Wednesday, April 25, 2007

American Idol, Landfills, and Juvenile Justice

Alright, I confess. I'm an American Idol fan. I'm all about the brainrot. It's pathetic, I know, but what's even more pathetic is that I don't even own a television and I watch a taped version of the Tuesday night show on Wednesday evenings. Last night's show revolved around "Idol Gives Back," this "big" war-against-poverty campaign they're doing. The big thing they kept mentioning is how for each vote, NewsCorp was going to donate $0.10, for up to five million dollars. They never really said where the money was going, except that it was to *gasp* Save Lives! Also nevermind that this is freaking NewsCorp and five million dollars is barely a drop in the bucket, if that. It probably did do some good and made a lot of people feel warm and fuzzy inside, so I can't complain too much.

So, last night, instead of forcing us to watch Bono "coach" the contestants (oh God thank you for sparing us that pain), we got to see a bunch of short segments of the host and the judges going around the US and Africa. The parts from Africa were ... familiar. (Nevermind that they never told us where in Africa they were; it's one big homogenous place, so it must not really matter anyhow. And while they did talk about how horrible of a disease malaria is, they didn't mention AIDS even once. American Idol is a family show, after all.) But, yes, the shots of people walking through landfills and of large groups of orphans happily eating in large bare rooms... it was a total deja vu, except the grinning kids in the video had darker skin that the ones in my memory.

In August 2005, in the middle of a month-long trip through southeast Asia, my father and I found ourselves in Phnom Penh, the capital of Cambodia. (If you don't know anything about Cambodia, quit being ignorant and go check out the wikipedia article or something. Especially the parts about the Khmer Rouge and Angkor.) We knew that Phnom Penh was going to be horrible, the worst combinations of a large dirty city and abject poverty in a country still recovering from large-scale genocide. Cambodia's tourist attractions are are elsewhere, and we were only in its capital out of necessity. My father's all-too-natural solution was to spend our one full day in town visiting the dump.

I'm not kidding. You just can't make this stuff up. We had met a couple in Siem Reap (the town near Angkor) who had spent a few days volunteering at the Centre for Children's Happiness in Phnom Penh. This organization actually runs two orphanages; the kids are separated by age and amount of time since they've lived in the landfill. Lived in the landfill. Like the girl in the picture on the left, these kids have all lived in the Phnom Penh dump as "garbage pickers" before coming to the orphanage. They go through the trash trying to find something, anything, they can sell for mere pennies in order to try to get enough money to buy food with. They literally live and sleep in the dump; the lucky ones might even live there with older siblings or even a parent. Most are orphans, or have parents in worse situations than them (e.g., missing a limb from the copious land mines scattered throughout the country). The CCH carefully picks children living in the dump to come live in the orphanage instead—and, importantly, the kids have to decide for themselves that this is a change they want in their lives. Usually the children coming straight from the dump have to spend about three months (if I remember correctly) in a hospital gaining strength and being treated for various diseases. (Actually, many only spend a few weeks, but some must spend many many months in recovery.) At the orphanages, they get a chance at having a "real childhood." They learn to read and write (in Khmer, English, and Japanese), they learn math, they learn job skills, they learn traditional Khmer dance and art, they learn how to care for one another and how society runs better if people treat each other with respect, have jobs, and take care of themselves. And, oh yes, they learn math. The walls of the courtyard in the main orphanage are covered with painted lessons: vocabulary, useful math formulas and ideas, proverbs, etc. I spent a while talking to one of the older students, a 16 year old boy who had been in the orphanage for three years. He said he really liked math, "especially trigonometry," and working on the computer. This is what we call a "motivated player." He said that when he turned 18, he wanted to work for the orphanage as a full-time employee; this was two years ago, and I do not know what he has wound up doing. The founder of CCH, Mech Sokha, is very open about the workings of the orphanage; the main office (where the computers live, and thus where many of the children spend much of their time) has a whiteboard dedicated to a breakdown of exactly how much it costs per child per day, and where all of that money both comes from and goes, as he is explaining to my father in the picture on the left. This is one of my favorite pictures (aside from all of the math!) from the orphanage because the kid you see standing next to Mech is so typical. For the first time in their lives, these children are somewhere safe, and it was so obvious just how safe they felt. Kids were running around, hugging each other, hugging Mech (like this one here), and generally just being happy. (I was the one with the camera, so many of them while I was there were taking turns having their picture taken, inspecting the preview on the screen on the back, informing me it wasn't good enough, and making me retake pictures. Oh, the cuteness.)

