Astronomy and Planetary Science Thread

Flyaway

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General purpose astronomy thread.


The search for radio emission from the exoplanetary systems 55 Cancri, υ Andromedae, and τ Boötis using LOFAR beam-formed observations

Observing planetary auroral radio emission is the most promising method to detect exoplanetary magnetic fields, the knowledge of which will provide valuable insights into the planet's interior structure, atmospheric escape, and habitability. We present LOFAR-LBA circularly polarized beamformed observations of the exoplanetary systems 55 Cancri, υ Andromedae, and τ Boötis. We tentatively detect circularly polarized bursty emission from the τ Boötis system in the range 14-21 MHz with a flux density of ∼890 mJy and with a significance of ∼3σ. For this detection, no signal is seen in the OFF-beams, and we do not find any potential causes which might cause false positives. We also tentatively detect slowly variable circularly polarized emission from τ Boötis in the range 21-30 MHz with a flux density of ∼400 mJy and with a statistical significance of >8σ. The slow emission is structured in the time-frequency plane and shows an excess in the ON-beam with respect to the two simultaneous OFF-beams. Close examination casts some doubts on the reality of the slowly varying signal. We discuss in detail all the arguments for and against an actual detection. Furthermore, a ∼2σ marginal signal is found from the υ Andromedae system and no signal is detected from the 55 Cancri system. Assuming the detected signals are real, we discuss their potential origin. Their source probably is the τ Bootis planetary system, and a possible explanation is radio emission from the exoplanet τ Bootis b via the cyclotron maser mechanism. Assuming a planetary origin, we derived limits for the planetary polar surface magnetic field strength, finding values compatible with theoretical predictions. Further low-frequency observations are required to confirm this possible first detection of an exoplanetary radio signal. [Abridged]

 
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Flyaway

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Exploring Primordial Black Holes from the Multiverse with Optical Telescopes

Primordial black holes (PBHs) are a viable candidate for dark matter if the PBH masses are in the currently unconstrained "sublunar" mass range. We revisit the possibility that PBHs were produced by nucleation of false vacuum bubbles during inflation. We show that this scenario can produce a population of PBHs that simultaneously accounts for all dark matter, explains the candidate event in Subaru Hyper Suprime-Cam (HSC) data, and contains both heavy black holes as observed by LIGO and very heavy seeds of supermassive black holes. We demonstrate with numerical studies that future observations of HSC, as well as other optical surveys, such as LSST, will be able to provide a definitive test for this generic PBH formation mechanism if it is the dominant source of dark matter.


Why was the HSC indispensable in this research? The HSC has a unique capability to image the entire Andromeda galaxy every few minutes. If a black hole passes through the line of sight to one of the stars, the black hole’s gravity bends the light rays and makes the star appear brighter than before for a short period of time. The duration of the star’s brightening tells the astronomers the mass of the black hole. With HSC observations, one can simultaneously observe one hundred million stars, casting a wide net for primordial black holes that may be crossing one of the lines of sight.

The first HSC observations have already reported a very intriguing candidate event consistent with a PBH from the “multiverse,” with a black hole mass comparable to the mass of the Moon. Encouraged by this first sign, and guided by the new theoretical understanding, the team is conducting a new round of observations to extend the search and to provide a definitive test of whether PBHs from the multiverse scenario can account for all dark matter.

 

Flyaway

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Looks like they accidentally proved one aspect of the MOND theory.

Testing the Strong Equivalence Principle: Detection of the External Field Effect in Rotationally Supported Galaxies

Abstract
The strong equivalence principle (SEP) distinguishes general relativity (GR) from other viable theories of gravity. The SEP demands that the internal dynamics of a self-gravitating system under freefall in an external gravitational field should not depend on the external field strength. We test the SEP by investigating the external field effect (EFE) in Milgromian dynamics (MOND), proposed as an alternative to dark matter in interpreting galactic kinematics. We report a detection of this EFE using galaxies from the Spitzer Photometry and Accurate Rotation Curves (SPARC) sample together with estimates of the large-scale external gravitational field from an all-sky galaxy catalog. Our detection is threefold: (1) the EFE is individually detected at 8σ to 11σ in "golden" galaxies subjected to exceptionally strong external fields, while it is not detected in exceptionally isolated galaxies, (2) the EFE is statistically detected at more than 4σ from a blind test of 153 SPARC rotating galaxies, giving a mean value of the external field consistent with an independent estimate from the galaxies' environments, and (3) we detect a systematic downward trend in the weak gravity part of the radial acceleration relation at the right acceleration predicted by the EFE of the MOND modified gravity. Tidal effects from neighboring galaxies in the Λ cold dark matter (CDM) context are not strong enough to explain these phenomena. They are not predicted by existing ΛCDM models of galaxy formation and evolution, adding a new small-scale challenge to the ΛCDM paradigm. Our results point to a breakdown of the SEP, supporting modified gravity theories beyond GR.


