Pub Date : 2024-07-03DOI: 10.1146/annurev-astro-071221-052651
E. Schinnerer, A.K. Leroy
Observations that resolve nearby galaxies into individual regions across multiple phases of the gas–star formation feedback “matter cycle” have provided a sharp new view of molecular clouds, star-formation efficiencies, timescales for region evolution, and stellar feedback. We synthesize these results, covering aspects relevant to the interpretation of observables, and conclude the following: ▪ The observed cloud-scale molecular gas surface density, line width, and internal pressure all reflect the large-scale galactic environment while also appearing mostly consistent with properties of a turbulent medium strongly affected by self-gravity. ▪ Cloud-scale data allow for statistical inference of both evolutionary and physical timescales. These suggest a period of cloud collapse on the order of the free-fall or turbulent crossing time (∼10–30 Myr) followed by forming massive stars and subsequent rapid (≲5 Myr) gas clearing after the onset of star formation. The star-formation efficiency per free-fall time is well determined over thousands of individual regions at εff ≈ 0.5−0.3+0.7%. ▪ The role of stellar feedback is now measured using multiple observational approaches. The net yield is constrained by the requirement to support the vertical weight of the galaxy disk. Meanwhile, the short gas-clearing timescales suggest a large role for presupernova feedback in cloud disruption. This leaves the supernovae free to exert a large influence on the larger galaxy, including stirring turbulence, launching galactic-scale winds, and carving superbubbles.
{"title":"Molecular Gas and the Star-Formation Process on Cloud Scales in Nearby Galaxies","authors":"E. Schinnerer, A.K. Leroy","doi":"10.1146/annurev-astro-071221-052651","DOIUrl":"https://doi.org/10.1146/annurev-astro-071221-052651","url":null,"abstract":"Observations that resolve nearby galaxies into individual regions across multiple phases of the gas–star formation feedback “matter cycle” have provided a sharp new view of molecular clouds, star-formation efficiencies, timescales for region evolution, and stellar feedback. We synthesize these results, covering aspects relevant to the interpretation of observables, and conclude the following: <jats:list list-type=\"bullet\"> <jats:list-item> <jats:label>▪</jats:label> The observed cloud-scale molecular gas surface density, line width, and internal pressure all reflect the large-scale galactic environment while also appearing mostly consistent with properties of a turbulent medium strongly affected by self-gravity. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> Cloud-scale data allow for statistical inference of both evolutionary and physical timescales. These suggest a period of cloud collapse on the order of the free-fall or turbulent crossing time (∼10–30 Myr) followed by forming massive stars and subsequent rapid (≲5 Myr) gas clearing after the onset of star formation. The star-formation efficiency per free-fall time is well determined over thousands of individual regions at ε<jats:sub>ff</jats:sub> ≈ 0.5<jats:sub>−0.3</jats:sub> <jats:sup>+0.7</jats:sup>%. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> The role of stellar feedback is now measured using multiple observational approaches. The net yield is constrained by the requirement to support the vertical weight of the galaxy disk. Meanwhile, the short gas-clearing timescales suggest a large role for presupernova feedback in cloud disruption. This leaves the supernovae free to exert a large influence on the larger galaxy, including stirring turbulence, launching galactic-scale winds, and carving superbubbles. </jats:list-item> </jats:list>","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141521946","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1146/annurev-astro-052722-102740
Todd J. Henry, Wei-Chun Jao
M dwarfs dominate the stellar population, accounting for three of every four stars, the nearest of which is Proxima Centauri, the closest destination beyond our Solar System. These cool stars span large ranges in luminosities (one ten-thousandth to 6% L⊙) and temperatures (2,100–3,900 K) and have spectra dominated by absorption bands of titanium oxide (TiO) and, for the latest spectral types, vanadium oxide (VO). They have masses that span 0.075 to 0.61 M⊙, a factor of eight, which is comparable with a spread in masses for dwarf types mid-B through K. Unlike these more massive stars, in the age of the Universe no M dwarfs have evolved in any significant way. M dwarf systems are multiple roughly one-quarter of the time, with the closest binaries found in orbits that have been circularized via tides for orbital periods of about one week. Unlike any other type of main sequence star, there is a gap in the distribution of M dwarfs near masses of 0.35 M⊙ that pinpoints the separation of partially and fully convective stars, yet both types of M dwarfs are often active, showing both Hα in emission and flares. Many planets are found orbiting M dwarfs, and most of them are terrestrial or neptunian in size, rather than jovian, yet much more work remains to be done to characterize the exoplanet population. Overall, the Solar Neighborhood is dominated by M dwarfs that are likely orbited by many small, as yet unseen, planets—some of which may harbor life very near to that in our Solar System. ▪ M dwarfs account for three of every four stars. ▪ M dwarf counts increase all the way to the end of the main sequence. ▪ M dwarfs are partially radiative at high masses and fully convective at low masses.
