Universe Today
For about a century, astronomers have known that the Universe is in a constant state of expansion. The rate at which it expands is known as the Hubble Constant(aka. the Hubble-Lemaitre Constant), in honor of Edwin Hubble and Georges Lemaitre - the two astronomers who confirmed it. Since then, astronomers have been trying to get an accurate measure of it, which requires highly accurate distance measurements of the cosmos. This is no easy task, and astronomers have run into some complications with their measurements.
For starters, different methods are needed to measure objects at different distances, which is known as the Cosmic Distance Ladder. When comparing measurements of the local Universe to the most distant objects in the Universe, astronomers obtained inconsistent results - what has come to be known as the Hubble Tension. In a recent paper, a team of researchers suggests that Fast Radio Bursts (FRBs) could be used to measure cosmic distances and constrain the Hubble Constant.
The study was led by Eduard Fernando Piratova-Moreno, a Professor of Systems Engineering at the Fundación Universitaria Los Libertadores (FULL). He was joined by Carolina Cabrera, the Director of the Systems Engineering Program with FULL;Luz Ángela García, an astronomical researcher at the ECCI University,****and Carlos A. Benavides-Gallego, a Postdoctoral Research Scientist at Shanghai Jiao Tong University. The paper that details their findings recently appeared online and is being reviewed for publication in .
The Hubble Tension
The Cosmological Distance Ladder consists of several methods that correspond to cosmic distances. For location distances, for objects between 10,000 and 100,000 light-years away, astronomers rely on parallax measurements using Cepheid variable stars as "standard candles." For objects 100,000 to 100 million light-years away, astronomers rely on Cepheids and RR Lyraes variables. For objects up to 1 billion light-years distant, astronomers require much brighter candles and rely on Type 1a supernovae.
Beyond this, astronomers must rely on redshift measurements to obtain distance measurements. Before the 1990s when the Hubble Space Telescope launched, observations and redshift measurements were restricted to objects within four billion light-years. However, thanks to Hubble's observations - including the Hubble Deep Field(HDF) in 1995 and Hubble Deep Field South(HDF-2) in 1996 - astronomers were able to conduct redshift measurements of galaxies up to 13 billion light years away.
These were accompanied by redshift measurements of the earliest light in the Universe, known as the Cosmic Microwave Background (CMB) by NASA's Cosmic Background Explorer(COBE) and ESA's Planck mission. Unfortunately, these measurements were inconsistent with local distance measurements. Basically, redshift measurements of the CMB indicated Hubble Constant was about 68 km/s per megaparsec (Mpc), meaning that the Universe is expanding by 68 km (42.25 mi) a second per every million parsecs (about 3.26 million light-years).
Meanwhile, local measurements produced a value of 74 km/s/Mpc (or 46 mi/s). Scientists have named this mystery the Hubble Tension since measurements of the Hubble Constant were in "tension" with each other.
We leverage the sensitivity of the Dispersion Measure (DM) from Fast Radio Bursts (FRBs) with the Hubble factor to investigate the Hubble tension. We build a catalog of 98 localized FRBs and an independent mock catalog and employ three methods to calculate the best value of the Hubble Constant.
our predictions are compatible with reports from the Planck collaboration in 2018,
maximum likelihood of 65.13 ± 2.52 km/s/Mpc and 57.67 ± 11.99 km/s/Mpc
arithmetic mean, respectively.
Further Reading:arXiv
