Not so long ago, the New Horizons research spacecraft measured the average light level in the far open space. Based on the results of these measurements, astronomers came to a very unexpected conclusion, it is in the sky in outer space to see "only" a few hundred billion galaxies, the rest of the galaxies glow too dimly to be seen without the use of powerful astronomical instruments. And the surprise of this discovery lies precisely in the number of visible galaxies, which turned out to be much less than the preliminary estimates.
You have probably noticed more than once that in order to fully enjoy the beauty of the night sky you need to go somewhere far away from the big city and the light "pollution" it
creates. The same can be said about the cosmos, the inner regions of our solar system are quite strongly filled with tiny dust particles that reflect and scatter sunlight, creating an analogue of light "pollution". Therefore, space researchers have the opportunity to obtain data on the weakest light only if they manage to get to the outer regions of our system.
The New Horizons spacecraft is ideal for such observations, as it is one of the few spacecraft that has traveled a considerable distance from Earth. After flying past Pluto in 2015 and staying in the Kuiper Belt in 2019, the spacecraft is now 6.4 billion miles away. And the night sky surrounding this spacecraft turns out to be 10 times darker than the sky that the Hubble telescope, which is far from Earth, is relatively close.
Scientists used New Horizons equipment to measure cosmic optical background radiation, a diffused light of the visible range that is so weak that it is invisible for most terrestrial and space telescopes because it is below the level of local lightpollution. "Relic cosmic microwave radiation contains information about the first 450,000 years after the Big Bang. And the optical cosmic background emit contains the total information about all the stars that have formed since then" - write the researchers, "Moreover, this light carries information about the number of galaxies, the place and time of their formation."
According to the results of studies, in outer space in the sky you can see no more than a few hundred billiongalaxies. This number seems extremely large, however, it is much less than two trillion, the previous estimate made based on the approximation of data of the Hubble Space Telescope. "We take the number of galaxies that the Hubble telescope sees, divide it into two, and get the number of things we can see in the sky at all." In the course of the research, the scientists conducted a thorough analysis of many of the latest images taken by the New Horizons spacecraft.
Using special algorithms, direct light from the stars of our galaxy and their own light scattered by clouds of cosmic dust was removed from these images. And as a result, a very weak background residue was obtained, which is exactly the cosmic optical background radiation.
It is only natural that scientists have already wondered the origin of this background
radiation. They believe that this light may have been emitted by very small dwarf galaxies accompanying the Milky Way, or (and) very dim galaxies farther away from ours. Also, the source of background light can be star wanderers, loners not tied to galaxies. In addition, galactic halos, glowing more brightly than previously thought, can contribute to optical background radiation.
The search for answers to the above questions can only help with additional observations, which will be carried out with the help of the latest telescopes, such as the James Webb Telescope, which will be launched in October this year, if it is not postponed again for a later period.