Mark Megahan
The spiral type galaxy we call home is named the “Milky Way.” Because our “small unregarded yellow sun” is stuck “far out in the uncharted backwaters of the unfashionable end of the western spiral arm” of it, we see the Milky Way edge on. When we can see it at all, through the smog. Even with clear conditions you can’t tell with the naked eye that the Milky Way wobbles. That’s because it’s warped. The professional astronomers had a hard time figuring it out. There’s a really good chance that mysterious “dark matter” is what’s twisting space out of shape like an old vinyl record that was left in the sun.
Galaxy warped and wobbling
The pundits are “laying the blame on a football-shaped, tilted halo of dark matter that envelopes our galaxy.” The Milky Way, experts at Space point out, “is twisted, and astronomers may finally know why.” They’re the ones who came up with the record analogy.
Most people say the Milky Way “resembles a flattened disk similar to a vinyl record.” It’s actually more like a Frisbee, with a rounded lip at the edge.
When they finally got the tools to study the structure in three dimensional detail, they noticed that it’s also warped. “Meaning it’s a bit closer to a Frisbee twisted and bent by an angry child.” They note that these “features have remained sort of mysterious for quite a while.”
Recently, astronomers from the Center for Astrophysics “have performed calculations that indicate the halo of dark matter enveloping the Milky Way could be off-kilter, and this could be causing the flared edge and warped shape of our galaxy.”
Even though dark matter seems to make up most of the universe, nobody knows much about it. Ours isn’t the only galaxy with the same problem but the important thing is that it gives us more clues to “the nature of dark matter and how it shapes the overall development of galaxies.”
Dark matter is so funky that it doesn’t interact with light in any way. Not only is the stuff totally invisible, it’s not really “matter” either. If it was any sort of matter as we understand that concept, it would have mass and interact with light. Whatever it is, the bizarre substance “makes up as much as 85% of the matter content of the universe.”
Influence on gravity
While dark matter is totally ignored by light, gravity can be disturbed. Trying to detect that is really tricky but it can be done. The only way astrophysicists were able to “infer the presence of dark matter is via its interactions with gravity and the influence this has on everyday matter and light.”
It’s impossible to notice any effect at small scale but you can see them at the galactic level. Nearly any galaxy can rotate like the platter of a hard drive, “so utterly fast that, in some cases, the gravitational effect of visible matter within these entities wouldn’t be sufficient to prevent them from flying apart.”
Since they’re spinning wildly and not falling apart, there must be some sort of galactic glue holding the whole thing in place. That’s how “researchers have deduced that most, if not all, galaxies are wrapped in a halo of dark matter.”
With our Milky Way galaxy, “that halo of dark matter is thought to extend out past the halo of stars surrounding the galaxy’s main disk and central galactic nucleus.” Then there’s the black hole lurking in the middle like the Tootsie Roll center of a tootsie pop.
“Last year, the same Harvard team was able to calculate the Milky Way’s stellar halo to hold an elliptical or football-like shape, angled at a tilt relative to the galaxy’s main disk.” Since then, they used computer models “to calculate that the orbit of those stars fits within a tilted, football-shaped dark matter halo.”
The good news is that it matches our observations. Their model “turned out to be a near-perfect match” with everything we know about our own Milky Way galaxy, flared edge, warp and all. “A tilted dark halo is actually fairly common in simulations, but no one had explored its effect on the Milky Way,” Charlie Conroy, study team member and a professor of astronomy at the CfA, relates in a statement.
