The Andromeda galaxy is our closest galactic neighbour, roughly 2.5 million light-years away. Though it is 140,000 light-years across, it isn't bright enough to be seen in the night sky by our eyes. Black holes are formed when some very large stars collapse and condense all of their mass into a very small area, known as the Schwarzschild radius. Earth's Schwarzschild radius is just below nine mm (1/3 inch), and if it were to be compressed below that...