Neutron star collisions hold key to universe expansion


Measuring gravitational wave events might solve Hubble constant uncertainties. Lauren Fuge reports.


Edwin Hubble, after whom the Hubble constant is named.

Edwin Hubble, after whom the Hubble constant is named.

Photo by Universal History Archive/Getty Images

Observing cosmic fireballs might hold the key to determining how fast the universe is expanding, according to a team of international astronomers.

In 2017, the cataclysmic clash of two neutron stars was observed for the first time.

This merger sent out an explosive flash of radiation, as well as ripples through space-time known as gravitational waves.

The ripples were picked up by ultra-sensitive receivers here on Earth, 130 million light-years away from the collision.

This first detection provided staggering insights about the cosmos, confirming theories about gamma-ray bursts, the origin of gold and other heavy elements, and more.

Now, astronomers think that these epic mergers might yet yield further information.

A new study, published in the journal Physical Review Letters, proposes that measuring gravitational waves from many different binary neutron star mergers can solve a long-raging debate about how fast the universe is expanding.

Over the years, astronomers have devised a few different ways to estimate the rate of expansion, otherwise known as the Hubble constant, but they give conflicting results.

This has cast doubt on the accuracy of our understanding of the universe’s structure and evolution, as well as our predictions of its eventual fate.

But binary neutron stars might settle the debate once and for all.

“We've calculated that by observing 50 binary neutron stars over the next decade, we will have sufficient gravitational wave data to independently determine the best measurement of the Hubble constant,” says lead author Stephen Feeney, a cosmologist from the Centre for Computational Astrophysics at the Flatiron Institute in New York, US.

“We should be able to detect enough mergers to answer this question within five to 10 years.”

Though neutron star mergers are rare, the gravitational waves they send out can be detected by super-sensitive observatories such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo experiments. These detections can tell us each star system’s exact distance from Earth.

By additionally observing the burst of light accompanying the merger, astronomers can determine the speed of the system through space – and thus use the Hubble-Lemaitre law to calculate the Hubble constant.

Feeney and his team modelled approximately how many mergers were needed to accurately measure the Hubble constant. Turns out, it’s a fairly small number: just 50.

Co-author Hiranya Peiris, from the University College London in the UK, concludes: “This will lead to the most accurate picture of how the universe is expanding and help us improve the standard cosmological model.”

  1. https://cosmosmagazine.com/physics/cosmic-fireball-sheds-light-on-source-of-gravitational-waves
  2. https://doi.org/10.1103/PhysRevLett.122.061105
  3. https://cosmosmagazine.com/physics/new-physics-needed-to-explain-the-universe-study-finds
  4. https://www.ligo.caltech.edu/
  5. http://www.virgo-gw.eu/
  6. https://cosmosmagazine.com/space/hubble-s-law-no-more
Latest Stories
MoreMore Articles