Starship Asterisk*

X-ray (top row) and optical pseudo-color (bottom row) images images of three low mass clusters identified in the eFEDS survey data. The highest redshift cluster come from a time when the Universe was approximately 10 billion years younger than today. The cluster galaxies in that case are clearly much redder than the galaxies in the other two clusters. These galaxy clusters were used to determine th extent of dark matter across space and time. Courtesy: eRosita

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The Force is with us, according to cosmologists working to understand a mysterious “something” that’s making the universe expand. Its name? Dark energy. And, it turns out that it’s been present everywhere throughout cosmic history.

Astronomers have known since the 1920s that the universe is expanding. That understanding began with Edwin Hubble’s groundbreaking observation of a Type I supernova in the Andromeda Galaxy. And, astronomy trucked along for many years, using that expansion to measure distances and other parameters in the cosmos. Then, in 1998, something happened. Astronomers discovered that the cosmic expansion is speeding up.

The culprit? This completely not-at-all-understood dark energy force which can’t be seen, but with effects that can be detected. Some explain it as a property of space that causes the universe to expand faster and faster. Others suggest that it’s some kind of new energy fluid or a field that fits throughout space, but has an effect on the expansion of the Universe. It could also be something that doesn’t fit our current theories about gravity, and that a new theory of gravity could account for dark energy’s effects.

There’s no consensus yet about which of these theories is correct. However, its discovery immediately raised a bunch of questions, such as, when did the expansion rate accelerate? Will that change, too? Was it the same rate throughout the universe across all time? ...

• Monthly Notices of the RAS 522(2):1601 (June 2023) DOI: 10.1093/mnras/stad957
• arXiv > astro-ph > arXiv:2207.12429 > 25 Jul 2022 (v1), 28 Mar 2023 (v2)