Strong constraints on the gravitational law from Gaia DR3 wide binaries

We test Milgromian dynamics (MOND) using wide binary stars (WBs) with separations of 2−30 kAU. Locally, the WB orbital velocity in MOND should exceed the Newtonian prediction by ≈20% at asymptotically large separations given the Galactic external field effect (EFE). We investigate this with a detailed statistical analysis of \emph{Gaia} DR3 data on 8611 WBs within 250 pc of the Sun. Orbits are integrated in a rigorously calculated gravitational field that directly includes the EFE. We also allow line of sight contamination and undetected close binary companions to the stars in each WB. We interpolate between the Newtonian and Milgromian predictions using the parameter αgrav, with 0 indicating Newtonian gravity and 1 indicating MOND. Directly comparing the best Newtonian and Milgromian models reveals that Newtonian dynamics is preferred at 19σ confidence. Using a complementary Markov Chain Monte Carlo analysis, we find that αgrav=−0.021+0.065−0.045, which is fully consistent with Newtonian gravity but excludes MOND at 16σ confidence. This is in line with the similar result of Pittordis and Sutherland using a somewhat different sample selection and less thoroughly explored population model. We show that although our best-fitting model does not fully reproduce the observations, an overwhelmingly strong preference for Newtonian gravity remains in a considerable range of variations to our analysis. Adapting the MOND interpolating function to explain this result would cause tension with rotation curve constraints. We discuss the broader implications of our results in light of other works, concluding that MOND must be substantially modified on small scales to account for local WBs.
http://arxiv.org/abs/2311.03436

Robust Evidence for the Breakdown of Standard Gravity at Low Acceleration from Statistically Pure Binaries Free of Hidden Companions

It is found that Gaia DR3 binary stars selected with stringent requirements on astrometric measurements and radial velocities naturally satisfy Newtonian dynamics without hidden close companions when projected separation s>2 kau, showing that pure binaries can be selected. It is then found that pure binaries selected with the same criteria show a systematic deviation from the Newtonian expectation when s<2 kau. When both proper motions and parallaxes are required to have precision better than 0.003 and radial velocities better than 0.2, I obtain 1558 statistically pure binaries within a 'clean' G-band absolute magnitude range. From this sample, I obtain an observed to Newtonian predicted kinematic acceleration ratio of γg=gobs/gpred=1.43+0.23−0.19 for acceleration <10−10 m s−2, in excellent agreement with a recent finding 1.43±0.06 for a much larger general sample with the amount of hidden close companions self-calibrated. I also investigate the radial profile of stacked sky-projected relative velocities without a deprojection to the 3D space. The observed profile matches the Newtonian predicted profile for s<2 kau without any free parameters but shows a clear deviation at a larger separation with a significance of 4.6σ. The projected velocity boost factor for s>8 kau is measured to be γvp=1.18±0.06 matching γg−−√. Finally, for a small sample of 23 binaries with exceptionally precise radial velocities (precision <0.0043) the directly measured relative velocities in the 3D space also show a boost at larger separations. These results robustly confirm the recently reported gravitational anomaly at low acceleration for a general sample.
http://arxiv.org/abs/2309.10404

Discovery of the elusive carbonic acid (HOCOOH) in space

After a quarter century since the detection of the last interstellar carboxylic acid, acetic acid (CH3COOH), we report the discovery of a new one, the cis-trans form of carbonic acid (HOCOOH), toward the Galactic Center molecular cloud G+0.693-0.027. HOCOOH stands as the first interstellar molecule containing three oxygen atoms and also the third carboxylic acid detected so far in the interstellar medium. Albeit the limited available laboratory measurements (up to 65 GHz), we have also identified several pairs of unblended lines directly in the astronomical data (between 75-120 GHz), which allowed us to slightly improve the set of spectroscopic constants. We derive a column density for cis-trans HOCOOH of N = (6.4 ± 0.4) × 1012 cm−2, which yields an abundance with respect to molecular H2 of 4.7 × 10−11. Meanwhile, the extremely low dipole moment (about fifteen times lower) of the lower-energy conformer, cis-cis HOCOOH, precludes its detection. We obtain an upper limit to its abundance with respect to H2 of ≤ 1.2 ×10−9, which suggests that cis-cis HOCOOH might be fairly abundant in interstellar space, although it is nearly undetectable by radio astronomical observations. We derive a cis-cis/cis-trans ratio ≤ 25, consistent with the smaller energy difference between both conformers compared with the relative stability of trans- and cis-formic acid (HCOOH). Finally, we compare the abundance of these acids in different astronomical environments, further suggesting a relationship between the chemical content found in the interstellar medium and the chemical composition of the minor bodies of the Solar System, which could be inherited during the star formation process.
http://arxiv.org/abs/2307.08644

