Black Hole Sound Waves
the Perseus cluster.
The black hole resides in the Perseus cluster of galaxies located 250 million light years from Earth. In 2002, astronomers obtained a deep Chandra observation that shows ripples in the gas filling the cluster. These ripples are evidence for sound waves that have traveled hundreds of thousands of light years away from the cluster's central black hole.
Right: The Perseus cluster of galaxies. Each fuzzy object is a galaxy. Unseen is a vast cloud of hot gas filling the cluster. Near the center of it all lies a supermassive black hole.
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In musical terms, the pitch of the sound generated by the black hole translates into the note of B flat. But, a human would have no chance of hearing this cosmic performance because the note is 57 octaves lower than middle-C. For comparison, a typical piano contains only about seven octaves. At a frequency over a million billion times deeper than the limits of human hearing, this is the deepest note ever detected from an object in the Universe.
"The Perseus sound waves are much more than just an interesting form of black hole acoustics," says Steve Allen, also of the Institute of Astronomy and a co-investigator in the research. "These sound waves may be the key in figuring out how galaxy clusters, the largest structures in the Universe, grow."
Above: Peering into the heart of the Perseus Cluster (left), the Chandra X-ray Observatory detected sound waves rippling through the gas (right). [more]
For years astronomers have tried to understand why there is so much hot gas in galaxy clusters and so little cool gas. Hot gas glowing with X-rays ought to cool because X-rays carry away some of the gas' energy. Dense gas near the cluster's center where X-ray emission is brightest should cool the fastest. As the gas cools, say researchers, the pressure should drop, causing gas from further out to sink toward the center. Trillions of stars ought to be forming in these gaseous flows.
Yet scant evidence has been found for flows of cool gas or for star formation. This forced astronomers to invent several different ways to explain how gas contained in clusters remained hot. None of them were satisfactory.
Black hole sound waves, however, might do the trick.
Right: an illustration of cavities and sound waves in the hot gas filling the Perseus cluster. [more]
A tremendous amount of energy is needed to generate the cavities, as much as the combined energy from 100 million supernovas. Much of this energy is carried by the sound waves and should dissipate in the cluster gas, keeping the gas warm and possibly preventing a cooling flow. If so, the B-flat pitch of the sound wave, 57 octaves below middle-C, would have remained roughly constant for about 2.5 billion years.
Perseus is the brightest cluster of galaxies in X-rays, and therefore was a perfect Chandra target for finding sound waves rippling through the hot cluster gas. Other clusters show X-ray cavities, and future Chandra observations may yet detect sound waves in those clusters, too.
The Chandra X-Ray Observatory -- learn more about Chandra and its many discoveries.
Chandra "Hears" A Black Hole For The First Time (NASA) -- the complete press release, including animations and a photo album.
Galaxy Clusters -- (CXO) Galaxy clusters are the largest gravitationally bound objects in the universe.
X-Ray Astronomy vs. Medical X-Rays -- (CXO) It's natural to associate the X-rays from cosmic objects with an X-ray from the doctor's office, but the comparison is a bit tricky.
more: The Perseus Cluster (APOD); The Perseus Cluster's X-ray Skull (APOD);
