NASA | MSFC | SAO | Chandra X-ray Observatory | 2020 Apr 08
This graphic contains a map of the full sky and shows four of the hundreds of galaxy clusters that were analyzed to test whether the Universe is the same in all directions over large scales, as described in our latest press release. Galaxy clusters are the largest objects in the Universe bound by gravity and astronomers can use them to measure important cosmological properties. This latest study uses data from NASA's Chandra X-ray Observatory and ESA's XMM-Newton to investigate whether or not the Universe is "isotropic."
The sky map in this schematic is in "galactic coordinates," with the plane of the Milky Way running along the middle (instead of the equator like is used for Earth). Galactic longitude runs in the horizontal, or "x" direction, and galactic latitude runs in the vertical, or "y" direction. The dark points show the location in the sky map of the 313 galaxy clusters observed with Chandra and XMM-Newton and included in this study. The four Chandra images of galaxy clusters from the new study are, in a clockwise direction from the top left, Abell 2199, RXCJ1504.1-0248, Abell 3667 and Abell 85. Galaxy clusters with galactic latitudes less than 20 degrees were not included in the survey to avoid obscuration from the Galaxy itself, which has most of its stars, gas and dust along a thin plane. Similarly, galaxy clusters behind two nearby galaxies, the Small Magellanic Cloud and the Large Magellanic Cloud, and behind the Virgo galaxy cluster were not included to avoid obscuration.
Astronomers generally agree that after the Big Bang, the cosmos has continuously expanded like a baking loaf of raisin bread. As the bread bakes, the raisins (which represent cosmic objects like galaxies and galaxy clusters) all move away from one another as the entire loaf (representing space) expands. With an even mix the expansion should be uniform in all directions, as it should be with an isotropic Universe.
This latest test uses a powerful, novel and independent technique and suggests the concept of an isotropic Universe may not entirely fit. The study capitalizes on the relationship between the temperature of the hot gas pervading a galaxy cluster and the amount of X-rays it produces, known as the cluster's X-ray luminosity. The higher the temperature of the gas in a cluster, the higher the X-ray luminosity is. Once the temperature of the cluster gas is measured, the X-ray luminosity can be estimated. This method is independent of cosmological quantities, including the expansion speed of the Universe.
Once they estimated the X-ray luminosities of their clusters using this technique, scientists then calculated luminosities using a different method that does depend on cosmological quantities, including the Universe's expansion speed. The results gave the researchers apparent expansion speeds across the whole sky — revealing that the Universe appears to be moving away from us faster in some directions than others. ...
Rethinking Cosmology: Universe Expansion May Not Be Uniform
ESA | Space Science | Science & Technology | XMM-Newton | 2020 Apr 08
Probing cosmic isotropy with a new X-ray galaxy cluster
sample through the LX−T scaling relation ~ K. Migkas et al
- Astronomy & Astrophysics 636:A15 (Apr 2020) DOI: 10.1051/0004-6361/201936602
- arXiv.org > astro-ph > arXiv:2004.03305 > 07 Apr 2020