8/18/2023 0 Comments Gravitational redshift galaxyThis gravity affects the light being sent out into space from the galaxies. Galaxy clusters are accumulations of thousands of galaxies, held together by their own gravity. Radek Wojtak, together with colleagues Steen Hansen and Jens Hjorth, has analysed measurements of light from galaxies in approximately 8,000 galaxy clusters. We live in an era with the technological ability to actually measure such phenomena as cosmological gravitational redshift", says astrophysicist Radek Wojtak, Dark Cosmology Centre under the Niels Bohr Institute at the University of Copenhagen. But the gravitational influence of light has never before been measured on a cosmological scale. Furthermore, according to Einstein's general theory of relativity, the light and thus the redshift is also affected by the gravity from large masses like galaxy clusters and causes a gravitational redshift of the light. The redshift indicates how much the universe has expanded from when the light left until it was measured on Earth. Observations of large distances in the universe are based on measurements of the redshift, which is a phenomenon where the wavelength of the light from distant galaxies is shifted more and more towards the red with greater distance. The results have been published in the prestigious scientific journal, Nature. The observations confirm the theoretical predictions. Now astrophysicists at the Dark Cosmology Centre at the Niels Bohr Institute have managed to measure how the light is affected by gravity on its way out of galaxy clusters. At the same time all interpretations in astronomy are based on the correctness of the theory of relatively, but it has never before been possible to test Einstein's theory of gravity on scales larger than the solar system. view moreĪll observations in astronomy are based on light emitted from stars and galaxies and, according to the general theory of relativity, the light will be affected by gravity. This gravity affects the light that is sent out into space from the galaxies. Galaxy clusters are accumulations of thousands of galaxies (every light in the image is a galaxy), which are held together by their own gravity. Overall, our results are consistent with both GR and DGP predictions, while they are in marginal disagreement with the predictions of the considered $f(R)$ strong field model.Image: Researchers have analyzed measurements of the light from galaxies in approximately 8,000 galaxy clusters. We recover an integrated gravitational redshift signal of $-11.4 \pm 3.3$ km s$^$, which is in agreement, within the errors, with past literature works. We clearly detect the gravitational redshift effect in the exploited cluster member catalogue. Finally, we investigate the systematic uncertainties possibly affecting the analysis. A new statistical procedure is used to fit the measured gravitational redshift signal and thus to discriminate among the considered gravity theories. We compare our measurements with the theoretical predictions of three different gravity theories: general relativity (GR), the $f(R)$ model, and the Dvali-Gabadadze-Porrati (DGP) model. We find that this centre definition provides a better estimation of the centre of the cluster gravitational potential wells, relative to simply assuming the brightest cluster galaxies as the cluster centres, as done in the past literature. We accurately estimate the cluster centres, computing them as the average of angular positions and redshifts of the closest galaxies to the brightest cluster galaxies. We analyse the velocity distribution of the cluster member galaxies to make new measurements of the gravitational redshift effect inside galaxy clusters. We consider a spectroscopic sample of $3058$ galaxy clusters, with a maximum redshift of $0.5$. We exploit spectroscopic galaxy and galaxy cluster samples extracted from the latest releases of the Sloan Digital Sky Survey (SDSS) to derive new constraints on the gravity theory. The peculiar velocity distribution of cluster member galaxies provides a powerful tool to directly investigate the gravitational potentials within galaxy clusters and to test the gravity theory on megaparsec scales.
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