Sunday, December 25, 2011

Merry Christmas!

Many years ago on this day, an amazing child was born. This child forever changed the way we understood the world, and his ideas opened up an unprecedented era of enlightenment and discovery.
Happy birthday, Isaac Newton! 
* Thank you, Sam Collopy, for pointing this out. *

Tuesday, December 20, 2011

Merging Black Holes Pt. 2: Ripples in Spacetime

The above Youtube video shows a merging event generating gravitational waves. Now, this video shows two merging white dwarfs, but two merging black holes will do the same thing - only on a much larger scale. It seems crazy to think that this sort of event happens in the universe, but is currently invisible to us. However, in the coming years, that should change.

Gravitational waves are a hot topic in modern astrophysics. They are analogous to most waves, such as water waves or electromagnetic waves (light), except that they are ripples on the background curvature of spacetime itself.

So, what's the big deal with gravitational waves, aside from the fact that they're a cool physics buzzword?

Well, the most exciting prospect of gravitational waves is their potential in the study of different astrophysical phenomena. For most of astronomy, electromagnetic radiation has been the sole source of probing the universe (or, photons for short... it's amazing what we can learn from light rays). Electromagnetic radiation comes from the superposition of (mostly) randomly oriented photons being emitted or absorbed from electrons, atoms, or molecules. Gravitational waves, on the other hand, are generated most strongly from large bulk motions of mass. And, even more incredibly, gravitational waves are not dampened by intervening matter. As a result, the detection of gravitational waves should open an entirely new area of astrophysics previously unseen.  Perhaps, like the advent of infrared and radio astronomy, gravitational wave astronomy will usher in a new era of unprecedented scientific discovery and advancement.

Interferometers like the Laser Interferometer Space Antenna (LISA) and the Laser Interferometer Gravitational-Wave Observatory (LIGO) are currently the most promising ways to detect gravitational waves. Simply put, like most interferometers, a laser is shot at a beamsplitter, which splits the laser beam into two directions (usually perpendicular to each other). These beams hit mirrors, and are then reflected back to a detector, where they are recombined. *Note: I have simplified the process quite dramatically - I have never been very good with instrumentation, so I'm not going to try to go into any specifics.*

(Is it bad that I can't ever say laser without thinking of Dr. Evil's "laser")?

Very simple interferometer design, except for gravitational wave detectors, the movable mirror would not be moved by anything other than gravitational waves. The screen has a great example of what fringe patterns look like.
Since gravitational waves are ripples in the fabric of spacetime itself, a gravitational wave passing through a point in space causes the gravitational field to increase or decrease in magnitude. As a result, if a gravitational wave hits one of the mirrors, the oscillation in gravitational strength should shift the mirror back and forth. This causes the path length for one of the mirrors to deviate from the original value, so that when the beams are later recombined at the detector, the observed fringe patterns should change in accordance with the mirror oscillations. These fringe patterns can then be used to deduce the strength of the passing gravitational wave.

Gravitational wave schematic. The top portion shows the three phases of coalescence: the quasi-circular inspiral phase, the plunge and merger, and the ringdown. The bottom portion shows the amplitude of the emitted gravitational waves that correspond to the above merger process. (Image credit: Baumgarte and Shapiro 2011).
Black hole mergers, incidentally, are especially interesting in the study of gravitational waves. This is because gravitational waves are theorized to carry away most of the angular momentum and energy from these systems, which causes the merging black holes to coalesce. The above figure (that I scanned, sorry for the poor quality, ha ha!) shows a schematic of the phases of a black hole merger, and how those phases relate to gravitational wave strength. The top portion shows a cartoon of the merger, including the early quasi-circular inspiral phase, the plunge and merger phase, and the final ringdown stage. The bottom part shows the wave amplitude (or, strength) versus time. For two black holes approaching each other in the early inspiral phase, the emission of gravitational radiation causes the orbits to circularize and decay. Gravitational waves at this point will be at relatively low levels. But during the late inspiral phase, when the binary is in tight, circular orbits, and during the actual merger, gravitational waves should be at their strongest. This is where LIGO and LISA will be able to detect gravitational waves.

Unfortunately, even though the very early and late stages of coalescence has been simulated fairly easily, the actual late inspiral and merging phases are not as simple. For that part of the merger, post-Newtonian and perturbation methods break down. Therefore, providing templates for the signatures of merging black holes requires advancements in numerical relativity, which will push computational techniques to their limits. 

For more info, please see:
Abramovici, A. et. al 1992, Science, Vol. 256, pp. 325-333
Baumgarte, T. W. & Shapiro, S. L. 2011, Physics Today, Vol. 64 No. 10, pp. 32-3
Berti, E., Cardoso, V. & Will, C. M. 2006, Phys. Rev., 73, 6

Monday, December 12, 2011

Merging Black Holes Pt. 1: An Introduction

There are monsters in the night sky. If you were unfortunate enough to pass by one, there would be nothing to stop the inexorable pull toward destruction. But for such behemoths, you wouldn't be able to see them. You could see the effects of their hunger (if they happened to be hungry) in bright, energetic X-rays. But that's all. That's all you could see of one of the mysteries of astrophysics today - supermassive black holes.

However, funny enough, these monsters may see and remember you. According to Stephen Hawking, black holes can dissipate, because the huge gravitational field may occasionally pop out particles (it's all about E=mc2, where energy is converted to mass). Over time, as more and more particles are ejected from the black hole, the mass that originally fed the black hole will once again return to the universe, making the black hole no more.

