Galactic Pyrotechnics on Display
A galaxy about 23 million light years away is the site of impressive, ongoing
fireworks. Rather than paper, powder and fire, this galactic light show involves
a giant black hole, shock waves and vast reservoirs of gas.
This galactic fireworks display is taking place in NGC 4258, also known as
M106, a spiral galaxy like the Milky Way. This galaxy is famous, however, for
something that our galaxy doesn’t have – two extra spiral arms that glow in
X-ray, optical and radio light. These features, or anomalous arms, are not
aligned with the plane of the galaxy, but instead intersect with it.
The anomalous arms are seen in this new composite image of NGC 4258, where
X-rays from NASA’s Chandra X-ray Observatory are blue, radio data from the NSF’s
Karl Jansky Very Large Array are purple, optical data from NASA’s Hubble Space
Telescope are yellow and infrared data from NASA’s Spitzer Space Telescope are
red.
A new study made with Spitzer shows that shock waves, similar to sonic booms
from supersonic planes, are heating large amounts of gas – equivalent to about
10 million suns. What is generating these shock waves? Researchers think that
the supermassive black hole at the center of NGC 4258 is producing powerful jets
of high-energy particles. These jets strike the disk of the galaxy and generate
shock waves. These shock waves, in turn, heat the gas – composed mainly of
hydrogen molecules – to thousands of degrees.
The Chandra X-ray image reveals huge bubbles of hot gas above and below the
plane of the galaxy. These bubbles indicate that much of the gas that was
originally in the disk of the galaxy has been heated and ejected into the outer
regions by the jets from the black hole.
The ejection of gas from the disk by the jets has important implications for
the fate of this galaxy. Researchers estimate that all of the remaining gas will
be ejected within the next 300 million years – very soon on cosmic time scales –
unless it is somehow replenished. Because most of the gas in the disk has
already been ejected, less gas is available for new stars to form. Indeed, the
researchers used Spitzer data to estimate that stars are forming in the central
regions of NGC 4258, at a rate which is about ten times less than in the Milky
Way galaxy.
The European Space Agency’s Herschel Space Observatory was used to confirm
the estimate from Spitzer data of the low star formation rate in the central
regions of NGC 4258. Herschel was also used to make an independent estimate of
how much gas remains in the center of the galaxy. After allowing for the large
boost in infrared emission caused by the shocks, the researchers found that the
gas mass is ten times smaller than had been previously estimated.
Because NGC 4258 is relatively close to Earth, astronomers can study how this
black hole is affecting its galaxy in great detail. The supermassive black hole
at the center of NGC 4258 is about ten times larger than the one in the Milky
Way and is consuming material at a faster rate, potentially increasing its
impact on the evolution of its host galaxy.
These results were published in the June 20, 2014 issue of The Astrophysical
Journal Letters and are available
online. The authors are Patrick Ogle, Lauranne Lanz and Philip Appleton from
the California Institute of Technology in Pasadena, California.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the
Chandra program for NASA's Science Mission Directorate in Washington. The
Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls
Chandra's science and flight operations.
Image credit: X-ray: NASA/CXC/Caltech/P.Ogle et al; Optical: NASA/STScI; IR:
NASA/JPL-Caltech; Radio: NSF/NRAO/VLA
NASA
Guillermo Gonzalo Sánchez Achutegui
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