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During the dawn of chemistry.sup.1,2, when the temperature of the young Universe had fallen below some 4,000 kelvin, the ions of the light elements produced in Big Bang nucleosynthesis recombined in reverse order of their ionization potential. With their higher ionization potentials, the helium ions He.sup.2+ and He.sup.+ were the first to combine with free electrons, forming the first neutral atoms; the recombination of hydrogen followed. In this metal-free and low-density environment, neutral helium atoms formed the Universe's first molecular bond in the helium hydride ion HeH.sup.+ through radiative association with protons. As recombination progressed, the destruction of HeH.sup.+ created a path to the formation of molecular hydrogen. Despite its unquestioned importance in the evolution of the early Universe, the HeH.sup.+ ion has so far eluded unequivocal detection in interstellar space. In the laboratory the ion was discovered.sup.3 as long ago as 1925, but only in the late 1970s was the possibility that HeH.sup.+ might exist in local astrophysical plasmas discussed.sup.4-7. In particular, the conditions in planetary nebulae were shown to be suitable for producing potentially detectable column densities of HeH.sup.+. Here we report observations, based on advances in terahertz spectroscopy.sup.8,9 and a high-altitude observatory.sup.10, of the rotational ground-state transition of HeH.sup.+ at a wavelength of 149.1 micrometres in the planetary nebula NGC 7027. This confirmation of the existence of HeH.sup.+ in nearby interstellar space constrains our understanding of the chemical networks that control the formation of this molecular ion, in particular the rates of radiative association and dissociative recombination. Studies of the planetary nebula NGC 7027, using an upgraded spectrometer onboard a high-altitude observatory, have identified the rotational ground-state transition of the helium hydride ion--the first molecule to form after the Big Bang and an essential precursor to molecular hydrogen., Author(s): Rolf Güsten [sup.1] , Helmut Wiesemeyer [sup.1] , David Neufeld [sup.2] , Karl M. Menten [sup.1] , Urs U. Graf [sup.3] , Karl Jacobs [sup.3] , Bernd Klein [sup.1] [...]

CK Vulpeculae was observed in outburst in 1670-1672 (ref. 1), but no counterpart was seen until 1982, when a bipolar nebula was found at its location (1-3). Historically, CK Vul has been considered to be a nova (Nova Vul 1670), but its similarity to 'red transients', which are more luminous than classical novae and thought to be the results of stellar collisions (4), has re-opened the question of CK Vul's status (5,6). Red transients cool to resemble late M-type stars, surrounded by circumstellar material rich in molecules and dust (7-9). No stellar source has been seen in CK Vul, though a radio continuum source was identified at the expansion centre of the nebula (3). Here we report that CK Vul is surrounded by chemically rich molecular gas in the form of an outflow, as well as dust. The gas has peculiar isotopic ratios, revealing that CK Vul's composition was strongly enhanced by the nuclear ashes of hydrogen burning. The chemical composition cannot be reconciled with a nova or indeed any other known explosion. In addition, the mass of the surrounding gas is too large for a nova, though the conversion from observations of CO to a total mass is uncertain. We conclude that CK Vul is best explained as the remnant of a merger of two stars., Using the submillimetre-wave Atacama Pathfinder Experiment (APEX) telescope, located in the Chilean Andes, we discovered bright and chemically complex molecular gas in emission, which has not been observed before in [...]

