Metal Pollution of the Solar White Dwarf by Solar System Small Bodies

White dwarfs (WDs) often show metal lines in their spectra, indicating accretion of asteroidal material. Our Sun is to become a WD in several gigayears. Here, we examine how the solar WD accretes from the three major small body populations: the main belt asteroids (MBAs), Jovian Trojan asteroids (JTAs), and trans-Neptunian objects (TNOs). Owing to the solar mass loss during the giant branch, 40% of the JTAs are lost but the vast majority of MBAs and TNOs survive. During the WD phase, objects from all three populations are sporadically scattered onto the WD, implying ongoing accretion. For young cooling ages ≲100 Myr, accretion of MBAs predominates; our predicted accretion rate ∼106 g s−1 falls short of observations by two orders of magnitude. On gigayear timescales, thanks to the consumption of the TNOs that kicks in ≳100 Myr, the rate oscillates around 106–107 g s−1 until several gigayears and drops to ∼105 g s−1 at 10 Gyr. Our solar WD accretion rate from 1 Gyr and beyond agrees well with those of the extrasolar WDs. We show that for the solar WD, the accretion source region evolves in an inside-out pattern. Moreover, in a realistic small body population with individual sizes covering a wide range as WD pollutants, the accretion is dictated by the largest objects. As a consequence, the accretion rate is lower by an order of magnitude than that from a population of bodies of a uniform size and the same total mass and shows greater scatter.

Exploring the early Universe with Gaia and Theia

It has recently been pointed out that Gaia is capable of detecting a stochastic gravitational wave background in the sensitivity band between the frequency of pulsar timing arrays and LISA. We argue that Gaia and Theia have great potential for early universe cosmology, since such a frequency range is ideal for probing phase transitions in asymmetric dark matter, SIMP and the cosmological QCD transition. Furthermore, there is the potential for detecting primordial black holes in the solar mass range produced during such an early universe transition and distinguish them from those expected from the QCD epoch. Finally, we discuss the potential for Gaia and Theia to probe topological defects and the ability of Gaia to potentially shed light on the recent NANOGrav results.

Observational Limits on the Early-time Dust Mass in SN 1987A

In recent years, dust masses of a few tenths of a solar mass have been found in the expanding ejecta of a number of core-collapse supernovae. How dust forms in such quantities remains poorly understood; theories of dust formation predict lower total masses and much faster formation rates than observations imply. One suggestion to reconcile observations and theory was made by Dwek et al., who proposed that the dust forms very rapidly, and because of its optical depth, is not initially observationally detectable, only being gradually revealed as the ejecta expand. Observational dust masses at early times would then only be lower limits. Using a large grid of radiative transfer models covering dust masses from 10−4 to 1 M ⊙ to calculate both the spectral energy distribution and the emission line profiles from clumpy dust shells, we show that this cannot be the case. Some clump distributions allow dust masses of ∼0.01 M ⊙ to be concealed in clumps and still predict an SED consistent with the observations. However, these geometries predict emission line profiles that are inconsistent with the observations. Similarly, clump geometries that reproduce the observed emission line profiles with dust masses >0.01 M ⊙ do not reproduce the SED. However, models with ∼10−3 M ⊙ of amorphous carbon can reproduce both the SED and the emission line profiles. We conclude that no large masses of dust can be hidden from view in the ejecta of SN 1987A at early epochs, and that the majority of dust must thus have formed at epochs >1000 days.

The ALFALFA Almost Dark Galaxy AGC 229101: A 2 Billion Solar Mass H i Cloud with a Very Low Surface Brightness Optical Counterpart

