This officially marks the end of my Antarctic adventures (at least for now). As I have now started my thesis work and my research is unlikely to take me back to Antarctica soon, this is also the end of Kate Goes South. Thanks for reading! I hope you enjoyed reading about my trip to Antarctica as much as I enjoyed writing about it.
December 29, 2015
As I write this I’m back in McMurdo, on my way back to the United States. I may be here for a few days, as flights are running slow due to weather and the holidays, but it feels good to have started my journey home. After over a month on the Ice, I’m ready to get back.
My last few days at Pole were a mix of work and last-minute sightseeing. On the day after Christmas I finally got a chance to see the ice tunnels under the station, which I had wanted to visit for weeks. The tunnels are cut to carry pipes that bring water to the station and waste back out. The station’s fresh water comes from an extraction site deep underground, where heat from the station’s waste is used to melt the ice. One of the carpenters who works in the tunnels gave me a tour. His job is to cut blocks of ice out of the tunnel walls with a chainsaw and remove them, to widen the tunnels and prevent them from collapsing inwards. (Due to the pressure of the snow and ice overhead, the tunnels are slowly bowing inwards and would eventually crush the pipes if left unchecked.) It’s one of the coldest jobs on station – the temperature in the ice tunnels is a fairly constant -55F. Fortunately there is no wind, which helps. In fact, the air is so still that in some places beautiful ice crystals extend from the ceiling and walls. They are so delicate that breathing on them causes them to fall.
The tunnels are also an interesting display of station culture over the years – here and there the carpenters and other visitors have carved niches out of the walls, which house a variety of “shrines” ranging from artistic to serious to downright weird. Some are memorials to people on station who passed away, while others celebrate a specific winter or a random artifact.
After seeing the ice tunnels, I went out to the traverse open house. This second traverse of the season (SPoT2) was similar to the first one (SPoT1), which I saw around Thanksgiving, but they had a slightly different setup. Notably, they had four people per bedroom instead of two and a slightly smaller team. The SPoT1 team is preparing to head back to Pole from McMurdo, which will be the first time the South Pole has received three traverses in a single season. SPoT2 plan to do some trail improvement work on their way back to the coast, to make sure that the trip goes smoothly and quickly for SPoT1. No one wants the traverse team to get stuck on the ice cap with winter coming on.
The next day, Saturday, was the day that I was supposed to fly back to McMurdo, but a mechanical problem canceled the flight and I ended up staying until Monday. I spent most of my extra time at Pole helping to design and build a safety net for the new BICEP3 groundshield. Unlike the previous groundshield, the new one was built with a two-foot wide gap between the bottom and the roof, to allow it to tip sideways to perform calibration measurements. The net was designed to prevent anyone from slipping and falling through the gap while working on the roof. I worked on this project with Sam, who will be spending a full winter at the South Pole to take care of BICEP3 during its first season. By the time I left, we had completed the net and installed almost all of the sections.
On my last morning at Pole I also helped remove a flammables cabinet from the old VIPER control room. It is completely covered in snow after a decade of abandonment, but there are still many useful supplies to be scavenged. (Sam and I also got the wire cable we used for our net from VIPER.) The stairs down to the entrance were completely covered in snow, so Rachel and I were able to slide the heavy metal cabinet up the slope, rather than having to lift it. The VIPER building and groundshield are scheduled to be taken down later this summer, leaving MAPO entirely on its own. (The two buildings were originally connected, but this passage has already been removed.)
After a final lunch my plane arrived, and the rest of the team came out to welcome the new arrivals and say goodbye to me and the three other team members who were leaving. One of the new arrivals was Bryan – and with him came the long-awaited Keck focal planes! Everyone was thrilled that they had arrived safely and Kirit carried the focal plane case straight out to MAPO, to get to work installing them. I was a little sad not to be able to stay to help, but I know that Kirit, Grant, Abby, and the rest of the team will do a great job. As the plane took off, I felt excited to be heading north again.