Artist rendition of a black hole. All images stolen shamlessly from the internet.
Massive black holes are everywhere in the universe, yet their formation is still largely unknown. Cosmological models suggest that massive black holes form from the mergers of smaller seed black holes, but can we reproduce this behaviour in simulations? Do these simulations generate surprises about relativity we previously didn't know about? In the next 5 posts, I'll discuss recent simulations of black hole mergers, some of the main techniques used for handling computational relativity, and possible observational signatures of these merging monster systems. Oh, and spoiler alert - there will be a surprise from these simulations, which suggests that there are some things about General Relativity that can continue to surprise us.
Feeding black hole.

Black holes are relatively simple objects compared to most physical systems. They are described by analytic solutions to Einstein's equations of General Relativity, and depend on only three parameters: charge, mass, and spin. For most astrophysical black holes, the description is further simplified because the charge is usually set to zero. This happens because in the accretion disk, the charged, ionized material rearranges itself to neutralize the black hole charge at large scales. More specifically, the gas is treated as having infinite conductivity and is therefore able to support infinite currents. These currents are generated from charge imbalances and move charges in such a way as to cancel charge imbalances, thus causing the whole system to neutralize.

Black holes also span a ridiculously large range of masses, from the predicted tiny holes from string theory to supermassive holes as large as some small galaxies. However, it is still unclear how supermassive black holes are formed. Population III stars are thought to be one of the most likely sources of the first seed black holes. These stars are the theorized first generation of stars, and consequently form from the primordial gas of pure hydrogen. A consequence of this is that the gas is unable to fragment during the formation process, meaning that these stars are extremely massive and live fairly short lives. It is predicted that the stars with masses of 25 and 140 times the mass of our sun formed the first seed black holes.

However, there is a problem with this scenario. This problem arises in the growth of these smaller seed black holes to the supermassive black holes seen today. If black hole growth proceeds purely by accretion, a liberal estimate of a growth timescale can be computed if the black hole accretes at the Eddington rate. If it is assumed that Population III stars form 100 solar mass seed black holes, then it would take roughly 0.8 Gyrs (or 800 million years) of continuous, uninterrupted accretion to form a black hole of 1 billion times the mass of our sun. But, according to observations, quasars at a redshift of z=6 have been observed. This means that massive black holes must have been in place when the Universe was only about 1 Gyr (1 billion years) old. This means that given even the best estimates for black hole growth, black holes would have had to start accretion in the universe's infancy. Therefore, there must be another mechanism that increases the black hole mass rather quickly.

The current cosmological understanding is that large black holes must then grow bottom up, where small seed black holes merge to form successively larger black holes. In this way, the formation of supermassive black holes can proceed at the quick pace observations seem to imply. But how common are black hole mergers? And if they did merge, do we know if they'll act the way we think they'll act? 
Rendition of a quasar.

In addition to the growth rate of black hole formation, supermassive black hole formation scenarios must also provide explanations for their role in galactic evolution. It is undeniable that large black hole formation is a common occurrence, since they reside in the vast majority of galaxies (in particular bulge galaxies). They are also known to be the source of quasars and active galactic nuclei. To date, though, the interaction between black hole formation and their environments are only just being explored.

But, even though this field is in it's infancy, it seems like a promising avenue to study how the universe works in conditions wholly alien to us - to push the boundaries of the physics we know into the physics of the unknown. 

* Note * This is just a compilation of knowledge I have read from people who actually do this kind of research. I haven't included references in the proper style for fear that someone may use this as a paper. But, I don't feel right about not acknowledging the people who provided us with this knowledge. If you are interested in this subject, please please please look at these sources!

Baumgarte, T. W. & Shapiro, S. L. 2011, Physics Today, Vol. 64 No. 10, pp. 32-37

Carroll, B. W. & Ostlie, D. A. 2007, An Introduction to Modern Astrophysics: 2nd ed., Pearson Education Inc.

Fan, X. et. al 2001, AJ, 121, 54-65

Madau, P. & Rees, M. J. 2001, ApJ, 551, L27-L30

Madau, P. & Quataert, E. 2004, ApJ, 606, L17-L20

Volonteri, M. 2010, Astron. Astrophys. Rev., 18, 279-315
This is a really good review paper on black holes, by the way!

Monday, November 14, 2011

Grad School Lesson #1

Well, I feel like a jerk. I wrote a post about how much schoolwork we grad students get, but then we get a week off of homework. Dang.

So, now I've decided to keep a running, improvised set of lessons from grad school. Perhaps these tidbits will be useful to you. Or... perhaps not. But, for the sake of knowledge, my first lesson is:

Lunchables are made for children, and do not make a good meal substitute.

I was hungry the entire day, and the sugar from the dang thing put me in a very silly mood. Case in point: this picture made me laugh for way longer than it should have....

Hmmm... I really should have wolfed down some caffeine, just to see the awesomeness that would have ensued. But, alas, I didn't, and I spent the rest of the day giggling in my office. I wonder what my office mates thought about that...

Also, do not touch other people's erasers.

Don't even do this by accident. Some grad students are very territorial about this.  Even if it's not their erasers.

Until next time, happy computing. I'll be kicking my computer in anticipation of the next post. :)

Tuesday, October 25, 2011

Advisor Meeting Analog

I'm pretty sure this is how most advisor meetings go.Thanks to Ryan Shea for finding this. Hopefully he won't find out that I shamelessly stole this from him on facebook.

Sunday, September 25, 2011

The World Is Beautiful

This past week was a bit stressful. I felt like I was running around doing things, but not really accomplishing anything. Things happened that were out of my control. 

Sometimes it's hard to let these things go.

Sometimes it's hard to keep going through grad school, because I realize how little I know. Sometimes I get caught up with trying to be the best, when the "best" is some ficticious concept we all made up.

