally bound to them, observational studies treat the central halo and subhaloes as connected but separate entities, each with their own potential well. A counterpart to observational studies are simulations of dark matter: a bunch of massive (but visible to us!) DM particles are put in a box and allowed to interact for some time, allowing astrophysicists to watch a halo being formed and draw conclusions. In these simulations, researchers tend to include all the mass into one, total halo, thus making them hard to compare directly to observed data. The authors of today’s paper try to bridge that gap by removing subhaloes from existing simulation datasets, calculating the profiles of just the central, host halo, and comparing them with common halo profile models. ...

Illuminating Dark Matter Halo Density Profiles Without Subhaloes ~ Catherine E. Fielder et al
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Re: The Faint Young Sun (is not a) Problem

Post by BDanielMayfield » Sat Jul 18, 2020 5:45 pm

bystander wrote:
Sat Jul 18, 2020 4:13 pm
The Faint Young Sun (is not a) Problem
astrobites | Daily Paper Summaries | 2020 Jul 11
Anthony Maue wrote:
Like other stars, our Sun has likely evolved and changed during its life—born of a molecular cloud, coalesced in a disk, and currently burning through its supply of hydrogen as a rather typical main sequence star. We infer this history by studying other stars at different stages of their life cycle and by creating models to help us simulate our own star’s evolution. An early realization of these studies was that the young Sun would have been 20–25% less luminous, resulting in a much colder Earth. However, our geologic record contradicts this lower solar luminosity with clear evidence that liquid water was abundant during the Archean (an early geologic eon stretching 3.8–2.5 billion years ago, AKA 3.8–2.5 Ga). This apparent discrepancy, known as the faint young Sun problem, has plagued researchers for decades. Greenhouse gases like carbon dioxide (CO2) could have kept the early Earth warm despite a less luminous Sun, but geochemical studies indicate there likely wasn’t enough present on early Earth. Today’s paper reviews the many possible solutions to this infamous problem and suggests that recent advances in modelling may be able to finally close the book on this so-called paradox. ...

Is the Faint Young Sun Problem for Earth Solved? ~ Benjamin Charnay et al
Here is the abstract of the paper this report is about:
Stellar evolution models predict that the solar luminosity was lower in the past, typically 20-25 % lower during the Archean (3.8-2.5 Ga). Despite the fainter Sun, there is strong evidence for the presence of liquid water on Earth's surface at that time. This "faint young Sun problem" is a fundamental question in paleoclimatology, with important implications for the habitability of the early Earth, early Mars and exoplanets. Many solutions have been proposed based on the effects of greenhouse gases, atmospheric pressure, clouds, land distribution and Earth's rotation rate. Here we review the faint young Sun problem for Earth, highlighting the latest geological and geochemical constraints on the early Earth's atmosphere, and recent results from 3D global climate models and carbon cycle models. Based on these works, we argue that the faint young Sun problem for Earth has essentially been solved. Unfrozen Archean oceans were likely maintained by higher concentrations of CO2, consistent with the latest geological proxies, potentially helped by additional warming processes. This reinforces the expected key role of the carbon cycle for maintaining the habitability of terrestrial planets. Additional constraints on the Archean atmosphere and 3D fully coupled atmosphere-ocean models are required to validate this conclusion.
As the Faint Young Sun Problem is a favorite of Young Earth Creationists (who I disagree with because their views are so unscientific and therefore damaging to belief in God) I was happy to see this astrobite.

I'd like to posit another heat source that would have warmed the Earth billions of years ago, internal heating, both from the leftover heat of Earth's formation (even today after 4.6 billion years thought to account for half of Earth's internal heat) and radioactive decay, which would have been a far stronger heat source billions of years ago. Perhaps the paper's authors factor this in, but this wasn't made clear in the abstract. This is a paper that I intend on reading.

