Mean temperature of the universe is rising over billions of years
Earth isn’t the only place that’s heating up of late – the universe seems to be too. Astronomers at Ohio State University have taken the mean temperature of cosmic gas at different distances and ages, and found that it’s roughly 10 times hotter today than it was 10 billion years ago.
When you look out into space, you’re also effectively looking back in time. Since light travels at a set speed, if an object is one light-year away, we’re seeing that object as it was one year ago. By extension, if observatories study an object that’s billions of light-years away, we’re actually peering back almost to the dawn of the universe itself.
For the new study, the team used this phenomenon to measure the temperature of gas from 10 billion light-years away – ie, 10 billion years ago – and compared it to gas that’s much closer to us in space and time.
The team started with data from two wide-ranging space observation missions – Planck and the Sloan Digital Sky Survey. They combined the two datasets, then calculated the distances to pockets of hot gases by measuring the redshift of their light. Essentially, while that light is travelling such huge distances, its wavelengths become stretched out as the universe expands, making them appear more red. Measuring the “redness” of that light can determine how far away the gas is.
Next, the team was able to estimate the temperature of that gas based on its light. The mean temperature of the “modern” gas was found to be almost 2 million °C (3.6 million °F) – making it some 10 times hotter than the gas from 10 billion years ago.
The reason for that sweltering increase has to do with the evolution of the universe over the better part of its lifetime. As the large-scale structure of the universe settled into galaxies and clusters, the gas naturally heated up. That warming will continue into the future as well.
“As the universe evolves, gravity pulls dark matter and gas in space together into galaxies and clusters of galaxies,” says Yi-Kuan Chiang, lead author of the study. “The drag is violent – so violent that more and more gas is shocked and heated up.”
While it’s an intriguing finding, the study isn’t saying that the universe as a whole is heating up – this study focused on the mean temperature of gas near objects. The average temperature of the universe is far, far colder – approximately -270.4 °C (-454.8 °F), just a hair above absolute zero.
Still, the new study can give astronomers a more complete understanding of the long-term evolution of the structure of the universe.
The research was published in the Astrophysical Journal.
Source: Ohio State University