Breakdown of the Newton-Einstein Standard Gravity at Low Acceleration in Internal Dynamics of Wide Binary Stars

A gravitational anomaly is found at weak gravitational acceleration gN<10−9 m s−2 from analyses of the dynamics of wide binary stars selected from the Gaia DR3 database that have accurate distances, proper motions, and reliably inferred stellar masses. Implicit high-order multiplicities are required and the multiplicity fraction is calibrated so that binary internal motions agree statistically with Newtonian dynamics at a high enough acceleration of 10−8 m s−2. The observed sky-projected motions and separation are deprojected to the three-dimensional relative velocity v and separation r through a Monte Carlo method, and a statistical relation between the Newtonian acceleration gN≡GM/r2 (where M is the total mass of the binary system) and a kinematic acceleration g≡v2/r is compared with the corresponding relation predicted by Newtonian dynamics. The empirical acceleration relation at less than 10^−9 m s−2 systematically deviates from the Newtonian expectation. A gravitational anomaly parameter δobs−newt between the observed acceleration at gN and the Newtonian prediction is measured to be: δobs−newt=0.034±0.007 and 0.109±0.013 at gN≈10−8.91 and 10−10.15 m s−2, from the main sample of 26,615 wide binaries within 200 pc. These two deviations in the same direction represent a 10σ significance. The deviation represents a direct evidence for the breakdown of standard gravity at weak acceleration. At gN=10−10.15 m s−2, the observed to Newton predicted acceleration ratio is gobs/gpred=102√δobs−newt=1.43±0.06. This systematic deviation agrees with the boost factor that the AQUAL theory predicts for kinematic accelerations in circular orbits under the Galactic external field.
http://arxiv.org/abs/2305.04613

G 68-34: A Double-Lined M-Dwarf Eclipsing Binary in a Hierarchical Triple System

Using high-resolution spectra from the Tillinghast Reflector Echelle Spectrograph (TRES) and photometry from sector 56 of the Transiting Exoplanet Survey Satellite (TESS), we report that the nearby M dwarf G 68-34 is a double-lined eclipsing binary. The pair is spin-orbit synchronized with a period of 0.655 days. The light curve shows significant spot modulation with a larger photometric amplitude than that of the grazing eclipses. We perform a joint fit to the spectroscopic and photometric data, obtaining masses of 0.3280±0.0034M⊙ and 0.3207±0.0036M⊙ and radii of 0.345±0.014R⊙ and 0.342±0.014R⊙ after marginalizing over unknowns in the starspot distribution. This system adds to the small but growing population of fully convective M dwarfs with precisely measured masses and radii that can be used to test models of stellar structure. The pair also has a white dwarf primary at 9" separation, with the system known to be older than 5 Gyr from the white-dwarf cooling age. The binarity of G 68-34 confirms our hypothesis from Pass et al. (2022): in that work, we noted that G 68-34 was both rapidly rotating and old, highly unusual given our understanding of the spindown of M dwarfs, and that a close binary companion may be responsible.
http://arxiv.org/abs/2304.02466

Direct Discovery of the Inner Exoplanet in the HD206893 System

Long term precise radial velocity (RV) monitoring of the nearby star HD206893, as well as anomalies in the system proper motion, have suggested the presence of an additional, inner companion in the system. Here we describe the results of a multi-epoch search for the companion responsible for this RV drift and proper motion anomaly using the VLTI/GRAVITY instrument. Utilizing information from ongoing precision RV measurements with the HARPS spectrograph, as well as Gaia host star astrometry, we report a high significance detection of the companion HD206893c over three epochs, with clear evidence for Keplerian orbital motion. Our astrometry with ∼50-100 μarcsec precision afforded by GRAVITY allows us to derive a dynamical mass of 12.7+1.2−1.0 MJup and an orbital separation of 3.53+0.08−0.06 au for HD206893c. Our fits to the orbits of both companions in the system utilize both Gaia astrometry and RVs to also provide a precise dynamical estimate of the previously uncertain mass of the B component, and therefore derive an age of 155±15 Myr. We find that theoretical atmospheric/evolutionary models incorporating deuterium burning for HD206893c, parameterized by cloudy atmospheres provide a good simultaneous fit to the luminosity of both HD206893B and c. In addition to utilizing long-term RV information, this effort is an early example of a direct imaging discovery of a bona fide exoplanet that was guided in part with Gaia astrometry. Utilizing Gaia astrometry is expected to be one of the primary techniques going forward to identify and characterize additional directly imaged planets. Lastly, this discovery is another example of the power of optical interferometry to directly detect and characterize extrasolar planets where they form at ice-line orbital separations of 2-4\,au.
http://arxiv.org/abs/2208.04867

