Astronomy Monday: Looking for light from the end of the Dark Ages

My friend and colleague Greg has the coolest thesis topic ever. He used to be my office mate and we had the same supervisor for our first graduate research projects. I was doing a numerical project, which involved running simulations of dark matter particles clustering and doing lots of statistics on their power spectra... maybe another story for another day. Anyway, most of my work was done sitting at a computer in my office, running code. Greg, on the other hand, was smart enough to choose the observational project, which would land him several free trips to India.

To understand Greg's project, I guess we should first go over a brief history of the universe, which began 13.7 billion years ago. In the beginning, and for the first few hundred thousand years, the universe was filled with a hot dense plasma, that is, a gaseous state where the electrons are separated from the nuclei in most of the atoms. In this state, light couldn't travel very far because the photons were easily scattered by all the free electrons. As the universe expanded, it eventually became cool enough for the free electrons to recombine with their atoms, and all the light that had been bouncing around between these electrons was allowed to escape. We call this light, now red-shifted to the microwave part of the electromagnetic spectrum, the Cosmic Microwave Background.

For a while after this, the universe was pretty boring. For a few hundred million years, it was filled with this neutral hydrogen gas, which slowly started to clump together into what would become the first structures in the universe. Astronomers like to call this time the "dark ages" because there was no new light being produced. Eventually, the first stars formed from the collapse of hydrogen gas and there was again a source of photons in the universe. This new source of energy caused all the neutral hydrogen gas to again become ionized, and the electrons were once again separated from their nuclei, but now, since the universe had expanded and cooled considerably, light could travel long distances without being scattered. We call this the Epoch of Reionization.

Here's a pretty picture, shamelessly stolen from Wikipedia (and before that from the WMAP site, I think), which nicely illustrates this history of the universe:

My friend Greg is actually trying to observe this transition, to basically get a picture of the universe as it changed from neutral hydrogen to ionized hydrogen. But how, you may ask, would you be able to distinguish this neutral gas from its ionized counterpart? Well, it turns out that it's very difficult and necessitates the exploitation of quantum mechanics.

Neutral hydrogen is made up of an electron orbiting around a proton nucleus. These subatomic particles have something called "spin", which has to do with their angular momentum. When the spins of the electron and proton are aligned, the atom is in a slightly higher energy state than when they are anti-aligned. Thus, there is a very small probability (something like 0.000000000000003 times per second) that the electron will change its spin, and give off a low-energy photon. Here's a picture illustrating this from Hyperphysics (where you can also find out more details about this transition):

Even though this transition is extremely unlikely for a single atom, when you get a big bunch of neutral hydrogen together, it happens quite often. The emission of 21-cm radiation from neutral hydrogen gas has helped us map out this gas in our galaxy and in other galaxies. And Greg is looking for the 21-cm emission from the neutral hydrogen at reionization as it started to change into ionized gas, a process that would have happened gradually, in clumps around the first stars. Computer simulations seem to indicate that it would look something like this, where the ionized gas is indicated in orange, and the neutral gas in green:

Now, this 21-cm radiation is visible to radio telescopes, which is why Greg got to go to India... He went to the GMRT (Giant Metrewave Radio Telescope) array, near Pune, which is the largest radio dish array for metre-wavelength range of radiation. He keeps telling me that India isn't so great, but when I see pictures like this (taken in the middle of winter, no less), I can't help but be a little envious:

A lot of his time there has been spent looking for radio interference on the ground, caused by transformers, power line junctions, and loose wires in contact with power lines, and finding these means spending a lot of time wandering around in a farmer's field with a goofy-looking radio-wave receiver:

Unfortunately, the 21-cm signature of reionization is still much fainter than the foreground sources from the ground and in space, and so Greg hasn't been able to detect it yet. He did, however put some upper limits on its power spectrum, which you can read all about in his most recent paper!

P.S. Pictures from India provided by Greg himself.

More astronomy, less... hooks?

