Deepest image of a galaxy

The Gran Telescopio Canarias (GTC), the world’s largest single-aperture optical telescope on the island of La Palma in Spain, has captured an image of a galaxy which is 10 times deeper than any other obtained from the ground.

GTC researchers managed the rare feat while observing a faint halo of stars around the galaxy UGC0180, which is 500 million light years away from the Earth.

The galaxy UGC00180 was chosen because it is quite similar to our neighbour, the Andromeda Galaxy, and to other galaxies to which the researchers have references.

They used the OSIRIS camera on the GTC, also known as the Great Canary Telescope, which has a field big enough to cover a decent area of sky around the galaxy, in order to explore its possible halo.

After 8.1 hours of exposure they could show that it does have a weak halo composed of four thousand million stars, about the same number as those in the Magellanic Clouds, which are satellite galaxies of the Milky Way.

With this measurement, recently published in Astrophysical Journal, the existence of the stellar haloes predicted by theoretical models is confirmed, and it has become possible to study low surface brightness phenomena.

As well as beating the previous surface brightness limit by a factor of 10, the observation shows that it will be possible to explore the universe not only to the same depth to which we can go using the conventional technique of star counts, but also out to distances where this cannot be achieved.