Nature. 2017 Nov 2;551(7678):85-88. doi: 10.1038/nature24471. Epub 2017 Oct 16.
On 17 August 2017, the Advanced LIGO and Virgo detectors observed the gravitational-wave event GW170817-a strong signal from the merger of a binary neutron-star system. Less than two seconds after the merger, a γ-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO-Virgo-derived location of the gravitational-wave source. This sky region was subsequently observed by optical astronomy facilities, resulting in the identification of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first 'multi-messenger' astronomical observation. Such observations enable GW170817 to be used as a 'standard siren' (meaning that the absolute distance to the source can be determined directly from the gravitational-wave measurements) to measure the Hubble constant. This quantity represents the local expansion rate of the Universe, sets the overall scale of the Universe and is of fundamental importance to cosmology. Here we report a measurement of the Hubble constant that combines the distance to the source inferred purely from the gravitational-wave signal with the recession velocity inferred from measurements of the redshift using the electromagnetic data. In contrast to previous measurements, ours does not require the use of a cosmic 'distance ladder': the gravitational-wave analysis can be used to estimate the luminosity distance out to cosmological scales directly, without the use of intermediate astronomical distance measurements. We determine the Hubble constant to be about 70 kilometres per second per megaparsec. This value is consistent with existing measurements, while being completely independent of them. Additional standard siren measurements from future gravitational-wave sources will enable the Hubble constant to be constrained to high precision.
2017 年 8 月 17 日，高级 LIGO 和 Virgo 探测器观测到引力波事件 GW170817——这是来自双中子星系统合并的强信号。在合并后不到两秒钟，在与 LIGO-Virgo 推断的引力波源位置一致的天空区域内检测到了伽马射线暴（GRB 170817A）。随后，该天空区域被光学天文设施观测到，导致在 NGC 4993 星系附近约十个角秒的范围内识别出了一个光学暂现源信号。GW170817 在引力波和电磁波中的同时探测代表了首个“多信使”天文观测。这种观测使 GW170817 能够作为“标准的 sirens”（这意味着可以直接从引力波测量中确定源的绝对距离），用于测量哈勃常数。这个量代表了宇宙的局部膨胀率，设定了宇宙的整体规模，对宇宙学具有根本重要性。在这里，我们报告了一种测量哈勃常数的方法，该方法结合了仅从引力波信号推断出的源距离以及从电磁数据中测量的红移推断出的退行速度。与以前的测量方法不同，我们的方法不需要使用宇宙“距离阶梯”：引力波分析可以直接用于估计到宇宙尺度的光度距离，而无需使用中间的天文距离测量。我们确定哈勃常数约为 70 千米/秒/百万秒差距。这个值与现有测量值一致，同时完全独立于它们。未来引力波源的更多标准 sirens 测量将使哈勃常数能够被高精度地约束。