I really enjoyed writing about that astronomy colloquium the other day, so I think I might write more about cool astronomy things here. Maybe I'll do an "Astronomy Monday" thing or something, though that isn't nearly as alliterative as I'd like. Anyway, today is still Monday (for a little while), so this will hopefully be the first of many sciencey posts.

On Thursday, November 18th, astronomers reported in Science Express that they had found the first extra-solar planet, called HIP 13044 B, that originated outside of the Milky Way galaxy. It's actually part of our galaxy now, but it originated in a galaxy that the Milky Way cannibalized, that is, ripped apart and absorbed.

Now, how can we possibly tell that this planet is of extra-galactic origin? Because of the great distances involved, the 500-something extrasolar planets discovered so far lie within a few hundred light-years of the Earth. (Though some people at UofT think they might have found a way to find planets in other galaxies.) However, the movement of HIP 13044, the star around which this planet revolves, seems to indicate that it's part of the Helmi Stream, a long string of stars which has been tidally distorted and pulled to form a loop around the galaxy. Numerical simulations and observations seem to indicate that each tidal stream around our galaxy used to be a dwarf galaxy or globular cluster that was pulled apart by the Milky Way. Here's a pretty artist's rendition of tidal streams from Wikipedia:

There are a couple of other peculiar things about this newly-discovered planet. The first is that the host star, HIP 13044, is extremely low metallicity, which means it contains very few heavy elements. In astronomy terms, heavy elements are any element heavier than helium, such as carbon, oxygen, up to iron. Anyway, this star has the lowest metallicity of any planet-bearing star discovered, at about 1% of the sun's metallicity. This is remarkable because the metals within a star are thought to be essential to the formation of planets, and this star having so little of them seems to challenge our knowledge of planet formation. Looky! A graph showing this star's metallicity compared to other stars that host planets:

The other peculiar thing is that the host star is in its red giant phase, which means that it has stopped fusing hydrogen into helium at its core, which causes it to become bloated and red. When the sun enters this phase, it will expand beyond Earth's orbit, totally destroying our planet. But don't worry, this won't happen for a few billion years. Here's a pretty picture of the life cycle of our sun from Wikipedia:

So if HIP 13044 is in its red giant phase, it might have engulfed other planets in the system that were closer in, and in fact, the higher than expected rotation rate of the star seems to indicate that this did indeed happen. In addition, it looks like the planet HIP 13044 B might be about to fall into the star itself as it enters its next phase of red giant expansion.

Finally, this planet was found using the radial velocity method of detection. In a nutshell, the presence of a planet around a star will cause it to wobble in its orbit. Because of the Doppler effect, as the star wobbles towards us, its light is slightly blue-shifted, and as it wobbles away from us, its light is slightly red-shifted. Here's a nice little animation, again from Wikipedia:

From the wobble of the star, we can tell that the planet has a mass at least 1.25 times that of Jupiter and an orbital period of 16.2 days. And it isn't Monday anymore. Darn.

A return(?) to potholder fame

As you may recall, a few months ago, I posted that Star Trek Potholder pattern, and then the next day, I was super excited because I got almost 100 favourites and five comments on Ravelry in the first 24 hours it was up. The pattern, in case you're interested, is currently up to 57 projects, in 381 queues, and has been favourited 742 times.

Anyway, to further boost my already inflated ego, I was featured on CRAFT Magazine! You can find the post here with 37 (38 if you count contractions as two words) whole words extolling my awesomeness. Thanks for posting, Rachel Hobson!

Speaking of which, I still haven't made any double-knit potholders for myself. I should really get on that... maybe with Star Wars designs!

Taking pictures of stars

Today was the Karl Kamper Memorial Lecture here in the ol' DAA, and one of the first astronomy talks in a while that has actually gotten me excited about astronomy. Prof. John D. Monnier of the University of Michigan gave a talk entitled "Imaging the Surfaces of Stars", where he described his involvement in using the Michigan Infrared Combiner (MIRC) of the CHARA Array on Mt. Wilson, CA to actually get an image of the surface of stars.