Bruce
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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The Fault in Our (Unaligned) Stars

Post by bystander » Sat Jul 18, 2020 6:06 pm

The Fault in Our (Unaligned) Stars
astrobites | Daily Paper Summaries | 2020 Jul 16
Lukas Zalesky wrote:
Perhaps the greatest and most pressing problem in modern astrophysics is the problem of dark matter. Dark matter is a purported physical substance that emits no electromagnetic radiation and appears to interact only with ordinary matter and itself through gravity. The existence of dark matter is hypothesized in order to explain numerous key observations throughout the universe, most notably: Unfortunately, despite more than a decade of searching, there has yet to be a definitive detection of particle-like dark matter by any of the numerous laboratory experiments done on Earth (e.g., the XENON1T experiment). It is then natural to wonder, could a solution to the problem of dark matter reside in a new understanding of gravity which avoids invoking a mysterious undetected material?

Alternative theories of gravity must satisfy observational tests already met by General Relativity, our current best understanding of gravity. One regime of such tests, as noted above, is in gravitational lensing by galaxy clusters. Without dark matter, all mass in the universe should be associated with visible sources (baryonic matter), and if dark matter did not exist, the mass of the baryonic matter should be sufficient to create the observed gravitational lenses we see throughout the universe. In today’s astrobite, we explore a work that uses a unique lensing system to put this possibility to the test. ...

Geometric Support for Dark Matter by an Unaligned Einstein Ring in Abell 3827 ~ Mandy C. Chen et al
viewtopic.php?t=34661
viewtopic.php?t=19381
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Re: Is it a Black Hole? Is it a Neutron Star?

Post by BDanielMayfield » Sat Jul 18, 2020 6:19 pm

Chris Peterson wrote:
Sat Jul 18, 2020 5:24 pm
BDanielMayfield wrote:
Sat Jul 18, 2020 4:57 pm
bystander wrote:
Sat Jul 18, 2020 4:35 pm
Look, Up in the Sky! Is it a Black Hole?
Is it a Neutron Star? Good Question.

astrobites | Daily Paper Summaries | 2020 Jul 13

GW190814: Gravitational Waves from the Coalescence of a 23 M Black Hole
with a 2.6 M Compact Object
~ LIGO Scientific Collaboration, Virgo Collaboration: R. Abbott et al
viewtopic.php?t=40706
This astrobite totally ignores other interesting possibilities, such as quark stars, that might populate the observed mass gap between 2.5 and 5 solar masses.
To be fair, we know that black holes exist. We know that neutron stars exist. We have no evidence at all that quark stars exist.
Yet. Just saying... GW astronomy might be on the verge of proving that the mass gap is full of things not previously confirmed to exist. That would be really big news, I think.
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Re: Is it a Black Hole? Is it a Neutron Star?

Post by Chris Peterson » Sat Jul 18, 2020 6:25 pm

BDanielMayfield wrote:
Sat Jul 18, 2020 6:19 pm
Chris Peterson wrote:
Sat Jul 18, 2020 5:24 pm
BDanielMayfield wrote:
Sat Jul 18, 2020 4:57 pm


This astrobite totally ignores other interesting possibilities, such as quark stars, that might populate the observed mass gap between 2.5 and 5 solar masses.
To be fair, we know that black holes exist. We know that neutron stars exist. We have no evidence at all that quark stars exist.
Yet. Just saying... GW astronomy might be on the verge of proving that the mass gap is full of things not previously confirmed to exist. That would be really big news, I think.
We do live in interesting times. (Both in the best sense, and the worst.)
Chris

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http://www.cloudbait.com

BDanielMayfield
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Re: The Faint Young Sun (is not a) Problem

