Lock and load!

I have now left the South Pole, although the last 72 hours were a blur of occasional cat-naps as I struggled to get the rest of my work done.  This final push is a common experience there, and was certainly my experience the last time I went as well.  The moment I sat down on our "herc" to fly out, I was out cold until we arrived in McMurdo Sound.

As a result of my efforts and that of my colleagues, we now have 3 cameras on the sky, seeing "first light" over this past weekend.  Two are now on Keck Array, set to map the sky at the "blue" 220GHz, and the much larger BICEP-3, set to map the sky at the "red" 95GHz.

Above is a time-lapse video of us loading BICEP-3 into the mount, spanning about 1 hour of work.  You don't see me much because I'm the one in the back turing the wench and actually lifting the camera (1200 lbs) up into place.  I like this slightly blurred photo that someone took of me:

You also don't see the 3-4 people up in the mount watching to make sure the camera does not crush any cables or lines during lifting.  Here's an artistically modified photo of some of them working on that, made to look like a comic book drawing:

Finally, a photo of the gang experiencing "first light" of BICEP-3 on Tuesday:

I missed out on that, although I did get to watch one of the Keck-220s turn on.  This happened the same evening that our friends on the Event Horizon Telescope turned on and made a quick low-resolution map of the center of our galaxy.  As is the custom, we all drank a celebratory wee dram.  And as I described earlier, we enjoy a healthy camaraderie with our DSL colleagues (in this context, Event Horizon is an extension of the South Pole Telescope)

As of now, all three cameras "work" inasmuch that they can look at the sky without the sky appearing too bright and saturating the sensors.  The team is currently in the process of characterizing how they work, and the results of these measurements will be used when analyzing the maps made by the camera as well as for understanding any flaws so we can fabricate better detectors in the future.  Now it's time for science

The Traverse

I was recently asked “How does the station here generate electricity?”  The answer, unsurprisingly, is that we burn fuel to run generators, heat the buildings, melt ice into water, etc.  Historically, the fuel was delivered by aircraft-- LC-130 skier planes fly from McMurdo to Pole with far more fuel than they need and unload some when on the ground.

However, airlifting fuel is not that efficient: each flight can only deliver 1/3 of its fuel at best.  Starting 12 years ago, the Antarctic Programs began building a Highway from McMurdo to the South Pole so they could use large tractors to drag bags (“bladders”) of fuel across the ice (seen arriving at the South Pole Station in the picture below).  There are currently three traverses per season, and each delivers 100,000 gallons of fuel to the station, which nearly satisfies the station needs.  They get the last 100,000 gallons from a dozen planes.

The route that the traverse takes is a bit different that the route taken by the early explorers.  Amundsen, Scott, and Shakleton all chose routes that were nearly direct shots from the Ross Sea, scaling glaciers in the Trans-antarctic Mountains.  The modern traverse path circumvents much of the mountains and ascends a 15% grade on the side of the continent nearest South America. 

This route also minimizes the number of crevaces.  Crevaces at the edges of glaciers can be perilous, and the traverse uses ground radar to watch for them.  When found, they dynamite them to clear out snow bridges and then use their trucks to shovel in snow fill.  This is a constant maintenance task.

In addition to the fuel bladders, they drag a few RV-style living quarters.  These contain a small kitchenette, a bathroom and shower, and sets of bunk-beds.  Their living quarters are far less rugged than I envisioned.

SPIDER launched

After nearly a decade of preparation, SPIDER launched today.  You can see a video of the launch here:

I described what they were up to in this blog-post a few weeks back.  While I don't directly work on this project, I and many others loosely connected to the project really want to see it succeed.  This is the proving grounds for a future satellite mission using the technology that I have worked really hard on for years now.  Regardless of the science that comes out of this mission, if all goes according to plan, they will have demonstrated a huge technological leap forward.

My colleagues down in McMurdo are now frantically communicating with the balloon by radio to try to get all the electronics tuned up.  Many of the detection systems cannot be tuned until they are at high altitude, and while that team has worked very hard at automating this, they still need some human intervention.  But there’s a limited time because once the balloon passes over the horizon (about 48 hours), it must function nearly autonomously.  Once out of sight, their bandwidth for communication isn’t much better than sending a “tweet” every few minutes.  (as of Jan 5, all systems are "go".)

They will be mapping this region of sky, shown at left and outlined in white a figure from a recent paper:

The colors in the background show a model of dust from our galaxy and you can see what we've focused on with the BICEP and Keck telescopes in the grey box in the lower right.  So their map will be much larger, albeit not as deep (i.e. more noise in each part of the map than we have).  But that should let them look at larger modes on the sky, which will be exciting.

Happy New Years from the South Pole

Our time-zone is completely arbitrary down here, but since operations for McMurdo and South Pole are coordinated through Christchurch, we’re on New Zealand time.  This puts us just on the other side of the date-line and makes us one of the first to celebrate the New Years.

We managed to get all three of our new cameras cooling down by the New Years so we could enjoy the holiday and maybe work at a slightly lighter pace over the next week.  This includes two small cameras that will go into Keck Array and let us map at a color (220GHz) where galactic dust is bright and then one large camera that will provide lots of sensitivity at a color (90GHz) where we can ignore dust.  We will begin characterizing them in a week or so once cold enough to operate and then hopefully load them into their mounts a week yet later.