We present results from deep H i and optical imaging of AGC 229101, an unusual H i source detected at v helio =7116 km s−1 in the Arecibo Legacy Fast ALFA (ALFALFA) blind H i survey. Initially classified as a candidate “dark” source because it lacks a clear optical counterpart in Sloan Digital Sky Survey (SDSS) or Digitized Sky Survey 2 (DSS2) imaging, AGC 229101 has 109.31±0.05 M ⊙ of H i, but an H i line width of only 43 ± 9 km s−1. Low-resolution Westerbork Synthesis Radio Telescope (WSRT) imaging and higher-resolution Very Large Array (VLA) B-array imaging show that the source is significantly elongated, stretching over a projected length of ∼80 kpc. The H i imaging resolves the source into two parts of roughly equal mass. WIYN partially populated One Degree Imager (pODI) optical imaging reveals a faint, blue optical counterpart coincident with the northern portion of the H i. The peak surface brightness of the optical source is only μ g ∼ 26.6 mag arcsec−2, well below the typical cutoff that defines the isophotal edge of a galaxy, and its estimated stellar mass is only 107.32±0.33 M ⊙, yielding an overall neutral gas-to-stellar mass ratio of M/M * = 98 − 52 + 111 . We demonstrate the extreme nature of this object by comparing its properties with those of other H i-rich sources in ALFALFA and the literature. We also explore potential scenarios that might explain the existence of AGC 229101, including a tidal encounter with neighboring objects and a merger of two dark H i clouds.

Generalized Transport Equation of The Autocovariance Function of the Density Field and Mass Invariant in Star-forming Clouds

In this Letter, we study the evolution of the autocovariance function of density-field fluctuations in star-forming clouds and thus of the correlation length l c (ρ) of these fluctuations, which can be identified as the average size of the most correlated structures within the cloud. Generalizing the transport equation derived by Chandrasekhar for static, homogeneous turbulence, we show that the mass contained within these structures is an invariant, i.e., that the average mass contained in the most correlated structures remains constant during the evolution of the cloud, whatever dominates the global dynamics (gravity or turbulence). We show that the growing impact of gravity on the turbulent flow yields an increase of the variance of the density fluctuations and thus a drastic decrease of the correlation length. Theoretical relations are successfully compared to numerical simulations. This picture brings a robust support to star formation paradigms where the mass concentration in turbulent star-forming clouds evolves from initially large, weakly correlated filamentary structures to smaller, denser, more correlated ones, and eventually to small, tightly correlated, prestellar cores. We stress that the present results rely on a pure statistical approach of density fluctuations and do not involve any specific condition for the formation of prestellar cores. Interestingly enough, we show that, under average conditions typical of Milky-Way molecular clouds, this invariant average mass is about a solar mass, providing an appealing explanation for the apparent universality of the IMF in such environments.

Conditions for the appearance of stars with a rotation opposite to the orbital rotation of their planets

Обнаружение планетной системы K2-290 A с двумя копланарными планетами, которые обращаются в направлении, обратном вращению центральной звезды, ставит задачу поиска адекватного сценария возникновения таких систем. В данной статье представленные нами ранее сценарии образования планетных систем пересматриваются для оценки возможности формирования в их рамках планет с орбитальным вращением, обратным вращению их центральных звезд. Оценки показывают, что аккреция холодного газа гигантских молекулярных облаков старыми звездами солнечной массы, движущимися в этих облаках с низкой относительной скоростью менее ∼ 1 км/с - это наиболее вероятный сценарий возникновения таких планетных систем. С другой стороны, обратное вращение только одной из нескольких планет системы может быть результатом взаимодействия близких массивных планет на неустойчивых орбитах. Detection of planetary system K2-290 A with two coplanar planets, which rotate in the direction opposite to the rotation of the central star, poses the problem of finding an adequate scenario for the emergence of such systems. In this article, the scenarios for the formation of planetary systems are revised to assess the possibility of forming within their framework planets with orbital rotation opposite to the rotation of their central stars. Estimates show that the accretion of cold gas from giant molecular clouds (GMOs) by old solar-mass stars moving in GMOs with a relative speed less than ∼ 1 km/s - this is the most probable scenario for the emergence of such planetary systems. On the other hand, the opposite rotation of only one of the several planets of the system can be the result of interaction of nearby massive planets in unstable orbits.

