[ad_1]
Astronomers have already achieved the best test of general relativity at the scale of galaxies, and it excludes some (but not all) theories of modified gravity.
General relativity – which describes our modern understanding of gravity as the curvature that mass induces over space-time – has been extensively tested in our solar system. He has passed each of these tests with flying colors.
But fewer tests exist at scales of thousands or millions of light-years. It is precisely these scales that are relevant to theories of modified gravity, which provide an alternative to the existence of dark matter. They predict that gravity behaves differently over great distances than in our solar system. Although some tests were performed on galactic scales, they were not accurate enough to exclude the modified gravity.
Now, a study conducted by Thomas Collett (University of Portsmouth, UK) on June 22 Science (preprint available here) has provided such a test using the Hubble Space Telescope and the observations of the very large telescope of a lens galaxy. The light emitted by a star-shaped galaxy in a universe only 3 billion years old passed through a nearby galaxy, whose gravity acted as a lens, and bent the light of the background galaxy into a blue circle.
An image of the neighboring galaxy ESO 325-G004, created from data collected by NASA / ESA's Hubble Space Telescope and the MUSE instrument on the ESO's Very Large Telescope. The inset shows the Einstein ring resulting from the distortion of light from a farther source through the ESO 325-004 lens, which becomes visible after the subtraction of the light from the lens of the foreground.
ESO / ESA / Hubble / NASA
Collett and his colleagues first calculated the mass of the intermediate galaxy by measuring the motions of the stars inside it. Then they measured the spatial curvature generated by each unit mass of the intervening galaxy. The mass deduced by the curvature of space-time is precisely in agreement with the mass measured by the stars, exactly as predicted by general relativity.
Unlike previous lens relativity tests, the Collett team relies less on assumptions about the nature of the intervening galaxy. This test is therefore relatively free of systematic uncertainties that have plagued previous studies.
This infographic compares the two methods used to measure the mass of galaxy ESO 325-G004.
ESA / Hubble / ESO / NASA
Lucas Lombriser (University of Edinburgh, UK), who was not involved in the study, calls the measurements, "the most robust gravity test of this type and on these scales of length to date. "
"However," he adds, "while this new test excludes some alternative gravitational theories, there are still many others that are consistent with the measurement." While this study limited gravity variations to lower scales at 6000 light-years, will always be necessary to exclude severity modified more generally.
Source link
