The Very Large Telescope (VLT) of the European Southern Observatory (ESO) in Paranal, Chile, has obtained a spectacular image of a collision between two galaxies that led to the formation of a single giant galaxy: NGC 7727. The merger event started around a billion years ago.
Individual stars do not generally collide since the distances between them are very large compared with their sizes, but galaxies do. With gravity creating tidal forces that dramatically change the look of nearby galaxies, they dance around each other.
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The consequences of this cosmic bump are spectacularly evident in this image of the galaxy. One can see the tangled tails created as the two galaxies merged, which are the result of them stripping stars and dust from one another to create spectacular long arms embracing the galaxy. Parts of these arms are dotted with stars, which appear as bright blue-purplish spots in this image.
Also visible in this image are two bright points at the centre of the galaxy, another telltale sign of its dramatic past. The core of NGC 7727 consists of the original two galactic cores, each hosting a supermassive black hole. Located about 89 million light years away from the earth in the constellation of Aquarius, this is the closest pair of supermassive black holes ever found. The two black holes, which are just about 1,600 light years apart, are fated to coalesce into an even more massive black hole. They are expected to merge within 250 million years, the blink of an eye in astronomical time.
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With the ESO’s upcoming Extremely Large Telescope set to start operating later this decade in Chile’s Atacama Desert, many more such hidden supermassive black hole pairs at the centres of galaxy-merger events are expected to be discovered. Our home galaxy, which also sports a supermassive black hole at its centre, is on a path to merge with our closest large neighbour, the Andromeda Galaxy, billions of years from now.