Pulsars are the remnants of the explosion of massive stars at the end of their lives. The event is known as a supernova and as they rapidly spin they sweep a high energy beam across the cosmos much like a lighthouse. The alignment of some pulsar beams mean they sweep across Earth predictably and with precise regularity. They can be, and often are used as timing gauges but a team of astronomers have found subtle timing changes in some pulsars hinting at unseen mass between pulsars and telescopes—possibly dark matter entities.
The discovery in 1967 of pulsars has revolutionised our understanding of stellar evolution. The are formed during the collapse of supermassive stars at the end of their life. As the fusion in the core ceases, the inrushing stellar material crashing down onto the core compresses it to incredible density. The material that once made up the star is, through this process compressed into a sphere just a few tens of kilometres across. Pulsars are closely related to neutron stars which are formed though the same process and it is believed, the only difference is that one has a highly energetic beam that flashes across the Earth and one doesn’t.
A team studying pulsars has recently detected hints of potential dark matter objects through changes in pulsar timing events as they rotate. Professor John LoSecco from the University of Notre Dame, presented at the National Astronomy Meeting at the University of Hull and emphasised the precision of pulsar-based timekeeping. “Science has advanced with precise time measurement methods,” he noted, comparing Earth’s atomic clocks with pulsars in space. While gravitational effects on light have been understood for over a century, their applications in uncovering hidden masses remain largely unexplored until now.
Professor LoSecco and the team noted tiny deviations in the pulsar timing, suggesting that radio waves may be getting redirected around an unseen mass located somewhere between the pulsar and the telescope. LoSecco theorised that the masses could potentially be dark matter!
By examining the delays and analysing the radio pulse arrivals (which were typically accurate to within a nanosecond) they explored the pathway of radio signals within the latest Parkes Pulsar Timing Array survey. Other telescopes involved in this initiative were the Effelsberg, Nançay, Westerbork, Green Bank, Arecibo, Parkes, and the Lovell telescope in Cheshire. Using this and Parkes data, the pulse arrival times were analysed.
The results showed that the pulses occur regularly every three weeks across three observational bands. However, when dark matter causes delays in arrival times, these delays display distinct shapes proportional to the mass of the dark matter. Regions with dark matter slow down the passage of light and effect the pulsar timings. The Sun for example, could produce a delay of about 10 microseconds however the timing differences 10,000 times smaller. A detailed examination of precise data from 65 ‘millisecond pulsars’ has identified approximately twelve instances suggestive of interactions with dark matter.
Source : How astronomers are using pulsars to observe evidence of dark matter
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