Milky Way Galaxy Being Warped By Dark Matter?
The spiral shape of the Milky Way galaxy is well known, but most people don’t realize that it is twisted, and, according to Space.com, astronomers have discovered that it might be due to dark matter. When we think of our galaxy floating in space, we usually think of its spiral arms reaching out in a flat disc, like a pancake in a pan. But if you imagine that pancake being tossed a little bit, you get an idea of the wavy curve seen around the edge of our galaxy.
The shape of the Milky Way is inconsistent, and not perfectly flat, but slightly twisted, and new research seems to think it’s the pressure of dark matter bending it out of shape.
This vision of the Milky Way galaxy has developed over years of careful research of the shape of the galaxy, whose structure isn’t as straightforward as it had originally appeared. Its warped nature has puzzled astronomers for a long time, but at the Center for Astrophysics | Harvard and Smithsonian (CfA), astronomers have hypothesized that the shape of the Milky Way could be the effect of the football-shaped warp of the dark matter that surrounds our galaxy. This finding could give us new insight into the nature of dark matter, how it behaves, and its role in shaping galaxies like ours, not to mention a more detailed perspective of the history and the development of our galaxy.
Though it exists throughout and surrounds the Milky Way galaxy, dark matter has only been inferred by scientists on the basis of the way it interacts with normal matter.
While the Milky Way galaxy is familiar enough as a subject of study, dark matter is a bit more difficult to explain. While scientists know dark matter exists, it is essentially invisible as it does not interact with light, meaning it is not composed of ordinary atoms like all other matter in the universe. Still, 85 percent of the matter contained in the universe is dark matter, so all of the matter we can see—from stars and planets to flowers and people—accounts for only 15% percent of the matter in the known universe.
Though it exists throughout and surrounds the Milky Way galaxy, dark matter has only been inferred by scientists on the basis of the way it interacts with normal matter. This interaction is vitally important to the continued survival of galaxies as their speed of rotation is so great that at times the mass of their visible matter would not be sufficient to hold them together. Therefore, it is dark matter that keeps galaxies from falling apart.
This means that the Milky way, like potentially every galaxy but definitely most of them, is enveloped in dark matter. The edge of the galaxy is held in by this surrounding halo that keeps it from flying apart. The researchers at Harvard were able, just last year, to calculate that this dark matter halo exists in a football-like elliptical shape that tilts at an angle. This is inferred from the shape of the stellar halo of the galaxy—that is, its outer ring—which also bends in a similar manner.
This inference led the team to create computer models of the Milky Way that show that the orbit of the stars within the star halo fits inside a dark matter halo with a football shape. This matches almost perfectly with the warp and flared edge of the Milky Way galaxy. In a statement, professor of astronomy at the CfA and study team member Charlie Conroy said that such a tilted dark matter halo comes up frequently in simulations, but that scientists had not yet looked at how it affected the Milky Way.
The wobble of the Milky Way galaxy’s disc turns out to be elegantly explained by the presence of the warped dark matter halo. The team had also hypothesized that the Milky Way has expanded by means of colliding with other galaxies, an idea these new findings also support. CfA-affiliated scientist and study team leader Jiwon Jesse Han confirms that our idea of a galaxy that spreads out in a flat disc is correct, but only if that galaxy has evolved entirely on its own without such collisions.
This inference led the team to create computer models of the Milky Way that show that the orbit of the stars within the star halo fits inside a dark matter halo with a football shape.
This means that the warped disc of the Milky Way indicates a merger event—the collision of two galaxies. As the shape of the dark Matter disc is calculated, it could help scientists understand the particles dark matter has instead of atoms, their properties, and how they behave. It could also tell us more about the history and development of our galaxy and perhaps even provide insight regarding the “blobs” of dark matter that astronomers believe float freely between galaxies.
