Magnetar Near Black Hole Could Put Einstein's Theory Of General Relativity To The Test

A supermassive black hole near the center of the Milky Way has astronomers all abuzz for a variety of reasons.

One reason is that the supermassive black hole at the center of our galaxy, Sagittarius A (Sag A), is set to devour a gas cloud, named G2, with the mass of three Earths in September. That event will allow astronomers the rare opportunity to learn how, and how long, objects accrete into black holes.

But then there's the bonus prize: a rare magnetar –– only 24 are known to exist, according to Sky & Telescope –– located near Sgr A. A magnetar, according to Nature, is a highly magnetized type of pulsar or rotating neutron star. Like most pulsars, a magnetar emits pulses of radio waves on a regular basis, making them reliable tools for testing theories.

This magnetar in particular, Nature says, could be used to test Einstein's general theory of relativity by measuring warping of space-time near the black hole.

"According to Einstein's general theory of relativity, clocks in high gravitational fields run slow, as a result of the warping of space-time," Nature's Eugenie Reich writes. "So if the magnetar is following an elliptical orbit around the black hole, its clock-like spin rate should speed up and slow down as its distance from the black hole varies –– an effect that, with luck, could be disentangled from the gradual slow-down caused by the magnetar's magnetic field."

But first astronomers need to know where, exactly, the magnetar is.

So, in late April, NASA pointed its Nuclear Spectroscopic Telescope Array (NuSTAR) satellite to Sgr A in an effort to measure the magnetar's spin. The spin is measured by marking how often the object emits X-rays. In this case, NuSTAR found the magnetar had a spin of 3.76 seconds.

The Chandra X-ray Observatory, aimed at Sgr A a few days later, placed the magnetar .38 lightyears away from the black hole. It's still possible the magnetar is located further away, Sky & Telescope's Monica Young writes, but it is likely the object resides in the galactic center.

"There's huge interest in finding pulsars around supermassive black holes, and this is the first example," Geoffrey Bower, a radioastronomer at the University of California, Berkeley, told Nature. "There's a lot we can learn from this."

Whether or not G2 hits the Sgr A in mid-September as planned remains to be seen, but excited astronomers will be observing the area for sometime regardless.

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