I remember when, as an adolescent, I picked up a telescope and stared at the wonders of the sky. I felt pretty good about myself. Then I went through high school and college and got into a great grad school. University of Arizona is the $#&%. Everybody is intelligent. Everybody is passionate. Compared to these people, I felt at best average. Suddenly, being good wasn't... well... good enough. I wanted to be best. It wasn't enough to pick up a telescope anymore and have fun.

Ah...  the shackles I imprison myself in!

So, this morning (while procrastinating on starting on some homework), I was surfing through some youtube videos. I stumbled on one made by the amazing photographer Terje Sorgjerd. I don't know if everyone has already seen this video, but I think it's breathtakingly beautiful. It reminds me that the world is beautiful and that it's more than made-up definitions of success. But enough of me, I'll let you decide for yourself (only, I highly recommend you go full screen on this one).

Tuesday, September 13, 2011

AGN Activity Increased by Galaxy Mergers?

Sometimes I forget the amazing things we take as given. Some months ago, a friend of mine asked if scientists had ever figured out if black holes exist. I replied by saying:

"Well, DUH! Of course they exist! They exist at the centers of every known galaxy. That's something everybody knows, right?".

If you really think about it, though, black holes, and their existence, are astounding. They are so astounding, in fact, that the man who predicted their existence was convinced they were too weird to exist in nature. That man was Albert Einstein.

Today, it's pretty conclusive that black holes are ubiquitous throughout the universe. They range in size from about the mass of our sun to gargantuan masses of billions of times as large (although there seems to be a curious deficiency in intermediate mass black holes - which would connect the smaller, stellar mass ones with the supermassive ones at galactic centers).

Establishing that black holes do exist, and are quite common, I'm going to go further and say that astronomers have seen two main types - those that are actively accreting gas, and those that lie dormant. Our Milky Way's black hole is a dormant type, and the ones currently feeding are called AGNs (Active Galactic Nuclei).The pretty picture below (stolen shamelessly from somewhere on the internet), shows a representation of an AGN.

Though there are different types of AGNs, they all are thought to stem from one physical model (more or less, there are still fights about specifics). In short, the rotating supermassive black hole is surrounded by a heated accretion disk. The continuum radiation from the infall of gas into the black hole photoionizes the surrounding gas, which creates emission lines we can see on Earth. In addition, a large disk of clumpy, optically thick clouds (or, clouds too thick to see through in some wavelengths, mainly optical in this case) surround the accretion disk, which can obscure some AGNs if the AGN is oriented in such a way that the clouds are between us and the black hole. Some AGNs also host twin collimated jets. These outflows emerge in opposite directions from the central black hole, and travel at velocities close to the speed of light. Heated bubbles from these jets can reach massive sizes, and how these jets impact galactic evolution (for it seems very likely they must have some effect), is not well known.

This all brings me to a paper I presented at Science Coffee last Thursday: The Impact of Galaxy Interactions on AGN Activity in zCOSMOS by Silverman et al. This study looked at pairs of interacting galaxies using Chandra X-ray data and the spectroscopic redshifts from zCOSMOS. The main point of this study was to see if galaxy mergers could increase the chances of AGN activity. The main thought is that if a gas-rich galaxy began the process of merging, the gas transferred from that galaxy could provide the fuel to feed the supermassive black hole.

Previous studies have been inconclusive about the effect of galaxy mergers on the probability of AGN activity. These studies (well, the ones mentioned) used Hubble Space Telescope (HST) observations to detect AGN activity, and they tended to conclude that they saw no significant increase in AGNs with merging galaxies. However, Hubble observes in optical wavelengths. Because of this, the thick clouds around the accretion disk could hide AGN activity, depending on the orientation of the galaxy. In an effort to get a more complete sample of AGNs, this new study uses X-rays from Chandra to detect AGNs, which are able to pass through the clouds.

To determine if galaxies in their survey sample were interacting, the authors looked at interacting pairs of galaxies between 0.25<z<1.05, distances of less than 75 kpc apart, and velocity differences of less than 500 km/s. This, of course, does not include galaxies that have already merged. The figure below shows some of their interacting pairs. The left panels show Chandra X-ray data (AGN detections), and the right panels show HST images. The red crosses denote AGNs, and the yellow crosses denote centers of normal galaxies. (Sorry this is so small. This is the largest size I can get on the blog).

They found that AGN activity was more common for interacting systems by about a factor of 2 over AGN activity in galaxies not interacting. In addition, for just the interacting pairs, they found a higher fraction of AGNs for lower physical separations and lower velocity differences. This seems to support the idea that more closely interacting galaxies were more likely to host an AGN. They even found a slight increase in AGN probability for interacting galaxies that were more comparable in size (though their sample was not statistically large enough to make that a very strong conclusion).

I think this study does make a point that galaxy mergers may have an effect on the probability of a galaxy hosting an AGN. How big is that effect? I don't know. Like the authors, I do agree that galaxy mergers can't be a dominant factor in deciding if a galaxy is active or not (about 80% of the AGN sample were in galaxies not interacting). However, they do seem more likely to spur AGN activity, and because of that, shouldn't be discounted entirely. 

Tuesday, September 6, 2011


Hello all! I realize that I've been on a doom and gloom mood as far as blog posts go. My life could be much worse right now - I could, in fact, have been forced to TA. For those of you who do, I give you full permission to slap me across the face whenever I complain about anything.

I'm not kidding about this. 

I am actually in quite a good mood right now, despite the fact that SExtractor doesn't work consistently for all my survey images. Overall, I'd say this semester is going much better than last year. I've only cried a couple of times so far (just kidding... mostly) :) .

