The Milky Way is huge, but much heavier is the volume of dark matter that is presumed to pervade our home galaxy. And a few scientists have proposed that the cumulative force of dark matter in our galaxy is large enough to affect interstellar spacecraft, according to a recent study shared on a pre-print server.
While the study still needs peer review, it also says the Pioneer & New Horizons spacecraft are already affected, as are planetary astronomy and astrophysics.
This could change not only the way we travel through space, but also the way we study it.
Gravity On Interstellar Spacecraft
When an asteroid, comet, or even a spacecraft moves around the sun, the main force in its motion is the gravity of our host star. Beyond Pluto, it is the entire solar system that serves as main gravitational force.
Even-out in Kuiper Belt, the cloud of ancient primordial asteroids at the edge of our solar system, any net-zero calculation of the gravitational forces on a spacecraft is best calculate as a 2 body problem: between the mass of the spacecraft and the space of the whole solar system. But all that changes when you move too far from sun.
“If an object moves far enough away from the Sun, then there is another gravitational force that could play a main role,” the study authors write. The lead author of the study is Professor of Celestial Mathematics and Mechanics Edward A. Belbruno of Yeshiva University, who is also a Visiting Research Fellow in the Department of Astrophysical Sciences at Princeton University.
According to an agency blog post, he worked with NASA chief scientist Jim Green, a co-lead author on the study, who is retiring earlier this year. But together, Green & Belbruno analysed another force that comes to play for spacecraft that travel in interstellar space.
As you can imagine, they found it to be the cumulative gravitational pull of the Milky Way. But surprisingly, the vast majority of this force is not generated by the disc, the central bulge & the stellar halo of our galaxy.
While they are there, the main force of gravitational attraction comes from dark matter. And although “it’s small,” the collective power of all dark matter in our galaxy ” can cumulatively add up & significantly affect the trajectory of motion over long periods of time.
Interstellar probe to analyze dark matter beyond solar system
According to the study, ordinary or “baryonic” matter accounts for about 5% of the total energy in the observable universe. Dark matter (non-baryonic matter), which we cannot observe directly, accounts for 25%. That’s 5 times the energy: about the same strength difference between an average human & a grizzly bear.
Yikes! “The dark matter halo contains most of the galaxy’s mass,” the study’s authors write. “Dark matter is measured in the Milky Way by observing the circular motion of the galaxy’s rotation” around the galactic center & Measuring their velocity relative to radial distance has shown in the past reveal that the galaxy’s rotational speed “levels off” as it moves away from core.
This is the reason why the spacecraft so far from the core of solar system, will influenced by the gravitational force of dark matter in our galaxy, as well as every thing else in the galaxy, almost independent of the radial distance from core.
“The existence of this force has many implications for planetary astronomy & astrophysics,” as tracking the movement of extraterrestrial worlds beyond our solar system has become a core practice in these fields. But, and perhaps the most exhilarating to consider:
“It may be possible to detect ‘this cumulative gravitational force of dark matter’ in a proposed mission called the Interstellar Probe,” the authors suggest. There’s a lot going on in space-travel, especially with the success of the James Webb Space Telescope (JWST), not to mention SpaceX, NASA & China. But on macro level & future that awaits us beyond the solar system, we are just getting started.