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<jats:title>Abstract</jats:title> <jats:p>Recent observations of globular clusters (GCs) provide evidence that the stellar initial mass function (IMF) may not be universal, suggesting specifically that the IMF grows increasingly top-heavy with decreasing metallicity and increasing gas density. Noncanonical IMFs can greatly affect the evolution of GCs, mainly because the high end determines how many black holes (BHs) form. Here we compute a new set of GC models, varying the IMF within observational uncertainties. We find that GCs with top-heavy IMFs lose most of their mass within a few gigayears through stellar winds and tidal stripping. Heating of the cluster through BH mass segregation greatly enhances this process. We show that, as they approach complete dissolution, GCs with top-heavy IMFs can evolve into “dark clusters” consisting of mostly BHs by mass. In addition to producing more BHs, GCs with top-heavy IMFs also produce many more binary BH (BBH) mergers. Even though these clusters are short-lived, mergers of ejected BBHs continue at a rate comparable to, or greater than, what is found for long-lived GCs with canonical IMFs. Therefore, these clusters, though they are no longer visible today, could still contribute significantly to the local BBH merger rate detectable by LIGO/Virgo, especially for sources with higher component masses well into the BH mass gap. We also report that one of our GC models with a top-heavy IMF produces dozens of intermediate-mass black holes (IMBHs) with masses <jats:inline-formula> <jats:tex-math> <?CDATA $M\gt 100\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabd79cieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, including one with <jats:inline-formula> <jats:tex-math> <?CDATA $M\gt 500\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabd79cieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Ultimately, additional gravitational wave observations will provide strong constraints on the stellar IMF in old GCs and the formation of IMBHs at high redshift.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use compiled high-precision pulsar timing measurements to directly measure the Galactic acceleration of binary pulsars relative to the solar system barycenter. Given the vertical accelerations, we use the Poisson equation to derive the Oort limit, i.e., the total volume mass density in the Galactic mid-plane. Our best-fitting model gives an Oort limit of <jats:inline-formula> <jats:tex-math> <?CDATA ${0.08}_{-0.02}^{0.05}{M}_{\odot }\,{\mathrm{pc}}^{-3}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.08</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.02</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>0.05</mml:mn> </mml:mrow> </mml:msubsup> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>pc</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabd635ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, which is close to estimates from recent Jeans analyses. Given the accounting of the baryon budget from McKee et al., we obtain a local dark matter density of <jats:inline-formula> <jats:tex-math> <?CDATA $-{0.004}_{-0.02}^{0.05}\,{M}_{\odot }\,{\mathrm{pc}}^{-3}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.004</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.02</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>0.05</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>pc</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabd635ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, which is slightly below other modern estimates but consistent within the current uncertainties of our method. The error bars are currently about five times larger than kinematical estimates, but should improve in the future for this novel dynamical method. We also constrain the oblateness of the potential, finding it consistent with that expected from the disk and inconsistent with a potential dominated by a spherical halo, as is appropriate for our sample that is within a ∼kpc of the Sun. We find that current measurements of binary pulsar accelerations lead to large uncertainties in the slope of the rotation curve. We give a fitting function for the vertical acceleration <jats:italic>a</jats:italic> <jats:sub> <jats:italic>z</jats:italic> </jats:sub>: <jats:italic>a</jats:italic> <jats:sub> <jats:italic>z</jats:italic> </jats:sub> = − <jats:italic>α</jats:italic> <jats:sub>1</jats:sub> <jats:italic>z</jats:italic>; <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{log}}_{10}({\alpha }_{1}/{\mathrm{Gyr}}^{-2})={3.69}_{-0.12}^{0.19}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msup> <mml:mrow> <mml:mi>Gyr</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>3.69</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.12</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>0.19</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabd635ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>. By analyzing interacting simulations of the Milky Way, we find that large asymmetric variations in <jats:italic>da</jats:italic> <jats:sub> <jats:italic>z</jats:italic> </jats:sub>/<jats:italic>dz</jats:italic> as a function of vertical height may be a signature of sub-structure. We end by discussing the power of combining constraints from pulsar timing and high-precision radial velocity measurements toward lines-of-sight near pulsars, to test theories of gravity and constrain dark matter sub-structure.