The recently reported Cosmic Himalayas (CH)—an extreme quasar overdensity at z ∼ 2—poses an apparent challenge to the Lambda cold dark matter (ΛCDM) framework, with a reported significance of δ = 16.9σ under Gaussian assumptions. Such an event appears improbably rare, with a formal probability of P ∼ 10−68. In this work, we investigate whether CH-like structures can naturally arise in cosmological hydrodynamic simulations. Using the CROCODILE simulation, which self-consistently models galaxy–black hole coevolution, we examine quasar clustering through two complementary approaches: the count-in-cells (CIC) statistic, which probes large-scale overdensities, and the nearest-neighbor distribution (NND), sensitive to small-scale environments. CIC analysis reveals that the underlying distribution is heavy-tailed and non-Gaussian, and that conventional Gaussian-based evaluation substantially overestimates the significance of extreme events. When modeled with an asymmetric generalized normal distribution (AGND), the inferred rarity of the CH is substantially reduced and reconciled with standard ΛCDM; for instance, regions appearing as 12σGauss outliers under Gaussian assumptions (P ∼ 10−33) are found to occur in AGND regimes with a probability of P ∼ 10−4. NND analysis further demonstrates that extreme overdense regions within the simulation can naturally sustain two-point correlation function values similar to those observed in the CH ( ), suggesting that the strong clustering stems from sample selection biases and local environmental variations. These two analyses conclusively highlight the importance of adopting non-Gaussian statistics when quantifying extreme overdensities of quasars and establish that the CH is not an anomaly, but a natural outcome of structure formation in the ΛCDM universe.
{"title":"Cosmic Himalayas in CROCODILE: Probing the Extreme Quasar Overdensities by Count-in-cells Analysis and Nearest-neighbor Distribution","authors":"Yuto Kuwayama, 裕斗 桑山, Yongming Liang, 永明 梁, Kentaro Nagamine, 健太郎 長峯, Yuri Oku, 裕理 奥, Daisuke Nishihama, 大将 西濱, Daisuke Toyouchi, 大輔 豊内, Keita Fukushima, 啓太 福島, Hidenobu Yajima, 秀伸 矢島, Hyunbae Park, 현배 박, Masami Ouchi and 正己 大内","doi":"10.3847/1538-4357/ae5798","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5798","url":null,"abstract":"The recently reported Cosmic Himalayas (CH)—an extreme quasar overdensity at z ∼ 2—poses an apparent challenge to the Lambda cold dark matter (ΛCDM) framework, with a reported significance of δ = 16.9σ under Gaussian assumptions. Such an event appears improbably rare, with a formal probability of P ∼ 10−68. In this work, we investigate whether CH-like structures can naturally arise in cosmological hydrodynamic simulations. Using the CROCODILE simulation, which self-consistently models galaxy–black hole coevolution, we examine quasar clustering through two complementary approaches: the count-in-cells (CIC) statistic, which probes large-scale overdensities, and the nearest-neighbor distribution (NND), sensitive to small-scale environments. CIC analysis reveals that the underlying distribution is heavy-tailed and non-Gaussian, and that conventional Gaussian-based evaluation substantially overestimates the significance of extreme events. When modeled with an asymmetric generalized normal distribution (AGND), the inferred rarity of the CH is substantially reduced and reconciled with standard ΛCDM; for instance, regions appearing as 12σGauss outliers under Gaussian assumptions (P ∼ 10−33) are found to occur in AGND regimes with a probability of P ∼ 10−4. NND analysis further demonstrates that extreme overdense regions within the simulation can naturally sustain two-point correlation function values similar to those observed in the CH ( ), suggesting that the strong clustering stems from sample selection biases and local environmental variations. These two analyses conclusively highlight the importance of adopting non-Gaussian statistics when quantifying extreme overdensities of quasars and establish that the CH is not an anomaly, but a natural outcome of structure formation in the ΛCDM universe.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"133 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147682049","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-14DOI: 10.3847/1538-4357/ae5177
Katherine E. Whitaker, Sam E. Cutler, Rupali Chandar, Richard Pan, David J. Setton, Lukas J. Furtak, Rachel Bezanson, Ivo Labbe, Joel Leja, Katherine A. Suess, Bingjie Wang, 冰洁 王, John R. Weaver, Hakim Atek, Gabriel B. Brammer, Robert Feldmann, Natascha M. Förster Schreiber, Karl Glazebrook, Anna de Graaff, Jenny E. Greene, Gourav Khullar, Danilo Marchesini, Michael V. Maseda, Tim B. Miller, Houjun Mo, Lamiya A. Mowla, Themiya Nanayakkara, Erica J. Nelson, Sedona H. Price, Francesca Rizzo, Pieter van Dokkum, Christina C. Williams, Yanzhe Zhang, Yunchong Zhang and Adi Zitrin
