The Big Bang fossil is a billion light years across!

It was in September 2014 that the discovery was announced Laniakea (“Immeasurable Heaven” or “Immense Heavenly Horizon”, in Hawaiian), a super masssuper mass (super Collection, In English) from GalaxiesGalaxies Includes Virgo supergroup of which milky waymilky way. We owe it to an international team ofAstronomy scientistsAstronomy scientists Brent Tully, of the University of Hawaii at Manoa, Hélène Courtois, of the University of Leon I, Yehuda Hoffman, of the Hebrew University of Jerusalem, and Daniel Bomarede, of the CEA.

Richard Brent Tully had already made a name for himself by discovering with J. Richard Fisher a relationship that allows the distance of A spiral galaxyspiral galaxyIt is an experimental method known today internationally as the Tully-Fisher Law. The American researcher published a new article today in Astrophysical Journal With Daniel Pomaridy and their Australian colleague Colan Howlett.

Nine years later, the three men announced their discovery Holilanaterm from singingsinging Creation Hawaii, IL Komolipowhich evokes the origin of the world. It is one of the great structuresbeingbeing Pool can be seen A group of galaxiesA group of galaxies. In this case, a kind of spherical crust about a billion in sizeLight yearLight year In the diameter where there is a greater density of galaxy clusters with the Bouvier supercluster in the center (shoesin English) at a distance of 820 million light-years from the Milky Way.

Half a century forecast

This is the first time a sphere of this type has been directly illuminated by measuring the distances and velocities of galaxies to map galaxies. UniverseUniverse Can be noticed. However, it is an example of a structure that has already been discovered indirectly by performing scientific analyzes of so-called statistical correlations in SamplesSamples Populations of galaxies and groups of galaxies. These spherical structures are manifestations of so-called baryonic acoustic waves, or BAO (baryon acoustic oscillations).

As Daniel Pomaridy explains TwitterTwitterThese galactic bubbles were predicted nearly 50 years ago by Nobel Prize winner in physics James Peebles. But in fact, it had already been predicted within the framework of what Andrei Sakharov called the cold Big Bang theory as early as the mid-1960s, a few years before Peebles. Today we only refer to the Nobel laureate’s work with one of his colleagues as it relates to theory the great explosionthe great explosion Hot, a definitive achievement of Standard Model of CosmologyStandard Model of Cosmologywhich “maybe” is not the case for substantia nigrasubstantia nigra no onedark energydark energy.

BAOs in particular are a phenomenon that cosmologists have used for years to measure parameters of the Standard Model of cosmology such as the Hubble-Lemaitre constant, the curvature of the universe, or dark energy. We can consider that Ho’oleilana is a kind of fossilfossil The Big Bang, although it was somehow born about 380 thousand years after it, at the time fossil radiationfossil radiation has been issued.

At this point, the reader must have been wondering what these baryonic acoustic oscillations, as they are sometimes called, are for a while.

During the Big Bang, according to the Standard Model, quantum fluctuations in matter density are produced that cause dark matter concentrations to rapidly collapse. These concentrations attract ordinary baryonic matter made up of protons and neutrons, but unlike dark matter, these baryons are sensitive to the electromagnetic force, so that the gas of photons engulfing all matter resists its pressure on the baryonic matter. This results in spherical sound waves that propagate, much like waves do around the impact points of raindrops in a pond, and as shown in this animation. These waves interfere, but when the atoms form at the time of recombination, the radiation pressure no longer exists and the bubbles of matter freeze. Well almost, because the expansion of space will cause it to expand. © Castro

BAOs, sound waves that travel at half the speed of light

After the beginning of the visible universe and at least some time ago NucleosynthesisNucleosynthesis Primal, a few minutes from the legendary Planck timePlanck timeThe universe is a jumble of paired baryons photonsphotonsAlready taking a shower ThemeTheme black.

Then fluctuations in dark matter density are generated sound wavessound waves Spherical objects move away at about half the speed of light from regions of dark matter excess density. At a time ReassembleReassemblewhen i atomsatoms Neutral waves appear 380,000 years after the Big Bang, light is separated from baryonic matter, and the front of these sound waves driven by the flow of photons is temporarily frozen.

As a result, regions of excess density of ordinary matter forming shells (the diameter of which is determined by the speed of sound waves generated by acoustic oscillations) form in the observable universe. These regions will be distinct places for the formation of galaxies and their accumulation in the form of clusters. Later, the increasingly dominant presence of dark energy (which was not the case in the first billion years) will affect the growth rate of galaxy clusters.

First of all, if we consider a large sample of galaxies on the surface of a sphere centered by the Earth observer (and therefore at the same time in the history of the universe and at the same distance from us for each galaxy) and if we measure the distances between two pairs, an excess of these pairs will appear for a distance value associated with the value of Material shells we discussed earlier, as shown in the video above.

Excellent show for BAOs. For a fairly accurate French translation, click on the white rectangle at the bottom right. The English translation should then appear. Then click on the nut to the right of the rectangle, then on “Translations” and finally on “Translate automatically.” Select “French”. © PBS SpaceTime

Key to the study of dark energy

We then have a kind of standard scale whose intrinsic length is known at a given period of cosmic history. By measuring the apparent value of this length to us, we can deduce the absolute distance. If we measure different spectral shifts, we can draw a curve linking cosmic distance, spectral shift, and measurements of distance and time, making it possible to estimate the expansion speeds of space on a given date. She plays this game, but with brightnessbrightness Clear brightness standards – what are they supernovaesupernovae SN Ia – We have just discovered the accelerating expansion of space over the past few billion years.

However, depending on which cosmological model we consider, with or without dark energy, it is the latter or not cosmological constantcosmological constant, we do not get the same curve. Likewise, the growth rate of galaxy clusters is not the same. It is therefore a second way, along with supernovae, to prove the existence of dark energy and explore its nature.

BAOs and Ho’oleilana. © Danielle Bomarede

So much for theory about Hula’ilana, but for practice, this discovery is the latest result of a program launched in the late 2000s Helen Courtois and Brent Tully under the name “Cosmic Streams”. The first was based on a catalog of velocities of 1,700 galaxies, but over the years we have moved from Cosmicflows-1 to Cosmicflows-1. Cosmic flows-4 With 30,000 galaxies. “Daniel Bomarede” Responsible for mapping, 3D and interactive Cosmicflows catalogs since 2010.” As indicated in the CEA press release, which concluded with the following statements:

” Ho’oleilana has the geometric properties of a theoretically expected acoustic baryon oscillation, including the prominence of a rich supercluster at its center, but it protrudes more strongly than expected. Ho’oleilana is slightly larger than expected and Hubble constantHubble constant What we can infer from its size is consistent with measurements in the local universe (supernovae, CepheidsCepheids…) and in tension with measurements made in the distant universe (Planck with CMB, SDSS and quasarsquasars…).

More in-depth prospective data, such as that from Dark energy spectroscopy instrument (Desi) or 4MOST Hemispheric Survey It could make it possible to detect similar structures elsewhere in the near universe. Researchers will use this data to study and confirm more details regarding Ho’oleilana, the BAO, and the expansion rate of the universe. »

Let us remember that there is a tension in cosmology between the two main measurements of the Hubble-Lemaitre constant.

In February 2023, Daniel Bomarede, a cosmologist at CEA, came to CentraleSupélec to talk about his research work on giant galaxy clusters. © CosmiCS, Astronomy Club CentraleSupélec