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Cosmological gamma-ray bursts (GRBs) are known to arise from distinct progenitor channels: short GRBs mostly from neutron star mergers and long GRBs from a rare type of core-collapse supernova (CCSN) called collapsars. Highly magnetized neutron stars called magnetars also generate energetic, short-duration gamma-ray transients called magnetar giant flares (MGFs). Three have been observed from the Milky Way and its satellite galaxies, and they have long been suspected to constitute a third class of extragalactic GRBs. We report the unambiguous identification of a distinct population of four local (&lt;5 Mpc) short GRBs, adding GRB 070222 to previously discussed events. While identified solely based on alignment with nearby star-forming galaxies, their rise time and isotropic energy release are independently inconsistent with the larger short GRB population at &gt;99.9% confidence. These properties, the host galaxies, and nondetection in gravitational waves all point to an extragalactic MGF origin. Despite the small sample, the inferred volumetric rates for events above 4 × 10<jats:sup>44</jats:sup> erg of <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{\mathrm{MGF}}={3.8}_{-3.1}^{+4.0}\times {10}^{5}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabd8c8ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> Gpc<jats:sup>−3</jats:sup> yr<jats:sup>−1</jats:sup> make MGFs the dominant gamma-ray transient detected from extragalactic sources. As previously suggested, these rates imply that some magnetars produce multiple MGFs, providing a source of repeating GRBs. The rates and host galaxies favor common CCSN as key progenitors of magnetars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>With the localization of fast radio bursts (FRBs) to galaxies similar to the Milky Way and the detection of a bright radio burst from SGR J1935+2154 with energy comparable to extragalactic radio bursts, a magnetar origin for FRBs is evident. By studying the environments of FRBs, evidence for magnetar formation mechanisms not observed in the Milky Way may become apparent. In this Letter, we use a sample of FRB host galaxies and a complete sample of core-collapse supernova (CCSN) hosts to determine whether FRB progenitors are consistent with a population of magnetars born in CCSNe. We also compare the FRB hosts to the hosts of hydrogen-poor superluminous supernovae (SLSNe-I) and long gamma-ray bursts (LGRBs) to determine whether the population of FRB hosts is compatible with a population of transients that may be connected to millisecond magnetars. After using a novel approach to scale the stellar masses and star formation rates of each host galaxy to be statistically representative of <jats:italic>z</jats:italic> = 0 galaxies, we find that the CCSN hosts and FRBs are consistent with arising from the same distribution. Furthermore, the FRB host distribution is inconsistent with the distribution of SLSNe-I and LGRB hosts. With the current sample of FRB host galaxies, our analysis shows that FRBs are consistent with a population of magnetars born through the collapse of giant, highly magnetic stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Previous analyses of various standard candles observed by the Gaia satellite have reported statistically significant systematics in the parallaxes that have improved from ∼250 <jats:italic>μ</jats:italic>as in the first data release (DR1) to 50–80 <jats:italic>μ</jats:italic>as in the second data release (DR2). Here we examine the parallaxes newly reported in the Gaia early third data release (EDR3) using the same sample of benchmark eclipsing binaries (EBs) we used to assess the DR1 and DR2 parallaxes. We find a mean offset of −37 ± 20 <jats:italic>μ</jats:italic>as (Gaia − EB), which decreases to −15 ± 18 <jats:italic>μ</jats:italic>as after applying the corrections recommended by the Gaia Mission team; global systematics in the Gaia parallaxes have clearly improved and are no longer statistically significant for the EB sample, which spans 5 ≲ <jats:italic>G</jats:italic> ≲ 12 in brightness and 0.03–3 kpc in distance. We also find that the Renormalized Unit Weight Error (RUWE) goodness-of-fit statistic reported in Gaia DR3 is highly sensitive to unresolved companions (tertiaries in the case of our EB sample) as well as to photocenter motion of the binaries themselves. RUWE is nearly perfectly correlated (<jats:italic>r</jats:italic> <jats:sup>2</jats:sup> = 0.82) with photocenter motions down to ≲0.1 mas, and surprisingly this correlation exists entirely within the nominal “good” RUWE range of 1.0–1.4. This suggests that RUWE values even slightly greater than 1.0 may signify unresolved binaries in Gaia, and that the RUWE value can serve as a quantitative predictor of the photocenter motion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Rotating outflows from protostellar disks might trace extended magnetohydrodynamic (MHD) disk winds (DWs), providing a solution to the angular