Deep space is even darker than we imagined

New Horizons is offering a fresh perspective on one of the universe’s greatest mysteries: the depth and darkness of space, revealing hidden insights into the cosmic light that permeates our universe.

Thanks to the advanced instruments aboard this pioneering spacecraft, astronomers have conducted the most accurate and direct measurements of the total amount of light that the universe produces.

The findings bring us closer to answering the age-old question about the true nature of cosmic darkness.

New Horizons spacecraft

New Horizons, which is at a whopping distance of more than 7.3 billion kilometers from our planet, is situated in an area of the solar system that’s far enough from the Sun to offer the darkest skies available to any existing telescope.

This provides a particularly unique vantage point to measure the overall brightness of the distant universe.

“One of the interesting questions we sought to answer was: ‘If you hold up your hand in deep space, how much light does the universe shine on it?'” said Marc Postman, an astronomer at the Space Telescope Science Institute in Baltimore and lead author of a new paper detailing the research.

“The results show that the great majority of visible light we receive from the universe was generated in galaxies. Importantly, we also found that there is no evidence for significant levels of light produced by sources not presently known to astronomers.”

Measuring the total light output of the universe

Astronomers have been grappling with a cosmic conundrum since the 1960s when it was discovered that space is permeated by strong microwave radiation predicted to be leftover from the universe’s creation.

Later, evidence was discovered of background light from X-rays, gamma rays, and infrared radiation. However, measuring the total light output of the universe is extremely challenging, especially from Earth or anywhere within the inner solar system.

The efforts to measure the strength of the cosmic optical background (COB), the “ordinary” or visible light, have been fraught with large uncertainties.

What’s intriguing is that the cosmic optical background provides a way to add up all the light generated by galaxies over the lifetime of the universe.

Imaging the universe with New Horizons

This is where New Horizons, billions of miles into its journey beyond the planets, comes into play.

Protected from the Sun by the spacecraft’s main body, the Long Range Reconnaissance Imager (LORRI) scanned the universe and collected distinct imaging fields that were positioned away from the bright disk and core of the Milky Way and nearby bright stars.

Data from the European Space Agency’s Planck mission was also used in fields with a range in dust density to calibrate the level of those far-infrared emissions to the level of ordinary visible light. This helped in predicting and correcting for the presence of dust-scattered Milky Way light in the COB images.

Light produced by all the galaxies

After accounting for all known sources of light like background stars and light scattered by thin clouds of dust within the Milky Way galaxy, the researchers discovered that the remaining level of visible light was precisely in line with the intensity of light produced by all galaxies over the past 12.6 billion years.

“The simplest interpretation is that the COB is completely due to galaxies. Looking outside the galaxies, we find darkness there and nothing more,” noted Tod Lauer, a New Horizons co-investigator and astronomer at the National Science Foundation NOIRLab.

Uncharted territories in space

This breakthrough research has greatly contributed to our understanding of fundamental cosmology. The extended mission of New Horizons is providing crucial insights, expanding far beyond its original mission to explore Pluto and Kuiper Belt objects.

The New Horizons spacecraft is managed by the Johns Hopkins Applied Physics Laboratory (APL) and the mission is directed by the Southwest Research Institute. It is a part of NASA’s New Frontiers program.

As New Horizons continues its journey into the uncharted territories of the solar system, it promises to deliver even more exciting insight into the awe-inspiring universe we live in.

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