This is super cool because it's really really hard to take a picture of the surface of a star. As prof. Monnier explained, the size of a star compared to the distance between stars is about one to 5 million, and so to be able to resolve the disk of a star, your telescope would have to be able to resolve about 0.000001 degrees, or a few milliarcseconds. That's equivalent to being able to see a penny from about five hundred kilometres. The size of the telescope needed resolve even the closest star in visible light would have to be at least 40 meters across, which is bigger than any telescope built to date. (So whenever you look at any star through a telescope, it looks like a point of light, and not a resolved disk, and so isn't much more interesting than looking at it with the naked eye.)

Fortunately, prof. Monnier and his group are able to image stars through the magic of interferometry! This is basically combining the light from many small telescopes to make it seem like one big telescope. This is fairly easy to do with radio waves, but considerably harder to do with shorter wavelengths, like visible light. However, on Mount Wilson, they've managed to do this with an array of infrared telescopes, and have taken the image of the surfaces of several stars. Here's a picture of Altair they took in 2007:

Now, you may notice that Altair is not uniform in colour (and thus in temperature). This is because the rotation of the star causes it to be more flattened along its axis of rotation, and bulges around the equator. This means that the surface at the equator of the star is further from its core, and is therefore cooler at the equator than at the poles. (This is really an over-simplification, but the idea is essentially right.) Monnier's group has found that for very rapidly rotating stars, the temperature gradient between the equator and the poles can be several thousands of degrees, and that's where the trouble begins.

Why would this be a problem, you may ask? Well, astronomers like to classify stars by their temperature, and when the difference in temperatures on the surface of a star is larger than the classification temperature range, this makes their lives very difficult. And knowing the actual temperature of a star is very important for, say, placing it on the Hertzsprung-Russell diagram:

Prof. Monnier also talked about his work in imaging the star Epsilon Aurigae. This is a very special object because every 27 years, it is eclipsed by something. It was postulated that there was some sort of compact object in a binary orbit with the star that has a large dusty disk, and whenever this disk would pass in front of the star, the star's light would be blocked. Sean Carroll wrote a really long blog entry about it a few months ago, so I won't go into too much detail. The really cool thing is that in 2009, Monnier's group was actually able to image this dusty disk passing in front of Epsilon Aurigae.

There were also a few other things that I can't remember off the top of my head right now, and obviously I didn't take notes because I was busy knitting. Observational astronomy and stellar astrophysics aren't really my thing, but when cool stuff like this is going on, it's hard not to get excited!

My very own Hitchhiker's Guide to the Galaxy

So, I didn't actually acquire the fictitious encyclopedia from Douglas Adam's Trilogy in Five Parts, but I did buy myself a Kindle. However, with unlimited access to Wikipedia a lot of other websites (email, facebook, or anything with flash don't work so well), it's pretty close to being the electronic guide to the known universe. Good ol' XKCD illustrates it pretty well:

I haven't actually bought any of the Kindle books off Amazon yet, but so far, it's pretty damn amazing. I've loaded up a bunch of pdfs of my favourite knitting patterns, of ebooks I got off Project Gutenberg, and of scientific papers I use for my research. Also, I can access the internet all the time, from anywhere... for free. Take that, iPad!

Because I love it, and because everything I love must be wrapped in yarn, I had to make it a case. Also, the case had to be awesome. I thought I'd model it after the cases they sell on amazon specifically for the Kindle, with the fancy leather top cover and elastic holding it together. I had planned to make it double-knitted, with pockets that I could fit cardboard into to make it stiff... Anyway, I ended up with this monstrosity...

It just wasn't going to work... Discouraged, I went the simple route. I looked through the Harmony Guide "101 Stitches to Crochet" and found a neat checkerboard colourwork pattern. Of course, then I ran out of yarn three quarters of the way to completion, and had to continue in a different yarn, and figured I may as well change the stitch pattern as well.

And then I sewed in a zipper because zippers are cool.

I'm actually really happy with the result. It's sort of hip and quirky. The plan is to next stitch on the words "Don't Panic" in neon green. It'll be awesome.

