Comparative Analysis of Complex Organic Molecule Abundances Across Diverse Astrophysical Environments: IRAS 16293B, Sgr B2(N2), Chemical Models, and Comet 67P

1. Introduction

Complex organic molecules (COMs) are now recognized as ubiquitous constituents of star-forming regions and constitute a central component of modern astrochemistry, owing to their potential role as chemical precursors to prebiotic and biologically relevant species [1]. Over the past decade, the detection of an increasingly large number of COMs in both hot cores associated with high-mass star formation and hot corinos surrounding low-mass protostars has intensified efforts to understand their formation pathways, survival mechanisms, and observed abundance patterns [2,3]. High-sensitivity and high-angular-resolution observations carried out with ALMA and complementary facilities have revealed remarkably rich molecular inventories across a wide range of astrophysical environments, spanning from deeply embedded low-mass protostellar systems to chemically evolved high-mass hot cores [4,5].

In parallel, in situ compositional measurements obtained by the Rosetta mission toward the comet $67P/Churyumov-Gerasimenko$ have provided an unprecedented opportunity to directly compare the chemical makeup of primitive Solar System bodies with that of interstellar and protostellar sources [6]. Despite these substantial observational advances, several fundamental issues remain unresolved, including the extent to which low-mass and high-mass star-forming regions share a common chemical heritage, the presence of systematic differences between oxygen-bearing and nitrogen-bearing COM populations, the degree of chemical continuity between interstellar material and cometary ices, and the overall predictive capability of current astrochemical models. In this work, we address these questions through a comprehensive statistical analysis of COM abundances derived from the prototypical low-mass hot corino IRAS 16293B, the archetypal high-mass hot core Sgr B2(N2), state-of-the-art theoretical chemical models, and the comet $67P/Churyumov-Gerasimenko$. By employing multiple visualization techniques and correlation-based analyses, we quantitatively assess chemical similarities across these environments and identify robust systematic trends that provide new insights into the origin and evolution of complex organic chemistry in star- and planet-forming regions.

In the context of the above mentioned direct motivation, we would also like to add here that a series of works in the field of astrochemistry have been taken into considered by some of the authors of the present group where they have opened up new avenue by connecting chemistry with astrophysics [7,8,9] such as research status of the periodic table, Hertzsprung–Russell diagram, from Color–Magnitude diagram and Hertzsprung–Russell diagram: mapping the bibliometric trajectory of stellar evolution diagrams.

Our scheme of the present work is as follows: in section 2, we have discussed about data and methodology whereas in section 3, we present the results obtained under the present study. In section 4, we have done a discussion on our overall results and in section 5 a few comments are made on the present work.

2. Methodology

2.1. Data Sources

Our analysis is based on abundance measurements of 26 molecular species observed across four distinct astrophysical environments, with all molecular abundances normalized to that of methanol (CH3OH) = 100%). The dataset includes observations of IRAS 16293B, a well-studied Class 0 protostellar binary system located at a distance of approximately 120 pc and representative of low-mass star formation [5,10]; Sgr B2(N2), a massive hot core within the Sgr B2 molecular cloud complex at a distance of about 8.2 kpc, which is among the most chemically rich regions in the Galaxy [4,11]; abundance predictions from gas–grain chemical models that incorporate warm-up evolutionary scenarios characteristic of hot core chemistry [12]; and in situ molecular abundance measurements obtained by the ROSINA instrument aboard the Rosetta spacecraft during its encounter with comet 67P/Churyumov-Gerasimenko [6,13]. The molecular sample comprises 20 oxygen-bearing species and 6 nitrogen-bearing species, spanning a broad range of chemical complexity from relatively simple molecules such as formaldehyde to more complex species including ethylene glycol ((CH₂OH)₂). The complete set of molecular abundances employed in this study is summarized in Table A1.

