From Astrobites : “Is One Really the Loneliest Number? Void Galaxies Compared to Their More Popular Counterparts in the Field”

From Astrobites

4.22.23
Sonja Panjkov

Title: The Loneliest Galaxies in the Universe: A GAMA and GalaxyZoo Study on Void Galaxy Morphology

Authors: Lori E. Porter, Benne W. Holwerda, Sandor Kruk, Maritza Lara-López, Kevin Pimbblet, Christopher Henry, Sarah Casura and Lee Kelvin

First Author’s Institution: University of Louisville, Kentucky, USA

Status: Accepted for publication in the Monthly Notices of the Royal Astronomical Society

Astronomers have long attempted to understand precisely how the environment in which galaxies evolve affects their fate. But what do we mean by environment? Well, in cosmology, we are often referring to the cosmic web.

Cosmic web Millenium Simulation Cosmic web Millenium Simulation via The MPG Institute for Astrophysics [MPG Institut für Astrophysik](DE).

It’s a complex network of filaments of ordinary and dark matter resembling a spider’s haunt, which are separated by extremely empty regions of space, known as voids.

While galaxy clusters tend to accumulate along the dense filaments and tendrils of the cosmic web due to the never-ending tug of gravity, it is still possible for some lonely galaxies to evolve in the void. These galaxies are some of the most isolated objects in the universe, and thus, it’s very possible that their evolution differed from their more social counterparts, imbuing them with distinct properties and morphologies.

The authors of today’s bite attempted to see if this is indeed the case by studying the properties of void galaxies and their twins, or equivalent galaxies in the dense filaments and tendrils of the cosmic web that the authors refer to as field galaxies. By comparing the void galaxies to their twins in the field, the authors were able to control for other galaxy properties such as redshift (a proxy for distance), star formation rate and stellar mass. This enabled them to focus on whether environment is an important factor in galactic evolution.

Selecting Samples within Samples

Galaxies in the study were identified as part of the GAMA (Galaxy and Mass Assembly) Survey, with the void and field galaxy samples being selected from the GAMA Large Scale Structure Catalogue (GLSSC). To understand the morphological properties of their samples, the authors relied on data from the GAMA-KiDS Galaxy Zoo survey, an exciting example of citizen science in which members of the public are invited to help classify galaxies based on their physical features. If you’re interested in taking part, you can get started and help to classify galaxies here!

In addition, since galaxy morphological features are known to vary with redshift, the authors further divided their void and field galaxy samples into local and distant groups, with redshifts between 0 and 0.075, and 0.075 and 0.15, respectively. Moreover, to increase their sample size, the authors considered two samples of twins, one with stricter conditions to be counted as a twin and another with looser conditions. By using the sample with looser conditions, the authors were able to increase their sample size of twins, allowing stronger conclusions to be drawn in that case. However, the downside is that these twins are slightly less comparable on the whole to the void galaxies.

Figure 2. Plots of the local star formation rate (SFR) and effective radius Reff as a function of stellar mass (M*) for the local data set. The void data is shown in the middle, and the left panels use the twin data with the strictest conditions, while the right uses the data from all twins. Based on their Sersic indices, disk-like galaxies are shown as blue data points, while more elliptical galaxies are shown in green and yellow. The black lines in the lower panels are the best fit size-mass relations, with uncertainties shown as the black dashed lines. Adapted from figure 3 in the paper.

Armed with their samples, the authors then set about to see how certain properties varied amongst the populations. Figure 2 shows plots of the star formation rate (SFR) and effective radius (Reff) as a function of stellar mass (M*) for the void galaxies compared to their twins for the local dataset.

The data points are coloured according to their Sersic Index, which describes how the intensity of light from a galaxy varies radially. A Sersic index greater than 2 indicates that the light is centrally peaked and falls off quickly, as one might expect from an elliptical galaxy. On the other hand, Sersic indices of less than 2 are typical of disk-type galaxies, such as spiral galaxies, as they indicate that the intensity is more constant throughout the galaxy. Looking at figure 2, it is clear that the two morphological groups cluster together, with disk-type galaxies in blue and elliptical galaxies in green and yellow.

Also of note in figure 2 is the size-mass relation that the authors fitted to the data in the bottom three panels, shown as the black lines with the error indicated in dashes. The size-mass relation is often used to understand how evolved a galaxy is, since larger galaxies with greater radii tend to have more mass, likely indicating past mergers with other galaxies and hence a longer lifetime. The bottom middle panel showing the void galaxy data appears to have a different trend compared to the two twins data sets on either side, possibly indicating a different evolutionary history. However, the authors caution any strong conclusions given the small sample size.

Next, the authors turn their attention to the morphological features studied by the citizen scientists of the Galaxy Zoo survey. As part of the survey, one question participants were asked was ‘How prominent is the central bulge, compared with the rest of the galaxy?’

Figure 3. Cumulative histograms indicating the fraction of Galaxy Zoo participants that agreed with there being no bulge in the galaxies in the study, with void galaxies in black and field galaxies in blue. The top panels show the local galaxy data, while those below show the more distant sample. The left panels use the stricter conditions on twins and thus have smaller field sample sizes, compared to the right panels which use all twins. Adapted from figure 12 in the paper.

Figure 3 shows cumulative histograms of the voting fractions for the local and distant samples, and compares the void galaxies in black to the field galaxies in blue. The voting fraction (on the x-axis) indicates what percentage of the population agreed that there was no bulge in the image they were shown. For example, a voting fraction of 0.6 indicates that 60% of respondents agreed there was no bulge present in the image they were shown. The y-axis then shows the cumulative distribution of voting fractions for the populations, so a curve that is initially steep and then plateaus out indicates that most galaxies in the sample had low voting fractions and hence had a bulge. The left panels use the field galaxies with the strictest conditions to be considered a twin, while the data from all twins were used in the right panels.

For the local dataset (top row of figure 3), both the void and field samples have 75% of galaxies within a voting fraction of 0.25, meaning participants strongly disagree with there being no bulge in these populations. More simply, these populations on the whole showed evidence of a bulge. In the distant sample below, the same holds for the void galaxies, however, the field galaxies show more diversity and do not always have a bulge present as there is a flatter, more even distribution of voting fractions.

Given the small sample sizes of the study, the authors ultimately conclude that void galaxies are largely similar to their filament and tendril twins, particularly in the local universe regime. That being said, there are hints that isolated galaxies may evolve differently to their counterparts in denser regions of the universe. With a larger sample size, things will become clearer. However, at least for now, the void galaxies appear to be doing just fine, even if one is the loneliest number.

See the full article here .

Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”

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Please help promote STEM in your local schools.

Stem Education Coalition

What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

From Astrobites : “Gravitational Waves – à la General Relativity or Scrambled?”

From Astrobites

Paper: Probing lens-induced gravitational-wave birefringence as a test of general relativity

Authors: Srashti Goyal, Aditya Vijaykumar, Jose Maria Ezquiaga, Miguel Zumalacarregui

Author Institutions: International Centre for Theoretical Science, Tata Institute of Fundamental Research; Department of Physics, The University of Chicago; Niels Bohr International Academy, Niels Bohr Institute; Max Planck Institute for Gravitational Physics

Status: Submitted to arXiv [12 Jan 2023]

Albert Einstein’s Theory of General Relativity is undoubtedly an extremely successful theory of Gravity, having passed all experimental and observational tests so far. Nonetheless, alternative theories of gravity are actively explored for various theoretical motivations, such as explaining the accelerating expansion of the universe. One such example is a scalar-tensor theory which includes a scalar field in addition to the tensor field (the ‘metric’ tensor) which GR is based on. However, such a theory is of little use if it cannot be tested. Fortunately, the authors of today’s paper propose a method for testing GR and its possible extensions by studying the ‘scrambling’ of gravitational waves (GWs).

