A unique threesome of stars locked in tight, circular orbits could help astronomers test the leading theory of gravity to unprecedented precision. The discovery of the celestial trio is reported January 5 in Nature.
“We should be grateful to the universe for making such things,” says Paulo Freire, an astrophysicist at the Max Planck Institute for Radio Astronomy in Bonn, Germany, who applauds the finding. “Part of me wishes I were involved.”
Our galaxy is full of stellar couples and trios. But the formations and motions of the stars in PSR J0337+1715 make the system unique among those found by astronomers. The triad consists of an extremely dense, fast-rotating stellar corpse called a pulsar and two less massive dying stars known as white dwarfs. Pulsars form when stars at least 1.4 times larger than our sun blow up in supernovas; these powerful explosions usually knock nearby stars out of their orbits. In PSR J0337+1715, however, all three stars remain closer to each other than the sun is to Earth and travel in nearly circular orbits, with one white dwarf much closer to the pulsar and one farther away.