Merry Christmas from the bottom of the world! As I write this it is still Christmas across the US, but I’m enjoying some post-Christmas time off after a full day of celebrations yesterday. The South Pole Station knows how to throw a pretty good party! I was sorry to miss celebrating at home this year, but I had a really good time here too.
The first event of the day was the Race Around the World, a South Pole Christmas morning tradition. The race starts and ends at the geographic South Pole and follows a figure eight loop out to DSL and IceCube and back, covering a total of about two miles. Any mode of transportation is allowed, although most people choose to run or walk. Running in costume is highly encouraged, and we had some good ones this year: crazy hats and neon, a Hercules airplane, and even a team of firefighters in full fire protection gear, with face masks and oxygen tanks (everyone gave them a resounding cheer when they walked across the finish line). Four people from our group ran and one of the BICEP3 graduate students (Jimmy) even came in second! Two others joined the race by riding on a couch that had been rigged up behind a snowmobile. I watched the start of the race from the galley and then went outside to cheer everyone as they crossed the finish line.
The race awards ceremony was held after Christmas brunch, which was very tasty (cherry and almond crepes, eggs Benedict, and chocolate-covered strawberries were among the offerings). The first-prize winners for the men and women’s divisions hit the jackpot: one five-minute shower each. The runners up each got a certificate entitling the bearer to spend several hours shadowing a member of a specific department on station. Jimmy chose the department that operates the heavy machinery, so he is hoping to get to drive exciting machines like bulldozers and loaders. Other people may get to learn how to fuel airplanes and guide a plane in for landing, launch weather balloons, or hang out with the galley staff and do some cooking. The overall first-place winner also gets a free flight to McMurdo to compete in this year’s marathon race there. Apparently the marathon is often won by a South Pole contestant, as we have the advantage here of being able to train at altitude.
After brunch, a dozen of us gathered in the station communications center for some Christmas caroling over the high-frequency radio. We were joined by the McMurdo holiday choir, the Italian base, and people at half a dozen field camps all over Antarctica. Each group led at least one song and the caroling continued for about 45 minutes. I thought it was the most magical part of the day – that even in such remote locations, people could still come together and share the Christmas spirit.
In the afternoon many people gathered to watch classic Christmas movies, but I elected to read and take a nap instead. After that, I had to hurry to wake up and get dressed for dinner! Most of my research group was in the first seating, so we started on appetizers at 4:30. The setup was very similar to Thanksgiving, and the food was equally good (or possibly even better). After a spread of delicious appetizers that included eggnog, shrimp cocktail, scallops, duck comfit, and New Zealand brie, we all sat down to a main course of beef Wellington and Maine lobster. The meal was accompanied by copious amounts of wine and everyone partook in a range of cakes, homemade truffles, and peppermint bark for dessert.
After dinner, we all retired to the lounge and talked late into the evening. One of the Harvard grad students who wasn’t able to come down this year, Jake, packed a bottle of nice scotch into one of the BICEP3 shipping crates as a Christmas surprise, so we all toasted him and enjoyed that together. Eventually interest built in watching a movie, so a group of us searched through the collection for Die Hard. We couldn’t find the first one, so we ended up watching the third one instead. It wasn’t quite as good as the original, but it was an entertaining end to the day nevertheless.
It was past midnight when we all went to bed, so I was very happy that we chose not to have a group meeting this morning. We have basically finished all of the prep work on Keck that we need to finish to be ready for the focal planes, so the Keck team mostly took another full day off today too. Tomorrow morning we’ll head out to the telescope and wrap up everything else, and hope that we get a plane! If we do, I will be flying back to McMurdo and I will have ended my South Pole trip as I started it: with a holiday celebration. Despite a few bouts of frustration at the hardware delays, I am really glad that I had a chance to come here and meet so many amazing people. The South Pole is a unique and special place and I feel very lucky to have had the chance to live here for a while.