My dad actually got really excited by the entire experience. One thing we noted is that their computers were all really old and crappy; they had about ten, but only one or two would ever work at a time. My dad thought, "I have a lot of friends; we could easily get dozens of nice computers here." So he tried to help, to forge a bond, but apparently Mech just quit responding to his emails, the last I heard. I personally found the entire experience depressing rather than invigorating; it is difficult to see people making so much out of so little and not feel guilty for making so little out of so much opportunity in my own life. I'm still naive and idealistic; instead of seeing one potentially solvable situation, I see a whole helpless world full of Things That Should Not Be. In my head, I know what the world should be like, but the real world around me is so different that it's overwhelming to know how to go about fixing it. Well, there's that, and the fact that I'm incredibly cynical and impatient and people annoy me.

My father, you see, is different. (It takes a special kind of person to decide to visit the Phnom Penh dump on a tour of southeast Asia, yes?) He was a high school guidance counselor for almost 30 years, and somewhere along the way got involved with a volunteer organization associated with the state's Department for Juvenile Justice. Whereby "involved with," I really mean "founded," and whereby "Department for Juvenile Justice," I'm referring to "juvy," the prison where kids under 18 go. My strongest memories of Christmas morning when I was a kid don't center around getting up at the crack of dawn to run downstairs and see what presents I got; they revolve around getting up before the crack of dawn to drive out to DJJ to hand out bags of Christmas gifts to the teenage inmates there—gifts like pads of paper, pre-stamped envelopes, an orange, and a toothbrush. Since his retirement my senior year of high school, my father has poured himself into running this multimillion dollar philanthropic adventure. Explaining everything they do would require a whole other post, not to mention actually listening when he's going on about all of it on the phone.

My father's philosophy is that charity has its limitations; money can only go so far, and if you actually want to make a difference, then you need to actually do something. Charity is trying to treat symptoms ("we need to feed these hungry children!"), while philanthropy is trying to cure the cause ("we need to help these children's parents feed them!"). Charity makes people feel all warm and fuzzy inside; it has immediate gratification and results, and it's easier, but it the results aren't lasting. Philanthropy, on the other hand, is hard. Philanthropy requires thought, action, and inspiration in additon to mere money. It's one thing to give incarcerated kids prestamped envelopes, but it's something all together to try to change their lives and keep track of them so that when they get out of jail they don't go back to their old (criminal) habits upon returning home.

This is part of what has me cynical about the whole "Idol Gives Back" nonsense. I'm not saying it's bad; I'm saying it sounds like it isn't going to be as effective and useful as it could be. Money going to food doesn't solve problems; it merely postpones them until the next meal, while teaching people that they don't have to work for what they get. In Africa, wouldn't the money be better spent teaching safe sex and supplying condoms so fewer unwanted kids are born? Shouldn't we be trying to attack the problems instead of simply making ourselves feel better?

And, yes, I was glad to see Sanjaya go.

