Which star orbiting Sagittarius A* has a period of about 16 years? S2 does.
S2, also called S0–2, is a young, massive star orbiting Sagittarius A*, the supermassive black hole at the center of the Milky Way. Its measured orbital period is about 16.05 years, making it one of the best-observed stars in the Galactic Center.
Astronomers have tracked S2 since the 1990s because its tight, highly eccentric orbit provides a powerful test of gravity. It swings to within roughly 120 astronomical units of Sagittarius A* and reaches several thousand kilometers per second near closest approach. Its 2018 passage produced measurable gravitational redshift and later evidence of relativistic orbital precession, matching predictions of general relativity.
A common mix-up is S55, also known as S0–102. S55 has an even shorter orbit of about 12.8 years, but it is not the star usually identified with the famous approximately 16-year orbit. S2’s observations also helped establish the mass and distance of the Milky Way’s central black hole.