M 矮星在恒星群中占主导地位，每四颗恒星中就有三颗是 M 矮星，其中最近的一颗是半人马座比邻星，它是太阳系外最近的目的地。这些冷恒星的光度（万分之一到 6% L⊙）和温度（2,100-3,900 K）跨度很大，光谱以氧化钛（TiO）吸收带为主，最新的光谱类型则以氧化钒（VO）吸收带为主。它们的质量从 0.075 到 0.61 M⊙，相差 8 倍，与中 B 到 K 矮星类型的质量分布相当。M矮星系统大约有四分之一的时间是多重的，最接近的双星的轨道是通过潮汐环绕的，轨道周期大约为一周。与其他任何类型的主序星不同，质量接近 0.35 M⊙的 M 矮星的分布中存在一个缺口，这个缺口将部分对流恒星和完全对流恒星区分开来，但这两种类型的 M 矮星通常都很活跃，都会出现 Hα 发射和耀斑。许多行星被发现环绕着M矮星运行，其中大多数行星的大小是类地行星或海王星，而不是类木行星，但要确定系外行星群的特征，还有许多工作要做。总之，太阳邻近地区主要是 M 矮星，它们的轨道上可能有许多尚未发现的小行星--其中一些可能蕴藏着与太阳系非常接近的生命。 每四颗恒星中就有三颗是 M 矮星。 M矮星的数量一直增加到主序的末端。 ▪ M 矮星在质量高时是部分辐射性的，而在质量低时则是完全对流性的。
{"title":"The Character of M Dwarfs","authors":"Todd J. Henry, Wei-Chun Jao","doi":"10.1146/annurev-astro-052722-102740","DOIUrl":"https://doi.org/10.1146/annurev-astro-052722-102740","url":null,"abstract":"M dwarfs dominate the stellar population, accounting for three of every four stars, the nearest of which is Proxima Centauri, the closest destination beyond our Solar System. These cool stars span large ranges in luminosities (one ten-thousandth to 6% L<jats:sub>⊙</jats:sub>) and temperatures (2,100–3,900 K) and have spectra dominated by absorption bands of titanium oxide (TiO) and, for the latest spectral types, vanadium oxide (VO). They have masses that span 0.075 to 0.61 M<jats:sub>⊙</jats:sub>, a factor of eight, which is comparable with a spread in masses for dwarf types mid-<jats:italic>B</jats:italic> through <jats:italic>K</jats:italic>. Unlike these more massive stars, in the age of the Universe no M dwarfs have evolved in any significant way. M dwarf systems are multiple roughly one-quarter of the time, with the closest binaries found in orbits that have been circularized via tides for orbital periods of about one week. Unlike any other type of main sequence star, there is a gap in the distribution of M dwarfs near masses of 0.35 M<jats:sub>⊙</jats:sub> that pinpoints the separation of partially and fully convective stars, yet both types of M dwarfs are often active, showing both Hα in emission and flares. Many planets are found orbiting M dwarfs, and most of them are terrestrial or neptunian in size, rather than jovian, yet much more work remains to be done to characterize the exoplanet population. Overall, the Solar Neighborhood is dominated by M dwarfs that are likely orbited by many small, as yet unseen, planets—some of which may harbor life very near to that in our Solar System. <jats:list list-type=\"bullet\"> <jats:list-item> <jats:label>▪</jats:label> M dwarfs account for three of every four stars. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> M dwarf counts increase all the way to the end of the main sequence. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> M dwarfs are partially radiative at high masses and fully convective at low masses. </jats:list-item> </jats:list>","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141489490","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-17DOI: 10.1146/annurev-astro-052722-103557
Karin Lind, Anish M. Amarsi
The chemical compositions of stars encode the history of the universe and are thus fundamental for advancing our knowledge of astrophysics and cosmology. However, measurements of elemental abundances ratios, and our interpretations of them, strongly depend on the physical assumptions that dictate the generation of synthetic stellar spectra. Three-dimensional radiation-hydrodynamic (3D RHD) box-in-a-star simulations of stellar atmospheres offer a more realistic representation of surface convection occurring in late-type stars than do traditional one-dimensional (1D) hydrostatic models. As evident from a multitude of observational tests, the coupling of 3D RHD models with line formation in nonlocal thermodynamic equilibrium (non-LTE) today provides a solid foundation for abundance analysis for many elements. This review describes the ongoing and transformational work to advance the state of the art and replace 1D LTE spectrum synthesis with its 3D non-LTE counterpart. In summary: ▪ 3D and non-LTE effects are intricately coupled, and consistent modeling thereof is necessary for high-precision abundances; such modeling is currently feasible for individual elements in large surveys. Mean 3D (〈3D〉) models are not adequate as substitutes. ▪ The solar abundance debate is presently dominated by choices and systematic uncertainties that are not specific to 3D non-LTE modeling. ▪ 3D non-LTE abundance corrections have a profound impact on our understanding of FGK-type stars, exoplanets, and the nucleosynthetic origins of the elements.
