An absence of signal that says a lot about the first galaxies
Directly observing the first galaxies in our Universe is still beyond our reach. But recent results obtained by researchers, while studying what they call the 21 centimeter line, are a major step in understanding how the Universe went from an almost empty place to a place filled with stars.
Radio astronomy catches distant galaxies giving birth to stars Thanks to the International Low Frequency Array (LOFAR), a large network of 70,000 radio telescopes spread over Europe, astronomers have obtained breathtaking images the youth of our Universe. Tens of thousands of galaxies captured as they formed stars. This video proposes to fly over a part of the studied sky.
Jurgen de Jong, Leiden UniversityThe line at 21 centimeters. What a strange expression! Yet it was this parting, at the end of the 1950s, which enabled theastronomerDutchman Jan Oort, to demonstrate the spiral structure of our Milky Way . Today, it is still this line, or rather its non-detection, which allows researchers at the University of Cambridge (United Kingdom) to learn a little more about this period than theastrophysicistscall theDawncosmic. This period of theUniverseparamount during which the firststarsand the firstgalaxieshave started to emerge.
Before going any further, it should be noted that the expression "21 centimeter line" designates, for researchers, aspectral lineissued by theatomofhydrogenneutral. 21 centimeters fromwave length. In the fieldradio, So. And if the James-Webb space telescope is able to image individual galaxies in the early Universe, the study of the line at 21 centimeters is likely to provide information on entire populations of even older galaxies.
A particular interest
Thanks to this specific signal of the first stars re-radiated by thickcloudsof hydrogen. Hence its particular interest. At least until the Square Kilometer Array project (SKA, South Africa and Australia) which astronomers hope will be able -- by the end of this decade -- to produce images of our early Universe .
In 2018, the experience teamEdges had suggested a possible detection, through thefogof the early universe, of thelightof the first stars. But the signal seemed too strong. Data fromradiotélescopeIndian Saras3 questioned this detection. It is these data that researchers from the University of Cambridge have analyzed in detail. Data that goes back only 200 million years after theBig Bang. They tested several scenariosastrophysicswhich could explain the result of the Edges experiment. At no time did they detect the famous line at 21 centimeters.
Limits to the properties of the first stars
But all this work was not in vain. The astrophysicists indeed explain that the fact of not having found the signal of a certain amplitude which they sought thanks to their techniques ofmodelizationstatistics provides almost equally interesting information. What, according to them, set limits to the physical properties of the first stars and the first galaxies.
This analysis thus gives indications on themassesof the first galaxies and on theirbrightness. It also provides information on the efficiency with which these galaxies could form stars. And on the efficiency with which these stars emitted in the field ofX-rays, in the radio field or in the field ofultraviolet. A first step, therefore, on the way to understanding how our Universe went from darkness and emptiness to a region populated by stars and galaxies.
The Cambridge University astronomers, therefore, now rule out scenarios in which early galaxies were both more than a thousand times brighter than current galaxies in their radio emission and poor hydrogen gas heaters. Their data also reveals something that has been suggested before, that early stars and galaxies may have had a measurable contribution to the background radiation that appeared in the aftermath of the Big Bang .
First stars in the universe: signals finally detected!
In a few years theJames Webb Space Telescopewill be able to observe the first stars of the universe. The feat has just been achieved from the ground by a modest radio telescope, which allowed a first detection, indirect, thanks to the line 21 cm from hydrogen. With a surprise in store: the signal is abnormal and could betray the existence of particles ofblack matter.
AN ARTIST'S IMPRESSION OF THE FIRST STARS. THEY HAD TO BE VERY MASSIVE AND LIVE FOR A VERY SHORT TIME.
NR FULLER, NATIONAL SCIENCE FOUNDATIONAbout 380,000 years after the Big Bang, the temperature of the observable universe dropped due to its expansion, and enough so that the first atoms of hydrogen andheliumneutrals form from a plasma of light nuclei andelectrons. Thenucleosynthesisprimordial must have produced a few nuclei ofoxygen, ofcarbonand D'nitrogenbut in proportion a million billion times less, therefore in negligible quantity. These are the stars that will later produce heavy nuclei.
The phenomenon was accompanied by the emission of the famous fossil radiation which reaches us today from regions located more than 45 billionlight yearsfrom us, due to the expansion of thecosmosobservable. Remember that it is about 13.7 billion years old. This is what is known as the "period ofrecombinationwhich was not instantaneous. This curious term is a historical vestige dating back at least to the 1960s, when this radiation was discovered. Robert Dicke and James Peebles , among other pioneers ofcosmologyof the time, considered in particular that the initial hydrogen and helium atoms came, perhaps, from an earlier phase of contraction of the observable universe (which would therefore be cyclic), and which had dissociated nuclei and electrons at high temperatures, before a new phase of expansion begins, the one we are observing.
