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Astronomers Search for Pulsars to Test Einstein's Theory of Gravity

A team of astronomers is searching for millisecond pulsars near the Milky Way's supermassive black hole, Sagittarius A*. Pulsars are rapidly rotating neutron stars that emit beams of radio waves. If astronomers can find millisecond pulsars orbiting Sgr A*, they could use them to test Einstein's theory of general relativity in ways that are not currently possible.

Visualization of a fast-rotating pulsar. Credit: NASA's Goddard Space Flight Center Conceptual Image Lab
Visualization of a fast-rotating pulsar. Credit: NASA's Goddard Space Flight Center Conceptual Image Lab

The center of the Milky Way is shrouded in gas and dust, but thanks to radio astronomy, astronomers can peer through the veil to see the region. By observing the motions of stars orbiting Sgr A*, astronomers have been able to confirm that general relativity holds true even in the strong gravitational fields near a black hole. However, our measurements aren't precise enough to distinguish between the predictions of general relativity and rival gravitational theories.

Millisecond pulsars would allow astronomers to measure orbital dynamics near Sgr A* precisely, giving us a detailed view of how strong gravitational fields interact with mass. It could provide experimental tests precise enough to distinguish between general relativity and other models.

The team of astronomers is using data from the Event Horizon Telescope (EHT) to search for millisecond pulsars near Sgr A*. The EHT is a global network of radio telescopes that was used to create the first image of a black hole. The EHT data contains observations of the surrounding area, and if there are millisecond pulsars in the region, evidence for them could be buried in the data.

The team used three detection methods based on Fourier analysis to search for pulsar signals in the EHT data. Fourier analysis is a mathematical technique that can detect patterns within data. Since pulsars emit regular pulses, they would tend to stand out against random noise.

Unfortunately, the team didn't find evidence for any new, previously unknown pulsars. That isn't too surprising given that even the team estimated the EHT data would be able to detect 2% of pulsars at best. And this is only a study of the first round of data. There is plenty more EHT data to examine, and EHT continues to gather data on the region.

Even if EHT hasn't detected any pulsars, that doesn't mean they aren't there. Millisecond pulsars are almost certainly orbiting the Milky Way's supermassive black holes, just like the stars we can currently see. It is only a matter of time before we find them.

The team's findings were published in the journal arXiv.

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