An international team of astronomers used gravitational waves, generated by a merger of two incredibly dense neutron stars, to refine the measurement of the Hubble constant. The neutron star merger was first picked up in 2017 by gravitational wave detection efforts on Earth, known as LIGO and Virgo, and is designated GW170817.
Fortunately, the merger was also noticed by a gamma-ray detector and optical astronomy facilities, giving the star-gazing scientists more than one pair of specialized eyes on the event.
The gravitational waves generated by the event helped astronomers estimate how bright the merger should be. They then looked at how bright the merger actually was and worked out the distance -- allowing the constant to be estimated.
A collaboration of astronomers looked at GW170817 and used this method to determine the Hubble constant in 2017, but the new research used high-resolution radio data to assess a huge jet of energy that bolted out of the merger. That allowed the team to paint a more accurate picture of how the neutron stars were oriented in 3D space than previous studies, using models generated on supercomputers.
Several groups have made this calculation using the GW170817 data, but we were able to do it more accurately because the radio data provided the inclination (of the merger) more accurately, which otherwise is a source of uncertainty in the calculation of the gravitational wave brightness," says Adam Deller, an astrophysicist at the Swinburne University of Technology in Australia and co-author of the article.
For the numbers nerds: Previous measurements using GW170817 estimated the universe was expanding at around 74 kilometers per second per megaparsec. The new study puts it around 70 kilometers per second per megaparsec. But that doesn't mean the universe is expanding slower than we believed
"Knowledge of it helps us interpret observational data and get a better handle on what the properties of dark energy and dark matter are -- and ultimately, hopefully, what they are." - 2 minutes ago