In celebration of this, and because I'm a pro at procrastinating, I give you two montages. Montages are always fun. These particular ones are stellar-centric, because I'm supposed to be doing work for my Stars and Accretion class right now. My homework guilt has convinced me that if these videos are related, I'm doing something productive... Anyway, less words, more show!

Life of a Star: 12 Billion Years in 6 Minutes
Sorry, this video won't embed. Just click on the title. It'll link you to the youtube video.

Sol Invictus
This video has some annoying text over some of the images, but I still enjoy it. If you know me on facebook, you'll have seen this before. So deal with it!

Wednesday, August 31, 2011

The Future of Astronomy?

Let me start off by saying that I had a really, really bad day.

I started off by making a major mistake. After I made sure my program was still chugging along, I surfed the web for current outlooks on the astronomy job market. Yes, I'm an f-ing genius. It was, as so many post docs say, positively depressing. Too many PhDs, too little money, too little opportunities... etc.

Post docs spend the majority of their time stressing about the number of papers they publish. It's considered that any less than 1-2 papers a year is a death sentence for getting a faculty job, no matter how good their papers may be. Despite what most people say, in astronomy, quantity trumps quality.

Then, in a quirky twist of fate, I went to Science Coffee, where we briefly discussed a paper on applying economic principles to astronomy. The gist of the paper was about how the scientific community could gauge the "value" of a theory (though I assume this applies to most research projects in general). The value of a theory could be determined by such factors as growth rate in the field, number of faculty jobs, number of cited papers, etc. With this in mind, appropriate projects could be pursued, and grant money would be allocated to the projects deemed most valuable. Now, this paper in and of itself may not have much lasting impact. Most people in the room kind of snickered at it or dismissed it entirely, but it made me angry.

No. It made me really, really angry.

My idealized, rose-colored vision of how astronomy functions is quickly diminishing, and this paper is a symptom of it. With all this focus on publication rates, it's no wonder arXiv papers have become so boring. Nobody can tell me why their research is important, because nobody wants to do a risky project. Nobody wants to do a project that will take longer than 1-2 years to complete. That could impact publication rates! No, it's much better to choose a safe, non-threatening project that can be done will minimal effort. Plus, if it's safe, it's much easier to get that research grant approved.

This, in my opinion, has only one effect. It breeds conservatism and stagnation within the field.

Once upon a time, I thought scientists were the heroic people who did science for the love of science. In reality, scientists are forced to do science for the publications. I understand that research will always be impacted by what money-granting institution thinks is in vogue, but that's no reason to buy into it entirely. Yes, some major discoveries were intentional, but the vast majority of major discoveries came by accident. If we all knew where to look, don't you think we would have done it already?

Discoveries are built upon surprises and the unexplained. They are built upon innovation, creativity, and a healthy heap of luck. How can you put a number of publications on that? How do you define if this risk is good or bad?

I was once told that the hard work science demanded was rewarded when you got to be the first person in the world to understand something. Think about that feeling for a second. I wonder how much it happens anymore.

A part of me understands that astronomy is a field in contraction. The competition is so fierce for so few academic job openings, that nobody will dare go against the status quo. That would be career suicide. But some part of me wistfully thinks back to Agent Fox Mulder of the X-Files, who always pushed his wild theories because he knew he was onto something. It didn't matter what the people around him said, or how much he jeopardized his career. He was going to try and collect the proof he needed.

Corny, I know, but I think the spirit of it is beautiful.

Wednesday, August 24, 2011

Why Intrinsic Ability Does Not Matter

I'll let you in on a secret.

I am not naturally good at math. I am not naturally intelligent. If you were to put me on a distribution of general "smartness", I would be smack dab in the middle.

This is not easy for me to say.

In third grade, I remember being tested for the Gifted Program, which was just a group dedicated to teaching the best and brightest kids at an accelerated rate. Though I scored extremely high on the reading portion, I tested two grades below on mathematics. Needless to say, I did not get in.

I remember when I was told of my deficiency in math. At that time, I didn't want to be a scientist. I didn't want to be anything. To tell you the truth, I would have been perfectly happy to spend all my days reading. But, for some reason, my lack of mathematical ability bothered me. It truly, truly made me upset - not at the teachers, but at myself. So I went home and told my mother that I had to learn the subject, and that I would be willing to devote my entire summer to it if I had to.

I kept true to my word.

In high school, I consistently scored perfectly on anything written or literature based. I always scored consistently lower on math. It was a great source of shame for me, because by that time, I knew I wanted to go into science. What scientist isn't good at math? I knew that if I didn't understand math, the framework for how the universe works fundamentally, then my understanding of how the world works would be severely impaired. So I kept trying, and enrolled in the highest level math classes I could. By the time I graduated high school, I had taken two years of Calculus. Not shabby for someone who used to be two grades behind.

My friends at the time told me they admired my natural math ability. They said they couldn't ever do math because they weren't wired for it. They claimed people had to be born with the ability, because it couldn't be taught. I tried to tell them how wrong they were.

I now have a minor in Mathematics. I have more training in math than most people in the world. The thing is, I'm not naturally "wired" to do it. I just did it.

Now, I don't want to claim that intrinsic ability doesn't matter at all. It does. I will always have to work twice as hard to learn concepts or complete research. I positively suck at programming. I probably won't ever stand a chance getting a job in academia, because truly talented people work just as hard as I do. But you know what? I've made my peace with that. I went into a hard field because I like it and because I needed to at least try.

There comes a time in most people's lives when they realize that life isn't fair. Some people are born with it all - whether it be beauty, intelligence, charisma, or all these things. I don't know what separated me from my old friends, the ones who were content to throw their hands up in the air. I don't know why I was spurred into action, when so many people around me passively accepted their "inabilities". I don't know why knowledge, for it's own sake, was so important to me, but not necessarily to others. I usually give up pretty easily, to tell you the truth. Today, I could learn a lot from my younger self.

