Astronomers have discovered a mysterious new class of objects at the heart of the Milky Way, unlike anything else found previously in our galaxy. The objects “look like gas but behave like stars,” according to senior researcher Andrea Ghez, as they start off small and compact but are stretched to a larger size when they approach the supermassive black hole in the center of the galaxy.

The researchers believe these objects could teach us about the evolution of stars and what happens to celestial bodies in environments of extreme gravity.

The puzzle began in 2005 when astronomers identified an object near the center of our galaxy called G1, which seemed to be orbiting around the supermassive black hole there in a strange way. In following years, five more objects numbered G2 to G6 were discovered. At first, these objects were thought to be clouds of gas. But one odd thing researchers noticed was that when the object G2 came very close to the event horizon of the black hole, it wasn’t torn apart in the way they would have expected. Instead, it initially stretched out, before rebounding back toward its original state.