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Advances in space

A new way of measuring precise distances to galaxies tens of millions of light years away has been developed by scientists from the University of Southampton.

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Scientists lead the way in measuring distances in space

The galaxy Credit: Press Association

A new way of measuring precise distances to galaxies tens of millions of light years away has been developed by scientists from the University of Southampton. Dr Sebastian Hoenig has created the method which is similar to what land surveyors use on earth, by measuring the physical and angular, or "apparent", size of a standard ruler in the galaxy, to calibrate the distance from this information. The research,which is published in the journal Nature, was used to identify the accurate distance of the nearby NGC 4151 galaxy, which wasn't previously available. The galaxy NGC 4151, which is dubbed the Eye of Sauron by astronomers for its similarity to the film depiction of the eye of the character in The Lord Of The Rings, is important for accurately measuring black hole masses. Recently reported distances range from 4 to 29 megaparsecs, but using this new method the researchers calculated the distance of 19 megaparsecs to the supermassive black hole.

One of the key findings is that the distance determined in this new fashion is quite precise - with only about 10% uncertainty. In fact, if the current result for NGC 4151 holds for other objects, it can potentially beat any other current methods to reach the same precision to determine distances for remote galaxies directly based on simple geometrical principles. Moreover, it can be readily used on many more sources than the current most precise method. Such distances are key in pinning down the cosmological parameters that characterise our universe or for accurately measuring black hole masses. Indeed, NGC 4151 is a crucial anchor to calibrate various techniques to estimate black hole masses. Our new distance implies that these masses may have been systematically underestimated by 40%.

– Dr Hoenig, University of Southampton

A university spokesman explained that the method involves measuring the dust rings that form around supermassive black holes. The 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 this ring is so small that the observations were carried out using infrared interferometry to combine WM Keck Observatory's twin 10m telescopes, to achieve the resolution 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 very close to the black hole and the infrared emission. This delay is the distance the light has to travel (at the speed-of-light) from close to the black hole out to the hot dust. By combining this physical size of the dust ring with the apparent size measured with the data from the Keck interferometer, the researchers were able to determine a distance to the galaxy NGC 4151. Dr Hoenig, together with colleagues in Denmark and Japan, is currently setting up a new programme to extend their work to establish precise distances to a dozen galaxies in this new way and use them to constrain cosmological parameters to within a few per cent. In combination with other measurements, this will provide a better understanding of the history of expansion of our universe.

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