I don't know if there's a point to this, other than nothing should hamper your ability to learn. Don't believe for a second that anything is above your understanding - not math, not physics, not anything. Don't let other people make up your mind for you. It all comes down to what skills you actively pursue.

And though it may be above my level to be the best scientist, I can certainly become a good one. That counts for something.

Monday, August 15, 2011

If I’m So Smart, Why Did I Wear Pants Today?

Aaaaaaah . . . the start of a new semester is in a week. I feel strange now that I’m a second year grad student. I’m also a bit sad that once classes start, I’ll have to put a hold on watching the X-Files while eating rainbow sherbet.

It occurs to me that I haven’t written about actually being a grad student. It also occurs to me that this might be because it’s not really that interesting. But, unfortunately for you, this is what I’m going to attempt to do. So ha!

I wake up and it’s always hot. Really, really hot. . . . and humid sometimes. I decide today to wear pants instead of shorts, because I’m not really a shorts kind of person. I actually hate wearing shorts and flip-flops, but summers in Tucson are like the death throes of Sylvia Plath – you feel like your head is in an oven, frying your brain until you go slightly crazy with each passing day. So, I usually make due with the least amount of clothes I can live with. If I make it to my air-conditioned car before death, I can watch fried people on the street do stupid things. For instance, I saw a woman screaming to herself on campus today. Some may call her crazy, but I call her a “Native Tucsonian”.

When I make it to my office, I prove (like I always do) that I’m not as smart as I think I am. I volunteer to give two talks during the semester over email. Why? Because I can. Was that a smart thing to do? Absolutely not. Nonetheless, I notice that my email must be controlled by a secret government project, because the next time I look at the clock, it’s time for a meeting with my advisor.

Advisor meetings always go the same. They go something like this:
Advisor: Hello. How’s it going?
Me: I made progress! See?! See?! Please believe me . . . LOOK AT MY PLOTS!
Advisor: They look a little funny. Did you think of [insert easily foreseeable problem].
Me: Oh. Yes. I should have thought of that.
Advisor: Ok. See you later.
This takes 3 minutes (ok, I may be exaggerating a little here. It takes around 5 minutes).

After I get direction, the real work begins. It starts with me looking sadly at my iraf script (iraf is a computer language I use to do some of my work). Then I open up lots of internet browsers in search of something to fix my code. I get a headache within 20 minutes. However, it’s ok, because now it’s lunch time!

I walk through the scorching desert heat in search of food. I wish I had worn shorts instead of pants.

I get back into the office. I’m uncomfortable because my pants are now sticking to my legs. Ugh…. I hate that feeling. Now, where was I? Oh yes, trying to understand iraf… I get my headache back again. I curse and scream because iraf uses different parsers for the command line and its scripts. So, even though I find something that works on the command line, it doesn’t work in the script. After a couple of hours, I find out the weird little problem that kept my script from working. It was something about assigning structures before strings? Heck if I know . . .

I get tired of working. I visit another person’s office, steal their wheelie chair, and push myself in circles for half an hour. I make a lame joke and laugh for way too hard, way too long. It is at this insane moment that I decide I can tackle iraf again.

I run my program again. It doesn’t work, even though I changed nothing. I finally realize that iraf was made by the Devil . . . er, no . . . Astronomers . . . what’s the difference? I laugh out loud. I decide to go home. I walk to my car.

It’s really hot outside.

When I get home, I put the X-Files on. I change into my pajamas, eating rainbow sherbet. I write this blog. I’ll repeat this day tomorrow, and perhaps the day after that, but one thing will be different: I’m going to wear shorts instead of pants.

Tuesday, August 9, 2011

Thick Disk Formation and Finding Missing Baryons

I read a recent paper some days ago, entitled “Thick Disks of Edge-On Galaxies Seen Through the Spitzer Survey of Stellar Structure in Galaxies (S4G): Lair of Missing Baryons?” by Comeron et al. I decided to read this paper mainly because the authors were using the S4G survey, which is the same survey I'm using. The S4G survey is an infrared survey using 3.6 micron and 4.5 micron data from IRAC. These wavelengths are sensitive to older stellar populations and have reduced contamination from dust and star formation.

These authors looked at 46 edge on galaxies, to determine properties of the thick and thin disks. A thick disk in a galaxy is characterized as having a larger scale height (or, roughly, thicker cross section) than its flatter thin disk. The thick disk also tends to have older stars and a lower surface density (7% of that of the thin disk for the Milky Way). It's been a bit of a puzzle why these two disk populations exist, but an understanding of how the two disk components are related to galaxy formation will help us unravel clues to the processes that drive galactic evolution (hmmm... seems to be my favorite subject, but too bad! It's my blog!).

There are a couple of interesting things these authors found. First, they claim that thick disks may have a larger stellar population than previously thought, and second, they claim to have a better understanding of how thick disks formed.

Most of the paper is on the specifics of their model, which is way too complicated for a blog post. If you're interested in their modeling techniques, I suggest you read their paper. Long story short, the authors fit two stellar populations together to represent the thick and thin disks, Then, after they decided on what to assume for the numbers of small stars formed vs massive stars, they generated a mathematical description of how the luminosity of these galaxies should look like. They generated multiple models, assuming different stellar populations in the disks. Then, they simply compared those luminosity models to the actual data.

What they found was that the best fit to their models was a thick disk comprised of ¾ to as much as 3 times what we had previously thought, depending on which model was used. Of course, this may be highly model dependent, but all the models agreed that there is a higher stellar population in the thick disk. Now, why is this important? It's important because we haven't been able to account for all the universe's baryons. There was some speculation that the missing baryons were driven into the intergalactic medium from supernova feedback, but that scenario can't account for all the missing baryons. Perhaps this is the missing reservoir (hence the title of their paper!).