Globular clusters (GCs) are some of the oldest bound structures in the Universe, holding clues to the earliest epochs of star formation and galaxy assembly. However, accurate age measurements of ancient clusters are challenging due to the age–metallicity degeneracy. Here, we report the discovery of 36 compact stellar systems within the “Relic,” a massive, quiescent galaxy at z = 2.53. The Relic resides in an overdensity behind the Abell 2744 cluster, with a prominent tidal tail extending towards two low-mass companions. Using deep data from the UNCOVER/MegaScience JWST Surveys, we find that clusters formed in age intervals ranging from 8 Myr up to ∼2 Gyr, suggesting a rich formation history starting at z ∼ 10. While the cluster-based star formation history is broadly consistent with the high past star formation rates derived from the diffuse host galaxy light, one potential discrepancy is a tentative ∼2–3× higher rate in the cluster population for the past Gyr. Taken together with the spatial distribution and low inferred metallicities of these young-to-intermediate age clusters, we may be seeing direct evidence for the accretion of star clusters in addition to their early in situ formation. The cluster masses are high, ∼106–107M⊙, which may explain why we are able to detect them around this likely post-merger galaxy. Overall, the Relic clusters are consistent with being precursors of the most-massive present-day GCs. This unique laboratory enables the first connection between long-lived, high-redshift clusters and local stellar populations, offering insights into the early stages of GC evolution and the broader processes of galaxy assembly.
{"title":"Discovery of Ancient Globular Cluster Candidates in the Relic, a Quiescent Galaxy at z = 2.5","authors":"Katherine E. Whitaker, Sam E. Cutler, Rupali Chandar, Richard Pan, David J. Setton, Lukas J. Furtak, Rachel Bezanson, Ivo Labbe, Joel Leja, Katherine A. Suess, Bingjie Wang, 冰洁 王, John R. Weaver, Hakim Atek, Gabriel B. Brammer, Robert Feldmann, Natascha M. Förster Schreiber, Karl Glazebrook, Anna de Graaff, Jenny E. Greene, Gourav Khullar, Danilo Marchesini, Michael V. Maseda, Tim B. Miller, Houjun Mo, Lamiya A. Mowla, Themiya Nanayakkara, Erica J. Nelson, Sedona H. Price, Francesca Rizzo, Pieter van Dokkum, Christina C. Williams, Yanzhe Zhang, Yunchong Zhang and Adi Zitrin","doi":"10.3847/1538-4357/ae5177","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5177","url":null,"abstract":"Globular clusters (GCs) are some of the oldest bound structures in the Universe, holding clues to the earliest epochs of star formation and galaxy assembly. However, accurate age measurements of ancient clusters are challenging due to the age–metallicity degeneracy. Here, we report the discovery of 36 compact stellar systems within the “Relic,” a massive, quiescent galaxy at z = 2.53. The Relic resides in an overdensity behind the Abell 2744 cluster, with a prominent tidal tail extending towards two low-mass companions. Using deep data from the UNCOVER/MegaScience JWST Surveys, we find that clusters formed in age intervals ranging from 8 Myr up to ∼2 Gyr, suggesting a rich formation history starting at z ∼ 10. While the cluster-based star formation history is broadly consistent with the high past star formation rates derived from the diffuse host galaxy light, one potential discrepancy is a tentative ∼2–3× higher rate in the cluster population for the past Gyr. Taken together with the spatial distribution and low inferred metallicities of these young-to-intermediate age clusters, we may be seeing direct evidence for the accretion of star clusters in addition to their early in situ formation. The cluster masses are high, ∼106–107M⊙, which may explain why we are able to detect them around this likely post-merger galaxy. Overall, the Relic clusters are consistent with being precursors of the most-massive present-day GCs. This unique laboratory enables the first connection between long-lived, high-redshift clusters and local stellar populations, offering insights into the early stages of GC evolution and the broader processes of galaxy assembly.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"124 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147695393","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-14DOI: 10.3847/1538-4357/ae5633
Xunzhou Chen, Tiancheng Sun, Yuxi (Lucy) Lu, Zixuan Lu and Lifei Ye
