Apply the special theory of relativity, counting the galaxies

This image made from a composite of photos taken between September 2003 and January 2004 by the NASA/ESA Hubble Space Telescope shows nearly 10,000 galaxies in the deepest visible light image of the cosmos, covering billions of light years. Credit: NASA, ESA, S. Beckwith (STScI), HUDF team

Scientists who study the cosmos have a favorite philosophy known as the “mediocrity principle”, which, in essence, suggests that there really is nothing special about the Earth, the sun, or the galaxy of The Way. Milky Way relative to the rest of the universe.

Now, new research from CU Boulder adds yet another piece of evidence to the mediocrity argument: galaxies are, on average, quiescent relative to the early universe. Jeremy Darling, professor of astrophysics at CU Boulder, recently published this new cosmological discovery in Letters from the Astrophysical Journal.

“What this research tells us is that we have a fun move, but this fun move is consistent with everything we know about the universe – there’s nothing special going on here,” Darling said. “We are not special as a galaxy or as observers.”

About 35 years ago, researchers discovered the cosmic microwave background, which is electromagnetic radiation left over from the formation of the universe during the Big Bang. The cosmic microwave background appears warmer in the direction of our motion and cooler away from the direction of our motion.

From this glow of the early universe, scientists can deduce that the sun – and the Earth that orbits around it – are moving in a certain direction, at a certain speed. The researchers found that our inferred speed is a fraction of one percent of the speed of light – small, but not zero.

Scientists can independently test this inference by counting the galaxies visible from Earth or by summing their brightness. They can do this largely thanks to Albert Einstein’s 1905 special theory of relativity, which explains how speed affects time and space. In this application, a person on Earth looking at the universe in one direction – the same direction the sun and Earth are moving – should see brighter, bluer, more concentrated galaxies. Similarly, looking the other way, the person should see galaxies that are darker, redder, and further apart.

But when researchers have tried counting galaxies in recent years – a difficult process to do accurately – they found figures that suggest the sun is moving much faster than previously thought, which is at odds. with standard cosmology.

“It’s hard to count galaxies in the whole sky — you’re usually stuck with a hemisphere or less,” Darling said. “And, on top of that, our own galaxy is in the way. It contains dust that will cause you to find fewer galaxies and darken them as you get closer to our galaxy.”

Darling was intrigued and perplexed by this cosmological puzzle, so he decided to investigate on his own. He also knew that there were two recently published surveys that could help improve the accuracy of a galaxy count and unravel the mystery of speed: one called the Very Large Array Sky Survey (VLASS) in New Mexico , and the other called Rapid Australian Square Kilometer Array Pathfinder Continuum Survey (RACS) in Australia.

Together, these surveys allowed Darling to study the entire sky by combining views from the northern and southern hemispheres. Importantly, the new surveys also used radio waves, which made it easier to “see” through the dust of the Milky Way, improving our view of the universe.

When Darling analyzed the readings, he found that the number of galaxies and their brightness were in perfect agreement with the speed the researchers had previously inferred from the cosmic microwave background.

“We find a bright direction and a dark direction – we find a direction where there are more galaxies and a direction where there are fewer galaxies,” he said. “The big difference is that it lines up with the early universe from the cosmic microwave background and has the right speed. Our cosmology is doing very well.”

Because Darling’s findings differ from earlier findings, his paper will likely prompt various follow-up studies to either confirm or dispute his findings.

But as well as advancing the field of cosmology, the results are a good working example of Einstein’s special theory of relativity – and they demonstrate how researchers are still putting the theory into practice, more than 100 years after the famous physicist proposed it for the first time. .

“I like the idea that this basic principle that Einstein told us about a long time ago is something you can see,” Darling said. “It’s a really esoteric thing that looks super weird, but if you go out and count the galaxies, you can see this neat effect. It’s not as esoteric or weird as you might think.”


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More information:
Jeremy Darling, The Universe is Brighter in the Direction of Our Motion: Galaxy Counts and Fluxes Are Consistent with the CMB Dipole, Letters from the Astrophysical Journal (2022). DOI: 10.3847/2041-8213/ac6f08

Provided by the University of Colorado at Boulder

Quote: Putting Special Theory of Relativity into Practice, Counting Galaxies (2022, June 3) Retrieved June 4, 2022, from https://phys.org/news/2022-06-theory-special-relativity-galaxies.html

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