This post is for those of you who have been reading this blog and wondering “I’m not a scientist; how can I get to the South Pole?” For those who want to visit and work in Antarctica for an extended period of time, the United States Antarctic Program (USAP) is currently hiring. (Citizens of other countries should check whether their country has a program in Antarctica; many nations do.) Those interested in the humanities can check out the NSF’s Antarctic Artists and Writers Program. For those fortunate enough to have $50,000 to spare, there are a number of companies that run private expeditions to the South Pole. Some are package tours of Antarctica that include a day trip to the Pole, while others are more adventurous and involve skiing either all the way from the coast (a two month trek) or “skiing the last degree” (getting airlifted to 89 degrees south and skiing the remaining ~70 miles to the South Pole). Wikitravel has a partial list on their South Pole page, along with some of the activities available to tourists. (The main attraction is taking photos at the Pole marker, as all of the buildings housing scientific experiments are off-limits to unauthorized visitors and the main station generally is as well – although some groups are allowed to make carefully chaperoned visits to the gift shop to mail postcards and buy other souvenirs.)
During my stay here, I have seen a number of tourist groups come and go. Most of them arrive in small planes, swing by the tiny “visitors center,” take photos at the pole marker, and fly out again. (Many of these “day trippers” don’t seem to know the difference between the ceremonial pole marker and the real one; all of them take photos at the ceremonial pole, but I only saw a few walk the extra few hundred feet over to the official geographic south pole marker! So if you ever get the chance to go, make sure that you walk the last few feet to 90.0 degrees south.) Most of the skiing expeditions don’t arrive until later in the season, although one of the “ski the last degree” groups showed up recently. The tourists are generally kept away from the scientists – all expeditions have to be completely self-sufficient, so those expeditions staying overnight usually camp in tents in an area set aside for tourist use – but some of the guides have been leading trips for years and are friends with old hands on the station, so I got to meet one or two of them. Skiing for 7-9 hours everyday and camping on the ice cap in tents for two weeks is very different from my Antarctic experience of sleeping in a cushy, heated private room and getting three hot, cooked meals per day.
Apart from the Congressional delegation, the most interesting tourist we have had so far this season is Tractor Girl, a Dutch actress who drove a farm tractor over 23,000 miles from the Netherlands to the South Pole and is making a documentary about her experiences. She and her crew camped and filmed at the Pole for a few days, then started the long drive back to the coast. Her visit generated much more excitement than the average tourist excursion; even the galley staff had fun with the novelty of her visit.
Like most of the scientists and USAP employees, the tourists retreat from the South Pole by mid-February, as the sun creeps toward the horizon and the temperatures drop. Between mid-February and late October, the only inhabitants of the South Pole station are the skeleton winterover crew, who watch over the experiments during the nine months that it is too cold and too dangerous to fly planes to and from the ice cap. Despite the isolation and the lack of sunlight, most of the people who winter love it – Robert Schwarz, who has watched over our Keck telescope for the past few years, has taken some amazing photos and videos of the aurora. 2015 will be his eleventh winter at the South Pole. Although I don’t ever want to winter over myself, it is still amazing to see such a beautiful, dark night sky. I hope to someday see aurora that spectacular, although preferably from a more accessible location.
Sunday, December 21, 2014
Another week has passed, and things are starting to feel like Christmas here! Last weekend the station decorated the galley (dining hall) with a full-sized (fake) Christmas tree, Christmas wreathes, and various decorations along the windowsills. My favorite is a family of ice skating penguins, happily cavorting in front of the view of the snow-covered plains surrounding the station.
