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Scientists have found new evidence that supermassive black holes may be responsible for generating gravitational waves
Ten years ago, a discovery changed physics. Using detectors in Washington and Louisiana, scientists detected, for the first time, gravitational waves – tiny ripples in space-time.
The confirmation of Albert Einstein's theory earned him the 2017 Nobel Prize in Physics and opened a new window for the study of the cosmos.
Now, a new detection is further advancing this field. Scientists have identified a background hum generated by a different type of gravitational wave, possibly produced by black holes supermassive.
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The discovery raises intriguing questions and could lead to a deeper understanding of the structure of the universe.
What are gravitational waves?
Gravitational waves occur whenever a massive object accelerates. In the case of the first detection, in 2015, they were produced by two black holes within our galaxy that collided after orbiting each other.
The concern was picked up by LIGO (Laser Interferometer Gravitational-Wave Observatory), which has 4 km arms and detected tiny variations smaller than the width of an atom.
This time, the signal is different. Instead of high-frequency gravitational waves, which last only a few seconds, astronomers are detecting low-frequency waves, with wavelengths that can extend for light years.
They appear to come from all corners of the sky and are produced by supermassive black holes that orbit each other for millions of years before merging.
How was the new detection made?
To identify this cosmic hum, scientists have developed radio telescopes known as “pulsar timing sets".
Pulsars are extremely dense, rotating neutron stars that emit very precise radio signals.
As a low-frequency gravitational wave passes through, these signals undergo small changes. Researchers analyze these changes to infer the presence of gravitational waves.
The latest data was obtained by the MeerKAT radio telescope in South Africa. With just four and a half years of observation, MeerKAT achieved similar results to previous studies, which required more than 15 years of data collection.
The discovery was published in the journal Monthly Notices of the Royal Astronomical Society.
Matthew Miles, an astrophysicist at Swinburne University of Technology in Australia, explains that low-frequency gravitational waves stretch or contract the universe by about 20 meters.
This means that pulsars, located thousands of light years away, act as a natural detector, much larger than any equipment built by humanity.
Mysteries still unanswered
The new data raises a few puzzles. One is that the background hum appears louder than expected. This could mean there are more supermassive black holes in the universe than previously thought, or that these objects are even larger than previous models suggest.
Another mystery is the gradual increase in the intensity of the hum. One hypothesis is that some source of gravitational waves is relatively close to our solar system, affecting the data.
Additionally, the intensity of gravitational waves appears greater in the sky of the Southern Hemisphere than in the Northern Hemisphere, something scientists call a “hot spot.”
One possibility is that one pair of supermassive black holes in question is closer together than the others, biasing the data. However, it is not yet clear whether this asymmetry is real or just a statistical error.
The future of gravitational wave astronomy
New telescopes and technologies are expected to help clarify these questions. The Square Kilometre Array (SKA), a large array of radio telescopes in South Africa and Australia, is set to become operational in 2027 and promises to significantly improve the accuracy of directions.
Scientists believe that within the next decade, it will be possible to directly detect pairs of individual supermassive black holes, rather than just a fuzzy hum in the background of the universe. This will allow us to better study the origin and evolution of these cosmic structures.
Astrophysicist Floor Broekgaarden of the University of California compares this discovery to listening to different types of sounds in a busy square.
If the first gravitational waves detected in 2015 were like the high-pitched vocals of a choir, now scientists are starting to hear the lower-pitched instruments.
The existence of supermassive black holes at the centers of galaxies was already known. The one in the Milky Way, called Sagittarius A*, was detected in the 1970s by its radio emissions and photographed in 2022 by the Event Horizon Telescope.
Now, astronomers want to understand how these giants form and interact over time.
With information Smithsonianmag.
