Formic Acid, a Building Block of Life, Detected in Distant Star-Forming Region

Scientists investigate the prevalence of formic acid within interstellar space, a molecule crucial to the formation of glycine, the simplest amino acid. Arijit Manna, Sabyasachi Pal, Sekhar Sinha, and Sushanta Kumar Mondal, from Midnapore City College and Sidho-Kanho-Birsha University, report the first detection of the rotational emission lines of a specific conformer of formic acid towards the hot molecular core G358.93, 0.03 MM1, utilising high-resolution ALMA observations. This finding significantly advances our understanding of prebiotic chemistry in star-forming regions, demonstrating the presence of oxygen-bearing molecules and providing insights into the pathways by which complex organic molecules arise in these environments. Their detailed analysis, incorporating gas-grain chemical modelling with UCLCHEM, confirms a likely formation route for formic acid via the reaction of HCO and OH on grain surfaces, bolstering theories about the origins of life’s building blocks.

This groundbreaking work employed high-resolution observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 7 to identify the specific molecular signature of t-HCOOH within this active star-forming region.

The detection is particularly noteworthy because formic acid shares structural similarities with glycine, an amino acid crucial for biological processes, suggesting a potential pathway for the formation of more complex biomolecules in interstellar environments. This research establishes a crucial link between simple organic molecules present in space and the potential for prebiotic chemistry within star-forming regions.
The observed emission lines allowed researchers to determine the column density and excitation temperature of t-HCOOH, quantifying the amount of this molecule present and its energetic state. Specifically, the column density of the detected t-HCOOH is (8.13 ±0.72) x 10 15cm -2 , a value that provides a benchmark for comparison with theoretical models of interstellar chemical processes.

The excitation temperature was determined to be 120 ±15 K. Furthermore, the study reveals a fractional abundance of t-HCOOH relative to hydrogen (H 2 ) of (2.62 ±0.29) x 10 -9 , offering insights into the molecule’s prevalence within the dense molecular cloud. Researchers also calculated the relative abundances of different molecular species, providing a more complete picture of the chemical composition of the hot molecular core. To validate these findings, a detailed chemical model was developed, incorporating the observed abundances and physical conditions of G358.93-0.03 MM1, to explore the formation pathways of t-HCOOH and its role in the synthesis of more complex organic molecules.

ALMA Band 7 Observations and Spectral Analysis of Formic Acid in G358.93-0.03 MM1 and MM3

Observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 7 underpinned this study’s first detection of the rotational emission lines of the trans-conformer of formic acid (t-HCOOH). High-resolution spectral images were obtained, with synthesized beam sizes of 0.42′′×0.37′′, 0.43′′×0.37′′, 0.41′′×0.37′′, and 0.41′′×0.36′′ across frequency ranges of 290.51, 292.39GHz, 292.49, 294.37GHz, 302.62, 304.49GHz, and 304.14, 306.01GHz respectively.

These observations targeted the hot molecular core G358.93-0.03 MM1, a region within the massive star formation area G358.93-0.03. Following data acquisition, line spectra were extracted from both G358.93-0.03 MM1 and G358.93-0.03 MM3 using a 0.52′′ diameter circular region, carefully encompassing the line-emitting areas of both hot cores.

The CASSIS software package was then employed to identify molecules and analyse the extracted spectra, utilising a local thermodynamic equilibrium (LTE) model and referencing spectroscopic databases from the Jet Propulsion Laboratory and the Cologne Database for Molecular Spectroscopy. To determine excitation temperatures and column densities of identified molecules, CASSIS fitted LTE-modelled spectra to the observed spectra.

This process involved calculating the brightness temperature (Tb) using the formula Tb = TCe−τ + (1 −e−τ)(Jν(Tex) −Jν(CMB)), where parameters represent continuum temperature, optical depth, radiation temperature, and cosmic microwave background temperature. The Markov chain Monte Carlo (MCMC) technique was implemented within CASSIS, initiating with a random point in a four-dimensional parameter space and iteratively refining it based on χ2 value comparisons to achieve optimal spectral fits. This rigorous approach enabled the quantification of the t-HCOOH column density at (8.13 ±0.72) x 10 15cm -2 , a key value for comparison with theoretical models and a crucial step towards understanding prebiotic chemistry in star-forming regions.

Detection and abundance of trans-formic acid in hot molecular core G358.93-0.03 MM1

Scientists have, for the first time, detected the rotational emission lines of the trans-conformer of formic acid (t-HCOOH) towards the hot molecular core G358.93-0.03 MM1. This groundbreaking observation provides crucial insights into the chemical origins of potential building blocks of life within star-forming regions.

The column density of the detected t-HCOOH is quantified as (8.13 ±0.72) x 10 15cm -2 , establishing a precise measurement of the molecule’s abundance in this specific interstellar environment. High-resolution observations from the Atacama Large Millimeter/submillimeter Array (ALMA) were utilised to identify these emissions.

Analysis of the spectral data reveals that G358.93, 0.03 MM1 is chemically richer than G358.93, 0.03 MM3, with detections of several molecular species including methanol, formaldehyde, and carbon monosulfide, indicative of outflow activity. The rotational diagram derived from the observed transitions yields a total column density of (8.10 ±1.12) × 10 15cm -2 for t-HCOOH, alongside a rotational temperature of 116.11 ±7.62 K.

Radiative transfer modelling of the dust continuum emission indicates that the dust temperatures of G358.93, 0.03 MM1 and MM3 are elevated compared to other cores within the region, consistent with their classification as hot molecular cores. The densities of G358.93, 0.03 MM1 and G358.93, 0.03 MM3 are 1.08×10 8 and 5.28×10 7cm -3 , respectively, further supporting their status as prime locations for complex organic molecule formation.

Trans-formic acid detection constrains prebiotic chemical pathways

Scientists have, for the first time, detected the rotational emission lines of trans-formic acid (t-HCOOH) in the hot molecular core G358.93-0.03 MM1. This detection provides new insights into the chemical origins of potential building blocks of life within star-forming regions. The observed column density of t-HCOOH is (8.13 ±0.72) x 10 15cm -2 , a value that allows for detailed comparison with existing theoretical models of interstellar chemistry.

This finding is significant because formic acid shares structural similarities with glycine, a crucial amino acid, and may participate in the formation of more complex biomolecules. Chemical modelling indicates that t-HCOOH likely forms through the reaction of HCO and OH on grain surfaces, subsequently being released into the gas phase.

The observed and modelled abundances of formic acid align closely, differing by only a factor of 0.89, which supports the proposed formation pathway. The authors acknowledge that further research is needed to fully understand the complex interplay of chemical processes occurring within hot molecular cores.

Future studies could focus on expanding the search for other prebiotic molecules and refining chemical models to account for a wider range of physical and chemical conditions. These observations represent a step towards characterising the chemical complexity of star-forming regions and assessing the potential for prebiotic chemistry in the universe.