Massachusetts Institute of Technology | 2018 Jul 12
Signals from rare black hole-neutron star pairs could pinpoint rate at which universe is growing, researchers say.
Since it first exploded into existence 13.8 billion years ago, the universe has been expanding, dragging along with it hundreds of billions of galaxies and stars, much like raisins in a rapidly rising dough.
Astronomers have pointed telescopes to certain stars and other cosmic sources to measure their distance from Earth and how fast they are moving away from us — two parameters that are essential to estimating the Hubble constant, a unit of measurement that describes the rate at which the universe is expanding.
But to date, the most precise efforts have landed on very different values of the Hubble constant, offering no definitive resolution to exactly how fast the universe is growing. This information, scientists believe, could shed light on the universe’s origins, as well as its fate, and whether the cosmos will expand indefinitely or ultimately collapse.
Now scientists from MIT and Harvard University have proposed a more accurate and independent way to measure the Hubble constant, using gravitational waves emitted by a relatively rare system: a black hole-neutron star binary, a hugely energetic pairing of a spiraling black hole and a neutron star. As these objects circle in toward each other, they should produce space-shaking gravitational waves and a flash of light when they ultimately collide.
In a paper published today in Physical Review Letters, the researchers report that the flash of light would give scientists an estimate of the system’s velocity, or how fast it is moving away from the Earth. The emitted gravitational waves, if detected on Earth, should provide an independent and precise measurement of the system’s distance. Even though black hole-neutron star binaries are incredibly rare, the researchers calculate that detecting even a few should yield the most accurate value yet for the Hubble constant and the rate of the expanding universe. ...
Ideal Mergers for Measuring Cosmic Expansion
Physics Synopsis | American Physical Society | 2018 Jul 12
Measuring the Hubble Constant with Neutron Star Black Hole Mergers - Salvatore Vitale, Hsin-Yu Chen
- Physical Review Letters 121(02):1303 (12 Jul 2018) DOI: 10.1103/PhysRevLett.121.021303
arXiv.org > astro-ph > arXiv:1804.07337 > 19 Apr 2018 (v1), 30 Jun 2018 (v3)