 

Nik

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FWIW, I vaguely remember a suggestion on PhysOrg that, given Jupiter is a powerful source of auroral etc RF, hypothetical planets X, XI , even XII might be sought thus ...

Notion derided. But, clearly, a seed was planted. 'Nearby' exoplanets were duly scanned for RF...
 

Flyaway

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591 High-velocity Stars in the Galactic Halo Selected from LAMOST DR7 and Gaia DR2

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In this paper, we report 591 high-velocity star candidates (HiVelSCs) selected from over 10 million spectra of Data Release 7 (DR7) of the Large Sky Area Multi-object Fiber Spectroscopic Telescope and the second Gaia data release, with three-dimensional velocities in the Galactic rest frame larger than 445 km s−1. We show that at least 43 HiVelSCs are unbound to the Galaxy with escape probabilities larger than 50%, and this number decreases to eight if the possible parallax zero-point error is corrected. Most of these HiVelSCs are metal-poor and slightly α-enhanced inner halo stars. Only 14% of them have [Fe/H] > −1, which may be the metal-rich "in situ" stars in the halo formed in the initial collapse of the Milky Way or metal-rich stars formed in the disk or bulge but kinematically heated. The low ratio of 14% implies that the bulk of the stellar halo was formed from the accretion and tidal disruption of satellite galaxies. In addition, HiVelSCs on retrograde orbits have slightly lower metallicities on average compared with those on prograde orbits; meanwhile, metal-poor HiVelSCs with [Fe/H] < −1 have an even faster mean retrograde velocity compared with metal-rich HiVelSCs. To investigate the origins of HiVelSCs, we perform orbit integrations and divide them into four types, i.e., hypervelocity stars, hyper-runaway stars, runaway stars and fast halo stars. A catalog for these 591 HiVelSCs, including radial velocities, atmospheric parameters, Gaia astrometric parameters, spatial positions, and velocities, etc., is available in the China-VO PaperData Repository at doi:10.12149/101038.


Source: https://www.universetoday.com/14946...s-many-on-their-way-out-of-the-milky-way/amp/
 

Flyaway

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Cosmic Distances Calibrated to 1% Precision with Gaia EDR3 Parallaxes and Hubble Space Telescope Photometry of 75 Milky Way Cepheids Confirm Tension with LambdaCDM

We present an expanded sample of 75 Milky Way Cepheids with Hubble Space Telescope (HST) photometry and Gaia EDR3 parallaxes which we use to recalibrate the extragalactic distance ladder and refine the determination of the Hubble constant. All HST observations were obtained with the same instrument (WFC3) and filters (F555W, F814W, F160W) used for imaging of extragalactic Cepheids in Type Ia supernova (SN Ia) hosts. The HST observations used the WFC3 spatial scanning mode to mitigate saturation and reduce pixel-to-pixel calibration errors, reaching a mean photometric error of 5 millimags per observation. We use new Gaia EDR3 parallaxes, vastly improved since DR2, and the Period-Luminosity (PL) relation of these Cepheids to simultaneously calibrate the extragalactic distance ladder and to refine the determination of the Gaia EDR3 parallax offset. The resulting geometric calibration of Cepheid luminosities has 1.0% precision, better than any alternative geometric anchor. Applied to the calibration of SNe~Ia, it results in a measurement of the Hubble constant of 73.0 +/- 1.4 km/sec/Mpc, in good agreement with conclusions based on earlier Gaia data releases. We also find the slope of the Cepheid PL relation in the Milky Way, and the metallicity dependence of its zeropoint, to be in good agreement with the mean values derived from other galaxies. In combination with the best complementary sources of Cepheid calibration, we reach 1.8% precision and find H_0=73.2 +/- 1.3 km/sec/Mpc, a 4.2 sigma difference with the prediction from Planck CMB observations under LambdaCDM. We expect to reach ~1.3% precision in the near term from an expanded sample of ~40 SNe Ia in Cepheid hosts.


