Star seen “dancing” around supermassive black hole proves Einstein was right

A star seen orbiting a supermassive black hole for the first time was just what Einstein’s general theory of relativity had predicted.

The Very Large Telescope of the European Southern Observatory (ESO) has revealed the first sighting of a star orbiting a supermassive black hole in a rather unique way in the center of the Milky Way. This advance, nearly 30 years in development, was predicted by Albert Einstein’s general theory of relativity.

Writing in Astronomy and Astrophysics, a team of researchers described that the star’s orbit had a rosette shape, as opposed to the ellipse shape as predicted by Isaac Newton’s theory of gravity.

Located 26,000 light years from the sun, ESO describes Sagittarius A * and its dense cluster of surrounding stars as a “unique laboratory for evaluating physics” in an otherwise unexplored regime of gravity.

One of these stars, called S2, sweeps toward the supermassive black hole and approaches 20 billion km at the closest approach to the star. Equivalent to 120 times the distance from Earth to the Sun, this makes it one of the closest stars ever found orbiting the black hole.

This simulation shows the orbits of the stars very close to the supermassive black hole at the heart of the Milky Way. Image: ESO / L Calçada / spaceengine.org

4m times the mass of our sun

When S2 is on its closest approach to the black hole, it rushes through space at 3pc from the speed of light, completing an orbit once every 16 years. Using these latest figures, astronomers can predict that Sagittarius A * must have a mass 4m times that of our sun.

S2’s orbit makes it a significant outlier, as stars and planets will generally zoom in and out of the object they spin. However, the precesses of S2’s orbit, which means that the location of its point closest to the supermassive black hole changes with each turn that results in the rosette shape.

This effect, known as the Schwarzschild precession, has never before been measured for a star around a supermassive black hole.

During 27 years of observations of the S2 star, ESO instruments made more than 330 measurements. Now with the organization’s upcoming Extremely Large Telescope, the team believes it will be possible to see even fainter stars orbiting the supermassive black hole.

“If we’re lucky, we could capture stars close enough that they really feel the rotation, the spin, of the black hole,” said Andreas Eckart of Cologne University, one of the project’s leading scientists. “That would be a completely different level of relativity testing again.”