“Using the pulsars we observe across the Milky Way galaxy, we are trying to be like a spider sitting in stillness in the middle of its web,” says Stephen Taylor of Vanderbilt, assistant professor of physics and astronomy and former astronomer at the NASA Jet Propulsion Laboratory. (JPL) on the location of absolute stillness in our solar system, the center of gravity with which to measure the gravitational waves that signal the existence of the invisible paradoxes we call black holes, which have no memory, and contain the earliest memories of the universe.
“How well we understand the center of gravity of the solar system, its barycenter, the location where the masses of all planets, moons, and asteroids balance, is critical when trying to feel even the smallest tickling on the web,” adds Taylor.
NANOGrav points to the center of gravity
In search of previously undetected black holes that are billions of times more massive than the sun, Taylor, in collaboration with the Nanohertz Observatory of Gravitational Waves (NANOGrav) in North America, has advanced the field of research by finding the precise location of the barycenter.
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Finding the most titanic black holes in the Universe that lurk at the heart of galaxies will help us understand how those galaxies (including ours) have grown and evolved for billions of years since their formation. These black holes are also unmatched labs for testing fundamental assumptions about physics.
LIGO joins the search
Gravitational waves are waves in space-time predicted by Einstein’s general theory of relativity. When black holes orbit each other in pairs, they radiate gravitational waves that warp space-time, stretching and squeezing the space. Gravitational waves were first detected by the Laser Interferometer Gravitational Wave Observatory (LIGO) in 2015, opening up new views of the most extreme objects in the universe. While LIGO observes relatively short gravitational waves by looking for changes in the shape of a 4km long detector, NANOGrav looks for changes in the shape of our entire galaxy.
Detect changes in Pulsar patterns
Taylor and his team are looking for changes in the rate of arrival of regular flashes of radio waves from pulsars. These pulsars are fast-spinning neutron stars, and some go as fast as a kitchen blender. They also send out beams of radio waves, which appear as interstellar beacons when these beams spread out over Earth. More than 15 years of data have shown that these pulsars are extremely reliable in their pulse arrival frequencies, acting as outstanding galactic clocks. Any deviation in time that is correlated in many of these pulsars could indicate the influence of gravitational waves that warp our galaxy.
Jupiter ImpAct
Where is the center of our website, the location of absolute stillness in our solar system? Not in the center of the sun as many might suppose, but is closer to the surface of the star. This is due to Jupiter’s mass and our imperfect knowledge of its orbit. It takes 12 years for Jupiter to orbit the sun, just under the 15 years that NANOGrav has been collecting data. JPL’s Galileo probe (named after the famous scientist who used a telescope to observe Jupiter’s moons) studied Jupiter between 1995 and 2003, but experienced technical illnesses that affected the quality of measurements taken during the mission.
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The identification of the center of gravity of the solar system has long been calculated with Doppler tracking data to obtain an estimate of the location and trajectories of bodies in orbit around the sun. “The problem is that errors in masses and orbits will translate into pulsar timing artifacts that may well appear to be gravitational waves,” explains JPL astronomer and co-author Joe Simon.
Inconsistent results
Taylor and his collaborators found that working with existing models of the solar system to analyze the NANOGrav data yielded inconsistent results. “We weren’t detecting anything significant in our searches for gravitational waves between models in the solar system, but we were getting huge systematic differences in our calculations,” says JPL astronomer and lead article author Michele Vallisneri. “Typically, more data gives a more accurate result, but there was always a shift in our calculations.”
The group decided to search for the center of gravity of the solar system while searching for gravitational waves. The researchers obtained more robust responses to find gravitational waves and were able to more accurately locate the center of gravity of the solar system within 100 meters. To understand that scale, if the sun were the size of a soccer field, 100 meters would be the diameter of a lock of hair.
“Our accurate observation of pulsars scattered across the galaxy has located us in the cosmos better than ever,” said Taylor. “By finding gravitational waves in this way, in addition to other experiments, we get a more holistic view of all the different types of black holes in the Universe.”
As NANOGrav continues to collect increasingly abundant and precise pulsar time data, astronomers are confident that massive black holes will appear unequivocally soon in the data.
Source: M. Vallisneri et al. Modeling the uncertainties of ephemeris in the solar system for robust gravitational wave searches with Pulsar timing matrices, The Astrophysical Journal (2020). DOI: 10.3847 / 1538-4357 / ab7b67
The Daily Galaxy, Max Goldberg, via Vanderbilt University and ArXiv, org