Gravitational waves. Credit: W.Benger-Zib. MPG Institute for Gravitational Physics (DE).

GW Modes

GWs, like electromagnetic waves (light), have a property called polarization which describes the geometry of the wave oscillations. GR predicts the existence of only two polarization modes for GWs: the tensor plus (+) and cross (×) modes (Figure 1).

In GR, the two modes propagate independently from each other and move at the speed of light [in a vacuum]. The evolution of a GW is described by a sum of the independent evolution of the two (+ and ×) modes.

The situation differs in alternative theories of gravity with extra degrees of freedom (such as an additional scalar) which allow additional GW polarizations. The extra modes can appear and mix as the GWs propagate. In particular, in scalar-tensor theories, regions of strongly curved space can lead to interactions between the tensor and scalar degrees of freedom that cause the standard + and × modes to move at different speeds. Thus, studies of only the propagation of the modes allowed by GR can also probe signatures of additional modes forbidden by GR. The existence of additional modes would indicate a violation of GR and require an extension of the current model of gravity! But how does one go about searching for such a signal?

How to Scramble GWs: Lens-Induced Birefringence

The authors study the difference in the propagation speeds of the + and × modes in an effect called lens-induced birefringence (LIB). An analogous effect which may be more familiar (and illustrative) is optical birefringence in crystals. Under this effect, light incident on an anisotropic crystal undergoes double refraction and is split by polarization into two rays that travel with slightly different velocities. This produces two images, one slightly displaced from the other (Figure 2).

Figure 2. Optical birefringence in calcite causes the double refraction of the graph paper lines (image from wikimedia commons).

In the case of GWs, birefringence occurs when a large mass, such as a super massive black hole or galaxy, splits the original signal by polarization mode and speed (which may differ among the modes in non-GR theories) depending on the incident position and direction (Figure 3). This separation causes each polarization mode to arrive at the GW detector at a different time, resulting in a relative time delay between modes– the main observable in this study.

Figure 3: Figure 1 of Ezquiaga & Zumalacárregui (2020) PRD. A GW emitted from a black hole binary (left) splits into its component polarization modes (the eigenstates represented by three colors) in the relevant region around a large mass. Depending on whether the delay in the modes is shorter or longer than the duration of the signal, the resulting waveform could be ‘scrambled’ (discussed here) or ‘echoed’, respectively.

Effects of Scrambling

If the delay between the two tensor modes is shorter than the total duration of the signal, the waveform is distorted or “scrambled” due to the interference of the polarizations. In this paper, the authors look at the difference in the arrival times between the two GR polarization states due to different propagation speeds as a result of LIB.

They calculate the GW signal measured at the detector after LIB ‘scrambling’ (of the polarization amplitudes) by a spherically symmetric lens as a function of the time delay and angle between the lens and source (relative to the direction of GW propagation). Under LIB, the polarizations interfere, leading to waveform distortions. The authors quantify the distortions due to GW birefringence by computing how much the birefringence ‘scrambles’ the GR signal. Examples are shown in Figure 4.

Figure 4: Figure 1 of the paper. GW signals for different LIB time delays. The left side shows the signal broken down into contributions from the + (blue) and × (green) polarization modes. The right column shows the total waveform– a linear combination of the two modes. The LIB ‘scrambled’ signal (red) is compared with the GR signal (black). Note that the interference of the delayed polarizations in LIB leads to a distorted total waveform.

Taste Test (i.e. Results)

The authors apply their time-delay analyses to GW signals from merging binary black holes and neutron stars detected by LIGO-VIRGO.

Caltech/MIT Advanced aLigo at Hanford, WA, Livingston, LA; and VIRGO Gravitational Wave interferometer, near Pisa(IT).

They find that almost all events were consistent with no LIB time-delay, i.e. GR. Only a few events show a preference for LIB. Upon further analysis, they conclude that there is no strong evidence for birefringence in the data.

Figure 5. LIB test of GW events, Figure 5 of the paper (and winner of the Physics Plot of the Week earlier this year). For each of the GW events the posterior (statistical estimate of the value) for the time delay is shown on the vertical axis and the Bayes factor is given on the upper horizontal axis. A Bayes factor > 1 (or logarithm of this factor > 0), indicates a preference for LIB over GR.

This non-observation of birefringence in the events analyzed translates to constraints on the phenomenological model parameters. As an example, they apply their results to a specific scalar-tensor theory of gravity which predicts LIB and places constraints on parameters in that theory.

Although the authors find no strong evidence for birefringence, they note that with improving detector sensitivity, measurements of smaller birefringence time delays which may be missed in current data will be possible. This will allow better constraints on birefringence probabilities.

Furthermore, developing LIB predictions for other alternative theories of gravity and applying the results of this work will offer more tests of the landscape of theories beyond GR.

See the full article here .

Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”

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Please help promote STEM in your local schools.

Stem Education Coalition

What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

From Astrobites : “Two Earth-sized habitable zone planets in the same system!”

From Astrobites

4.6.23
Isabella Trierweiler

Title: A Second Earth-Sized Planet in the Habitable Zone of the M Dwarf, TOI-700

Authors: Emily A. Gilbert, Andrew Vanderburg, Joseph E. Rodriguez, et al.

First Author’s Institution: NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA.

Status: Published in The Astrophysical Journal Letters [open access]

TESS and Dr. Emily Gilbert have done it again! Three years ago, Dr. Gilbert, then a graduate student, and her team found the first Earth-sized planet in the habitable zone of a TESS exoplanet system called TOI-700.

Massachusetts Institute of Technology TESS – Transiting Exoplanet Survey X-ray Satellite replaced the Kepler Space Telescope in search for exoplanets. TESS is a NASA Astrophysics Explorer mission led and operated by The Massachusetts Institute of Technology, and managed by NASA’s Goddard Space Flight Center.

Planets in habitable zones are close enough to their host planets to harbor liquid water, and are some of the best places to consider in the search for life. Now, analysis of new TESS data has yielded another Earth-sized habitable zone planet, hidden in the same TOI-700 system!

The host star of TOI-700 is an M-dwarf star. M dwarfs are some of the smallest and most plentiful stars in our galaxy – astronomers estimate they may account for up to 75% of the stars in the Milky Way. Because they are so small, M dwarfs are extremely long lived, far exceeding the 10 billion-year lifetimes of stars like our Sun. Astronomers have been interested in planets around M dwarfs for years now. The small size and low brightness of M-dwarfs make it easier to detect planets around these stars, meaning M-dwarfs are a great place to start to search for habitable zone planets.

TESS finds exoplanets using the transit method, monitoring stars for the tell-tale brightness variations that occur when planets pass in front of their host stars (you can help astronomers find transiting TESS planets here!).

Planet transit. NASA/Ames.

The TOI-700 system was observed multiple times in the first three years of TESS’ mission, and the first analysis of TOI-700 yielded three planets, referred to as b, c, and d (the star itself typically gets ‘a’). Those initial three planets all had radii between 1-2 Earth radii. Planets b and c are orbiting very close to the host star, with orbital periods of less than 16 days. However planet d, with a period of ~40 days, falls within the habitable zone for the star TOI-700!

Figure 1: Lightcurves for the four TOI-700 planets. Each plot shows the change in observed brightness of the host star when the planet passes in front of the star. Planets d and e are both in the habitable zone of the system! Credit: Figure 3 from today’s paper.

Today’s authors used existing TESS data, along with new observations at the Campocatino Austral Observatory (CAO) in Chile, to discover yet another habitable zone planet in the TOI-700 system, planet e! The CAO data was taken to make sure no binary stars were interfering with the observed light curves.

