Key Takeaways:
- Scientists for the first time detected low-frequency gravitational waves, ripples in spacetime caused by massive objects moving in space.
- These low-frequency waves are likely from supermassive black holes orbiting each other and are too slow to be picked up by current high-frequency detectors.
- Scientists used pulsars, like cosmic clocks, to detect these waves by measuring changes in their radio wave signals.
- The discovery suggests a universe filled with more black hole mergers than previously thought or even new wave sources.
- This research opens a new window to studying the evolution of galaxies and black holes through “cosmic archaeology.”
For the first time, scientists have seen the small ripples that result from black holes’ motion, which are gently stretching and squeezing everything in the universe.
They revealed that they could “hear” low-frequency gravitational waves, which are produced by massive objects colliding and moving around in space and causing changes in the universe’s fabric.
Co-director of the research team NANOGrav, Maura McLaughlin said, “It’s really the first time that we have evidence of just this large-scale motion of everything in the universe.” The findings were published in The Astrophysical Journal Letters.
According to Einstein’s prediction, when extremely heavy objects move through spacetime, which is the fabric that makes up our universe, they cause ripples to propagate throughout it. Sometimes, scientists compare these ripples to the universe’s background music.
In 2015, scientists used an experiment called LIGO to detect gravitational waves for the first time and showed Einstein was right. However, astrophysicist Chiara Mingarelli of Yale University, a member of NANOGrav, noted that those techniques have only been able to detect waves at very high frequencies thus far.
According to Mingarelli, those brief “chirps” are produced at particular times when relatively tiny black holes and dead stars collide.
In the most recent study, researchers looked for waves at much lower frequencies. These slow ripples, which may cycle up and down over years or even decades, are most likely caused by supermassive black holes, which are billions of times more massive than the sun. They are among the largest objects in the universe.
The universe’s galaxies are constantly crashing into one another and merging. Scientists believe that as this is happening, the massive black holes at the centers of these galaxies also come together and become locked in a dance before they ultimately collapse into one another, according to Szabolcs Marka, a Columbia University astrophysicist who was not involved in the study.
In these pairings, called binaries, the black holes revolve around each other and produce gravitational waves.
“The tenors and bass of the cosmic opera are supermassive black hole binaries, orbiting each other slowly and calmly,” Marka stated.
Earthly instruments were unable to record the echoes from these giants. Thus, according to SETI Institute researcher Michael Lam, who works on NANOGrav, “we had to build a detector that was roughly the size of the galaxy.”
The findings comprised fifteen years of data from NANOGrav, an organization that has been looking for waves across North America with telescopes. Numerous other groups of researchers studying gravitational waves, including those in Europe, China, India, and Australia, have also published their findings.
The pulsars, which are dead stars that spin around in space like lighthouses, emit radio wave flares that the scientists observed through their telescopes.
Astrophysicist Sarah Vigeland of the University of Wisconsin-Milwaukee, a member of NANOGrav, described these bursts as “like a perfectly regular clock ticking away far out in space,” noting that scientists can precisely predict when the radio waves are expected to reach Earth. However, gravitational waves alter the distance between Earth and these pulsars by warping spacetime, which disrupts the pulsars’ regular beat.
Scientists were able to determine that gravitational waves were passing through pulsars by examining minute variations in the ticking rate of various pulsars, with some pulses occurring slightly early and others later.
Using the Very Large Array in New Mexico, the Arecibo telescope in Puerto Rico, and the Green Bank Telescope in West Virginia, the NANOGrav team observed 68 pulsars throughout the sky. Similar data was discovered by other groups observing dozens of other pulsars with telescopes all over the world.
Until now, this technique has not been able to determine the precise location of these low-frequency waves, according to Marc Kamionkowski, a Johns Hopkins University astrophysicist who was not involved in the study.
Rather, it’s exposing the background din that permeates everything around us. For example, if you’re at a party, “you’ll hear all of these people talking, but you won’t hear anything in particular,” according to Kamionkowski.
According to Mingarelli, the background noise they discovered is “louder” than some scientists had predicted. This could indicate that the number of black hole mergers occurring in space is higher than previously believed, or it could indicate the existence of additional gravitational wave sources that could complicate our understanding of the cosmos.
The goal of this type of gravitational wave research is to advance our understanding of the largest objects in the universe. According to Marka, it might lead to new discoveries in “cosmic archaeology,” which traces the evolution of galaxies and black holes around us.
“We’re starting to open up this new window on the universe,” Vigeland said.
