Hubble details a cannibal galaxy

The American & European space telescope shows that galaxies are not always "good neighbours"…

 

ESO 306-17: a giant elliptic galaxy that has literally devoured its smaller neighbours. Galaxies of this type can be 4 times bigger than our Milky Way. Picture by the NASA and ESA space telescope, Hubble. Credit: NASA/ESA/Michael West (ESO)

It is with good reason that galaxies are often referred to as "island universes": they group together between tens and hundreds of thousands of stars! Today, it is thought that they gradually formed by joining smaller versions of themselves together.

Often in a group, occasionally solitary...
Our own Milky Way therefore literally absorbed dwarf galaxies around it, thus increasing its own size. It is estimated that the Milky Way accommodates between 200 and 400 billion stars within a spiral that has a diameter of 100,000 light years. Despite their "appetite", galaxies generally form groups called clusters, which themselves regroup into superclusters. These are the biggest known structures in our universe.
However, some galaxies go it alone. They seem not to belong to any group or cluster. It is an "island universe" of this type that the Hubble space telescope detailed in a striking portrait with its ACS (Advanced Camera for Surveys), and that is the subject of a publication today. Approximately 500 million light years away from us, ESO 306-17 (hardly a poetic name – it is, in fact, a catalogue number) is a giant elliptic galaxy that reigns within a huge void brimming with hot gas and black matter (an invisible matter with recognised gravitational effects). The snapshot from Hubble shows other small galaxies. But it turns out that they are located in the foreground, confirming that ESO 306-17 cleaned up the neighbourhood, acting like a "cannibal" among its smaller neighbours.

Hubble tops the bill at the Cité de l’Espace
Hubble and other space observatories have triggered significant advances in our understanding of the mechanisms behind how galaxies form - be they "good neighbours" living in clusters or solitary monsters that devour those around them, like ESO 306-17. On a larger scale, such information helps astronomers to fine tune the history of the Cosmos, from the Big Bang to today.



Hubble was made as good as new by the shuttle mission STS-125 in May 2009 (see this Enjoy Space portfolio) and will celebrate the twentieth anniversary of its launch next April. To mark the occasion, the Cité de l’Espace in Toulouse is hosting what promises to be a memorable evening on 28 April 2010, with events, encounters, debates and… the brand new IMAX 3D film! You will remember that the film contains superb sequences in relief, filmed in space during the STS-125 flight (see this Enjoy Space article).

Published on 4 March 2010