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The Galaxy NGC 4151 called the, ‘Eye of Sauron’ due to its similarity to the eye in the film Lord of the Rings. The image shows the supermassive black hole, which is still active, that is to say that it engulfs gas and dust clouds from its surroundings. In this process, it emits ultraviolet radiation, which heats the ring-shaped dust cloud that orbits around the black hole at a distance and this causes the dust cloud to emit infrared radiation. Credit: NASA
MAUNA KEA, Hawaii — A team of scientists, led by Dr. Sebastian Hoenig from the University
of Southampton, has accurately
measured the distance to the nearby NGC4151 galaxy, using the W. M. Keck
Observatory Interferometer. The team employed a new technique they developed,
which allows them to measure precise distances to galaxies tens of
millions of light years away. The
research was published today in the journal Nature.
new technique is similar to that used by land surveyors on earth, who measure
both the physical
and angular – or ‘apparent’ – size of a distant
object, to calculate its distance from Earth.
reported distances to NGC 4151, which contains a supermassive black hole, ranged
from 4- to 29-megaparsecs, but using this new, more accurate method, the
researchers calculated the distance to the supermassive black hole as 19
galaxy NGC415 is dubbed the ‘Eye of Sauron’ by astronomers for the similarity to its
namesake in the film trilogy The Lord of the Rings. As in the famous saga, a ring plays a crucial role in this
new measurement. All big galaxies in the universe host a supermassive black
hole in their center and in about 10 percent of all galaxies, these
supermassive black holes are growing by swallowing huge amounts of gas and dust
from their surrounding environments. In this process, the material heats up and
becomes very bright — becoming the most energetic sources of emission in the
universe known as active galactic nuclei (AGN).
This hot dust forms a ring around the supermassive black hole and
emits infrared radiation, which the researchers used as the ruler. However, the
apparent size of the Eye of Sauron’s ring is so small, the observations were
carried out using the Keck Interferometer, which combines Keck Observatory’s
twin 10-meter telescopes — already the largest telescopes on Earth — to achieve
the resolving power of an 85m telescope.
To measure the physical size of the dusty ring, the researchers measured
the time delay between the emission of light from close to the black hole and
the more distant infrared emission. The distance from the center to the hot
dust is simply this delay divided by the speed of light.
By combining the physical size of the dust ring with the apparent size
measured with the Keck Interferometer, the researchers were able to determine a
distance to NGC 4151.
“One of the key findings is that the
distance determined in this new
fashion is quite precise — with 90
percent accuracy,” Hoenig said.
“In fact, this method, based on simple geometrical principles, gives the
precise distances for remote galaxies. Moreover, it can be readily used
more sources than current methods. Such distances are key in pinning
down the cosmological parameters that characterize our universe or in
accurately measuring black hole masses. Indeed,
NGC 4151 is a key to calibrating various techniques of estimating black
masses. Our new distance implies that these masses may have been
underestimated by 40 percent.”
Hoenig, together with colleagues in Denmark and Japan, is currently
setting up a new program to extend their work to many more AGN. The goal is to
establish precise distances to a dozen galaxies using this technique and use
them to constrain cosmological parameters to within few per cent. Combined with
other measurements, this will provide a better understanding of the history of
expansion of our universe.
The W. M. Keck Observatory operates the most scientifically productive telescopes on Earth. The two, 10-meter
optical/infrared telescopes near the summit of Mauna Kea on the Island of
Hawaii feature a suite of advanced instruments including imagers, multi-object
spectrographs, high-resolution spectrographs, integral-field spectrographs and
world-leading laser guide star adaptive optics systems.
Interferometer began construction in 1997, and finished its mission in
2012. It was funded by NASA and managed by JPL. JPL is managed by
Caltech for NASA.
Keck Observatory is a private 501(c) 3
non-profit organization and a scientific partnership of the California
Institute of Technology, the University of California and NASA.