Liveblog: Jim Gunn on the Sloan Digital Sky Survey
As Chris mentioned last Saturday, scientists from the Sloan Digital Sky Survey have gathered in Chicago to review accomplishments and look ahead to the future. The Sloan Digital Sky Survey (SDSS) is the project that provided all the images for Galaxy Zoo; but additionally, it has provided some of the most amazing results in astronomy over the past decade or so.
The final talk of the conference was given by Jim Gunn, an astronomer at Princeton who has spent most of the past 20 years guiding SDSS from its initial planning stages to today. Jim was an excellent choice to give the talk. Chris was in the audience too, and liveblogged the talk from his blog, so you can see how two people from the same audience interpret in the same talk.
Here is what I recorded during the talk yesterday:
Gunn has just started speaking. “In the next 20 minutes, I will describe a large chunk of astrophysics,” he says. That’s quite a promise. He says that Sloan was first thought up in 1987. Now it’s 2008; if the project were born here in the States then, it would now be old enough to drink.
The original goal of the SDSS came from a desire to get caught up with technology. Astronomers before had always worked with photographic plates, which can be hard to use to get quantitative data. They wanted to design a project that would use digital cameras to see the sky instead. This is common today but was a new idea in 1987.
It became clear that just getting images of the sky wasn’t enough; we also needed to know what the distances to galaxies were. To do that, SDSS needed to get spectra to find redshifts. To get the number of distances they needed, they would need to get spectra for a million galaxies. The problem is that it takes 1 hour to get a spectrum, and 1 hour x 1 million galaxies = 1,000 years. So they came up with a clever solution to get 600 spectra at once.
“SDSS has touched almost all the fields of astrophysics,” Gunn said. He’s reviewing some of those areas now.
The field of large-scale structure (the way galaxies are distributed into a map of the universe) was the main scientific justification for the SDSS. The survey has always billed itself as a “map of the universe.” SDSS has made key contributions to what Gunn calls “precision cosmology” – making large-scale measurements to learn something about the properties of the universe as a whole. SDSS has led to the discovery of lots of new tools for measuring these parameters.
“I think the richest part of SDSS has been galaxies,” Gunn said. That is a significant statement – the original promise of SDSS was to learn about large-scale structure, but what we have learned about the nature of galaxies has been amazing too. SDSS spectra are amazingly good. For a long time, a lot of great telescopes, including Hubble, were seeing the universe, but just a few galaxies at a time. By seeing millions of galaxies at once, all over the sky, the SDSS has helped us learn more about what galaxies are like.
Gunn just mentioned Steven’s Galaxy Zoo talk. “I’m glad to see that the subject of morphology [the study of galaxy shape] has come to the fore again,” he said. He described our project as the “democratic Galaxy Zoo” Galaxy Morphology – this used to be all we knew about galaxies. “I’m very glad to see that the subject has come to the fore again.” Gunn described our project as “democratic Galaxy Zoo,” which I’m pleased to hear; part of the excitement was the chance to work democratically with so many of you to learn about the universe.
The SDSS has also led to exciting discoveries about our own galaxy, the Milky Way. It’s a much more complex place than we had previously thought; it’s been built up by nearly constant combinations of smaller galaxies into our own larger one. One of the talks here was about the Monoceros Stream, a long stream of stars discovered by the SDSS, which Gunn described as “still a bit of a mystery.”
SDSS has also led to discoveries about stars and about our solar system. One particularly interesting result announced at this meeting was the discovery of a new “minor planet” called 2006 SQ 372, an icy ball so distant that it takes 22,000 years to orbit the Sun. There is a good possibility that it is either the first or second object from the Inner Oort Cloud. The SDSS has also produced exciting results in understanding supernovae, the exploding stars that can tell us something about the history of the universe.
The future of astronomy is bright – there are lots of new surveys planned, including a 6-year extension to the SDSS called SDSS-III, PanSTARRS, and LSST. Gunn is now reviewing lessons that he thinks we learned from the SDSS. The one that stands out for me is his last one: “it really is possible for hundreds of people at tens of institutions to work together in a ‘non-cat-herded’ manner.” He adds, “it’s been fun as well.”
Gunn just received a standing ovation, the longest one I’ve ever seen at a scientific conference. People here are really proud of what the SDSS has accomplished, and Galaxy Zoo is a part of that.