Chuck Bednar for redOrbit.com – Your Universe Online
A titanic eruption took that took place at least two million years ago forced gases and other materials outward at speeds of up to two million miles per hour, and astronomers are just now witnessing the aftermath of the explosion thanks to NASA’s Hubble Space Telescope.
Lead researcher Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland, and his colleagues report that they have observed billowing clouds of gas that are approximately 30,000 light-years both above and below the plane of our galaxy.
This structure, which was discovered five years ago as a gamma-ray glow on the sky in the direction of the galactic center, have since been observed in X-rays and radio waves as well, the study authors explained. Recently, however, Hubble was used to measure the composition and velocity of the mysterious loves for the first time.
Fox’s team, who will be publishing a paper detailing their findings in The Astrophysical Journal Letters as well as presenting them at this year’s meeting of the American Astronomical Society (AAS) in Seattle, will now attempt to calculate the mass of the material that is being blow out of the Milky Way, which could help them determine the exact cause of this phenomenon.
Scientists have developed two possible origins for the bipolar lobes: the eruption of the supermassive black hole at its center, or a firestorm of star birth taking place in roughly the same region. While astronomers have spotted composed of streams of charged particles called gaseous winds emanating from the cores of other galaxies, the fact that a similar event is taking place in our own galaxy is giving them a unique, up-close view of the fireworks.
“When you look at the centers of other galaxies, the outflows appear much smaller because the galaxies are farther away. But the outflowing clouds we’re seeing are only 25,000 light-years away in our galaxy,” Fox explained. “We have a front-row seat. We can study the details of these structures. We can look at how big the bubbles are and can measure how much of the sky they are covering.”
These giant lobes are known as Fermi Bubbles, since they were initially detected using NASA’s Fermi Gamma-ray Space Telescope, and the researchers explain that the discovery of the high-energy gamma rays indicates that the energized gas in being forcefully launched into space as the result of a violent event taking place in the core of the galaxy.
In an attempt to learn more about these outflows, Fox and his colleagues used Hubble’s Cosmic Origins Spectrograph (COS) to probe the ultraviolet light from a distant quasar located behind the base of the northern bubble. Information about the velocity, composition, and temperature of the expanding gas inside the bubble is imprinted on that light, and only COS can detect it.
Using the spectrograph, they were able to measure that the gas on the near side of the bubble is moving towards Earth, while the gas on the far side is travelling away from our planet. It also indicated that the gas is travelling from the galactic center at approximately two million miles per hour, or three million kilometers per hour.
“This is exactly the signature we knew we would get if this was a bipolar outflow. This is the closest sightline we have to the galaxy’s center where we can see the bubble being blown outward and energized,” said co-author Rongmon Bordoloi, also of the Space Telescope Science Institute.
The COS observations also include the first-ever measurements of the composition of material being swept up into the gaseous cloud. The instrument was able to detect silicon, carbon, and aluminum, which indicates that the gas is enriched in the heavy elements produced inside stars and represents the fossil remnants of star formation.
The Hubble spectrograph also measured the temperature of the gas at approximately 17,500 degrees Fahrenheit, which is far cooler than most of the super-hot gas in the outflow, believed to be at about 18 million degrees Fahrenheit. Fox explained that the observations indicate the cooler gas, possibly interstellar gas in our galaxy’s disk, was being swept up into the hot outflow.
“This is the first result in a survey of 20 faraway quasars whose light passes through gas inside or just outside the Fermi Bubbles,” the Institute said in a statement. “An analysis of the full sample will yield the amount of mass being ejected. The astronomers can then compare the outflow mass with the velocities at various locations in the bubbles to determine the amount of energy needed to drive the outburst and possibly the origin of the explosive event.”
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