Friday, April 20, 2007

Please Step AWAY from the Dark Energy

An interesting essay by Simon White showed up on astro-ph Wednesday night entitled "Fundamentalist physics: why Dark Energy is bad for Astronomy." The whole thing is an interesting sociological read, highlighting in very clear terms the adage (mantra?) that astronomy doesn't want to become like particle physics:

Dark Energy is the Pied Piper's pipe, luring astronomers away from their home territory to follow high-energy physicists down the path to professional extinction.
This topic is big enough that both Rob and Sean have already commented on it (I was travelling! no interenet!). As someone who got into astronomy because cosmology was so interesting (I didn't like astronomy as a kid, and MIT doesn't have a separate astronomy department), I find this topic to be quite enlightening. Sure, we could all be working on what is arguably the "most interesting" topic, but what's the fun in that?

What I found most interesting in the essay, though, were the cold hard numbers behind the reality of the situation, i.e., how the culture of writing and citing papers has changed in the last, say, 30 years. The final figure in the essay outlines how the number of refereed papers, distinct authors, authors per paper, and references per paper have changed from 1975 to 2006.

The numbers in parentheses are the 1975 values.
By 2006 the number of authors had quadrupled but the number of papers had only doubled. On the other hand, the mean number of authors per paper also doubled, so that the number of papers signed by a typical astronomer remained constant at about 2 per year. The size of the astronomical community has thus increased dramatically and a drop in the mean productivity of its members has been masked by the tendency for more individuals to sign each paper. In 1975 over 40% of all papers in the major journals had a single author and fewer than 3% had 6 or more authors. In 2006 only 9% of papers had a single author while almost 28% had 6 or more authors.
As an extreme example, the fourth ranked astrophysicist by citations to papers published over the last decade has never written a first-author paper for a refereed journal and has gained almost all his citations through his right to sign official papers by a large collaboration in which he played a purely functional role
Why these trends occur and just how bad (or good) they are is harder to pin down. I know that big long author lists are extremely uncommon in most fields; are there even any other fields within physics that support papers with more than 6 authors on an "oh, that's normal" basis? I doubt we've found a nice equlibrium within the collaboration system yet: the benefits of "more people means more ideas" has to be balanced out by the fact inidividuals can get lost, e.g., that after the first author, it's difficult to track down just how much each author contributed.

Tuesday, April 17, 2007

I'm a Published Photographer!

Check out page 34 of the current edition (Spring/Summer 2007) of the Harvard Design Magazine! The issue, subtitled "New Skyscrapers in Megacities on a Warming Globe," has several articles discussing the interplay of urbanization and high-rise buildings. It's an interesting dichotomy I've never considered: on the one hand, it's presumably better for the environment for people to move to the cities and get around on foot and via public transportation than to live in the suburbs and guzzle gallons of gas each day, but on the other hand, if moving to the city means building tall buildings, then the fact that tall buildings consumer enormous amounts of resources should also be considered. This being a "Design" magazine, the role tall buildings play in their cities is also discussed at length; essentially, no one has yet found a way to pleasantly incorporate skyscrapers into cities that isn't off-putting or mildly hostile. They go over the history of skyscrapers; in the 1960s it was all about maximum volume efficiency, but then not only was it discovered that people are unhappy working in cubicle farms, but also that these new-fangled "computers" need lots of wiring, which requires extra space between floors. Additionally, all these extra electronics means extra cooling is needed; extra cooling in turn means more energy consumption. And so on. After several articles of people talking about buildings generating their own energy and being "green," they have a nice article entitled, "No Building is an Island." It pleases me to know that there are people actually thinking about these kinds of impacts, both on local and global scales.

