Since I subscribe to the online edition of the New York Times, I get frequent notifications of new stories on my iPhone. Some interest me. Some don't.
This morning it was a pleasure to be sent a story about how scientists were able to discover a background hum of gravitational waves, building on the first detection of these waves in 2015.
I've made a PDF file of the story, "The Cosmos is Thrumming With Gravitational Waves, Astronomers Find." It's well worth a read, having been written by a science reporter with a Ph.D. in particle physics. I'll share a few excerpts to whet your appetite for the whole story.
Download The Cosmos Is Thrumming With Gravitational Waves Astronomers Find - The New York Times
On Wednesday evening, an international consortium of research collaborations revealed compelling evidence for the existence of a low-pitch hum of gravitational waves reverberating across the universe.
The scientists strongly suspect that these gravitational waves are the collective echo of pairs of supermassive black holes — thousands of them, some as massive as a billion suns, sitting at the hearts of ancient galaxies up to 10 billion light-years away — as they slowly merge and generate ripples in space-time.
“I like to think of it as a choir, or an orchestra,” said Xavier Siemens, a physicist at Oregon State University who is part of the North American Nanohertz Observatory for Gravitational Waves, or NANOGrav, collaboration, which led the effort. Each pair of supermassive black holes is generating a different note, Dr. Siemens said, “and what we’re receiving is the sum of all those signals at once.”
The findings were highly anticipated, coming more than 15 years after NANOGrav began taking data. Scientists said that, so far, the results were consistent with Albert Einstein’s theory of general relativity, which describes how matter and energy warp space-time to create what we call gravity. As more data is gathered, this cosmic hum could help researchers understand how the universe achieved its current structure and perhaps reveal exotic types of matter that may have existed shortly after the Big Bang 13.7 billion years ago.
“The gravitational-wave background was always going to be the loudest, most obvious thing to find,” said Chiara Mingarelli, an astrophysicist at Yale University and a member of NANOGrav, which is funded by the National Science Foundation. “This is really just the beginning of a whole new way to observe the universe.”
...To detect the gravitational-wave background, researchers took advantage of the lighthouse-like nature of pulsars spread across the Milky Way. “Our detector isn’t something you can build in a lab or even launch into space,” said Thankful Cromartie, an astronomer at Cornell University, during Thursday’s news conference. “It’s closer to the size of the galaxy.”
Pulsars act like cosmic clocks, emitting beams of radio waves that can be periodically measured on Earth. Einstein’s theory of general relativity predicts that as gravitational waves sweep past pulsars, they should expand and shrink the distance between these objects and Earth, changing the time it takes for the radio signals to arrive at observers. And if the gravitational-wave background is indeed everywhere, pulsars across the universe should be affected in a correlated way.
Rather than build a dedicated instrument, the NANOGrav team took advantage of existing radio telescopes around the world: the Very Large Array in New Mexico, the Green Bank Telescope in West Virginia and Arecibo Observatory in Puerto Rico (before its fateful collapse three years ago).
In 2020, after more than 12 years of gathering data, the NANOGrav team released results from monitoring the timing of 45 pulsars. Even then, Dr. Siemens said, the researchers saw tantalizing hints of a gravitational-wave background, but they needed to track more pulsars for longer amounts of time to confirm that they were indeed correlated, and to claim a discovery. So the NANOGrav team approached colleagues through the International Pulsar Timing Array — an umbrella organization that includes collaborations based in India, Europe, China and Australia — and coordinated an effort to uncover the gravitational-wave background together.
This discovery shows why I love science so much.
The researchers showed amazing creativity, competence, and dedication. They produced a scientific instrument the size of a galaxy by using data from pulsars spread throughout our Milky Way galaxy. This required a tremendous amount of teamwork from scientists across the globe.
It's mind-blowing enough that the general theory of relativity says that gravity is the warping of space-time, which often is described as being akin to placing a heavy object on a stretchy piece of rubber. The object distends the rubber, just as mass distends the fabric of space-time.
But to discover gravitational waves that traverse the universe at the speed of light, given how faint evidence for those waves is, that's beyond mind-blowing. A story on Space.com describes the precision that had to be achieved.
In the new research, the "critical evidence" that betrays the source of the signals to be supermassive black holes is a unique pattern found in the arrival times of pulses from a galaxy-sized cosmic antenna of nearly 70 millisecond pulsars in the Milky Way, according to a consortium of astronomers known as The North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Gravitational wave signals from black hole binaries overlap "like voices in a crowd" and result in an incessant hum that embeds as a unique pattern in the pulsar timing data, scientists say.
Scientists extracted that pattern by observing lighthouse-like beams from pairs of pulsars. Using various radio telescopes like the now-collapsed Arecibo Observatory in Puerto Rico, the Green Bank Observatory in West Virginia, the Karl G. Jansky Very Large Array in New Mexico and the Canadian Hydrogen Intensity Mapping Experiment (CHIME) in Canada, they collected data about the timing of those pulses every month for 15 years. Then, they calculated the difference between the pulses' actual arrival times and their predicted arrival times — which they could estimate within 1 microsecond, comparable to measuring the distance to the moon to within a thousandth of a millimeter, scientists say.
It amuses me when religiously-minded people say that scientists aren't interested in finding evidence for life after death, consciousness existing outside of the brain, supernatural phenomena, and such. That's totally wrong.
Scientists are devoted to learning the truth about ourselves, our world, and our universe. This newest detection of gravitational waves shows the lengths scientists will go to learn something important about reality.
Believe me, if there was substantial evidence in anything supernatural, scientists would be falling over themselves in the rush to study this phenomenon, since it would overturn longstanding assumptions about reality.
But religion never comes up with anything newsworthy about the nature of the cosmos. That's because religions deal in dogma, not facts. Which is why I'm a big fan of science, not of religion.