The most detailed three-dimensional map yet on the Milky Way has been revealed, showing that our galaxy is not a flat disc but has a "slant" shape like a fascinator hat or vinyl record left in the sun
"The stars 60,000 light years away from the center of the Milky Way is as far as 4,500 [light years] above or below the galactic plane – this is a large percentage, "says Dr. Dorota Skowron of the University of Warsaw, the first author of the latest research.
Both the new study and an earlier one published in February, which found a similar shape, are based on the scattering across the galaxy of stars known as Cepheid's bodies whose brightness varies in a regular cycle over time. This phenomenon of dimming and brightening is the key to creating the maps.
Although a star may be weaker because it is farther away, it may also be due to it being less brilliant. For Cepheids, the star's maximum brightness is related to how long the cycle of brightening and dimming takes, with lighter Cepheids having longer cycles. By comparing this inherent brightness with how bright the star appears to be, scientists can find out how far away a Cepheid is.
The new study, published in the journal Science, includes data from more than 2,400 Cepheider, enabling the team to build the most detailed three-dimensional map yet on the Milky Way.
” Cepheids are relatively young – younger than 200 million years – while the Milky Way is believed to be about 10 billion years old. This means we can use Cepheids to study our galaxy's relatively recent history, "Skowron said.
The new research shows that our galaxy, which Skowron notes has a radius of about 70,000 light-years and four spiral arms, is" oblique " , With the outer regions of one side curved "up" from the galactic plane toward the northern galactic pole and the other curved "down". The thickness of the disc is not the same all the way – it flares against the edges, like a pair of jeans from the 1970s
These findings also coincide with other work showing a warp and flare, including studies of the hydrogen distribution atoms across the Milky Way, although Skowron states that uncertain distances mean that the shape of the warp could not be removed from these studies.
Prof Richard de Grijs from Macquarie University, co-author of the previous Cepheid study, said there were a number of explanations for our galaxy warp, which include mergers with smaller galaxies, or that the gravity of the Milky Way becomes weaker in its outer regions, which means that bodies there can be diverted from the galactic plane by the drawbar of other stars. Alternatively, he said, "gravitational interactions with nearby galaxies … could distort the gravitationally weakly bound outer regions into a warlike structure."
Skowron said that rotation was not seen in the central regions of the Milky Way because the gravitational forces there were so strong that it was difficult to deflect stars and gas from the galactic plane.
The new study suggests the bending away from the galaxy's plane starts about 26,000 light years from the center of the galaxy – about where our solar system is located – but becomes steeper from about 32,000 light years.
A distorted galaxy was not uncommon, Skowron said. “It is actually estimated that about half of the galaxies may have some detectable rotation. But the warping of our galaxy is quite significant compared to others. "
As with the previous work, the new study shows the Cepheids disproportionately lying on one side of the oblique galaxy and forming an arcuate spread.
The Polish team also found that younger Cepheider was closer to the center of the Milky Way. while older Cepheider is further out. A computer simulation revealed that there would have been star-forming events 64m, 113m and 175m years ago to produce the distribution of Cepheids seen today.
Dr. Vivienne Wild, an expert on galaxies from the University of St. Andrews said it was much more difficult to explore the structure of our own galaxy than to others.
"This is because we are inside it, and determining the distance to stars is really difficult," she said.
Wild welcomed the exploration of how and why the Cepheids gather on one side of the galaxy. "By measuring the ages of the stars and plotting their 3D positions on the Milky Way," she said, "we can see how they were originally formed in Milky Way's spiral arms up to 175m years ago."