Recent discoveries by scientists using NASA's New Horizons spacecraft have revealed the most detailed data on the cosmic optical background (COB), the faint light that fills the universe. This light, although invisible to the human eye, provides crucial information about the history of the universe from the very beginning of the Big Bang. The spacecraft, which passed by Pluto in 2015, is now located at a distance of over 5.4 billion miles from Earth, allowing scientists to avoid the light pollution present in the nearer regions of the Sun and Earth. This position of New Horizons offers a unique opportunity to study the dark parts of the universe.

The study, published in late August 2024 in the journal The Astrophysical Journal, provides the most accurate measurements to date and confirms that the cosmic optical background is produced by the light of all known galaxies. This faint glow, which is roughly 100 billion times fainter than sunlight, originates from billions of stars and galaxies that existed and vanished throughout the history of the universe. Scientists have used precise measurements to rule out the possibility of some unknown sources of light, further strengthening the existing theories about the evolution of the universe.

One of the leading authors of the study, Michael Shull, explains that this research helps 'cosmic accountants' calculate the total amount of light produced in the universe. These results are crucial for understanding how galaxies formed during epochs like the Cosmic Dawn, when the first galaxies appeared hundreds of millions of years after the Big Bang. According to the current picture of the universe's evolution, starlight peaked about 10 billion years ago, and since then the universe has been getting darker as galaxies and stars die out.

This research was conducted using the LORRI (Long Range Reconnaissance Imager) camera on New Horizons, which is sensitive to light in the range of 0.4 to 0.9 micrometers. Scientists were able to calculate how dust and other light from galaxies affect the total measurements and precisely remove all sources of light to obtain a clear image of the cosmic optical background. Using data collected over several weeks in the summer of 2023, the team of scientists led by Marc Postman was able to rule out all known sources of light and analyze only the COB.

It was precisely due to the spacecraft's distance from the Sun that such accurate measurements were possible. The light of the Sun and dust in the inner part of the Solar System create pollution that makes such observations from Earth or closer space telescopes like Hubble difficult or impossible. This is why New Horizons is perfectly positioned for such studies as it is far from these sources of interference.

Measurements show that the remaining light detected by New Horizons is fully consistent with the amount of light expected to come from all known galaxies. Scientists found no evidence of unknown objects or sources of light that could contribute to the cosmic optical background, which rules out the possibility of exotic particles or objects emitting light. This discovery further confirms the current understanding of cosmology and the evolution of the universe from the Big Bang to the present day.

New Horizons, which was originally tasked with exploring Pluto and other objects in the Kuiper Belt, is now entering a new phase of its mission. It is expected to continue sending important data about the outer parts of the Solar System, as well as the heliosphere, which will help scientists better understand how our Solar System interacts with interstellar space. This spacecraft provides a unique opportunity for further research of the universe from a perspective that no other mission can offer in the near future.

In conclusion, although New Horizons is now focused on studying the Kuiper Belt, its research on the cosmic optical background provides important data on the history of the universe. These measurements are likely to remain the most accurate until a new spacecraft capable of similar measurements is launched, which is not expected in the near future. Overall, these discoveries open new possibilities for exploring how galaxies and stars have shaped the universe as we know it today.

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Source: University of Colorado Boulder