Astronomers using NASA’s Chandra X-ray Observatory have found evidence for an “awesome upheaval” in a massive cluster of galaxies. A bright arc of ferociously hot gas extending more than two million light years requires one of the most energetic events ever detected.
“The
huge feature we detected in the cluster combined with its high temperature (170 million oC) points to an exceptionally dramatic event in the nearby Universe,” says Ralph Kraft of the Harvard-Smithsonian Center for Astrophysics, leader of a team of astronomers involved in this research. “While we’re not sure what caused it, we have narrowed it down to a couple of exciting possibilities.”
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The
favored explanation is that two massive galaxy clusters are running into each other at about 4 million miles per hour. When hot clouds of gas in the two clusters meet, shock waves produce a sharp change in pressure along the boundary where the collision is taking place, giving rise to the observed arc, which resembles an titanic weather front.
“Although this would be an extreme collision, one of the most powerful ever seen, we think this may be what is going on,” says team member Martin Hardcastle of the University of Hertfordshire in the United Kingdom.
One problem with the collision theory is that only a single peak in the X-ray emission is seen, whereas two would be expected. Longer observations with Chandra and the XMM-Newton X-ray observatories should help determine how serious this problem is for the collision hypothesis.
Another
possible explanation is that the disturbance was caused by an outburst generated by matter falling into a supermassive black hole. In this scenario, the black hole would inhale most of the matter but expel some of it outward in a pair of high-speed jets, heating and pushing aside surrounding gas.
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Such
events are known to occur in this cluster. A galaxy named 3C438 near the center of the cluster is a powerful source of explosive activity–presumably due to a supermassive black hole. But the energy in these outbursts is not nearly large enough to explain the Chandra data.
Right:
A radio map of 3C438 reveals jets spewing from the galaxy’s core–a sign of explosive activity. [More]
“If this event was an outburst from a supermassive black hole, then it’s by far the most powerful one ever seen,” says team member Bill Forman, also from the Center for Astrophysics.
The phenomenal amount of energy involved implies a very large amount of mass swallowed by the black hole, about 30 billion times the Sun’s mass consumed over a period of 200 million years. The authors consider this rate of black hole growth implausible.
“These values have never been seen before and, truthfully, are hard to believe,” notes Kraft. Until these issues are sorted out, the awesome upheaval remains a mystery.
These results were presented at the American Astronomical Society meeting in Honolulu, HI, and will appear in an upcoming issue of The Astrophysical Journal. NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency’s Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center, Cambridge, Mass.
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Filed under: Deep Space
First of all, the expansion of space is not limited by the speed of light. We estimate the universe is about 13.7 billion years old. In all that time it has been expanding. A distant galaxy that shows a large amount of red shift is measured to be, say 10 billion light years away. That is "look back" time. The actual distance may be more like 40 billion light years. In other words, the light we're seeing now from that object left 10 billion years ago. Since that time that object has evolved and space has expanded even more.
The nearest large spiral galaxy to our own, the Andromeda Galaxy, is 2.6 million light years away. On a scale of billions of years of time, this is not much time for light to have traveled from there to here, and this galaxy is indeed gravitationally bound with ours and is a next door neighbor.
The thing to stress is that it is empty space that is expanding, and that expansion is not limited to the speed of light. Indeed, according to Hubble's law, the reason we can only see so far into the universe is because the further things are away from us, the faster they are receding from us. Our "horizon" is where things are receding from us at greater than light speed.
If you study Inflation Theory put forth by respected astrophysicist Alan Guth, it is that in the very early beginnings, at the tiniest imaginable fraction of a second of when time first began, the universe expanded exponentially, much faster than light speed. This theory dovetails well with Big Bang theory. Cosmology is complicated and sounds absurd when you try to explain it in simple terms. There is much free reading available on the subject just over the Internet alone, but a subscription to Astronomy Magazine is fun and enlightening, and Tim Ferris' cosmology novel "The Whole Shebang" covers your question quite well when it discusses the "horizon problem" and the cosmic microwave background radiation, those light echoes from the Big Bang that were accidentally discovered a few decades ago.