Astronomers have found that in the last eight billion years, the temperature of the substance in the universe has tripled. All because of the heating of the intergalactic substance. Theorists find a simple explanation for this. When the germs of galaxies collided and merged with each other, it caused shock waves in the intergalactic environment.
Although the epoch of the fastest heating of intergalactic matter is over, this process continues even now. Galaxies still collide, generating waves in the surrounding gas. Fortunately, this phenomenon does not threaten our galaxy or its inhabitants in any way. First, the intergalactic gas is outside the Milky Way. Secondly, it is incredibly thin: from a practical point of view, it is not even gas, but emptiness. Even a spacecraft would not be heated from it if someone was able to launch it outside the Galaxy. Thirdly, we hardly have to worry about any processes that take billions of years.