A team of astronomers led by Dr Sebastian Hoenig from the University of Copenhagen and the University of Southampton has developed a new method for determining precise distances to very distant galaxies and used it to accurately measure the distance to a nearby galaxy called NGC 4151.
This image shows the spiral Seyfert galaxy NGC 4151, also known as the Eye of Sauron. Image credit: NASA.
NGC 4151 is an intermediate spiral Seyfert galaxy located in the constellation Canes Venatici. It is dubbed the Eye of Sauron for its similarity to the film depiction of the eye of the character in The Lord of the Rings.
Recent estimates of the distance to the NGC 4151’s central supermassive black hole range from 13 million to 95 million light-years.
But using the newly-developed method Dr Hoenig and his colleagues calculated the distance of 62 million light-years. As in the famous saga, a ring plays a crucial role in this measurement.
All big galaxies in the Universe host a supermassive black hole in their center and in about a tenth 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.
The hot dust forms a ring around the supermassive black hole and emits infrared radiation, which the scientists used as the ruler.
By combining the light from the two 10-m Keck telescopes on Mauna Kea on Hawaii using a method called interferometry, the scientists achieved an effective resolution equivalent to a telescope with a perfect 85-meter diameter mirror. This provided very high resolution – a hundred times better resolution than the Hubble Space Telescope – and allowed them to measure the angular size of the dust ring on the sky.
By combining the physical size of 30 light-days with the apparent size measured with the data from the Keck interferometer, the astronomers were able to determine the distance to NGC 4151.
“We calculated the distance to be 62 million light-years,” said Dr Darach Watson of the University of Copenhagen’s Niels Bohr Institute, who is a co-author of the paper published in the journal Nature.
“The previous calculations based on redshift were between 13 million and 95 million light-years, so we have gone from a great deal of uncertainty to now being able to determine the precise distance. This is very significant for astronomical calculations of cosmic scale distances.”
“Such distances are key in pinning down the cosmological parameters that characterize our Universe or for accurately measuring black hole masses,” Dr Hoenig added.
“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 per cent.”
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Sebastian F. Hoenig et al. 2014. A dust-parallax distance of 19 megaparsecs to the supermassive black hole in NGC 4151. Nature 515, 528–530; doi: 10.1038/nature13914
