5 unsolved mysteries of space

For 10 years, scientists had been observing one of the largest known stars in the universe, located in a galaxy 75 million lightyears away.

Then one day, it disappeared — and no one knows why. Read more.

Is this a neutron star or black hole?

This strange object is about 2.6 times the mass of the Sun and resulted from a collision between two unknown cosmic objects. Read more.