One of the ways in which astronomers differ from physicists is that we know an absurd number of small facts about the Universe. As you may have surmised, the Universe is a fairly complicated place, and astronomers revel in collecting details about the various bits of stuff within it. While this process is frequently dismissed as “stamp collecting” (the lowest blow that one can level at an astronomer, no offense to the philatelists among the CV readership), it’s actually an essential feature. At its best, astronomy is a search for underlying patterns and missed opportunities that can be used to contstrain fundamental physical processes. In the past, I’ve likened astronomy to gathering an enormous bag of puzzle pieces, but maybe there’s multiple puzzles in the bag, and probably some of the pieces are lost, or chewed on, and perhaps someone threw some extra pieces from some other puzzle in there. But, if you’re very persistent, perceptive, and have collected a lot of pieces, you might notice that some of the pieces would look a bit like a cat if you put them together just so.
A by-product of the need to gather puzzle pieces is that to make any headway, there are lots of facts one just has to know, without going back to first sources. When I first started teaching, I was shocked to discover what a large fraction of my astronomical knowledge was based upon “Jim Gunn told me so”. Now, Jim is well known as a clever fellow, so there are worse foundations to build from. However, I spent quite a bit of time those first few years trying to track down exactly why Jim told me various things were true. In most cases, the truths were established recently enough that tracking down sources was straightforward. Correlations and important processes were named after specific people, important calculations were cited in reference lists, all leaving a clear paper trail.
Once in a while, though, I run across a piece of astronomical knowledge that is so fundamental to our thinking that we’ve lost all trace of who said it first. The puzzle piece seems so obvious that it’s hard to imagine that there was a time when we didn’t have it in our bag. Most recently, I spent several days tracking down the genesis of the Milky Way’s stellar halo. The stellar halo, like the dark matter halo, is extensive and elusive. It consists of a diffuse smattering of very old stars, dating from the earliest assembly of the Galaxy. While halo stars are only a miniscule fraction of the stars in the Milky Way, their motions and their distribution around the Galaxy are superb tracers of the details of how structure first assembled, which in turn constrains the behavior of dark matter. Moreover, because they are some of the earliest stars formed, halo stars contain nearly pristine gas that has experienced little processing through other stars. The Universe forms mostly hydrogen and helium during Big Bang nucleosynthesis, and the paucity of all other elements (known as “metals” to astronomers — yes, we consider oxygen to be a metal. sue me.) in halo stars therefore indicates that most of their gas is close to primordial. Astronomers have even found individual halo stars where what little “pollution” there is seems to have come from a single supernova, allowing one to shake out a fair bit of tasty nuclear physics. The upshot is that the stellar halo contains a pretty useful set of puzzle pieces to toss in the bag.
However, how did anyone figure out that it was there? An electronic search finds that the term “halo” pops into the literature in the early- to mid-50’s, right before a flurry of papers establishing that the halo stars were “metal poor”. (Actually, “halo” appeared plenty of times before, but mostly in the context of coronae surrounding images of stars or the moon.) However, one of the papers from the mid-50’s came from an entire symposium on how best to map out the structure of the Galaxy, including the stellar halo. So, if astronomers were already planning a full assault on the problem, they must have been long convinced that it existed. Indeed, they were so convinced that they didn’t bother to reference any of the papers that established its existence. I transferred my sleuthing to the human abstract service, namely Extremely Sharp Professors in their 70’s. One of the ESP’s said “I think it was Oort”. And indeed, in 1924 J. H. Oort published a note in the Procedings of the National Academy of Sciences titled “On a Possible Relation between Globular Clusters and Stars of High Velocity”. What Oort did was note that if one took the orbits of nearby faint stars with unusual velocities and traced them backwards, then the high velocity stars could not be orbiting in a disk like most Milky Way stars, but instead would be travelling in a cloud surrounding the Galaxy, much like the globular clusters (which Harlow Shapley had earlier used to deduce that the position of the Sun with respect to the center of the Galaxy). So the ESP was right. It was Oort.
Now, the point of this post is not to drag Oort out of obscurity. Oort doesn’t need it, as the guy even has important astronomical constants named after him. The point is that if you do really good work, and discover something fundamental about how the Universe is put together, you might be forgotten. And that’s ok. Indeed, it’s a strange form of respect, to be forgotten. It means that there was something so obviously right about what you said that it was quickly absorbed by the scientific hive-mind, until it seemed like we knew it all along.
January 15th, 2007 at 1:41 pm
Let’s see…comet Dalcanton is thought to have emerged from the Inner Oort Cloud. Looks like we have a new candidate for an astronomical version of “The Six Degrees of Kevin Bacon.” What shall we call it? “The Seven Couplings of J.H. Oort” ??? Regardless, looks like you’re an easy way to win the game. Welcome to the blog!
January 15th, 2007 at 4:41 pm
If he were alive today, wouldn’t Oort be emailing everyone, insisting that they reference him every time they refer to the galactic halo?
January 15th, 2007 at 4:57 pm
Really great inaugural post. However, I think that “consider oxygen to be a metal” remark might call for a class action. Any lawyers reading this?
January 15th, 2007 at 5:00 pm
Apparently he wasn’t doing it in the 1950’s, since he didn’t even reference himself in his 1958 Vatican paper. He may have just been a chill dude. And really, he was so well regarded for so many different discoveries that he probably didn’t need to fight over the crumbs.
I should probably hold forth about Oort again in the future. Lots of interesting backstory.
January 15th, 2007 at 5:57 pm
While we’re talking about Jim Gunn, can we gossip about the secret science fiction careers of that generation? I know Jim wrote about sci fi, and there was a rumor too strong to be entirely baseless that Sidney Coleman had written a novel under a pseudonym… any others?
