In an unprecedented discovery, physicists are now reporting significant evidence for the existence of low-frequency gravitational waves. Often instigated by colossal cosmic objects in orbital movement, these gravitational waves likely originate from pairs of the universe’s most mammoth black holes, whose movement in space can cause enough cosmic disturbance to generate a discernable signal for scientists.
These extraordinary findings are brought to us by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), who shared the information through a collection of papers in the Astrophysical Journal Letters. The researchers, based in the United States, will showcase their results at the National Science Foundation and on YouTube for the public to access. The NANOGrav team wasn’t alone in their endeavor; international partners from Europe, India, Australia, and China simultaneously reported similar findings, adding credibility to the conclusion that these hypothesized waves truly exist.
For the past 15 years, NANOGrav has been dedicated to discovering a subtle hum of gravitational waves reverberating through the universe, according to Stephen Taylor, NANOGrav chair, during a press briefing. The team’s relentless pursuit to measure the warping of space-time due to these waves finally bore fruit, bringing an exciting breakthrough in their mission.
The latest findings align with Albert Einstein’s general relativity theory, indicating that the spiraling of black holes into each other can cause space-time wrinkles that propagate at light speed. Though the concept seemed virtually improbable to validate a century ago, these barely perceptible waves were first discovered by the US-based Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015, causing a stir in the physics community.
Since then, LIGO and the Virgo collaboration in Europe have discovered dozens more such phenomena, predominantly from merging pairs of star-sized black holes and occasional mergers between black holes and neutron stars. The gravitational waves NANOGrav focuses on are unique, originating from supermassive black holes with masses that could rival hundreds of millions or billions of suns. The published documents reveal an analysis of these gravitational waves that suffuse the cosmos, as well as alternate possible origins.
The NANOGrav team, alongside other international groups, used pulsars (also known as “space lighthouses”) to measure gravitational waves. Pulsars are remnants of massive stars that have imploded and become supernova, emitting radiation while rotating at astounding speeds. By pinpointing the location of these cosmic clocks, researchers can identify the occurrence of a gravitational wave.
A decade’s worth of data collection and analysis allowed researchers to reduce measurement uncertainties and verify the signal’s origin from gravitational waves, not other cosmic phenomena or simple noise. Researchers, cautious about premature conclusions due to past misinterpretations of data, refrain from using the term “detection” to describe their results. Nevertheless, statistical analysis shows less than a one-in-a-thousand chance that their signal could be accidental, indicating a strong likelihood of real gravitational waves.
A variety of radio telescopes, including the iconic Arecibo Observatory in Puerto Rico, the Green Bank Observatory, and the Very Large Array, helped capture the data. Notably, despite political challenges, collaboration between US and Chinese scientists proved beneficial. The combined data, gathered from different time zones through a mega-collaboration called the International Pulsar Timing Array, enhances the precision and confidence of their findings.
Michael Keith, an astrophysicist part of the European Pulsar Timing Array executive committee, affirms the importance of collective effort, explaining that constructing a galaxy-sized gravitational wave telescope is an endeavor that requires a joint effort from hundreds of astronomers, theorists, engineers, and administrators.