Source: https://www.universetoday.com/14948...t-doesnt-resolve-the-crisis-in-cosmology/amp/[/B]
 

Raberto

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I see Harvard professor Avi Loeb has been out and about promoting his book about Oumuamua. He appears to be convinced it was ‘alien’ junk.

New Scientist 'Big Thinkers' online lecture by Professor Loeb on Feb 11th if anyone else is interested? I'm attending =)

 

Flyaway

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Flyaway

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The future large obliquity of Jupiter

Aims: We aim to determine whether Jupiter's obliquity is bound to remain exceptionally small in the Solar System, or if it could grow in the future and reach values comparable to those of the other giant planets.
Methods: The spin axis of Jupiter is subject to the gravitational torques from its regular satellites and from the Sun. These torques evolve over time due to the long-term variations of its orbit and to the migration of its satellites. With numerical simulations, we explore the future evolution of Jupiter's spin axis for different values of its moment of inertia and for different migration rates of its satellites. Analytical formulas show the location and properties of all relevant resonances.
Results: Because of the migration of the Galilean satellites, Jupiter's obliquity is currently increasing, as it adiabatically follows the drift of a secular spin-orbit resonance with the nodal precession mode of Uranus. Using the current estimates of the migration rate of the satellites, the obliquity of Jupiter can reach values ranging from 6° to 37° after 5 Gyrs from now, according to the precise value of its polar moment of inertia. A faster migration for the satellites would produce a larger increase in obliquity, as long as the drift remains adiabatic.
Conclusions: Despite its peculiarly small current value, the obliquity of Jupiter is no different from other obliquities in the Solar System: It is equally sensitive to secular spin-orbit resonances and it will probably reach comparable values in the future.

 

Flyaway

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rooster

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I see Harvard professor Avi Loeb has been out and about promoting his book about Oumuamua. He appears to be convinced it was ‘alien’ junk.

I have read the book but I've seen him on TV. He doesn't think its junk but a lightsail type of probe.

I think its interesting that this is the first object from outside our solar system and it was like no one was interested in it especially given its fairly unique 1x10 proportion.
 

Grey Havoc

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Flyaway

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Flyaway

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GEO600 reaches 6 dB of squeezing

Gravitational waves cause tiny length changes in the kilometer-size detectors of the international network (GEO600, KAGRA, LIGO, Virgo). The instruments use laser light to detect these effects and are so sensitive that they are fundamentally limited by quantum mechanics. This limit manifests as an ever-present background noise which can never be fully removed and which overlaps with gravitational-wave signals. But one can change the noise properties – using a process called squeezing – such that it does not disturb the measurements as much. Now, GEO600 researchers have achieved the strongest squeezing ever seen in a gravitational-wave detector. They lowered the quantum mechanical noise by up to a factor of two. This is a big step to third-generation detectors such as the Einstein Telescope and Cosmic Explorer. The GEO600 team is confident to reach even better squeezing in the future.

 

Flyaway

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Evidence for chromium hydride in the atmosphere of hot Jupiter WASP-31b

Context. The characterisation of exoplanet atmospheres has shown a wide diversity of compositions. Hot Jupiters have the appropriate temperatures to host metallic compounds, which should be detectable through transmission spectroscopy.
Aims. We aim to detect exotic species in the transmission spectra of hot Jupiters, specifically WASP-31b, by testing a variety of chemical species to explain the spectrum.
Methods. We conduct a re-analysis of publicly available transmission data of WASP-31b using the Bayesian retrieval framework TAUREX II. We retrieve various combinations of the opacities of 25 atomic and molecular species to determine the minimum set that is needed to fit the observed spectrum.
Results. We report evidence for the spectroscopic signatures of chromium hydride (CrH), H2O, and K in WASP-31b. Compared to a flat model without any signatures, a CrH-only model is preferred with a statistical significance of ~3.9σ. A model consisting of both CrH and H2O is found with ~2.6 and ~3σ confidence over a CrH-only model and an H2O-only model, respectively. Furthermore, weak evidence for the addition of K is found at ~2.2σ over the H2O+CrH model, although the fidelity of the data point associated with this signature was questioned in earlier studies. Finally, the inclusion of collision-induced absorption and a Rayleigh scattering slope (indicating the presence of aerosols) is found with ~3.5σ confidence over the flat model. This analysis presents the first evidence for signatures of CrH in a hot Jupiter atmosphere. At a retrieved temperature of 1481−355+264 K, the atmosphere of WASP-31b is hot enough to host gaseous Cr-bearing species, and the retrieved abundances agree well with predictions from thermal equilibrium chemistry. Furthermore, the retrieved abundance of CrH agrees with the abundance in an L-type brown dwarf atmosphere. However, additional retrievals using VLT FORS2 data lead to a non-detection of CrH. Future observations with James Webb Space Telescope have the potential to confirm the detection and/or discover other CrH features.