The other aspect discussed at length is the rapid increase in skyscrapers: apparently, as of June 2006, "40% of the world's 200 tallest buildings have been completed since 2000." Furthermore, many of these buildings are in countries essentially saying, "Look! Our *ahem* building is taller than yours; we must be important!!" I definitely found this to be the ambiance surrounding the Petronas Twin Towers in Kuala Lumpor (I took the picture above, which was featured in this issue, looking down from the skybridge connecting the two towers about halfway up). The Petronas Towers were basically bought in order to showcase Kuala Lumpor for the rest of the world: in 1998, people were like, "Kuala Lumpor? Where's that? They have the tallest building(s) in the world now??" They are situated in the middle of a large park, the Kuala Lumpor City Centre (commonly referred to as the KLCC). There are essentially no other tall buildings nearby; the Menera Maxis building is actually directly adjacent and connected underground to the Towers, but as it is more than half as tall as the Towers themselves, from ground level they are nigh indistinguishable. From the sidewalk, there is just no good perspective; sure, they're tall, but I for one couldn't tell they were all that tall. For comparison, in March 2001 I stayed for a few nights at the Marriott World Trade Center in New York, and, yes, the World Trade Towers seemed quite tall, in part because they were noticeably so much taller than their already tall surroundings.

Having never even considered picking up and reading an architecture magazine before, I'm finding this to be rather entertaining and educational. If you can, you should go pick up a copy and read it. And check out the most excellent photography on page 34.

Monday, April 16, 2007

Post #100: Happy Blogiversary!

I apologize to my three loyal readers for having not posted much the last few weeks. I tried to make up for it by making the few posts much longer than usual, but the truth is, there has to be a good reason for my not mentioning such things as Coffee being mentioned on Cosmic Variance (apparently, we're fiesty!) or my winning a book for correctly picking The Number. You see, I am extremely silly and therefore had no choice to seize the opportunity to make my 100th post be one year after my first post. It wasn't very substantial, I know, and I didn't really start posting regularly until August or so, but still, a first post is a first post and a blogiversary is a blogiversary.

I could wank about how things here have changed over the past year (e.g., I no longer change the colors and template once a week, and I've even picked a title and everything), or ask for the zillionth time what people would like to read posts on in a desperate attempt to increase readership, but that would be both boring and pathetic. Instead, I've decided to celebrate this auspicious day by writing all about all of the topics I never write about.

First, there are all sorts of personal things I don't tell you about. For example:

  • Any significant other(s) I may or may not have or have had
  • The fact that though I live right next to a very active set of train tracks, the only irritating source of noise pollution in my apartment comes from the couple in the apartment above mine. They fight. A lot. Usually around 3a.m. (Hint: if she's yelling, "get the fuck off of me," you might be doing something wrong, man.) And then they freaking get up at 7a.m. and start banging around and vacuuming. Seriously, what kinds of people vacuum that early on a Saturday morning?? They must be vampires. Or, zombies. And I have started keeping my broom under my bed for just such special occasions.
  • Actually, there are all sorts of people who get on my nerves, and were this a non-anonymous blog, the title would probably be "a geocentric rant" rather than "a geocentric view," and you would be privileged with an explicit insight to one of my officemate's eating habits.
You may have also noticed I generally don't link to other people's stuff, blog posts or articles or youtube videos or what-have-you. Other than just not feeling inclined to, I suppose it's because I don't see much of a point in discussing what everyone else has already said. I also don't typically discuss "issues," though whether this is out of shyness or apathy depends on the specific topic. Take, for example, these two:
  • Gender/feminism/"women in math/science/technology"/blahblahblah: Apparently, this topic makes me rather snarky. The thing is, to first order, I just don't care. It's not that I'm particularly pleased with the current gender ratio in science, and it's not that I think "girls are dumb" (generally, I am inclusive enough to include all gender identifications in such a generalization). A lot of my frustration with this topic is centered on the fact that I don't think of myself as a "woman in science"—I think of myself as a scientist, and so when it comes to science, I get annoyed when people feel the need to apply such labels, even if it is to "applaud" all of the "obstacles" I've "overcome." The next level of frustration is do to the fact that, at least on the internets, a good number of the people who like talking about this crap are the types who blame every obstacle someone with two X chromosomes encounters on her gender. Maybe their parents didn't read "The Boy Who Cried Wolf" to them when they were little or something.
  • Religion or the lack thereof: I happen to have rather strong opinions on this particular topic, and like everyone else with an opinion on religion&c, I know my view is correct and yours is wrong and it's my duty as a human being to enlighten you. And, were we to meet in person in a non-professional setting and you were to bring up the subject, I'd let you know exactly what I think. But the interweb is different, and, for now, I'm just not ready to come out of this particular closet; in general, my family believes in a God and my readership does not, and it's up to the latter group to guess which camp my tent is in.
Well, now that I've effectively ruled out almost every non-science topic other science-oriented blogging types discuss, I'm sure I'll have no problem resuming a regular blogging-rate this week.