Campocatino Austral Observatory (CAO)

The transit data show that planet e is actually a little closer to the host star than planet d, technically placing planet e in what is called the “optimistic” habitable zone (Figure 2). The difference between the “optimistic” and “conservative” habitable zones is small, but the distinction is a sign of our uncertainty on what constitutes habitability. While we define the habitable zone as the range of radii away from a host star where planets can sustain liquid water, calculating those radii can vary based on our assumptions about where liquid water exists in the solar system. A conservative estimate of the habitable zone is calculated based on maximum greenhouse effects that could apply to a planet, whereas the optimistic zone is based on estimating the history of liquid water on Venus and Mars.

Figure 2: Diagram of the TOI-700 system, with the newly discovered planet e in red. The darker green region is the “conservative” habitable zone while the lighter green is the “optimistic” zone. Credit: Figure 4 from today’s paper.

The radius of a planet can be determined based on the depth of the transit light curve, since the depth corresponds with the ratio of the cross section of the planet relative to the size of the host star. Planet e has a radius of about 0.95 Earth radii, and the authors found that the planet is most likely rocky, with a mass of about 0.85 Earth masses. From that mass, the authors were able to further estimate that the planet would have become tidally locked with the host star within a few million years of its formation, remaining so to the present day.

So what does it mean to have two habitable zone planets in one system? In short, it’s an exceptional opportunity to learn about habitability and exoplanet climates! The TOI-700 planets all have similar masses and radii to the Earth, so they provide a really good opportunity to compare the terrestrial planets in our solar system to exoplanets overall. Very few detected planetary systems have multiple low-mass planets inside or outside of the habitable zone. The notable existing example is the TRAPPIST system, and it will be really interesting to compare the two systems going forwards.

A size comparison of the planets of the TRAPPIST-1 system, lined up in order of increasing distance from their host star. The planetary surfaces are portrayed with an artist’s impression of their potential surface features, including water, ice, and atmospheres. Credit: NASA.

The TRAPPIST host star is much more active than TOI-700, so together these two systems could shed light on how different stellar properties affect planets.

The TOI-700 planets are also all on nearly circular orbits, meaning they are more likely to have long-term, stable climates than more eccentric planets. The brightness of the TOI-700 host star is sufficient for observing the atmospheres of the planets in the future, so we could learn a lot more about planetary climates and how they can vary throughout solar systems.

Finally, planet e is especially compelling because it receives a stellar flux from the host star that’s similar to what Earth and Venus get from the Sun. So planet e could be a really interesting Earth/Venus analog and maybe even help us understand whether Venus had liquid water, and if so what happened to it.

The discovery of TOI-700’s newest planet is just the tip of the iceberg for this system! TESS is planning to observe the system again in an upcoming observing cycle, to check for any more hidden planets. The authors are also gathering radial velocity data for the system to get better constraints on the masses of the planets. Keep an eye out for future TOI-700 results, because there’s so much exciting science to do with this system!

See the full article here .

Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

From Astrobites : “Dark matter and Neutrinos walk into a (nano)bar(n); can we observe νDM interactions in the CMB?”

From Astrobites

4.8.23
Cole Meldorf

Title: New Insight on Neutrino Dark Matter Interactions from Small-Scale CMB Observations

Authors: Philippe Brax, Carsten van de Bruck, Eleonora Di Valentino, William Giarè, and Sebastian Trojanowski

First Author’s Institution: Institut de Physique Théorique, Université Paris-Saclay, Gif-sur-Yvette Cedex, France

Status: Submitted to ArXiv [28 Feb 2022]

Despite our best efforts, most powerful telescopes, and biggest atom-smashers, dark matter (DM) slipperily continues to avoid direct detection. While we can measure its effects on the surrounding universe, and theorize that it must exist in order for modern space to look the way it does, we have yet to figure out exactly what it’s made of. The main reason it is so hard to determine what dark matter is made of is that it seems to only interact with other particles through gravity. If it interacted through any other means (i.e. the electromagnetic, weak, or strong forces) we believe we should have found it in the shattered remains of particles annihilated in colliders. At the very least, our accelerator-based experiments show us that if DM does interact through anything other than gravity, its cross-section is incredibly small. But what if we could use the oldest light in the universe we can see, the Cosmic Microwave Background (CMB), to infer how dark matter could interact with other particles? Today’s paper does just that, looking for an interaction between neutrinos and DM (νDM) in the CMB.

Neutrinos. Credit: J-PARC T2K Neutrino Experiment.

CMB per European Space Agency(EU) Planck.

Figure 1.

How does one show that neutrinos can interact with DM from just the CMB observations? From Figure 1 you can see that the CMB looks a lot like TV static (fun fact, that’s because it quite literally is), so the first step is to manipulate that mess into something more palatable. We do this by converting the 2D sky map into a 1D graph, called the angular power spectrum.

Figure 2: The angular power spectrum of the CMB temperature anisotropies, (devations from average) as a function of angular scale and multipole moment. This plot encapsulates the patchiness of the CMB at different scales. Image Source: Planck 2013 Cosmology Results.

The spectrum encapsulates how different the temperatures at different points on the CMB are from each other on average, as a function of angular separation. In other words, how smooth or rough the CMB is at different angular scales. For example, in Figure 2, we see a major peak at about 1 degree (see the upper x-axis); this is the main degree of “patchiness” that our eyes pick out when we look at the CMB map. (For an in-depth understanding, see this article.) Typically, the x-axis of the power spectrum is given in terms of the multipole moment l, but all you need to know is that high l corresponds to small angular scales and vice versa.

Conveniently, our models of cosmology can predict what they expect the power spectrum to look like. The authors therefore ask, what would the power spectrum look like if we include a νDM interaction in our model of the universe? With some key assumptions, one can include this νDM correction as a singular term, called \mathrm{u}_{\nu DM}, in the model proportional to the cross-section of the interaction and mass of the hypothetical DM particle. \mathrm{u}_{\nu DM} = 0 means DM and neutrinos do not interact, larger values mean they interact more frequently. The authors then study the shape of the angular power spectrum as a function of different values of \mathrm{u}_{\nu DM}, see the larger plot of Figure 3 [Figure 1 in the Paper, which is absent in the article].

Evidently, the difference between a universe without νDM interactions and one with is indistinguishable at most angular scales on the CMB. However, it seems that the difference becomes apparent at high multipoles, which is the same thing as saying very small angles. Great! So we just look at these small angular scales and see what the CMB tells us, right? Well, that’s the idea, but it turns out these tiny angular scales quickly become difficult to measure, hence the Planck satellite not covering ranges higher than l > 2500 (see Figure 2). Thankfully, the ground-based Atacama Cosmology Telescope’s most recent data release is capable of probing these high multipole regions.

Princeton 6 meter Atacama Cosmology Telescope, on Cerro Toco in the Atacama Desert in the north of Chile, near the Llano de Chajnantor Observatory, Altitude 4800 m (15700 ft).

What happens, then, if we fit our νDM model to this power spectrum? Surprisingly, the data seems to prefer a non-zero cross-section between neutrinos and dark matter, meaning the two species could interact! Specifically, they estimate that the size of this term is log (\mathrm{u}_{\nu DM}) = -5.20^{+1.2}_{-0.74}. Due to the limits set by the data, the authors are only able to rule out a cross-section of zero at a 1σ level, when generally 5σ accuracy is required to be certain. Hence, an interacting DM is not confirmed, only tantalizingly hinted at. Nonetheless, the data’s preference for a non-zero interaction is exciting and encourages further study. For instance, what would a new standard model where a neutrino-DM interaction existed look like?

