- 3376 - PULSARS - astronomy’s precision clocks? Einstein’s “General relativity” is not compatible with the other fundamental forces, described by “quantum mechanics“. It is therefore important to continue to place the most stringent tests upon general relativity as possible, to discover how and when the theory breaks down.
--------------------- 3376 - PULSARS - astronomy’s precision clocks?
- Researchers have conducted a 16-year long experiment looking at a pair of extreme stars called “pulsars” through seven radio telescopes across the globe. These pulsars are a pair of “extreme” stars.
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- Finding any deviation from general relativity would constitute a major discovery that would open a window on new physics beyond our current theoretical understanding of the Universe.
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- A pulsar are a highly magnetized rotating compact star that emits beams of electromagnetic radiation out of its magnetic poles. Pulsars weigh more than our sun but they are only about 15 miles in diameter. They are incredibly dense objects that produce radio beams that sweep the sky like a lighthouse.
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- Astronomers are studying this double pulsar consisting of two pulsars which orbit each other in just 147 minutes with velocities of about 1 million kilometers / hour. One pulsar is spinning 44 times a second. The companion is younger and has a rotation period of 2.8 seconds. It is their motion around each other which can be used as a near perfect gravity laboratory.
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- Seven sensitive radio telescopes were used to observe this double pulsar in Australia, the US, France, Germany, the Netherlands and in the UK (the Lovell Radio Telescope).
The goal as to use this system of compact stars as an unrivalled laboratory to test gravity theories in the presence of very strong gravitational fields.
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- Astronomers were able to test Einstein's theory, the energy carried by gravitational waves, with a precision that is 25 times better than with the Hulse-Taylor pulsar, and 1000 times better than currently possible with gravitational wave detectors. These observations were still in agreement with the theory.
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- The pulsars were the only known instance of two cosmic clocks which allow precise measurement of the structure and evolution of an intense gravitational field. The Lovell Telescope at the Jodrell Bank Observatory has been monitoring it every couple of weeks since then. This long baseline of high quality and frequent observations provided an excellent data set to be combined with those from observatories around the world.
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- They follow the propagation of radio photons emitted from a cosmic lighthouse, a pulsar, and track their motion in the strong gravitational field of a companion pulsar.
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- The light is not only delayed due to a strong curvature of spacetime around the companion, but also that the light is deflected by a small angle of 0.04 degrees that we can detect. Never before has such an experiment been conducted at such a high spacetime curvature.
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- Such fast orbital motion of compact objects like these, They are about 30 per cent more massive than the Sun but only about 24 kilometers across allowing testing many different predictions of general relativity, seven in total!
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- Apart from gravitational waves and light propagation, this precision allows astronomers to measure the effect of "time dilation" that makes clocks run slower in gravitational fields.
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- They take Einstein's famous equation E = mc^2 into account when considering the effect of the electromagnetic radiation emitted by the fast-spinning pulsar on the orbital motion.
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- This radiation corresponds to a mass loss of 8 million tons per second! While this seems a lot, it is only a tiny fraction - 3 parts in a thousand billion billion - of the mass of the pulsar per second.
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- The researchers also measured - with a precision of 1 part in a million - that the orbit changes its orientation, a relativistic effect also well known from the orbit of Mercury, but here 140,000 times stronger.
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- This level of precision is needed to consider the impact of the pulsar's rotation on the surrounding spacetime, which is "dragged along" with the spinning pulsar. This is the “Lense-Thirring effect” or “frame-dragging“.
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- The measurements allow for the first time to use the precision tracking of the rotations of the neutron star, a technique that we call “pulsar timing” to provide constraints on the extension of a neutron star.
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- The technique of pulsar timing was combined with careful interferometer measurements of the system to determine its distance with high resolution imaging, a distance of 2,400 light years with only 8 per cent error margin.
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December 12, 2021 PULSARS - astronomy’s precision clocks? 3375
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