Season 17, Episode 34: The Vera C. Rubin Observatory’s Search for Quasars

Hey StarTalkians! In episode 34 of season 17, Neil and Chuck sat down with PBS Spacetime host Matt O’Dowd to discuss quasars and sky surveys:

Quasar Quirks & Sky Surveys with Matt O’Dowd - StarTalk Radio

(from 23:20)

Matt mentions that the Rubin Observatory will find tons of quasars, but what will the observatory be doing? How many quasars will they find? And why study them at all?

The Legacy Survey of Space and Time

The flagship project of the Vera C. Rubin observatory is the Legacy Survey of Space and Time (LSST). The observatory is based in Chile, atop the Cerro Pachón mountain, and features the largest camera ever built, with a resolution of 3,200 megapixels.

This camera will take images of the entire southern night sky every three days. Over the 10-year observing period, this aims to track changes across the sky and give an incredibly rich window into variable stars and other cosmic objects that change with time. The resulting time-lapse will contain about 500 petabytes of data.

Why Look for Quasars?

The LSST Science Book details what astronomers expect to learn from the study of quasars and active galactic nuclei (AGN). As described in the podcast, AGNs are supermassive black holes currently “feeding” on the matter in their accretion disc, with quasars being the most well-known category. This feeding creates variations in luminosity that make them perfect targets for the LSST.

Long-term observation of this activity will help astronomers understand how this changes over time and provide insights into the formation and evolution of galaxies. The clustering of AGNs provides insights into dark matter distribution, and detailed study of gravitationally lensed quasars can help pin down the value of the Hubble constant.

How Many Quasars They’ll Find

Estimates of the number of new quasars that will be detected by the Rubin Observatory range from the thousands to the millions. In one paper, they use quasar counts from the Chandra Deep Field-South survey and the characteristics of the LSST survey to estimate that each of the six frequency bands will detect between 6 and 12 million quasars.

They also break their estimates down based on the number of months of observation, and calculate that 70% of quasar detections will take place in the first year of observation. So we should expect some news sooner rather than later.