Warning, Particle Physics ahead, abandon all hope ye who enter here

Assuming a dark matter particle with a mass of ~1 GeV (1.79 \times 10^{-27} kg), the size of the parameter governing the interaction corresponds to a cross-section size of about a nanobarn, hence my hilarious title. However, due to the close relationship between leptons (electrons, muons, and tauons) and neutrinos, a neutrino interaction with a cross-section of this size should have produced dark matter particles in our electron collider experiments already. We thus have to be careful how we add dark matter into the Standard Model Lagrangian to avoid these constraints: enter the sterile neutrino. The sterile neutrino is a hypothetical 4th neutrino particle that interacts only via gravity. If this sterile neutrino was coupled to DM particles and was itself quite heavy, it could explain why we see cosmological signals of νDM interactions but not in a collider, as this sterile neutrino could be too heavy for our current colliders to produce, hence preventing any decays into DM particles. They would also be too heavy for other neutrinos to oscillate into, further explaining our lack of detection. While other models beyond this use of the sterile neutrino are possible, the authors note that the interaction strength calculated when using a model of this kind agrees well with other papers that use different cosmological detection methods.

What’s Next?

While it is far too soon to declare that dark matter has made friends with neutrinos, the data’s preference for a potential interaction is exciting. With upcoming CMB experiments – such as the Simons Observatory – we can make better measurements of the high multipole region of the CMB, allowing for an even more precise measurement of \mathrm{u}_{\nu DM} .

The Simons Array in the Atacama in Chile, altitude 5,200 m (17,100 ft) with the 6 meter Atacama Cosmology Telescope.

If a non-zero interaction is detected, our improved understanding of DM’s connection to the rest of the standard model could point us in the right direction for finding DM particles in an accelerator. These exotic particle interactions could lead us to new exciting extensions to the Standard Model and rewrite our understanding of the evolution of the universe!

See the full article here .

Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

From Astrobites : “STARS IN THE DUST? Signs of Previously Unknown Companions in the Southern Ring Nebula revealed by JWST”

From Astrobites

4.4.23
Aldo Panfichi

Title: The messy death of a multiple star system and the resulting planetary nebula as observed by JWST

Authors: Orsola De Marco et al.

First Author’s Institution: School of Mathematical and Physical Sciences, Macquarie University, Sydney, NSW 2109, Australia.

Status: Published in Nature Astronomy [closed access]

Some stars end their lives with a bang; others not with a whimper, but a glow. Stars of “intermediate mass” (between 1–8 solar masses — not too small, and not too large!), when reaching the end of the red giant stage of their lives, will eject their outermost layers as an expanding cloud of ionized gas, pushed outwards by stellar winds from the slowly dying star. These structures are called “planetary nebulae,” though they have nothing to do with planets — the name is historical, as the astronomers in the 1700s who first observed these objects thought they looked like planets. Examples of well-known planetary nebulae include the Dumbbell Nebula, the Ring Nebula, and the Southern Ring Nebula, also known as NGC 3132. It is this last example on which today’s paper is focused.

NGC 3132 is a bright planetary nebula (hereafter, PN) located about 2000 light years from Earth. Within the nebula, two stars have been observed. One is a white dwarf, at the center of the PN, and is likely the progenitor of the nebula; the other is an A-type, main-sequence star orbiting the white dwarf at a radius of over 1200 AU, making this pair a wide binary. In 2022, infrared images of NGC 3132 taken by JWST were released as part of its Early Release Observations program. The authors of today’s paper claim that within these images, there is evidence that NGC 3132’s progenitor system was not merely a binary, but a system of at least four or five stars.

Hidden in the Halo

A typical PN consists of a hot wind bubble, surrounded by a shell of ionized gas from the red giant’s atmosphere. Often that shell is itself surrounded by stellar ejecta of molecular gas and dust. When PNe originate from a lone star, they are generally spherical. If the giant interacted gravitationally with a stellar companion (or more than one!) during its later years, however, then one would expect the PN to contain evidence of these interactions. These signs are seen in departures from spherical symmetry in the shape of the nebula, as well as structures such as rings, arcs, spirals, and jets in the gas.

Figure 1 shows colored images of JWST’s observations of NGC 3132 in different infrared bands. In particular, distinction is made between the emission bands of H-II (ionized hydrogen, which traces the PN’s ionized gas) and H2 (molecular hydrogen, tracing the molecular gas).

Figure 1: Colored JWST images of NGC 3132. Upper left: H-II emission, tracing the ionized gas region. Lower left: H2 emission, tracing the molecular gas halo. Right: greyscale, single-filter zoomed-in image of the molecular halo to show detail. Note the extension of the halo way further than the ionized gas reaches, and the concentric arc features present within it. Figure 1 in the paper.

The molecular gas halo is seen in unprecedented detail by JWST’s images. Regular structures such as those described previously can be seen in the halo, which is much clumpier and more irregular than the ionized gas. Of the many features, one of particular interest is a series of concentric arcs similar to those observed in other PNe; the most accepted explanation for these is the stellar wind being influenced by a stellar or sub-stellar companion. Should this be the case, the average size and separation of the arcs indicates such a companion would orbit the central white dwarf at a radius of 40-60 AU; the bright A-star at >1200 AU cannot be responsible, which implies NGC 3132 is at least a triple star system. Given the fact that the hypothetical new star is not directly visible in the glare of the dwarf, the authors place an upper limit of 0.2 solar masses on what would presumably be a main-sequence companion.

Four (or Five)’s a Crowd?

The hypothesis of a close binary companion is reinforced by the shape of the innermost cavity and ionized gas shell. Combining the JWST images with spectroscopic observations of the PN, the authors were able to reconstruct a 3D visualization of this component of the nebula, as can be seen in Figure 2.

Figure 2: Author’s reconstruction of the ionized cavity of NGC 3132. Color-coding indicates Doppler shift as seen from Earth, with bluer regions approaching the observers and redder regions moving away. Figure 3 in the paper.

In the 3D reconstruction, the shape of this cavity is very clearly not smooth — it is covered in numerous protuberances, which could be due to intermittent jets. If this is the case, these jets are being generated over a huge range of axes — too many for a single close binary to cause. This leads the authors to conjecture that the central dwarf is not a member of a close binary, but at least a close triple. If there is indeed another companion, then combined with the wide-orbiting A-star, this brings the total number of gravitationally bound stars in the system to four…

…or possibly even more! JWST also discovered a disk of hot dust around the central white dwarf. The presence of this disk also favors the existence of a close binary companion, which would have donated a significant amount of material and angular momentum to the disk. One could think that this companion could be the same as the first new hypothesized companion: the one at 40-60 AU with a maximum mass of 0.2 solar masses.

However, when the authors attempted to use 2D hydrodynamic simulations to replicate the structures found in the larger molecular halo (as seen in Figure 1), they found that the arches in the gas — those produced by the first hypothesized companion — were much sharper in the JWST images than in their geometric model. This would possibly indicate that the arches are aligned close to the plane of the sky from our point of view, and thus that said hypothetical companion is closely aligned to the waist of the elliptical-shaped PN. If this is true, then this companion cannot be the one partaking in the formation of the hot dust disk. Furthermore, it cannot be the one launching strong jets into the ionized region, as the accretion rate at these orbital distances would not be large enough to do so. Combined, these could be signs of yet another stellar companion, bringing the total number of stars in the system to five!

A Tale of Stars Revealed

All in all, the sensitivity and precision of JWST’s instruments can help shed great light into the underlying history of NGC 3132, and other PNe. The observed structures in the nebula help paint a picture of this multiple-star system. Before it became the central white dwarf, there was a red giant in a wide orbit with a main sequence A-star. Alongside these, a smaller, closer companion at 40-60 AU, which left its presence in the form of arcs in the molecular gas; another close companion, the source of the dusty disk, which either escapes detection or perished in an interaction with the giant; and, if the jets and protuberances are as complex as they seem, a possible third close companion, similarly undetected. While speculation about the nature of the origin of these features still remains, the authors are confident in claiming that the original star system that became NGC 3132 was at least a quartet (if not a quintet) — something rare, but not impossible, given the range of masses of the stars at interest.