Also, the authors propose a formation scenario for thick disks. There are four different models for thick disk formation, which I'll abbreviate here:

Model 1: The clumpiness of galaxies can create overdensities that may perturb stellar orbits. These overdensities may come from spiral arms or molecular clouds. Astronomers do believe that young galaxies may have had a clumpier structure, but this model has difficulty describing the highest velocity stars.

Model 2: The young galaxies could have passed through dark matter clouds or other galaxies. This scenario, though, cannot produce a a thick enough thick disk when large quantities of gas is present. Also, these interactions usually produce a flared disk, which is not seen in the galaxies in this survey.

Model 3: Thick disk formation could have been a result of in situ star formation. The best candidate for this is . . . surprise . . . galactic mergers. The gas forming the thick disk would be dynamically hot from the merger, which could produce a thicker disk. The only problem with this model is that the accretion of external gas shrinks the disk, making it virtually indistinguishable from the thin disk. However, if you increase the mass in the thick disk, the net shrinkage would not be such a problem.

Model 4: Interactions with other galaxies may have donated stars via tidal stripping. However, this mechanism can't produce a large enough stellar population at present.

The authors suggest, in light of their observations, a thick disk formation scenario favoring in situ star formation. They believe that young protogalctic clusters may have merged, producing a hot disk of stars. Since they detected a higher population of thick disk stars, the later accretion of external material did not shrink the size of the thick disk by much. Then, once the galaxy aged and accreted cold gas, the thin disk was formed.

I was pleasantly surprised by this paper. I initially thought it would have nothing to do with my research, but in the end, it may. The conclusions seem to support galactic mergers as an important mechanism for galactic evolution, which is something I'm looking for. It would be interesting to see if thick disks vary depending on cluster environment, and, if so (or if not!), why that would be the case.

Saturday, July 30, 2011

A Look At Our Solar System

I love showing this youtube video about the asteroid discoveries in our inner solar system. Scott Manley takes the positions of detected asteroids, and highlights them as they are discovered. The final colors indicate how close they are to the Earth's orbit:

Red= Earth Crosser
Yellow= Earth Approachers (coming within 1.3 AU)
Green = All Others

The discoveries tend to follow the Earth's orbit because asteroids are best seen opposite the sun, when they are most illuminated. It's also interesting to see that discoveries go way up in the 1990's, when satellites start coming online. This is a cool way to highlight the importance of technological advances to scientific discoveries.

And, if you think this looks like a crowded mess, the Kuiper belt around the outer solar system is about 20 times as wide!

I love videos like this because they are sobering reminders of the vastness of space. As dense as these asteroids look, they won't collide with each other. In fact, movie scenes of spaceships dodging chunks of rocks in the Asteroid Belt is just plain wrong. The Asteroid Belt is mostly made of empty space. Yup. That's right. That's how BIG space is!

In the spirit of the late Carl Sagan, I sometimes think about how tiny the Earth is in this video. I really try to visualize it's place in our tiny corner of the Milky Way. It's just one planet circling one average sun with a half million other chunks of rock. Then, sometimes I think about the wars fought over this planet - the wars of death and human misery that were caused by zealous rulers intent on owning a piece of this tiny rock. You wouldn't be able to see the boundaries we fight so fervently for. Astronomy is, like so many people say, a humbling field. In the grand scheme of things, everything just seems so . . . small.

Thursday, July 28, 2011

How Grad School Differs From Undergrad (In My Experience)

It seems insufficient to say that grad school is way different from undergrad. It just doesn’t seem to communicate the true significance of the change in environment and expectations as the transition is made from one to the other. I guess it really depends on where you came from, and where you are going, but some people handle it better than others. I was not one of those people. I will probably write a bit about why I feel I’ve faltered in some sense with grad school. It’s been on my mind for nearly a year now, and now I think I see things more rationally.

I came from a small undergraduate institution, called the New Mexico Institute of Mining and Technology – or, New Mexico Tech for short. Though most people have never heard of it, this school is actually quite a diamond in the rough. The National Radio Astronomy Observatory (the very same one that runs the Very Large Array) was right off campus. An optical interferometer owned by the school was in its construction phase during my time as a student, which will be built right next to the Magdalena Ridge Observatory. Military money for research was donated in such copious amounts that the school had funds coming out of its ears. Because of that, I was able to earn a college degree with absolutely NO debt. Heck, when I moved off campus, NMT wrote me a check.

Along with being dirt cheap, New Mexico Tech also had the best physics department around. Whereas most people never see their department heads, mine knew I was a member of the Astronomy and Physics clubs without my having to tell him. When it was time to write grad school applications, he sent me his personal proposals (some that were effective, some that weren’t) and edited my essays not once, but three times! Making friends was effortless. I felt so connected to every person on campus, be it faculty or student, that I knew if I ran into any problems, there would people to help me whether I wanted help or not.

Those years were some of the happiest in my life. And perhaps, this is my plea for you to understand why I was so unprepared for the dynamics of a large school.

I assumed every place worked like Tech. Ridiculous assumption, of course, since a larger school simply cannot support such a tight knit community. The biggest thing I needed to learn about grad school, and the thing that new grad students should know, is that your advisor can’t dedicate as much time to you as you may need. Unlike the professors at Tech, they simply don’t have the time for it.

This seems a bit harsh, but in the end, it may be a necessity. My former advisor told me that he was so swamped with work that the only time he had for his own research was Sunday nights, when he supposedly wasn’t supposed to be working at all. Adding the emotional frailty of a self-conscious student with huge confidence issues would be too much. Besides, what was he supposed to say?

