What is the age and size of our universe? The largest-ever collection of high-precision galaxy distances, known as Cosmicflows-4, has been compiled by a team of researchers led by astronomers Brent Tully and Ehsan Kourkchi from the Institute for Astronomy at the University of Hawai’i at Manoa. They calculated the distances to a staggering 56,000 galaxies using eight different techniques. The Astrophysical Journal has published the study.
The building blocks of the universe are galaxies like the Milky Way, each of which contains up to several hundred billion stars. As a result of the universe’s expansion, which started at the moment of the Big Bang, galaxies beyond our immediate area are vanishing faster if they are farther away. The size of the universe and how long it has been since it was created are calculated from measurements of the distances of galaxies and data on their velocities away from us.
Astronomers have been attempting to calculate the distances between galaxies ever since they were discovered to be distinct from the Milky Way a century ago, according to Tully. With the help of better and more tools, we can now measure the distances between galaxies, the rate at which the universe is expanding, and the age of the universe to within a few percent.
The Hubble Constant, or H0, or rate of universe expansion, was calculated by the researchers using recently published measurements.According to the team’s research, H0 is equal to 75 km/s per megaparsec, or Mpc (1 megaparsec is equal to 3.26 million light years), with a very low statistical uncertainty of just 1.5%.
There are various techniques for calculating galaxy distances. Individual researchers typically concentrate on a particular approach. Tully and Kourkchi’s Cosmicflows program also incorporates data from numerous earlier studies in addition to their own original material from two methods. Intercomparisons should keep a big systematic error from happening because Cosmicflows-4 uses distances from a number of different, independent distance estimators.
Cosmic conundrum
The universe is believed to be slightly older than 13 billion years old according to the framework that astronomers have put together, but there is a significant problem with the details.
The speed of H0 = 67.5 km/s/Mpc is predicted by the physics of the universe’s evolution based on the standard cosmological model, with a 1 km/s/Mpc uncertainty. The Hubble Constant’s measured and predicted values differ by 7.5 km/s/Mpc, which is much more than the statistical uncertainties would suggest. Either there is a hidden systematic error in the way we measure the distances between galaxies, or we don’t understand the physics of the universe well enough.
In addition to studying how galaxies move collectively as the universe expands, Cosmicflows-4 is also being used to study how galaxies move individually. The gravitational effects of matter clumps on scales ranging from our Earth and sun up to gatherings of galaxies on scales of a half billion light years cause deviations from this smooth expansion. On larger scales, the mysterious dark matter predominates. We can recreate the orbits that galaxies have followed since they were formed using knowledge of how galaxies move in response to the mass around them. This knowledge will help us better understand how the universe’s vast, dark-matter dominated structures have evolved over eons of time.
