The stars orbiting Sag A*. Click for original image.

Based on a ten year study of the motions of nine stars orbiting close to Sagittarius A* (pronounced A-star), the supermassive black hole at the center of the Milky Way, scientists have concluded that they are single stars, not binaries as would be expected.

Using W. M. Keck Observatory on Maunakea, Hawaiʻi Island, Devin Chu of Hilo, an astronomer with the UCLA Galactic Center Orbits Initiative, led a 10-year survey that found these ‘S-stars,’ where ‘S’ stands for Sagittarius A*, the name of the monster black hole at our galaxy’s core, are all single.

The result is surprising given the S-stars Chu’s team observed included young, massive main-sequence stars that are only about six million years old. Normally, stars at this age that are 10 times more massive than our Sun spend their childhood years paired with a twin in a binary system, or sometimes even as triplets.

This finding suggests that the black hole’s massive gravitational field causes the binaries to be pulled apart, or somehow to merge during their formation.

This data point and the questions it raises pales before the more fundamental question that astronomers have been asking since these stars were first discovered in the 1990s: How is it possible for any stars to form so close to such a disruptive gravitational field?