Discoveries like these are only the start for the era of JWST. With complementary observations from other instruments, JWST has the potential to revolutionize what we know in many fields of astronomy; among them the histories and evolution of PNe, and the role of stellar companions in shaping these impressive structures of our universe.

See the full article here .

Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”

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Please help promote STEM in your local schools.

Stem Education Coalition

What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

From Astrobites : “The Kozai-Lidov Tango – The Ups and Downs of being a Polar Circumbinary Disk”

From Astrobites

Title: Formation of polar circumstellar discs in binary star systems

Authors: Jeremy L. Smallwood, Rebecca G. Martin, and Stephen H. Lubow

First author’s institution: Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan; and Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154, USA

Status: Published on ArXiv, 27 Jan 2023. Accepted for publication in MNRAS.

When stars are born, they are usually orbited by a protoplanetary (or circumstellar) disk which contains gas and dust that may eventually form planets. Many stars, however, are not alone in space but instead have a binary companion — another star of oftentimes very similar mass that orbits the primary star.

Today’s authors investigate a polar circumbinary disk: a disk around both binary stars that is in a “polar” configuration with respect to the inner binary orbit. A polar orbit in astronomy references if the path of the orbit crosses the poles of the object that is being orbited. For example a satellite that is in a polar orbit around Earth would fly above the North and South poles. In today’s case, the gas in the circumbinary protoplanetary disk passes above the poles of the binary orbit, and therefore does not orbit in the same plane as two stars. This corresponds to a relative inclination of 90 degrees.

Figure 1: Initial configuration of the systems (top panel) and final state after 25 binary orbital periods). The orange dots show the two stars. The left panels show an edge-on view of the circumbinary disk whereas the right panels show a face-on view. Over the time of the simulation, gas is accreted from the circumbinary disk onto the two binary stars which get circumstellar disks themselves. (Figure 7 in the paper)

Figure 2: Edge-on view of the simulated systems after 5 orbital periods. The binary is shown as green dots and the colors indicate the density of the gas in the system. The black arrows in the figure correspond to the velocity vectors of the gas flow. The gas has formed two asymmetric lobes around the circumbinary disk. (Figure 9 in the paper)

Such a setup may seem exotic, but it has indeed been observed, for example around the protostars IRS 43, or HD 98800 BaBb. Consequently, the questions on these systems’ origin, and dynamical behavior arise naturally.

The authors set up a hydrodynamical simulation of a polar circumbinary disk. The top panels of Fig. 1 shows the initial setup, whereas the bottom panels show the system after 25 orbital periods. Gas from the circumbinary disk has flown from the outer disk onto both of the binary stars and formed two circumstellar disks around each star. These two secondary disks likewise are in polar alignment with respect to the binary orbit. There is also a cavity that is relatively devoid of gas in between the larger circumbinary disks and the inner circumstellar disks.

Interestingly, since the binary orbit is set up with an eccentricity of 0.1, the so-called Kozai-Lidov mechanism can operate . For two polar circumstellar disks the Kozai-Lidov effect is manifested in an oscillation of their eccentricities and tilt. The masses of the circumstellar disks likewise oscillate in time due to this oscillating eccentricity. Some material is flung outwards out of circumstellar disks into the gap between the binary stars and the circumbinary disk. This is shown in Fig. 2, which shows an edge-on view of the entire system. The gas that is displaced relative to the plane of the circumbinary disk is distributed asymmetrically around the binary, and will fall back into the disk gap. (Also see this Astrobite for a similar application of the Kozai-Lidov mechanism).

Figure 3: Like Figure 1 but a zoom-in onto the binary stars and their circumstellar disks. Shown are a snapshot at 20.2 orbital periods (left panels) and at 20.7 orbital periods (right panels). The latter corresponds to alignment between binary stars and circumbinary disk so the two stars appear on top of each-other in the edge-on view. This is when the material stream from the circumbinary disk onto the smaller disks is the greatest. (Part of Figure 11 in the paper)

Figure 3 shows a zoomed-in perspective of two snapshots of the simulation at hand, this time, with the smaller, circumstellar disks in the focus rather than the larger circumbinary disk. The two panels on the right show the time where the two circumstellar disks are aligned with the circumbinary disk. Each time this happens, material flows on the smaller circumstellar disks resulting in their masses increasing. However, due to the aforementioned Kozai-Lidov mechanism, which flings gas away from the disks into the gap in between, over the course of many orbits, the masses of the circumstellar disks decrease. This is shown in Fig. 4 which depicts the mass evolution over five orbital periods.

Figure 4: Mass evolution of the smaller circumstellar disks over the course of five orbits. Each orbit is shown in a different color. The vertical lines indicate alignment between binary and circumstellar disks (see Fig. 3), and thus correspond to a mass increase. Overall, the disks lose mass because of the Kozai-Lidov mechanism. (Figure 12 in the paper)

Each orbital period is shown in a different color starting from black, over blue, red, green and finally yellow. While an alignment with the circumbinary disks (indicated in vertical dashed lines) can temporarily increase the circumstellar disk masses, the Kozai-Lidov effect ultimately wins, and the disks lose mass overall.

Whether or not such systems can indeed persist remains to be seen. Luckily for the new-born circumstellar disks, the Kozai-Lidov oscillations weaken over time so the disks may survive their Kozai-Lidov tango with the circumbinary disk after-all.

See the full article here .

Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”

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Please help promote STEM in your local schools.

Stem Education Coalition

What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

From Astrobites : “Age is Just a Number – Radioactive Dating in Stars”

From Astrobites

2.21.23
Mark Popinchalk

Title: Uranium Abundances and Ages of R-process Enhanced Stars with Novel U II Lines

Authors: Shivani P. Shah, Rana Ezzeddine, Alexander P. Ji, Terese Hansen, Ian U. Roederer, Márcio Catelan, Zoe Hackshaw, Erika M. Holmbeck, Timothy C. Beers, Rebecca Surman

First Authors Institution: Department of Astronomy, University of Florida, Gainesville, Florida.

Status: Resubmitted to ApJ [open access on Arxiv]

As someone who has recently left their 20’s, I think a lot about how age shows up in my body. I can look up my birth date on the calendar, even count all the minutes of my existence, but I don’t need to go through all that work, something inside of me just feels… older. While the self realization of the unyielding passage of time on my mortal form may be daunting, I find solace in the fact that I’m no different than the stars –they also carry around their own clocks.

Today’s paper is about an interesting technique to determine how old a star is, by looking at how much Uranium is “ticking” in its atmosphere.

The smallest hand of the clock

The technique is based on radioactive dating, a tool used in a variety of fields but most famously in Carbon Dating. Living things on earth have atoms of carbon in their bodies, some of which are carbon 14 (C14). C14 is a radioactive isotope of carbon, meaning it has a slightly different mass than other carbon atoms, and it decays over time. Even though it decays, C14 is regularly replaced while an organism is alive, and so the ratio between regular carbon and C14 within living things stays mostly steady. Once the flow of carbon 14 stops (aka something dies), the ratio between carbon and C14 changes as the latter decays. By 1) measuring what the remaining ratio is, and 2) understanding what the ratio is normally, we can 3) calculate how much time has passed for the correct amount to decay.