Thursday, April 12, 2007

"a geocentric view" is Not a Geocentric Universe

I recently got my first comment from some kook ascribing to the idea that the Earth really and truly is the center of the universe (of the, "I interpret the Bible as saying so so it must be true" type). I figure he can't be the only nutjob googling for support of the geocentric "theory" of the universe who finds themself on my blog, and every now and then geocentric whackos with too much power make the news, so I'll take this opportunity to make this perfectly clear:

Having a blog title "a geocentric view" is not the same as believing the Earth is the natural center of the universe; furthermore, anyone who actually believes that the Earth is the center of Everything is an arrogant, egotistical idiot of the worst kind.

Glad we got that settled. The idea (and the deluded who believe in the idea) that the Earth is the center of the universe is inane and archaic enough that I really don't see any sense in trying to explain it with off-center circles and diagrams and history lessons. If you are interested in the history and the math, though, I highly recommend the book "The Eye of Heaven: Ptolomy, Copernicus, Kepler" by Owen Gingerich. He gave a quite interesting talk here sometime last year which touched on a similar topic (though I think the material covered then was related to his more recent book, "The Book Nobody Read").

So since I'm on the topic, why did I choose "a geocentric view" to be my blog's title, if as an alive not brain-dead person in the 21st century I clearly know the Earth goes around the Sun? As I've already explained, the phrase comes from a poem by Auden; I like good poetry, so that's a good start. Partly from the context of the poem, the concept I get from the phrase "a geocentric view" is that regardless of whether or not the math and the paradigms are easier to stomach if the Earth is going around the Sun and the Sun is going around the Galactic center and the Milky Way is going towards Andromeda and the Local Group is going away from pretty much everything else in the universe—regardless of all of that—we are still people on Earth, observing the universe around us from the viewpoint of Earth. It's a geocentric view; no matter how much we know about the rest of the universe and our "real" place in it, those things that really matter to us (even to us astronomers) are those things confined to this pale blue dot, and no amount of learning will take that biased stance away from us.

On the other hand, the math really is easier if we let the Sun or the Galactic center the the origin of our coordinate system ...

Monday, April 09, 2007


Our department's chair of graduate studies met this afternoon with the students who will be taking qualifying exams this summer to (unsurprisingly enough) talk about taking qualifying exams this summer. The matter is made slightly more complicated than usual because the faculty are apparently discussing a new format for the written component of the qualifying exam.

Let me back up. The general idea is that graduate school consists of two components: becoming familiar with the language and basic material of the field, typically via classes, and contributing to the field via new research and publishing papers. Because one needs to have at least a rough grasp of and familiarity with the material in the field, it's standard for the first two years of a PhD program to be primarily dedicated to taking classes, and for the following years to be class-free and dedicated to towards the "dissertation," i.e., research. At the end of the first two years (or, rather, the completion of classes), students have to take "qualifying exams" (the exact name varies from institution to institution) to demonstrate that they have mastered knowledge of the field; after passing quals, they are given a Master's Degree. In a PhD program, the Master's Degree really doesn't matter... it's like getting a shiny gold star, or a consolation prize if at this point in their academic careers someone doesn't go for the PhD. (This is, of course, a markedly different paradigm from programs in which the Master's is the end goal.)

