Lecture Liveblog : Jim Gunn
Jim Gunn from Princeton – one of the founders of the Sloan – is presenting the final conference summary. A large part of the design was influenced by the impact of people coming into astronomy from other parts of physics, doing things in the x-ray, the radio and the infrared and who were used to working with data, not with the pictures that were the stock in trade of the optical astronomer. Sloan was supposed to fill the gap, taking both images and data in the form of spectra.
The crucial technology were the fibre optic cables that allowed hundreds of spectrographs to be fed at the same time. Without them, the survey would have taken a thousand or so years assuming that everything worked with 100% efficiency. The new technology made much more rapid progress possible, and Sloan has touched every part of astrophysics.
Jim started his run down with the work on large scale structure. Among the surprises were the work on gravitational lenses, which it had never occurred to anyone might be possible. The net result is that our current cosmology is much better than we have any right to expect, and as Jim said ‘there are no obvious cracks – yet’. However, he warned that eventually as data improves it will crack, and said he’d be very surprised if it didn’t.
The study of galaxies themselves has been revolutionized by Sloan. The spectra were of a much greater quality than was necessary just to determine the distance to the galaxies SDSS targeted. Jim’s slide claims that establishing the properties of modern day galaxies was one of the primary purposes of the Sloan. The headline result is probably the discovery that large populations of galaxies can be divided into red and blue sub-populations. One of the current challenges driving research as a result is the need to explain how sufficient galaxies move quickly from the ‘blue cloud’ to the ‘red sequence’, let alone trying to work out what happens to them once they are there. The majority vote is that black holes have something to do with these mysteries, but the details are very sketchy.
Yet we have still made huge progress; as Jim said, when Sloan started we didn’t even know enough about galaxies to ask these questions, let alone to start answering them. Plenty of work has also been done on galaxies’ active cousins, the quasars, and on the Milky Way itself. The most striking thing – which has crept up on my consciousness for starters – is the acceptance of the idea that the Milky Way has grown by the accretion of smaller satellite galaxies.
Jim’s award for the most unsettling talk goes to ‘Pierre Bergeron’ whose talk on white dwarfs – the dense remnant of Sun-sized stars – lead to conclusion that the hydrogen atom, at least in these extreme conditions, is ‘not well understood’! In a more reassuring pocket lie some of the solar system work (the talks on which I missed by being busy elsewhere) where great strides have been made in identifying asteroids, ruling out threats to Earth.
Supernovae – exploding stars – have been the gold standard for cosmology for the last decade, but at current errors we’re getting close to the point where we have to understand the explosions themselves in order to make further progress. A task for the future, probably, but there are a new set of surveys on the horizon. What advice can the Sloan team offer them?
The most important is probably ‘do it right’ rather than take shortcuts. More interestingly, the lesson from Sloan is not to design surveys which are suited only for one task, but can do a whole host of things, most of which you haven’t thought of yet. Finally, one last discovery. It really is possible for hundreds of astronomers to work together across many institutions with very few constraints on who should do what. That’s something that just wasn’t known when Sloan started, and it’s illustrated by the fact that four of Jim’s academic grandchildren gave talks at this conference.
That’s a suitable end to a wide-ranging conference, so I shall leave it there. I hope you enjoyed my coverage.
on August 18th, 2008 at 9:55 pm
[...] SDSS Conference : Summary to end all summariesAugust 18th, 2008Like it? Digg-it | Reddit | del.icio.usby ChrisLintottI hope you’ve enjoyed our coverage of the Sloan Digital Sky Survey’sbirthday conference; one of the project’s founders, Jim Gunn, has just received a standing ovation from the gathered scientists which marked the end of his summary of the conference. If you’d like my interpretation of what he said, then click here to read on. [...]
on August 19th, 2008 at 10:23 am
Hi Chris -
I’ve followed your postings with fascination and wonderment.
I’d like to thank you for taking time out of your schedule, in order to enlighten and educate those of us not fortunate enough to be involved in this academic pursuit…
Nathanial BB
on August 19th, 2008 at 1:47 pm
Yes, there’s no denying it: the SDSS did a very nice job of reproducing the results of the 2dFGRS on the galaxies/largescale structure side, and confirming everything that the 2dfGRS team had already found for a tiny fraction of the SDSS budget. Of course, that tends not to be the way they sell it at SDSS…
As for your final discovery, personally I find that deeply depressing: if I wanted to work like a particle physicist, I would have become a particle physicist. To me, the attraction of astronomy has always been the possibility of seeing a project all the way from the back of a beermat to the scientific result, without a list of coauthors longer than the paper. I really don’t want to be sucked into a giant astronomical sausage factory.
on August 19th, 2008 at 5:05 pm
Hi Michael
I was reporting Jim’s comments, not my own opinion. To be fair, 2dF was given lots of attention during the conference including a very nice review by Ofer.
As for my opinion, Sloan has enabled many more beermat-paper projects by making the data freely available. I don’t know about what life inside the collaboration is like, but that’s been the effect for me on the outside at least.
on August 19th, 2008 at 10:42 pm
Michael,
I don’t think for even one nanosecond anyone, in the SDSS collaboration or out, understates the importance of the various 2dF projects (and extensions)!
At perhaps the most basic level, the two projects were entirely independent, used quite different approaches, etc, etc, etc, … yet the results were mutually consistent. And where they weren’t, much good science has been done subsequently. Sure, astronomers are human, just like you and me, and some of them are vain, egotistical, selfish, … but just as many are magnanimous, generous in the extreme, self-effacing, …
And to second Chris’ comment, if you were around in the 1960s or earlier, try to imagine just how vastly different your access to the highest quality data was, compared to what you can get from SDSS today … for free!
Whatever papers you want to write, based on the TB (PB?) and more of SDSS, 2dF, 2MASS, FIRST, GALEX, WMAP, HST, … data (for free!), you are free to write, with or without collaborators.
on August 20th, 2008 at 9:08 am
Oh, don’t get me wrong. I think the SDSS is an excellent resource, and agree entirely that it opens up many new avenues for research. Particularly exciting is the way that it provides access to World-quality data to some of the great minds in the developing World. I just wanted to express some degree of balance to its claims, and pojt out that there may be cheaper ways to do the same science.
I am, however, saddened by the mind set of the survey mentality of “if you do it, thoughts will come.” Telescope allocation committees these days seem captivated by phrases like “complete sample,” and seldom seem to do the calculation of whether a 600-night broad survey will actually generate a greater scientific return than 200 3-night projects that have been targeted intelligently to address specific questions. It is undeniably a difficult calculation, since each approach must somehow factor in the unexpected, but one should at least ask the question.
Maybe, though, in the upcoming era we will be forced to think more like particle physicists as there would be little point in giving every astronomer their fifteen minutes of fame driving an ELT. This does, however, raise interesting issues about how one trains the next generation of astronomers in the broad skills of seeing a project all the way from beermat through instrument building to scientific returns (as, for example, Jim Gunn himself has proved so brilliant), as one surely must if they are going to run big projects in the future.