January 15th, 2007 at 5:58 pm
hello… thank you for this post… i have been watching things from my cloud out here and it is refreshing to finally see some SCIENTIFIC HONESTY…
oort
January 15th, 2007 at 6:04 pm
If you read the link attatched to Jim’s name, you’ll find that he disavows being the same Jim Gunn as the science fiction author. I hadn’t heard about Sidney though.
January 15th, 2007 at 10:40 pm
hmmm….. I don’t think there’s really too much difference in physics and astronomy in that regard. Not that Rutherford’s quote isn’t great fun at times, but the minutiae that keep things working in a condensed matter physics lab (or at least every one I’ve ever participated in!) are frankly stunning.
There’s a funny paleo-physics anecdote along similar lines in magnetics. The person largely responsible for the initial study of magnetic memory was a fellow named Erwin Madelung. Back at the start of the 20th century he wrote his thesis on magnetic hysteresis and came up with some rules for classifying the magnetic memory properties (or lack of) in different materials. His name has often been overshadowed by those that followed him even though his rules and language are still used today. And I’m sure you can readily appreciate how important magnetic memory is today!
What makes this a bit more fun, is that I can guarantee that many of you (especially the physicists?) have actually seen Madelung’s published work with your own eyes. You see, he also happens to hold a rather unique place in the history of physics. If you go and look for his very first published paper, the bound journal should fall open almost directly to his paper. In fact, the book should open to the last page of his paper. Why might you ask?
His very first paper appeared in 1905 and just happens to immediately precede the special relativity paper by Albert Einstein. So, as many young physical scientists are prone to seek out those most famous of papers at least once in their lives, they see at least the very last page of Erwin Madelung’s great paper on magnetic hysteresis.
January 16th, 2007 at 12:19 am
Oh no! Illusions shattered! :(!
January 16th, 2007 at 12:44 am
Didn’t Oort do, well, basically everything?
It would be like referencing Zwicky.
I am idly wondering who the ESP was….
January 16th, 2007 at 1:02 am
Julianne said “… yes, we consider oxygen to be a metal. sue me …”.
Chris W asked “… Any lawyers reading this? …”.
Yes, I am a lawyer, and as such I try to check facts before suing (unfortunately, that is not a universal practice among lawyers). In doing so, I found a Phys. Rev. Lett. paper by Weck, Loubeyre, and Letoullec - see
http://cat.inist.fr/?aModele=afficheN&cpsidt=13578182
entitled “Observation of structural transformations in metal oxygen”.
The abstract says:
“X-ray diffraction and Raman measurements have been performed on solid oxygen up to, respectively, 115 and 120 GPa. Metallization at 96 GPa is shown to be associated with a continuous displacive structural transformation. At 110 GPa, a new structure is stabilized. The evolution of the vibron mode reflects also the sequence of phase transitions through the continuity of the vibron frequency at 96 GPa, then the broadening of the vibron peak into the background and finally the reappearance of a sharp vibron at 110 GPa with a -2.5% discontinuity in the frequency. The observation of the vibron peak demonstrates that metallic oxygen is molecular up to at least 120 GPa.”.
So, it seems to me that Julianne and her fellow astronomers have solid ground to refer to oxygen as a metal, and would probably win any lawsuit asserting otherwise.
Tony Smith
http://www.valdostamuseum.org/hamsmith/
PS - Thanks, Julianne, for a very interesting blog entry.
January 16th, 2007 at 1:22 am
[…] links « The Honor of Being Forgotten […]
January 20th, 2007 at 3:35 am
JD,
you’re quite probably familiar with plotting the density of stars in a color-magnitude diagram and calling it a “Hess diagram.” this raises a natural question, namely “Who the heck is Hess?”
searching google is not much help; the ADS abstracts turn up a use as early as 1948 by Payne-Gaposchkin but even she doesn’t give a citation. the only way i know to solve this problem is that i once heard Bob Kraft (an ESP) once say he knew the Hess Identity - but either he didn’t give it up that day, or i forgot.
it is like bit rot in uncommented code. there is lore that everybody knows, and therefore no one knows it at all.
January 22nd, 2007 at 1:41 pm
Hey Ben! My local ESP suggested checking Trumpler & Weaver (1953) (after pronouncing it “A terrible book. They do many things badly. But it was all we had at the time”). Chapter 4.3 states “Such a representation is often called a Hess diagram after R. Hess[27] who, in 1924, first constructed a contour map of L(M,S)”. The reference is:
[27] R. Hess, “Die Verteilungsfunktion der absol. Helligkeiten etc”. Seeliger Festschrift, Springer, Berlin, 1924.
The one I want to track down is the person who first figured out that it would useful to take images of astronomical objects through different filters. George Preston (yet another ESP) told me the name, but I forgot.
January 23rd, 2007 at 7:52 pm
Sic transit gloria mundi. That’s probably the best thing one can hope anybody ever says about one’s thesis … Nice detective work. That means “The distribution function of absolute luminosity.”
I think it is actually an article in a book; there is one in our library titled “Probleme der Astronomie. Festschrift fur Hugo v. Seeliger” and I bet that’s it. Also the title yielded enough to find this glossary entry, skip down to the entry for Hess diagram. There is a figure.
I have no idea when people even started using filters! Hearnshaw’s book might say; it is more interesting than the title sounds. Or we could just ask George. A fond memory of my first day as a new postdoc at the Carwash is when George, accompanied by Andy McWilliam, barged into my new office and announced, “Did you know that this is the office in which technetium was discovered in stars???” by way of introduction.