momentum problem in disk accretion for star formation. In the jet system HH 212, a rotating outflow was detected in SO around an episodic jet detected in SiO. Here we spatially resolve this SO outflow into three components: a collimated jet aligned with the SiO jet, the wide-angle disk outflow, and an evacuated cavity in between created by a large jet-driven bow shock. Although it was theoretically predicted, this is the first time that such a jet–DW interaction has been directly observed and resolved, and it is crucial for the proper interpretation and modeling of non-resolved DW candidates. The resolved kinematics and brightness distribution both support the wide-angle outflow to be an extended MHD DW dominating the local angular momentum extraction out to 40 au, but with an inner launching radius truncated to ≳4 au. Inside 4 au, where the DW may not exist, the magnetorotational instability might be transporting angular momentum outward. The jet–DW interaction in HH 212, potentially present in other similar systems, opens an entirely new avenue to probe the large-scale magnetic field in protostellar disks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Characterizing habitable exoplanets and/or their moons is of paramount importance. Here we show the results of our magnetic field topological modeling, which demonstrate that terrestrial exoplanet–exomoon coupled magnetospheres work together to protect the early atmospheres of both the exoplanet and the exomoon. When exomoon magnetospheres are within the exoplanet's magnetospheric cavity, the exomoon magnetosphere acts like a protective magnetic bubble providing an additional magnetopause confronting the stellar winds when the moon is on the dayside. In addition, magnetic reconnection would create a critical pathway for the atmosphere exchange between the early exoplanet and exomoon. When the exomoon's magnetosphere is outside of the exoplanet's magnetosphere it then becomes the first line of defense against strong stellar winds, reducing the exoplanet's atmospheric loss to space. A brief discussion is given on how this type of exomoon would modify radio emissions from magnetized exoplanets.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use the latest measurements of the Milky Way satellite population from the Dark Energy Survey and Pan-STARRS1 to infer the most stringent astrophysical bound to date on velocity-dependent interactions between dark matter particles and protons. We model the momentum-transfer cross section as a power law of the relative particle velocity <jats:italic>v</jats:italic> with a free normalizing amplitude, <jats:italic>σ</jats:italic> <jats:sub>MT</jats:sub> = <jats:italic>σ</jats:italic> <jats:sub>0</jats:sub> <jats:italic>v</jats:italic> <jats:sup> <jats:italic>n</jats:italic> </jats:sup>, to broadly capture the interactions arising within the nonrelativistic effective theory of dark matter–proton scattering. The scattering leads to a momentum and heat transfer between the baryon and dark matter fluids in the early universe, ultimately erasing structure on small physical scales and reducing the abundance of low-mass halos that host dwarf galaxies today. From the consistency of observations with the cold collisionless dark matter paradigm, using a new method that relies on the most robust predictions of the linear perturbation theory, we infer an upper limit on <jats:italic>σ</jats:italic> <jats:sub>0</jats:sub> of 1.4 × 10<jats:sup>−23</jats:sup>, 2.1 × 10<jats:sup>−19</jats:sup>, and 1.0 × 10<jats:sup>−12</jats:sup> cm<jats:sup>2</jats:sup>, for interaction models with <jats:italic>n</jats:italic> = 2, 4, and 6, respectively, for a dark matter particle mass of 10 MeV. These results improve observational limits on dark matter–proton scattering by orders of magnitude and thus provide an important guide for viable sub-GeV dark matter candidates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Titan, Saturn’s largest moon, has its atmosphere filled with a thick organic photochemical haze. These suspended solid nanoparticles are one of the most complex organic materials in the Solar System. In situ measurements from the successful Cassini space mission gave first clues on the aerosol's chemical composition: pyrolysis coupled to mass spectrometry revealed a nitrogen-rich core, whereas infrared measurements highlighted poly-aromatic-hydrocarbon (PAH) signatures. The combination of these observations supports a general model of nitrogenated-polycyclic aromatic hydrocarbon (N-PAH). To constrain the generic picture and understand the formation of such macromolecules in Titan’s atmosphere, we simulated the haze synthesis in the laboratory. Small (3–10 rings) N-PAH molecules composing the material were extracted, focusing on the prime aromatization and growth processes. By high-resolution atomic force microscopy (AFM), we imaged key chemical structures with atomic resolution. We resolved N-rich elongated molecules involving five-membered aromatic rings, consistent with a repetitive <jats:italic>cata</jats:italic>-condensation pattern via addition of C<jats:sub>3</jats:sub>N units. These atomic-scale observations bridge the gap between gas phase atmospheric reactants and the macroscopic structure of Titan’s haze.</jats:p>