Radioactive dating isn’t just for living things. C14 decays at such a rate that you can use it up to around 50,000 years ago, but the same technique works for any element with a radioactive isotope. Our best estimate for the age of our planet and solar system comes from radioactive dating using different elements that have radioactive isotopes, but which decay at slower rates.

Uranium (U) is an element that is perfect for this as its radioactive isotope takes billions of years to decay.

Uranium in the Periodic Table.

Fig 1 – An example U feature in a star’s spectra. The black points are the data. The red line is the best model for the spectra that includes U. They also fit a model that doesn’t include U, which is the blue dashed line. By measuring the difference in the two models, the authors estimated an abundance of U responsible for absorbing the missing light. (Adapted from figure 1 in the paper)

Tiny atoms in massive stars

It might seem incredibly difficult to detect atoms in a massive star that is light years away, but it’s actually one of astronomy’s oldest tricks (astrobites has a whole guide about it!). Each element and molecule has its own characteristic fingerprint, its spectral signature, which is the specific wavelengths of light that it absorbs (called spectral lines). These can be measured in a lab, and then by looking at the light coming from a star and seeing which wavelengths are being absorbed we can tell what’s in the star’s atmosphere.

This works great until elements and molecules have lines very close to one another, which is a major challenge with Uranium. As it turns out, the typical line used to measure Uranium abundance is blended with both an Iron (Fe) line and a Cyanide (CN) feature. (Figure 1) It’s still possible to get a measurement, but today’s authors wanted to use two new Uranium lines to measure abundances and see how well they agreed with the single line method. Even though these new lines are blended too, by having three measurements the authors can do a better job of describing the certainty of the measurement by using statistics to compare the abundances measured between the three lines.

Do you have the time?

The authors measured the abundances of Uranium for four stars, and compared the results from a fit using just a single line measurement in each of the stars, to one using all of the U lines. They found that they had a pretty good agreement, the abundances from both methods were within a reasonable range of one another.

When they went to use the abundances to measure an age , they found ages that were similar to those calculated with just the single measurement. You might notice that the age estimates have big error bars, some that stretch to an age older than the universe! There are clearly still some challenges with the method in general, in part because it’s hard to know how much Uranium was in the star to begin with. The authors chose these four stars for the study because they are examples of stars that should have had more Uranium. Regardless, the production rates of Uranium remain a big question mark.

The clocks keep spinning

It’s worth mentioning that the Uranium that makes these stellar clocks tick formed in merging neutron stars, the dramatic burst of atomic creation when two “dead” stars collide. A star’s clock, even its very existence is due in part to the stars that came before them. Makes me think about how even if my body feels old, that my time being alive has been traced through thousands of lifetimes similar to my own. 30(+) be damned, I’m going for a walk.

See the full article here .

Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

From Astrobites : “Journey to the center of terrestrial planets”

From Astrobites

2.10.23
Keighley Rockcliffe

Title: Detailed chemical compositions of planet-hosting stars – II. Exploration of the interiors of terrestrial-type exoplanets

First Author’s Institution: Institute for Particle Physics and Astrophysics, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland

Authors: H. S. Wang, S. P. Quanz, D. Yong, F. Liu, F. Seidler, L. Acuña, S. J. Mojzsis

Status: Published in MNRAS [closed access]

“In 1995, when I was born, there were only a few – hotly contested – exoplanets discovered. Now, there are close to 5000 planets found outside of our Solar System, and many more on the way. The growing population of known exoplanets mixed with the insatiable desire to know if humans are alone in the universe motivates astronomers to measure or estimate the properties of these planets and the environments they exist in.

Two important properties are a planet’s interior structure and its composition. These can influence many other properties of the planet, such as the presence of an ocean, magnetic field, or volcanoes with the ability to provide gas to the planet’s atmosphere. The only planetary interiors that we are able to directly explore are within our own Solar System. Even then, we have been limited to our nearest neighbors, Venus and Mars, with Venus being historically unkind to our technology (“The Venus Curse”). What, then, are we supposed to do when faced with so many exoplanets to characterize? How can we even begin to speculate at what their surfaces and interiors are like? The authors of today’s paper are taking steps to answer these questions.

These volatile delights have volatile ends

The authors base their method on a simple history of the Solar System. When the Earth was formed, it had roughly the same composition of elements as the Sun. Over time, the Earth has lost some of the elements most sensitive to vaporization (“volatiles” – e.g., hydrogen, nitrogen, etc); this is what the authors refer to as the “devolatilisation of Earth”, which is estimated by a factor reducing the Earth’s starting composition to its current composition.

Figure 1: Earth’s cores. Credit: Yuri Arcurs/Getty Images/iStockphoto.

If we only focus on terrestrial planets that are like Earth – “exo-Earths”, mostly rocky planets within the habitable zone of their Sun-like host star – then the authors suggest that we can assume a similar loss process happens on those planets. The authors hypothesize that if we know how much of a certain element existed when a planet was formed (found by observing and measuring the composition of the planet’s host star), we can use the Earth’s depletion factor for that element to estimate how much of the element currently exists on that planet. The authors limit their analysis to rock-forming volatile elements, such as magnesium, iron, and silicon.

With the aim of exploring the diversity of exo-Earth interiors today’s authors choose 13 known exoplanet systems with Sun-like host stars which have precise chemical abundance measurements, including measurements for rock-forming volatile elements. Instead of looking at the actual planets around these stars, which vary in size, orbital distance, and potentially also depletion factor, the authors modeled what the interior of an exo-Earth hosted by each star would look like. They plugged the measured amount of rock-forming volatile elements and their depletion factors into the software ExoInt, which output the composition and structure of an exo-Earth core + mantle that best matches the inputs. The output exo-Earth composition and structure was then fed into the software Perple_X to estimate the mineral phases present within the mantle and the temperature, pressure and density of the planet’s interior. Rinse and repeat for all 13 exoplanet systems!

The main result is that most of the modeled exo-Earths show interiors similar to that of Earth itself. In Figure 2, the shaded parallelograms show the range of molecule-to-molecule ratios that could fit each exo-Earth. Both diagrams show how similar the mantle compositions of all the exo-Earth models are to that of Earth and Mars.Two systems, Kepler-10 and Kepler-37, contain more oxygen than the other systems; oxygen is important in determining how much iron is split between an exo-Earth’s mantle and core. Kepler-10 and Kepler-37 likely have smaller cores because of their higher oxygen content.

Figure 2: Two ternary diagrams depict a mixture of three chemical components within the mantle: MgO (blue) increasing downwards along the left side of the diagram, SiO2 (red) increasing upwards along the right side, and FeO (green) increasing rightwards along the bottom side. The arrows indicate increasing abundance of the molecule within the mantle.The modeled exo-Earths are split between the two diagrams, which also have the compositions of Earth and Mars marked by blue and red ⨁ symbols, respectively. Not all of the planets are immediately visible because they are on top of one another, especially in the right panel. Image credit: Figure 3 in today’s paper.

Implications for exoplanet astronomy

We are currently limited to assuming the depletion/devolatilisation factors of the studied exo-Earths are the same as Earth’s, although the authors show that interior structures may change when these factors are varied. The interior structure models are also limited to only considering a mantle and a one-component core – unlike the two components, inner and outer, that make up Earth’s core. Nevertheless, this work shows that astronomers can use currently available planetary radii and mass measurements along with host star compositions to estimate the interiors of terrestrial planets in the habitable zones of Sun-like stars; combining this with atmospheric observations from telescopes like Hubble and JWST brings us one step closer to finding Earth2.0!”

See the full article here .

Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”

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Please help promote STEM in your local schools.

Stem Education Coalition

What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

From Astrobites : “Asymmetries are red – violets are blue – superflares are seen in white light – and H-alpha too!”