{"title":"Three-Dimensional Non–Local Thermodynamic Equilibrium Abundance Analyses of Late-Type Stars","authors":"Karin Lind, Anish M. Amarsi","doi":"10.1146/annurev-astro-052722-103557","DOIUrl":"https://doi.org/10.1146/annurev-astro-052722-103557","url":null,"abstract":"The chemical compositions of stars encode the history of the universe and are thus fundamental for advancing our knowledge of astrophysics and cosmology. However, measurements of elemental abundances ratios, and our interpretations of them, strongly depend on the physical assumptions that dictate the generation of synthetic stellar spectra. Three-dimensional radiation-hydrodynamic (3D RHD) box-in-a-star simulations of stellar atmospheres offer a more realistic representation of surface convection occurring in late-type stars than do traditional one-dimensional (1D) hydrostatic models. As evident from a multitude of observational tests, the coupling of 3D RHD models with line formation in nonlocal thermodynamic equilibrium (non-LTE) today provides a solid foundation for abundance analysis for many elements. This review describes the ongoing and transformational work to advance the state of the art and replace 1D LTE spectrum synthesis with its 3D non-LTE counterpart. In summary: <jats:list list-type=\"bullet\"> <jats:list-item> <jats:label>▪</jats:label> 3D and non-LTE effects are intricately coupled, and consistent modeling thereof is necessary for high-precision abundances; such modeling is currently feasible for individual elements in large surveys. Mean 3D (〈3D〉) models are not adequate as substitutes. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> The solar abundance debate is presently dominated by choices and systematic uncertainties that are not specific to 3D non-LTE modeling. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> 3D non-LTE abundance corrections have a profound impact on our understanding of FGK-type stars, exoplanets, and the nucleosynthetic origins of the elements. </jats:list-item> </jats:list>","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2024-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141530256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-07DOI: 10.1146/annurev-astro-071221-052732
H. Cuppen, H. Linnartz, S. Ioppolo
Ice mantles play a crucial role in shaping the astrochemical inventory of molecules during star and planet formation. Small-scale molecular processes have a profound impact on large-scale astronomical evolution. The areas of solid-state laboratory astrophysics and computational chemistry involve the study of these processes. We review laboratory efforts in ice spectroscopy, methodological advances and challenges, and laboratory and computational studies of ice physics and ice chemistry. We place the last of these in context with ice evolution from clouds to disks. Three takeaway messages from this review are: ▪ Laboratory and computational studies allow interpretation of astronomical ice spectra in terms of identification, ice morphology, and local environmental conditions as well as the formation of the involved chemical compounds. ▪ A detailed understanding of the underlying processes is needed to build reliable astrochemical models to make predictions about abundances in space. ▪ The relative importance of the different ice processes studied in the laboratory and computationally changes during the process of star and planet formation.
