By Dr David Whitehouse BBC News Online science editor

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The composite image shows towering filaments of warm and hot gas that astronomers believe lie on the surface of a superbubble of gas that has been blown from the heart of the galaxy.

A central superwind has carved a cavity in the cool gas of the galactic disc and then stripped fragments of gas off the walls of the cavity, stretched them into long filaments, and heated them.

The superwind comes from either a central supermassive black hole or from a burst of exploding stars. The full extent of the superwind shows up as a fainter cloud of X-ray emission surrounding the filaments, say researchers.

Heavy elements

NGC 3079 lies at a distance of 50 million light-years - relatively close in cosmic terms - in the constellation of Ursa Major, the Great Bear.

Because the galaxy is so close and is a spiral galaxy seen edge-on, astronomers are able to obtain a detailed view of the strange events taking place at its core.

Superwinds coming from a galaxy's central regions are thought to play a key role in the evolution of galaxies by dispersing gas, thereby regulating the formation of new stars. These winds also push heavy elements to the outer parts of the galaxy and beyond.

Some researchers believe that the latest Chandra data indicate the mass lost in superwinds may have been underestimated.

Radio investigations

The HST image reveals a bubble of hot gas rising from a cauldron of glowing matter. The bubble is more than 3,000 light-years wide and rises 3,500 light-years above the galaxy's disc.

Observations of the spectra of the bubble suggest it is being blown outwards at a speed of six million kilometres per hour.

Astronomers are as yet unable to determine the origin of NCG 3097's superwind.

It could be from agitated gas surrounding a supermassive black hole. Detailed high-resolution observations of the galaxy's core made by radio telescopes do show a series of gas clouds rushing outwards at 10% of the speed of light.

New beginning

Alternatively the wind could be the combined force from many newly formed stars. Astronomers know that some young stars can have vigorous stellar winds.

Whatever their origin, the superwind and the filaments it creates do remarkable things when they reach the galaxy's outskirts.

Gaseous filaments at the top of the bubble are whirling around in a vortex before being expelled into space.

Some of this gas will rain down upon the galaxy's disc where it may collide with gas clouds, compress them, and form a new generation of stars.