From Astrobites

2.14.23
Ivey Davis

Title: A Superflare on YZ Canis Minoris Observed by Seimei Telescope and TESS: Red Asymmetry of Hα Emission Associated with White-Light Emission

Authors: Keiichi Namizaki, Kosuke Namekata, Hiroyuki Maehara, Yuta Notsu, Satoshi Honda, Daisaku Nogami, Kazunari Shibata

First Author’s Institution: Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan

Status: Accepted to The Astrophysical Journal [open access]

Although humans have been monitoring the Sun’s surface activity for millenia, solar flares were only identified in the past ~150 years. These extremely energetic releases of electromagnetic emission occur when the Sun’s magnetic field is reconfigured. While our Sun’s flares can cause particle storms strong enough to knock out power for millions, we regularly see stars experiencing flares as much as 100,000 times larger than the most energetic solar flare ever observed. A large flare from a young cool star called YZ CMi was observed simultaneously in H-alpha and optical wavelengths using the Seimei telescope and the Transiting Exoplanet Survey Satellite (TESS) respectively. The authors of this paper tackle the analysis of the anomalously redshifted component of H-alpha observed in this flare.

KYOTO UNIVERSITY[京都大学](JP)Seimei telescope interior.

KYOTO UNIVERSITY[京都大学](JP) 3.8-m Seimei telescope.

Massachusetts Institute of Technology TESS – Transiting Exoplanet Survey Satellite replaced the Kepler Space Telescope in search for exoplanets. TESS is a NASA Astrophysics Explorer mission led and operated by The Massachusetts Institute of Technology, and managed by NASA’s Goddard Space Flight Center.

Origin of H-alpha Asymmetries on the Sun

Hydrogen emission lines like H-alpha are great for studying properties of chromospheres and coronae. The effects of pressure and rotational velocity can produce equal amounts of red and blue-shifted H-alpha emission so that the line is symmetrically broadened. However, net motion of the emitting hydrogen towards or away from us leads to excess blue or red-shifted H-alpha emission– this results in an asymmetry. On the Sun, we see a red asymmetry in H-alpha at the beginning of a flare. This is because huge swaths of hydrogen get accelerated towards where the solar magnetic field connects with the Sun’s surface– called the footpoints– in a process called chromospheric condensation. The opposite reaction is called chromospheric evaporation, and produces a blueshift. Chromospheric condensation deposits a bunch of high energy particles that heat the magnetic field’s footpoints, resulting in additional blackbody emissions that we call the white light (WL) component of a flare. As the flare decays following this initial part of the flare– known as the impulsive phase– there remain some red asymmetries as magnetic field loops continue to gradually funnel the hydrogen downwards.

Observations of YZ CMi

YZ CMi is an M-dwarf, meaning it’s a very cool and very small star. This makes increases in temperature, like those that cause the WL flare components, much easier to see than they are on the hotter and larger Sun. YZ CMi is also known to frequently flare. These properties make it a prime candidate to look for flares with multiple instruments for simultaneous, multi-wavelength studies of stellar flares. The authors observed YZ CMi with a spectrograph on the 3.8m, Seimei telescope at the Okoyama Observatory in Japan during a period that it also was present in a TESS field. During this time of overlap, the two instruments witnessed a flare with ~1034 erg of bolometric energy (100 times what we’ve ever observed from the Sun!), for which 1032 erg was contained in the H-alpha component (see figure 1).

Figure 1: The normalized WL flux from TESS in blue, H-alpha flux from Seimei in green, and the EW of H-alpha in red. The time axis indicates time since the start of the flare. Although the WL and H-alpha components seem to rise together at the flare onset, the WL component decays more rapidly than the H-alpha flux. (Figure 2 in the paper)

The authors analyzed the H-alpha flux and equivalent width (EW) of this event to be able to look more in depth at the different components of the flare. To do this, the authors fit a line profile to the H-alpha spectrum. Following this, they subtracted the model from the data to extract a red asymmetry component from the spectrum, as shown in figure 2. This data processing means that, all together, these observations reveal three components of the flare: the WL emission, the central H-alpha emission fit by the model, and the red, asymmetric H-alpha emission.

Figure 2: The observed H-alpha (blue circles) fit by an emission line model (red line). Subtracting the model from the data reveals the red asymmetry (green x’s) which has its own emission line model fit to it. The left figure is for the flare 0.67 hours after onset and the right figure is for the flare 2.1 hours after onset, which corresponds to the two times where the H-alpha EW and flux peaked. (Figure 4 in the paper)

Results

Between the three components, there are three main features that the authors address in this paper. Firstly, the H-alpha central linewidth– defined as twice the width of just the blue side of the line so as to exclude the red asymmetry– shows a similar time-evolution as the WL flux. Secondly, the redshift velocity of the H-alpha also shows a similar time-evolution as the WL flux. These two features together suggest that the H-alpha broadening and redshifting mechanism is linked to the WL emission mechanism. The authors suggest that the amount of broadening observed can only be explained by a unique pressure environment. One possibility is electrons heating material deep in the chromosphere, just as in chromospheric condensation on the Sun.

The third feature they address is the ratio of the red asymmetry’s EW to the central component’s EW. The ratio is small in the initial phase, and reaches 20% while the flare emission decays. This could imply that we’re seeing an evolution in the H-alpha emission origin: at the beginning of the flare, the relative strength of the red asymmetry may appear weaker if there’s also a blue asymmetry due to chromospheric evaporation, making the ratio appear smaller. Later in the flare we stop seeing the effects of evaporation, and strictly see the effects of the remaining magnetic field loops funneling hydrogen to YZ CMi’s surface, making the asymmetry seem stronger and, thus, the ratio larger. This is consistent with what we see on the Sun!

Simultaneous photometric and spectroscopic observations provide an opportunity to study transient events like flares incredibly robustly– there are still more features in the data presented in this work that the authors intend to address. These observations are a great step towards understanding how stellar flares compare to solar flares and exemplifies the importance of simultaneous, multi-wavelength observations.

See the full article here .

Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

From Astrobites : “Earth as an Exoplanet”

From Astrobites

2.13.23
Jack Lubin

Title: Which stars can see Earth as a transiting exoplanet?

Authors: Lisa Kaltenegger and Josh Pepper

Authors’ Institution: Cornell University and Lehigh University

Status: Published in MNRAS [open access]

An exoplanet is a planet that orbits another star that is not our Sun, and in the nearly 30 years of exoplanet science, we have discovered over 5000 of them. But, if you were an astronomer living on one of these exoplanets, then looking back at our Earth, you would say that it is an exoplanet from your perspective! This begs the question: have alien scientists discovered Earth? Is anyone looking back at us? While these questions border on science fiction, we can still begin to quantify scientifically-based answers.

The most successful technique we have used for discovering exoplanets is the transit method, in which we continuously observe a star and look for periodic dimming events from the exoplanet passing in between us and the host star, blocking some of the star light for a short time.

Planet transit. NASA/Ames.

This method has proven very powerful for discovering many exoplanets because we can observe thousands of stars simultaneously, as opposed to other discovery methods in which we must observe one star at a time. Through the transit method alone, we have discovered almost 4000 of the 5000+ known exoplanets, that’s nearly 80%! This begs the question, if we are so successful in leveraging the transit method, could alien exoplanet scientists be doing the same thing? And if so, could they have seen our Earth transit our Sun?