In reality, you are no longer viewed as a young undergrad. Grad school is training for a job, and your job is to turn out product (papers) as fast and as efficiently as you can. You cannot earn the respect of other professors or scientists by whining about how alone you feel.

Understand, too, that your project will not be a major focus in your advisor’s life. You will have to deal with untimely delays, and you will have to be the one to search for help when you need it. Nobody will hold your hand through the process.

Then again, would I really want it any other way? How can I become an independent scientist if I’m not weaned from “free” projects?

Please know that I am not ragging on the Astronomy Department here at the University of Arizona. Along with the small growing pains of the first couple of years, there are many more opportunities at a larger university than I would have had at a smaller one. Instead of one colloquium a week, there are many, many more. There are small discussion groups dedicated to specific research topics. One professor gave me awesome advice when searching for an advisor, and another one gave me great criticism on a talk I had given. I’ve even found that when I crossed the street to the National Optical Astronomy Observatory for Friday Social Hour, the astronomers there were kind and warm.

And, the other grad students are an awesome resource as well! I cannot stress this enough. They can help you with coding/homework problems, give you inside information on people’s advising style, and teach you how to write proposals effectively. Do NOT pass up your peers – they’ll probably know a lot more than you, and will be happy to put off doing their own work to help you out.

Monday, July 25, 2011

Amazing Picture of a Planetary Nebula

While waiting for my code to run at work today, I stumbled across this image of Kn 61 from the Gemini Telescope. This is known as a planetary nebula, where bubbles of gas are thrown out from a dying star. Ultraviolet light from the hot, dense core light up the expelled gas, creating the beautiful object seen below.

I've seen a lot of astronomy-related images, but this one is one of the coolest I've seen in a while. Wow!

Wednesday, July 20, 2011

Globular Clusters: Tracers of Galactic Evolution

Globular clusters are a tight aggregation of hundreds of thousands to millions of stars. They are very old, devoid of gas, and have stellar populations that share the same age and chemical composition. To give you an idea of how old these systems are, it’s known that the Milky Way's globular clusters have ages ranging from 10-15 billion years. This means that these clusters could be relics of the formation of the Milky Way itself!

Empirical observations show that globular cluster luminosities are roughly proportional to the stellar mass of their host galaxy, which suggests that the formation of globular clusters and galaxies are related. However, how they are related is currently not well understood.

In addition, globular cluster populations in the Milky Way exhibit a curious bimodal distribution in their metallicities, where one group belongs to a metal-poor, spherical halo surrounding our galaxy, and another group belongs to a metal-rich, flattened distribution in the bulge and disk portion of the galaxy. Metallicity in astronomy simply refers to how much iron (or metals) is in proportion to hydrogen - the higher the metallicity, the higher the fraction of metals and vice versa. West et al (2004) provided the shown histogram of cluster metallicities for three galaxies. Again, why there are two distinct populations of globular clusters remains in disagreement. What is known is that the vast majority of other galaxies also have metallicty distributions with two or more peaks.

Although globular clusters are interesting in their own right, and can fill many books, I'm particularly interested in what they can tell us about galaxy evolution. There are two competing theories about cluster formation, with different implications about galactic evolution depending on which model is correct:

Model 1: Globular clusters are formed early in their respective galaxies, but are captured or cannibalized from subsequent mergers. If two galaxies collide, it is not unusual for the smaller galaxy to be ripped apart or absorbed by the larger galaxy. In this case, even though the progenitor galaxy would be destroyed, the globular clusters within it would remain intact. There are many such clusters in our galaxy that we think could have been captured this way.The image to the right shows the remains of galaxies absorbed by a giant elliptical galaxy in Abell 3827.

Model 2: The different populations of clusters correspond to distinct periods of star formation. The hydrogen rich, metal-poor clusters formed first, and then, after supernovae enriched the galaxy with metals, the metal-rich population came after. But how is this star formation triggered? It’s expected that star formation occurs steadily throughout a galaxy’s lifetime. However, if that were the case, the globular cluster populations should have metallicities that smear out into many different peaks. The double peaked distribution suggests that specific periods of star formation are needed, with the bulk of cluster formation occurring within relatively short bursts of time. This behavior could be explained by a merger of gas-rich galaxies. Shocks from two colliding galaxies could compress gas enough to form new globular clusters. In some interacting galaxies, massive star clusters that look tantalizingly like young clusters have been observed.The image to the left shows a Hubble image of a pair of colliding galaxies, which seems to have sparked a burst of star formation and over 1,000 massive star clusters (recognized by big blue clumps).

My suspicion is that clusters form in both these ways. The question, then, is which of these processes dominate cluster formation?

If Model 1 is correct, then the large star formation processes that produced globular clusters must have ceased a long time ago. Could this give us information about how galaxies evolved in the young universe? What would give rise to such vigorous star formation in the past, but not today?

If Model 2 is correct, could we then infer the metallities and kinematics of progenitor galaxies? What kinds of progenitor galaxies merged to form the large galaxies we see today? Is it possible large galaxies formed from a couple of gas-rich mergers? In that case, we'd expect to see over densities in globular cluster populations. Or, do large galaxies form from many mergers? If this is the case, the gases in the progenitor galaxies may have been used up in star formation from the multiple merging events, which could effectively deplete the materials needed for cluster formation. Perhaps this could provide another avenue to study the poorly understood physics of galactic mergers in general, such as gas heating and cooling, feedback from star formation, and the complex interplay between them.

