A researcher at West Virginia University's Center for Gravitational Waves and Cosmology is revealing an unseen universe of gravitational radiation that distorts the space-time continuum. Emmanuel Fonseca, an assistant professor of astronomy at the Eberly College of Arts and Sciences at West Virginia University, uses precisely timed signals from stars known as "radio pulsars" to detect gravitational waves.
These gravitational waves are created when massive objects such as stars or black holes accelerate and contain information about phenomena and celestial bodies in distant galaxies that can reveal how the matter inside a neutron star behaves. The research was supported by a $416,000 grant from the National Science Foundation of United States.
"Gravitational waves permeate everything — the solar system, the Earth, us — but we haven't been able to detect them until the last five to eight years," Fonseca said. "Gravitational waves are a unique window into the universe, as distinct from electromagnetic radiation such as light, X-rays, and ultraviolet rays. These forms of radiation are produced by charged particles, while gravitational waves are caused by objects accelerating in space and perturbing space-time. Supermassive black holes in all binary star systems in the universe are emitting gravitational waves at us. The sum of the effects of these signals is a wavering, seemingly random pattern known as the 'gravitational wave background'. As this study increases our sensitivity to this background, we will become more sensitive to gravitational waves from nearby galaxies. Once we find the local sources of gravitational waves, we can point our electromagnetic telescopes at them and start making sense of things, which will be very interesting. "
West Virginia University astronomer Emmanuel Fonseca (second from right) uses data from the Green Bank and CHIME radio telescopes to find gravitational waves. Photo credit: West Virginia University Photo/Brian Persinger
Albert Einstein proposed the theory of gravitational waves in 1916, but it wasn't until last spring that NANOGrav, an international research collaboration, announced definitive evidence of the existence of gravitational waves.
"NANOGrav is a team of researchers, including me, who have been using data from the Green Bank Telescope in Bocahontas County to detect gravitational waves," Fonseca said. "We've been trying to find evidence of gravitational waves for years. Now all of a sudden, we can not only detect them, but also understand them. "
Emmanuel Fonseca, Assistant Professor, Department of Physics and Astronomy, Eberley College of Arts and Sciences, West Virginia University. Photo credit: West Virginia University Photo/Brian Persinger
The study will combine data from the Green Bank Telescope with data from the CHIME Radio Telescope in Canada, which Fonseca helped build. The two observatories record similar information at different intervals and frequencies.
"Combining the data means we can achieve comprehensive coverage of every wave. We can 'see' from one trough, over the crest, to the next," he said. Gravitational waves can cross galaxies. Gravitational waves exist in the low-frequency spectrum, so it can take a year or two between the first and second peaks recorded by radio telescopes. As gravitational waves oscillate, they cause ripples in the universe, and any object they encounter will be slightly displaced in time and space.
Pulsars – a pair of rotating neutron stars – allow astronomers to detect gravitational waves. Pulsars emit radio pulses that reach Earth at precise, predictable intervals.
"We use pulsars as probes, as beacons in the distance," Fonseca said. When we see a correlation deviation in a pulsar array that affects timing, that's a sign that gravitational waves are affecting the Earth. The deviation occurs because gravitational radiation passes through us, shrinking and squeezing our observatories and instruments. "
Using pulsars as detectors requires learning as much as possible about the pulsars themselves and phenomena like "scintillation", the flickering of stars, which affects the pulsar's signal as it flies towards Earth.
"The flicker appears to be random, and astronomers have historically considered it a distraction. But I believe that the information it encodes can improve gravitational wave detection. "
Fonseca highlighted the integration of data from the Green Bank Telescope and CHIME pulsars, which means astronomers will learn more than gravitational waves – they will also be able to calculate the mass of neutron stars.
"Calculating quality is a rare and difficult thing in astronomy. We don't have a balance to measure the weight of a star. But we now have the means to extract very precise gravitational information from these signals, allowing us to measure the mass of neutron stars, which in turn tells us what's going on inside them," he said.
A pulsar is a rotating neutron star that is "the most extreme environment we can currently observe." Its environment is similar to that of a black hole, but since its gravitational pull is not as extreme, we can technically understand what is going on inside them.
J. Robert Oppenheimer is the most famous 'father of the atomic bomb', but he was also one of the first to question the behavior of neutron stars, such as how nuclear physics works under such extreme gravity, or what kind of matter might exist there. That was nearly a hundred years ago, and it's only in the last five years that we've started to uncover some intriguing clues from NANOGrav data.
Fonseca also works with graduate research assistants at West Virginia University, Swarali Patil from Pune, India, and Matthew Batnick from Chicago.
编译自/SciTechDaily