I know the temperature of the universe is decreasing due to it's expansion after the big bang but after I came up with this article in AOP(please note I don't have the access of the journal,so I have just read the abstract) after reading this I am quite confused.
A news media states that:
The study by the Ohio State University Center for Cosmology and AstroParticle Physics shows that the "universe is getting hotter". This big revelation came amid the scientists' restless examinations on the thermal history of the universe over the last 10 billion years.
It has been also stated that:
The study also explained how, with the evolution of the universe, gravity pulls dark matter and gas in space together into galaxies and clusters of galaxies. The pull is so violent that more and more gas is shocked and heated up. Scientists used a new method to measure the temperature of gas farther away from Earth. The scientists, during the research, then compared those measurements to gases closer to Earth and near the present time. They said the "universe is getting hotter over time due to the gravitational collapse of cosmic structure, and the heating will likely continue". Data from the Planck and the Sloan Digital Sky Survey was used to observe how the universe's temperature has gone up.The universe is warming because of the natural process of galaxy and structure formation.
So my question is:
•Is it indirectly violating the principle that the universe is cooling down due to expansion? Or is it just a additional factor in a small region of our space? Or is it happening as a regular phenomenon for a long time?
•Can someone explain to me the whole phenomenon with more science/ or any scientific explanation more than what I found?
•If the findings are true then what are the probable effects?
I am hoping to have clarity on the paper, maybe, being naive I haven't understood it completely, besides answer further suggestions are welcomed.