In Conversation

Sloan survey gives Yale astronomers an eye in the sky

Yale astronomer Meg Urry discusses the Sloan Digital Sky Survey, Yale’s role in mapping the cosmos, and the impact of COVID-19 on astronomical research.
A time-domain spectroscopic survey of quasars and X-ray sources.

A time-domain spectroscopic survey of quasars and X-ray sources. (Image credit: ESO/M. Kornmesser)

After 20 years and four previous phases, the Sloan Digital Sky Survey’s Phase V(SDSS V) is ready to give Yale astronomers a new look at the wonders of the cosmos.

The survey’s mission is ambitious: It aims to create a detailed, three-dimensional map of the universe, using a 2.5-meter, wide-angle optical telescope located at the Apache Point Observatory in New Mexico.

Previous SDSS surveys have mapped one-third of the sky. SDSS data have been used in more than 7,700 peer-reviewed, scientific papers, offering insights into the chemical makeup of the Milky Way and the structure of distant galaxies. It has also helped produce multi-color imaging for hundreds of millions of stars, and gleaned information about 100,000 asteroids and other objects within Earth’s solar system. The fifth iteration of the survey will add more information about each object observed.

Yale is a full participating member of the SDSS collaboration, which includes dozens of research institutions around the world. Yale astrophysicists have used SDSS data to contribute groundbreaking research on black holes, quasars, galaxy formation, and other cosmological phenomena. For example, Yale researchers identified the first “changing-look” quasar, discovered dwarf galaxies that contain massive black holes, and helped find a rare group of galaxies called the “Green Peas.”

Meg Urry
Meg Urry

Meg Urry, Yale’s Israel Munson Professor of Physics and Astronomy, who served on the advisory committee for both SDSS-III and SDSS-IV, spoke to YaleNews about SDSS’s latest phase and its potential use by Yale researchers.

How long has Yale been involved in SDSS?

Yale was a partner in SDSS-III, which ran from 2008 to 2014, and SDSS-IV, which ran from 2014 to 2020. These are large efforts to take enormous amounts of data covering a large fraction of the sky, with increasingly sophisticated instrumentation. Each survey consists of a few sub-projects, each with its own instruments, and a dedicated telescope in New Mexico. Starting with SDSS-IV, we also have a telescope in the southern hemisphere, at Las Campanas Observatory in Chile.

Yale is a full institutional partner in SDSS. What does that entail?

It means that any student, postdoc, or faculty member has open access to all the data. All data become public eventually but institutional partners like Yale have an inside track to the early science, by virtue of having contributed to the cost of the survey.

What are some of the new experiments that Yale researchers plan to use?

Some of us — including Priyamvada NatarajanPaolo Coppi, and myself — are interested in the Black Hole Mapper experiment, which will obtain spectra of all the X-ray sources from the eROSITA satellite, which was launched just over a year ago. This will greatly increase our understanding of the growth of the most massive, most distant black holes. In particular, Priya Natarajan plans to address the critical question of the origin of the first black holes, and I personally am excited about finalizing our census of black hole growth across the past approximately 12 billion years.

Other faculty, including Marla GehaBob Zinn, and Jeff Kenney, and their research groups will be involved in the Local Volume Mapper, which will explore the local group of galaxies. Sarbani BasuHector Arce, and Charles Bailyn are among the faculty interested in the Milky Way Mapper, which, as its name suggests, is an exploration of more than 4 million stars through the Milky Way and local group.

Are students also able to use SDSS data?

These massive data sets are suitable for big science — such as my group’s work on modeling the growth of black holes over the past 12 billion years — as well as more focused student projects. Any undergraduate can download some data and learn something new, something that has never been studied before. It is a very powerful laboratory for astrophysics.

Has the COVID-19 pandemic had an effect on how SDSS-V is taking shape?

The COVID pandemic has indeed affected SDSS. It has affected every facet of the operations by restricting travel to the sites for installing new instruments and limiting working conditions at the two observatories. The health of people working at the telescopes is paramount. It is hoped that we can still get the full survey, but each night the observatories are closed is a night we are not taking data.


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