The age of dense interstellar cloud cores, where stars and planets form, is a crucial parameter in star formation and difficult to measure. Some models predict rapid collapse (1,2), whereas others predict timescales of more than one million years (ref. 3). One possible approach to determining the age is through chemical changes as cloud contraction occurs, in particular through indirect measurements of the ratio of the two spin isomers (ortho/para) of molecular hydrogen, [H.sub.2], which decreases monotonically with age (4-6). This has been done for the dense cloud core L183, for which the deuterium fractionation of diazenylium ([N.sub.2][H.sup.+]) was used as a chemical clock to infer (7) that the core has contracted rapidly (on a timescale of less than 700,000 years). Among astronomically observable molecules, the spin isomers of the deuterated trihydrogen cation, ortho-[H.sub.2][D.sup.+] and para-[H.sub.2][D.sup.+], have the most direct chemical connections to [H.sub.2] (refs 8-12) and their abundance ratio provides a chemical clock that is sensitive to greater cloud core ages. So far this ratio has not been determined because para-[H.sub.2][D.sup.+] is very difficult to observe. The detection of its rotational ground-state line has only now become possible thanks to accurate measurements of its transition frequency in the laboratory (13), and recent progress in instrumentation technology (14,15). Here we report observations of ortho- and para-[H.sub.2][D.sup.+] emission and absorption, respectively, from the dense cloud core hosting IRAS 16293-2422 A/B, a group of nascent solar-type stars (with ages of less than 100,000 years). Using the ortho/para ratio in conjunction with chemical models, we find that the dense core has been chemically processed for at least one million years. The apparent discrepancy with the earlier [N.sub.2][H.sup.+] work (7) arises because that chemical clock turns off sooner than the [H.sub.2][D.sup.+] clock, but both results imply that star-forming dense cores have ages of about one million years, rather than 100,000 years., We detected the ground-state rotational transition of the para spin isomer of the deuterated trihydrogen cation (para-[H.sub.2][D.sup.+]) at 1.370085 THz (ref. 13) (wavelength λ = 219 µm) towards IRAS 16293-2422 [...]

The Hubble Deep Field provides one of the deepest multiwave-length views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time (1). An early map of the Hubble Deep Field at a wavelength of 850 micrometres, which is sensitive to dust emission powered by star formation, revealed the brightest source in the field, dubbed HDF 850.1 (ref. 2). For more than a decade, and despite significant efforts, no counterpart was found at shorter wavelengths, and it was not possible to determine its redshift, size or mass (3-7). Here we report a redshift of z = 5.183 for HDF 850.1, from a millimetre-wave molecular line scan. This places HDF 850.1 in a galaxy overdensity at z ≅ 5.2, corresponding to a cosmic age of only 1.1 billion years after the Big Bang. This redshift is significantly higher than earlier estimates (3,4,6,8) and higher than those of most of the hundreds of submillimetre-bright galaxies identified so far. The source has a star-formation rate of 850 solar masses per year and is spatially resolved on scales of 5 kiloparsecs, with an implied dynamical mass of about 1.3 X 10 (11) solar masses, a significant fraction of which is present in the form of molecular gas. Despite our accurate determination of redshift and position, a counterpart emitting starlight remains elusive., We have obtained a full-frequency scan of the 3-mm band towards the Hubble Deep Field using the IRAM (Institut de Radioastronomie Millinietrique) Plateau de Bure Interferometer. The observations covered the [...]

High-mass stars on disk Crucial aspects about the life cycle of high-mass stars remain unclear, in particular the early evolutionary phases. For instance, it is still debated whether high-mass stars form in the same way as low- and intermediate-mass stars, through disk accretion, and if so, whether the structure of these disks would differ from their low-mass counterparts. New observations from the Very Large Telescope Interferometer at the European Southern Observatory now reveal a hot compact disk around a massive young stellar object, the protostar IRAS 13481-6124. The image shows an elongated structure about 13 × 19 astronomical units in size, consistent with a disk seen at an inclination angle of ~45°, the properties of which are qualitatively and quantitatively similar to the disks observed during the formation of low-mass stars. Circumstellar disks are an essential ingredient of the formation of low-mass stars, but it is unclear whether they are also required for the formation of stars more massive than about 10 solar masses. Clear observational evidence is needed, for example the detection of dusty disks around massive young stellar objects. Here, near-infrared interferometric observations are reported that spatially resolve the distribution of hot material around a high-mass young stellar object. Circumstellar disks are an essential ingredient of the formation.sup.1 of low-mass stars. It is unclear, however, whether the accretion-disk paradigm can also account for the formation of stars more massive than about 10 solar masses.sup.2, in which strong radiation pressure might halt mass infall.sup.3,4. Massive stars may form by stellar merging.sup.5, although more recent theoretical investigations suggest that the radiative-pressure limit may be overcome by considering more complex, non-spherical infall geometries.sup.6,7. Clear observational evidence, such as the detection of compact dusty disks.sup.8 around massive young stellar objects, is needed to identify unambiguously the formation mode of the most massive stars. Here we report near-infrared interferometric observations that spatially resolve the astronomical-unit-scale distribution of hot material around a high-mass (~20 solar masses) young stellar object. The image shows an elongated structure with a size of ~13 × 19 astronomical units, consistent with a disk seen at an inclination angle of ~45°. Using geometric and detailed physical models, we found a radial temperature gradient in the disk, with a dust-free region less than 9.5 astronomical units from the star, qualitatively and quantitatively similar to the disks observed in low-mass star formation. Perpendicular to the disk plane we observed a molecular outflow and two bow shocks, indicating that a bipolar outflow emanates from the inner regions of the system., Author(s): Stefan Kraus [sup.1] , Karl-Heinz Hofmann [sup.2] , Karl M. Menten [sup.2] , Dieter Schertl [sup.2] , Gerd Weigelt [sup.2] , Friedrich Wyrowski [sup.2] , Anthony Meilland [sup.2] [sup.3] [...]