2.2. Statistical Techniques

To quantitatively assess chemical similarities and systematic trends among the different environments, we employ several complementary statistical techniques. Correlation analysis is performed by computing Pearson correlation coefficients in logarithmic abundance space for pairs of molecular species, allowing for a robust comparison across several orders of magnitude. The overall distribution of molecular abundances is examined using histograms and box–whisker plots to characterize the spread, central tendencies, and potential outliers within each environment. In addition, direct abundance ratio analyses are carried out to identify relative enrichment or depletion factors between sources and molecular classes. To further investigate chemical differentiation, the analysis is conducted separately for oxygen-bearing and nitrogen-bearing species, enabling a comparative assessment of these two chemically distinct populations. All measurement uncertainties are propagated using standard error analysis techniques, and the statistical significance of the results is evaluated at the 95% confidence level.

3. Results

3.1. Correlation Between Sources

Figure 1 presents log–log scatter plots comparing molecular abundances between different source pairs. The comparison between IRAS 16293B and Sgr B2(N2) reveals a strong positive correlation ($r=0.680$, $n=21$) despite the markedly different physical conditions characterizing low-mass and high-mass star-forming environments. Most molecular species lie within a factor of approximately 3–10 of the one-to-one relation, consistent with earlier observational studies [4]. Comparisons involving chemical model predictions show a weaker but still significant correlation ($r=0.523$), with noticeably larger scatter, indicating that while current models reproduce broad abundance trends, they fail to fully capture source-specific chemical processes. The comparison with comet 67P/Churyumov-Gerasimenko exhibits the lowest degree of correlation ($r=0.445$), reflecting substantial chemical divergence between interstellar material and cometary reservoirs. Across all comparisons, oxygen-bearing molecules (shown as blue circles) generally adhere more closely to the correlation trends than nitrogen-bearing molecules (red triangles), which display systematic deviations suggestive of distinct formation pathways or subsequent chemical processing.

3.2. Abundance Distributions

The abundance distribution histograms shown in Figure 2, separated by molecular class, reveal pronounced differences among the four environments. In IRAS 16293B , oxygen-bearing molecules exhibit a broad distribution with a mean abundance of 1.67%, whereas nitrogen-bearing species are tightly clustered around a much lower mean value of 0.16%. In contrast, Sgr B2(N2) displays a comparable mean abundance for oxygen-bearing molecules (1.49%) but shows a dramatic enhancement of nitrogen-bearing species, which reach a mean abundance of 6.13%. Chemical models predict broader abundance distributions than those observed, particularly for oxygen-bearing molecules, suggesting an overestimation of chemical diversity or efficiency in model reaction networks. The cometary abundances exhibit a bimodal distribution, characterized by a subset of highly abundant species such as C₂H₅OH (19%) and CH₃CHO (22%), alongside a population of significantly less abundant molecules. Notably, the factor-of-38 enhancement in nitrogen-bearing species between IRAS 16293B and Sgr B2(N2) represents one of the most striking systematic variations identified in this analysis.

3.3. Isomeric Family Variations

Figure 3 focuses on selected isomeric molecular families and reveals significant deviations from equilibrium expectations. The C₂H₄O₂ isomer group, consisting of glycolaldehyde, methyl formate, and acetic acid, shows particularly strong abundance contrasts across sources. Glycolaldehyde exhibits an abundance of 0.34% in IRAS 16293B but reaches 3.8% in chemical models, while methyl formate displays relatively consistent abundances of 2.6% in IRAS 16293B and 3.0% in Sgr B2(N2). Acetic acid remains extremely underabundant in all environments, with values ranging from 0.028% to 0.05%. These pronounced disparities are inconsistent with the nearly equal abundances expected under thermal equilibrium conditions, indicating that kinetic effects and formation pathway efficiencies play a dominant role in shaping isomeric abundance ratios.

3.4. Statistical Distributions

The box-and-whisker plots presented in Figure 4 summarize the statistical spread of molecular abundances and highlight the exceptionally large dynamic ranges involved. For oxygen-bearing species in IRAS 16293B, abundances span a factor of approximately 640, ranging from 0.022% to 14%, while nitrogen-bearing species in Sgr B2(N2) exhibit a similarly large range of 640, extending from 0.025% to 16%. The chemical models display the widest spread, spanning nearly four orders of magnitude (a factor of $\sim 4\times {10}^4$), from 0.0012% up to 150%. These extensive dynamic ranges underscore the inherent difficulty of producing universal abundance predictions and emphasize the critical importance of molecule-specific formation, destruction, and evolutionary pathways in astrochemical environments.

