On 2017 August 17, gravitational waves were detected from a binary neutron star merger, GW170817, along with a coincident short gamma-ray burst,GRB170817A. An optical transient source, Swope Supernova Survey 17a (SSS17a), was subsequently identified as the counterpart of this event. We present ultraviolet, optical and infrared light curves of SSS17a extending from 10.9 hours to 18 days post-merger. We constrain the radioactively-powered transient resulting from the ejection of neutron-rich material. The fast rise of the light curves, subsequent decay, and rapid color evolution are consistent with multiple ejecta components of differing lanthanide abundance. The late-time light curve in-2 dicates that SSS17a produced at least ∼0.05 solar masses of heavy elements, demonstrating that neutron star mergers play a role in r-process nucleosynthesis in the Universe.The discovery of gravitational waves (GWs) from coalescing binary black holes by the Laser Interferometer Gravitational Wave Observatory (LIGO) has transformed the study of compact objects in the Universe (1, 2). Unlike black holes, merging neutron stars are expected to produce electromagnetic radiation. The electromagnetic signature of such an event can provide more information than the GW signal alone: constraining location of the source, reducing the degeneracies in GW parameter estimation (3), probing the expansion rate of the Universe (4,5), and producing a more complete picture of the merger process (6, 7).Short gamma-ray bursts (GRBs) have long been expected to result from neutron star mergers (8, 9), and therefore would be a natural electromagnetic counterpart to GWs (10). Unfortunately, their emission is beamed, so that it may not intersect our line of sight (11). The possibility that only a small fraction of GRBs may be detectable has motivated theoretical and observational searches for more-isotropic electromagnetic signatures, such as an astronomical transient powered by the radioactive decay of neutron-rich ejecta from the merger. (12)(13)(14)(15)(16)(17). Referred to as a macronova or kilonova, the detection of these events would provide information on the origin of many of the heaviest elements in the periodic table (18).It has long been realized that approximately half of the elements heavier than iron are created via r-process nucleosynthesis-the capture of neutrons onto lighter seed nuclei on a timescale more rapid than β-decay pathways (19,20). However, it is less clear where the r-process predominantly occurs, namely whether the primary sources of these elements are core-collapse supernovae or compact binary mergers (black hole-neutron star or neutron starneutron star) (21,22). For supernovae, direct detection of the electromagnetic signatures from r-process nucleosynthesis is obscured by the much larger luminosity originating from hydrogen 3 recombination (for hydrogen-rich supernovae) or nickel-56 and cobalt-56 decay (for hydrogenpoor supernovae). By contrast, it may be possible to measure the r-process nucleosynthesis after a compact ob...

On 17 August 2017, Swope Supernova Survey 2017a (SSS17a) was discovered as the optical counterpart of the binary neutron star gravitational wave event GW170817. We report time-series spectroscopy of SSS17a from 11.75 hours until 8.5 days after the merger. Over the first hour of observations, the ejecta rapidly expanded and cooled. Applying blackbody fits to the spectra, we measured the photosphere cooling from [Formula: see text] to [Formula: see text] kelvin, and determined a photospheric velocity of roughly 30% of the speed of light. The spectra of SSS17a began displaying broad features after 1.46 days and evolved qualitatively over each subsequent day, with distinct blue (early-time) and red (late-time) components. The late-time component is consistent with theoretical models of r-process-enriched neutron star ejecta, whereas the blue component requires high-velocity, lanthanide-free material.

NGC 1266 is a nearby lenticular galaxy that harbors a massive outflow of molecular gas powered by the mechanical energy of an active galactic nucleus (AGN). It has been speculated that such outflows hinder star formation (SF) in their host galaxies, providing a form of feedback to the process of galaxy formation. Previous studies, however, indicated that only jets from extremely rare, high power quasars or radio galaxies could impart significant feedback on their hosts. Here we present detailed observations of the gas and dust continuum of NGC 1266 at millimeter wavelengths. Our observations show that molecular gas is being driven out of the nuclear region atṀ out ≈ 110 M ⊙ yr −1 , of which the vast majority cannot escape the nucleus. Only 2 M ⊙ yr −1 is actually capable of escaping the galaxy. Most of the molecular gas that remains is very inefficient at forming stars. The far-infrared emission is dominated by an ultra-compact ( 50 pc) source that could either be powered by an AGN or by an ultra-compact starburst. The ratio of the SF surface density (Σ SFR ) to the gas surface density (Σ H2 ) indicates that SF is suppressed by a factor of ≈ 50 compared to normal star-forming galaxies if all gas is forming stars, and ≈150 for the outskirt (98%) dense molecular gas if the central region is is powered by an ultra-compact starburst. The AGN-driven bulk outflow could account for this extreme suppression by hindering the fragmentation and gravitational collapse necessary to form stars through a process of turbulent injection. This result suggests that even relatively common, low-power AGNs are able to alter the evolution of their host galaxies as their black holes grow onto the M-σ relation.