There’s trouble brewing at the Milky Way’s edge: new measurements show that a peculiar distortion of the galactic disk is moving slowly, contradicting previous reports.
As yet, nobody knows which result will be correct. Some crucial details in the structure and genesis of spiral galaxies throughout the cosmos are at stake.
The Milky Way is characterized by astronomers as a flat disk-shaped, double-armed spiral galaxy twirling and twinkling with stars. However, astronomers have known since the mid-twentieth century that this picture is partially inaccurate.
Observations in the radio region of the electromagnetic spectrum initially indicated that our galaxy’s farthest borders are warped, with some parts drooping down and others bending upward, similar to a vinyl record left on a hot plate.
Subsequent data has shown that this feature, known as a galactic warp, is common for spiral galaxies, Žofia Chrobáková, an astrophysics doctoral candidate at the Institute of Astrophysics of the Canary Islands (IAC) in Spain, told Live Science.
Various explanations for the warp’s formation have been offered, including the possibility that it is caused by surrounding material falling onto the galactic disk, according to Chrobáková. The distortion would most likely be static or moving very slowly in that case.
Other theories propose that warps are produced by more dynamic mechanisms, such as interactions with dark matter at the galaxy’s edge or smaller galaxies orbiting their larger brethren, tugging on them gravitationally and causing ripples. These principles would result in an active warp that might spin like a top, a movement known as precession.
“If we know how fast or if the warp rotates, it could be like a piece of a puzzle,” Chrobáková said. “It tells us a lot of information about how the warp was created.”
Last year, a team reported in the journal Nature Astronomy that our galaxy’s warp was spinning using data from the European Space Agency’s Gaia satellite, which gives ultraprecise measurements of the location of the Milky Way’s stars. A second paper, published in The Astrophysical Journal in December, confirmed these results, indicating that the warp was zipping along rather quickly, orbiting with a period of 600 million to 700 million years.
If this is the case, the procession will be roughly 10 times faster than previous models predicted, according to Chrobáková.
However, in a new study, she and her IAC co-author Martn López-Corredoira put the brakes on the previous measurements. Chrobáková and López-Corredoira found that the warp is traveling about 3.4 times faster than the results announced last year by looking at the identical Gaia data but modeling the features differently. Their findings were published in The Astrophysical Journal on May 13th. “My research puts down this new breakthrough and says we are back to where we started,” Chrobáková said. “We call it an anti-discovery.”
However, the error bars on Chrobáková’s findings are large enough to leave the matter unsolved, according to Ronald Drimmel, an astronomer at Italy’s University of Turin who was part of the team that first measured a precessing warp.
“It might be indicating that there’s no motion, or that it has a large motion,” he told Live Science. “There’s quite a bit of uncertainty.”
Much of the disagreement comes down to the precise shape of the warp itself, which neither team has a perfect handle on, Drimmel said. “Making such measurements is hard. We’re right in the disk of the galaxy, and dust clouds limit how far we can see.”
Chrobáková agreed that further information is needed to address this problem. Gaia is expected to produce a new catalog next year, which may contain additional information on this controversy. That’s a good thing, because other galaxies are likely too far away to settle the debate. “The Milky Way is the galaxy we have the best chance of exploring in such detail,” Chrobáková said.