The study referred to was published in The Astrophysical Journal in 2021 and is titled "New Horizons Observations of the Cosmic Optical Background" by Michael E. Zemcov et al.

In this study, the researchers analyzed data collected by the New Horizons spacecraft's dust-detection instruments during its flyby of Pluto in 2015. They specifically looked at the "blank sky" images captured by the spacecraft's camera and subtracted all known sources of light to isolate the "cosmic optical background," which is the residual light that remains.

The study found that even after subtracting all known sources of light, including light from stars, galaxies, and interstellar dust, there was still a significant amount of unexplained light. This light may be coming from sources that are currently unknown, such as the first stars or black holes, or it may be due to some unknown property of the universe.

If you're interested in learning more about this study or the cosmic optical background in general, I would recommend reading the original research article.

Resource links:
1.    https://arxiv.org/abs/2010.04021
2.    https://arxiv.org/abs/2011.03052

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