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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| First observation of gravitational waves | 3/6 | https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves | reference | science, encyclopedia | 2026-05-05T10:01:16.701964+00:00 | kb-cron |
The event happened at a luminosity distance of 440+160−180 megaparsecs (determined by the amplitude of the signal), or 1.4±0.6 billion light years, corresponding to a cosmological redshift of 0.093+0.030−0.036 (90% credible intervals). Analysis of the signal along with the inferred redshift suggested that it was produced by the merger of two black holes with masses of 35+5−3 times and 30+3−4 times the mass of the Sun (in the source frame), resulting in a post-merger black hole of 62+4−3 M☉. The mass–energy of the missing 3.0±0.5 M☉ was radiated away in the form of gravitational waves. During the final 20 milliseconds of the merger, the power of the radiated gravitational waves peaked at about 3.6×1049 watts or 526 dBm – 50 times greater than the combined power of all light radiated by all the stars in the observable universe. The amount of this energy that was received by the entire planet Earth was about 36 billion joules, of which only a small amount was absorbed. Across the 0.2-second duration of the detectable signal, the relative tangential (orbiting) velocity of the black holes increased from 30% to 60% of the speed of light. The orbital frequency of 75 Hz (half the gravitational wave frequency) means that the objects were orbiting each other at a distance of only 350 km by the time they merged. The phase changes to the signal's polarization allowed calculation of the objects' orbital frequency, and taken together with the amplitude and pattern of the signal, allowed calculation of their masses and therefore their extreme final velocities and orbital separation (distance apart) when they merged. That information showed that the objects had to be black holes, as any other kind of known objects with these masses would have been physically larger and therefore merged before that point, or would not have reached such velocities in such a small orbit. The highest observed neutron star mass is 2 M☉, with a conservative upper limit for the mass of a stable neutron star of 3 M☉, so that a pair of neutron stars would not have had sufficient mass to account for the merger (unless exotic alternatives exist, for example, boson stars), while a black hole-neutron star pair would have merged sooner, resulting in a final orbital frequency that was not so high. The decay of the waveform after it peaked was consistent with the damped oscillations of a black hole as it relaxed to a final merged configuration. Although the inspiral motion of compact binaries can be described well from post-Newtonian calculations, the strong gravitational field merger stage can only be solved in full generality by large-scale numerical relativity simulations. In the improved model and analysis, the post-merger object is found to be a rotating Kerr black hole with a spin parameter of 0.68+0.05−0.06, i.e. one with 2/3 of the maximum possible angular momentum for its mass. The two stars which formed the two black holes were likely formed about 2 billion years after the Big Bang with masses of between 40 and 100 times the mass of the Sun.
=== Location in the sky === Gravitational wave instruments are whole-sky monitors with little ability to resolve signals spatially. A network of such instruments is needed to locate the source in the sky through triangulation. With only the two LIGO instruments in observational mode, GW150914's source location could only be confined to an arc on the sky. This was done via analysis of the 6.9+0.5−0.4 ms time-delay, along with amplitude and phase consistency across both detectors. This analysis produced a credible region of 150 deg2 with a probability of 50% or 610 deg2 with a probability of 90% located mainly in the Southern Celestial Hemisphere, in the rough direction of (but much farther than) the Magellanic Clouds. For comparison, the area of the constellation Orion is 594 deg2.