Astronomers measure 'warp speed' of Milky Way galaxy

A recent study led by Chinese astronomers uncovers fascinating insights into our Milky Way galaxy. Through meticulous observations and data analysis, the researchers have shed light on a crucial aspect of our galaxy's structure - its warp. By measuring the precession rate of the warp, they have unraveled valuable information regarding the alignment and movement of this distinct feature.

The Milky Way's disk-shaped structure bears a noticeable warp, believed to have originated from a collision with another galaxy billions of years in the past. However, the ongoing maintenance of this warp involves various factors, including interactions with satellite galaxies, magnetic fields between galaxies, and the influx of immense gas clouds. Among these contributors, the primary force dictating the warp's behavior is the invisible dark matter halo enveloping the disk, influencing its alignment and rotation.

The warp's precession describes the changing alignment of the warp in relation to the galaxy's rotational axis. This phenomenon reflects similarities with the wobbling motion observed in spinning tops. Previous attempts to measure the warp's rate of precession faced significant challenges, relying on the motion of aged giant stars as tracers. Unfortunately, such tracers present imprecise results with some significantly opposing theories that the disk precesses in the same direction as the galaxy's rotation, rather than retrograde as expected.

Lead scientist Yang Huang of the Chinese Academy of Sciences and a team of astronomers pursued a more accurate approach in determining the warp's precession rate. They employed the use of Cepheid variable stars, which function as pulsating massive stars with a period of pulsation that correlates with their intrinsic brightness. This characteristic enables the calculation of their distance from Earth, making them exceptional for mapping the intricate features of the warp.

By harnessing data from the European Space Agency's Gaia astrometric spacecraft, which accurately records the positions and properties of billions of stars, the team meticulously examined 2,613 Cepheids of different ages using a method referred to as the "motion picture" approach. Through this method, they constructed maps representing the shape and position of the warp at different time points spanning 200 million years. By aligning these maps into a sequence, much like watching a motion picture, the team successfully observed the warp's retrograde precession. Their findings indicate a rate of 2 kilometers (1.24 miles) per second per kiloparsec (3,261 light-years) of space, or approximately 0.12 degrees every million years.

Furthermore, the researchers discovered that the precession rate diminishes as the distance from the galactic center increases, a pattern suggestive of the oblate shape of the dark matter halo. This intriguing revelation holds significance for theorists studying the nature and composition of dark matter, as it provides crucial data for their models and contributes to our understanding of the Milky Way's history and formation processes.

The remarkable discovery of the warp's precession rate opens up new avenues for exploring the galaxy's hidden matter and uncovering further revelations about its structure. Published in Nature Astronomy on June 27, this study marks a significant milestone in unraveling the secrets of our extraordinary Milky Way galaxy.