Direct imaging discovery of a super-Jovian around the young Sun-like star AF Leporis

Expanding the sample of directly imaged companions to nearby, young stars that are amenable to detailed astrometric and spectroscopic studies is critical for the continued development and validation of theories of their evolution and atmospheric processes. The recent release of the {\it Gaia} astrometric catalogue allows us to efficiently search for these elusive companions by targeting those stars that exhibit the astrometric reflex motion induced by an orbiting companion. The nearby (27 pc), young (24 Myr) star AF Leporis (AF Lep) was targeted because of its astrometric acceleration, consistent with a wide-orbit planetary companion detectable with high-contrast imaging. We used the SPHERE instrument on the VLT to search for faint substellar companions in the immediate vicinity of AF Lep. We used observations of a nearby star interleaved with those of AF Lep to efficiently subtract the residual point spread function. This provided sensitivity to faint planetary-mass companions within 1 arcsec (∼30 au) of the star. We detected the companion AF Lep b at a separation of 339 mas (9 au), within the inner edge of its unresolved debris disk. The measured K-band contrast and the age of the star yield a model-dependent mass of 4 and 6 MJup, consistent with the mass derived from an orbital fit of 4.3+2.9−1.2 MJup. The near-infrared SED of the planet is consistent with an object at the L--T spectral type transition, but under-luminous with respect to field-gravity objects. AF Lep b joins a growing number of substellar companions imaged around stars in the young β Pic moving group. With a mass of between 3 and 7 MJup, it occupies a gap in this isochronal sequence between the hotter, more massive companions like PZ~Tel~B and β~Pic~b, and the cooler 51~Eri~b, which is sufficiently cool for methane to form within its photosphere.
http://arxiv.org/abs/2302.06332

A red giant orbiting a black hole

We report spectroscopic and photometric follow-up of a dormant black hole (BH) candidate from Gaia DR3. We show that the system, which we call Gaia BH2, contains a ∼1M⊙ red giant and a dark companion with mass M2=8.9±0.3M⊙ that is very likely a BH. The orbital period, Porb=1277 days, is much longer than that of any previously studied BH binary. Our radial velocity (RV) follow-up over a 6-month period spans most of the orbit's dynamic range in RV and is in excellent agreement with predictions of the Gaia solution. UV imaging and high-resolution optical spectra rule out all plausible luminous companions that could explain the orbit. The star is a bright (G=12.3), slightly metal-poor ([Fe/H]=−0.22) low-luminosity giant (Teff=4600K; R=7.9R⊙; log[g/(cms−2)]=2.6). The binary's orbit is moderately eccentric (e=0.52). The giant is strongly enhanced in α−elements, with [α/Fe]=+0.26, but the system's Galactocentric orbit is typical of the thin disk. We obtained X-ray and radio nondetections of the source near periastron, which support BH accretion models in which the net accretion rate at the horizon is much lower than the Bondi-Hoyle-Lyttleton rate. At a distance of 1.16 kpc, Gaia BH2 is the second-nearest known BH, after Gaia BH1. Its orbit -- like that of Gaia BH1 -- seems too wide to have formed through common envelope evolution. Gaia BH1 and BH2 have orbital periods at opposite edges of the Gaia DR3 sensitivity curve, perhaps hinting at a bimodal intrinsic period distribution for wide BH binaries. Dormant BH binaries like Gaia BH1 and Gaia BH2 likely significantly outnumber their close, X-ray bright cousins, but their formation pathways remain uncertain.
http://arxiv.org/abs/2302.07880

An Ice Age JWST inventory of dense molecular cloud ices

Icy grain mantles are the main reservoir of the volatile elements that link chemical processes in dark, interstellar clouds with the formation of planets and composition of their atmospheres. The initial ice composition is set in the cold, dense parts of molecular clouds, prior to the onset of star formation. With the exquisite sensitivity of JWST, this critical stage of ice evolution is now accessible for detailed study. Here we show the first results of the Early Release Science program "Ice Age" that reveal the rich composition of these dense cloud ices. Weak ices, including, 13CO2, OCN−, 13CO, OCS, and COMs functional groups are now detected along two pre-stellar lines of sight. The 12CO2 ice profile indicates modest growth of the icy grains. Column densities of the major and minor ice species indicate that ices contribute between 2 and 19% of the bulk budgets of the key C, O, N, and S elements. Our results suggest that the formation of simple and complex molecules could begin early in a water-ice rich environment.
http://arxiv.org/abs/2301.09140