 

Flyaway

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Size and structures of disks around very low mass stars in the Taurus star-forming region★

Context. The discovery of giant planets orbiting very low mass stars (VLMS) and the recent observed substructures in disks around VLMS is challenging planet formation models. Specifically, radial drift of dust particles is a catastrophic barrier in these disks, which prevents the formation of planetesimals and therefore planets.
Aims. We aim to estimate if structures, such as cavities, rings, and gaps, are common in disks around VLMS and to test models of structure formation in these disks. We also aim to compare the radial extent of the gas and dust emission in disks around VLMS, which can give us insight about radial drift.
Methods. We studied six disks around VLMS in the Taurus star-forming region using ALMA Band 7 (~340 GHz) at a resolution of ~0.1″. The targets were selected because of their high disk dust content in their stellar mass regime.
Results. Our observations resolve the disk dust continuum in all disks. In addition, we detect the 12CO (J = 3−2) emission line in all targets and 13CO (J = 3−2) in five of the six sources. The angular resolution allows the detection of dust substructures in three out of the six disks, which we studied by using UV-modeling. Central cavities are observed in the disks around stars MHO 6 (M 5.0) and CIDA 1 (M 4.5), while we have a tentative detection of a multi-ringed disk around J0433. We estimate that a planet mass of ~0.1 MJup or ~0.4 MSaturn is required for a single planet to create the first gap in J0433. For the cavities of MHO 6 and CIDA 1, a Saturn-mass planet (~0.3 MJup) is required. The other three disks with no observed structures are the most compact and faintest in our sample, with the radius enclosing 90% of the continuum emission varying between ~13 and 21 au. The emission of 12CO and 13CO is more extended than the dust continuum emission in all disks of our sample. When using the 12CO emission to determine the gas disk extension Rgas, the ratio of Rgas∕Rdust in our sample varies from 2.3 to 6.0. One of the disks in our sample, CIDA 7, has the largest Rgas∕Rdust ratio observed so far, which is consistent with models of radial drift being very efficient around VLMS in the absence of substructures.
Conclusions. Given our limited angular resolution, substructures were only directly detected in the most extended disks, which represent 50% of our sample, and there are hints of unresolved structured emission in one of the bright smooth sources. Our observations do not exclude giant planet formation on the substructures observed. A comparison of the size and luminosity of VLMS disks with their counterparts around higher mass stars shows that they follow a similar relation.

 

Flyaway

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Six transiting planets and a chain of Laplace resonances in TOI-178

Determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. Resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present. In this context, TOI-178 has been the subject of particular attention since the first TESS observations hinted at a 2:3:3 resonant chain. Here we report the results of observations from CHEOPS, ESPRESSO, NGTS, and SPECULOOS with the aim of deciphering the peculiar orbital architecture of the system. We show that TOI-178 harbours at least six planets in the super-Earth to mini-Neptune regimes, with radii ranging from 1.152(-0.070/+0.073) to 2.87(-0.13/+0.14) Earth radii and periods of 1.91, 3.24, 6.56, 9.96, 15.23, and 20.71 days. All planets but the innermost one form a 2:4:6:9:12 chain of Laplace resonances, and the planetary densities show important variations from planet to planet, jumping from 1.02(+0.28/-0.23) to 0.177(+0.055/-0.061) times the Earth's density between planets c and d. Using Bayesian interior structure retrieval models, we show that the amount of gas in the planets does not vary in a monotonous way, contrary to what one would expect from simple formation and evolution models and unlike other known systems in a chain of Laplace resonances. The brightness of TOI-178 allows for a precise characterisation of its orbital architecture as well as of the physical nature of the six presently known transiting planets it harbours. The peculiar orbital configuration and the diversity in average density among the planets in the system will enable the study of interior planetary structures and atmospheric evolution, providing important clues on the formation of super-Earths and mini-Neptunes.