In our department, we have to take nine classes our first two years. This isn't as heavy as it sounds, since we're strange and on the quarter system; at any given point, we aren't taking more than 2 "real" classes. Because we're a small department (compared to, say, a physics or engineering department), all of the students take classes at the same time, so the graduate classes are offered every other year. At the end of the year, the 2nd year graduate students (e.g., me, this year) take the qualifying exams. Typically, qualifying exams ("quals") have both a written and an oral component. Currently, the written component consists of being tested—again—on the material from the nine classes. There are nine 45-minute exams (or eight if the professor from the last class [i.e., the last class ever!!] we took is feeling magnanimous and is willing to use the final as a qualifying exam) spread out, morning and afternoon, over two days. Each individual exam is written by the professor who taught us the corresponding class. To pass, one must average at least 60% over all of the exams. As you can expect, these exams are preceded by lots of freaking out and studying, and the time spent freaking out and studying is generally not accompanied by nice productive research. We're told we shouldn't worry about quals, and that if we have a good research track record by the time we take them, we'll pass, but from what I understand, that message doesn't exactly... sink in, shall we say. It is true that it's almost unheard of for someone to flunk quals here—rumor has it that it has happened once in the last five years, but no one seems to admit to knowing who it was. This is quite unlike other places who try their best to weed people out of the program. Why admit students you're just going to try to get rid of later? You prospective graduate students out there: when you visit schools you're considering, try to get a solid answer of what percentage of students in an entering class pass quals, and what percentage of students in an entering class actually leave with a PhD.

So the format of the qualifying exams might change. The philosophy behind the possible new format is that we've already passed all those silly classes; why be tested again on material we've already demonstrated mastery of? So, instead, we could do an in-depth excursion into a field of research we're interested in, like "brown dwarfs" or "galaxy formation." The proposed format consists of three parts: (1) summarize three papers in the field (two to three pages per summary); (2) do, and write up, some order-of-magnitude calcuation related to the field; (3) write a 5–10 page description/review of the current state of the field. One complication is that the University wants a guarantee that this is our own work, so none of these papers can include a copy-pasted bit from some other paper we've co-authored elsewhere (even if it's published and we are the first author).

If the faculty approve this change—and as uninformed graduate students, we don't know whether or not it will be approved—then we second-years get a choice between the old and new formats, because we've been told since we arrived that we would be given the old format. We each get to decide individually, which is nice, I suppose. I currently don't know which format I prefer. One the one hand, I absolutely loathe timed, written tests, and I think I know what I would do for the research field excursion format. On the other hand, the test-taking format is over at a set time: if I decide half an hour before the exam is supposed to start that I want to study for another week, then I'm shit out of luck because I have to take the exam anyhow. But for the paper-writing format, if I decide half an hour before I plan on turning the stack of papers in that I'd like to put another week of work in, I'm basically free to do so... which also means that I'm more likely to spend more time than desired (i.e., being a silly perfectionist) on the paper-writing format than on the test-taking format. Either way, it's a chunk of time spent not doing research; the question is simply how to minimize that amount of time and effort.

The oral component of our qualifying exams consists of a short presentation on some (not necessarily published) research we've done while at OSU. The trickiest part of this component is timing: it has to happen within 30 days of the completion of the written component, and we have to have a committee for it. A committee means four faculty members who are both in town and willing to basically sit and listen to the presentation; ideally, this is the same committee as one's thesis committee, but doesn't necessarily have to be. The problem with that idea, of course, is that it assumes that we know what the hell we want to do our thesis on, which some of us *ahem* most certainly do not. One of the problems with the old sit-down-and-take-tests format of the written component is that, since they are tests, all of the second years took them at the same time, so the 30 day clocks were all set at the same time. This year, there will be 7 students taking qualifying exams, so if our clocks all started simultaneously, this would mean that in one thirty day window, seven days would have to be found in which four faculty could administer the oral component of the qualifying exam. Not impossible, but since it's probably June or July, lots of people are out of town, and therefore it's common for the same faculty members to end up on lots of committees, which tends to make them grumpy, and no one wants a committee full of grumpy faculty members.