Post by BDanielMayfield » Tue Jul 21, 2020 3:14 am

BDanielMayfield wrote:
Sat Jul 18, 2020 5:45 pm
bystander wrote:
Sat Jul 18, 2020 4:13 pm
The Faint Young Sun (is not a) Problem
astrobites | Daily Paper Summaries | 2020 Jul 11
Anthony Maue wrote:
Like other stars, our Sun has likely evolved and changed during its life—born of a molecular cloud, coalesced in a disk, and currently burning through its supply of hydrogen as a rather typical main sequence star. We infer this history by studying other stars at different stages of their life cycle and by creating models to help us simulate our own star’s evolution. An early realization of these studies was that the young Sun would have been 20–25% less luminous, resulting in a much colder Earth. However, our geologic record contradicts this lower solar luminosity with clear evidence that liquid water was abundant during the Archean (an early geologic eon stretching 3.8–2.5 billion years ago, AKA 3.8–2.5 Ga). This apparent discrepancy, known as the faint young Sun problem, has plagued researchers for decades. Greenhouse gases like carbon dioxide (CO2) could have kept the early Earth warm despite a less luminous Sun, but geochemical studies indicate there likely wasn’t enough present on early Earth. Today’s paper reviews the many possible solutions to this infamous problem and suggests that recent advances in modelling may be able to finally close the book on this so-called paradox. ...

Is the Faint Young Sun Problem for Earth Solved? ~ Benjamin Charnay et al
Here is the abstract of the paper this report is about:
Stellar evolution models predict that the solar luminosity was lower in the past, typically 20-25 % lower during the Archean (3.8-2.5 Ga). Despite the fainter Sun, there is strong evidence for the presence of liquid water on Earth's surface at that time. This "faint young Sun problem" is a fundamental question in paleoclimatology, with important implications for the habitability of the early Earth, early Mars and exoplanets. Many solutions have been proposed based on the effects of greenhouse gases, atmospheric pressure, clouds, land distribution and Earth's rotation rate. Here we review the faint young Sun problem for Earth, highlighting the latest geological and geochemical constraints on the early Earth's atmosphere, and recent results from 3D global climate models and carbon cycle models. Based on these works, we argue that the faint young Sun problem for Earth has essentially been solved. Unfrozen Archean oceans were likely maintained by higher concentrations of CO2, consistent with the latest geological proxies, potentially helped by additional warming processes. This reinforces the expected key role of the carbon cycle for maintaining the habitability of terrestrial planets. Additional constraints on the Archean atmosphere and 3D fully coupled atmosphere-ocean models are required to validate this conclusion.
As the Faint Young Sun Problem is a favorite of Young Earth Creationists (who I disagree with because their views are so unscientific and therefore damaging to belief in God) I was happy to see this astrobite.

I'd like to posit another heat source that would have warmed the Earth billions of years ago, internal heating, both from the leftover heat of Earth's formation (even today after 4.6 billion years thought to account for half of Earth's internal heat) and radioactive decay, which would have been a far stronger heat source billions of years ago. Perhaps the paper's authors factor this in, but this wasn't made clear in the abstract. This is a paper that I intend on reading.

Bruce
I read the paper, which sums up earlier work on the FYS problem. I must say that, while many possible parts of the solution have been put foreword, and while the authors suggest that the sum of these parts working together amounts to a possible solution, even they do not claim that there is a complete solution yet. They conservatively titled there paper "Is the Faint Young Sun Problem Solved?" and leave it as an open question. The astrobite reviewer goes further than the authors intended, IMHO.

Also, the paper had zero mention of any contribution from Earth's internal heat sources. I will now post a question about this in the Asterisk Cafe about this issue.

Bruce
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Do Aluminum Abundances Foil Our Theory of Galaxy Evolution?

Post by bystander » Thu Jul 23, 2020 7:09 pm

Do Aluminum Abundances Foil Our Theory of Galaxy Evolution?
astrobites | Daily Paper Summaries | 2020 Jul 20
Michael Foley wrote:
Most people know that aluminum is very useful for cooking an excellent steak or holding your favorite soft drink. Remarkably, it can also help us trace past supernova explosions and star formation in a galaxy! One of the isotopes of aluminum, aluminum-26 (Al-26), is produced in the cores of massive stars through fusion. These atoms are then expelled into the interstellar medium via stellar winds and supernovae. Al-26 is also radioactive with a very short half-life, meaning that, wherever we find Al-26, star formation and supernovae must have recently happended.

