Gravitationswellen -ein leichtes Zittern der raumzeitVor 1,3 Milliarden Jahren: Seit langer Zeit schon haben sich in einer fernen Galaxie zwei schwarze Löcher umkreist, Gebilde von so ungeheurer Dichte, das selbst Licht ihrer Schwerkraft nicht mehr entweichen kann und von ihnen eingefangen wird. Seit Jahrmillionen haben sie bei ihrem Tanz umeinander mit ihrer masse die Raumzeit verformt und dabei Gravitationswellen abgestrahlt. ihr Abstand wurde dabei immer kleiner, ihre Geschwindigkeit immer höher, bis sie schließlich unter einem gewaltigen Ausbruch von Gravitationswellen zu einem einzelnen schwarzen Loch verschmelzen. Später werden wir diese Wellen GW150914 nennen. Für einen kurzen Augenblick wird durch sie mehr Leistung abgestrahlt als von allen Sternen im gesamten sichtbaren Universum in Form von elektromagnetischer Strahlung zusammen. Diese Gravitationswellen rasen mit Lichtgeschwindigkeit durch das Weltall und lassen auf ihrem Weg die Raumzeit erzittern.25. November 1915: GW150914 ist schon längst in unserer milchstra-

We report the observation of a gravitational-wave signal produced by the coalescence of two stellar-mass black holes. The signal, GW151226, was observed by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on December 26, 2015 at 03:38:53 UTC. The signal was initially identified within 70 s by an online matched-filter search targeting binary coalescences. Subsequent off-line analyses recovered GW151226 with a network signal-to-noise ratio of 13 and a significance greater than 5σ. The signal persisted in the LIGO frequency band for approximately 1 s, increasing in frequency and amplitude over about 55 cycles from 35 to 450 Hz, and reached a peak gravitational strain of 3.4 −0.04 . All uncertainties define a 90% credible interval. This second gravitational-wave observation provides improved constraints on stellar populations and on deviations from general relativity.

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ∼ 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40 − 8 + 8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M ⊙ . An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ∼ 40 Mpc ) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ∼ 9 and ∼ 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

On 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB170817A and GW170817 occurring by chance is 5.0 10 8 -. We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB170817A provides new insight into fundamental physics and the origin of short GRBs. We use the observed time delay of 1.74 0.05 s +  () between GRB170817A and GW170817 to: (i) constrain the difference between the speed of gravity and the speed of light to be between 3 10 15 -´and 7 10 16 +´times the speed of light, (ii) place new bounds on the violation of Lorentz invariance, (iii) present a new test of the equivalence principle by constraining the Shapiro delay between gravitational and electromagnetic radiation. We also use the time delay to constrain the size and bulk Lorentz factor of the region emitting the gamma-rays. GRB170817A is the closest short GRB with a known distance, but is between 2 and 6 orders of magnitude less energetic than other bursts with measured redshift. A new generation of gamma-ray detectors, and subthreshold searches in existing detectors, will be essential to detect similar short bursts at greater distances. Finally, we predict a joint detection rate for the Fermi Gamma-ray Burst Monitor and the Advanced LIGO and Virgo detectors of 0.1-1.4 per year during the 2018-2019 observing run and 0.3-1.7 per year at design sensitivity.

GW170817: Measurements of neutron star radii and equation of state The LIGO Scientific Collaboration and The Virgo Collaboration On August 17, 2017, the LIGO and Virgo observatories made the first direct detection of gravitational waves from the coalescence of a neutron star binary system. The detection of this gravitational wave signal, GW170817, offers a novel opportunity to directly probe the properties of matter at the extreme conditions found in the interior of these stars. The initial, minimal-assumption analysis of the LIGO and Virgo data placed constraints on the tidal effects of the coalescing bodies, which were then translated to constraints on neutron star radii. Here, we expand upon previous analyses by working under the hypothesis that both bodies were neutron stars that are described by the same equation of state and have spins within the range observed in Galactic binary neutron stars. Our analysis employs two methods: the use of equation-of-state-insensitive relations between various macroscopic properties of the neutron stars and the use of an efficient parameterization of the defining function p(ρ) of the equation of state itself. From the LIGO and Virgo data alone and the first method, we measure the two neutron star radii as R 1 = 10.8 +2.0 −1.7 km for the heavier star and R 2 = 10.7 +2.1 −1.5 km for the lighter star at the 90% credible level. If we additionally require that the equation of state supports neutron stars with masses larger than 1.97 M as required from electromagnetic observations and employ the equation of state parametrization, we further constrain R 1 = 11.9 +1.4 −1.4 km and R 2 = 11.9 +1.4 −1.4 km at the 90% credible level. Finally, we obtain constraints on p(ρ) at supranuclear densities, with pressure at twice nuclear saturation density measured at 3.5 +2.7 −1.7 × 10 34 dyn cm −2 at the 90% level.