There are a variety of Christmas activities planned for next week – from screenings of Christmas movies to a cookie-decorating party to caroling over the radio with McMurdo – and everyone has signed up for Christmas dinner on Thursday. I’m hoping to go to at least some of the activities leading up to Christmas Day, but I probably won’t have time for all of them – because it looks like the Keck team may finally have some real work to do! Both of our focal planes left the US last night with Bryan, the latest member of our team to deploy, and are officially en route to Pole. This means that we can finally start preparing for their arrival, which will be several days of hard work. We have to take two telescope receivers out of the mount, warm them up to room temperature, and open them up all the way to the innermost section where the focal planes sit. In addition to putting the new focal planes in, we will be replacing the lenses and filters in the telescope tube with new optics that are optimized for 220 GHz. If we are very lucky with the weather, the focal planes could arrive before Christmas – in which case we will all keep working through the holiday to install them and get ready to test them before putting the reassembled receivers back into the telescope mount. If the weather doesn’t cooperate, then Bryan won’t arrive until after Christmas and we will have time to relax until he gets here. I’m scheduled to leave on the first plane after Christmas, so either way I will probably only cross paths with the focal planes briefly.
Other than the big news about the focal planes, there isn’t much to report on the work front about Keck. Last week we replaced the clear plastic membrane in front of one of the telescope receivers that we use to keep snow out of the optics (because last summer it broke and was replaced with the wrong kind of plastic, which made data from that receiver extra noisy all year), so this week the main thing I did was take some observations to make sure that the new membrane is working correctly. I ran up against the limitations of the computers here while attempting to analyze some of this test data – data reduction that would normally take only a few hours to run on Harvard’s computers instead took over a day – but it looks like the new membrane is indeed better than the old one. I spent the rest of the week helping out with BICEP3, which is continuing to take shape. The most interesting part of this was helping out with the BICEP3 groundshield, which is a 5,800-pound aluminum construction that will surround the BICEP3 telescope receiver on the roof of DSL. The groundshield – as one might expect given the name – blocks the telescope from seeing emission from the ground. (Since the ground, while cold, is still warmer than the microwave sky and therefore emits lots of microwave radiation, we need to make sure that radiation from the ground doesn’t overwhelm the radiation from the sky that we are trying to observe.) I helped cover the seams between the sheets of aluminum with metal aluminum tape and helped with a “tip test” in which we jacked up one side of the groundshield to verify that the entire construction is stable when it is tilted. Tilting the groundshield will need to be done once per summer, so that BICEP3’s far-field focus can be calibrated.
In non-work news, the most exciting event of the week was the three-hour visit of a Congressional delegation. Ten members of the House of Representatives, several congressional aides, and several top members of the National Science Foundation visited as part of a multi-day tour of US science operations in Antarctica. We heard rumors that the NSF is angling for more funding to upgrade facilities in McMurdo, while some of the Congressmen had a different agenda – finding and eliminating examples of wasteful government spending. So it will be interesting to see what, if anything, comes out of this visit. The delegation was originally planning to spend a full afternoon here and get a tour of the telescopes, but due to bad weather their time on the continent was cut short by a day, which resulted in a shorter visit here. So instead, they arrived around lunchtime and went straight to the South Pole markers for photos – while everyone watched from the galley and made fun of the fact that they were chauffeured to the Pole in a train of vehicles because no one trusted them to walk the few hundred feet there from the runway – and then got a quick tour of the main station. As part of their tour they came through the Science Lab, which is a space set aside on the main station for scientists to do work. We use our workspace there for analysis and to check up on our telescopes without having to go all the way out to MAPO and DSL. Our group shares the space with several other collaborations, including the South Pole Telescope (SPT), IceCube (a neutrino experiment), and SPIceCore (a group drilling hundreds of feet into the ice cap to extract ice cores that date back thousands of years). Each group sent representatives to briefly summarize their science to the delegation. John Carlstrom, the PI of the South Pole Telescope, gave an overview of CMB science at the South Pole. He asked all of the BICEP/Keck and SPT scientists to be present during the tour, both to make a good impression and so that he could show off how many students are making “key contributions” to our science. I got to shake a few hands, but otherwise had very little chance to interact with any of the visitors before they were whisked away back to their airplane.
