Space and astronomy news
The region near the Milky Way’s centre is dominated by the supermassive black hole that resides there. Sagittarius A*’s overwhelming gravity creates a chaotic region where tightly packed, high-speed stars crash into one another like cars in a demolition derby.
These collisions and glancing blows change the stars forever. Some become strange, stripped-down, low-mass stars, while others gain new life.
Continue reading “The Stellar Demolition Derby in the Centre of the Galaxy”
The Milky Way is a spiral galaxy. More specifically, it is a barred spiral galaxy, meaning that within its central region, there is a bar shape off of which the spirals emanate. About two-thirds of spiral galaxies are barred spirals, and astronomers have thought this difference is just a variance in how density waves cluster stars in a galaxy. But a new study suggests that the bar of the Milky Way may have been caused by an ancient collision with another galaxy.
Continue reading “Did the Last Great Galactic Merger Create the Milky Way's Bar?”
Since it was first theorized in the 1970s, astrophysicists and cosmologists have done their best to resolve the mystery that is Dark Matter. This invisible mass is believed to make up 85% of the matter in the Universe and accounts for 27% of its mass-energy density. But more than that, it also provides the large-scale skeletal structure of the Universe (the cosmic web), which dictates the motions of galaxies and material because of its gravitational influence.
Unfortunately, the mysterious nature of Dark Matter means that astronomers cannot study it directly, thus prevented them from measuring its distribution. However, it is possible to infer its distribution based on the observable influence its gravity has on local galaxies and other celestial objects. Using cutting-edge machine-learning techniques, a team of Korean-American astrophysicists was able to produce the most detailed map yet of the local Universe that shows what the “cosmic web” looks like.
Continue reading “A Dark Matter map of our Local Cosmic Neighborhood”
A high-velocity cloud hurtling toward the Milky Way should have disintegrated long ago when it first collided with and passed through our Galaxy. The fact that it’s still intact suggests it’s encased in a shell of dark matter, like a Hobbit wrapped in a mithril coat.
Mapping dark matter — the unseen stuff that makes up more than 80 percent of cosmic matter — near our Galaxy is crucial to fully understanding how the Milky Way assembled over cosmic time.
This firstly requires detailed observations of nearby dwarf galaxies — galaxies each totaling a mass less than 10% of the Milky Way’s 200 to 400 billion stars — because they’re enshrouded in dark matter. More recently, it has been suggested that nearby high velocity clouds of hydrogen gas are encased in dark matter as well. But the effects of their dark matter halos remain unknown.
So Matthew Nichols from the Sauverny Observatory in Switzerland and colleagues set out to observe the Smith Cloud — a high-velocity cloud of hydrogen gas located 8,000 lightyears away in the constellation Aquila — in order to better constrain its dark matter halo. They used the Green Bank Telescope (GBT) in west Virginia in order to detect the faint radio emission of neutral hydrogen.
“The Smith Cloud is really one of a kind. It’s fast, quite extensive, and close enough to study in detail,” said Nichols in a press release. At its distance the cloud (9,800 lightyears long and 3,300 lightyears wide) covers almost as much sky as the constellation Orion.
“It’s also a bit of a mystery; an object like this simply shouldn’t survive a trip through the Milky Way, but all the evidence points to the fact that it did,” said Nichols. Previous studies of the Smith Cloud revealed that it first passed through our Galaxy many millions of years ago. By reexamining and carefully modeling the cloud, Nichols’ team now believes that it’s actually wrapped in a substantial halo of dark matter.
“Based on the currently predicted orbit, we show that a dark matter free cloud would be unlikely to survive this disk crossing,” said coauthor Jay Lockman from the National Radio Astronomy Observatory. “While a cloud with dark matter easily survives the passage and produces an object that looks like the Smith Cloud today.”
Not only does this study help astronomers start to characterize the dark matter enshrouding these seemingly harmless clouds, but it helps strengthen the case that the Smith Cloud isn’t purely a cloud of hydrogen gas, but a failed dwarf galaxy, originating from farther away in space. The presence of dark matter, however, will have to be further confirmed.
The paper has been submitted to the Monthly Notices of the Royal Astronomical Society and is available for download here.