International team of scientists announces groundbreaking discovery report on gravitational wave background radiation | pulsars | gravitational waves

There is something that you cannot see or feel, but everything around you, including your own body, slowly shrinks and expands due to it. This is a strange spacetime distortion effect caused by gravitational waves passing through our galaxy.

After 15 years of data collection, scientists are now, for the first time, "listening" to the eternal chorus of gravitational waves rippling through the universe, much louder than expected.

This is an epoch-making discovery against the background of gravitational waves.

This is the upper limit of what humans can measure.

The gravitational wave background radiation is formed by the superposition of many different gravitational wave sources. Their frequency and intensity are different, but they are all very low. They should exist around us and may tell us important information that it has been hiding for a long time. Unfortunately, its existence and composition have always been the product of theorization.

In a series of new papers published in the Astrophysical Journal Letters on the 29th, scientists report their results. The most likely source of the detected gravitational wave background is a pair of supermassive black holes trapped in a "death spiral. These black holes are as large as billions of solar masses. Because almost all galaxies, including the center of the Milky Way, are entrenched in such a black hole monster. So when two galaxies merge, their supermassive black holes meet and start orbiting each other. Once the two black holes are close enough, they may be observed by the pulsar timing array.

If the gravitational wave background is likened to an ancient and mysterious song, then the "choir" is performed at a different frequency every day. Now, through the monitoring of pulsars, scientists have finally heard the song, in other words, the first evidence of the background of gravitational waves.

Scientists at the Nahertz Gravitational Wave Observatory in North America say they can only measure the overall gravitational wave background, not the radiation of individual singers or instruments. Even so, it is enough to surprise the entire astrophysics community.

Because "the gravitational wave background is about twice as loud as I expected," said Mingarelli, now an assistant professor at Yale University, "this is the upper limit of the model our model can create from a supermassive black hole."

Scientists have opened up uncharted territory. Due to experimental limitations, they cannot estimate whether it is possible that something else is also generating powerful gravitational waves, such as the mechanism predicted by string theory or other explanations for the birth of the universe.

This is the beginning of a slow puzzle.

A galactic experiment

The gravitational waves captured this time are very different from any previously measured.

Ground instruments such as the Laser Interferometer Gravitational Wave Observatory and the European Virgo Interferometer have detected high-frequency waves several times before, and the gravitational wave background is composed of ultra-low frequency waves. The single ups and downs of one of the waves may also take years or even decades to pass through. Since gravitational waves travel at the speed of light, a single wavelength can be as long as tens of light years.

No experiment on Earth has been able to detect such a huge wave, but the "cosmic beacon" pulsar can.

Pulsar is a kind of high-speed rotation, high stability, strong radiation electromagnetic waves of stars. The law of the pulse reaching the earth is as precise as a metronome. When the gravitational wave passes between the earth and the pulsar, the radio wave timing will be immediately disturbed. Pulsar timing array has become the most promising method to detect the background of gravitational waves.

For 15 years, astronomers have closely timed the radio waves of dozens of millisecond pulsars in the Milky Way, and this new discovery comes as a result of a detailed analysis of an array of 67 pulsars.

For this result, scientists need to spend thousands of hours a year on the world's largest telescopes. Because, as powerful as they sound, "pulsars are also very weak radio sources," said Maura McLaughlin, co-director of the NANOGrav Frontier Center for Physics.

Looking forward to future performances of "Cosmic Orchestra"

Human beings still have a lot to understand about the physical nature of the universe, which is inseparable from the cooperation of international scientists.

NANOGrav team is not the only one reporting the background of gravitational waves. Multiple papers published by the Chinese, European, Indian and Australian teams report the presence of the same gravitational wave background signal in their data. Through the International Pulsar Timing Array Consortium, various groups are also pooling their data to better characterize the signal and identify its source.

Sesleman Panchana, director of the National Science Foundation of the United States, said that the scientists "essentially created a galaxy-wide detector to reveal the gravitational waves that pervade the universe". This is the result of a collaboration between research institutions in the United States and around the world.

The world's search for the background of gravitational waves will continue.

Xavier Simmons, co-director of the NANOGrav and an Oregon State University astrophysicist, said that while humans continue to listen sideways, individual "instruments" will stand out in the "cosmic orchestra.