New Horizons tells us: 'How Dark Is Space!'

[orin stepanek]

More light than figured!
https://hubblesite.org/contents/news-re ... ws-2021-01

low_STScI-NH-p2101a-k-1340x520.png (180.57 KiB) Viewed 3040 times

NEW MEASUREMENTS OF THE SKY’S BLACKNESS SHOW MORE LIGHT THAN CAN BE ACCOUNTED FOR BY KNOWN GALAXIES.
How dark is the sky, and what does that tell us about the number of galaxies in the visible universe? Astronomers can estimate the total number of galaxies by counting everything visible in a Hubble deep field and then multiplying them by the total area of the sky. But other galaxies are too faint and distant to directly detect. Yet while we can’t count them, their light suffuses space with a feeble glow.

To measure that glow, astronomers have to escape the inner solar system and its light pollution, caused by sunlight reflecting off dust. A team of scientists has used observations by NASA’s New Horizons mission to Pluto and the Kuiper Belt to determine the brightness of this cosmic optical background. Their result sets an upper limit to the starlight emitted by faint, unresolved galaxies, showing that there is about twice as much optical

[Ann]

How interesting, Orin! Thanks for the link!

NASA/Hubblesite wrote:

The cosmic optical background that the team sought to measure is the visible-light equivalent of the more well-known cosmic microwave background – the weak afterglow of the big bang itself, before stars ever existed.

“While the cosmic microwave background tells us about the first 450,000 years after the big bang, the cosmic optical background tells us something about the sum total of all the stars that have ever formed since then,” explained Postman. “It puts a constraint on the total starlight from galaxies that have been created, and where they might be in time.”

Wow!

And like you said, Orin, it was up to New Horizons to do the job of measuring the cosmic optical background:

As powerful as Hubble is, the team couldn’t use it to make these observations. Although located in space, Hubble orbits Earth and still suffers from light pollution. The inner solar system is filled with tiny dust particles from disintegrated asteroids and comets. Sunlight reflects off those particles, creating a glow called the zodiacal light that can be observed even by skywatchers on the ground.

To escape the zodiacal light, the team had to use an observatory that has escaped the inner solar system. Fortunately the New Horizons spacecraft, which has delivered the closest ever images of Pluto and the Kuiper Belt object Arrokoth, is far enough to make these measurements. At its distance (more than 4 billion miles away when these observations were taken), New Horizons experiences an ambient sky 10 times darker than the darkest sky accessible to Hubble.

And the astronomers concluded, like you said, that there is twice as much starlight in the cosmos than can be explained by the number and types of galaxies that can be inferred from measurements by Hubble. So maybe there are many more really small galaxies out there than predicted. Or maybe the extended halos around galaxies contain more stars than astronomers had calculated, or maybe there are more rogue stars out there, sailing the cosmos on their own.

Fantastic!

Ann
Wow again!

[bystander]

New Horizons Spacecraft Answers
Question: How Dark Is Space?
NASA | New Horizons | 2021 Jan 12

Scientist Finds the Universe
to be Brighter than Expected
NSF | NOIRLab | 2021 Jan 12

New Horizons Observations of the Cosmic Optical Background ~ Tod R. Lauer et al

• Astrophysical Journal 906(2):77 (2021 Jan 11) DOI: 10.3847/1538-4357/abc881
• arXiv.org > astro-ph > arXiv:2011.03052 > 05 Nov 2020 (v1), 09 Nov 2020 (v2)