{"title":"Laboratory and Computational Studies of Interstellar Ices","authors":"H. Cuppen, H. Linnartz, S. Ioppolo","doi":"10.1146/annurev-astro-071221-052732","DOIUrl":"https://doi.org/10.1146/annurev-astro-071221-052732","url":null,"abstract":"Ice mantles play a crucial role in shaping the astrochemical inventory of molecules during star and planet formation. Small-scale molecular processes have a profound impact on large-scale astronomical evolution. The areas of solid-state laboratory astrophysics and computational chemistry involve the study of these processes. We review laboratory efforts in ice spectroscopy, methodological advances and challenges, and laboratory and computational studies of ice physics and ice chemistry. We place the last of these in context with ice evolution from clouds to disks. Three takeaway messages from this review are: \u0000\u0000 \u0000 ▪\u0000 Laboratory and computational studies allow interpretation of astronomical ice spectra in terms of identification, ice morphology, and local environmental conditions as well as the formation of the involved chemical compounds.\u0000 \u0000 \u0000 ▪\u0000 A detailed understanding of the underlying processes is needed to build reliable astrochemical models to make predictions about abundances in space.\u0000 \u0000 \u0000 ▪\u0000 The relative importance of the different ice processes studied in the laboratory and computationally changes during the process of star and planet formation.\u0000 \u0000 \u0000","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2024-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141373258","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-09DOI: 10.1146/annurev-astro-052920-103752
John J. Tobin, Patrick D. Sheehan
The envelopes and disks that surround protostars reflect the initial conditions of star and planet formation and govern the assembly of stellar masses. Characterizing these structures requires observations that span the near-IR to centimeter wavelengths. Consequently, the past two decades have seen progress driven by numerous advances in observational facilities across this spectrum, including the Spitzer Space Telescope, Herschel Space Observatory, the Atacama Large Millimeter/submillimeter Array, and a host of other ground-based interferometers and single-dish radio telescopes. ▪ Nearly all protostars have well-formed circumstellar disks that are likely to be rotationally supported; the ability to detect a disk around a protostar is more a question of spatial resolution rather than whether or not a disk is present. ▪ The disks around protostars have inherently higher millimeter/submillimeter luminosities as compared to disks around more-evolved pre-main-sequence stars, though there may be systematic variations between star-forming regions. ▪ The envelopes around protostars are inherently asymmetric, and streamers emphasize that mass flow through the envelopes to the disks may not be homogeneous. ▪ The current mass distribution of protostars may be impacted by selection bias given that it is skewed toward solar-mass protostars, which is inconsistent with the stellar initial mass function.
