Around 370,000 years after the Big Bang, the universe experienced a time that cosmologists call the “cosmic dark age”.
During this time, the universe was covered by a hot, dense plasma that obscured all visible light and made it invisible to astronomers.
When the first stars and galaxies formed over the next few hundred million years, the radiation they emitted ionized this plasma and made the universe transparent.
One of the greatest cosmological puzzles is the beginning of “cosmic reionization”. To find out, astronomers looked deeper into the cosmos (and further back in time) to discover the first visible galaxies.
Thanks to recent research by a team of astronomers from University College London (UCL), a glowing galaxy has been observed that reionized the intergalactic medium 1
The research was presented last week (July 2) during the annual meeting of the European Astronomical Society (EAS) – due to the pandemic, this year’s meeting was virtual.
Romain Meyer (PhD student at UCL and lead author of the study) and his colleagues shared their results during their lecture. This is the first solid evidence that reionization was completed 13 billion years ago.
The team responsible for this discovery was led by Romain Meyer, a PhD student from the UCL Astrophysics Group. The UCL researcher Dr. Nicolas Laporte and Prof. Richard S. Ellis as well as Prof. Anne Verhamme and Dr. Thibault Garel from the University of Geneva. Their results are also the subject of a paper that was recently submitted The monthly communications from the Royal Astronomical Society.
The study of galaxies that existed in this early phase of the universe is important to understand the origins of the cosmos and its later development.
According to our current cosmological models, the first galaxies were formed from merging star clusters, which in turn formed when the first stars in the universe came together.
Over time, these galaxies emitted the radiation that the neutral gas in the intergalactic medium (IGM) stripped of its electrons (AKA the ionization process). Astronomers know this because we have clear evidence of it, in the form of the cosmic dark age and the way the universe is transparent today.
However, the key questions of how and when this all happened are unknown. Like Dr. Meyer Universe Today emailed:
“When we look at distant galaxies, we look into the early universe because light traveled billions of years before it reached us. This is fantastic because we can see how galaxies were billions of years ago, but it has some Disadvantage . “
For starters, Meyer explained, distant objects are very weak and can only be observed with the most powerful ground-based and space-based telescopes.
At this distance there is also the delicate problem of redshift, in which the expansion of the cosmos causes the wavelength of light from distant galaxies to stretch towards the red end of the spectrum.
In galaxies that are several billion years old, the light has been shifted so far that it is only visible infrared (especially the UV light that Meyer and his colleagues were looking for).
To take a good look at A370p_z1, a glowing galaxy 13 billion light years away, the team consulted the use of data from the Hubble Frontier Fields program that astronomers are still analyzing.
The Hubble data indicate that this galaxy was shifted very red, indicating that it was particularly old.
They then followed up with the Very Large Telescope (VLT) to get a better feel for the spectra of this galaxy. In particular, they looked for the bright line emitted by ionized hydrogen and known as the Lyman Alpha line. Meyer said:
“The big surprise was that this line, discovered at 9480 angstroms, was a double line. This is extremely rare to find in early galaxies, and this is only the fourth galaxy we know to have a double lyman Alpha Line has been in the first billion years. The nice thing about double Lyman Alpha Lines is that you can use them to derive a very important amount of early galaxies: what proportion of energetic photons do they leak into the intergalactic medium. “
Another big surprise was the fact that A370p_z1 seemed to release 60 to 100 percent of its ionized photons into the intergalactic space and was probably responsible for ionizing the IGM bubble around it.
Galaxies that are closer to the Milky Way typically have around 5 percent escapes (50 percent in some rare cases). However, observations by the IGM show that early galaxies on average had to escape by 10 to 20 percent.
This discovery was extremely important as it could help resolve an ongoing debate in cosmological circles.
So far, the question of when and how the reionization took place has resulted in two possible scenarios.
In one case it was a population of numerous weak galaxies from which about 10 percent of their energetic photons emerged. In the other, it was an “oligarchy” of luminous galaxies with a much larger percentage (50 percent or more) of the emerging photons.
In both cases, previous evidence suggests that the first galaxies were very different from today’s.
“The discovery of a galaxy with almost 100 percent escape was really nice, as it confirms what astrophysicists suspect: early galaxies were very different from today’s objects and licked energetic photons much more efficiently,” said Meyer.
Examining galaxies from the time of reionization on Lyman alpha lines has always been difficult because they are surrounded by neutral gas that absorbs this characteristic hydrogen emission.
However, we now have strong evidence that reionization was completed 800 million years after the Big Bang, and that it was probably due to some glowing galaxies.
If what Meyer and his colleagues observed is typical of reionization-era galaxies, we can assume that reionization was caused by a small group of galaxies that created large bubbles of ionized gas around them that grew and grew overlapped.
As Meyer explained, this discovery could lead the way to the creation of a new cosmological model that accurately predicts how and when big changes took place in the early universe:
This discovery confirms that early galaxies can emit ionizing photons extremely efficiently. This is an important hypothesis for our understanding of “cosmic reionization” – the epoch in which the intergalactic medium changed from neutral to ionized 13 billion years ago (e.g. electrons) hydrogen atoms torn off by these energetic photons).
According to Meyer, more objects like A370p_z1 have to be found so that astronomers can determine the average flight fractions of earlier galaxies.
In the meantime, the next step will be to find out why these early galaxies were so efficient at licking energetic photons.
Several scenarios have been suggested, and a better look at the early universe allows astronomers to test them.
As Meyer has surely noticed, much of it will depend on next generation telescopes that will very soon fly into space. The most notable of these is the James Webb Space Telescope (JWST), which (after several delays) is expected to hit the market next year.
This is of further importance for studies like this. In this way, they can help the James Webb team decide which cosmological secrets to investigate.
“With the James Webb space telescope, we will pursue this goal deeper in the infrared to gain access to what was originally emitted in optical light,” said Meyer.
“This gives us more insight into the physical mechanisms that play in early galaxies. JWST’s mission is limited in time, which is why it is so important to discover these extreme objects now: to know which objects are strange in the first billion years or are extreme In our universe we will know what to look for when JWST is finally started! “
Exciting times lie ahead for astronomers, astrophysicists, exoplanet hunters, SETI researchers and cosmologists. It’s hard to know who should be the most excited, but something tells me that it is like asking a parent which of their children they love most. The answer is always “everyone!”
This article was originally published by Universe Today. Read the original article.