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

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speed extensions space the observable is accelerating over several billion years, as if it contained pressure as a result of the energy density exotic which is calleddark energy and which does not dilute when expanded, unlike matter. The opening of this accelerated expansion, while standard cosmological model until the late 1990s predicted the opposite after big Bangmade possible through the use of phenomena astrophysics which to a large extent can be considered as standard candles, in particular supernovae CH I.

Determining the nature of dark energy depends on the definition of fateUniverse observable. But for this 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 the international teamastrophysicists under the guidance of Maria Dainotti, Associate Professor at the National Astronomical Observatory of Japan (Naoji), just reported this in an article about arXivthat we could use for this some jerks gamma. Actually, this is the confirmation Read more solid results achieved over the years.

To understand what is at stake, let’s go back to what Futura explained about standard candles and how they build on top of each other to make up what is known as the cosmic distance scale.

The problem of the scale of cosmic distances

Here are some reminders giving additional explanations for the videos below that illustrate what is explained below.

cepheids are variable stars individuals who see their brightness change over time with a given period. In 1912, while studying the Cepheids of the Small Magellanic Cloud, Henrietta Leavitt found that this period correlated with their apparent magnitude keep in mind. The brighter they are, the slower they change. Therefore, one might hope to deduce the intrinsic luminosity of a Cepheid by measuring its period.

The method was calibrated thanks to nearby Cepheids, the distance to which could be estimated using the parallax method, which allows one to estimate the distances to the nearest stars in Milky Way. Therefore, it was possible to determine the distance to more distant Cepheids directly from the rate of change in their brightness. Indeed, the farther away a star is, the less bright it appears, but if we know its intrinsic luminosity, we can estimate its distance.

In cosmology, we talk about the cosmic distance scale to refer to a set of methods that rely on each other to determine, step by step, the distances to stars in observable space. It all starts with measurements of parallax in the solar system, that is, the angles that a nearby star makes in the firmament twice a year. The geometry of the triangle then allows the distance to be inferred if the angles are large enough to be measured. © Hubble, ESA

Thus, Cepheids have become a kind of standard candle, allowing you to estimate the distance separating the Milky Way from the Sun. galaxiesagain coming ones like Andromeda or Large Magellanic Cloud. Edwin Hubble used the relationship of Henrietta Leavitt, first to discover the expansion of the universe, and then to calibrate Hubble-Lemaitre law relating the distance of a galaxy to its spectral shift.

To measure even more distant distances in the distant universe, another type of star can be used, these are not quite standard candles, but they can serve as good indicators of distances. These are supernovae SN Ia.

These stars as a result of the explosion white dwarfs in binary system. The luminosity of SN Ia cannot deviate much from some average value, and since it can represent the luminosity of hundreds of billions of stars, they can be seen from afar. Using Cepheids, we can calibrate the relationship that gives the apparent luminosity of the supernova SN Ia with its distance. Knowing its redshift, we can then relate its distance to that redshift and, by the Hubble-Lemaitre law, to the expansion rate of the universe at a given moment in its history—because to look far is to look earlier.

It is through the construction curve relating the spectral shift of SN Ia to their luminosity it is obvious that Riess, Perlmutter and their colleagues discoveredaccelerated expansion of the universe in 1998 and 1999.

We could do the same with GRBwhich can help, in particular, to solve the current problem with measurement of the Hubble-Lemaitre constant.

An overview of gamma rays and gamma ray bursts. For a fairly accurate French translation, click on the white box in the lower right corner. After that, English subtitles should 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 bursts in the form of standard candles

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

To take into account the intensity and energy of gamma radiation observed with the Gamma Ray Burt (GRB), as we say in English, two classes of processes have been proposed. One is related to collisionsneutron stars and we know that this scenario explains some gamma ray bursts well, since we demonstrated this a few years ago by combining the detectiongravitational waves with electromagnetic waves emitted kilonova.

Astrophysicist Maria Dinotti already explained in 2017 the results regarding bursts that we have combined today. For a fairly accurate French translation, click on the white box in the lower right corner. Italian subtitles should appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Select “French”. © MEDIANAF TV

Another class includes explosions of very massive stars that collapse under the influence of gravity. black hole. Now, however, Maria Dainotti and her colleagues believe they have isolated the second fission of gamma-ray bursts by looking at data recorded since the 1990s, both by ground-based telescopes operating in the visible range, such as Subaru in Hawaii, and by space-based telescopes. telescopes operating in the visible range. both gamma and X regions, especially with the Nile Gerels satellite Quick Observatory.

Finally, observations in the visible range of 500 gamma-ray bursts were combed, and it turned out that the curves light 179 of them had characteristics that allow it to be used as a regular candle. Since gamma-ray bursts are especially bright, they can be seen from afar, allowing us to study the evolution of the expansion rate of the observable universe up to more than 11 billion years ago in the past.

A summary of the discovery with gamma-ray bursts. For a fairly accurate French translation, click on the white box in the lower right corner. After that, English subtitles should 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 Levin, Sam Young, Maria Dinotti

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