{"title":"An Observational View of Structure in Protostellar Systems","authors":"John J. Tobin, Patrick D. Sheehan","doi":"10.1146/annurev-astro-052920-103752","DOIUrl":"https://doi.org/10.1146/annurev-astro-052920-103752","url":null,"abstract":"The envelopes and disks that surround protostars reflect the initial conditions of star and planet formation and govern the assembly of stellar masses. Characterizing these structures requires observations that span the near-IR to centimeter wavelengths. Consequently, the past two decades have seen progress driven by numerous advances in observational facilities across this spectrum, including the <jats:italic>Spitzer Space Telescope</jats:italic>, <jats:italic>Herschel Space Observatory</jats:italic>, the Atacama Large Millimeter/submillimeter Array, and a host of other ground-based interferometers and single-dish radio telescopes. <jats:list list-type=\"bullet\"> <jats:list-item> <jats:label>▪</jats:label> Nearly all protostars have well-formed circumstellar disks that are likely to be rotationally supported; the ability to detect a disk around a protostar is more a question of spatial resolution rather than whether or not a disk is present. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> The disks around protostars have inherently higher millimeter/submillimeter luminosities as compared to disks around more-evolved pre-main-sequence stars, though there may be systematic variations between star-forming regions. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> The envelopes around protostars are inherently asymmetric, and streamers emphasize that mass flow through the envelopes to the disks may not be homogeneous. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> The current mass distribution of protostars may be impacted by selection bias given that it is skewed toward solar-mass protostars, which is inconsistent with the stellar initial mass function. </jats:list-item> </jats:list>","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140902950","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-23DOI: 10.1146/annurev-astro-052622-031748
P. Hennebelle, M.Y. Grudić
Stars are among the most fundamental structures of our Universe. They comprise most of the baryonic and luminous mass of galaxies; synthesize heavy elements; and inject mass, momentum, and energy into the interstellar medium. They are also home to the planets. Because stellar properties are primarily decided by their mass, the so-called stellar initial mass function (IMF) is critical to the structuring of our Universe. We review the various physical processes and theories that have been put forward as well as the numerical simulations that have been carried out to explain the origin of the stellar IMF. Key messages from this review include the following: ▪ Gravity and turbulence most likely determine the power-law, high-mass part of the IMF. ▪ Depending of the Mach number and the density distribution, several regimes are possible, including ΓIMF ≃ 0, −0.8, −1, or −1.3, where dN/d log M ∝ MΓIMF. These regimes are likely universal; however, the transition between these regimes is not. ▪ Protostellar jets can play a regulating influence on the IMF by injecting momentum into collapsing clumps and unbinding gas. ▪ The peak of the IMF may be a consequence of dust opacity and molecular hydrogen physics at the origin of the first hydrostatic core. This depends weakly on large-scale environmental conditions such as radiation, magnetic field, turbulence, or metallicity. This likely constitutes one reason for the relative universality of the IMF.
恒星是我们宇宙中最基本的结构之一。它们构成了星系的大部分重子质量和发光质量；合成重元素；并向星际介质注入质量、动量和能量。它们也是行星的家园。由于恒星的性质主要由其质量决定，因此所谓的恒星初始质量函数（IMF）对我们宇宙的结构至关重要。我们回顾了为解释恒星初始质量函数的起源而提出的各种物理过程和理论，以及进行的数值模拟。本综述的主要信息包括以下几点： 引力和湍流最有可能决定 IMF 的幂律、高质部分。 根据马赫数和密度分布的不同，可能存在几种状态，包括 ΓIMF ≃0、-0.8、-1 或-1.3，其中 dN/d log M ∝ M ΓIMF 。这些状态很可能是普遍存在的；但是，这些状态之间的转换并不普遍。 原恒星喷流可以通过向坍缩团块注入动量和解除气体束缚来对 IMF 起调节作用。 IMF的峰值可能是尘埃不透明度和分子氢物理学在第一个静水核心起源处的结果。这对辐射、磁场、湍流或金属性等大尺度环境条件的依赖性很弱。这可能是 IMF 具有相对普遍性的原因之一。
{"title":"The Physical Origin of the Stellar Initial Mass Function","authors":"P. Hennebelle, M.Y. Grudić","doi":"10.1146/annurev-astro-052622-031748","DOIUrl":"https://doi.org/10.1146/annurev-astro-052622-031748","url":null,"abstract":"Stars are among the most fundamental structures of our Universe. They comprise most of the baryonic and luminous mass of galaxies; synthesize heavy elements; and inject mass, momentum, and energy into the interstellar medium. They are also home to the planets. Because stellar properties are primarily decided by their mass, the so-called stellar initial mass function (IMF) is critical to the structuring of our Universe. We review the various physical processes and theories that have been put forward as well as the numerical simulations that have been carried out to explain the origin of the stellar IMF. Key messages from this review include the following: <jats:list list-type=\"bullet\"> <jats:list-item> <jats:label>▪</jats:label> Gravity and turbulence most likely determine the power-law, high-mass part of the IMF. