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NASA’s Roman Nancy Grace Space Telescope will detect vestiges of sound waves that once rippled in the primeval cosmic sea. According to new simulations, Roman’s observations could extend these measurements into an unproven epoch between the childhood of the universe and the present day. Studying the echoes of this era will help us chart the evolution of the universe and solve the pressing cosmic puzzles.
Sound waves from the nascent universe, called baryon acoustic oscillations (BAOs), have left their mark on the cosmos by affecting the distribution of the galaxy. Researchers explored this footprint until the universe was three billion years old, or about 20 percent of its current age of 13.8 billion years – BAO studies from Roman’s own era are optimized to investigate. Now a team of scientists has shown that the mission could go even further back in time to explore the impressions left by the BAOs.
“This isn’t something you can study in a lab, so we created fictional universes and ran simulations,” said Siddharth Satpathy, who led the study. Now a machine learning engineer at Cisco in San Francisco, he conducted this research while earning a PhD in computational astrophysics from Carnegie Mellon University in Pittsburgh. “We were thrilled to find that Roman will be powerful enough to study BAO’s remains in the youth of the universe,” he added.
Hot plasma soup
For most of its first half million years, the universe looked extremely different than it does today. Instead of being dotted with stars and galaxies, the cosmos was filled with a sea of charged plasma particles – forming a dense, almost uniform fluid.
There were small fluctuations of about one part in 100,000. The few variations that existed took the form of slightly denser grains of matter, such as an ounce of cinnamon sprinkled into about 13,000 cups of cookie dough. Because the lumps had more mass, their gravity attracted additional material.
It was so hot that the particles couldn’t stick together when they collided – they just bounced off each other. The alternation between the force of gravity and this repellent effect created pressure waves – the sound – that propagated through the plasma.
Over time, the universe cooled and the particles combined to form neutral atoms. As the particles stopped repelling each other, the waves ceased. Their traces, however, are still etched in the cosmos.
Frozen echoes
As the atoms formed, the ripples essentially froze in place, carrying a little more matter into them than the average for the universe. With the repulsive pressure of the plasma gone, gravity became the dominant force.
Over hundreds of millions of years, the clumps of plasma that once filled the universe have absorbed more material to become stars. Their mutual gravity united the stars into groups, eventually forming the galaxies we see today. And a little more galaxies have formed along the ripples than anywhere else.
As the waves no longer propagated, the icy ripples lengthened as the universe expanded, increasing the distance between galaxies. By looking at how galaxies are distributed across different cosmic epochs, we can explore how the universe has expanded over time.
“The BAOs have made their mark on the cosmos, but we haven’t fully examined their tracks,” said co-author Rupert Croft, a physics professor at Carnegie Mellon University. “By studying BAO impressions in an untested region, we can excavate cosmic fossils, which will allow us to unearth new insights into the forces that shaped the universe.”
Scientists have noticed a pattern in the way galaxies cluster from nearby universe measurements. For any galaxy today, we are more likely to find another galaxy about 500 million light-years away than slightly closer or further away. But looking more into space, in early cosmic times, means that this distance – the residue of the frozen ripples of the BAO – will decrease.
Roman will extend the previous research by mapping the expansion of the universe to unprecedented detail. Satpathy and his team showed that Roman’s polls will be able to probe BAO’s remains five times farther than originally predicted, back when the universe was only about 600 million years old – just 4% of its age. current.
Learning more about how the cosmos has expanded over time will allow scientists to explore dark energy, a mysterious pressure that is accelerating the expansion of the universe. Roman is optimized to scan the cosmos for BAO impressions in the middle of its current age, because that’s when scientists think dark energy has gone from being a minor contributor to the contents of the universe to the most dominant force.
But some theories assume a period of dark energy activity when the universe was much younger. Peering further into the universe’s past will help add pieces to the puzzle.
“We haven’t explored the BAO footprints extensively since the universe was very young because we need a huge sample of galaxies to do that,” said Jason Rhodes, senior researcher at NASA’s Jet Propulsion Lab in Pasadena, California. “This is where Roman comes in. The mission has such a large field of view that observations like this will be possible.”
Roman’s high-latitude spectroscopic survey will measure precise distances and positions for millions of galaxies. The scientists intend to analyze how their distribution varies with distance by creating a 3D map of the universe, which will help us decipher how dark energy has shaped the cosmos over time.
Two further Roman investigations will also study dark energy, and each technique will test the others. The mission will provide important data to help scientists investigate, and perhaps even predict, the fate of the universe.
The team’s findings were published September 11 in the Royal Astronomical Society’s monthly notices.
Research paper
Related links
Nancy Grace Roman Space Telescope
Understanding time and space
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Columbus OH (SPX) November 11, 2020
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