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