Pulsars, neutron stars that emit rotating beams of radio waves, were key in identifying these mysterious hidden masses.
These pulsars, known for their precision in emitting electromagnetic radiation at regular intervals, serve as extremely accurate timekeepers, ranging from milliseconds to seconds.
"Science has developed very precise methods to measure time," said Professor John LoSecco of the University of Notre Dame, who presented his findings at this week's National Astronomy Meeting at the University of Hull. "On Earth we have atomic clocks and in space we have pulsars."
Gravitational effects on light have been known for over a century, yet there have been few practical applications. Professor LoSecco observed variations and delays in pulsar timings, suggesting that the radio beams are being affected by an unseen concentration of mass between the pulsar and the telescope. He believes these invisible masses are potential dark matter objects.
Professor LoSecco's study focused on delays in the arrival times of radio pulses, which typically have nanosecond accuracy. Using data from the PPTA2 survey release of the Parkes Pulsar Timing Array, he traced the paths of radio pulses. This project involves precise pulse arrival measurements from seven radio telescopes: Effelsberg, Nancay, Westerbork, Green Bank, Arecibo, Parkes, and Lovell in Cheshire. The pulses are observed approximately every three weeks in three different bands.
The arrival time deviations due to dark matter have a distinct shape and their size is proportional to the mass causing the delay. Light passing near dark matter regions is slowed by its presence. Analysis of data from 65 'millisecond pulsars' revealed about a dozen interactions indicative of dark matter.
Professor LoSecco explained: "We take advantage of the fact that the Earth is moving, the Sun is moving, the pulsar is moving, and even the dark matter is moving."
"We observe the deviations in the arrival time caused by the change in distance between the mass we are observing and the line of sight to our 'clock' pulsar."
A mass equivalent to the Sun can cause a delay of about 10 microseconds, but Professor LoSecco's observations have nanosecond resolution, 10,000 times smaller. "One of the findings suggests a distortion of about 20 per cent of the mass of the Sun," he said. "This object could be a candidate for dark matter."
This research also enhances the pulsar timing data sample, initially collected to search for low-frequency gravitational waves. Dark matter objects add 'noise' to this data, so identifying and removing them will refine the sample, improving the accuracy for other gravitational radiation searches.
"The true nature of dark matter is a mystery," said Professor LoSecco. "This research sheds new light on the nature of dark matter and its distribution in the Milky Way and may also improve the accuracy of the precision pulsar data."
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