Scientists at the International Centre for Theoretical Sciences in Bengaluru have unveiled a new technique for determining the rate of expansion of the universe by observing gravitational waves emitted from combining black hole pairs. Through the use of sophisticated gravitational wave detectors, the team aims to analyze repeated black hole mergers and the time lag between them to gauge the expansion rate, without the need for specific data on the involved galaxies or black hole duos.
In 1929, astronomers found that galaxies are moving apart from each other and us. This movement led to the realization that the universe is in a state of expansion. Nonetheless, inconsistent findings arose when they tried to measure the speed of this expansion using various techniques. This inconsistency has remained a persistent issue in describing the growing universe.
A potential remedy has been put forth by a group of researchers led by Souvik Jana from the International Centre for Theoretical Sciences in Bengaluru. Their study, recently featured in the Physical Review Letters, has been spotlighted as an Editor’s recommendation.
The proposed solution is anchored in the examination of gravitational waves or spacetime ripples, first detected in 2015, and the study of how gravity impacts these waves.
During the merging of two black holes into a single entity, gravitational waves are emitted. Upon reaching Earth, these waves are studied with kilometer-length detectors to investigate the characteristics of the black hole pairs. Gravitational lensing occurs when large galaxies between the Earth and the black holes alter the trajectory of these waves, leading to multiple copies being recorded by the detectors.
Parameswaran Ajith, a study co-author, stated, “We have observed the gravitational lensing of light for over a hundred years. We anticipate the initial observation of lensed gravitational waves in the upcoming few years!”
Over the next twenty years, scientists will commence operation of advanced gravitational wave detectors to search for merging black holes. “The future detectors will have a much broader range than current ones,” clarified Shasvath J. Kapadia from the Inter-University Centre for Astronomy and Astrophysics in Pune, another co-author. Tejaswi Venumadhav from the University of California at Santa Barbara mentioned that they would be able to spot weaker gravitational wave signals currently masked by noise.
Experts project that these advanced devices will capture signals from several million merging black hole pairs, creating gigantic black holes. About 10,000 of these mergers will be registered more than once in the same detector due to gravitational lensing.
Souvik’s team showcased that by tallying the repeated black hole mergers and analyzing the time between them, the universe’s expansion rate could be measured. Their technique could precisely assess the expansion rate over the next two decades as data from advanced gravitational wave detectors gradually becomes available.
Souvik emphasized that their proposal doesn’t necessitate information about the particular galaxies that generate multiple gravitational wave copies or the precise distances or locations of the black hole pairs. The method only requires a precise way of determining which signals are lensed. Efforts to recognize these repeated signals are being enhanced, added Shasvath.
Gravitational lensing needs a distant astronomical source, a criterion met by the black hole pairs, some originating a staggering 13.3 billion years ago, merely 500 million years after the universe’s inception.
Shasvath warns that their proposed technique will only be effective when advanced detectors register millions of black hole mergers. The team is currently exploring how future observations can differentiate between various cosmological models.
These models, the researchers elaborated, aim to unravel the puzzles surrounding dark matter, a type of matter that doesn’t interact with light. Though the dark matter hypothesis explains the observed mass of galaxies, the characteristics of dark matter remain uncertain, leading to different models.
The ongoing investigation by the team indicates that future observations of lensed gravitational waves could be utilized to probe the characteristics of dark matter.
Reference: “Cosmography Using Strongly Lensed Gravitational Waves from Binary Black Holes” by Souvik Jana, Shasvath J. Kapadia, Tejaswi Venumadhav, and Parameswaran Ajith, 30 June 2023, Physical Review Letters. DOI: 10.1103/PhysRevLett.130.261401
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Frequently Asked Questions (FAQs) about fokus keyword: gravitational waves
What is the new method for measuring the universe’s expansion rate?
The researchers from the International Centre for Theoretical Sciences in Bengaluru have proposed a method to measure the universe’s expansion rate using gravitational waves from merging black hole pairs. Utilizing advanced gravitational wave detectors, they plan to examine repeated black hole mergers and the delay between them to calculate the expansion rate without needing exact information about the galaxies or black hole pairs involved.
Who are the researchers responsible for this new method?
The research team is headed by Souvik Jana from the International Centre for Theoretical Sciences in Bengaluru, with co-authors including Parameswaran Ajith, Shasvath J. Kapadia, and Tejaswi Venumadhav.
Gravitational waves are ripples in spacetime. As pairs of black holes merge into a single black hole, they emit gravitational waves. The researchers’ method hinges on studying these gravitational waves, including how gravity itself affects them, to measure the universe’s expansion rate.
How do advanced gravitational wave detectors contribute to this research?
Advanced gravitational wave detectors will be used to study the properties of black hole pairs and the gravitational waves they emit. Future detectors will be able to see much larger distances and detect weaker gravitational wave signals. These observations will allow the researchers to count repeated black hole mergers and study the delay between them, leading to a measurement of the universe’s expansion rate.
What is gravitational lensing, and how does it play a role in the study?
Gravitational lensing is a phenomenon where massive galaxies occupying space between the black holes and Earth change the paths of spacetime ripples (gravitational waves), resulting in the detectors recording multiple copies of the same waves. This is central to the study as it will enable the detection of repeat black hole mergers, a crucial aspect of the proposed method to measure the universe’s expansion rate.
Can this method also help in understanding dark matter?
Yes, the team’s ongoing research suggests that future observations of lensed gravitational waves will serve as a tool to study the properties of dark matter, adding another dimension to the understanding of this elusive form of matter.
More about fokus keyword: gravitational waves
- Physical Review Letters
- International Centre for Theoretical Sciences
- Inter-University Centre for Astronomy and Astrophysics
