Gli scienziati della NASA esplorano l’energia oscura: è tempo di rielaborare la teoria gravitazionale di Albert Einstein?

Illustra l’energia oscura. Credito: visualizzazione di Frank Summers, Space Telescope Science Institute. Simulazione di Martin White, UC Berkeley e Lars Hernquist, Harvard University

Uno dei più grandi misteri dell’astrofisica può essere risolto parafrasando la teoria della gravità di Albert Einstein? Non ancora, secondo un nuovo studio di cui è coautore[{” attribute=””>NASA scientists.

The universe is expanding at an accelerating rate, and physicists don’t know why. This phenomenon seems to contradict everything scientists understand about gravity’s effect on the cosmos: It’s as if you threw an apple in the air and instead of coming back down, it continued upward, faster and faster. The cause of the cosmic acceleration, dubbed dark energy, remains a mystery.

A new study marks the latest effort to determine whether this is all simply a misunderstanding: that expectations for how gravity works at the scale of the entire universe are flawed or incomplete. This potential misunderstanding might help researchers explain dark energy. However, the study – one of the most precise tests yet of Albert Einstein’s theory of gravity at cosmic scales – finds that the current understanding still appears to be correct. The study was from the international Dark Energy Survey, using the Victor M. Blanco 4-meter Telescope in Chile.

The results, authored by a group of scientists that includes some from NASA’s Jet Propulsion Laboratory (JPL), were presented Wednesday, August 24, at the International Conference on Particle Physics and Cosmology (COSMO’22) in Rio de Janeiro. The work helps set the stage for two upcoming space telescopes that will probe our understanding of gravity with even higher precision than the new study and perhaps finally solve the mystery.

This image – the first released from NASA’s James Webb Space Telescope – shows the galaxy cluster SMACS 0723. Some of the galaxies appear smeared or stretched due to a phenomenon called gravitational lensing. This effect can help scientists map the presence of dark matter in the universe. Credit: NASA, ESA, CSA, and STScI

More than a century ago, Albert Einstein developed his Theory of General Relativity to describe gravity. Thus far it has accurately predicted everything from the orbit of Mercury to the existence of black holes. But some scientists have argued that if this theory can’t explain dark energy, then maybe they need to modify some of its equations or add new components.

To find out if that’s the case, members of the Dark Energy Survey looked for evidence that gravity’s strength has varied throughout the universe’s history or over cosmic distances. A positive finding would indicate that Einstein’s theory is incomplete, which might help explain the universe’s accelerating expansion. They also examined data from other telescopes in addition to Blanco, including the ESA (European Space Agency) Planck satellite, and reached the same conclusion.

Einstein’s theory still works, according to the study. So no there’s no explanation for dark energy yet. However, this research will feed into two upcoming missions: ESA’s Euclid mission, slated for launch no earlier than 2023, which has contributions from NASA; and NASA’s Nancy Grace Roman Space Telescope, targeted for launch no later than May 2027. Both telescopes will search for changes in the strength of gravity over time or distance.

Blurred Vision

How do scientists know what happened in the universe’s past? By looking at distant objects. A light-year is a measure of the distance light can travel in a year (about 6 trillion miles, or about 9.5 trillion kilometers). That means an object one light-year away appears to us as it was one year ago, when the light first left the object. And galaxies billions of light-years away appear to us as they did billions of years ago. The new study looked at galaxies stretching back about 5 billion years in the past. Euclid will peer 8 billion years into the past, and Roman will look back 11 billion years.

The galaxies themselves don’t reveal the strength of gravity, but how they look when viewed from Earth does. Most matter in our universe is dark matter, which does not emit, reflect, or otherwise interact with light. While physicists don’t know what it’s made of, they know it’s there, because its gravity gives it away: Large reservoirs of dark matter in our universe warp space itself. As light travels through space, it encounters these portions of warped space, causing images of distant galaxies to appear curved or smeared. This was on display in one of first images released from NASA’s James Webb Space Telescope.

