BEIJING, Dec. 12 (Xinhua) — According tomedia reports, the universe has been dark for hundreds of millions of years, and an atom may be the key to unlocking this forgotten era. Once upon a time, the universe was dark for millions of years before the first star was formed. This cosmic “dark age”, which began about 400,000 years after the Big Bang and lasted hundreds of millions of years, marks the latest real vacuum; there are no planets, no stars, no galaxies, no life in the universe, and only a fog of hydrogen atoms formed by the Big Bang floats in the endless darkness.
The Murchison Wide Area Array is a network of radio telescopes in the Australian outback that scientists use to search the sky for traces of neutral hydrogen, possibly the last remains of the dark ages of the universe
Today, telescopes around the world are trying to get a glimpse of these primitive hydrogens, known as neutral hydrogen atoms, to determine the end of the dark ages and the moment when the first galaxies formed. Although these ancient atoms are very elusive, a team of researchers observing them in the Australian interior may have been very close to finding them.
According to a new study published in the preprint database arXiv, astronomers used the Murchison Widefield Array radio telescope to drill down into the universe’s past, searching for the iconic wavelengths of neutral hydrogen. Unfortunately, the researchers didn’t find what they were looking for, but using the telescope array’s recently updated settings, the team determined a minimum of neutral hydrogen signal strength.
If the neutral hydrogen signal is stronger than the limit we set in the paper, the telescope will detect them. This means that the search for these ancient molecules continues, and researchers now know that traces of neutral hydrogen are actually more blurred than expected.
The first atom.
The energy that ran through the early universe was so strong that the electrons of each atom were taken away to obtain a positive charge. The first atom is a positively charged hydrogen ion. Over hundreds of thousands of years, the universe cooled and expanded enough to allow these hydrogen ions to regain electrons and become neutral again. These neutral hydrogen atoms are considered to be the main features of the dark ages of the universe. Eventually, when enough atoms gather to form the first stars, they are re-ionised by the radiation energy of those stars.
Scientists already know that neutral hydrogen emits radiation at a wavelength of 21 cm. However, as the universe has expanded over the past 12 billion years, these wavelengths have lengthened. The authors of the new study estimate that the wavelength of the neutral hydrogen has extended to about 2 meters, and they used the WMA telescope to search the sky for the signal.
The problem is that many light sources (both man-made and natural) radiate at the same wavelength. All of these other light sources are many orders of magnitude stronger than the signals we are trying to detect, and even FM radio signals reflected from an aircraft just above the telescope are enough to contaminate the data.
So the researchers wrote a set of equations to identify and remove these disturbances from the observations. After taking more than 1,200 snapshots of the sky’s radio waves, the researchers determined that every trace signal they found at a 2-meter wavelength came from sources other than neutral hydrogen.
Although the most important neutral hydrogen atom signals have yet to be discovered, the new study has succeeded in narrowing the range of future searches for neutral hydrogen. The researchers say the results are a powerful indication that observations by the MWA telescope are leading us along the right path in search of neutral hydrogen. With further research, the last remains of the dark ages of the universe may soon be discovered.
What is the “dark ages” of the universe?
The “dark period” in the history of the universe’s evolution refers to the formation of plasma compounding at the end of the Big Bang to the beginning of the formation of the first generation of stars. Previously, the universe was filled with high-energy photons, causing ordinary matter in the universe (mainly hydrogen and helium) to be ionated. About 400,000 years after the Big Bang, as the universe expanded, the energy of these photons was not enough to ionise hydrogen and helium, so free electrons and hydrogen and helium atoms formed neutral atoms. As free electrons disappear, photons can travel freely and no longer scatter, making the universe transparent. These photons eventually move red to the microwave band, forming the cosmic microwave background radiation we observe today. The universe at this time is so uniform that there are no stars, and there are no elements other than hydrogen, helium, and a small number of light cores such as thorium, helium-3, and lithium produced during the Synthesis of the Big Bang nucleus, so it is known as the Dark Ages.
Currently, existing astronomical observations can see the universe before the Dark Ages, i.e. the cosmic microwave background radiation, and the universe after the Dark Ages, including stars, galaxies, quasars, etc., but still cannot observe the dark period. Understanding and observing the physical processes that occurred during this period is a very important scientific issue in astronomy. (Any day)