Artist animation of the system:

View: https://youtu.be/-WevvRG9ysY
 
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Flyaway

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Refining the Transit-timing and Photometric Analysis of TRAPPIST-1: Masses, Radii, Densities, Dynamics, and Ephemerides

Abstract
We have collected transit times for the TRAPPIST-1 system with the Spitzer Space Telescope over four years. We add to these ground-based, HST, and K2 transit-time measurements, and revisit an N-body dynamical analysis of the seven-planet system using our complete set of times from which we refine the mass ratios of the planets to the star. We next carry out a photodynamical analysis of the Spitzer light curves to derive the density of the host star and the planet densities. We find that all seven planets' densities may be described with a single rocky mass–radius relation which is depleted in iron relative to Earth, with Fe 21 wt% versus 32 wt% for Earth, and otherwise Earth-like in composition. Alternatively, the planets may have an Earth-like composition but enhanced in light elements, such as a surface water layer or a core-free structure with oxidized iron in the mantle. We measure planet masses to a precision of 3%–5%, equivalent to a radial-velocity (RV) precision of 2.5 cm s−1, or two orders of magnitude more precise than current RV capabilities. We find the eccentricities of the planets are very small, the orbits are extremely coplanar, and the system is stable on 10 Myr timescales. We find evidence of infrequent timing outliers, which we cannot explain with an eighth planet; we instead account for the outliers using a robust likelihood function. We forecast JWST timing observations and speculate on possible implications of the planet densities for the formation, migration, and evolution of the planet system.


 

robunos

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New analysis finds the super-giant star is dimming and has entered helium-burning phase


 

Flyaway

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Related paper to the above.


Standing on the Shoulders of Giants: New Mass and Distance Estimates for Betelgeuse through Combined Evolutionary, Asteroseismic, and Hydrodynamic Simulations with MESA

Abstract
We conduct a rigorous examination of the nearby red supergiant Betelgeuse by drawing on the synthesis of new observational data and three different modeling techniques. Our observational results include the release of new, processed photometric measurements collected with the space-based Solar Mass Ejection Imager instrument prior to Betelgeuse's recent, unprecedented dimming event. We detect the first radial overtone in the photometric data and report a period of 185 ± 13.5 days. Our theoretical predictions include self-consistent results from multi-timescale evolutionary, oscillatory, and hydrodynamic simulations conducted with the Modules for Experiments in Stellar Astrophysics software suite. Significant outcomes of our modeling efforts include a precise prediction for the star's radius: ${764}_{-62}^{+116}\,{R}_{\odot }$. In concert with additional constraints, this allows us to derive a new, independent distance estimate of ${168}_{-15}^{+27}$ pc and a parallax of $\pi ={5.95}_{-0.85}^{+0.58}$ mas, in good agreement with Hipparcos but less so with recent radio measurements. Seismic results from both perturbed hydrostatic and evolving hydrodynamic simulations constrain the period and driving mechanisms of Betelgeuse's dominant periodicities in new ways. Our analyses converge to the conclusion that Betelgeuse's ≈400 day period is the result of pulsation in the fundamental mode, driven by the κ-mechanism. Grid-based hydrodynamic modeling reveals that the behavior of the oscillating envelope is mass-dependent, and likewise suggests that the nonlinear pulsation excitation time could serve as a mass constraint. Our results place α Orionis definitively in the early core helium-burning phase of the red supergiant branch. We report a present-day mass of 16.5–19 M ⊙—slightly lower than typical literature values.

 

Flyaway

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Now it’s the turn of Alpha Centauri A to host a possible exoplanet following in the footsteps of Proxima Centauri, in this case it’s a warm Neptune in its habitable zone. As ever more data is needed as instrumental artefact cannot be ruled at this time.

Imaging low-mass planets within the habitable zone of α Centauri

Giant exoplanets on wide orbits have been directly imaged around young stars. If the thermal background in the mid-infrared can be mitigated, then exoplanets with lower masses can also be imaged. Here we present a ground-based mid-infrared observing approach that enables imaging low-mass temperate exoplanets around nearby stars, and in particular within the closest stellar system, α Centauri. Based on 75–80% of the best quality images from 100 h of cumulative observations, we demonstrate sensitivity to warm sub-Neptune-sized planets throughout much of the habitable zone of α Centauri A. This is an order of magnitude more sensitive than state-of-the-art exoplanet imaging mass detection limits. We also discuss a possible exoplanet or exozodiacal disk detection around α Centauri A. However, an instrumental artifact of unknown origin cannot be ruled out. These results demonstrate the feasibility of imaging rocky habitable-zone exoplanets with current and upcoming telescopes.


 

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I would like Alpha Centauri A to have a planet orbiting it just like Proxima Centauri, though it is a pity it is not an Earth like planet. The astronomers will need to be careful with the data that they have, and go over it with a fine tooth comb before releasing it in full.
 

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