3.5. Abundance Ratio Analysis

Figure 5 displays individual molecular abundance ratios between Sgr B2(N2) and IRAS 16293B. The ratios span nearly three orders of magnitude:

• Minimum: CH₃CHO (0.92×) – nearly identical abundances
• Maximum: HC₃N (488.89×) – extreme enrichment in IRAS 16293B
• Median: ∼3× for O-bearing, ∼15× for N-bearing

N-bearing molecules systematically show higher ratios, with CH₃CN (13.75×), HNCO (13.51×), C₂H₅CN (444.44×), and C₂H₃CN (148.65×) all dramatically enriched in IRAS 16293B.

3.6. Molecular Class Comparison

Figure 6 compares mean abundances between O-bearing and N-bearing species. The key finding is the systematic N-enrichment in Sgr B2(N2):

$${\displaystyle \frac{{\mathrm{N}-\mathrm{bearing}}_{\mathrm{Sgr}}}{{\mathrm{N}-\mathrm{bearing}}_{\mathrm{IRAS}}}}\approx 38\times {\displaystyle \frac{{\mathrm{O}-\mathrm{bearing}}_{\mathrm{Sgr}}}{{\mathrm{O}-\mathrm{bearing}}_{\mathrm{IRAS}}}}$$

(1)

This suggests that high-mass hot cores provide more efficient pathways for N-bearing COM formation, possibly through higher temperatures enabling gas-phase nitrogen chemistry or different initial ice compositions.

4. Discussion

4.1. Chemical Similarity Across Mass Scales

The strong correlation ($r=0.680$) between IRAS 16293B and Sgr B2(N2) abundances is remarkable given the >10⁴ difference in luminosity and ∼10³ difference in mass. This suggests that COM chemistry is largely governed by similar formation mechanisms (grain surface reactions followed by thermal desorption) across a wide range of protostellar masses.

However, the systematic differences in N-bearing molecules indicate that temperature, density, or radiation field variations do affect specific chemical pathways. The N-enrichment in Sgr B2(N2) might result from higher gas-phase temperatures (>200 K) activating endothermic N-bearing reactions, different ice layer compositions in the initial cloud material, enhanced cosmic ray flux in the Galactic Center region, or longer timescales for nitrogen chemistry in massive cores.

4.2. Model Comparison

The moderate correlation with chemical models ($r=0.523$) indicates that current gas-grain models capture first-order COM abundance patterns but miss important source-specific effects. The models particularly struggle with:

• Predicting the correct isomeric ratios (e.g., C₂H₄O₂ family)
• Matching the observed N-bearing/O-bearing abundance ratios
• Reproducing the narrow observed abundance ranges

Future modeling efforts should incorporate more detailed ice mantle structures and formation histories, better constraints on reactive desorption yields, improved nitrogen chemistry networks, and source-specific physical parameters including density and temperature profiles.

4.3. Comet-Interstellar Connection

The modest correlation between cometary and interstellar abundances ($r=0.445$) reflects substantial chemical processing during solar system formation. Key differences include:

• Extreme enrichment of C2H5OH and CH₃CHO in 67P/Churyumov-Gerasimenko
• Near-absence of some interstellar-abundant species (e.g., CH₃OCH₃)
• Generally higher absolute abundances in cometary ice

These differences could arise from selective processing during the proto-planetary disk phase, temperature-dependent ice fractionation, different formation locations within the solar nebula, or cometary outgassing biases affecting measured ratios.

Despite the differences, the detection of many identical species supports the interstellar heritage of cometary ices and validates the connection between star and planet formation chemistry.