During the dawn of chemistry1,2, when the temperature of the young Universe had fallen below some 4,000 kelvin, the ions of the light elements produced in Big Bang nucleosynthesis recombined in reverse order of their ionization potential. With their higher ionization potentials, the helium ions He2+ and He+ were the first to combine with free electrons, forming the first neutral atoms; the recombination of hydrogen followed. In this metal-free and low-density environment, neutral helium atoms formed the Universe's first molecular bond in the helium hydride ion HeH+ through radiative association with protons. As recombination progressed, the destruction of HeH+ created a path to the formation of molecular hydrogen. Despite its unquestioned importance in the evolution of the early Universe, the HeH+ ion has so far eluded unequivocal detection in interstellar space. In the laboratory the ion was discovered3 as long ago as 1925, but only in the late 1970s was the possibility that HeH+ might exist in local astrophysical plasmas discussed4–7. In particular, the conditions in planetary nebulae were shown to be suitable for producing potentially detectable column densities of HeH+. Here we report observations, based on advances in terahertz spectroscopy8,9 and a high-altitude observatory10, of the rotational ground-state transition of HeH+ at a wavelength of 149.1 micrometres in the planetary nebula NGC 7027. This confirmation of the existence of HeH+ in nearby interstellar space constrains our understanding of the chemical networks that control the formation of this molecular ion, in particular the rates of radiative association and dissociative recombination. Studies of the planetary nebula NGC 7027, using an upgraded spectrometer onboard a high-altitude observatory, have identified the rotational ground-state transition of the helium hydride ion—the first molecule to form after the Big Bang and an essential precursor to molecular hydrogen. [ABSTRACT FROM AUTHOR]

The age of dense interstellar cloud cores, where stars and planets form, is a crucial parameter in star formation and difficult to measure. Some models predict rapid collapse, whereas others predict timescales of more than one million years (ref. 3). One possible approach to determining the age is through chemical changes as cloud contraction occurs, in particular through indirect measurements of the ratio of the two spin isomers (ortho/para) of molecular hydrogen, H2, which decreases monotonically with age. This has been done for the dense cloud core L183, for which the deuterium fractionation of diazenylium (N2H+) was used as a chemical clock to infer that the core has contracted rapidly (on a timescale of less than 700,000 years). Among astronomically observable molecules, the spin isomers of the deuterated trihydrogen cation, ortho-H2D+ and para-H2D+, have the most direct chemical connections to H2 (refs 8, 9, 10, 11, 12) and their abundance ratio provides a chemical clock that is sensitive to greater cloud core ages. So far this ratio has not been determined because para-H2D+ is very difficult to observe. The detection of its rotational ground-state line has only now become possible thanks to accurate measurements of its transition frequency in the laboratory, and recent progress in instrumentation technology. Here we report observations of ortho- and para-H2D+ emission and absorption, respectively, from the dense cloud core hosting IRAS 16293-2422 A/B, a group of nascent solar-type stars (with ages of less than 100,000 years). Using the ortho/para ratio in conjunction with chemical models, we find that the dense core has been chemically processed for at least one million years. The apparent discrepancy with the earlier N2H+ work arises because that chemical clock turns off sooner than the H2D+ clock, but both results imply that star-forming dense cores have ages of about one million years, rather than 100,000 years. [ABSTRACT FROM AUTHOR]