Today’s paper conducts a Milky Way-like galaxy simulation to study two mysteries that have emerged from recent observations of Al-26 in our own galaxy:
  1. Al-26 has a scale height of nearly 800 parsecs above the galactic plane, almost an order of magnitude greater than the 50 parsec scale height of both stars and star-forming gas.
  2. The mean rotation speed of Al-26 is 100-200 km/s greater than the rest of the galactic disk.
Given the importance of Al-26 as a tracer of stellar feedback, solving these mysteries could yield many more insights about the process of galaxy evolution. ...

Distribution and Kinematics of 26Al in the Galactic Disc ~ Yusuke Fujimoto, Mark R. Krumholz, Shu-ichiro Inutsuka
arXiv.org > astro-ph > [url=https://arx ... 2006.03057 > 04 Jun 2020 (v1), 10 Jul 2020 (v2) [/url]
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The “Power Couple” in the Universe

Post by bystander » Thu Jul 23, 2020 7:20 pm

The “Power Couple” in the Universe
astrobites | Daily Paper Summaries | 2020 Jul 22
Wei Vivyan Yan wrote:
The scales in the Universe are beyond our imagination. From the huge scale of galaxy superclusters, to the giant mass contained within dark matter halos, to the astonishing density of bodies like supermassive black holes (SMBHs), all are natural wonders evolving with cosmic time. Scientists believe that all these enormous structures grew from a much smaller scale, through processes like merging (Figure 1). Therefore, galaxy mergers are essential to better understand the evolutionary history of the most powerful and luminous objects in the Universe.

When two SMBHs collide into each other, the central region of the merger may ignite a long-lasting burst of light, which shines over one trillion (~1012) times brighter than the Sun. This pair of merging SMBHs, a luminous dual quasar, is among the most powerful and luminous objects in the Universe. In fact, due to their luminosity, scientists have found many of these “power couples”. However, most previous discoveries only contain dual quasars with relatively large separation. If the distance between the two rotating quasars is closer than 20 kpc (e.g., stage c in Figure 1), it is very challenging for scientists to separate them due to the instrumental limits of current telescopes. As a result, a dual SMBH can sometimes be misclassified as one single SMBH.

One way to solve this problem is to exploit the superb instrumental advantages of the Subaru telescope, used by the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP). In today’s paper, the authors use optical imaging from the HSC along with spectroscopy to improve the identification of luminous dual quasars at close separation. By discovering more of these BH “power couples”, the authors are able to probe the growth of SMBHs across cosmic time. ...

Dual supermassive black holes at close separation revealed by the
Hyper Suprime-Cam Subaru Strategic Program
~ John D. Silverman et al
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Discovering The Brilliance of Dwarf Galaxies

Post by bystander » Mon Jul 27, 2020 5:37 pm

Faint Jewels: Discovering The Brilliance of Dwarf Galaxies
astrobites | Daily Paper Summaries | 2020 Jul 27
James Negus wrote:
Beneath the radiant tapestry of massive galaxies that thread our universe, lesser-known cosmic entities lurk – dwarf galaxies. Weighing in with a stellar mass below 3 billion solar masses, these low luminosity celestial islands barely tip the scale (many individual supermassive black holes outweigh them)! Furthermore, despite being the most abundant type of galaxy in the universe, their formation and evolution are still not very well understood.

Active Galactic Nuclei (AGN) glow vibrantly in the darkness of space. Fueled by the rapid accretion of matter onto compact black holes within galactic cores, they can outshine the collective starlight of their host galaxies. Additionally, their powerful outflows can heat and disperse cold molecular gas, which astronomers believe may quell star formation and regulate galactic growth.

Most AGN are suspected to feature supermassive black holes (SMBHs; black holes with masses greater than one million solar masses) at their centers; however, today’s authors present exciting evidence, in tandem with previous studies that have uncovered hundreds of AGN within dwarf galaxies that harbor lower mass black holes, that is compelling astronomers to return to the drawing board. ...

