2023-05-29 14:45:13
Since the first detection of gravitational waves in 2015, multiple black hole collisions have been recorded by the Laser Interferometer Gravitational-Wave Observatory
(LIGO) and the partner observatories, Virgo and KAGRA. Recent updates allow the detectors to be even more sensitive. A new observation campaign was started on May 24 for a period of 20 months. It aims to explore the deepest secrets of the Universe.
Predicted in 1915 by Albert Einstein, as part of his general theory of relativity, gravitational waves are ripples in space-time, generated by particularly violent cosmic events, such as a collision of neutron stars or a merger of black holes. The first direct detection of these waves took place in 2015, by LIGO interferometers — a joint project of MIT, Caltech, and many other institutions. This observatory consists of two detectors, one located in Washington State, the other in Louisiana.
Over the past two years, the installation has benefited from numerous improvements, which make the detectors even more sensitive. To exploit these new capacities, a new observation campaign of the LIGO-Virgo-KAGRA (LVK) collaboration started on May 24, for a period of 20 months – including a two-month break for maintenance, during which other work will be undertaken to further improve the performance of the instrument. Only LIGO is active at the moment; Virgo, the observatory located in Italy, and KAGRA, located in Japan, will join this campaign later this year, following some updates.
Increased sensitivity of approximately 30%
The first gravitational wave signals were detected in 2015, following the collision of two black holes whose mass was regarding 30 times greater than that of the Sun (this was also the first observation of a merger of binary black holes ). The ripple in space-time generated by the event — located more than a billion light-years away — caused a tiny change in length (on the order of one-thousandth of the width of a proton!) at the level of the four kilometer arm of the interferometer.
Aerial view of the LIGO Observatory site in Hanford, Washington, and its two four-kilometer-long arms. © Wikimedia Commons
In 2017, LIGO and Virgo detected the gravitational waves linked to the merger of two neutron stars : the event caused an explosion, called kilonova, which was observed by dozens of telescopes around the world. This was the first time that gravitational waves and electromagnetic radiation emanating from the same source were observed simultaneously.
So far, the LVK collaboration has detected more than 80 black hole mergers, two probable neutron star mergers, and a few events that were most likely black hole mergers with neutron stars.
Thanks to recent updates, LIGO’s detectors show an increased sensitivity of approximately 30%. This means they can observe a larger fraction of the Universe, up to 5 billion light-years away, and are able to detect gravitational waves at an even higher rate. Michael Landry, head of the LIGO observatory at the Hanford Nuclear Complex in Washington State, estimates that several hundred events will be detected during the campaign.
This increased sensitivity will allow scientists to collect more data on black holes and neutron stars, and “increases the chances of finding something new,” said Jess McIver, deputy spokesperson for the LIGO Science Collaboration; they will also have the opportunity to better test the general theory of relativity, which until now has never been faulted.
Determine the origin of black hole binaries
Scientists hope to detect new types of gravitational wave sources, including an isolated neutron star, explains Landry to Live
Science : « It would produce a continuous gravitational wave signal, present for the lifetime of the experiment. If we detect it, it will be a considerable event ».
They also hope to support their knowledge of binary systems of black holes, which remain one of the largest sources of gravitational waves, but whose origin remains unclear. The data collected by the interferometers might, for example, help to determine whether these systems originated from two separate stars, born together, which evolved simultaneously into supernovae or whether they are two isolated black holes which ended up approaching each other. each other.
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Albert Lazzarini, deputy director of the LIGO laboratory, says that a number of candidate events have already been identified even before the official start of the campaign. ” Most of these events involve black hole binary systems, although one may include a neutron star. Rates seem in line with expectations “, did he declare. On May 18, LIGO detected what might be a collision between a neutron star and a black hole. ” Assuming the candidate is of astrophysical origin, the probability that the lighter compact object is consistent with a neutron star mass is >99%», say the researchers.
The observatory is expected to benefit from further upgrades by the end of the decade, which will enable it to detect several cosmic fusion events each day. And that’s not all: other observatories will be added to the LVK collaboration in a few years, such as the LIGO-Indiaor le
Cosmic Explorer et the einstein telescope. Eventually, this vast network of detectors will make it possible to probe the fabric of space-time at very high resolution and to detect millions of sources per year.
« If detectors are a factor of 10 more sensitive, we might go back to the very first stars and see every stellar-mass black hole merger in the history of the Universe. confirms Sheila Dwyer, scientist at the Hanford Observatory.
Source : LIGO Caltech
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