In other non-work news, I tried two new fun recreational activities this week: sledding and going to the station sauna. Kimmy, one of the BICEP3 grad students, had her birthday on Thursday, so to celebrate a group of us quit work early and went sledding. We borrowed a cargo sled from one of the snowmobiles parked in front of DSL and rode it down the giant mountain of snow next to the building. The top was approximately level with the roof of DSL, so we picked up some decent speed (and had a great view). With five or six people piled into the plastic sled, we managed to go quite a long distance.
On Friday I visited the sauna for the first time. Apparently “CMB sauna night” is a group tradition, but this was the first time we held one this season. I’ve never really liked saunas, but I now understand why people enjoy them – the humidity was a welcome change from the extremely dry ambient environment here, and the heat was made tolerable by the fact that one could periodically run outside to cool off. Even though it was -15F and windy, we found that we could stay out for five minutes or so without discomfort. Another tradition is running straight from the sauna out to the Pole in bathing suits and taking photos, but it was too windy for that on Friday. During the winter, especially adventurous people join the “300 Club” by running from the (+200F) sauna to the Pole and back when the outside temperature drops below -100F. It never gets that cold during the summer, but I hope to join the “200 Club” before I leave.
Next Saturday, if the weather cooperates, I will fly from the South Pole back to McMurdo on the first leg of my trip home. If I have no weather delays at all, I will be back in Boston on December 30th. However, weather is one thing that no one can take for granted here – so I could very well be in Antarctica for an extra week or more. Stay tuned!
In this post, I take a break from describing life in Antarctica to share some of the science behind our experiments. Many scientists, our group included, have spent years seeking the answers to some of the most fundamental questions about our Universe. As cosmologists, we want to know what the Universe is made of, how it began, and how it became what we see today. Our telescopes at the South Pole are designed to probe the earliest moments of the Universe’s existence: to learn more about what happened when the Universe was only a trillionth of a trillionth of a trillionth of a second old. Our best ideas of how the Universe has evolved throughout its history depend on understanding this beginning.
The Big Bang Theory
Our current knowledge of physics tells us that everything in the Universe – light, matter, space itself – exploded outward from a single point 13.8 billion years ago. This idea is called the Big Bang theory and is supported by a wide range of astronomical observations, made both by telescopes that can see the same kinds of light that our eyes can (but are much more sensitive) and by telescopes that can see different kinds of light, such as highly energetic X-rays and gamma rays and lower energy microwaves and radio waves. All of the telescopes that my group uses can only see microwaves, so the sky they see looks very different from the one that we see when we look up at the stars at night. A picture of the microwave sky is shown below. Rather than being mostly dark, the microwave sky shines brightly in all directions, with the disk of our galaxy the Milky Way appearing as a glowing band that stretches across the entire sky.
To understand why the microwave sky looks like this, we have to understand where microwave light comes from. Some of it comes from glowing clouds of dust in the Milky Way, or from other “local” sources. However, it turns out that most of the microwave light we see was emitted when the Universe was very young, and has been traveling through space to reach us ever since. This light forms the (nearly) uniform glow that we see in the background of the image above.
With everything jammed together in such a small space, the early Universe was a hot, chaotic place: fundamental particles of matter (protons and electrons) and photons (individual “packets” of light energy) all bounced around together, constantly colliding and ricocheting off in new directions. This early Universe was so hot that it glowed, like a fireball. It was so hot that protons and electrons bounced around freely because they were too energetic to settle down and form atoms. There were no planets, no stars, no galaxies – the whole Universe was a hot soup of particles and energy that looked the same in all directions.
As the Universe got older, it expanded and cooled. Around 380,000 years after the Big Bang it became cool enough that protons and electrons could combine to form atoms. When a photon encounters an atom, it will generally continue straight past without interacting with it. Therefore, after atoms formed, light and matter decoupled and each photon was able to keep streaming in a constant direction, rather than bouncing around as before. Light travels faster than anything else in the Universe, but it doesn’t move from one place to another instantly. This means that the further away we look, the further we look back in time. Light takes several seconds to reach the Moon, so if you bounce a laser off the Moon’s surface it will take several seconds before you see it bounce back. Light takes eight minutes to travel to Earth from the Sun, so when we look at the solar surface we are seeing light that is eight minutes old. When we look at the closest star outside the Solar System, we see light that is about four years old. And if we look far enough away, we can still see the glow from the early Universe, which has been traveling to us for over 13 billion years – the oldest light in the Universe.