Hidden AGN in dwarf galaxies revealed by MaNGA: light echoes, off-nuclear
wanderers, and a new broad-line AGN
~ M. Mezcua, H. Domínguez Sánchez
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A new method for cosmological inference

Post by bystander » Wed Aug 05, 2020 9:57 pm

Move over neural networks! – A new method for cosmological inference
astrobites | Daily Paper Summaries | 2020 Jul 30
Jamie Sullivan wrote:
Neural networks have seen a lot of hype in astronomy and cosmology recently (even just on this site! See these three bites). However, it may be that the neural networks used to classify images in typical machine learning applications are overkill. To quote the authors of today’s paper, “the cosmological density field is not as complex as random images of rabbits.” Today’s authors propose using a method called the “scattering transform” to take advantage of the best parts of neural networks with none of the limitations. ...

A new approach to observational cosmology using the scattering transform ~ Sihao Cheng et al
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Formalde-hyde and Seek

Post by bystander » Wed Aug 05, 2020 10:26 pm

Formalde-hyde and Seek
astrobites | Daily Paper Summaries | 2020 Aug 01
Jenny Calahan wrote:
Person. Woman. Man. Camera. TV. What do all of these have in common? They are complex organisms or objects which are made of organic molecules. If we want to understand the origins of such earthly things, we need to understand how and where they form within protoplanetary disks. H2CO, or formaldehyde, is one of the most abundant organic molecules in the universe, and can serve as a precursor to more complex organic molecules. Observing the location at which H2CO resides within a disk will shed insight into its formation, and thus the protoplanetary disk’s ability to form more complex molecules. Today’s paper surveys 15 protoplanetary disks looking at multiple H2CO lines. The authors seek to uncover the temperature, density, and origin of H2CO which will inform our knowledge of chemistry within disks. ...

An ALMA Survey of H2CO in Protoplanetary Disks ~ Jamila Pegues et al
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X Marks the Region

Post by bystander » Wed Aug 05, 2020 10:47 pm

X Marks the Region
astrobites | Daily Paper Summaries | 2020 Aug 03
Mitchell Cavanagh wrote:
Fans and writers of science fiction alike spend countless hours crafting intricate star systems, replete with planets, moons, and a menagerie of space-faring civilisations. The success of missions such as the Kepler Space Telescope (hereafter Kepler) and the Transiting Exoplanet Survey Satellite (TESS) have shown that our solar system is just one of many multi-planet systems present throughout the Milky Way. However, our ability to accurately determine the “planetary architecture” (the orbital configuration of the planets) of a given extrasolar system is severely lacking. Knowing how planets are configured in different extrasolar systems would greatly aid our understanding of how planets form, and how planetary systems evolve (e.g. via planetary migration). Exoplanets are inherently difficult to detect. The primary means of detecting them involves measuring the tiny dimming of a star as a planet moves in front of it. To better understand stellar systems, instead of considering each exoplanet individually, we can consider the entire population of exoplanets at once through statistical inference. This method has only recently become viable thanks to the wealth of data from modern exoplanet surveys. Today’s paper presents a statistical framework – DYNAmical Multi-planet Injection TEster (DYNAMITE) – designed to predict the presence of exoplanets that have so far eluded detection. ...

Hidden Worlds: Dynamical Architecture Predictions of Undetected Planets
in Multi-Planet Systems and Applications to TESS Systems
~ Jeremy Dietrich, Daniel Apai
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Schwarzschild precession in the orbit of the star S2

Post by bystander » Thu Aug 06, 2020 12:38 am

The first detection of the Schwarzschild precession in the orbit of the star S2
astrobites | Daily Paper Summaries | 2020 Aug 04
Sai Zhai wrote:
Over many decades, Einstein’s theory of general relativity (GR) has been confirmed by multiple tests, including the precession of Mercury’s orbit, emissions from the double pulsar PSR J0737−3039, and gravitational waves detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO).