While we cannot know for certain if any aliens are actually looking for Earth as a transiting exoplanet, we can constrain how many might even have the opportunity to find us. While so successful, the transit method has a serious drawback. It requires the precise alignment of our Earth, the exoplanet, and the host star. If the alignment is even a little off, observers on Earth will not see the exoplanet as transiting (see Figure 1). Furthermore, the transiting window becomes smaller the further the exoplanet is from its host star. Exoplanets with long orbital periods have extremely small transiting windows and so they are very rare finds via the transit method. For example, of the nearly 4000 exoplanets we have detected by transits, only 203 of them (5%) have orbital periods longer than 88 days, the orbital period of planet Mercury which is the shortest orbital period in our solar system. It is incredibly rare to find a planet with an orbital period as long as Earth’s, 365 days, not because they don’t exist, but solely because the odds of that perfect alignment are so small. Therefore, if alien astronomers even want to have a chance to detect Earth as transiting, their planetary system must have this alignment with our own system.

Figure 1: The Ecliptic Plane is an imaginary plane in the sky on which all the planets of our Solar System orbit (red line representing Earth’s orbital path). From Earth, we see the Ecliptic plane as a line in the sky (the dashed purple line). Some stars, by chance, lie on the line and those stars are the ones that can view Earth as a transiting exoplanet. Throughout different times of our year, indicated by different points in our orbital path by the two Earth’s in the image, different stars on the Ecliptic would see Earth transit. Stars not on the Ecliptic will never see Earth as a transiting exoplanet.

So which nearby stars have this rare alignment? Today’s paper has set out to answer this exact question. The authors use the Gaia and the TESS catalogs, two space-based observatories designed to scan the entire sky.

European Space Agency [La Agencia Espacial Europea][Agence spatiale européenne][Europäische Weltraumorganization](EU) GAIA satellite.

Massachusetts Institute of Technology TESS – Transiting Exoplanet Survey Satellite replaced the Kepler Space Telescope in search for exoplanets. TESS is a NASA Astrophysics Explorer mission led and operated by The Massachusetts Institute of Technology, and managed by NASA’s Goddard Space Flight Center.

Using these data sets, they can identify all stars that sit within 0.262 degrees of the Ecliptic Plane, the imaginary plane through space that all of our Solar System’s planets sit on with the Sun, see Figure 1. If this imaginary plane were extended to infinity in all directions, any other stars that sit on (or sufficiently close to) the plane are aligned with us, and therefore they are the stars which could host alien planets who could see Earth as transiting. The team surveyed only Main Sequence stars, specifically excluding evolved stars and cutting out stars without well defined parameters.

The team identified 1,004 stars within 100 parsecs (326 light years) from Earth that have this unique alignment. The authors provide a full table with parameters about the stars, including mass, radius, temperature, and more. Interestingly, 2 of these stars currently have known exoplanets. Furthermore, the team breaks down the sample by spectral type: 77% of the stars are M Dwarf stars, 12% are K Dwarf stars, 6% are G Dwarf stars like our own Sun, 4% are F Dwarf stars, and 1% are A Dwarf stars, see Figure 2. This sample spans the whole temperature range of stars, but is heavily weighted towards smaller, cooler stars, consistent with the overall occurrence rate of stellar types throughout the galaxy.

This work is important because it provides a valuable target list for our own extra-terrestrial searching teams, like SETI and Breakthrough Listen.

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SETI Institute

About The SETI Institute

The SETI Institute is a 501 (c)(3) nonprofit scientific research institute headquartered in Mountain View, California. We are a key research contractor to The National Aeronautics and Space Agency and the National Science Foundation, and we collaborate with industry partners throughout Silicon Valley and beyond.
SETI/Allen Telescope Array situated at the Hat Creek Radio Observatory, 290 miles (470 km) northeast of San Francisco, California, Altitude 986 m (3,235 ft), the origins of the Institute’s search.

Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

March 23, 2015
By Hilary Lebow

Alumna Shelley Wright, now an assistant professor of physics at University of California-San Diego,discusses the dichroic filter of the NIROSETI instrument, developed at the University of Toronto-Dunlap Institute for Astronomy and Astrophysics (CA) and brought to UCSD and installed at the UC Santa Cruz Lick Observatory Nickel Telescope (Photo by Laurie Hatch).

The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch).

NIROSETI team from left to right Rem Stone University of California Observatory Lick Observatory; Dan Werthimer, University of California-Berkeley; Jérôme Maire, University of Toronto; Shelley Wright, UCSD; Patrick Dorval, U Toronto; Richard Treffers, Starman Systems. (Image by Laurie Hatch).

Laser SETI

LaserSETI observatory installation at Haleakala Observatory in Maui, Hawai’i, aimed East.

There is also an installation at Robert Ferguson Observatory, Sonoma, CA aimed West for full coverage [no image available].

Also in the hunt, but not a part of the SETI Institute
SETI@home, a BOINC [Berkeley Open Infrastructure for Network Computing] project originated in the Space Science Lab at UC Berkeley.

BOINC is a leader in the field(s) of Distributed Computing, Grid Computing and Citizen Cyberscience. BOINC is more properly the Berkeley Open Infrastructure for Network Computing, developed at UC Berkeley.
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Breakthrough Listen Project

UC Observatories Lick Automated Planet Finder fully robotic 2.4-meter optical telescope at Lick Observatory, situated on the summit of Mount Hamilton, east of San Jose, California, USA.

Green Bank Radio Telescope, West Virginia, USA, now the center piece of the Green Bank Observatory(US), being cut loose by the National Science Foundation(US), supported by Breakthrough Listen Project, West Virginia University, and operated by the nonprofit Associated Universities, Inc.

CSIRO-Commonwealth Scientific and Industrial Research Organisation (AU) Parkes Observatory [ Murriyang, the traditional Indigenous name], located 20 kilometres north of the town of Parkes, New South Wales, Australia, 414.80m above sea level.

SKA SARAO Meerkat [SKA-Mid] Telescope (SA), 90 km outside the small Northern Cape town of Carnarvon, SA.

Newly added

University of Arizona Veritas Four Čerenkov telescopes A novel gamma ray telescope under construction at the CfA Fred Lawrence Whipple Observatory (US), Mount Hopkins, Arizona (US), altitude 2,606 m 8,550 ft. A large project known as the Čerenkov Telescope Array, composed of hundreds of similar telescopes to be situated at Roque de los Muchachos Observatory [Instituto de Astrofísica de Canarias ](ES) in the Canary Islands and Chile at European Southern Observatory Cerro Paranal(EU) site. The telescope on Mount Hopkins will be fitted with a prototype high-speed camera, assembled at the University of Wisconsin–Madison (US) and capable of taking pictures at a billion frames per second. Credit: Vladimir Vassiliev. _____________________________________________________________________________________

These initiatives can now focus on these 1,004 stars as high quality targets which conceivably might already know of our planet Earth via transit detection, and therefore might already be trying to contact us. We can also use the list to target these stars for further exoplanet searches. If we focus on these stars, we may discover more planets in these systems, opening the door to finding potential neighbors who might be able to see us back.

Lastly, the authors note that this list may be a bit deceptive – the list is compiled from a single snapshot in time. It makes use of the current positions of the stars, but the stars are not actually stationary, they are all constantly moving. Some stars not on this list will move into alignment with our system and other stars on the list will move out of alignment on the timescales of hundreds to thousands to millions of years. As all of these star systems, including our own, move through the galaxy, who knows if, or when, we may finally meet some neighbors.

Figure 2 : All 1,004 stars aligned with Earth plotted by their Ecliptic Latitude vs their Distance from Earth, with a heat map for their temperature, which maps to stellar type. Ecliptic Latitude is a proxy for direction in space. Since this plot shows a nice even spread along the y-axis direction, that means the 1,004 stars are nicely and evenly spread out in all directions. Meanwhile, most of these stars are at the far end of the search limit of 100 parsecs (326 lightyears). While the sample spans all temperatures, it is heavily weighted towards cooler, M Dwarf stars. Figure 2 in the paper.

See the full article here .

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What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.