Just like a hot coal that fades from orange to red to black, the color of this background light changed as the Universe expanded and cooled, getting redder and redder. Today, this light has redshifted so much that most of it is now in the form of microwaves (the same kind of energy used in microwave ovens to heat food). We call this light the Cosmic Microwave Background, or CMB. Our eyes can’t see this light, but other instruments can – for example, some of the static in your TV is from the CMB. Microwave telescopes like Europe’s Planck satellite have precisely measured the CMB, producing maps like the one above. Looking at the map, we can see that the temperature of the CMB varies ever so slightly across the sky, forming a pattern of “hot spots” and “cold spots” that correspond to areas that were slightly denser (i.e. contained more matter) than average and areas that were slightly less dense than average at the time the CMB formed. These tiny variations in density grew into the structures we see in the Universe today: galaxies and galaxy clusters.
Our telescopes contain cameras that are designed to see specific colors (or frequencies) of microwave light. Last year we observed at two frequencies: 100 GHz and 150. The new cameras we installed this year will allow us to observe at a third frequency, 220 GHz. Other experiments look at even more colors – the Planck satellite observed the entire sky at nine different microwave frequencies, providing much more information than any single-color picture could give alone. Looking at the maps below, we can see that the Milky Way is much brighter at some frequencies than others – meaning that it is easiest to study the light from outside our galaxy at frequencies around 100 GHz, where the galactic emission is faintest. We can combine observations at different frequencies to separate the extragalactic CMB light from galactic light, allowing us to study cosmology and galactic astrophysics independently.
Polarization and the CMB
The CMB was first discovered in 1964. This was a major result: the CMB was a key prediction of the Big Bang theory, and its detection represented a major validation of this theory. Since its discovery, scientists have used very precise observations of the properties of the CMB to refine a standard model of cosmology. Thanks in part to these measurements, cosmologists now have a very good understanding of the history and composition of the Universe.
When studying the light from the CMB, scientists can make different kinds of measurements. They can measure the intensity of the light (how bright the light is) at each point on the sky. They can also measure the polarization of the light. Light is a wave, so one can imagine it vibrating as it moves – like a person shaking a jump rope back and forth. Usually light vibrates equally in all directions, but sometimes various processes make it vibrate more strongly in one specific direction. (Imagine a person shaking a jump rope that passes through a picket fence. If the person shakes the rope up and down, the waves can pass straight through the vertical slats in the fence. But if the person shakes the rope side to side, the fence will block the motion.) Light that vibrates more strongly in one direction than another is said to be polarized.
The light in the CMB is slightly polarized. Both the amount and direction of this polarization change across the sky, forming a complicated pattern. Scientists break this pattern down into two different components: E-mode polarization and B-mode polarization. These two patterns are shown below. This particular way of dividing up the total polarization signal is useful because some physical processes produce only E-mode polarization and some produce both E-mode and B-mode polarization. By dividing up the signal in this way, scientists can determine how much polarization each process generates. Each process tells scientists something unique and important about the Universe.
In the CMB, the E-mode polarization component is much stronger than the B-mode polarization component. Almost all of the E-mode polarization signal arises from the small density variations in the early Universe. We therefore mainly use the E-mode polarization signal to learn about the Universe at the time the CMB was emitted, 13 billion years ago. E-mode polarization of the CMB was first detected in 2002 and provided additional confirmation of the Big Bang theory.
