Star death boosts measurement of universe’s expansion

By on 9 July, 2019

Ateam of international researcher including astronomers from Swinburne University of Technology have improved the measurement of the Hubble Constant, a unit of measurement describing the universe’s current rate of expansion.

The team of researchers used data collected in 2017 during observation of the death and merging of two neutron stars with radio and light telescopes — an event which occurred 130 million years ago.

Measurements of the gravitational waves generated in the event were used to refine the Hubble constant using a new technique.

The team now place the measurement of the Hubble Constant at 70.3 km per second per megaparsec (a megaparsec is around 3.3 million light years), down from past estimates of around 74 km per second per megaparsec.

The Hubble Constant is a fundamental piece of information in describing the universe’s past, present and future, a value representing the rate of its expansion.

Estimating its value can be done by with Planck observations of cosmic microwave radiation left over after the Big Bang, or from massive stars self destructing in the distant universe.

Two neutron stars is a monumentally energetic event — two stars larger than our Sun rotate around each other hundreds of times per second before merging, firing an enormous amount of material outwards at immense speed.

Measuring this burst of gravitational waves is a third means of estimating the Hubble constant. The shape of the gravitational wave signal shows how ‘bright’ the event should have been, against which observations of the event can be compared and its distance calculated.

Data to determine the orientation of the merger is needed for this calculation, in this case provided by an ultra high resolution radio imaging of the fireball of material emitted as the stars merged.

“In order to use the gravitational waves to measure the distance, we needed to know that orientation,” said Adam Deller, of Swinburne University of Technology.

This single measurement, of an event some 130 million light-years from Earth, is not yet sufficient to resolve the uncertainty, the scientists said, but the technique now can be applied to future neutron-star mergers detected with gravitational waves.

“We think that 15 more such events that can be observed both with gravitational waves and in great detail with radio telescopes, may be able to solve the problem,” said Kenta Hotokezaka, of Princeton University.

The results of the team’s research has been published today in Nature Astronomy.

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