Questo video spiega un fenomeno chiamato lente gravitazionale, che può far apparire le immagini delle galassie distorte o macchiate. Questa distorsione è causata dalla gravità e gli scienziati possono utilizzare l’effetto per rilevare la materia oscura, che non emette o riflette la luce. Credito: Goddard Space Flight Center della NASA

Gli scienziati del Dark Energy Survey osservano le immagini delle galassie per individuare distorsioni più sottili dovute alla flessione dello spazio della materia oscura, un effetto chiamato debole lente a gravità. La forza di gravità determina le dimensioni e la distribuzione delle strutture della materia oscura, e le dimensioni e la distribuzione, a loro volta, determinano quanto ci appaiono distorte queste galassie. È così che le immagini possono rivelare la forza di gravità a diverse distanze dalla Terra e in tempi lontani nel corso della storia dell’universo. Il gruppo ha ora misurato le forme di oltre 100 milioni di galassie e finora le osservazioni corrispondono a quanto previsto dalla teoria di Einstein.

“C’è ancora spazio per sfidare la teoria della gravità di Einstein, poiché le misurazioni diventano più accurate”, ha affermato la coautrice dello studio Agnes Ferti, che ha condotto la ricerca come ricercatrice post-dottorato al JPL. “Ma abbiamo ancora molto da fare prima di essere pronti per Euclide e Roman. Quindi è imperativo continuare a collaborare con scienziati di tutto il mondo su questo problema, come abbiamo fatto con l’indagine sull’energia oscura”.

Riferimento: “Risultati dell’indagine sull’energia oscura del terzo anno: vincoli di estensione per ΛCDM con lenti deboli e ammassi galattici” di DES Collaborazione: TMC Abbott, M. Aguena, A. Alarcon, O. Alves, A. Amon, J. Annis, S. Avila, D. Bacon, E. Baxter, K. Bechtol, M. R. Becker, G. M. Bernstein, S. Birrer, J. Blazek, S. Bocquet, A. Brandao-Souza, S. L. Bridle, D. Brooks, D. L. Burke, H. Camacho, a. Campos, A.; Carneiro-Roussell, M. Carrasco-Kinde, J. Carretero, FJ Castander, R. Cawthon, C. Chang, A. Chen, R. Chen, A. Choi, C. Consullis, J. Cordero, M.Costanzi, M. Crocce, LN da Costa, MES Pereira, C. Davis, TM Davis, J. DeRose, S. Desai, E. Di Valentino, HT Diehl, S. Dodelson, P. Doel, C. Doux, A. Drlica-Wagner, K. Eckert, T. F. Eifler, F. Elsner, J. Elvin-Poole, S. Everett, X. Fang, A. Farahi, I. Ferrero, A. Ferté, B. Flaugher, P Fosalba, D. Friedel, O. Friedrich, J. Frieman, J. García-Bellido, M. Gatti, L. Giani, T. Giannantonio, G. Giannini, D. Gruen, R. R. Gruendl, J. Gschwend, G. Gutierrez , N. Hammos, I. Harrison, W. G. Hartley, K. Herner, SR Hinton, DL; Honshed, H. Huang, M. Hof, de Hutterer, B. Jane, DJ James, M. Jarvis, N. Jeffrey, T. Geltima, A. Kovacs, Cross, K. Cohn, N.; Kuropatkin, O. Lahav, S.; Lee, P.-F. Leggett, B. Lemus, CD Leonard, AR Liddell, M. Lima, H. Lynn, N. McCran, J. L. Marshall, J. McCullough, J. Mina Fernandez, F. Minanto, R. Mikel, V. Miranda, J. J. Mohr, J. Muir, J. Miles, S. Nadthor, A. Navarro-Alsina, RC Nicoll, RLC Uganda, Y. Aomori, A. Palmis, S Pandey, Y Park, M Paterno, F Paz-Chinchon, WG Percival, A Perez, AA Plazas Malagon, A Buridon, J Pratt, M ​​Raveri, M Rodriguez-Monroy, B Rogozinski, RP Rollins, AK Romer Rodman, AR Rosenfeld, A. J. Ross, A. Rykoff e S. Rodman. Samorov, C. Sanchez, E. Sanchez, J. Sanchez e il dott. , M. Smith, M. Soares-Santos, E. Suchyta, M. Tabbutt, G. Tarle, D. Thomas, C. To, A. Troja, M. A. Troxel, I. Tutusaus, T. N. Varga, M. Vincenzi, AR Walker, N. Weverdick, R.H. Wechler, J. Wheeler, P. Yanni, P. Yin, Y. Zhang e J. Zontz, 12 luglio 2022, disponibile qui. Astrofisica > Cosmologia e astrofisica non galattica.
arXiv: 2207.05766