The radius valley—a bimodal feature in the size distribution of close-in small exoplanets—is widely interpreted as a signature of atmospheric loss and therefore provides a key constraint on the formation and atmospheric evolution of these planets. We investigate its dependence on host-star properties using 769 planets orbiting 558 stars, for which we derive stellar ages, chromospheric activity ( ), and Galactic birth radii, together with elemental abundances. We find that the radius valley is not fully established at ages ≲ 3 Gyr and evolves over gigayear timescales, with its prominence strongly affected by stellar population mixing. The dependence on magnetic activity is nonmonotonic: a clear valley is present even among magnetically quiet stars, while highly active systems do not show systematically stronger depletion. The valley morphology also varies with stellar composition: the valley is strongest in metal-poor stars, weakens near solar metallicity, and partially strengthens again at the highest metallicities. In addition, the valley shows sensitivity to refractory element ratios such as [Mg/Si], while correlations with [C/O] are weaker, indicating a dependence on planetary interior structure. Our results are more consistent with a dominant role for core-powered atmospheric mass loss than with purely irradiation-driven photoevaporation. Finally, the radius valley also depends on the Galactic birth environment, with systems near the estimated solar birth radius (Rbirth ≃ 4.5 ± 0.4 kpc) showing a high fraction of Earth-like planets and a well-defined bimodal structure, suggesting that the solar system formed in a region with a well-developed Earth-sized planet population.
{"title":"Insights into the Exoplanet Radius Valley from Host-star Ages, Activity, Chemistry, and Birth Radii","authors":"Xunzhou Chen, Tiancheng Sun, Yuxi (Lucy) Lu, Zixuan Lu and Lifei Ye","doi":"10.3847/1538-4357/ae5633","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5633","url":null,"abstract":"The radius valley—a bimodal feature in the size distribution of close-in small exoplanets—is widely interpreted as a signature of atmospheric loss and therefore provides a key constraint on the formation and atmospheric evolution of these planets. We investigate its dependence on host-star properties using 769 planets orbiting 558 stars, for which we derive stellar ages, chromospheric activity ( ), and Galactic birth radii, together with elemental abundances. We find that the radius valley is not fully established at ages ≲ 3 Gyr and evolves over gigayear timescales, with its prominence strongly affected by stellar population mixing. The dependence on magnetic activity is nonmonotonic: a clear valley is present even among magnetically quiet stars, while highly active systems do not show systematically stronger depletion. The valley morphology also varies with stellar composition: the valley is strongest in metal-poor stars, weakens near solar metallicity, and partially strengthens again at the highest metallicities. In addition, the valley shows sensitivity to refractory element ratios such as [Mg/Si], while correlations with [C/O] are weaker, indicating a dependence on planetary interior structure. Our results are more consistent with a dominant role for core-powered atmospheric mass loss than with purely irradiation-driven photoevaporation. Finally, the radius valley also depends on the Galactic birth environment, with systems near the estimated solar birth radius (Rbirth ≃ 4.5 ± 0.4 kpc) showing a high fraction of Earth-like planets and a well-defined bimodal structure, suggesting that the solar system formed in a region with a well-developed Earth-sized planet population.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681943","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-14DOI: 10.3847/1538-4357/ae5658
Yong Yuan, Minghui Du, Benyang Zhu, Xin-Yi Lin, Wen-Fan Feng, Peng Xu and Xilong Fan
The cosmic distance duality relation (CDDR), expressed as dL(z) = (1 + z)2DA(z), is a fundamental relation in modern cosmology. In this work, we apply a method to test the CDDR using simulated strongly lensed gravitational-wave (SLGW) signals from massive binary black holes as observed by proposed space-based detector networks. Our analysis is conducted under the point-mass lens model, considering the strong lensing scenario that produces two images. We generate 90 days of simulated SLGW data for 10 events based on the Population III stellar formation model, with source redshifts in the range zs ∈ [2, 6] and lens redshifts in zL ∈ [0.2, 1]. The deviation of CDDR is parameterized by η1(z) = 1 + η0z and η2(z) = 1 + η0z/(1 + z), and we incorporate the deviation parameter η0 directly into the waveform model. Parameter estimation is performed within a Bayesian statistical framework, combining simulated data from both Taiji and LISA. For a single lensed event, the joint Taiji+LISA analysis improves the measurement precision of η0 by roughly a factor of 2 compared with Taiji-only observations. By combining 10 simulated events, the population-level constraints on η0, quantified by the half width of the 95% credible interval, reach approximately 2.61 × 10−4 (1.72 × 10−4) for the η1(z) parameterization and 1.22 × 10−3 (6.86 × 10−4) for η2(z) in the Taiji-only (Taiji+LISA) scenario, respectively. The inferred values of η0 remain consistent with η0 = 0 within the estimated uncertainties, with no statistically significant evidence for deviations from the CDDR at the achieved precision. These results demonstrate the significant advantage of joint space-based observations for high-precision tests of the CDDR.
