Galaxies have gotten hotter as they've gotten older
Study of 10 billion years of microwaves reveals a warming predicted by dark matter theory
IMAGE: BRICE MÉNARD OF JOHNS HOPKINS AND YI-KUAN CHIANG OF OHIO STATE UNIVERSITY. view more
CREDIT: RON SCHEFFLER
Who says you can't get hotter with age?
Researchers from Johns Hopkins University and other institutions have found that, on average, the temperature of galaxy clusters today is 4 million degrees Fahrenheit. That is 10 times hotter than 10 billion years ago, and four times hotter than the Sun's outermost atmosphere called the corona. The findings are published in the Astrophysical Journal.
"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."
Yi-Kuan Chiang, lead author of the study who was a Johns Hopkins post-doctoral researcher until moving to Ohio State University last year, added: "This drag is so violent that more and more gas is shocked and heated up."
Imagine all those gas atoms being sucked towards galaxies like they were myriads of meteoroids piercing Earth's atmosphere, Ménard said. They accelerate as gravity pulls them toward the Earth's surface and heat up due to friction with the atmosphere before burning into what are seen as shooting stars, he added. This pattern of heating due to gravitational forces can be applied to entire galaxies, clusters of galaxies and beyond into the "large scale structures" of the universe formed by gravity - a theory attributed to James Peebles, the 2019 Nobel laureate in physics.
"Our measurements are a great confirmation of that theory," Ménard said.
To perform this analysis, the team used data collected by the astronomical community over two decades, first from a telescope on the ground that conducted the Sloan Digital Sky Survey and then the Planck mission, a space telescope led by the European Space Agency.
The team used a technique that Ménard developed with Chiang. With it, they estimated the "redshift" of gas concentrations seen in images of microwave light going back in time all the way to 10 billion years ago. "Redshift" describes the way wavelengths of light lengthen due to the expansion of the universe. The farther away something is, the longer its wavelength - and the older its origin.
The method allowed them to measure the gradual increase in the gas temperature as a function of the age of the universe. This trend is also predicted by numerical simulations showing how dark matter and the atoms present in the gas evolve with time. As illustrated in the figure, these visualizations show gas temperatures changing from a cool blue canvas from 10 billion years ago into one speckled with hot red today.
The warming of the universe has nothing to do with climate warming on Earth, Ménard said. It is a consequence of gravitational attraction that had been predicted but which now can be precisely measured with these novel techniques.
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Researchers from the University of Tokyo and the Max Planck Institute for Astrophysics contributed to this work, which was supported in part by NSF grant AST1313302 and NASA grant NNX16AF64G (Y.C., B.M.). Other support has come from the Excellence Cluster ORIGINS, which is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy--EXC-2094-390783311 (E.K.), and JSPS KAKENHI grant Nos. JP15H05896 (R.M., E.K.) and JP20K14515 (R.M.).
Reporters interested in speaking with Ménard can call Doug Donovan at 443-462-2947 or email him at dougdonovan@jhu.edu.
Johns Hopkins University news releases are available online, as is information for reporters. To arrange a video or audio interview with a Johns Hopkins expert, contact a media representative listed above or visit our studio web page. Find more Johns Hopkins stories on the Hub.
The universe is getting hot, hot, hot, a new study suggests
Temperature has increased about 10 times over the last 10 billion years
COLUMBUS, Ohio -- The universe is getting hotter, a new study has found.
The study, published Oct. 13 in the Astrophysical Journal, probed the thermal history of the universe over the last 10 billion years. It found that the mean temperature of gas across the universe has increased more than 10 times over that time period and reached about 2 million degrees Kelvin today -- approximately 4 million degrees Fahrenheit.
"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. It is formed by the gravitational collapse of dark matter and gas.
"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."
The findings, Chiang said, showed scientists how to clock the progress of cosmic structure formation by "checking the temperature" of the universe.
The researchers used a new method that allowed them to estimate the temperature of gas farther away from Earth -- which means further back in time -- and compare them to gases closer to Earth and near the present time. Now, he said, researchers have confirmed that the universe is getting hotter over time due to the gravitational collapse of cosmic structure, and the heating will likely continue.
To understand how the temperature of the universe has changed over time, researchers used data on light throughout space 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.
They combined data from the two missions and evaluated the distances of the hot gases near and far via measuring redshift, a notion that astrophysicists use to estimate the cosmic age at which distant objects are observed. ("Redshift" gets its name from the way wavelengths of light lengthen. The farther away something is in the universe, the longer its wavelength of light. Scientists who study the cosmos 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 longer journey to reach us. That fact, together with a method to estimate temperature from light, allowed the researchers to measure the mean temperature of gases in the early universe -- gases that surround objects farther away -- and compare that mean with the mean temperature of gases closer to Earth -- gases today.
Those gases in the universe today, the researchers found, reach temperatures of about 2 million degrees Kelvin -- approximately 4 million degrees Fahrenheit, around objects closer to Earth. That is about 10 times the temperature of the gases around objects farther away and further back in time.
The universe, Chiang said, is warming because of the natural process of galaxy and structure formation. It is unrelated to the warming on Earth. "These phenomena are happening on very different scales," he said. "They are not at all connected."
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This study was completed in collaborations with researchers at the Kavli Institute for the Physics and Mathematics of the Universe, Johns Hopkins University, and the Max Planck Institute for Astrophysics.
CONTACT: Yi-Kuan Chiang, chiang.224@osu.edu
Written by: Laura Arenschield, arenschield.2@osu.edu
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