Quasars are the brightest objects in the Universe. The most powerful ones are thousands of times more luminous than entire galaxies. They\u2019re the visible part of a supermassive black hole (SMBH) at the center of a galaxy. The intense light comes from gas drawn toward the black hole, emitting light across several wavelengths as it heats up. <\/p>\n
But quasars are more than just bright ancient objects. They have something important to show us about the dark matter. <\/p>\n
<\/p>\n Large galaxies have supermassive black holes at their centers. Even those only casually familiar with space know that black holes can suck everything in, even light. But as black holes draw nearby gas towards themselves, the gas doesn\u2019t all go into the hole, past the event horizon and into oblivion. Instead, much of the gas forms a rotating accretion disk around the black hole.<\/p>\n SMBHs aren\u2019t always actively drawing material to them, an act known as \u2018feeding.\u2019 But when an SMBH is actively feeding, it\u2019s called an active galactic nucleus (AGN.) When the material in the disk rotates, it heats up. As it heats, it emits different wavelengths of electromagnetic radiation. It can also emit jets. <\/p>\n When astronomers first began to detect this light, they only knew they were seeing objects that emitted radio waves. The name quasar means quasi-stellar radio source. But as time went on astronomers learned more, and the term active galactic nucleus was adopted. The term quasar is still used, but they\u2019re now a sub-class of AGN that are the most luminous AGN. <\/p>\n Quasars inhabit galaxies that are surrounded by enormous haloes of dark matter. Astronomers think there\u2019s a link between the dark matter haloes (DMH) and the quasars. The DMH may direct more matter toward the center of the galaxy, feeding the SMBH and igniting a quasar, and even aiding the formation of more massive galaxies. <\/p>\n A team of researchers has created a new catalogue of quasars that will be a powerful tool for probing quasars, DMHs, and SMBHs. Their results are in a new paper in The Astrophysical Journal titled \u201cQuaia, the Gaia-unWISE Quasar Catalog: An All-sky Spectroscopic Quasar Sample.\u201d The lead author is Kate Storey-Fisher, a postdoctoral researcher at the Donostia International Physics Center in Spain.<\/p>\n \u201cThis quasar catalogue is different from all previous catalogues in that it gives us a three-dimensional map of the largest-ever volume of the universe,\u201d said map co-creator David Hogg, a senior research scientist at the Flatiron Institute\u2019s\u00a0Center for Computational Astrophysics\u00a0in New York City and a professor of physics and data science at New York University. \u201cIt isn\u2019t the catalogue with\u00a0the most quasars, and it isn\u2019t the catalogue with the best-quality measurements of quasars, but it is the catalogue with the largest total volume of the universe mapped.\u201d<\/p>\n The fact that the new catalogue captures the largest total volume of the Universe mapped and all the quasars in that space is key to understanding its purpose. It\u2019s not meant as a survey that captures the largest number of quasars. The catalogue is meant to be a tool astrophysicists can use to understand the relationships between quasars, dark matter, black holes, and galaxies. <\/p>\n They call their catalogue Quaia because the data comes from the ESA\u2019s Gaia spacecraft. Gaia\u2019s mission is to map about one billion objects in the Milky Way, mostly stars. And it\u2019s going about its mission with extreme accuracy. But among the multitudes of stars Gaia has mapped is a large number of quasars well beyond the Milky Way. That generated the name \u201cQuaia.\u201d<\/p>\n \u201cWe were able to make measurements of how matter clusters together in the early universe that are as precise as some of those from major international survey projects \u2014 which is quite remarkable given that we got our data as a \u2018bonus\u2019 from the Milky Way\u2013focused Gaia project,\u201d Storey-Fisher says.<\/p>\n Dark matter tends to clump in haloes around galaxies, and studying the distribution of quasars can help explain the distribution of dark matter. In the large scale of the Universe, dark matter is organized as a web, and the catalogue of quasars helps map that web. <\/p>\n The Cosmic Microwave Background (CMB), a strong piece of evidence for the Big Bang, is also part of this. As the light from the CMB travels toward us through space, the dark matter web\u2019s massive gravitational power bends the light. Scientists can compare the CMB light we receive with the map of quasars and compare the two. The comparisons will them about the relationship between dark matter and quasars and how matter clumps together in the Universe. <\/p>\n Since quasars trace the cosmic web, their distribution gives information about the web that other sources can\u2019t. For example, it can trace the distribution of matter at higher redshifts than galaxies can. And since it\u2019s space-based, it avoids some of the data contamination that other quasar surveys suffer from, such as the Sloan Digital Sky Survey (SDSS.) <\/p>\n This is not the first quasar map\/catalogue to be created. There are several others, including one from the Sloan Digital Sky Survey. <\/p>\n As the animation below shows, Quaia is more complete than the SDSS\u2019s DR16Q, the SDSS\u2019s quasar catalogue that accompanied its data release 16. <\/p>\n![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/03\/Quasar-Catalogue.jpg\")
![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/03\/Five-Quasar-Maps-1003x1024.jpg\")