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Astronomers may have heard the background of the universe’s “hum”



According to our understanding of gravitational waves, the universe should be full of them. Every pair of colliding black holes or neutron stars, every supernova whose nucleus collapses-even the big bang itself, should give off ripples throughout time and space.

After all these times, these waves will be faint and difficult to detect, but it is predicted that they will all constitute a resonant “hum” that will penetrate into our universe, said As a gravity wave background. We may have just discovered its first hint.

You can imagine the background of gravitational waves as the sounds left over from large-scale events throughout the history of the universe. This may be of invaluable value to our understanding of the universe, but it is difficult to discover.

The collaboration between astrophysicist Joseph Simon and NANOGrav of the University of Colorado at Boulder said: “It’s exciting to see such a powerful signal coming from the data.”

“However, since the gravity wave signal we are searching for spans the entire observation process, we need to understand our noise carefully. This puts us in a very interesting place where we can strongly exclude some known noise sources. It is not yet possible to say whether the signal actually came from gravity waves. For this, we will need more data.”

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Nevertheless, the scientific community is still very excited. Since the team’s preprint was released to arXiv in September last year, more than 80 papers have cited the research.

The international team has been working hard, analyzing the data in an attempt to refute or confirm the team’s results. If it turns out that the signal is true, then it may open a whole new stage of gravitational wave astronomy-or reveal to us a whole new astrophysics phenomenon.

The signal comes from observations of a dead star called a pulsar. These are neutron stars, and they are oriented in such a way that when they spin at millisecond speeds, they emit radio beams from the poles at a speed comparable to a kitchen mixer.

The timing of these flashes is incredibly accurate, which means that pulsars may be the most useful stars in the universe. Their time changes can be used for navigation, detection of interstellar medium and study of gravity. Moreover, since the discovery of gravitational waves, astronomers have been using gravitational waves to find gravitational waves.

That’s because gravitational waves distort time and space when they fluctuate. Theoretically, the time of radio pulses emitted by pulsars should be changed, but only very small.

” [gravitational wave] The background stretches and shrinks the space-time between the pulsar and the Earth, causing the signal from the pulsar to arrive later (stretched) or earlier (contracted) than if there were no gravitational waves. “The technology that did not participate in the research cooperated with OzGrav to explain to ScienceAlert.

A single pulsar with irregular beats does not necessarily mean too many. However, if a whole group of pulsars show correlated patterns of temporal changes, it may constitute evidence of a gravitational wave background.

Such a collection of pulsars is called a pulsar timing array, which is what the NANOGrav team has been observing-45 of the most stable millisecond-level pulsars in the galaxy.

They have not yet fully detected the signals that can determine the background of gravitational waves.

But they have detected something-Shannon explained that a “common noise” signal changes between pulsars, but shows similar characteristics each time. Simon pointed out that these deviations caused a change of several hundred nanoseconds during the 13-year observation period.

There are other factors that may generate this signal. For example, a pulsar timing array needs to be analyzed from a non-accelerating reference frame, which means that any data needs to be transferred to the center of the solar system, the center of gravity, rather than the earth.

If the calculation of the center of gravity is incorrect-much harder than it sounds, because it is the center of gravity of all moving objects in the solar system-then you may get the wrong signal. Last year, the NANOGrav team announced that they had calculated that the center of gravity of the solar system was within 100 meters (328 feet).

Still this difference may be the source of the signal they found, and more work needs to be done to solve this problem.

Because if the signal does come from the hum of some kind of resonant gravity wave, it will be a lot of money, because the source of these background gravity waves is likely to be a supermassive black hole (SMBH).

Since gravitational waves show us phenomena that we cannot detect by electromagnetic means-such as black hole collisions-this can help solve problems such as the final parsec problem, which may cause supermassive black holes to be unable to merge and help us better Understand the evolution and growth of galaxies.

Farther away, we can even detect the gravitational waves generated after the Big Bang, which provides us with a unique window into the early universe.

Obviously, a lot of scientific work needs to be done before this point is reached.

Shannon said: “This is the first step towards nanohertz frequency gravitational wave detection.” “I want to remind the public and scientists not to over-interpret the results. In the next year or two, I think there will be related signal properties. evidence of.”

Other teams are also using pulsar timing arrays to detect gravity waves. OzGrav is part of the Parkes Pulsar timing array, which will soon publish an analysis of its 14-year data set. The European Pulsar Timing Array is also working hard. The results of NANOGrav only increase people’s excitement and expect to find something.

Simon told ScienceAlert: “It’s exciting to see our data send such a strong signal, but for me, the most exciting is the next step.”

“Although we still need to conduct further definitive testing, this is only the first step. In addition to our opportunity to find out the source of GWB, in addition to this, we can also discover the information universe they can tell us.”

The team’s research results have been published in Astrophysical Journal Letter.


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