{"title":"An Opacity-free Test of the Cosmic Distance Duality Relation Using Strongly Lensed Gravitational-wave Signals with Space-based Detector Networks","authors":"Yong Yuan, Minghui Du, Benyang Zhu, Xin-Yi Lin, Wen-Fan Feng, Peng Xu and Xilong Fan","doi":"10.3847/1538-4357/ae5658","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5658","url":null,"abstract":"The cosmic distance duality relation (CDDR), expressed as dL(z) = (1 + z)2DA(z), is a fundamental relation in modern cosmology. In this work, we apply a method to test the CDDR using simulated strongly lensed gravitational-wave (SLGW) signals from massive binary black holes as observed by proposed space-based detector networks. Our analysis is conducted under the point-mass lens model, considering the strong lensing scenario that produces two images. We generate 90 days of simulated SLGW data for 10 events based on the Population III stellar formation model, with source redshifts in the range zs ∈ [2, 6] and lens redshifts in zL ∈ [0.2, 1]. The deviation of CDDR is parameterized by η1(z) = 1 + η0z and η2(z) = 1 + η0z/(1 + z), and we incorporate the deviation parameter η0 directly into the waveform model. Parameter estimation is performed within a Bayesian statistical framework, combining simulated data from both Taiji and LISA. For a single lensed event, the joint Taiji+LISA analysis improves the measurement precision of η0 by roughly a factor of 2 compared with Taiji-only observations. By combining 10 simulated events, the population-level constraints on η0, quantified by the half width of the 95% credible interval, reach approximately 2.61 × 10−4 (1.72 × 10−4) for the η1(z) parameterization and 1.22 × 10−3 (6.86 × 10−4) for η2(z) in the Taiji-only (Taiji+LISA) scenario, respectively. The inferred values of η0 remain consistent with η0 = 0 within the estimated uncertainties, with no statistically significant evidence for deviations from the CDDR at the achieved precision. These results demonstrate the significant advantage of joint space-based observations for high-precision tests of the CDDR.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"24 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681944","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-14DOI: 10.3847/1538-4357/ae4de8
Fu-Xing Li, Sheng-Bang Qian, Eduardo Fernández Lajús, Lin-Jia Li, Er-Gang Zhao, Li-Ying Zhu, Cheng-Liang Jiao, Qi-Bin Sun, Wen-Xu Lin, Wen-Ping Liao, Xiang-Dong Shi and Min-Yu Li
The formation and structural configuration of V Pup have not yet been fully understood. Here we report the detection that V Pup is a massive hierarchical quadruple system. Through long-term photometric monitoring and a comprehensive analysis of multiple survey datasets, we have constructed an updated O − C curve showing two significant periodic variations. These cyclic modulations strongly suggest the presence of two additional stellar companions orbiting the central binary. Both the tertiary and quaternary components have B-type spectral classifications and are located at separations that are unresolved by Gaia. These findings indicate that V Pup is a massive hierarchical quadruple system. The mass ratios among the four components are approximately 4:2:2:1, corresponding to the primary, secondary, tertiary, and quaternary stars, respectively. The tertiary and quaternary components are approximately 1:2 apart from the central binary, and their orbital periods around the binary are approximately 1:3. It is likely that this system originated through disk fragmentation. This discovery suggests that V Pup may be an exceptional test bed. It could shed further light on the formation of massive multiple-star systems.
