Astronomers reveal the largest map of 56,000 galaxies to date

Cosmicflows-4 has been assembled using eight different methods.
Nergis Firtina
Full-sky map showing Cosmicflows-4’s 56,000 galaxies with distance measurements.
Full-sky map showing Cosmicflows-4’s 56,000 galaxies with distance measurements.

University of Hawai'i 

The largest-ever compilation of high-precision galaxy distances, Cosmicflows-4, has been assembled by a team of researchers led by the University of Hawai'i at Manoa astronomers Brent Tully and Ehsan Kourkchi from the Institute for Astronomy.

They measured the distances to 56,000 galaxies using eight different methods. The research was published in the Astrophysical Journal.

The building blocks of the cosmos 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 vanish quicker if they are farther away, as mentioned in the statement.

The size of the universe and how long it has been since it was created are calculated using measurements of the distances of galaxies and data on their velocity away from us.

“Since galaxies were identified as separate from the Milky Way a hundred years ago, astronomers have been trying to measure their distances,” said Tully.

“Now by combining our more accurate and abundant tools, we are able to measure distances of galaxies, and the related expansion rate of the universe and the time since the universe was born with a precision of a few percent.”

Astronomers reveal the largest map of 56,000 galaxies to date
Stephan’s Quintet. The four galaxies in a vertical line at 270 million light years.

The researchers derived the Hubble Constant, or H0, or rate of universe expansion, from the recently published findings. According to the team's research, H0=75 km/s per megaparsec, or Mpc (1 megaparsec is equal to 3.26 million light years), with an extremely low statistical uncertainty of only 1.5 percent. 

Many ways to measure galaxy

There are several methods for calculating galaxy distances. Individual researchers, in general, concentrate on a single method.

Tully and Kourkchi's Cosmicflows program incorporates their own original material from two methods, as well as information from numerous previous studies. Intercomparisons should mitigate against a large systematic error because Cosmicflows-4 includes distances derived from a variety of independent, distinct distance estimators.

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Physics of the universe's evolution based on the standard model of cosmology predicts H0=67.5 km/s/Mpc, with a 1 km/s/Mpc uncertainty. The difference between measured and predicted Hubble Constant values is 7.5 km/s/Mpc, which is much greater than expected, given the statistical uncertainties. Either there is a fundamental problem with our understanding of cosmic physics, or there is a hidden systematic error in galaxy distance measurements.


We present the distances of 9792 spiral galaxies lying within 15,000 km s−1 using the relation between luminosity and rotation rate of spiral galaxies. The sample is dominantly, but not exclusively, drawn from galaxies detected in the course of the ALFALFA H i survey with the Arecibo Telescope. Relations between H i line widths and luminosity are calibrated at SDSS u, g, r, i, z bands and WISE W1 and W2 bands. By exploiting secondary parameters, particularly color indices, we address discrepancies between measured distances at different wave bands with unprecedented detail. We provide a catalog that includes reduced kinematic, photometric, and inclination parameters. We also describe a machine-learning algorithm, based on the random forest technique, that predicts the dust attenuation in spirals lacking infrared photometry. We determine a Hubble Constant value of H0 = 75.1 ± 0.2(stat.), with potential systematics up to ±3 km s−1 Mpc−1.

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