A recent study examined the thermal history of our universe over the last 10 billion years. It concluded the universe is getting hotter as it gets older.
The new study by the Ohio State University Center for Cosmology and AstroParticle Physics probed the temperature of our Universe over the last 10 billion years in an attempt to understand its thermal history.
It found that the mean temperature of gas across the universe has increased more than 10 times over that time period. And it reached about 2 million Kelvin today or about 4 million degrees Fahrenheit.
The research – published last month in the Astrophysical Journal – relied on and confirmed work by Jim Peebles, who won the 2019 Nobel Prize in Physics for his work on the large-scale structure of the universe. The heating is a result of that structure and how it changes over time, as a result of the galaxies and galaxy clusters move around.
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“Our new measurement provides a direct confirmation of the seminal work by Jim Peebles—the 2019 Nobel Laureate in Physics—who laid out the theory of how the large-scale structure forms in the universe,” said Yi-Kuan Chiang, lead author of the study and a research fellow at The Ohio State University Center for Cosmology and AstroParticle Physics.
The large-scale structure of the universe refers to the global patterns of galaxies and galaxy clusters on scales beyond individual galaxies. The gravitational collapse of dark matter and gas forms this vast structure.
“As the universe evolves, gravity pulls dark matter and gas in space together into galaxies and clusters of galaxies,” Chiang said. “The drag is violent—so violent that more and more gas is shocked and heated up.”
“As the universe evolves, gravity pulls dark matter and gas in space together into galaxies and clusters of galaxies. The drag is violent—so violent that more and more gas is shocked and heated up.”
For this study, researchers devised a new method allowing them to measure the gas’s temperature farther away from Earth. They literally looked back in time. They then compared those measurements to gases closer to Earth and near the present time.
Chiang said, “Now, Scientists have confirmed that the universe is getting hotter over time due to the gravitational collapse of cosmic structure, and the heating will likely continue.”
Scientists gathered those measurements by using different properties of light collected by two missions, Planck and the Sloan Digital Sky Survey. Planck is the European Space Agency mission that operates with heavy involvement from NASA; Sloan collects detailed images and light spectra from the universe.
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After combining data from the two missions, scientists gauged the distances of hot gases near and far via measuring redshift. Astrophysicists use the notion of redshift to estimate the cosmic age at which distant objects are observed. The farther away something is in the universe the longer its wavelength of light. Astronomers call that lengthening the redshift effect.
The concept of redshift works because the light we see from objects farther away from Earth is older than the light we see from objects closer to Earth—the light from distant objects has traveled a long journey to reach us. That fact, along with estimating temperature from light, allowed scientists to measure the mean temperature of gases in the early universe—gases that surround objects farther away—and compare that means with the mean temperature of gases closer to Earth—gases today.
Bottom line: Gases in today’s universe, around objects closer to Earth, reach temperatures of about 2 million Kelvin. That is about 10 times the temperature of the gases around objects farther away and further back in time.
The difference between the two eras allowed scientists to understand the change over time. And it showed that it was indeed getting hotter and that it would likely continue over time.
“We have measured temperatures throughout the history of the universe,” said Brice Ménard, a Johns Hopkins professor of physics and astronomy. “As time has gone on, all those clusters of galaxies are getting hotter and hotter because their gravity pulls more and more gas toward them.”
The universe is getting hotter because of galaxy and structure formation and it doesn’t relate to the warming of Earth.