Astrophiz 61: Dr Natasha Hurley-Walker ~ Seeing the Universe in Radio Colour


Astrophiz 61: Dr. Natasha Hurley-Walker ~ Seeing the Universe in Radio Colour ~ on Soundcloud & iTunes

Dr Natasha Hurley-Walker is a GaLactic and Extragalactic MWA Survey Scientist who earned her PhD in Radio Astronomy at the University of Cambridge and is currently a Curtin Early Career Research Fellow who helped to commission the low-frequency SKA precursor radio telescope, the Murchison Widefield Array (MWA), located in outback Western Australia. 
Today in our feature interview we hear about some of her amazing research projects, including her all-sky survey of 300,000 galaxies and her Gleamoscope App. Last year she was named the WA Tall Poppy Scientist of the year, and right now we congratulate her for just being recognised as one of the 5 brightest science communicators in Australia for 2018.

Then Dr Ian “Astroblog’ Musgrave presents his regular segment ‘What’s Up Doc?  where he tells us what’s up in the evening, night and morning skies for the next two weeks, and in his tangent Ian explains how Earth, Mars, Titan and Comet 67P each has very different sands and yet very similar sand dunes.Dr Ian is a University pharmacology and toxicology lecturer, amateur astronomer and astrophotographer.

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In the news: (via Nature, ASTRON and Australia’s science Channel)

Einstein’s Theory of General Relativity has passed its biggest test yet, when even phenomenally dense neutron stars fall like a feather

Einstein’s Theory of General Relativity has faced its most extreme test yet, with a neutron star and two white dwarfs found to orbit together in agreement with his predictions one thousand times more exacting than ever before.

A weak field test would see a feather and a hammer being dropped on the moon will both hit the surface at the same time, which is exactly what happened in the famous Apollo Experiment by Commander David Scott At the end of the last Apollo 15 moon walk,

But theorists asked would Einstein’s GR hold true in the most extreme conditions, in a strong gravitational field.

The researchers from ASTRON, the Netherlands Institute for Radio Astronomy lead by by lead author Anne Archibald, and by Adam Deller from Swinburne OzGrav and 7 others from various research facilities around the world found the perfect naturally occurring system for a strong-field test,.

PSR J0337+1715 is a tight binary system of a neutron star and white dwarf orbiting each other every 1.6 days, with a more distant second white dwarf orbiting this binary in a 327-day orbit.

Critically the neutron star beams radiation towards Earth like a lighthouse, which we see as a ‘pulse’ of radiation 366 times a second, known as a millisecond pulsar.

 The timing of the pulsars is so regular and precise that any changes can be interpreted as being due to the gravitational pull of another body.

If General Relativity still applies at these strong-field scales, then the inner white dwarf and neutron star would be pulled towards the outer white dwarf star’s orbit equally, so the pulsar signals would stay regular.

However, if Einstein’s laws no longer applied and some different theory of gravity was at play, the neutron star and inner white dwarf would “fall” towards the outer white dwarf at different rates, changing the shape of their orbits, turning it more into ‘wobble’, and changing the timing of the pulsar received on Earth.

We were able to measure this by looking at the neutron star alone,” explains first author Anne Archibald, a postdoctoral researcher of the University of Amsterdam and ASTRON, the Netherlands Institute for Radio Astronomy. “The neutron star, a millisecond pulsar, behaves like a clock: it rotates 366 times per second, and beams of radio waves rotate along with it. They sweep over the earth at regular intervals, producing pulses like a cosmic lighthouse. We have used these radio pulses to track the motion of the neutron star.”

The team of astronomers followed the neutron star for six years using the Westerbork Synthesis Radio Telescope in the Netherlands, the Green Bank Telescope in West Virginia, US, and the Arecibo Observatory in Puerto Rico, US. Studying the 27000 pulses collected, the astronomers found that the pulsars are all arriving within 30 nanoseconds of the timing predicted by General Relativity.

 “We can account for every single pulse of the neutron star since we began our observations,” says Archibald. “And we can tell its location to within a few hundred meters. That is a really precise track of where the neutron star has been, and where it is going.” If the neutron star fell differently from the white dwarf, the pulses would arrive at a different time than expected.

Tests on this scale were not available to Einstein while developing General Relativity, and yet it has held true. No doubt Einstein would be impressed by the experiment, but unsurprised by the result.

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