I do not have the spectroscopy needed to date globular clusters, or to distinguish between different populations. However, I do have survey data of a large number of galaxies (on the order of thousands) from the Spitzer Space Telescope. I plan on looking at globular cluster populations to see if there are any over densities, and if so, what those over densities are related to. I do have some candidates that look promising, but at this point, it's too early to tell. Automating the detection and data reduction process has been difficult these past few months, but the prize is well worth the effort: a glimpse into galactic history.

Note: All of these images (except the top one of M80, which I jacked off of Wikipedia) come from the work of West, Cote, Marzke, and Jordan. They wrote a wonderful review paper in Nature on this very topic. If you're interested, I suggest you click here:

Wednesday, July 13, 2011

Reasons for This Blog

Yes, there is more to this than seeking attention. There are a number of things I hope to accomplish and share, with the main goal of re-fostering within myself a sense of wonderment in astronomy. Within the space of a year, my outlook on life went from the previous post to one of quiet desperation. I want to change that. No, I need to change that. For some reason, late at night a couple of nights ago, I figured this would be a way of fixing it. So, here are the main reasons for starting this blog:

1. Hold Myself Accountable for My Mistakes:

I failed my first year of grad school. I don’t mean my classes – I did ok in those. No, I failed at the most important part of being a grad student: starting my research. I went from an idealistic, hopeful student to a jaded, emotionally wrecked bum. I spent most of the year feeling depressed and hopeless, and I dealt with it by wallowing in self-pity. However, I didn’t have to! I was somewhat unlucky in how things turned out, but I am far from blameless. I hope that by reflecting on what I could have done better, I can face the rest of my grad school career with a sense of personal responsibility and purpose. I sincerely hope my mistakes won’t become yours.

2. Renew Self-Interest In My Research:

The intense frustration I felt at not making any progress in my research effectively killed any enthusiasm I had in astronomy. That’s bad, because there will always be failure in this field. In fact, there will always be failure in life, but I digress… I hope that I can use this forum to post things in astronomy that interest me, whether it’s related to my research or not. The important thing is, astronomy should have a bigger emphasis in my life, and if I’m not excited about my project, something needs to change.

3. Practice Writing Skills:

As a student in a STEM field, my practice in this is sorely lacking. I recommend finding some way of practicing writing skills, because it’s so important in communicating ideas. I have found that since I don’t write all that often, my writing is awkward, laborious, and time consuming. And I’m not even mentioning my public speaking skills!

4. Foster Public Interest In Astronomy:

This is pretty self-explanatory. As a T.A., I was shocked to discover last semester how little students knew about basic astronomy concepts. I was even more shocked to discover that their apathy toward the subject outweighed that even more. I understand that astronomy is not for everyone, but without public support, astronomy in this country will fail. Just look at the current funding situation.

5. Show That Astronomy Is An Important Aspect Of My Life:

This may be directed more toward me than it is at anybody else. While I have other passions, I need to remind myself that just because astronomy isn’t as well documented photographically, it’s not any less important. ☺

Well, that’s a lot of blogging within the past couple of days. This is really a lot of writing for me in my spare time. Until next time, happy computing!

Tuesday, July 12, 2011

Night Wonders (Or, Why I Love Astronomy)

I remember a drive my parents made once. It was in the dark of night, I was swaddled in a blanket, and the city lights had long since receded into oblivion. We stopped in the middle of a desert landscape, and when I got out, all I felt was the cold seeping into my bones and the desire to fall asleep again. My mother pulled me out of the road and gently told me to look into the night sky, and when I did, what I saw took my breath away. There, in the depths of what I thought was unchangeable and static, was a comet. This strange visitor from the unknown, this smudge of white light from the farthest reaches of space, had saw fit to grace us with its presence. I felt then neither the cold nor the tiredness I had felt earlier, but some strange sort of awakening. I must have been young, because the desert brush towered over me, but at that moment I wondered where it had come from and how it came to be there. I wondered what it meant, and why it was here. And then I looked past it into the stars gleaming coldly behind it and asked my questions again.

Later, there were times when I'd get upset - mainly about my insecurities, my weaknesses, my doubts. As an angsty teenager, I'd run out of the house, defiant of the authority my parents held over me but still unhappy about whatever it was I was running away from at the time. About four houses to the west of mine opened up to the mesa, and it was to there I'd run to for sanctuary. Out in the wilderness, again I'd look up, and again those points of scintillating light would shine down, enough to be seen but hard to understand. I would laugh at my foolish vanity, because in the face of forever, what did it matter? Looking into the universe, albeit a limited window into it, all my worries would seep away and become replaced with the awe of my childhood memory. What is our place in the universe? What is the meaning of it? How did it come into being? Are there other levels of consciousness far exceeding our own? And then an even stranger question: why is there the assumption that the universe holds any meaning? Is meaning, in fact, only a human construction? A human yearning to comfort ourselves that we are in fact important and that sentience is something more than molecules forming protein strands?

Today, I know the universe is not as static or unchanging as I had previously thought. It's a vibrant and violent place involving unimaginable distances and terrifyingly powerful energy. However, I still do not understand any more than I had earlier, because each new revelation brings with it new questions to outnumber the old. And my quest for meaning, or perhaps lack of it, is still as strong as it ever was. Maybe my reasons for going into astrophysics are cliche - the overall "meaning" of the universe, aliens, strange planets and their stranger horizons - but it's those basic questions that keep me going. It's still what I ask when I gaze up into the night sky, my head full of wonder. In fact, I feel like a child.

Monday, July 11, 2011

Hello, World!

In honor of my first post (and because I could think of nothing else), I will start my blog the traditional programmer's way - python style! So . . .

print "Hello, World!"

Simple as that! And if that 's not enough, here's a way you can say it in 366 other computer languages:
Click here!!