Theoretically, GR predicts the existence of a black hole in the center of our galaxy. There is a lot of evidence showing that galaxies host massive central black holes, such as the relativistically broadened, redshifted iron emission line seen in nearby Seyfert galaxies, high resolution millimeter imaging from the Event Horizon Telescope (EHT), and the atypical movements of stars close to the black hole candidate at the center of the Milky Way. In the last case, the precession of a star’s pericenter angle caused by the central supermassive black hole is called Schwarzschild precession (SP).

However, the SP of the star’s pericenter angle is hard to measure because it is so small. This measurement becomes even harder for the galaxies that are far away from us. Thus, the best place to observe this phenomenon is in the center of the Milky Way.

Sgr A* is the nearest supermassive black hole candidate to us. It is surrounded by a star cluster. Among those stars, S2 is the second closest star to the galactic center. Observations of S2’s orbit taken from 1992 to 2019 supplied enough imaging and spectroscopic data to measure the precession of S2 in high detail. Because of precession, S2 cannot return to its “original position” after one orbital period. Only the pericenter (the star’s position when it’s at its nearest to Sgr A*)and the apocenter (the furthest the star gets from Sgr A*) can be distinguished, and since the pericenter is easier to observe, precession studies tend to focus on the pericenter. During the observation period, S2 passed the pericenter twice, once on May 1, 2002, and again on May 19, 2018.

The paper discussed here describes the first detection of Schwarzschild precession in the orbit of the star S2. ...

Detection of the Schwarzschild precession in the orbit of the star S2
near the Galactic centre massive black hole
~ GRAVITY Collaboration: R. Abuter et al
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Opening the Envelope on Protostars

Post by bystander » Thu Aug 06, 2020 12:53 am

Opening the Envelope on Protostars
astrobites | Daily Paper Summaries | 2020 Aug 05
Ashley Piccone wrote:
Protostars are not quite stars– they have not finished collapsing from a molecular cloud into a hydrogen-burning star. They are, however, a very interesting stage in a star’s life. Protostars are accreting material, building their mass so that at some point they have enough gravitational energy to begin to fuse hydrogen into helium. Protostars gather more mass as material gets pulled in from their outer envelope. The gas and dust gets sucked in by gravity and forms a rotating disk around the protostar, from which it both grows and sometimes ejects material in an outflow. Figure 1 shows the structure of a protostar from Tobin et al 2012.

Protostars are an important phenomenon to study because they help us understand the conditions occurring during star formation. Today’s paper analyzes the magnetic field and dust properties in 10 protostars. ...

ALMA's Polarized View of 10 Protostars in the Perseus Molecular Cloud ~ Erin G. Cox et al
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Tuning in to Reveal Stellar Wobbles

Post by bystander » Thu Aug 13, 2020 4:01 pm

Tuning in to Reveal Stellar Wobbles
astrobites | Daily Paper Summaries | 2020 Aug 06
Jason Hinkle wrote:
Since the first detections of planets outside of our solar system in the 1990s (for a review see this link), the exoplanet field has quickly grown. Initially, exoplanet detections were dominated by searches for Doppler shifts in the spectra of bright stars caused by the gravitational pull of one of more planets (known as the radial velocity method). In the last decade however, space-based satellites such as Kepler and TESS have shifted the focus to the transit method, or searching for small dips in the light received from stars as planets pass in front of them.

However, these are not the only methods we can use to find planets. Astronomers have also made use of the light-bending power of gravity (known as microlensing) to find planets, which is a major science goal of the upcoming Nancy Grace Roman Space Telescope. Sometimes, it is even possible to directly image a planet if the light of the host star can be blocked. Combined, these various methods have allowed us to find more than 4000 exoplanets orbiting stars other than our Sun.

There is one exoplanet detection method that we haven’t discussed yet, known as the astrometric method. This method essentially looks at the position of a star over a period of time and tracks deviations from the expected position. Discovering a planet this way requires excellent precision though. Fortunately the Gaia satellite is capable of making such a measurement, and it is expected that by the end of the mission that we will find many new planets through this method (for more details see this bite). With that said, there is only one currently claimed discovery of an exoplanet through astrometry. Today’s paper increases that count to two! ...

