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Gravitational wave search found tempting new clues




An international team of scientists may be about to detect the faint ripples of space-time that fills the universe.


Double black holes, billions of times larger than the sun, may be circling each other, creating ripples in space itself. The NANOGrav Observatory has spent more than ten years using ground-based radio telescopes to find evidence of space-time ripples caused by the behemoth black hole. This week, the project announced that it had detected signals that could be attributed to gravitational waves, although members were not ready to claim success.

Gravitational waves were first proposed by Albert Einstein in 1916, but they were not directly discovered until nearly a century later. Einstein proved that space is not an elastic cosmic background, but a soft fabric that is twisted and bent by huge objects and is inseparable from time. In 201

5, the collaboration between the Laser Interferometer Gravitational Wave Observatory (LIGO) in the United States and the Virgo Interferometer in Europe announced the first direct detection of gravity waves: they are emitted from two black holes, each The mass is about 30 times larger than the sun-orbiting each other and merging.

In a new paper in the Astrophysical Journal Supplement published in January 2021, the NANOGrav project reported that 45 pulsars scattered in the sky and measured the span of time, found consistent with the influence of gravitational waves Unexplained fluctuations. 12 1/2 years.

A pulsar is a dense mass of matter remaining after a star explodes into a supernova. From the earth, the pulsar seems to be flickering. In fact, the light comes from two stable beams emitted from opposite sides of the pulsar as the pulsar rotates, like a lighthouse. If gravitational waves pass between the pulsar and the Earth, the slight stretching and compression of space-time seems to introduce a small deviation in the original regular timing of the pulsar. But this effect is subtle, and more than a dozen other factors are known to also affect the timing of pulsars. The main part of NANOGrav’s work is to subtract these factors from the timing data of each pulsar before looking for signs of gravitational waves.

LIGO and Virgo detect gravitational waves from pairs of black holes (or other dense objects called neutron stars). In contrast, NANOGrav is looking for a continuous “background” of gravitational waves, or a combination of billions of years of clutter generated by countless pairs of supermassive black holes orbiting each other throughout the universe. The wavelengths of the gravitational waves produced by these objects are much longer than those detected by LIGO and Virgo, so that it may take years for a single wave to pass through a fixed detector. Therefore, although LIGO and Virgo can detect thousands of waves per second, NANOGrav’s mission requires years of data.

Fascinatingly, the latest discovery is that the NANOGrav team is not yet ready to claim that it has found evidence of the gravitational wave background. Why hesitate? In order to confirm the direct detection of gravitational wave signatures, NANOGrav researchers will have to find unique patterns in the signals between pulsars. According to Einstein’s general theory of relativity, the influence of gravitational wave background should be based on the slight influence of the pulsar’s position relative to each other on the pulsar’s timing.

At this point, the signal is too weak to distinguish this pattern. Enhancing the signal will require NANOGrav to expand its data set to include more pulsars for longer periods of time, which will increase the sensitivity of the array. NANOGrav also combined its data with data from other pulsar timing array experiments under the joint efforts of the International Pulsar Timing Array. The researchers collaborated with the world’s largest radio telescope.

National Radio Astronomy Observatory and current NANOGrav chairman Scott Ransom (Scott Ransom) said: “Trying to detect gravitational waves with a pulsar timing array requires patience.” It may take more time. These new results are exactly what we expect to see as we get closer to the test results, which is great.”

The NANOGrav team discussed their findings at a press conference at the 237th meeting of the American Astronomical Society, held from January 11 to January 10 to 15. The two astrophysicists Michele Vallisneri and Joseph Lazio are both astrophysicists at NASA’s Jet Propulsion Laboratory in Southern California. The co-authors of the paper are Zaven Arzoumanian and Zaven Arzoumanian of NASA Goddard Space Flight Center in Maryland. Joseph Simon, a researcher at Boulder University in Colorado, and the lead author of the paper, as a postdoctoral researcher at JPL, conducted many analyses on the paper. During JPL, several NASA postdoctoral researchers participated in the NANOGrav research. NANOGrav is a collaboration of American and Canadian astrophysicists. The data in the new study was collected using Green Bank antennas in West Virginia and Arecibo antennas in Puerto Rico before the collapse of West Virginia.

News media contact

Ian O’Neill/Kalia Cofield
Jet Propulsion Laboratory in Pasadena, California.
818-354-2649 / 626-808-2469
ian.j.oneill@jpl.nasa.gov / calla.e.cofield@jpl.nasa.gov

2021-005


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