SN 2018bsz: significant dust formation in a nearby superluminous supernova

We investigate the thermal emission and extinction from dust associated with the nearby superluminous supernova (SLSN) 2018bsz. Our dataset has daily cadence and simultaneous optical and near-infrared coverage up to ~ 100 days, together with late time (+1.7 yr) MIR observations. At 230 days after light curve peak the SN is not detected in the optical, but shows a surprisingly strong near-infrared excess, with r - J > 3 mag and r - Ks > 5 mag. The time evolution of the infrared light curve enables us to investigate if the mid-infrared emission is from newly formed dust inside the SN ejecta, from a pre-existing circumstellar envelope, or interstellar material heated by the radiation from the SN. We find the latter two scenarios can be ruled out, and a scenario where new dust is forming in the SN ejecta at epochs > 200 days can self-consistently reproduce the evolution of the SN flux. We can fit the spectral energy distribution well at +230d with 5x10-4 solar mass of carbon dust, increasing over the following several hundred days to 10-2 solar mass by +535d. SN 2018bsz is the first SLSN showing evidence for dust formation within the SN ejecta, and appears to form ten times more dust than normal core-collapse SNe at similar epochs. Together with their preference for low mass, low metallicity host galaxies, we suggest that SLSNe may be a significant contributor to dust formation in the early Universe.

The Young Suns Exoplanet Survey: imaging infant planets around young, solar analogs

<p>Within the Young Suns Exoplanet Survey (YSES) we are observing a homogeneous sample of 70 solar-mass members of the approximately 16 Myr-old Lower Centaurus-Crux subgroup of the Scorpius-Centaurus association to search for sub-stellar companions.</p> <p>High-contrast imaging observations with VLT/SPHERE/IRDIS revealed (i) a shadowed transition disk around Wray 15-788 that shows significant signs of ongoing planet formation and (ii) one of the lowest-mass companions imaged to date: YSES-2 b has a mass of 6.5 Jupiter masses and is orbiting its solar-mass primary at a separation of 110 au. Most intriguing, though, was (iii) the discovery of the first directly imaged multi-planet system around a Sun-like star. The detection of two gas-giant companions of 14±3 and 6±1 Jupiter masses that are orbiting YSES-1 (TYC 8998-760-1) at separations of 160 au and 320 au, respectively, provides important implications for the outer architecture of planetary systems and the underlying formation mechanisms.</p> <p>In addition to the SPHERE observations, we identified further companions to our ‘Young Suns’ outside the instrument’s field of view in the third early data release of the <em>Gaia</em> mission. Based on parallaxes and proper motions provided in this catalogue, we detected eight additional sub-stellar companions at separations larger than 500 au amongst our sample.</p> <p>By combining <em>Gaia</em> astrometry with the high-contrast imaging capabilities of SPHERE, our survey will provide a complete census of wide-orbit sub-stellar companions for a statistically highly significant sample of young, solar analogues. From the current results we derived a preliminary probability of 14.3±3.1% for our solar-type stars to host wide-orbit, sub-stellar companions. As follow-up observations of 45 YSES targets are still pending, this ratio can be interpreted as a lower limit, which is tentatively indicating a higher companion yield than previous surveys.</p>

EFT compatible PBHs: effective spawning of the seeds for primordial black holes during inflation

Most of the inflationary scenarios that try to explain the origin of Primordial Black Holes (PBHs) from the enhancements of the power spectrum to values of order one, at the relevant scales, run into clashes with the Effective Field Theory (EFT) criteria or fail to enhance the power spectrum to such large amplitudes. In this paper, we unravel a mechanism for enhancing the power spectrum during inflation that does not use the flattening of the potential or reduction of the sound speed of scalar perturbations. The mechanism is based on this observation in the formalism of Extended EFT of inflation (EEFToI) with the sixth order polynomial dispersion relation for scalar perturbations that if the quartic coefficient in the dispersion relation is negative and smaller than a certain threshold, the amplitude of the power spectrum is enhanced substantially. The instability mechanism must arrange to kick in at the scales of interest related to the mass of the PBHs one would like to produce, which can be ten(s) of solar mass PBHs, suitable for LIGO events, or 10−17− 10−13 solar mass PBHs, which can comprise the whole dark matter energy density. We argue that the strong coupling is avoided for the range of parameters that the mechanisms enhance the power spectrum to the required amount.