23 May 2011

 

 

The Jets of Centaurus A in high resolution

 

Using a network of 9 radio telescopes called TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) a group of researchers, led by Cornelia Mueller (University of Erlangen-Nuremberg, Germany) has obtained the highest resolution image ever of the heart of Centaurus A (in NGC 5128), a giant radio galaxy with a super massive black hole in its centre.
The observations were centred on the black hole (with a mass 55 million times that of the Sun) and mapped the two jets that are emitted from it in opposite directions, with velocities of around 1/3 the speed of light.
Although jets are a feature of all radio galaxies, the mechanisms that generate and maintain them are still very poorly understood. However, it is fairly certain that material must fall onto the black hole from a surrounding accretion disk.
In the image above we see a composite image of Cantaurus A with white tones being mostly from the visible, X-rays in blue and microwave emission in orange. The jets, and so-called lobes at their ends, are clearly seen, and it is these that emit radio waves and make it one of the brightest and largest radio sources in the sky, extending over 20 times the size of the full Moon.
The new radio image, mapping the very central region of the radio jets, is shown as an inset to the upper right. At the resolution of the above figure, the field of view of the inset is less than one pixel of the main image! So the incredible thing about this new image is its resolution, resolving structures only 15 light days across, in a field only 4.2 light years across, less than the distance between the Sun and the nearest star.
These size scales, measured in a galaxy 12 million light years away, show what can be done with modern techniques of "very long baseline interferometry", a method of combining telescopes separated by large distances to create an instrument with exceptional resolution. The results of the study (to appear in the June issue of Astronomy and Astrophysics) will help to understand how super massive black holes create these very energetic jets, that, from a tiny region of space, form such gigantic structures; far larger than any single galaxy.

 

by Michele Ferrara & Marcel Clemens

credit: ESO/WFI (visible); MPIfR/ESO/APEX/A.Weiss et al.
(microwave); NASA/CXC/CfA/R.Kraft et al. (X-ray).
Inset: NASA/TANAMI/Müller et al