Using archival data from ESA's XMM-Newton orbital telescope, a team of astronomers from the University of Michigan has calculated the speed of the vast halo composed of incredibly hot gas that surrounds the Milky Way. The halo is thought to have a mass the equivalent of all of the stars in our galaxy combined, and by understanding it, we could gain insights into the formation, and future evolution of the Milky Way.
It has been less than five centuries since Copernicus proposed his theory that the Sun, rather than the Earth, lay at the center of our solar system. In the relatively short time since this humble beginning, mankind's understanding of our solar system, and the galaxy in which it resides, has advanced at an astonishing pace.
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We now know that we live in a barred spiral galaxy called the Milky Way, which is composed of billions of stars, all spinning around a supermassive black hole known as Sagittarius A*, that lurks at the galactic center. Our understanding of how the Milky Way came to coalesce and evolve is constantly being revised as we discover new characteristics and elements of our galaxy.
To further inform our understanding of the Milky Way, a team of researchers looked to the halo of hot gas that surrounds our galaxy. Previous observations carried out by NASA's Chandra X-ray Observatory suggest that the halo has a radius of around 300,000 light-years, though it could be far larger. Furthermore, the gas that makes up the halo is thought to be incredibly hot, with a temperature between 1 million and 2.5 million Kelvins, rendering the matter in the state of ionized plasma.
It had previously been believed that the halo, unlike the ever spinning disk of the Milky Way, was stationary. However, the new study appears to disprove the standing theory. To gauge the halo's speed, the researchers made use of data collected by ESA's XMM-Newton telescope, focusing on thin strips of oxygen embedded within the vast cloud.
Since movement stretches the wavelength of light, the team was able to observe the X-ray signature of the particles, and gauge the speed and direction of the halo. It was found that the halo was rotating in the same direction as the disk of the Milky Way, and at a comparable, if slightly slower, pace. The disk of our galaxy is estimated to spin at around 540,000 mph, while the halo moves at some 400,000 mph.
The discovery that the halo is traveling at a comparable speed and direction as our galaxy will require a rethink to current models regarding the evolution of our galaxy.
The results indicate that the halo is perhaps the source of a significant amount of the star and planet forming matter that makes up the disk of our Milky Way. Furthermore, by studying the spin of the halo, astronomers hope to gauge the rate at which the vast cloud may grant infusions of matter into the disk of the Milky Way in the distant future.
The Milky Way's gas halo could prove vital in mankind's ongoing mission to gain a deeper understanding of the myriad of galaxies that populate the cosmos. It is now thought possible that these vast galactic halos could account for some of the ordinary, or baryonic matter, which is expected, yet missing, in surveys made of the observable universe.