IT IS DARK! In space, all the light comes from only one type of source

Space is dark, we all know that. But how dark? Astronomers have tried to answer this big question with the New Horizons spacecraft. The NASA probe has finally helped experts shed more light on the topic by making the most precise and direct measurements ever of the total amount of light generated by the universe.

Launched 18 years ago, the spacecraft is now more than 5.4 billion miles from Earth, far away from the planets in our solar system. It is in the darkest possible place in space where the glow of background dust in our system does not affect it in any way.

Being present in the darkest skies available to any existing telescope, the probe has the best viewpoint to measure the overall brightness, or darkness, of the distant universe.

The new research has been published in The Astrophysical Journal.

"If you hold up your hand in deep space, how much light does the universe shine on it?” asks Marc Postman, an astronomer at the Space Telescope Science Institute in Baltimore and lead author of the paper.

The researchers found that the glow coming from different background galaxies alone fills the universe. Nothing else was found to generate light.

“We now have a good idea of just how dark space really is. The results show that the great majority of visible light we receive from the universe is 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.”

Also Read:Nearly 1,700 ancient viruses spanning 41,000 years unearthed from Himalayas

In the 1960s, astronomers Arno Penzias and Robert Wilson discovered that space is filled with strong microwave radiation, which was likely left over from the creation of the universe itself. Later, astronomers also found evidence for the existence of X-rays, gamma rays and infrared radiation.

They needed toadd up all the light generated by galaxies over the lifetime of the universe.Detecting the background of "ordinary" (or visible) light, also known as cosmic optical background, or COB, was one way.

Once Hubble and James Webb came, astronomers measured the COB to detect light that might come from sources other than these known galaxies.But, there was a problem.

Measuring total light produced by the universe

It is not possible to measure the total light generated by the universe from Earth or anywhere in the inner solar system, Tod Lauer, a New Horizons co-investigator, said.

"There’s just too much sunlight and reflected interplanetary dust that scatters the light around into a hazy fog that obscures the faint light from the distant universe,” he said.

Once New Horizons was billions of miles away, it scanned the universe with its Long Range Reconnaissance Imager (LORRI), collecting two dozen separate imaging fields from a distance of 57 times farther from the Sun than Earth.

The data, combined with previous information, showed that after taking into account all known sources of light, like background stars and light scattered by thin clouds of dust within the Milky Way, the remaining level of visible light matched the intensity of light generated by all galaxies over the past 12.6 billion years.

"The simplest interpretation is that the COB is completely due to galaxies," Lauer said. "Looking outside the galaxies, we find darkness there and nothing more."