The good old stalwart, takes a licking keeps on ticking, Hubble Space Telescope, has discovered the answer to a long perplexing puzzle by resolving giant but delicate filaments shaped by the strong magnetic field around the active galaxy NGC 1275; a most striking example of the influence of these immense tentacles of extra-galactic magnetic fields, according to scientists.


Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

Acknowledgment: A. Fabian (Institute of Astronomy, University of Cambridge, UK)

NGC 1275, an active galaxy, lies at the center of the Perseus Cluster of galaxies. It hosts a supermassive black hole at its core that blows bubbles of radio-wave emitting material into the surrounding cluster gas and its most interesting characteristic is the lacy filigree of gaseous filaments extending out beyond the galaxy into the multi-million degree X-ray emitting gas that fills the cluster.

These filaments provide important clues about how giant black holes affect their surrounding environment and are the only visible-light evidence of the intricate relationship between the core’s black hole and the surrounding cluster gas.

A team of astronomers using the NASA/ESA Hubble Space Telescope Advanced Camera for Surveys (ACS) have for the first time resolved individual threads of gas which make up the filaments. The amount of gas contained in a typical thread is about one million times the mass of our Sun. And at a mere 200 light-years wide, are unusually straight, extending out for up to 20 000 light-years distant. The filaments are formed when cold gas from the galaxy’s core is dragged out in the wake of rising bubbles blown by the black hole.

A challenge for astronomers is to understand how the delicate structures have withstood the hostile high-energy environment of the galaxy cluster for more than 100 million years. One would have expected them to have heated up, dispersed, and evaporated over a very short period of time, possibly collapsing under their own gravity to form stars. Also, the fact that they haven’t been ripped apart by the strong tidal pull of gravity in the cluster’s core is unusual.

Andy Fabian from the University of Cambridge, UK, published a new study in Nature today, August 21, 2008 that proposes the magnetic fields hold the charged gas in place and resist forces that would distort the filaments. This skeletal structure has been able to contain and suspend these peculiarly long threads for over 100 million years. “We can see that the magnetic fields are crucial for these complex filaments – both for their survival and for their integrity,” said Fabian.

The new Hubble data also allowed the strength of the magnetic fields in the filaments to be determined from their size. Thinner filaments are more fragile, requiring stronger magnetic fields for support. However, the finer the filaments, the more difficult they are to observe.

The filamentary system in NGC 1275 provides the most striking example of the workings of extra-galactic magnetic fields so far and is a spectacular by-product of the complex interaction between the cluster gas and the supermassive black hole at the galaxy’s heart. Similar networks of filaments are found around many other, even more remote, central cluster galaxies. They cannot be observed in anything like the detail of NGC 1275, so the team will apply the understanding gained here to interpret observations of these more distant galaxies.