Mountain Views News          Saturday, December 6, 2014

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Mountain Views-News Saturday, December 6, 2014 


“EYE OF SAURON” PROVIDES NEW WAY OF MEASURING DISTANCES TO GALAXIES


A team of scientists, led by Dr. Sebastian Hoenig 
from the University of Southampton, has 
measured the distance to the NGC 4151 (“Eye of 
Sauron”) galaxy with unprecedented accuracy, 
using the W. M. Keck Observatory Interferometer 
in Hawaii. 

 The team employed a new technique they 
developed, which allows them to measure 
distances to galaxies tens of millions of light-years 
away with 90 percent precision. The technique 
is similar to that used by land surveyors on 
Earth, who calculate distances by measuring 
the angular—or “apparent”—size of an object of 
known dimensions.

 Previous reported distances to NGC 4151, 
which contains a supermassive black hole, were 
far from consistent—ranging all the way from 4 
to 29 megaparsecs. Using this new, more accurate 
method, the researchers calculated the distance to 
the supermassive black hole as 19 megaparsecs (a 
megaparsec is equal to 3.26 million light-years).

 Galaxy NGC 4151 is dubbed the “Eye of Sauron” 
by astronomers for the similarity of its appearance 
to its namesake in the film trilogy, “The Lord of the 
Rings.” As in that 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 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—resulting in 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—and the researchers in this study used 
this dusty ring as their “ruler.” However, the 
apparent size of the Eye of Sauron’s ring is so small 
that the observations had to be carried out using 
the Keck Interferometer, which combines Keck 
Observatory’s twin 10-meter telescopes—already 
the largest telescopes on Earth—to achieve a 
resolving power equal to that of an 85-meter 
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 the 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 most precise distances for remote galaxies. 
Moreover, it can be readily used on many 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 hole masses. Our new distance implies 
that these masses may have been systematically 
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 active galactic 
nuclei. The goal is to establish precise distances to 
a dozen galaxies using this technique—and then 
use these precise distances as stepping-stones 
to vastly improve the precision of all distance 
measurements for the cosmos.

 You can contact Bob Eklund at: b.eklund@
MtnViewsNews.com.