The next stage of this complicated process is the thesis proposal. The clock for the thesis proposal starts after the oral component of the qualifying exam; we have one year to get our thesis committees together and propose some topic for our theses. This typically means that thesis proposals happen in the late winter, early spring; the third year graduate students are currently wrapping up this process. There are some places that require a written thesis proposal, but since that's just unnecessary paperwork, here it's just another 15-minute presentation. This is actually the part that has me the most scared, but since I've got another year to stall on thinking about it, it's not so bad quite yet.

Friday, April 06, 2007

It Seemed Better Than Getting a Real Job

As a prize for myself for finishing my paper recently, I bought this t-shirt from PhD Comics. The text reads,


Which is, of course, fantastic. It's also completely true, in that I didn't have any desire whatsoever to get a "real job," and grad school was really the only choice for someone wanting to make a career out of astrophysics research. Annoyingly, the shirt is short-sleeved, and it's been freaking snowing here in Ohio the last few days, so I won't get a chance to wear it for a while. And, yes, after complaining bitterly about how too hot it was in my office, now I am complaining it is too cold.

Incidentally, Jorge Cham, the writer of Phd Comics, will be giving a talk at OSU the beginning of May. He gave a talk at MIT about two years ago, right as I was finishing my undergrad thesis. I really was planning on going, and I was looking forward to it it and everything, but I wound up taking a nice four-hour nap instead. A good friend of mine, who was a graduate student in physics at MIT at the time, went and bought both of the PhD books for me, and got them autographed. The third book is coming out soon, but unfortunately won't be available until after Cham's visit.

Monday, April 02, 2007

The Stryngbohtyk Model of the Universe

To the left is a figure depicting the shape of the universe according to the stryngbohtyk model of the universe, from Miralda-Escude (2007). The author recommends, "For better inspiration to think on the stryngbohtyk model, it is recommended to place an object as shown in the figure on top of one’s head." While this paper is not the only significant contribution to comedic cosmology on astro-ph today (see also Scott & Frolop 2007; Follop et al 2007, and be sure to read all of the footnotes contained therein), it is perhaps the one offering the best enlightenment on the relationship between dark energy and a certain famous equation:

As a note, the name dark energy for a component driving the acceleration is particularly bad among all the bad terminology that astronomers have made up, because Einstein discovered that
E = mc2,
(this equation is written here in case anybody had forgotten it), so everything in the universe is energy (and the name “dark stuff” would be no worse than dark energy). Moreover, dark means something that absorbs the light, whereas something that lets all the light go through without interaction should be called transparent, or invisible (which means detectable only through gravity, because Einstein found that nothing can be invisible to gravity).

Sunday, April 01, 2007

Variable Stars Near the Galactic Center

I'll try to make it through this post without making any snide or snarky remarks about how boring stars are and how they're really just point particles and how caring about any one in particular is just stamp collecting.


So apparently the majority of the papers I have first authored at this point in my career are about stars. I've even published an entire paper on just two stars (or one, depending on how you count ... the idea that "a binary star" is really two stars hasn't fully infiltrated the nomenclature, it seems). It took a lot of doing while writing this paper to figure out just why anyone would care about a bunch of variable stars; for the paper I wrote about dust structures at other galactic center, the explanation of why the topic is interesting was much easier to sink my teeth into (though "centers of galaxies are interesting because I get to look at pretty galaxies" is apparently not a sound argument).

This paper is about "variable stars near the Galactic center," where "near" is defined as within about 2 pc (about 6.5 lightyears) of the supermassive black hole, Sgr A*, at the Milky Way's center. I've put a completely gratuitous picture of the field below; the yellow X marks where Sgr A* is, the dots are on variable stars, and the cyan dots are the stars I actually talk about in the paper. The bar denoting how much 30'' is corresponds to 3.6 lightyears. This field of view (i.e., how much we can see) is larger than many of the stellar variability studies near the Galactic center, but still small enough that we can basically assume that all of the stars we are looking at are pretty close to Sgr A*. The metric I usually keep in mind is that the size of a resolution element when looking at nearby galaxies with the Hubble Space Telescope is 1–15 pc. In other words, this entire field of view would look like just a few bright pixels if it were in another galaxy.

