The Solar System doesn’t have the Sun in the center, and everything else orbits around it. Rather, every cosmic body in the system impacts the star with their gravitational pull, making it move around a bit. This means that the accurate gravitational core – or barycenter – of the Solar System is not in the middle of the Sun, but somewhere closer to its surface, or even outside it.
It hasn’t been easy for researchers to figure out where exactly this barycenter is, mainly because of the plethora of gravitational influences at play. Now, using specially developed software, an international team of astronomers has managed to discover the location of the Solar System’s barycenter to within 100 meters (328 feet), which could immensely enhance our measurements of gravitational waves.
It’s all About Pulsars
Simply put, it all has to do with pulsars. These dead stars can spin really fast, on millisecond timescales, emitting beams of electromagnetic radiation from their poles. If they are placed just right, these flares fly pas Earth like an extremely fast cosmic beacon, creating a pulsed signature that is incredibly regular.
The regular pulse of these stars is useful for a number of things, including testing the interstellar medium or creating a potential navigation system in space. In the last few years, observatories such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) have been programmed to look for low-frequency gravitational waves, since gravitational waves should trigger very subtle disturbances in the timing of a whole network of pulsars throughout the sky.
“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 her web,” explained astronomer and physicist Stephen Taylor of Vanderbilt University and the NANOGrav Collaboration. “How well we understand the Solar System barycenter is critical as we attempt to sense even the smallest tingle to the web.”
That is due to the errors in the calculation of Earth’s position in proportion to the Solar System barycenter, which can affect our measurements of pulsar timing. This, in turn, can impact our searches for low-frequency gravitational waves.
The Barycenter of our Solar System
Part of the issue is Jupiter. By a rather wide scope, it has the most powerful gravitational effect on the Sun, as the pulls of the other planets are insignificant in comparison. Researchers have discovered how long Jupiter takes to rotate around the Sun – about 12 Earth years – but our understanding of its orbit is not complete.
The team used existing datasets to analyze NANOGrav data, but they kept receiving inconsistent results due to the errors in the previous estimates of the barycenter.
“We weren’t detecting anything significant in our gravitational wave searches between solar system models, but we were getting large systematic differences in our calculations,” said astronomer Michele Vallisneri of NASA’s Jet Propulsion Laboratory. “Typically, more data delivers a more precise result, but there was always an offset in our calculations.”
That’s why the team designed BayesEphem, a new software created to model and correct the uncertainties in Solar System orbits most concerned with gravitational wave searches using pulsars, as well as Jupiter.
When the researchers applied BayesEphem to the NANOGrav data, they could place a new upper limit on the gravitational wave record and detection statistics. They were also able to measure a new and more accurate location for the Solar System’s barycenter that could allow for much more precise low-frequency gravitational wave detections.
“Our precise observation of pulsars scattered across the galaxy has localized ourselves in the cosmos better than we ever could before,” Taylor said. “By finding gravitational waves this way, in addition to other experiments, we gain a more holistic overview of all different kinds of black holes in the Universe.”
A paper detailing the research has been published in The Astrophysical Journal.