Gamma-ray bursts can help understand the nature of dark energy

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[EN VIDÉO] Playlist: all about the cosmos with Jean-Pierre Luminet
Renowned astrophysicist Jean-Pierre Luminet talks to us about exoplanets, dark energy and black holes in this series of fascinating interviews compiled into a playlist.

That velocity of the expansion of cosmos observable has been accelerating for a few billion years as if it contained one pressure as a result of an energy density exotic which is calleddark energy and which does not dilute with expansion, in contrast to fabric. The discovery of this accelerated expansion, while the standard cosmological model prior to the late 1990s predicted the opposite after big bangwas made possible by using phenomena astrophysics that could pretty much be considered standard candles, especially those supernovae SN Ia.

Determining the nature of dark energy depends on determining the fate ofUniverse observable. But for that, it is necessary to increase the detection of supernovae NS Ia or other cosmic events to calculate distances and spectral shifts. It turns out that an international team ofastrophysicists conducted by Maria Dainotti, assistant professor at the National Astronomical Observatory of Japan (Naoj), has just announced via an article about arXivwhich we could use for that some jerk gamma. In fact, this is the confirmation more solid results achieved over many years.

To understand what this is all about, let’s go back to what Futura explained about standard light and how they build on each other to make up what is called the cosmic distance scale.

The problem of the scale of cosmic distances

Here are some reminders that provide additional explanations regarding the video below that illustrates what is explained below.

That Cepheids is variable stars individuals who see their brightness change over time with a given period. It was in 1912, while studying the Cepheids in the Small Magellanic Cloud, that Henrietta Leavitt discovered that this period correlated with theirs apparent size mean. The brighter they are, the slower they vary. One could therefore hope to infer the intrinsic luminosity of a Cepheid by measuring its period.

The method was calibrated thanks to the nearby Cepheids, the distance of which could be evaluated using the parallax method, which makes it possible to estimate the distances to the nearest stars in The Milky Way. It was therefore possible to deduce the distance of more distant Cepheids directly from their brightness variation. The farther a star is, the less luminous it appears, but if we know its intrinsic luminosity, we can estimate its distance.

In cosmology, we speak of the scale of cosmic distances to designate a set of interdependent methods for determining, step by step, the distances to the stars in the observable cosmos. It all starts with parallax measurements in the Solar System, that is, the angles that a nearby star makes on the firmament at two times of the year. The geometry of the triangle then makes it possible to derive a distance if the angles are large enough to be measured. © Hubble, ESA

The Cepheids have thus become a kind of standard light that makes it possible to estimate the distance between the Milky Way and galaxiesagain the closest, such as Andromeda or Large Magellanic Cloud. Edwin Hubble used Henrietta Leavitt’s ratio, first to discover the expansion of the universe and then to calibrate The Hubble-Lemaître law relates the distance to a galaxy to its spectral shift.

To measure even longer distances in the distant universe it is possible to use another type of star, they are not exactly standard lights, but they can serve as good distance indicators. These are the SN Ia supernovae.

These stars consequence of the explosion of white dwarfs in a binary system. The luminosity of an SN Ia cannot deviate much from a certain average value, and since it can represent hundreds of billions of stars, they can be seen from a distance. Using the Cepheids, we can calibrate a relation that gives the apparent luminosity of a SN Ia with its distance. Knowing its redshift, we can then relate its distance to this shift and, by the Hubble-Lemaître law, to the rate of expansion of the universe at a given date in its history—since to observe far is to observe early.

It is being erected curve relating the spectral shift of SN Ia to their luminosity clearly that Riess, Perlmutter and their colleagues discoveredaccelerated expansion of the universe in 1998 and 1999.

We could do the same with the GRBswhich can especially help to solve the current problem with measurement of the Hubble-Lemaître constant.

An overview of gamma rays and GRBs. For 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”. Select “French”. © NASA Goddard Space Flight Center

Gamma ray bursts as standard candles

Let us now return to the work of Maria Dainotti and her 23 colleagues. The discovery of gamma-ray bursts decades ago came as a surprise because they were apparently extremely energetic events to produce the bursts of gamma energy that were initially detected by military satellites in space tasked with monitoring illegal weapons testing.air free or in the room.

To account for the intensity and energies of gamma radiation observed with Gamma Ray Burt (GRB) as we say in English, two classes of processes have been proposed. One involves collisions ofneutron stars and we know that this scenario explains certain GRBs well since we demonstrated it a few years ago by combining the detection ofgravitational waves with the electromagnetic waves emitted by a kilonova.

Already in 2017, astrophysicist Maria Dainotti explained the results regarding the GRBs that we have consolidated today. For a fairly accurate French translation, click on the white rectangle at the bottom right. The Italian subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Select “French”. © MEDIAINAF TV

The second class involves the explosion of very massive stars, which gravitationally collapse and give a black hole. But now Maria Dainotti and her peers believe they have highlighted another division with the GRBs by consulting the data recorded since the 1990s, both with ground-based telescopes operating in the visible, such as Subaru in Hawaii, and with space telescopes operating in both the gamma and X domains, notably with the Neil Gehrels satellite Swift Observatory.

Finally, it was the observations in the visible of 500 GRBs that were combed through, and it turned out that the curves of light 179 of them had characteristics that made it possible to use it as a standard light. Since GRBs are particularly luminous, they can be seen from a distance, making it possible to study the evolution of the expansion rate of the observable universe more than 11 billion years ago in the past.

A summary of the discovery with the GRBs. For 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”. Select “French”. © Kamil Kalinowski, Delina Levine, Sam Young, Maria Dainotti

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