On February 15, the Laser Interferometer Gravitational-Wave Observatory (LIGO) scientific Collaboration announced that it has received a total of $35 million in funding support from the US National Science Foundation, the UK Agency for Research and Innovation, and the Australian Research Council to carry out major upgrades to its two detectors.
LIGO heard gravitational waves, ripples in space-time, for the first time in human history in 2015. The upgraded LIGO will be called Advanced LIGO Plus, or ALIGO+, and is expected to start operating in 2024.
Frans Cordova, director of the National Science Foundation, said the upgrade will guarantee LIGO's continued leadership in gravitational wave science for the next 10 years.
Gravitational waves will be "heard" every day
Since 2015, LIGO has successfully detected 11 gravitational wave events, 10 from black hole merges and one from neutron stars. After the upgrade of ALIGO+, the detection capability will be further enhanced, and the detectable space will be 7 times higher than the present.
LIGO director David Reitz, a professor at the California Institute of Technology, said that with ALIGO+, it will be possible to detect gravitational waves generated by black holes on a daily basis. The detection of gravitational waves generated by the merger of neutron stars, although only once so far, will become more frequent in the future.
This is mainly because the upgraded ALIGO+ will apply quantum compressed light and new mirror coating technology.
"The current design sensitivity of LIGO is dominated by quantum noise, and quantum compressed light is used to reduce quantum noise." Miao Haixing, a member of the LIGO scientific cooperation organization who teaches at the School of Physics and Astronomy at the University of Birmingham in the United Kingdom, told Science and Technology Daily.
According to Miu Haixing, quantum compressed light can be understood as a "redistribution" of quantum fluctuations. ALIGO+ will apply frequency-dependent quantum compressed light, that is, to simultaneously reduce the low-frequency quantum radiation pressure noise and the high-frequency quantum shot noise, with the goal of doubling the amplitude sensitivity of ALIGO+.
As for the new mirror coating technology, Miu Haixing revealed that the material of the coating will not change, but through the new processing technology, the thermal noise of the mirror coating will be greatly reduced.
"This is equivalent to ALIGO+ using better 'noise-canceling' headphones, so we can hear clearer 'musical details' and weaker' mysterious songs. '" Fan Xilong, a member of LIGO scientific cooperation organization and a special researcher at the School of Physical Science and Technology of Wuhan University, said in an interview with Science and Technology Daily.
It could challenge theories of stellar and population evolution
"LIGO will definitely detect more and more gravitational waves over time. We can do this by increasing the sensitivity of the detector, rather than just observing and waiting." Professor Wang Yixiong of the University of Glasgow, a member of LIGO scientific Cooperation organization, said in an interview with Science and Technology Daily.
According to Wang Yixiong, ALIGO+ will detect the binary neutron star merger at a distance of 300 million parsecs (Mpc), while the detection distance of the binary black hole merger is more than half the radius of the universe.
"This means that ALIGO+ can detect more distant and numerous signals from the same type of gravitational wave source, such as the gravitational waves generated by the merger of binary neutron stars." Fan Xilong said.
Fan Xilong told reporters that more signals of the same kind can allow scientists to understand these systems from a statistical point of view, such as the mass distribution and spin distribution of binary neutron stars, like a "census" of relevant celestial bodies in the universe. With the help of statistical information, combined with stellar and population evolution theory, we can predict the evolution process of binary neutron stars.
At the same time, more distant gravitational wave signals have a greater chance of encountering other objects in the universe, resulting in strong gravitational lensing of gravitational waves. By studying this phenomenon, it will be possible to make important progress in a series of important questions such as the speed of gravitational waves, the Hubble constant, and the distribution of dark matter in galaxies.
"What I personally look forward to most is that ALIGO+ can observe more massive binary black holes at greater distances, so that the initial assumptions of a series of star and population evolution theories about binary star proportions, initial mass functions, etc., may be challenged." Fan Xilong said.
According to ALIGO+ project leader Michael Zucker, ALIGO+ will achieve the same number of detections in less than one week as it has in the past three years. In Fan Xilong's view, with the continuous upgrading of gravitational wave detectors, gravitational wave signals also need more detailed and complex data processing processes to mine.
"The rapid processing of large numbers of gravitational wave signals in the future will be a new area of research." Fan Xilong told the Science and Technology Daily reporter that in addition to using faster computers and improving the speed of traditional algorithms, machine learning technology has also begun to play a big role in the field of gravitational wave data processing.
Source: Science and Technology Daily