2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
The next observation period at the LIGO and Virgo gravitational-wave observatories will begin on April 1 and will last for a year. The expected accuracy during the new session should increase significantly compared to the previous one, which will allow, at the redistribution of possibilities, to record the mergers of astronomical objects in a much larger volume of the Universe. The corresponding press release is published on the Virgo website.
LIGO and Virgo are installations designed to search for gravitational waves from merging black holes and neutron stars. They are optical L-shaped optical interferometers, on the shoulders of which laser beams are constantly moving, reflecting from mirrors at the ends of the tunnels. After multiple reflections, the rays converge in the center and interfere. The passage of a gravitational wave slightly changes the distance between the mirrors, due to which a phase difference accumulates between lasers from different arms, which is calculated from the change in the interference pattern.
The existence of gravitational waves is predicted by the general theory of relativity (GR). According to it, with the accelerated motion of masses, in many cases, distortions of space-time will be generated, which will wave-like away from the source at the speed of light. The first indirect confirmation of gravitational waves was the observation of a double pulsar, that is, a binary system of a neutron star observed as a pulsar and a compact companion, revolving around a common center of mass at a relatively short distance. Detailed studies have revealed a gradual decrease in the orbital period of the pulsar, which agrees with high accuracy with the energy loss predicted by general relativity for the emission of gravitational waves.
In early 2016, it was announced that the first direct registration of a gravitational wave by the LIGO observatory took place in 2015. At the moment, 11 such events have been recorded, of which 10 are mergers of black holes, and one is a merger of neutron stars, which was also observed by ordinary telescopes that detect electromagnetic radiation. For these discoveries, the Nobel Prize in Physics was awarded in 2017.
The masses of the initial and final components of merging systems of black holes (above) and neutron stars (below), the gravitational waves from which were caught by the LIGO / Virgo detectors. Data for December 2018
The new report says that after improvements, which consisted of replacing lasers, mirrors and some other components, the observatories are ready to begin a new stage of observations, the third in a row, thanks to which it was named O3. The combined sensitivity of a pair of LIGO antennas should increase by about 40 percent over the previous O2 session, while Virgo should double. In addition to improving the individual installations, O3 will be the first observation period in which LIGO and Virgo will fully work together for a long time. Scientists estimate that now mergers of neutron stars will be able to register at distances of up to 170 megaparsecs against 110 during the last session.
The key engineering change was the replacement of lasers and mirrors. The radiation sources now deliver twice the power, the Virgo mirrors are supported by silica filaments instead of steel cables, and five of the eight LIGO mirrors have been replaced. Scientists will also begin to use new methods of dealing with quantum noise associated with random fluctuations in the number of photons in laser pulses. Physicists decided to take advantage of the developments of colleagues involved in the small gravitational telescope GEO600 - they began to use squeezed light technology several years ago, which makes it possible to reduce the inaccuracy in determining the phase of radiation associated with the fundamental Heisenberg uncertainty principle by increasing the amplitude error. Since in the operation of gravitational antennas, it is the phase that determines the interference of the beams that is primarily important, then such a modification can also increase the accuracy of the entire installation.
Scientists expect to receive a large amount of new information during the next observation period. In particular, the registration of mergers of black holes should become commonplace: according to optimistic estimates, such events will be recorded with a frequency of about once a week. However, the most valuable results are expected from mergers of rapidly rotating asymmetric neutron stars - such events are difficult to record, but the possibility of simultaneous observation of both gravitational and electromagnetic signals potentially allows the most detailed study of the physics of extremely strong gravitational fields. The new gravitational wave warning system should send notifications available to other scientists within five minutes, which will allow other devices to quickly point to the alleged source of the signal.
Scientists have long been planning to improve their installations after a new observation session. In particular, there is the LIGO A + improvement program, as well as the LIGO Voyager project, which will turn the installation into a third generation detector. By the end of O3, the Japanese antenna KAGRA should join the observations. There are preliminary agreements with the government of India on the construction of an analogue of LIGO in this country. Even more ambitious is the European Einstein Telescope project. According to the plans, it will be a triangular detector, which will allow investigating additional parameters of gravitational waves, but it is much more complicated in technical terms.
With new installations, there will be new technical problems. For example, new sources of noise that were previously much weaker than others will become significant. To combat them, scientists have created a device that can reproduce these quantum noises at room temperature. More details about the registration of gravitational waves can be found in the materials "On the crest of the metric tensor", "Sharpener for a quantum pencil" and "Thinner than a proton".
