Unveiling the Symphony of the Universe: Scientists ‘Hear’ Low-Frequency Gravitational Waves

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Scientists have for the first time ‘heard’ the chorus of low-frequency gravitational waves coursing through the Universe. This is not yet a full discovery, but the observations highly likely indicate something significant has been detected. Astronomers have managed to ‘hear’ low-frequency gravitational waves, the faint ripple in the fabric of the Universe caused by the motion of supermassive objects that stretch and compress space.

Preview of gravitational waves produced by supermassive black holes. Image source: nanograv.org

Einstein predicted that as superheavy objects move in space and time, they create a ripple that travels through the fabric of the Universe, sometimes referred to as the Universe’s background music. In 2015, the LIGO experiment helped detect gravitational waves and proved Einstein right, but until now, they were only recorded at high frequencies. These were individual fast ‘chirps’ that only occur at certain moments, for example, when relatively small black holes and dead stars collide with each other.

In the recent research project, scientists attempted to detect gravitational waves at much lower nanohertz frequencies – the periods of this slow ripple can be years and even decades long. It likely emanates from the largest objects in the Universe – supermassive black holes weighing billions of suns. But there are also other ‘suspects’: cosmic strings, phase changes in the Universe, rapid space expansion after the Big Bang. Perhaps even the Big Bang itself, but the length of the gravitational wave from it would be the size of the Universe, requiring a detector of comparable scales.

Galaxies in the Universe constantly collide and merge. Similar processes are observed in supermassive black holes at the cores of galaxies. They approach each other, revolve around each other, and eventually merge as well, emitting gravitational waves during the interaction. If you compare the collision of supermassive black holes with a stone thrown into a pond, the ripple it creates on the pond’s surface is low-frequency gravitational waves. They spread simultaneously in all directions at the speed of light, compressing and stretching space and time. It’s impossible to detect this ripple directly with human-available tools – the length of such a nanohertz wave can be measured in light-years. Simply put, the Earth is too small, and a detector of galactic scales would be needed. Detecting them indirectly took the NANOGrav scientists 15 years, and in their work, they used equipment installed all over North America. Astronomers from other countries relied on research results that lasted up to 18 years.

We live in a galaxy that is much larger than Earth, and it contains objects that can indirectly detect signs of low-frequency gravitational waves. These are radio pulsars – dead stars that emit bursts of electromagnetic radiation in the radio frequency range as they rotate. These bursts have strict periodicity, serving as a kind of perfectly accurate clocks located far in space. However, as gravitational waves distort the fabric of space and time, they change the distance between Earth and these pulsars, thereby distorting this extremely stable rhythm. A minor glitch in a periodic event is of course not enough. But if you monitor many pulsars over a long time and note related glitches in the frequency of radio bursts, you can indeed record signs of a low-frequency gravitational wave.

Observatory Very Large Array. Image source: nrao.edu

As part of the research project, NANOGrav astronomers observed 68 pulsars using the Green Bank (USA, West Virginia), Arecibo (Puerto Rico) and Very Large Array (USA, New Mexico) radio telescopes. Similar evidence was found by other teams of scientists who followed other pulsars using telescopes around the world. In total, material on 115 pulsars was collected over 18 years. Pulsar timing array astronomy is a long-term project, but scientists are already as close as possible to confirming the discovery. Researchers combined the data from their observations – the final result should be obtained within a year or two.

Unfortunately, this method does not allow tracking exactly where the specific low-frequency gravitational waves come from – it simply reveals a constant hum surrounding us. In a similar way, a person at a noisy party hears that many people are talking, but cannot hear anything specific.

There are already reasons to claim that the background noise of low-frequency gravitational waves detected by scientists turned out to be “louder” than expected. This may mean that black hole mergers occur more often than thought, or our understanding of the nature of the Universe does not fully correspond to reality. Researchers hope the discovery will help us learn more about the supermassive objects of the Universe, open new doors for “cosmic archaeology”, and trace the history of black hole and galaxy mergers around us.

Author Profile

Vasyl Kolomiiets
Vasyl Kolomiiets
I'm Vasyl Kolomiiets, a seasoned tech journalist regularly contributing to global publications. Having a profound background in information technologies, I seamlessly blended my technical expertise with my passion for writing, venturing into technology journalism. I've covered a wide range of topics including cutting-edge developments and their impacts on society, contributing to leading tech platforms.

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