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Modelling the electromagnetic emission of kilonovae enables the mass, velocity and composition (with some heavy elements) of the ejecta from a neutron-star merger to be derived from the observations. When neutron stars collide Merging neutron stars are potential sources of gravitational waves and have long been predicted to produce jets of material as part of a low-luminosity transient known as a 'kilonova'. There is growing evidence that neutron-star mergers also give rise to short, hard gamma-ray bursts. A group of papers in this issue report observations of a transient associated with the gravitational-wave event GW170817—a signature of two neutron stars merging and a gamma-ray flash—that was detected in August 2017. The observed gamma-ray, X-ray, optical and infrared radiation signatures support the predictions of an outflow of matter from double neutron-star mergers and present a clear origin for gamma-ray bursts. Previous predictions differ over whether the jet material would combine to form light or heavy elements. These papers now show that the early part of the outflow was associated with lighter elements whereas the later observations can be explained by heavier elements, the origins of which have been uncertain. However, one paper (by Stephen Smartt and colleagues) argues that only light elements are needed for the entire event. Additionally, Eleonora Troja and colleagues report X-ray observations and radio emissions that suggest that the 'kilonova' jet was observed off-axis, which could explain why gamma-ray-burst detections are seen as dim. The cosmic origin of elements heavier than iron has long been uncertain. Theoretical modelling 1 , 2 , 3 , 4 , 5 , 6 , 7 shows that the matter that is expelled in the violent merger of two neutron stars can assemble into heavy elements such as gold and platinum in a process known as rapid neutron capture (r-process) nucleosynthesis. The radioactive decay of isotopes of the heavy elements is predicted 8 , 9 , 10 , 11 , 12 to power a distinctive thermal glow (a ‘kilonova’). The discovery of an electromagnetic counterpart to the gravitational-wave source 13 GW170817 represents the first opportunity to detect and scrutinize a sample of freshly synthesized r-process elements 14 , 15 , 16 , 17 , 18 . Here we report models that predict the electromagnetic emission of kilonovae in detail and enable the mass, velocity and composition of ejecta to be derived from observations. We compare the models to the optical and infrared radiation associated with the GW170817 event to argue that the observed source is a kilonova. We infer the presence of two distinct components of ejecta, one composed primarily of light (atomic mass number less than 140) and one of heavy (atomic mass number greater than 140) r-process elements. The ejected mass and a merger rate inferred from GW170817 imply that such mergers are a dominant mode of r-process production in the Universe.

Star formation at a rate of more than 15 solar masses a year has been observed inside a massive outflow of gas from a nearby galaxy; this could also be happening inside other galactic outflows. Star birth in gas flows Massive, galactic-scale outflows of molecular gas with the physical conditions necessary to form stars have recently been observed and several models predict that star formation could ignite within the outflow itself. Roberto Maiolino et al . report spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448 and at an inferred rate exceeding 15 times the mass of the Sun per year. This new mode of star formation might be occurring in other galactic outflows and could have implications for the morphological evolution of galaxies, while contributing to the population of high-velocity stars. Recent observations have revealed massive galactic molecular outflows 1 , 2 , 3 that may have the physical conditions (high gas densities 4 , 5 , 6 ) required to form stars. Indeed, several recent models predict that such massive outflows may ignite star formation within the outflow itself 7 , 8 , 9 , 10 , 11 . This star-formation mode, in which stars form with high radial velocities, could contribute to the morphological evolution of galaxies 12 , to the evolution in size and velocity dispersion of the spheroidal component of galaxies 11 , 13 , and would contribute to the population of high-velocity stars, which could even escape the galaxy 13 . Such star formation could provide in situ chemical enrichment of the circumgalactic and intergalactic medium (through supernova explosions of young stars on large orbits), and some models also predict it to contribute substantially to the star-formation rate observed in distant galaxies 9 . Although there exists observational evidence for star formation triggered by outflows or jets into their host galaxy, as a consequence of gas compression, evidence for star formation occurring within galactic outflows is still missing. Here we report spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448. The inferred star-formation rate in the outflow is larger than 15 solar masses per year. Star formation may also be occurring in other galactic outflows, but may have been missed by previous observations owing to the lack of adequate diagnostics 14 , 15 .