{"title":"V Pup: A Hierarchical Massive Quadruple System","authors":"Fu-Xing Li, Sheng-Bang Qian, Eduardo Fernández Lajús, Lin-Jia Li, Er-Gang Zhao, Li-Ying Zhu, Cheng-Liang Jiao, Qi-Bin Sun, Wen-Xu Lin, Wen-Ping Liao, Xiang-Dong Shi and Min-Yu Li","doi":"10.3847/1538-4357/ae4de8","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4de8","url":null,"abstract":"The formation and structural configuration of V Pup have not yet been fully understood. Here we report the detection that V Pup is a massive hierarchical quadruple system. Through long-term photometric monitoring and a comprehensive analysis of multiple survey datasets, we have constructed an updated O − C curve showing two significant periodic variations. These cyclic modulations strongly suggest the presence of two additional stellar companions orbiting the central binary. Both the tertiary and quaternary components have B-type spectral classifications and are located at separations that are unresolved by Gaia. These findings indicate that V Pup is a massive hierarchical quadruple system. The mass ratios among the four components are approximately 4:2:2:1, corresponding to the primary, secondary, tertiary, and quaternary stars, respectively. The tertiary and quaternary components are approximately 1:2 apart from the central binary, and their orbital periods around the binary are approximately 1:3. It is likely that this system originated through disk fragmentation. This discovery suggests that V Pup may be an exceptional test bed. It could shed further light on the formation of massive multiple-star systems.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"21 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147682044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-14DOI: 10.3847/1538-4357/ae53e9
Germán Molpeceres and Joan Enrique-Romero
Motivated by the value of CN-bearing molecules as tracers of interstellar physical conditions, we investigate the reactions of adsorbed CN radicals with acetylene and ethylene (C2H2 and C2H4) on interstellar dust-grain analogs using quantum chemical calculations. We find that reactivity is strongly controlled by the relative orientation of the reactants. We further show that, on ice, these reactions differ qualitatively from their gas-phase counterparts, stalling at the formation of the adduct complexes and and exhibiting newly emerged kinetic barriers for the neutral-radical association. We contextualize our calculations in the same reaction–diffusion framework that would be employed in astrochemical models, finding that, depending on the diffusion energy of the hydrocarbons, these reactions can be either negligible or efficient, highlighting the importance of the local ice structure in interstellar grain chemistry. These findings caution against the use of CN-based tracers that assume barrierless, bimolecular surface reactions involving CN radicals.
{"title":"Can Cyanide Radicals Drive Molecular Backbone Growth on Interstellar Icy Grains?","authors":"Germán Molpeceres and Joan Enrique-Romero","doi":"10.3847/1538-4357/ae53e9","DOIUrl":"https://doi.org/10.3847/1538-4357/ae53e9","url":null,"abstract":"Motivated by the value of CN-bearing molecules as tracers of interstellar physical conditions, we investigate the reactions of adsorbed CN radicals with acetylene and ethylene (C2H2 and C2H4) on interstellar dust-grain analogs using quantum chemical calculations. We find that reactivity is strongly controlled by the relative orientation of the reactants. We further show that, on ice, these reactions differ qualitatively from their gas-phase counterparts, stalling at the formation of the adduct complexes and and exhibiting newly emerged kinetic barriers for the neutral-radical association. We contextualize our calculations in the same reaction–diffusion framework that would be employed in astrochemical models, finding that, depending on the diffusion energy of the hydrocarbons, these reactions can be either negligible or efficient, highlighting the importance of the local ice structure in interstellar grain chemistry. These findings caution against the use of CN-based tracers that assume barrierless, bimolecular surface reactions involving CN radicals.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"138 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147682045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-14DOI: 10.3847/1538-4357/ae4c38
B. Zuckerman
One of the most interesting questions that astronomy can hope to answer is: Are we alone in our Milky Way Galaxy? A detection of an electromagnetic (EM) signal generated by an extraterrestrial technological intelligence, or the presence in our solar system of an alien probe, would answer this question in the negative. Purposeful interstellar communication is a two-way street—the transmitting and receiving technological intelligences (TIs) both need to do their parts. As the receiving TI, our EM search programs should incorporate a model of what a transmitting TI is likely to be doing. Published works on the search for extraterrestrial technological intelligence (SETI) have generally not done so, and thus have often been suboptimally designed. We propose an improved search technique that more closely corresponds to astronomical surveys that have been undertaken for reasons that have nothing to do with SETI. Published non-SETI radio and optical surveys are sufficiently extensive that they already supply meaningful constraints on the prevalence of nearby, purposely communicative alien civilizations. Purposeful communication can also include the sending of spaceships (probes). The absence of evidence for alien probes in the solar system suggests that no alien civilization has passed within ∼100 lt-yr of Earth during the past few billion years.
