Bright streams of gas fan out from NGC 1275 — the giant elliptical galaxy at the centre of the Perseus constellation — making it look a bit like a supersized space jellyfish. These filaments are thought to be around 100 million years old, and although they appear static, they are buffeted by the extreme pressure and heat of the gases that surround them. Using images from the Hubble Space Telescope, astronomer Andrew Fabian at the Institute of Astronomy in Cambridge, UK, and his colleagues were able to discern how these filaments maintain their structure.

Images of the galaxy had already been attained by ground-based telescopes such as the WIYN telescope, which is owned and operated by a consortium comprising the University of Wisconsin, Indiana University, Yale University and the National Optical Astronomy Observatory. But to get finer detail, Fabian's team commissioned Hubble, which has tenfold better resolution than WIYN.

They booked four blocks of observations with the Advanced Camera for Surveys on the Hubble, one of the cameras responsible for the deepest view yet obtained of the cosmos. Two observations were made in August 2006 and one in January 2007, but before the final data collection could be made the camera broke down. “We only got three-quarters of the data we were hoping for,” says Fabian. “Nevertheless, we were able to get some wonderful images.”

These images allowed Fabian's team to shed light on the characteristics of the network of gaseous filaments that reach out from this galaxy. The filament system extends across a distance of 100,000 parsecs (1 parsec is about 206,000 times the distance between Earth and the Sun), making NGC 1275 almost ten times larger than the Milky Way.

The filaments are emitted from the galaxy either radially or at an angle, as exemplified by a characteristic filament dubbed 'horseshoe'. Embedded within the filaments, the team discovered long thin strands that they called threads. Some extend across a distance of about 6,000 parsecs, but are only 70 parsecs wide.

Fabian explains that although the filaments look static, there is nothing placid about their environment. A black hole inside the galaxy squirts out jets of gas into the cosmos, creating bubbles. The bubbles become buoyant and drag some of the cooler gas from the centre of the galaxy outwards. “The filaments we see are actually these gases being dragged outwards,” Fabian explains. “In order for the filaments to not be dragged or broken apart, they need magnetic fields to give them integrity and structure.” Fabian's group was able to calculate that the magnetic fields found within these threads, which are about one-ten-thousandth of the strength of Earth's field, help to give the filaments their stability amidst the cauldron of activity at the galaxy's centre (see page 968).

The team also found that most of the filaments do not have star clusters associated with them. “Normally, cold gases collapse under their own gravity to form stars. But in these structures it seems that the magnetic fields are preventing this,” says Fabian.

With a space-shuttle mission to refurbish Hubble planned for October 2008, Fabian hopes to use the telescope again to make further observations of this cluster. He also wants to look at similar filaments in other massive galaxies around the Universe, because these may hold the key to how stars are formed. “One third of the central galaxies in cluster galaxies have filamentary structures,” says Fabian. “We want to have a go at them.”