NANOGrav Discovers Stronger Gravitational Waves Than Ever, Apparently Created by Pairs of Supermassive Black Holes
After 15 years of collecting data in an experiment the size of a galaxy, scientists have for the first time "heard" the constant chorus of gravitational waves spreading throughout our universe - and they are louder than expected.
The groundbreaking discovery was made by scientists from NANOGrav (the North American Nanohertz Observatory for Gravitational Waves) who carefully observed stars called pulsars that act as celestial metronomes. The newly discovered gravitational waves - propagating through the fabric of space-time - are the most powerful in the gap ever measured: their energy is about a million times greater than the one-time bursts of gravitational waves from mergers of black holes and neutron stars detected by experiments such as LIGO and Virgo.
Most giant gravitational waves are likely generated by pairs of supermassive black holes spiraling toward cataclysmic collisions across the cosmos, NANOGrav scientists report in a series of new papers published June 29 in The Astrophysical Journal Letters.
"It's like a choir, with all these pairs of supermassive black holes ringing at different frequencies," said NANOGrav scientist Chiara Mingarelli, who worked on the new findings. "This is the first ever proof of the gravitational wave background. We opened a new observation window on the universe."
The existence and composition of the gravitational wave background—long theorized but never heard of before—presents a treasure trove of new insights into old questions, from the fate of pairs of supermassive black holes to the frequency of galaxy mergers.
Now NANOGrav can only measure the total gravitational wave background and not radiation from the individual "singers". But even in that there were surprises.
"The gravitational wave background is about twice as loud as I expected," says Mingarelli. "This is right at the top end of what our models can create for supermassive black holes alone." The deafening intensity may be the result of experimental limitations or heavier and more numerous supermassive black holes. But there is also the possibility that something else creates strong gravitational waves, says Mingarelli, such as mechanisms predicted by string theory or alternative explanations of the birth of the universe. "What happens next is everything," she says. "this is only the beginning".
Getting to this point has been a years-long challenge for the NANOGrav team. The gravitational waves they were looking for are unlike anything measured before. Unlike high-frequency waves detected by ground-based instruments such as LIGO and Virgo, the gravitational wave background is made of very low-frequency waves. One rise and fall cycle of one of the waves can last for years or even decades. Since gravitational waves travel at the speed of light, one wavelength can be tens of light years.
No experiment on Earth could ever detect such enormous waves, so the team turned to the stars. They carefully observed pulsars, the very dense remnants of massive stars that have gone supernova. Pulsars act like stellar beacons, shooting beams of radio waves from their magnetic poles. As the pulsars spin rapidly (sometimes hundreds of times per second), these beams move across the sky, visible from our perspective on Earth as rhythmic pulses of radio waves.
The pulses arrive in Israel like a meteor with perfect timing. The timing is so precise that when Jocelyn Bell measured the first radio waves from pulsars in 1967, astronomers thought they might be signals from an extraterrestrial civilization.
When a gravitational wave passes between us and a pulsar, it affects the timing of the radio wave. This is because, as Albert Einstein observed, gravitational waves stretch and compress space as they propagate through the cosmos, changing the distance radio waves have to travel. For 15 years, NANOGrav scientists have meticulously timed pulses of radio waves from tens of millisecond pulsars in our galaxy. The new findings are the result of a detailed analysis of an array of 67 pulsars.
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Those who want to know the real universe, will refer to the book "The Magical Journey of Asbar...
The real universe is, first of all, an infinite space filled with passive time, which is completely at rest and completely cold. Passive time exists right in physical reality, while the time we always talk about exists only as a thought in the human mind.
Energy also fills the infinite space. Energy and passive time are quantitative concepts, and the continuous star matter is formed by combining quantities of passive time and energy. When a star explodes and ceases to exist, it gives up its energy and passive time to infinite space.
The passive time also plays the role of an intermediary, transmitting the sunlight, in the form of waves of passive time. The real universe operates without gravity, but according to ideas that come true, such as the law of conservation of energy.
The law of putting matter does not exist at all, because matter is not a quantitative concept, and is within the scope of a physical form, which is perceived with the combination of amounts of passive time and energy.