{"title":"Broadband Searches for Extraterrestrial Technological Intelligence: A New Strategy to Find Nearby Alien Civilizations","authors":"B. Zuckerman","doi":"10.3847/1538-4357/ae4c38","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4c38","url":null,"abstract":"One of the most interesting questions that astronomy can hope to answer is: Are we alone in our Milky Way Galaxy? A detection of an electromagnetic (EM) signal generated by an extraterrestrial technological intelligence, or the presence in our solar system of an alien probe, would answer this question in the negative. Purposeful interstellar communication is a two-way street—the transmitting and receiving technological intelligences (TIs) both need to do their parts. As the receiving TI, our EM search programs should incorporate a model of what a transmitting TI is likely to be doing. Published works on the search for extraterrestrial technological intelligence (SETI) have generally not done so, and thus have often been suboptimally designed. We propose an improved search technique that more closely corresponds to astronomical surveys that have been undertaken for reasons that have nothing to do with SETI. Published non-SETI radio and optical surveys are sufficiently extensive that they already supply meaningful constraints on the prevalence of nearby, purposely communicative alien civilizations. Purposeful communication can also include the sending of spaceships (probes). The absence of evidence for alien probes in the solar system suggests that no alien civilization has passed within ∼100 lt-yr of Earth during the past few billion years.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681746","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-14DOI: 10.3847/1538-4357/ae56f7
Lorenzo Biasiotti, Paolo Simonetti, Riccardo Spinelli, Stavro L. Ivanovski, Lorenzo Calderone, Federico Dogo, Giovanna Jerse, Sergio Monai and Giovanni Vladilo
HD 20794 d is one of the best examples of a super-Earth planet in the habitable zone of a Sun-like star. Notably, due to the high eccentricity (e = 0.45 ) it partially lies in the conservative habitable zone, suggesting a dynamically variable climate. The system’s proximity (d = 6.0414 ± 0.0028 pc) makes it a high-priority target for future atmospheric characterization via direct imaging and positions HD 20794 d as an ideal benchmark for understanding the potential climate states of eccentric exoplanets. Assuming a rocky composition for HD 20794 d, we employ a seasonal-latitudinal energy balance model, EOS-ESTM, to explore the impact on surface temperature and habitability of climate factors unconstrained by observational data. To do so, first, we narrow ranges of surface pressures and CO2 fractions that enable potentially habitable conditions. Then, we vary the planetary rotation period, axial tilt, and orbital eccentricity. Finally, we evaluate the impact of the stellar UV radiation field on atmospheric stability and prebiotic chemistry. Our simulations indicate that habitable conditions are generally favored in regimes characterized by high-CO2 concentrations and elevated atmospheric pressure. Habitability also increases with higher axial obliquity (up to the point where an equatorial ice belt forms) and with longer rotation periods. We conclude that HD 20794 d can potentially maintain temperate surface conditions with modest seasonal temperature variations over a wide variety of planetary, orbital, and atmospheric conditions. Although no transits have yet been detected, our results underscore the importance of pursuing further observations of this benchmark system.
{"title":"Climates and Habitability of the Eccentric Super-Earth HD 20794 d: A Multi-parametric Investigation","authors":"Lorenzo Biasiotti, Paolo Simonetti, Riccardo Spinelli, Stavro L. Ivanovski, Lorenzo Calderone, Federico Dogo, Giovanna Jerse, Sergio Monai and Giovanni Vladilo","doi":"10.3847/1538-4357/ae56f7","DOIUrl":"https://doi.org/10.3847/1538-4357/ae56f7","url":null,"abstract":"HD 20794 d is one of the best examples of a super-Earth planet in the habitable zone of a Sun-like star. Notably, due to the high eccentricity (e = 0.45 ) it partially lies in the conservative habitable zone, suggesting a dynamically variable climate. The system’s proximity (d = 6.0414 ± 0.0028 pc) makes it a high-priority target for future atmospheric characterization via direct imaging and positions HD 20794 d as an ideal benchmark for understanding the potential climate states of eccentric exoplanets. Assuming a rocky composition for HD 20794 d, we employ a seasonal-latitudinal energy balance model, EOS-ESTM, to explore the impact on surface temperature and habitability of climate factors unconstrained by observational data. To do so, first, we narrow ranges of surface pressures and CO2 fractions that enable potentially habitable conditions. Then, we vary the planetary