The Dark Ages and the First Stars
Still, for at least 100 million years, the observable universe was not illuminated by stars and therefore even less by galaxies, while the temperature of thecosmic radiationhad fallen enough for it to no longer be visible. At the time of recombination, the cosmos must have been as bright as the surface of theSunsince it was filled with a plasma almost at the same temperature. This obscure period of the history of the universe is that known as thedark ages.
Stars finally began to form in large numbers. They must have been very massive, probably 100 to 1,000 solar masses, and their intense ultraviolet radiation began to re-ionize atoms, perhaps in conjunction with that of earlyquasars. The beginning of this period ofreionizationof the ordinary matter of the universe has sometimes been called the "cosmic rebirth" and this period itself is logically called reionization .
Cosmologists would like to specify the dates of these phenomena and of course study them. But how to obtain information on what happened during the dark ages when there were no stars to shine and how to observe these very first stars which are called population III stars ?
A PRESENTATION OF THE DETECTION OF THE FIRST STARS. TO OBTAIN A FAIRLY ACCURATE FRENCH TRANSLATION, CLICK ON THE WHITE RECTANGLE AT THE BOTTOM RIGHT. THE ENGLISH SUBTITLES SHOULD THEN APPEAR. THEN CLICK ON THE NUT TO THE RIGHT OF THE RECTANGLE, THEN ON “SUBTITLES” AND FINALLY ON “TRANSLATE AUTOMATICALLY”. CHOOSE “FRENCH”.
NATIONAL SCIENCE FOUNDATIONThe Wouthuysen–Field effect and cosmic radiation
There are strategies that researchers have been exploring for more than a decade. One of them is based on a curious phenomenon called the Wouthuysen–Field effect , named after thephysicistDutchman Siegfried Adolf Wouthuysen and American astrophysicist George B. Field. It uses the famous line at 21 cm from hydrogen which made it possible to map theMilky Way. Neutral hydrogen can indeed absorb or emitphotonsat this wavelength due to levels ofenergyparticular due to the interactions between theprotonand the electron of a hydrogen atom conducting thespinsof these particles to be either parallel or antiparallel. We can therefore use this line to detect and map the distribution of neutral hydrogen masses during the dark ages.
However, when the first stars lit up, quantum mechanics predicts that their ultraviolet photons will allow the Wouthuysen-Field effect to manifest itself in such a way that the still neutral hydrogen atoms begin to absorb the cosmic radiation photons located precisely at the wavelength of 21 cm. thespectrumof this radiation must therefore be notched by a small hollow corresponding to this depopulation effect.
However, due to the expansion of the universe, this dip in the background radiation spectrum is shifted to lower wavelengths, in the radio wave domain. The earlier the reionization occurred, the more the expansion of the observable cosmos will have had time to stretch the wavelength of these radio photons. By measuring it precisely, we therefore detect the ignition of the first stars and, above all, it is possible to date this event.
A team of researchers led by astronomer Judd Bowman of the Arizona State University School of Earth and Space Exploration embarked on the adventure more than 12 years ago by building a detector suitable for highlighting the signal researched as part of the Edges ( Experiment to Detect the Global EoR Signature ). She has just presented in the journal Nature the observation of the birth of the first stars. According to this result, this event would have occurred about 180 million years after the Big Bang.
A CHRONOLOGY OF THE OBSERVABLE UNIVERSE (RECALL THAT THE ENGLISH TRILLION MEANS BILLION).
NAOThis measurement is a tour de force because the desired signal is drowned in the radio background noise, including that of the Milky Way. As the video above explains, it's like listening to the flapping wings of a hummingbird in the middle of ahurricane. The researchers also had to isolate themselves as much as possible from human-made radio sources and that is why Edges took place far from everything in Australia, in theMRO( Murchison Radio-astronomy Observatory ), not far from one of the sites of the famous Square Kilometer Array radio telescope .
There may be acherryon the cake, as explained among others in an article posted on arXiv astrophysicist Rennan Barkana of Tel Aviv University. The intensity of theabsorptioncosmic radiation photons by Wouthuysen-Field effect is more than double what was expected. L'anomaly(3.8 σ) is however not at the 5 sigma level required for the result to be considered a discovery. Caution is therefore called for. But according to the researcher, this would indicate that the atoms of the hydrogen gas at that time were colder than previously thought. The reason ? Prior to reionization, the universe was denser and collisions with dark matter particles (which constitute a cooler gas in thestandard cosmological model) were more frequent, which would have cooled the gas of normal matter.
But this hypothesis works only under two conditions. On the one hand, dark matter particles must interact somewhat with normal matter through forces other thangravity. On the other hand, the particles constituting it must not be too heavy, less than five times the mass of the proton approximately, which would direct towards models of Wimps lighter than expected and perhaps towards models of warm dark matter and not cold.
Is Barkana right? It is too early to tell, but if so, this would be the first direct evidence of the existence of dark matter particles . A spectacular result to be credited to particle astrophysics.
The first stars in the universe begin to reveal their secrets
Thanks to Alma and also to the VLT, a team was able to glimpse what was happening a very long time ago, only 600 million years after the Big Bang, within a very young galaxy. What they saw rather surprised them.
