Hubble sights Milky Way's 'twin'

The spiral galaxy is some 50 million light-years away from Earth

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A stunning image taken by the Hubble Space Telescope shows a galaxy that looks like a twin of our own.

NGC 3949 is a large spiral galaxy and, in astronomical terms at least, is relatively nearby at around 50 million light-years away from Earth.

Galaxies like this help astronomers understand more about our own.

This is because the Sun and the Solar System are so embedded in the Milky Way that it is difficult to see our galaxy's large-scale structure.

Like the Milky Way, NGC 3949 has a blue disc of young stars peppered with bright pink star-birth regions.

In contrast to the blue disc, the bright central bulge is made up mainly of older, redder stars.

It is a member of more than 50 galaxies located in the direction of the Big Dipper, in the constellation Ursa Major (The Great Bear).

It is one of the largest galaxies in this cluster.

Hubble trouble

The image was created from data taken with the Hubble Space Telescope's Wide Field Planetary Camera 2 in 2001.

Separate exposures through blue, visible and near-infrared filters were combined to make the natural colour picture.

The US space agency Nasa announced on Friday that one of the four instruments on board the Hubble Space Telescope has stopped working.

The STIS, or Space Telescope Imaging Spectrograph, stopped working on 3 August and went into what Nasa officials call a "suspended mode".

Engineers are currently trying to track down the source of the problem and Nasa has convened an Anomaly Review Board to determine whether the failed instrument is recoverable.

Hubble's other instruments are all operating normally.