How do you probe a supermassive black hole? Take a look at the pulsars that orbit it. These rapidly spinning neutron stars flash regular radio pulses, and in an upcoming issue of The Astrophysical Journal astronomers say that the timing of such pulses could provide a new understanding of the 4 million solar mass black hole at the center of the Milky Way. Scientists have speculated that physics as we know it could break down in the presence of such a strong gravitational force. If that's the case, any flashes from nearby pulsars would appear to speed up or slow down when viewed from Earth, with their clocklike arrival times running early or late and likely dependent on where their orbits were in relation to the black hole. In the process, the astronomers also hope to determine Sagittarius A*'s spin rate and true mass down to an accuracy of about 1 part in a million. First, though, they have to find pulsars close enough to this gravitational monstrosity to be useful. And that's not expected to happen until the Square Kilometer Array comes online early next decade.
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