Cosmic insights offered by a new study have shattered the long-standing opinion that the Milky Way, the galaxy home to Earth and the solar system, is comparatively static.
The spiral-shaped disk constituting stars and planets is being pulled, twisted, and deformed very violently by the gravitational force of a smaller galaxy—the Large Magellanic Cloud (LMC).
Researchers consider that the LMC went beyond the Milky Way’s boundary nearly 700 million years ago—which is the latest according to cosmological standards—and because of its large dark matter content, it vigorously upset the galaxy’s fabric and motion while it fell in.
The impacts are evident even today and should thus necessitate a revision of how the Milky Way evolved, noted astronomers.
The LM is currently a satellite galaxy of the Milky Way and can be observed as a faint cloud during nighttime in the southern hemispheres—as viewed by its namesake Ferdinand Magellan, a 16th-century Portuguese explorer.
Earlier studies have shown that similar to the Milky Way, the LMC is surrounded by a halo of dark matter, which are elusive particles surrounding galaxies and do not emit or absorb light but have drastic gravitational effects on the movement of gas and stars in the universe.
The research team from the University of Edinburgh used an advanced statistical model that computed the speed of the most distant stars in the Milky Way to discover how the LMC warped the galaxy’s motion. Published in the Nature Astronomy journal, the study was financially supported by the UK Science and Technology Facilities Council (STFC).
The team discovered that the huge attraction of the dark matter halo of the LMC is pulling and twisting the Milky Way disk at a speed of 32 km/second or 115,200 km/hour towards the Pegasus constellation.
Fascinatingly, they also discovered that the Milky Way was not shifting toward the current location of the LMC, as considered earlier, but toward a point in its past trajectory.
They think this is due to the fact that the LMC, driven by its enormous gravitational force, is shifting away from the Milky Way at a much higher speed of 370 km/second, around 1.3 million km/hour.
According to astronomers, it seems as if the Milky Way is making hard efforts to hit a fast-moving target, but without a good aim.
This finding will enable scientists to devise new modeling methods to capture the vigorous dynamic interplay between the two galaxies.
As a next step, astronomers plan to discover the direction from which the LMC first fell into the Milky Way and the accurate time it happened. This will unravel the amount and distribution of dark matter in the LMC and the Milky Way with unmatched detail.
Our findings beg for a new generation of Milky Way models, to describe the evolution of our galaxy. We were able to show that stars at incredibly large distances, up to 300,000 light-years away, retain a memory of the Milky Way structure before the LMC fell in, and form a backdrop against which we measured the stellar disc flying through space, pulled by the gravitational force of the LMC.
Dr Michael Petersen, Study Lead Author and Postdoctoral Research Associate, School of Physics and Astronomy, The University of Edinburgh
According to Professor Jorge Peñarrubia, Personal Chair of Gravitational Dynamics, School of Physics and Astronomy, “This discovery definitely breaks the spell that our galaxy is in some sort of equilibrium state. Actually, the recent infall of the LMC is causing violent perturbations onto the Milky Way. Understanding these may give us an unparalleled view on the distribution of dark matter in both galaxies.”
Petersen, M. S., et al. (2020) Detection of the Milky Way reflex motion due to the Large Magellanic Cloud infall. Nature Astronomy. doi.org/10.1038/s41550-020-01254-3.