Survey the Universe?

How It Has Been Done with SDSS

The Perseus Cluster, as seen through the eyes of the Sloan Digital Sky Survey. Courtesy Robert Lupton. Click to biggify.

The universe is a strange and wonderful place.  How do I know this when I haven’t explored it all? When astronomers are still searching out the distant reaches and early history of the cosmos?  I know it from the work done by scientists using such observatories as the Hubble Space Telescope, the Spitzer Space Telescope, the Wilkinson Microwave Anisotropy Probe, and the phalanx of ground-based observatories such as the Subaru Telescope, the Gemini Observatory, the European Southern  Observatory, and many, many others.  Quite significantly, I know it from the results of a sky survey that revolutionized our view of the universe–mostly of the galaxies, galaxy clusters, and quasars — but also by looking at bodies in our own solar system.  That survey was the Sloan Digital Sky Survey, which has carried out deep multi-color surveys of more than a quarter of the sky. Data from its first surveys were used to create three-dimensional maps of nearly a billion galaxies and more than 120,000 quasars. It’s now in a new program of observations called SDSSIII that will continue until the year 2014.

All this work has been done using a 2.5-meter telescope on a mountain in southern New Mexico. A single telescope!  It’s an amazing and ongoing accomplishment.

The Sloan began operation in 2005, and I often wondered about the people who put it together. Certainly I’d heard plenty about the survey at meetings, and had met some of the Sloan planners. But, as with the Hubble Space Telescope, I really didn’t know much of the history of the project when I first signed on to work with an instrument team back in grad school.  HST piqued my curiosity, and so in 1992 and 1995, I worked on a book with co-author Jack Brandt (a former team lead for the Goddard High Resolution Spectrograph on HST, and now at the University of New Mexico) called Hubble Vision. I also did a planetarium/fulldome show called Hubble Vision about HST’s accomplishments, which I periodically update.

Working on those projects gave me a lot of insight into the people who make such instruments work, and their hopes and dreams for the outcome of their astronomy work.  Hubble’s history is replete with individuals who designed the instruments, solved the problems, recognized the errors of spherical aberration, and who have made the many,  many accomplishments possible.  Some of those same folks have been involved with the Sloan Digital Sky Survey, too.

I just finished reading a book about the Sloan Digital Sky Survey (SDSS, for short) and the folks who made it a reality. The book, called A Grand and Bold Thing, by Ann Finkbeiner, gives us a look not just at Sloan and its accomplishments, but at the dream it sprang from — beginning with the spiral bound notebooks of astronomer Jim Gunn (who first brought the idea up at a meeting in Tucson in 1987), and the further refinements of the first planning documents and taking us to the observations made by this project.  At one level,  the book does what Jack and I tried to do for Hubble: give readers a look at the PEOPLE behind the instruments and accomplishments.  Ann’s writing is clear and wonderful, and she really lets the reader see the history and growth of SDSS quite clearly, through the eyes of the astronomers who made it happen.  These are REAL people who sweated over the development and installation of SDSS, and their accomplishment is considerable.

Along the way, we also learn about the universe that SDSS (and all its observational siblings) has revealed to astronomers.  SDSS’s contributions to understanding the large-scale structure of the universe are considerably one of the most important achievements in astronomy.  Without the data that SDSS, and sibling surveys such as the 2DF and 6DF observations, astronomers might still literally be groping in the dark for an understanding of how matter is distributed throughout the universe.

Finkbeiner weaves in the story of thediscovery of the structure of the cosmos as she tells the story of the SDSS.  For me, entwining together the story of scientific discovery with the tale of the people who enabled the SDSS’s odyssey of discovery is a heady brew. You should drink it in for yourself!

UV FTW!

Breaking up is Easy to Do — With Ultraviolet

This is one of those stories that seems almost impossible at first glance: making water in space?  No way! Wouldn’t it all freeze out there?

Well, yeah… but  you can get water vapor if you happen to have really hot stars near a nebula that is rich with molecules of hydrogen gas (H2), carbon monoxide (CO) and silicon monoxide (SiO).  Those hot stars emit loads of ultraviolet radiation, which is energetic enough to break the oxygen molecules free. Once they are, they readily will bond with the hydrogen gas molecules to form water. Add in a heat source (like the nearby dying star and the heat from other stellar neighbors) and you get water vapor.

The star IRC+10216 -- where astronomers are studying a cloud of water vapor surrounding the star.

Of course, the water needs to have a stable environment to exist in, like a warm envelope of gas and dust.  Such a curcumstellar envelope is where the European Space Agency’s Herschel spacecraft has made a significant discovery.  It observed a cloud surrounding the  dying star IRC+10216 and studied its steamy vapor cloud. This stellar sauna has been known to exist since astronomers first saw evidence for the vapor in 2001.

At first, astronomers thought that maybe the dying carbon star was heating up nearby cometary bodies and creating the water vapor.  They even suspected that dwarf planets may have also been melted to make the cloud.  However, those ideas needed to be proved, and for that, astronomers needed a telescope with instruments that could peer through the cloud of dust and steam surrounding the star.

Herschel can do the job because it has infrared capability, which allows it to see where optical telescopes cannot due to the thickness (opacity) of the cloud that surrounds the star. Some observations had already revealed clumpy structure in the dusty envelope around IRC+10216. And, there was that water vapor in the areas of the cloud around the clumps.

So, astronomers trained Herschel’s infrared “eyes” to the cloud and measured the temperature of the water vapor. It ranged from -200 degrees Celsius to 800 degrees Celsius.  That’s quite warm, which means that the water vapor is being formed quite close to the star — closer, in fact, than comets could exist.

This is an interesting result and means that other carbon stars could also have the same type of water vapor cloud around them, provided there are sources of ultraviolet radiation nearby. So,  the next step is for astronomers to look at some of those carbon stars with Herschel and see what they can find.  Stay tuned!