To celebrate, we did some sledding.  Despite the terrible bandwidth here, I managed to get a video to load overnight:

I’m guessing this one got through because everyone else on base was recovering from New Years.

The Event Horizon Telescope

The picture above shows the South Pole Telescope, photobombing our's (BICEP-2) in the foreground.  Normally, the South Pole Telescope takes measurements of the microwave background (similar to us), but they are in the process of adding a second camera to allow them to join a world-wide network of telescopes called the Event Horizont Telescope (EHT) to study the black hole at the center of our galaxy.  As you can tell from the length of this post, this is one of my favorite projects that I have no involvement with.

When you throw an object in the air, it normally comes crashing back down.  But throw it hard enough, giving it what we call the escape velocity, and it will sail off into space.  This is how NASA launches rockets to other planets.  If you stood on something much larger than Earth like the sun or Jupiter (never mind that they're balls of gas), you'd have to throw it much harder than you would on Earth to reach the escape velocity.  But we're told in school that nothing can go faster than the speed of light, nature's ultimate speed limit.  What would happen if we stood on something so massive that the escape velocity was more than the speed of light?

This is the concept behind a black hole, something so massive that even light cannot escape if it strays too close.  You can mentally draw a sphere around a black hole called the event horizon. Anything that passes inside of that sphere, even light, will feel such as strong gravitational pull that it cannot escape and gets sucked down the hole; outside, things can, in principle, still escape.  It's a stellar point of no return.  Mind you, the light within the event horizon does not stop and then fall back inward like a baseball-- it must always travel at the speed of light and cannot slow down.  But any path the light might travel is bent to lead it back into the hole.  This is possible because the rules of geometry both inside and immediately surrounding the event horizon are altered from the “Euclidian” geometry we learned in high school.

Scientists strongly suspect that these things must exist, and are pretty certain that most galaxies, including ours, have a supermassive black hole at the center.  The one in the center of our galaxy is named Sagittarius A* (Sgr-A*).  However, we are limited in studying how these things look and operate, partially because black holes, by their very nature, pull in light and do not glow the way a typical star does.  Black holes also act like galactic vacuum machines, sucking in dust from all around them.  As a result, they tend to be surrounded in a hazy cloud of dust that also cloaks the surrounding space.

Dust and molecules tend to scatter away short wavelength light more so than longer wavelengths.  The wavelength is essentially the distance between peaks of a lightwave and corresponds to color in visible light: blue is shorter than red.  In fact, this scattering is why the sky is blue-- the blue and violet light from the sun scatter around the sky while the yellow, orange, and red can get through.  It's also why the sun appears red at sunrise or sunset-- at the ends of the day, sunlight grazes our atmosphere, has to travel through more of it, and scatters away even longer wavelengths of light leaving only red light.

This effect is also the key to how astronomers have gained knowledge about black holes.  While we cannot see through the dust with light visible to the eye, astronomers have been using infrared telescopes to peer through the dust and study Sgr-A*.  They have mapped the trajectories of stars near Sgr-A* to realize there is something invisible lurking there that is several million times more massive than our sun that flings other stars around it at highly elliptical orbits, as seen at right.

In principle, even longer wavelengths can let us see deeper into the dust cloud.  But there's a catch to going to longer wavelengths: you cannot resolve as fine features on the sky as you can with short wavelengths. To compensate, you can build a large dish to regain some resolution.  But what if you could build a dish nearly the size of Earth?

That's the idea behind the Event Horizon Telescope: link up a network of millimeter wavelength telescopes across the globe to observe at the same time, recording onto computers not only the brightness of the light they see, but also the phase.  The phase tells us if the light waves are at peaks, troughs, or somewhere between, whereas the brightness is essentially the height of the peaks and troughs.  Once recorded and brought to a common computer, the data can be combined in a way where all the telescopes act like small pieces of one giant mirror.  The fact that these are millimeter waves means that with really sophisticated hardware, you can actually record brightness and phase to a computer, whereas this would be impractical with infrared or shorter wavelengths.  To do this requires specialized cameras and sensors, as well as ultra-precise atomic clocks at each location to ensure that observations are synchronized.

The South Pole Telescope is the most remote in the network, and as seen above, its inclusion greatly increases the size of the effective area to be roughly that of the Earth.  Currently, the network can resolve features comparable to Sgr-A*' s event horizon, hence the name of the project.  This would appear about as large as a grapefruit on the surface of the moon, viewed from Earth.  With the inclusion of the South Pole, they will be able to see features over five times smaller—about the size of a golf-ball on the moon viewed from Earth.  Light just outside the event horizon should orbit many times before being flung off, which means that the black hole should look like a dark spot surrounded by a thin bright ring of light.

For the recent movie, Interstellar,  physicists at my home institution (Caltech) simulated and graphically rendered a black-hole, shown below:

The event horizon is within that black void and has a radius known as the Schwarzchild radius.  You can see that thin bright ring surrounding the black void.  If the South Pole installation of the Event Horizon Telescope succeeds, they may be able to see that ring.  And then they could test the very concrete prediction of the theory of relativity that this should be a perfect circle with a radius 1.5 times larger than the Schwarzchild radius.  Performing such a test would be really cool!