James Webb solves the mystery of Lyman alpha emission in cosmology

James Webb solves the mystery of Lyman alpha emission in cosmology

The entire astronomical community undoubtedly had high hopes when the James Webb Space Telescope (JWST) was launched on December 25, 2021. It reached the L2 Lagrange point, its destination, and thus the region of Earth's orbit where the Planck satellite conducted its astonishing study of fossil radiation, the oldest Observable light in the universe, telling us about its age, curvature, shape and content. On dark matter and energy.

Fossil radiation was emitted within a few thousand years about 380,000 years after the Big Bang. James Webb does not make such early observations of the history of the observable universe, but it may allow us to go back at least 250 million years after the Big Bang and at least to better understand the layers of light. Million and billion years, which was already reachable by Hubble but incompletely.

For 13.8 billion years, the universe continued to evolve. Contrary to what our eyes tell us when we gaze at the sky, what shapes it is far from static. Physicists have observations of different eras of the universe and perform simulations in which they recreate the universe and its evolution. Dark matter appears to have played a major role from the beginning of the universe to the formation of the large structures we observe today. © CEA Research

Primordial galaxies that should be invisible in Lyman alpha emission

However, an article published in natural astronomy, Which can be found for free at arXiv, Reports James Webb Space Telescope observations that solve a mystery that has been vexing cosmologists for some time. According to the standard cosmological model based on dark matter and dark energy, the most distant galaxies should not shine as much due to so-called Lyman-alpha emission from hydrogen atoms. They will even shine less when we observe them in ancient layers of light, to the point where they become invisible less than a billion years after the Big Bang.

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This is not the case, why? Does this point to another problem in standard cosmology such as the problem of the value of the famous Hubble-Lemaitre constant?

In order to understand the truth of the matter, we have to go back to the emission of fossil radiation. Within a few thousand years, the temperature of the universe's plasma cooled enough due to its expansion that during this period the first hydrogen and helium atoms were formed, with the nuclei capturing free electrons to give neutral atoms. This is the beginning of the famous one Dark Ages Because it will take a hundred million years before a large number of stars begin to appear.

Reionization occurred very early in the history of the universe, making it difficult to observe directly. A few minutes after the Big Bang, the universe was still too hot for atomic nuclei to capture electrons: it was then completely ionized. After that, the universe continued to expand and cool until its temperature became low enough to allow electrons to bind to nuclei and form the first atoms. This “recombination,” as it is called, occurred about 380,000 years after the Big Bang. This moment also represents another important event in the history of the universe: while light is easily scattered by electrons when they are free, this is much less so when they are bound to the nucleus. Thus, recombination also marks the moment when the universe became transparent, and when light became able to spread freely there. © HFI Plank

These stars are very hot and emit radiation in the ultraviolet, specifically Lyman-α emission. Except that also at that time, neutral hydrogen was still widely present, especially around young galaxies, and it would take hundreds of millions of years for radiation from stars in these young galaxies, and perhaps even the first supermassive black holes to accumulate matter to heat up. It radiates accordingly, ionizing this neutral intergalactic hydrogen and is rather opaque to Lyman-α emission. So the observable universe should only slowly become transparent during the so-called reionization period, which we know will end at most about a billion years after the Big Bang.

“Galaxies” consist of several colliding galaxies?

Astrophysicists believe they now hold the key to the mystery of the abnormal brightness of young galaxies, while reionization is not yet sufficient. So, it comes to us from the James Webb Space Telescope and its NIRCam, one of its instruments that monitors near-infrared light, and is able to see light shifted toward these frequencies for distant galaxies.

NIRCam has analyzed images of galaxies that show they are in fact large galaxies, but surrounded by nearby smaller galaxies that are interacting or even colliding.

Did you know ?

Lyman-alpha emission is light emitted at a wavelength of 121,567 nm when an electron in an excited hydrogen atom passes from an excited state in the n=2 orbital to its n=1 ground state (the lowest energy state an atom can have). Quantum physics dictates that electrons can only exist in very specific energy states, which means that some energy transitions—such as when a hydrogen atom's electron moves from an n=2 orbital to an n=1 orbital—can be determined by the wavelength of the hydrogen atom, light. emitted during this transformation. Lyman alpha emission is important in many branches of astronomy, partly because of the abundance of hydrogen in the universe, but also because hydrogen is usually excited by energetic processes such as energetic formation in the path of stars. As a result, Lyman-α emission can be used as a sign of active star formation. © European Space Agency

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The team behind the publication in Nature astronomy Computer simulations were then used to reproduce the phenomena that occur with these galaxies and, as an ESA press release explains, their members “ He found that the rapid accumulation of stellar mass due to the merger of galaxies led to strong hydrogen emission and facilitated the escape of this radiation through empty channels of abundant neutral gas. Thus, the high merger rate of smaller, previously unobserved galaxies provided a compelling solution to the long-standing mystery of the inexplicable early emission of hydrogen.

The team plans to follow up observations with galaxies in different stages of merger, to further develop their understanding of how hydrogen emissions are squeezed out of these evolving systems. Ultimately, this will allow them to improve our understanding of galaxy evolution “.

More clearly, close collisions between several dwarf galaxies and large galaxies that were initially surrounded by a halo of neutral hydrogen caused the ionization of this halo, allowing the formation of a transparent ionized bubble of alpha emission from hydrogen from the young star formation frenzy in these galaxies. Galaxies.

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