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> Depending of the Mach number and the density distribution, several regimes are possible, including Γ<jats:sub>IMF</jats:sub> ≃ 0, −0.8, −1, or −1.3, where d<jats:italic>N</jats:italic>/d log <jats:italic>M</jats:italic> ∝ <jats:italic>M</jats:italic> <jats:sup>Γ<jats:sub>IMF</jats:sub> </jats:sup>. These regimes are likely universal; however, the transition between these regimes is not. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> Protostellar jets can play a regulating influence on the IMF by injecting momentum into collapsing clumps and unbinding gas. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> The peak of the IMF may be a consequence of dust opacity and molecular hydrogen physics at the origin of the first hydrostatic core. This depends weakly on large-scale environmental conditions such as radiation, magnetic field, turbulence, or metallicity. This likely constitutes one reason for the relative universality of the IMF. </jats:list-item> </jats:list>","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2024-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140640384","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-19DOI: 10.1146/annurev-astro-071221-052705
Tilman Birnstiel
Over the past decade, advancement of observational capabilities, specifically the Atacama Large Millimeter/submillimeter Array (ALMA) and Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instruments, alongside theoretical innovations like pebble accretion, have reshaped our understanding of planet formation and the physics of protoplanetary disks. Despite this progress, mysteries persist along the winded path of micrometer-sized dust, from the interstellar medium, through transport and growth in the protoplanetary disk, to becoming gravitationally bound bodies. This review outlines our current knowledge of dust evolution in circumstellar disks, yielding the following insights: ▪ Theoretical and laboratory studies have accurately predicted the growth of dust particles to sizes that are susceptible to accumulation through transport processes like radial drift and settling. ▪ Critical uncertainties in that process remain the level of turbulence, the threshold collision velocities at which dust growth stalls, and the evolution of dust porosity. ▪ Symmetric and asymmetric substructure are widespread. Dust traps appear to be solving several long-standing issues in planet formation models, and they are observationally consistent with being sites of active planetesimal formation. ▪ In some instances, planets have been identified as the causes behind substructures. This underlines the need to study earlier stages of disks to understand how planets can form so rapidly. In the future, better probes of the physical conditions in optically thick regions, including densities, turbulence strength, kinematics, and particle properties will be essential for unraveling the physical processes at play.
{"title":"Dust Growth and Evolution in Protoplanetary Disks","authors":"Tilman Birnstiel","doi":"10.1146/annurev-astro-071221-052705","DOIUrl":"https://doi.org/10.1146/annurev-astro-071221-052705","url":null,"abstract":"Over the past decade, advancement of observational capabilities, specifically the Atacama Large Millimeter/submillimeter Array (ALMA) and Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instruments, alongside theoretical innovations like pebble accretion, have reshaped our understanding of planet formation and the physics of protoplanetary disks. Despite this progress, mysteries persist along the winded path of micrometer-sized dust, from the interstellar medium, through transport and growth in the protoplanetary disk, to becoming gravitationally bound bodies. This review outlines our current knowledge of dust evolution in circumstellar disks, yielding the following insights: <jats:list list-type=\"bullet\"> <jats:list-item> <jats:label>▪</jats:label> Theoretical and laboratory studies have accurately predicted the growth of dust particles to sizes that are susceptible to accumulation through transport processes like radial drift and settling. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> Critical uncertainties in that process remain the level of turbulence, the threshold collision velocities at which dust growth stalls, and the evolution of dust porosity. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> Symmetric and asymmetric substructure are widespread. Dust traps appear to be solving several long-standing issues in planet formation models, and they are observationally consistent with being sites of active planetesimal formation. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> In some instances, planets have been identified as the causes behind substructures. This underlines the need to study earlier stages of disks to understand how planets can form so rapidly. </jats:list-item> </jats:list> In the future, better probes of the physical conditions in optically thick regions, including densities, turbulence strength, kinematics, and particle properties will be essential for unraveling the physical processes at play.","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2024-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140621520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-19DOI: 10.1146/annurev-astro-052722-104109