In contrast to the E-mode signal, which is overwhelmingly generated at the moment the CMB is emitted, the weaker B-mode polarization signal can tell us about everything from the early Universe to the very local environment within our galaxy. After the light from the CMB is emitted, some of the original E-mode patterns are changed into B-mode patterns before reaching Earth as the CMB light travels past galaxies and galaxy clusters. These objects are so massive that their gravity can bend the light’s path, changing its polarization. This process is called gravitational lensing. The gravitational lensing B-mode polarization signal tells scientists about how matter is distributed in the Universe on the largest scales, which constrains models of cosmic evolution. This was the first type of B-mode polarization to be detected in the CMB and its amplitude is exactly as predicted by the standard Big Bang theory.
Various processes in the Milky Way can also generate microwave light with both E-mode polarization and B-mode polarization. The most significant process at the frequencies we observe is emission from galactic dust. Some regions of the sky contain much less dust than others, but no part of the sky is completely dust-free. The exact amount of polarized dust was not well known until recently, when the Planck satellite published polarization measurements of the entire sky at seven microwave frequencies. Planck found that the B-mode signal from polarized dust was at least as large as B-mode signals from other sources, even in the cleanest regions of the sky.
The final source of B-mode polarization in the CMB is the Big Bang itself. Measuring this type of B-mode polarization is the main goal of my group’s experiments. Scientists studying the beginning of the Universe have theorized that in the first fraction of a second of its existence, the Universe went through a period of ultra-fast expansion, doubling in size many times over. This theory is called inflation. The super-rapid expansion of space sent shockwaves called gravitational waves reverberating throughout the Universe. As a gravitational wave passes through a region of space, space itself expands and then contracts slightly. This stretching and squeezing of space distorts any light in that region of space, generating polarization. The gravitational waves produced by inflation were still echoing through the Universe 380,000 years later when the CMB formed, so they should have polarized the CMB as well. Different inflationary theories make different predictions about the strength of the gravitational waves produced – and therefore about the strength of the polarization signal they impart to the CMB – but all of the theories agree that inflation should generate both E-mode and B-mode polarization. We focus on the B-modes because inflationary E-modes will be swamped by the larger E-mode signal from density variations. Once we detect B-mode polarization and verify that it comes from gravitational waves rather than gravitational lensing or galactic dust, we can determine which of these theories is correct. It is a very difficult measurement to make, since the amount of polarization is very small, but if our group is successful we will be the first people to ever see back in time all the way to when the Universe was less than a second old. It is impossible to reproduce such extreme conditions in any laboratory on Earth, so we will truly be exploring new physics.
Searching for Inflation
Last March, my research group published a very exciting result: after three years of staring at the same small patch of sky, our BICEP2 telescope had detected B-mode polarization. The signal was partially due to gravitational lensing, but we needed a second component from either galactic dust or gravitational waves to explain the full signal. Based on the best models of galactic dust available at the time, we concluded that the excess signal was too strong to be entirely due to dust emission. It therefore seemed highly likely that we had detected evidence of gravitational waves. If true, this would be groundbreaking: direct experimental confirmation of the theory of inflation. BICEP2’s maps of the polarized microwave sky are shown below.
Since BICEP2 could only see one frequency, we couldn’t distinguish gravitational waves from dust using our data alone – we had to rely on models from other sources, which were known to be highly uncertain. Within a few months after our discovery, we therefore started working with the Planck team to combine our data with theirs to better understand the origin of the B-mode signal that we had seen. Planck had their own polarization measurements of the entire sky at seven frequencies, but their data was noisier than ours so they couldn’t directly confirm our observations by themselves. However, by averaging over a larger area of the sky, the Planck team had already begun to realize that dust in our region might produce stronger B-modes than models had predicted, making a joint data analysis even more critical. By using Planck’s high frequency observations to constrain the polarization of the dust in combination with our BICEP2 data and new data from our latest telescope (the Keck Array), we were able to gain more insight into the polarized microwave emission in our patch of sky. At the end of January, we published the results of this joint analysis.
