The Hubble Space Telescope has photographed an extraordinary structure 100,000 light years long containing clusters of young stars that form a sort of bridge around the nuclei of two ancient galaxies within the galaxy cluster known as SDSS J1531 +3414. This unique structure may provide new clues about the formation of star clusters as a result of galaxies mergers.
Finding two elliptical galaxies that are merging is rare but it’s even more uncommon to find that such a merger led to the formation of new stars. That’s because the galaxies that are part of clusters are generally considered depleted of gas. Instead, this new discovery shows clearly that in the two galaxies that merged there was still enough gas to cause the formation of new stars.
Initially, astronomers who studied the images of the Hubble Space Telescope speculated that this cluster of young stars actually belonged to one of the galaxies in the background. The idea was that the galactic cluster acted as a gravitational lens, providing a distorted image of a more distant star cluster, making it appear larger and therefore closer. However, an examination of the images has led to rule out this hypothesis.
The birth of this cluster of young stars is related to the Jeans instability, a phenomenon that is at the base of the gravitational collapse of interstellar gas clouds and star formation that follows it. Named after the British physicist James Jeans, it originates when the internal pressure of the gas is unable to counteract the gravitational collapse of a gas-rich cloud.
Now astronomers have to figure out the source of the gas that allowed the formation of a such a big star cluster. They currently have suggested three possibilities:
- cold gas could already have been present in the two galaxies that have merged even if their age suggested it was nearly depleted
- an atmosphere of very hot plasma around the two galaxies may have cooled, forming gas clouds cold enough to collapse starting the formation of stars
- a shockwave caused when two galaxies collided may have compressed the plasma generating the gas clouds that formed the stars
The investigation into this spectacular star cluster will continue to learn more about it. This is an exciting discovery because it shows that the birth of new stars can continue much longer in a galactic cluster than previously thought.
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