rotation period, axial tilt, and orbital eccentricity. Finally, we evaluate the impact of the stellar UV radiation field on atmospheric stability and prebiotic chemistry. Our simulations indicate that habitable conditions are generally favored in regimes characterized by high-CO2 concentrations and elevated atmospheric pressure. Habitability also increases with higher axial obliquity (up to the point where an equatorial ice belt forms) and with longer rotation periods. We conclude that HD 20794 d can potentially maintain temperate surface conditions with modest seasonal temperature variations over a wide variety of planetary, orbital, and atmospheric conditions. Although no transits have yet been detected, our results underscore the importance of pursuing further observations of this benchmark system.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"38 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147682048","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-14DOI: 10.3847/1538-4357/ae4725
Indrani Das, Shantanu Basu, Nagayoshi Ohashi, Eduard Vorobyov and Yusuke Aso
The observations of protostellar systems show a transition in the radial profile of specific angular momentum (and rotational velocity), as evolving from (vϕ ∼ r−1) in the infalling-rotating envelope to j ∝ r1/2 (vϕ ∼ r −1/2) in the Keplerian disk. We employ global MHD disk simulations of gravitational collapse starting from a supercritical prestellar core, that forms a disk and envelope structure in a self-consistent manner, in order to determine the physics of the envelope–disk transition zone (EnDTranZ). Our results show that the transition from the infalling-rotating envelope to Keplerian disk happens through a jump in the j − r profile, spanning over a finite radial width, which is characterized by the positive local gravitational torques. The outer edge of the EnDTranZ is identified where the radial infall speed (vr) begins a sharp decline in magnitude and j begins a transition from toward j ∼ r1/2. Moving radially inward, the centrifugal radius (rCR) is defined where vϕ first transitions to Keplerian velocity at the disk’s edge. Farther inward of rCR, the model disk develops a super-Keplerian rotation due to self-gravity. The inner edge of EnDTranZ is defined at model centrifugal barrier (rCB) where vr drops to negligible values. Inside rCB, a net negative gravitational torque drives mass accretion onto the protostar. On observational grounds, we identify a jump in the observed j − r profile of class 0/I protostar L1527 IRS for the first time using the ALMA Large Program Early Planet Formation in Embedded Disks (eDisk) data. Comparison with our numerical radial behavior suggests the observed j − r jump serves as a kinematical tracer for the existence of EnDTranZ. Our results offer insights into the observable imprint of angular momentum redistribution mechanisms during star–disk formation.
{"title":"Modeling the Break in the Specific Angular Momentum within the Envelope–Disk Transition Zone","authors":"Indrani Das, Shantanu Basu, Nagayoshi Ohashi, Eduard Vorobyov and Yusuke Aso","doi":"10.3847/1538-4357/ae4725","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4725","url":null,"abstract":"The observations of protostellar systems show a transition in the radial profile of specific angular momentum (and rotational velocity), as evolving from (vϕ ∼ r−1) in the infalling-rotating envelope to j ∝ r1/2 (vϕ ∼ r −1/2) in the Keplerian disk. We employ global MHD disk simulations of gravitational collapse starting from a supercritical prestellar core, that forms a disk and envelope structure in a self-consistent manner, in order to determine the physics of the envelope–disk transition zone (EnDTranZ). Our results show that the transition from the infalling-rotating envelope to Keplerian disk happens through a jump in the j − r profile, spanning over a finite radial width, which is characterized by the positive local gravitational torques. The outer edge of the EnDTranZ is identified where the radial infall speed (vr) begins a sharp decline in magnitude and j begins a transition from toward j ∼ r1/2. Moving radially inward, the centrifugal radius (rCR) is defined where vϕ first transitions to Keplerian velocity at the disk’s edge. Farther inward of rCR, the model disk develops a super-Keplerian rotation due to self-gravity. The inner edge of EnDTranZ is defined at model centrifugal barrier (rCB) where vr drops to negligible values. Inside rCB, a net negative gravitational torque drives mass accretion onto the protostar. On observational grounds, we identify a jump in the observed j − r profile of class 0/I protostar L1527 IRS for the first time using the ALMA Large Program Early Planet Formation in Embedded Disks (eDisk) data. Comparison with our numerical radial behavior suggests the observed j − r jump serves as a kinematical tracer for the existence of EnDTranZ. Our results offer insights into the observable imprint of angular momentum redistribution mechanisms during star–disk formation.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"316 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681744","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-14DOI: 10.3847/1538-4357/ae5180