The C[sub.3] H[sub.3] NO family of isomers is relevant in astrochemistry, even though its members are still elusive in the interstellar medium. To identify the best candidate for astronomical detection within this family, we developed a new computational protocol based on the minimum-energy principle. This approach aims to identify the most stable isomer of the family and consists of three steps. The first step is an extensive investigation that characterizes the vast number of compounds having the C[sub.3] H[sub.3] NO chemical formula, employing density functional theory for this purpose. The second step is an energy refinement, which is used to select isomers and relies on coupled cluster theory. The last step is a structural improvement with a final energy refinement that provides improved energies and a large set of accurate spectroscopic parameters for all isomers lying within 30 kJ mol[sup.−1] above the most stable one. According to this protocol, vinylisocyanate is the most stable isomer, followed by oxazole, which is about 5 kJ mol[sup.−1] higher in energy. The other stable species are pyruvonitrile, cyanoacetaldehyde, and cyanovinylalcohol. For all of these species, new computed rotational and vibrational spectroscopic data are reported, which complement those already available in the literature or fill current gaps.

This book emphasizes the interfaces between the seemingly diverse fields of biochemistry and cosmochemistry. This link provides the basis for understanding of how life began on Earth and whether this process is universal. This area of study helps us to understand the long-asked questions of whether there is life beyond Earth, and whether our planet is one example of how life could originate and evolve on other worlds. Biochemistry demonstrates how life has originated and evolved into complex life forms ranging from small microbial forms such as bacteria to the upright walking creatures we call humans. Cosmochemistry explores whether the origin of life, and its evolution into complex life forms, is possible in other worlds. The focus is on amino acids which play an essential role in biochemistry on Earth and also are present elsewhere in our solar system. The book explores these issues through personal anecdotes from the author's long and varied scientific career.

As part of a project to investigate the volatilities of so-called \"moderately volatile elements\" such as Zn, In, Tl, Ga, Ag, Sb, Pb, and Cl during planetary formation, we began by re-calculating the condensation temperatures of these elements from a solar gas at 10-4 bar. Our calculations highlighted three areas where currently available estimates of condensation temperature could be improved. One of these is the nature of mixing behavior of many important trace elements when dissolved in major condensates such as silicates, Fe-rich metals, and sulfides. Nonideal solution of the trace elements can alter (generally lower) condensation temperatures by up to 500 K. Second, recent measurements of the halogen contents of CI chondrites (Clay et al. 2017) indicate that the solar system abundance of chlorine is significantly overestimated, and this affects the stabilities of gaseous complexes of many elements of interest. Finally, we have attempted to improve on previous estimates of the free energies of chlorine-bearing solids since the temperature of chlorine condensation has an important control on the condensation temperatures of many trace elements. Our result for the 50% condensation temperature of chlorine, 472 K is nearly 500 K lower than the result of Lodders (2003), and this means that the HCl content of the solar gas at temperatures <900 K is higher than previously estimated. We based our calculations on the program PHEQ (Wood and Hashimoto 1993), which we modified to perform condensation calculations for the elements H, O, C, S, Na, Ca, Mg, Al, Si, Fe, F, Cl, P, N, Ni, and K by free energy minimization. Condensation calculations for minor elements were then performed using the output from PHEQ in conjunction with relevant thermodynamic data. We made explicit provision for nonidealities using information from phase diagrams, heat of solution measurements, partitioning data and by using the lattice strain model for FeS and ionic solids and the Miedema model for solutions in solid Fe. We computed the relative stabilities of gaseous chloride, sulfide, oxide, and hydroxide species of the trace elements of interest and used these, as appropriate in our condensation calculations. In general, our new 50% condensation temperatures are similar to or, because of the modifications noted above, lower than those of Lodders (2003).

As the chase for new elements slows, scientists focus on deepening their understanding of the superheavy ones they already know. As the chase for new elements slows, scientists focus on deepening their understanding of the superheavy ones they already know.

The Presolar Grain Database (PGD) contains the vast majority of isotope data (published and unpublished) on presolar grains and was first released as a collection of spreadsheets in 2009. It has been a helpful tool used by many researchers in cosmochemistry and astrophysics. However, over the years, accumulated errors compromised major parts of the PGD. Here, we provide a fresh start, with the PGD for silicon carbide (SiC) grains rebuilt from the ground up. We also provide updated rules for SiC grain type classification to unify previous efforts, taking into account newly discovered grain types. We also define a new grain type D, which includes some grains previously classified as ungrouped. Future work will focus on rebuilding the PGD for other kinds of presolar grains: graphite, oxides, silicates, and rarer phases.