4.4. Implications for COM Formation Mechanisms

Our results provide several constraints on COM formation theories:

Grain surface formation

The similar O-bearing abundances across sources support grain surface reactions as the primary formation pathway for O-containing COMs. The factor-of-3 scatter is consistent with variations in:

• Ice mantle thickness and layering
• Thermal history (peak temperature, warm-up timescale)
• Radiation field intensity affecting radical production

Gas-phase chemistry

The dramatic N-enrichment in Sgr B2(N2) suggests significant gas-phase contributions for N-bearing molecules. High temperatures (>200 K) in massive hot cores may:

• Activate ion-molecule reactions with N₂ or NH₃
• Enable efficient CN radical insertion into hydrocarbons
• Facilitate atomic nitrogen reactions with organic radicals

Isomeric selection

The non-equilibrium isomeric ratios (especially in the C₂H₄O₂ family) demonstrate kinetic rather than thermodynamic control. This implies:

• Formation occurs at specific temperatures where certain barriers become accessible
• Structural isomers form through different pathways, not by interconversion
• Observational abundance ratios preserve information about formation conditions

4.5. Systematic Uncertainties

Several systematic effects may influence our results. Different excitation conditions, including optical depths and excitation temperatures between sources, may bias derived column densities by up to a factor of 2–3. ALMA observations probe different physical scales (∼100 AU for IRAS 16293B, ∼5000 AU for Sgr B2(N2)r), potentially sampling different chemical zones. Sources may be at different evolutionary stages within the hot core/corino phase, and in chemically rich sources like Sgr B2(N2), line blending may affect weaker transitions.

Despite these uncertainties, the overall trends identified in this work (particularly the N-enrichment and correlation patterns) are robust at the factor-of-3 to factor-of-10 level.

5. Conclusions

We have conducted a comprehensive statistical analysis of complex organic molecule abundances across four diverse astrochemical environments: the low-mass hot corino IRAS 16293B, the high-mass hot core Sgr B2(N2), theoretical gas-grain chemical models, and comet 67P/Churyumov-Gerasimenko. Our principal findings demonstrate strong chemical similarity between low-mass and high-mass star-forming regions, with a Pearson correlation of $r=0.680$ for 21 common molecules, suggesting universal grain-surface formation mechanisms for oxygen-bearing COMs. We observe systematic nitrogen enrichment in the high-mass source Sgr B2(N2), where N-bearing molecules are elevated by a factor of 38 relative to O-bearing molecules compared to IRAS 16293B, indicating efficient gas-phase nitrogen chemistry at temperatures exceeding 200 K. Current chemical models reproduce first-order abundance patterns ($r=0.523$ correlation) but struggle to predict isomeric ratios and nitrogen chemistry, requiring improved reactive desorption treatments and nitrogen reaction networks. Cometary abundances show modest correlation with interstellar sources ($r=0.445$), reflecting chemical processing during solar system formation while preserving evidence of interstellar heritage. Non-equilibrium isomeric ratios in the C₂H₄O₂ family demonstrate kinetic control of COM formation, with abundance patterns preserving information about formation temperatures and pathways. Typical abundance scatter of factor-of-3 to factor-of-10 and dynamic ranges exceeding 600× emphasize the importance of molecule-specific formation and destruction pathways in determining observed COM inventories.

It is to be noted that (i) in Table 1, we have considered Abundances normalized to CH3OH = 100% [11], Sgr B2(N2) [12,13], Model [14], and 67P [15,16]. Typical uncertainties are factor of 2—3, (ii) in Table 2, we have considered Mean abundances and standard deviations for O-bearing and N-bearing molecular classes, however values exclude CH₃OH reference molecule, and (iii) in Table 3, we have considered Ratios calculated for molecules detected in both sources. N-bearing molecules show systematic enrichment in Sgr B2(N2).

These results provide new constraints on astrochemical models and demonstrate that while COM formation is largely universal across mass scales for oxygen-bearing species, nitrogen chemistry exhibits strong environmental dependencies related to temperature, density, and evolutionary timescale under astrophysical processes. Future high-resolution observations with ALMA and JWST, combined with improved laboratory constraints on ice chemistry, will further refine our understanding of complex organic chemistry in star- and planet-forming regions like nebulae and supernovae.