The largest map ever released of active supermassive black holes in the universe

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Astronomers have mapped the largest volume of the universe ever seen with a new map of active supermassive black holes at the centers of galaxies. Ironically, these black holes, called quasars, are among the brightest objects in the universe. The new map records the location in space and time of about 1.3 million quasars, the most distant of which shone brightly when the universe was only 1.5 billion years old (for comparison, the universe is now 13.7 billion years old).

“This catalog of quasars is different from all previous catalogs because it gives us a 3-D map of the largest volume of the universe ever seen,” said David Hoge, co-author of the map and senior research scientist at the Flatiron Institute's Center for Computational Sciences. Astrophysicist in New York City and Professor of Physics and Data Science at New York University. “It's not the catalog with the largest number of quasars, and it's not the catalog with the best quality measurements of quasars, but it is the catalog with the largest total volume of the universe ever mapped.”

Hough and his colleagues present the map in a paper published in the Astrophysical Journal. The lead author of this paper, Kate Storey-Fisher, is a postdoctoral researcher at the Donostia International Physics Center in Spain. Scientists built the new map using data from the European Space Agency's Gaia space telescope. Although Gaia's main goal is to map the stars in our galaxy, it also inadvertently sees objects outside the Milky Way, such as quasars and other galaxies, as it scans the sky.

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“We've been able to make measurements of how matter aggregated in the early universe that are as precise as some measurements from large international research projects — which is pretty remarkable, because we got our data as a bonus from the center of the Milky Way. Gaia Project,” Story-Fisher said. Quasars are powered by supermassive black holes at the centers of galaxies and can be hundreds of times brighter than the entire galaxy. When the black hole's gravity spins nearby gas, the process generates an extremely bright disk and sometimes rays of light that telescopes can detect.

The galaxies in which quasars live are surrounded by massive halos of invisible matter called dark matter. By studying quasars, astronomers can learn more about dark matter, such as how much it clumps together.

Astronomers can also use the locations of distant quasars and host galaxies to better understand how the universe expands over time. For example, scientists have already compared the new quasar map with the oldest light in our universe, the cosmic microwave background. When this light travels toward us, it is bent by the interwoven web of dark matter, the same web drawn by quasars. By comparing the two, scientists can measure how tightly the material clumps together.

“It's very exciting to see this catalog generating a lot of new science,” Storey-Fisher says. “Researchers around the world use the quasar map to measure everything from the primordial density fluctuations that seeded the cosmic web to the distribution of cosmic voids to the motion of our solar system through the universe.” The team used data from the Gaia Data Release III, which contains 6.6 million candidate quasar stars, and data from NASA's Wide Field Infrared Survey Explorer and the Sloan Digital Sky Survey. By combining the datasets, the team removed contaminants such as stars and galaxies from the original Gaia dataset and were able to determine the distances to the quasars more accurately.

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The team also created a map showing where dust, stars, and other disturbances are expected to obscure our view of some quasars, which is crucial to interpreting the quasar map. “This catalog of quasars is a great example of how productive astronomical projects can be,” Hogue says. “Gaia was designed to measure the stars in our galaxy, but at the same time it also found millions of quasars, giving us a map of the entire universe.”

Illustration: ESA/GAIA/DPAC


Winton Frazier

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