Or, it would look like a few dark pixels, if we were looking at the galaxy edge on. And, because we are in the disk of the Milky Way, we are looking at the Milky Way edge on. This is why things like exactly where the center of the Galaxy is and the fact that the Milky Way is a barred galaxy weren't known until recently. Spiral galaxies like the Milky Way have lots of gas and dust in them between all of the stars (so it is called the "interstellar medium," or ISM). This dust absorbs light, so it is very difficult to see stars near the center of the Galaxy (which is thought to be about 7600 pc away these days). Because dust absorbs more blue light than red light, something sitting behind a whole bunch of dust looks redder than it intrinsically is. This is why absorption due to dust is referred to as "reddening," and why we have to look at infrared wavelengths to be able to see stars near the Galactic center.

The paper is essentially just a list of the 110 variable stars we identified; about 90 of these are new (depending on how you count). "Look, here's a list of variable stars and their light curves" doesn't make for all that interesting a paper—even if most of the list is new—so I put a decent amount of effort into trying to cross-correlate our catalog with known sources (known variable stars, of course, but also X-ray and radio catalogs) at the Galactic center. Many of our variables that matched up to other sources are fairly well-known, and even have names. One of these stars was IRS 16SW, which we wrote a paper on last fall, but I think the most interesting of the previously-known objects in our catalog is IRS 10*. This is our light curve for IRS 10*; the vertical axis is the K-band magnitude (remember, smaller numbers means brighter!) and the horizontal axis is in days. What makes this object actually interesting isn't that its brightness changed so much, but that by poking around in the literature (literally—remember that big pile of papers?), I found that there are several stellar masers and a bright X-ray source sitting at pretty much the same location. When I started this project, I definitely didn't know anything about masers, so here's pretty much all you need to know: (1) they are like lasers, except at radio frequencies, and they actually amplify light instead of merely letting it coherently oscillate; and (2) masers associated with stars are generally associated with stars with lots of gunk around them (the stuff actually doing the masing); these stars are usually "asymptotic giant branch" (AGB) stars, which are basically old stars that are busy shedding their outer envelopes. The idea that IRS 10* is an AGB star isn't all that exciting; what is exciting is that AGB stars are not bright X-ray sources, so if the nearby X-ray source actually is associated with IRS 10*, then it probably means that IRS 10* has some dead companion (like a white dwarf) which is accreting mass from the AGB star. (If the X-ray source isn't associated with IRS 10*, the question then becomes: what can cause such a bright X-ray flux and not vary at these wavelengths?)

When astronomers hear about a new catalog of variable stars, the first thing they almost always ask is, "how many periodics?" I spend a lot of time in the paper talking about two "enigmatic" variables with periods of about 42 days; basically after a page or so of babble I get around to saying we don't know what the hell these things are, except that they're interesting and we'd like to know, and that someone needs to try to take more data to figure out what they are. These are their light curves to the left; H and K are the names of the two filters our data are in. (When people started naming their filters back in the day, they gave them sensible names like "b" for the one that let through blue light and "r" for the one that let through red light. The filter just redder of the r-band filter is "i," for infrared, so when the filters started getting further into the infrared they just kept going to j, H, K, L, etc. So K band is redder than H band. And, please, don't think too hard about how the alphabet works right there.) The left-hand panels of the light curves are in days, like the light curve of IRS 10* above; the right-hand panels are phased according the period P so you can see what the light curve is "really" doing.

And just to completely fulfill the promise of this post's title, here are some of my favorite (read: prettiest) light curves from the paper ... for all of these, K band is on top and H band is on the bottom and such, just like before...