Sometimes I just want to knit yards of stockinette...

After the labour of love that was my beautifully cabled sweater, I wanted to knit another sweater, but I wasn't up to knitting anything incredibly impressive. I wanted something easy that would just fly off the needles with minimal finishing. What I ended up with was this:

The pattern is the Buttony Sweater by Katie Marcus, and it certainly fit the bill for simple, mindless knitting with minimal finishing, being a top-down raglan and all. It took me less than a month to knit, which is really fast for me. The main reason I picked it was because I found all these green buttons in my big bag of buttons that I got from Zellers, and I wanted to use them all in the same project. I picked a yarn, Knit Picks Swish Bulky in the Tidepool Heather colourway, to match the buttons and I bought as much as was recommended on the pattern's Ravelry page.

As you can see from the picture, I ran out of yarn before I could finish the sleeves. In fact, because I didn't feel like knitting back, I did the ribbing in some left-over Marble Chunky. I was a little disappointed by that, but I got over it. It's super comfy and warm. To make sure my arms don't get cold, I wear it with either my belladonna sleeves or the arm-warmers that go with my icelandic non-turtle-neck.

I followed the pattern pretty closely and didn't bother with waist shaping. The sleeves I knit two at a time, using the magic loop technique with a really long cable, which ensured that they would be the same length. I'm not entirely happy with how the button band looks, but I don't care enough to go back and change it. I really like the construction of the top-down raglan, and I'll definitely make another. I'm eyeing the Painted Lady pattern off the Anticraft website.

In other news, the X-mas knitting has begun! Therefore, I won't be posting much about things I'm working on now until after the big day, but fortunately, I have enough of a backlog of stuff I've been meaning to blog about, that I should be able to hold out until then. Woohoo!

More baby things!

This is totally me right now:

I have a conference to go to on Friday, well, technically a meeting, and I'll be giving my very first talk in front of people who actually know what I'm talking about. We're supposed to have a practice talk session with my supervisor tomorrow afternoon, and I've finished... well, maybe the introduction slides. This is because I'm procrastinating. In fact, right now, I'm procrastinating from my procrastinating, since I got distracted from reading blogs on Google Reader to write this blog post. I sure hope my supervisor doesn't read this.

Anyway, I thought I'd take this opportunity to show y'all some baby things I made recently which I can now display proudly since the recipients have received them (yesh, I spreak the Engrish). First up, we have baby legwarmers!

I got the inspiration for these from Kelley Petkun's Knit Picks podcast (that lady is full of good ideas). The motivation behind baby legwarmers is that babies often wear these little onesies that are legless and their little legs might get cold. And the best part is that when you're changing the baby, you can leave them on!

I made these from a free ball of Patons Kroy Jacquards (in the colourway Cameo) that I got at the Stitch 'n Pitch, which means they're washable, and also adorable. I used the pattern Baby Leg Warmers by Erin Cowling over others, mostly because of the author's nickname. I made only one major change, which was to add increases for the thigh.

Next up, a baby-sized aviator cap!

I made this using some gifted Knit Picks Andean Silk in the Slate colourway, a highly inappropriate yarn for baby things, but I don't care. The little flower is crocheted out of some left over Noro from that baby surprise jacket I made. I used the Aviatrix baby hat pattern (Ravelry link only) by Justine Turner, which I am definitely going to do again in an adult size for myself (maybe in lime green?).

Finally, the world's saddest elephant:

I made this using some of the left-over Andean Silk, so it's super soft, but it's totally going to be ruined the first time it's washed. I used Cristina Bernardi Shiffman's Oliphaunt pattern, which has rather cryptic sewing up instructions, and thus I attribute my little guy's wonkiness to this fact. Of course, I also did the pattern in stockinette instead of garter stitch, which may have also contributed to the wonkiness. Whatever. He's cute.

And a bonus shot of my cousin's baby (who all the above things were for) wearing her handknit booties!

D'aw! Ok, now back to writing my talk... ahem...