New “quasar catalog” serves as a 3D history book of the universe

A growing black hole, called a quasar, is seen at the center of a faraway galaxy in this artistic concept. Credit: NASA/JPL-Caltech.
A growing black hole, called a quasar, is seen at the center of a faraway galaxy in this artistic concept. Credit: NASA/JPL-Caltech.

Astronomers have charted the largest-ever volume of the universe with a new map of active supermassive black holes living at the centers of galaxies. Called quasars, the glowing black holes are, ironically, some of the universe’s brightest objects.

The new map logs the location of about 1.3 million quasars in space and time, with the furthest shining bright when the 13.7-billion-year-old universe was only 1.5 billion years old.

“This quasar catalog is different from all previous catalogs in that it gives us a three-dimensional map of the largest-ever volume of the universe,” says map co-creator David Hogg, a senior research scientist at the Flatiron Institute’s Center for Computational Astrophysics in New York City and a professor of physics and data science at New York University. “It isn’t the catalog with the most quasars, and it isn’t the catalog with the best-quality measurements of quasars, but it is the catalog with the largest total volume of the universe mapped.”

Hogg and his colleagues present the map in a newly published paper in the Astrophysical Journal. The paper’s lead author, Kate Storey-Fisher, is a postdoctoral researcher at the Donostia International Physics Center in Spain.

Credit: ESA/Gaia/DPAC; Lucy Reading-Ikkanda/Simons Foundation; K. Storey-Fisher et al. 2023.

Credit: ESA/Gaia/DPAC; Lucy Reading-Ikkanda/Simons Foundation; K. Storey-Fisher et al. 2023.

The scientists built the new map using data from the European Space Agency’s Gaia space telescope. While Gaia’s main objective is to map the stars in our galaxy, in the process of scanning the sky, it also inadvertently spots objects outside the Milky Way, such as quasars and other galaxies.

“We 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—which is quite remarkable given that we got our data as a ‘bonus’ from the Milky Way-focused Gaia project,” says Storey-Fisher, who conducted some of the work as an NYU doctoral candidate.

Quasars are powered by supermassive black holes, which have hundreds of thousands to billions of times the Sun’s mass, at the center of galaxies and can be hundreds of times as bright as an entire galaxy. As the black hole’s gravitational pull spins up nearby gas, the process generates an extremely bright disk, and sometimes jets of light, that telescopes can observe.

The galaxies that quasars inhabit are surrounded by massive halos of invisible material 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 their host galaxies to better understand how the cosmos expanded over time. For example, scientists have already compared the new quasar map with the universe’s oldest light, called the cosmic microwave background, to study how strongly matter clusters in the universe.

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This video representation of the map shows the location of quasars from our vantage point, the center of the sphere. The regions empty of quasars are where the disc of our galaxy blocks our view. Quasars with larger redshifts are further away from us. Credit: ESA/Gaia/DPAC; Lucy Reading-Ikkanda/Simons Foundation; K. Storey-Fisher et al. 2023.

“It has been very exciting to see this catalog spurring so much new science,” says Storey-Fisher. “Researchers around the world are using the quasar map to measure everything from the initial 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 Gaia’s third data release, which contained 6.6 million quasar candidates, or possible quasars, along with 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 Gaia’s original dataset of contaminants and better pinpointed the distances to the quasars. The team also created a map of where dust, stars, and other nuisances are expected to block our view of some quasars, which is critical for interpreting the quasar map.

“This quasar catalog is a great example of how productive astronomical projects are,” Hogg says. “Gaia was designed to measure stars in our own galaxy, but it also found millions of quasars at the same time, which give us a map of the entire universe.”

Visuals depicting the work may be downloaded from Google Drive (Quasar caption: This graphic representation of the map shows the location of quasars from our vantage point, the center of the sphere. The regions empty of quasars are where the disc of our galaxy blocks our view. Quasars with larger redshifts are further away from us. Credit: ESA/Gaia/DPAC; Lucy Reading-Ikkanda/Simons Foundation; K. Storey-Fisher et al. 2023).

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