Panorama reveals thousands of growing galaxies

The visible universe has 80 billion galaxies. The number of stars is 3 x 10 to the power of 22. Each galaxy has on average 375 billion stars. As a rule of thumb i think of 100 billion galaxies each with 100 billion stars.

Now 150,000 galaxies have been photographed within the sky the width of your finger when held at arms length.

18:00 06 March 2007,

• NewScientist.com news service - Hazel Muir

Hundreds of images snapped by the Hubble Space Telescope have been woven together to create a rich tapestry of thousands of galaxies.

Astronomers created the panoramic view as part of a five-year project called AEGIS (All-wavelength Extended Groth strip International Survey). Eight of the world's best space- and ground-based observatories, including Hubble, made meticulous surveys inside one patch of the night sky with an area about twice the size of the full Moon.

The observatories peered up to 9 billion light years away to see about 150,000 galaxies evolving when the universe was much younger than today. They recorded the galaxies in all colours from X-rays to radio waves.

"The goal was to study the Universe as it was when it was about half as old as it is at present, or about 8 billion years ago, a time when youthful galaxies undergoing active formation were becoming quieter mature adults," says Marc Davis from the University of California in Berkeley, US, one of the AEGIS project leaders.

Galactic collisions

Hubble recorded images of more than 50,000 galaxies in visible light by taking more than 500 separate exposures. Astronomer Anton Koekemoer from the Space Telescope Science Institute in Maryland, US, and colleagues combined them to create a panoramic image containing more than 3 billion pixels.

"These images reveal a wealth of galaxies at many stages of their evolution through cosmic time," says Koekemoer. Some are beautiful spirals or massive elliptical galaxies, but others have very haphazard shapes. They are probably the wreckage of violent galactic collisions.

Watch an MPEG video of the AEGIS strip beginning with its location in the constellation Ursa Major (the Big Dipper) and ending with a pan across the strip (courtesy of NASA/ESA/L Barranger/STScI).

Among the discoveries so far in the Hubble images is a giant red galaxy with two black holes at its core. They appear to be about 4000 light years apart, and one is 10 times more massive than the other, weighing 5 million times the mass of the Sun. They appear to be the result of a galactic merger hundreds of millions of years earlier.

Astronomers hope all the AEGIS observations will reveal new clues about how galaxies evolved from their "pre-teen" years to young adulthood. A total of 19 papers describing the results of the project will appear in a future issue of Astrophysical Journal Letters.

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top picture: Nasa - 10,000 galaxies