Deidre A. Hunter, Bruce G. Elmegreen, Suzanne C. Madden
Dwarf irregular (dIrrs) galaxies are among the most common type of galaxy in the Universe. They typically have gas-rich, low surface-brightness, metal-poor, and relatively thick disks. Here, we summarize the current state of our knowledge of the interstellar medium (ISM), including atomic, molecular, and ionized gas, along with their dust properties and metals. We also discuss star-formation feedback, gas accretion, and mergers with other dwarfs that connect the ISM to the circumgalactic and intergalactic media. We highlight one of the most persistent mysteries: the nature of pervasive gas that is yet undetected as either molecular or cold hydrogen, the “dark gas.” Some highlights include the following: ▪ Significant quantities of Hi are in far-outer gas disks. ▪ Cold Hi in dIrrs would be molecular in the Milky Way, making the chemical properties of star-forming clouds significantly different. ▪ Stellar feedback has a much larger impact in dIrrs than in spiral galaxies. ▪ The escape fraction of ionizing photons is significant, making dIrrs a plausible source for reionization in the early Universe. ▪ Observations suggest a significantly higher abundance of hydrogen (H2 or cold Hi) associated with CO in star-forming regions than that traced by the CO alone.
矮不规则（dIrrs）星系是宇宙中最常见的星系类型之一。它们通常具有富含气体、低表面亮度、贫金属和相对较厚的星盘。在这里，我们总结了我们目前对星际介质（ISM）的了解，包括原子、分子和电离气体，以及它们的尘埃特性和金属。我们还讨论了恒星形成反馈、气体吸积以及与其他矮星的合并等问题，这些问题将星际介质与环银河系和星际介质联系在一起。我们将重点讨论最持久的谜团之一：尚未被探测到的分子气体或冷氢气--"暗气体"--的性质。其中一些亮点如下： 大量 Hi 存在于更远的气体盘中。 暗气体盘中的冷氢在银河系中是分子氢，这使得恒星形成云的化学性质大为不同。 恒星反馈对二轨道星系的影响比对螺旋星系的影响大得多。 电离光子的逃逸率很高，这使得 dIrrs 成为早期宇宙再电离的一个可信来源。 观测结果表明，在恒星形成区，与 CO 相关联的氢（H2 或冷 Hi）的丰度明显高于 CO 单独追踪到的丰度。
{"title":"The Interstellar Medium in Dwarf Irregular Galaxies","authors":"Deidre A. Hunter, Bruce G. Elmegreen, Suzanne C. Madden","doi":"10.1146/annurev-astro-052722-104109","DOIUrl":"https://doi.org/10.1146/annurev-astro-052722-104109","url":null,"abstract":"Dwarf irregular (dIrrs) galaxies are among the most common type of galaxy in the Universe. They typically have gas-rich, low surface-brightness, metal-poor, and relatively thick disks. Here, we summarize the current state of our knowledge of the interstellar medium (ISM), including atomic, molecular, and ionized gas, along with their dust properties and metals. We also discuss star-formation feedback, gas accretion, and mergers with other dwarfs that connect the ISM to the circumgalactic and intergalactic media. We highlight one of the most persistent mysteries: the nature of pervasive gas that is yet undetected as either molecular or cold hydrogen, the “dark gas.” Some highlights include the following: <jats:list list-type=\"symbol\"> <jats:list-item> <jats:label>▪</jats:label> Significant quantities of H<jats:sc>i</jats:sc> are in far-outer gas disks. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> Cold H<jats:sc>i</jats:sc> in dIrrs would be molecular in the Milky Way, making the chemical properties of star-forming clouds significantly different. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> Stellar feedback has a much larger impact in dIrrs than in spiral galaxies. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> The escape fraction of ionizing photons is significant, making dIrrs a plausible source for reionization in the early Universe. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> Observations suggest a significantly higher abundance of hydrogen (H<jats:sub>2</jats:sub> or cold H<jats:sc>i</jats:sc>) associated with CO in star-forming regions than that traced by the CO alone. </jats:list-item> </jats:list>","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2024-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140621600","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-19DOI: 10.1146/annurev-astro-071422-101131
Michel Mayor
Human interest in the possibility of other worlds in the Universe has existed for over two millennia. In recent centuries, this question has been translated into the following terms: Are there planetary systems linked to stars other than the Sun? Developments in astronomical instrumentation have transformed this philosophical dream into a new, vibrant chapter in astronomy. This article describes my journey that started over 40 years ago with the exploration of the dynamics of our Galaxy, that brought astonishing scientific progress to which my collaborators and I have contributed, and eventually led to the amazing discovery of the plurality of worlds.
