Astronomers recently looked at how the average gas temperature of the universe has changed over the past ten billion years. It shows that it increased considerably during this period. Today it is approaching two million degrees Celsius.
Watching the sky is a bit like time travel. Indeed, assuming that light travels at a set speed, if an object is ten light-years away, we see it as it was ten years ago. By extension, if astronomers examine an object positioned ten billion light-years away, they are examining said object as it was during the youth of the universe.
Thus, as part of a recent study, a team from Ohio State University sought to measure the evolution of the temperature of the gas contained in the Universe on about ten billion cosmic years.
To do this, the researchers relied on data from the Planck mission and the Sloan Digital Sky Survey to identify several pockets of gas. They then analyzed the redshift of their light. Indeed, as this light travels such huge distances, their wavelengths stretch as the universe expands, drawing more red. Concretely, measuring the redshift of these pockets of gas makes it possible to determine at what distance they are.
Astronomers then selected those ten billion years old, then increasingly younger structures. Finally, they sought to estimate the temperature of these gases based on their light. It eventually turned out that the average temperature of "modern" gas was close to two million degrees Celsius , which is about ten times hotter than the gas of ten billion years ago.
This increase in temperatures is not really surprising . As the large-scale structure of the universe transformed into galaxies and clusters, the gas did indeed naturally warm. And this warming will also continue in the future.
Note also that this study focused on the average temperature of gas near objects and therefore does not conclude that the universe is warming in its together. Indeed, the average temperature of the universe is much colder and is estimated to be around -270.4°C , slightly above absolute zero.
Details of this work are published in The Astrophysical Journal
