Sci-Tech

Evidence of a galactic cannibal

An image captured by the Hubble telescope shows a galaxy in the process of being devoured by a bigger galaxy nearby.

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The distorted form of spiral galaxy NGC 7714. ESA, NASA

Just because space is (theoretically) infinite, that doesn't mean everything out there is neatly spaced. Things collide, from tiny objects smashing into other tiny objects, to objects on the galactic scale -- quite literally.

Spiral galaxy NGC 7714, roughly 100 million light-years from Earth, is one of those galaxies for which crowding is proving a dramatically brutal affair: it has drifted a little too close to nearby smaller galaxy NGC 7715, and is taking its time cannibalising its neighbour, as seen in a new photo snapped by the Hubble Space Telescope.

Sometime between 100 million and 200 million years ago, the two galaxies reached a close enough distance from each other to start disrupting each other's shapes -- evidenced by the peculiarity of NGC 7714.

Unlike a normal spiral galaxy, its arms have stretched out and a smoky golden haze extends from the core.

Additionally, a ring and two long trails of stars have stretched towards NGC 7714 -- forming a sort of bridge between the two galaxies. That bridge funnels material from NGC 7715 to the larger NGC 7714 and feeds star formation in NGC 7714, most of which is occurring at its core, although the entire galaxy is active.

A large number of these new stars are what are known as Wolf-Rayet stars. These are stars that, when they are young, are massive -- at least 20 solar masses each. They are very hot, with surface temperatures ranging between 30,000 and 200,000 Kelvin (the Sun's surface temperature is around 5,778 Kelvin) and very luminous, shining with tens of thousands to several million times the luminosity of the sun (although most of that output is in the ultraviolet spectrum).

Wolf-Rayet stars are the "live fast, die young" stage in the evolution of massive stars. Although they burn very hot and bright, they also lose mass at an accelerated rate, about a billion times higher than the sun's rate, due to very strong solar winds. Eventually the star runs out of material, and ends its life in a dramatic supernova.

Because of this star formation, NGC 7714 has been classified as a Wolf-Rayet starburst galaxy.

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Wide field-of-view image that shows the two galaxies, just above the bright star in the centre. NGC 7714 is on the right, and NGC 7715 appears as a bright streak to its left. ESA, NASA