Astronomers have found a way to pinpoint our solar system's center of mass to within a mere 330 feet (100 meters), a recent study reports.
Such precision — equivalent to the width of a human hair on the scale of a football field — could substantially aid the search for powerful gravitational waves that warp our Milky Way galaxy, study team members said.
Astronomers have typically located our solar system's center of mass, or barycenter, by carefully tracking the movement of the planets and other bodies orbiting the sun. Such work has revealed that the barycenter is in constant motion; it can lie near the center of the sun, just beyond its scorching surface or pretty much anywhere in between, depending on the positions of the planets.
Related: Our solar system: A photo tour of the planets
But these previous calculations are compromised by an imperfect understanding of planetary motion, specifically that of Jupiter, which is the solar system's gravitational second-in-command. In the recent study, researchers took a new approach, analyzing observations of pulsars made over more than a decade by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project.
Pulsars are rapidly spinning neutron stars, superdense stellar corpses that pack a whole lot of mass into a sphere about the size of a city. Pulsars emit beams of radiation continuously from their poles. These beams appear to pulse (hence the name) because astronomers can only detect the radiation when it points at Earth.
NANOGrav closely monitors pulsars using radio telescopes, chiefly the big ones at the Arecibo Observatory in Puerto Rico and the Green Bank Observatory in West Virginia. Pulsars are incredibly consistent, so any deviation in the usual timing of their beams' arrival here on Earth could be evidence of warping by gravitational waves, the space-time ripples first predicted by Albert Einstein a century ago.
The Laser Interferometer Gravitational-Wave Observatory (LIGO) project made the first-ever direct detection of gravitational waves in 2015 and has added to its tally considerably in the ensuing years. Most of the detected ripples were generated by merging black holes, but two of the events involved colliding neutron stars.
In general, LIGO is designed to find short-period gravitational waves spawned by relatively low-mass objects spiraling toward each other. An April 2019 detection, for example, was traced to two neutron stars that together harbored just 3.4 times the mass of our sun.
NANOGrav is after bigger fish: long-period waves generated by merging supermassive black holes, the light-gobbling monsters that lurk at the heart of galaxies and can contain billions of solar masses. Detecting and studying such waves could shed considerable light on galaxy evolution and the relationship between galaxies and their central black holes, project team members have said.
And nailing down our solar system's center of mass is a key part of that effort.
"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," study co-author Stephen Taylor, an assistant professor of physics and astronomy at Vanderbilt University in Tennessee, said in a statement. "How well we understand the solar system barycenter is critical as we attempt to sense even the smallest tingle to the web."
So the recent study, which was published in April in The Astrophysical Journal, may end up being a step along the path toward a groundbreaking discovery.
"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."
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
https://ui.adsabs.harvard.edu/abs/2020ApJ...893..112V/abstract, 'Modeling the Uncertainties of Solar System Ephemerides for Robust Gravitational-wave Searches with Pulsar-timing Arrays, April 2020. “1. INTRODUCTION Pulsar timing exploits the remarkable regularity of millisecond-pulsar emissions to extract accurate system parameters from time-of-arrival (TOA) datasets (Lorimer & Kramer 2012), by fitting precise timing models that account for all pulse delays and advances, from generation near the neutron stars to detection at the radiotelescopes (Lommen & Demorest 2013). The largest time-dependent term in the model is the Rømer delay (Rømer 1676) due to the motion of Earth around the solar-system barycenter (SSB), with magnitude ~ 500 s. Solar-system ephemerides (SSEs), such as those produced by the Jet Propulsion Laboratory (JPL; see Folkner et al. 2009, 2014; Folkner et al. 2016; Folkner & Park 2016, 2018), are used to convert observatory TOAs to the notional coordinate time of an inertial frame centered at the SSB. It follows that errors in our estimate of Earth’s trajectory around the SSB produce a time-dependent bias in the TOAs.”
Interesting, dark matter does not play a role here but the motion of the Earth shows up. I plan to observe Jupiter tomorrow morning early around 0100 EDT using my telescopes. Jupiter is approaching opposition this month on 14-July and Saturn follows 20-July. Good to see studies testing ephemerides using Jupiter and pulsar timing :)
Dark matter should not play a role here - our system has an asteroid's worth of it and instruments are 10^5 times too insensitive to catch that - so that is honestly more (albeit weak) evidence.
Good luck with Jupiter! A teacher once took us out to see the Galilean moons, long before light pollution was too much of a bother.
Of course it changes position since our system orbits the Milky Way. And even from the reference point the NANOGrav project uses it could (and apparently does).
"In astronomy, the barycenter (or barycentre; from the Ancient Greek βαρύς heavy κέντρον center) is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit. ...
The distance from a body's center of mass to the barycenter can be calculated as a two-body problem.
If one of the two orbiting bodies is much more massive than the other and the bodies are relatively close to one another, the barycenter will typically be located within the more massive object. In this case, rather than the two bodies appearing to orbit a point between them, the less massive body will appear to orbit about the more massive body, while the more massive body might be observed to wobble slightly. ...
When the less massive object is far away, the barycenter can be located outside the more massive object. This is the case for Jupiter and the Sun; despite the Sun being a thousandfold more massive than Jupiter, their barycenter is slightly outside the Sun due to the relatively large distance between them. "
Seems the new observations has enabled scientists to model it to lie within the Sun (for whatever reference system NANAOGrav uses), when all planets are considered and way-out-of-system references are used.
Torbjorn Larsson, I enjoyed excellent views of Jupiter early Friday morning. I was out from midnight until 0530 EDT before sunrise viewing Saturn, Jupiter, Mars and the waxing gibbous Moon very bright (later hunt for comet NEOWISE and Venus brilliant). I used a 90-mm refractor telescope and 10-inch Newtonian at 158x views. Ganymede transited (I could see the moon) and Ganymede shadow transit too along with the Great Red Spot passing by. I enjoyed the reference in the space.com article to Jupiter because so much happened in astronomy there. When I view the Galilean moons moving around Jupiter and various Galilean moon eclipses using my telescopes, I am reassured that there is no dark matter there holding them in place :)
But it was, since the pulsar references are situated in the Milky Way so the common barycenter of the system moves in relation to them, and Earth moves in relation to the common barycenter of the system. Their reference system has to account for the relative movements.
No, dark matter is more holding systems together on the scale of dwarf galaxies up. That's one reason Newton didn't know about the stuff. :D
Good observation but note that Einstein in GR did not use DM either. My trusty book, 'Relativity The Special and the General Theory, A Clear Explanation that anyone can understand', 1961 does not show DM used in equations for GR, e.g. the principle of equivalence, inertial mass and gravitational mass. The space.com article in this discussion, 'This new, super-accurate way to pinpoint our solar system's center may help spot monster black hole crashes', is a good measurement for the barycenter of the solar system, the SSB. The Galilean moons do not show DM or need DM to predict their orbits and motion, neither does precise measurements for determining the SSB today. Dwarf galaxies (especially with fast stars in them) and spiral galaxy rotation curves apparently need the DM - assuming they have been in motion for billions of years.
General relativity describes all energy (and stress) as well as space time curvature - Einstein didn't include dark energy either.
Yes, if dark matter density is 10^-5 times from being observable in our measurements it can safely be ignored in modeling the system barycenter.