{"title":"Plurality of Worlds","authors":"Michel Mayor","doi":"10.1146/annurev-astro-071422-101131","DOIUrl":"https://doi.org/10.1146/annurev-astro-071422-101131","url":null,"abstract":"Human interest in the possibility of other worlds in the Universe has existed for over two millennia. In recent centuries, this question has been translated into the following terms: Are there planetary systems linked to stars other than the Sun? Developments in astronomical instrumentation have transformed this philosophical dream into a new, vibrant chapter in astronomy. This article describes my journey that started over 40 years ago with the exploration of the dynamics of our Galaxy, that brought astonishing scientific progress to which my collaborators and I have contributed, and eventually led to the amazing discovery of the plurality of worlds.","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2024-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140621606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-19DOI: 10.1146/annurev-astro-052722-105936
Pablo Marchant, Julia Bodensteiner
Massive stars play a major role in the evolution of their host galaxies and serve as important probes of the distant Universe. It has been established that the majority of massive stars reside in close binaries and interact with their companion stars during their lifetimes. Such interactions drastically alter their life cycles and complicate our understanding of their evolution, but are also responsible for the production of interesting and exotic interaction products. ▪ Extensive observation campaigns with well-understood detection sensitivities have enabled the conversion of observed properties into intrinsic characteristics, facilitating a direct comparison to theory. ▪ Studies of large samples of massive stars in our Galaxy and the Magellanic Clouds have unveiled new types of interaction products, providing critical constraints on the mass transfer phase and the formation of compact objects. ▪ The direct detection of gravitational waves has revolutionized the study of stellar mass compact objects, providing a new window to study massive star evolution. Their formation processes are, however, still unclear. The known sample of compact object mergers will increase by orders of magnitude in the coming decade, which is vastly outgrowing the number of stellar-mass compact objects detected through electromagnetic radiation.
{"title":"The Evolution of Massive Binary Stars","authors":"Pablo Marchant, Julia Bodensteiner","doi":"10.1146/annurev-astro-052722-105936","DOIUrl":"https://doi.org/10.1146/annurev-astro-052722-105936","url":null,"abstract":"Massive stars play a major role in the evolution of their host galaxies and serve as important probes of the distant Universe. It has been established that the majority of massive stars reside in close binaries and interact with their companion stars during their lifetimes. Such interactions drastically alter their life cycles and complicate our understanding of their evolution, but are also responsible for the production of interesting and exotic interaction products. <jats:list list-type=\"bullet\"> <jats:list-item> <jats:label>▪</jats:label> Extensive observation campaigns with well-understood detection sensitivities have enabled the conversion of observed properties into intrinsic characteristics, facilitating a direct comparison to theory. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> Studies of large samples of massive stars in our Galaxy and the Magellanic Clouds have unveiled new types of interaction products, providing critical constraints on the mass transfer phase and the formation of compact objects. </jats:list-item> <jats:list-item> <jats:label>▪</jats:label> The direct detection of gravitational waves has revolutionized the study of stellar mass compact objects, providing a new window to study massive star evolution. Their formation processes are, however, still unclear. The known sample of compact object mergers will increase by orders of magnitude in the coming decade, which is vastly outgrowing the number of stellar-mass compact objects detected through electromagnetic radiation. </jats:list-item> </jats:list>","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2024-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140621588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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