Mopra measures the distance to a neutron star using that trigonometry you learnt about in school!

Mopra has worked with NASA’s Chandra X-ray telescope to provide a direct measurement to a neutron star.  A paper published today in the Astrophysical Journal tells you all about it, but you might find it easier to read the press release first.

Rings in X-ray light surrounding the mysterious X-ray neutron binary star Circinus X-1, overlaid on a background image of the star field around the source. These are echoes from a bright flare that occurred in Circinus X-1, scattered off clouds of dust in interstellar space. They were seen as a expanding ring centred on the star over a period of 3 months following the flare.

Echo location, for bats and for astronomers.  Credit: Sebastian Heinz, lead scientist in the research program.
Echo location, for bats and for astronomers. Credit: Sebastian Heinz, lead scientist in the research program.

 

An analogy between the way bats locate their prey using echo location and the way the distance to the neutron star Circinus X-1 has been measured. Bats emit high-pitched audio pulses which are scattered off their prey. The time for the signal to return gives the distance to the prey. The distance to Circinus X-1 has been determined by the time difference measured by the Chandra telescope between receiving the X-ray flare from the neutron star followed by its echo reflected off the dust clouds. The Mopra telescope has determined the distance to these dust clouds by measuring their velocities, and then comparing these to our knowledge of how the speed of objects orbiting the Galaxy depends on their distance from its centre. Credit: Sebastian Heinz, lead scientist in the research.