One of our neighbouring galaxies is dying, and it is the Milky Way鈥檚 fault. Our galaxy is nearly done ripping the Sagittarius dwarf galaxy to shreds, according to a series of simulations of the pair鈥檚 epic dance.
The Sagittarius dwarf galaxy is one of the Milky Way鈥檚 satellites, and its orbit around the Milky Way has been slowly closing in over billions of years. Eugene Vasiliev and Vasily Belokurov at the University of Cambridge used data from the Gaia satellite to figure out which stars in the sky belong to Sagittarius by selecting only stars whose colours, brightness and motion were significantly different from those native to the Milky Way.
Once they had a sample of stars in Sagittarius, they ran a series of simulations to figure out the fate of our galactic neighbour and how it is affecting the Milky Way.
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They found that Sagittarius鈥檚 close orbit is causing wobbles in the structure of the Milky Way. 鈥淚f you imagine the disc of the Milky Way is the surface of a drum, it鈥檚 like someone is hitting the drum,鈥� says Belokurov.
But Sagittarius is less than a tenth the size of the Milky Way, so in the process of creating those wobbles it is being ripped apart. 鈥淚t鈥檚 like a fight, but it鈥檚 an unequal fight,鈥� says Belokurov. 鈥淭he Sagittarius galaxy is puny compared to the Milky Way, so even though it did some damage, the Milky Way won.鈥�
The simulations showed the colossal gravitational forces of the Milky Way ripping Sagittarius apart, causing it to shred completely within the next half a billion years. 鈥淩ight now it鈥檚 on the brink,鈥� says Belokurov. 鈥淲e are witnessing the very last days of the Sagittarius dwarf.鈥� What was once the third-largest satellite of the Milky Way 鈥� smaller only than the Magellanic Clouds 鈥� will soon be a barely visible wisp in the sky.
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