Joseph L. Hora, Jinyoung K. Noh, Gary J. Melnick, Brandon S. Hensley, Roberta Paladini, Jeong-Eun Lee, Matthew L. N. Ashby, Volker Tolls, Jaeyeong Kim, Michael W. Werner, James J. Bock, Sean Bruton, Shuang-Shuang Chen, Tzu-Ching Chang, Yi-Kuan Chiang, Asantha Cooray, Brendan P. Crill, Ari J. Cukierman, Olivier Doré, Andreas L. Faisst, Zhaoyu Huai, Howard Hui, Woong-Seob Jeong, Miju Kang, Phil M. Korngut, Ho-Gyu Lee, Carey M. Lisse, Daniel C. Masters, Giulia Murgia, Chi H. Nguyen, Zafar Rustamkulov, Ji Yeon Seok, Robin Y. Wen, Yujin Yang and Michael Zemcov
We present some of the first infrared spectral maps acquired by SPHEREx. These maps, which to our knowledge are the largest of their type ever compiled in the near-infrared, reveal multiple strong lines due to interstellar ices and polycyclic aromatic hydrocarbons (PAHs) throughout the Cygnus X and North American Nebula regions. The maps emphasize the strongest features arising from the 3 μm H2O, 4.27 μm CO2, and 4.67 μm CO lines and the 3.28 μm PAH feature, all of which are detected over large areas with complex and filamentary spatial distributions. The ice absorption maps of H2O and CO2 in particular broadly trace dense, cold, and well-shielded regions across Cygnus X, consistent with the established picture of efficient ice formation in dense molecular clouds. The interstellar ice features are also detected abundantly in diffuse absorption over wide areas. The relative strengths of the H2O and CO2 features vary among different lines of sight, indicating possible differences in local physical conditions or chemical variations. The 3.28 μm PAH emission correlates with the emission from the 7.7 and 11.2 μm features but shows small differences that may trace the grain-size distribution and variations in the ambient UV field. SPHEREx all-sky spectral imaging—only a small fraction of which is showcased in this work—will support numerous science investigations, including the structure of the Galaxy, the physics of the interstellar medium, and the chemistry of stars.
{"title":"SPHEREx Widefield Infrared Spectral Mapping of Interstellar Ices and Polycyclic Aromatic Hydrocarbons","authors":"Joseph L. Hora, Jinyoung K. Noh, Gary J. Melnick, Brandon S. Hensley, Roberta Paladini, Jeong-Eun Lee, Matthew L. N. Ashby, Volker Tolls, Jaeyeong Kim, Michael W. Werner, James J. Bock, Sean Bruton, Shuang-Shuang Chen, Tzu-Ching Chang, Yi-Kuan Chiang, Asantha Cooray, Brendan P. Crill, Ari J. Cukierman, Olivier Doré, Andreas L. Faisst, Zhaoyu Huai, Howard Hui, Woong-Seob Jeong, Miju Kang, Phil M. Korngut, Ho-Gyu Lee, Carey M. Lisse, Daniel C. Masters, Giulia Murgia, Chi H. Nguyen, Zafar Rustamkulov, Ji Yeon Seok, Robin Y. Wen, Yujin Yang and Michael Zemcov","doi":"10.3847/1538-4357/ae5180","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5180","url":null,"abstract":"We present some of the first infrared spectral maps acquired by SPHEREx. These maps, which to our knowledge are the largest of their type ever compiled in the near-infrared, reveal multiple strong lines due to interstellar ices and polycyclic aromatic hydrocarbons (PAHs) throughout the Cygnus X and North American Nebula regions. The maps emphasize the strongest features arising from the 3 μm H2O, 4.27 μm CO2, and 4.67 μm CO lines and the 3.28 μm PAH feature, all of which are detected over large areas with complex and filamentary spatial distributions. The ice absorption maps of H2O and CO2 in particular broadly trace dense, cold, and well-shielded regions across Cygnus X, consistent with the established picture of efficient ice formation in dense molecular clouds. The interstellar ice features are also detected abundantly in diffuse absorption over wide areas. The relative strengths of the H2O and CO2 features vary among different lines of sight, indicating possible differences in local physical conditions or chemical variations. The 3.28 μm PAH emission correlates with the emission from the 7.7 and 11.2 μm features but shows small differences that may trace the grain-size distribution and variations in the ambient UV field. SPHEREx all-sky spectral imaging—only a small fraction of which is showcased in this work—will support numerous science investigations, including the structure of the Galaxy, the physics of the interstellar medium, and the chemistry of stars.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"68 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681750","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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