56,000 Galaxies Tell Astronomy to Check its Math

Sep 29, 2022 | Cosmology, Daily Space, Galaxies

56,000 Galaxies Tell Astronomy to Check its Math
IMAGE: A full-sky map showing Cosmicflows-4’s 56,000 galaxies with distance measurements. Each dot represents a galaxy, and the color of the dot indicates distance from us, with blue tones nearby and redder tones farther away. In this view, the obscuring plane of the Milky Way mostly maps to the edges but also cuts across the center of the figure. CREDIT: University of Hawaiʻi

A new paper is coming out in The Astronomical Journal that looks at 55,877 galaxies that were imaged during a variety of different surveys, putting together all the data to try and understand the expansion of the universe.

This work is led by Brent Tully, a researcher who co-discovered with Richard Fisher in the 1970s that some kinds of galaxies have a correlation between their rotation rate and luminosity. This means that if you measure a galaxy’s rotation rate and how bright it appears you can use your knowledge of its luminosity to calculate its distance. In the intervening 40+ years, relationships between galaxy structures and luminosity have been detailed.

In this new paper, they use these relationships to measure distances instead of the more common techniques of looking at supernovae, variable stars, and other current or former stellar objects.

Combining these results with measurements of the galaxies’ velocities, they measured the expansion of the universe… And they got a number wildly different from everyone else: 75 km/s/Megaparsec.

Teams using current and former stellar objects like supernovae get 73 km/s/Mpc, and folks using the cosmic microwave background get 67.5 km/s/Mpc. The error bars on all these measurements are smaller than the separation of these values.

Somewhere in the maths or in the measurements or in both, there is a problem in our understanding of the evolution of our universe. It could be as simple as each project having a bad zero point, like a ruler with the first couple millimeters worn off, or there is just a difference in the scaling, like a set of photocopied tape measures that are accidentally zoomed in different amounts.

The smartest astronomers in the world are trying to sort these discrepancies, and we here at the Daily Space will bring you their progress as we take steps forward, and sometimes backward, in our understanding of the universe.

More Information

UH Manoa press release

“Cosmicflows-4,” R. Brent Tully et al., accepted to The Astronomical Journal (preprint)


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