Knowing our origins is one of the great motivations of scientists and, of course, for many astronomers, this means understanding the formation of the very first generations of stars . After all, we wouldn't be here, and nothing around us would exist, if they hadn't appeared. No small stars like the Sun, no planets, no complex matter, no lives ... Because for that, you need these big cauldrons that are massive stars and a lot of energy to produce the elements heavier than the planet. hydrogen and helium which were created during the first moments of the universe.
So how exactly did it happen? Thanks to the vast network of Alma radio telescopes ( Atacama Large Millimeter/submillimeter Array ) installed on a high plateau in thedesertof the Atacama and, still in Chile, the VLT ( Very Large Telescope ), a group of researchers was able to gather new clues for the profiling of these first stellar ancestors.
GALAXY A2744_YD4 MAGNIFIED BY GRAVITATIONAL LENSING CREATED BY THE MASS OF THE ABELL 2744 CLUSTER, CENTER FOREGROUND, IN THE TELESCOPE'S LINE OF SIGHT.
ALMA (ESO/NAOJ/NRAO), NASA, ESA, ESO, D. COE (STSCI)/J. MERTEN (HEIDELBERG/BOLOGNA)The most distant object observed by Alma
This information, they collected them within the young galaxy designated A2744_YD4. Located some 13.2 billion light-years from Earth, so only 600 million years after the Big Bang, it is to date the most distant object that Alma has ever observed. It is a light flake of gas, pale, which is however not insignificant, because it is already rich in interstellar dust – which has not failed to surprise astronomers. “The detection of such an abundance of dust indicates that the first supernovae had already polluted this galactic environment” comments the main author of this research, Nicolas Laporte, of University College London. They therefore succeed the previous generation ofdurationvery short-lived, exploded as supernovae.
It is with the help ofsuperamasof galaxies Abell 2744 aka the Pandora cluster -- presumably a reunion of fouryou love galaxiesabout 3.5 billion light-years from the Milky Way - whose mass of all its stars, gas, dust and especially dark matter has made it possible to amplify by the effect ofgravitational lens, the glow of the galactic baby located much further back in the background than the team could pin and study.
IN THIS ANIMATION, WE CAN SEE THE FIRST STARS EXPLODE IN A SUPERNOVA. THEIR ASHES WILL ENRICH THE YOUNG GALAXY AND ALLOW THE FORMATION OF NEW STARS AND ALSO PLANETS.
ESO, M. KORNMESSERThe first stars would have formed 200 million years earlier
By dissecting its light, they learned in particular that A2744_YD4, whose star population is estimated at two billion, concentrates the equivalent of six million solar masses of dust. Sizes of the order of a millionth of a centimetre, they are mainly made up ofsilicon, carbon andaluminum-- essential ingredients that we find, with others, in ourSolar system. The researchers also observed (and this is the most distant detection for this element) the emission of ionized oxygen.
Many stars are budding in this spying galaxy in the midst of reionization . According to the study to be published in The Astrophysical Journal Letters (available on arXiv ), about twenty of them come out of factories (molecular clouds) every year. "This rate is not unusual for such a distant galaxy [currently in the Milky Way , the rate offertilityhas come down well: the current rate is one star birth per year, Editor's note] , explains one of the co-authors Richard Ellis, of theTHATand University College . It reveals the sustained rate of dust formation within A2744_YD4. The time required is only around 200 million years – so we are observing this galaxy shortly after it formed.” Everything would therefore have started 200 million years earlier.
Clues to the first generation stars
CIRS article published on 06/20/2005
Two stars that were thought to be among the first in the Universe actually formed from the explosion of an older star, according to astrophysicists from the University of Tokyo. This result would allow a better knowledge of the nature of the first stars.
One of the most important challenges in astronomy consists in identifying the first stars of the Universe, those which were born from a primordial gas of hydrogen and helium. These early generations of stars were believed to contain very few heavy elements, collectively known as "metals". The discovery by astronomers of two stars, one in 2002 and the other this year, in which the iron/hydrogen ratio is around one hundred thousand times less than that of the Sun, has therefore aroused interest.
Now, however, a team led by Ken'ichi Nomoto of the University of Tokyo is claiming that these very metal-poor stars are actually second-generation stars. Their levels ofchemical elementsare very unusual, including a carbon/iron ratio ten thousand times that of the Sun. According to the Japanese team, the stars formed from chemically contaminated gas from a first-generation star that formed ablack holeafter explodingsupernova.
Almost all offersynthesized during the first supernovae was, according to the model, absorbed by the black holes which had then formed. This means that only a tiny fraction of the iron was ejected into interstellar space. The predictions were tested by comparing the levels of chemical elements observed in the two stars with those calculated from the model.
The result means that the nature of the first stars could be better known and predicted in quantitative terms. “The study shows that stars 20 to 130 times larger than the Sun, which ended in supernova and formed black holes, played an important role in the primitive chemical enrichment of the Universe” indicates Nomoto.
Source: websites
[/size]