An Astrometric Planetary Companion Candidate to the M9 Dwarf TVLM 513-46546 ~ Salvador Curiel et al
viewtopic.php?t=40859
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Powering Stellar Explosions Through Shock Cooling Emission

Post by bystander » Thu Aug 13, 2020 4:12 pm

Through Collision Comes Light: Powering Stellar Explosions Through Shock Cooling Emission
astrobites | Daily Paper Summaries | 2020 Aug 07
Wynn Jacobson-Galan wrote:
Supernovae are among the most turbulent, luminous explosions in the known universe. These brilliant displays of stellar demise are produced from an amalgam of scenarios such as the merging of compact stars or the violent collapse of a star much more massive than our own Sun. A key facet in understanding the origins of different supernovae comes from their light curve evolution, the change in luminosity over time. However, not all supernova light curves can be explained by identical physics and thus astronomers are always on the lookout for new models to explain peculiar behavior.

The explosion of any star will naturally provide us with a reservoir of energy that is released over the supernova lifetime. So, when trying to understand what is powering a supernova light curve, we have the following sources of energy at our disposal: (1) the decay of radioactive isotopes such as nickel that are synthesized in the intense explosion environment and (2) the initial heat generated by the explosion itself. This isn’t much to work with, but radioactive decay does an exceptionally good job at powering most supernovae!

But what about those “weird” light curves that rise too fast or have two peaks? As shown in Figure 1b/c, such light curves have additional luminosity that normal radioactive decay cannot supply. To solve this problem, the authors of today’s paper present an updated method for powering supernovae through a process known as shock cooling emission (SCE), which is capable of releasing the extra energy needed to match observations. Awesome! But how does it work? To understand this relatively complex physical mechanism, bear with me through a belabored but hopefully convincing analogy. ...

Shock Cooling Emission from Extended Material Revisited ~ Anthony L. Piro, Annastasia Haynie, Yuhan Yao
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The starry, dusty origin of a galaxy cluster at z = 4!

Post by bystander » Thu Aug 13, 2020 4:28 pm

The starry, dusty origin of a galaxy cluster at z = 4!
astrobites | Daily Paper Summaries | 2020 Aug 08
Sunayana Bhargava wrote:
Galaxy clusters are vast entities. They contain 100 to 1000 galaxies, making them the largest gravitationally stable structures in the cosmos. One of the assumptions of our understanding of the Universe is structures form hierarchically—smaller gravitational objects form first followed by the largest. Therefore, to form large objects like clusters, smaller objects such as galaxies need to collide and merge together over a long period of time.

Although we generally know how clusters form, the specific process by which they grow is not yet well understood. The progenitors of clusters, known as protoclusters, are typically found at redshifts greater than 2 (the higher the redshift, the farther back it is in time), when the Universe was about one third of its current size. Unlike the clusters we observe today, protoclusters do not appear to have an established population of “red and dead” elliptical galaxies, which makes them harder to identify. Instead, protoclusters are usually identified by overdensities of star forming galaxies known as Lyman-alpha emitters, which are typically studied using data in the optical and ultraviolet (UV) wavelength ranges. You can check out other Astrobites on the intriguing properties of protoclusters here, here and here.

Today’s paper offers an alternative method for identifying protoclusters via a certain galaxy population known as dusty star forming galaxies (DSFGs). These galaxies contain substantial amounts of dust, which obscures their optical/UV light, but allows them to glow in infrared (IR). DSFGs are capable of forming stars in a short period of time at higher redshifts, which allows them to become the large red elliptical galaxies we see in clusters later on. DSFGS are also typically found in the vicinity of other DSFGS, which suggests they are pivotal to protocluster evolution. ...

Emergence of an Ultrared, Ultramassive Galaxy Cluster Core at z = 4 ~ Arianna S. Long et al
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