There is one epoch in the history of the universe that scientists are still talking aboutknow very little.
There were no stars or planets in this epoch.The history of the early universe, which preceded the Dark Ages, can be judged by the cosmic microwave background radiation.But there's still no way for astrophysicists to observe what happened during the Dark Age.Although radio waves from this period still exist in space, the abundance of radio interference on Earth has obscured these signals fromobservers on our planet.
But researchers are not giving up trying to find a way to hear the signals of the dark ages. To do this, NASA plans to build the LuSEE-Night radio telescope on the far side of the Moon.
What are the dark ages of the universe?
Modern cosmological theory describes the universe as a place with extremely extreme conditions.All the energy and matter that exists in the universe has been concentrated into a tiny space, a billion times hotter than the centerSun.
Already in the first moments after the Big BangThe universe has cooled down enough to allow the formation of the first elementary particles, such as quarks and electrons. Quarks combined to form protons and neutrons, and deuterium, helium, and lithium nuclei formed soon after. Energy traveled through the nascent universe in the form of photons, but this early light ricocheted off free electrons, which had not yet been bound to any atom, at every turn.
By the end of this era, approximately 380 thousand yearsyears after the Big Bang, the universe cooled down enough to allow protons to begin to attract electrons and form neutral atoms for the first time. This process is called recombination, which is a general chemical term that describes the capture of free electrons by charged ions. At the beginning of the Dark Ages, such a capture occurred for the first time.
Astrophysicists know what the universe was like not long agobefore the beginning of the dark ages. When the first neutral atoms were formed, the process released photons of light that scattered throughout the universe, creating a "snapshot" of conditions. This cosmic microwave background or cosmic background radiation is still being recorded and shows that at that time the Universe was more or less uniform in density, with very small ripples.
Before the formation of the first stars, there was little light, apart from hydrogen atoms, which made up most of the baryonic matter at this time, most of the universe was made up of dark matter, which does not radiateSveti does not interact with electromagnetic waves at all.The researchers believe that the neutral hydrogen atoms that filled the universe scattered or absorbed most of the ultraviolet photons emitted by the very first stars.
The universe has become transparent to UV radiation againafter the formation of a sufficient number of the first stars and galaxies - several hundred million years after the Big Bang. Matter condensed and began to form structures that permeate the Universe today. Some of the first stars were massive and bright, their light energetic enough to knock electrons out of surrounding hydrogen atoms in a process known as ionization. And unlike neutral atoms, ionized hydrogen does not absorb or scatter light.
Map of the evolution of the universe. Image: Roen Kelly, Astronomy
Why the far side of the moon?
To study the distribution of neutral hydrogen,which made up most of the baryonic matter during the Dark Ages, one can use the analysis of the neutral hydrogen radio line or the 21 cm line. This is a hyperfine transition of neutral hydrogen, visible against the background of the CMB.
When the magnetic moment of an electron is spontaneously reversed, the neutral hydrogen atom emitsquantum electromagnetic radiation with a wavelength of 21.1 cm.Extremely rare, but on the scale of a huge number of individual atoms, powerful enough to become noticeable.
Due to the redshift caused byWith the expansion of the universe, the wavelength of the neutral hydrogen line from the atoms of the Dark Ages is further increased. This is an extremely weak signal that gets lost in a lot of radio interference.
The moon and earth are connected by tides, which meansthat a natural satellite rotates around its axis at the same speed as around the planet. This phenomenon is called tidal trapping and that is why the Moon always faces the Earth on one side. The reverse side of the satellite is protected from many sources of radio interference at night by its own mass.
The far side of the moon is in complete darknessduring 14 Earth days followed by 14 days of intense sunshine. This causes the temperature on its surface to fluctuate from -173 °C at night to +127 °C, and a sharp change can occur within a few hours.
These conditions create very difficult conditions forspacecraft operation. Devices that can survive several cycles of day and night must remove heat in a vacuum during the day and not freeze at night, and at the same time work in the dark, when the Sun does not create unnecessary interference.
How will LuSEE-Night work?
LuSEE-Night is a NASA exploration missionthe purpose of which is to land a radio telescope on the far side of the moon and make the most accurate measurements of the sky at frequencies below 0.1 to 50 MHz. It is expected to be delivered to the Moon in 2025 and operate for 18 months after landing.
The landing site of the LuSEE-Night mission. Image: Brookhaven National Laboratory
The telescope will be delivered to a point with coordinates 23°48′ 50″ S and 176° 49′ 47″ e.d. This is a convenient landing site, located close to the anti-meridian - a line connecting the poles of the satellite and facing away from the Earth, where radio interference from the planet is minimal. After landing, the LuSEE-Night lander will turn off permanently to avoid causing interference.
The antenna assembly of the telescope will consist of four3-meter unbalanced antennas. It will be mounted on a motorized platform called a turntable. Moving the antenna will help measure different combinations of signals. The collected LuSEE-Night data will be transmitted to a repeater satellite that orbits the Moon and transmits data to Earth.
LuSEE-Night is not a standard radio telescope.It's more like a radio. It will work like an FM radio, receiving radio signals in the same frequency band. The spectrometer is at the center of it all. Like a radio tuner, it can isolate radio frequencies and convert signals into electromagnetic radiation spectra.
Anje Slosar, physicist at Brookhaven National Laboratory, one of the developers of the LuSEE-Night telescope
Four antennas of the LuSEE-Night telescope. Image: Brookhaven National Laboratory
Although the researchers are not sure whether the telescope will be able toimmediately after starting work, fix the radio signal from the dark ages. They note that he is a pioneer, which should show what kind of data researchers can, in principle, get on the far side of the moon. Perhaps real discoveries will require new missions, but the first step is always one of the most difficult.
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On the cover: the other side of the moon. Image: NASA, Public domain, via Wikimedia Commons