By combining our data with Planck’s data, we learned that the dust in our galaxy is more highly polarized than expected in our patch of sky. This means that the dust’s glow could explain most or all of the signal that our group announced last spring. Any portion of the signal created in the early Universe is too small to robustly distinguish from background noise, even after using all of the data currently available. While this may seem disappointing, even being able to limit the maximum brightness of the B-mode signal from the early Universe already tells us something new about fundamental physics and rules out some theories. We will need more data to get a clearer picture – and our group is in an excellent position to do just that! Our Keck Array telescope continues to build on the dataset collected by BICEP2 and is in better shape than ever, thanks to the upgrades that I helped make in Antarctica this year. We also deployed an entirely new telescope this year, BICEP3. Both BICEP3 and the Keck Array will continue to collect more data of increasingly high quality, and several other teams have built their own experiments with the same goal in mind. It is very possible that within the next several years we will have enough data to measure the emission from galactic dust well enough to remove it from our maps of the sky and peer through it to the gravitational waves signal that may lie beyond. Over the past few decades, the CMB has provided a wealth of new information about our Universe – and the most exciting discoveries may still be ahead of us.
My research group’s science website: Learn more about our work, read our scientific papers, or download our datasets.
Wayne Hu’s online cosmology tutorials: If this post inspires you to learn more about cosmology and the cosmic microwave background, these are a good place to start.
The Surface of Light: If you love Disney and/or would rather sing songs than read about physics, then you’ll probably enjoy this musical number about some of the research discussed in this blog post.
Sunday, December 14, 2014
Today we held an open house in MAPO, the building housing the Keck Array, to show the rest of the station what our telescope looks like and to tell them about the science we are doing. In honor of this event, I think it’s finally time for a blog post containing a tour of the building where I’ve been spending most of my time. In a companion post, I will give an explanation of the science we are doing there.
MAPO (the Martin A. Pomerantz Observatory) is located in the Dark Sector, about half a mile from the main station. The Dark Sector is reserved for astrophysics experiments and the use of radios, wifi, or other sources of electromagnetic radiation that might interfere with our observations is forbidden. DSL (the Dark Sector Laboratory), the building housing BICEP3 and the South Pole Telescope (SPT), is also located in the Dark Sector, as is IceCube (an experiment designed to look for neutrinos). There are several other clusters of buildings surrounding the main station, each with a different scientific purpose. The Quiet Sector minimizes radio communications and vibrations and contains long-term seismic monitoring experiments (there are no earthquake faults nearby, but since the Earth spins about the South Pole this is a good place to monitor global seismic activity and long-term oscillations). The Clean Air Sector is located upwind of the main station and contains climate research experiments and the Atmospheric Research Observatory. Since the wind travels hundreds of miles across open ice before reaching the station, with no sources of human pollution (flights must detour around this area), the air is some of the cleanest in the world. Other types of science done here include meteorology (weather balloons are released from the roof of the main station twice daily) and the study of the aurora.
MAPO was built in 1994, which makes it the oldest building in the Dark Sector. Since then it has housed a number of astrophysics experiments, including several designed to observe the cosmic microwave background. The most recent of these is the Keck Array, the telescope I’m working on. We share the upstairs of the building with HEAT, an astronomy experiment designed to look at dust in our galaxy. The downstairs is occupied by a machine shop, which both Keck and BICEP3 have found very useful this year.
Since its construction, MAPO (like all buildings at the South Pole) has been slowly sinking into the snow. It’s impossible to build foundations on solid rock here, as the ice is thousands of feet deep, so the best engineers can do is design buildings that sit on compacted snow, which slowly subsides under the weight of the buildings and new snow accumulation. Most buildings sit on stilts to prolong their lifetime, but all will have to be replaced eventually before they are buried. MAPO is now twenty years old, so this natural settling is starting to become problematic. The first floor is now several feet below the natural snow level, meaning that the station crew has to work hard to dig it out during the summers. An adjacent building, which housed the CMB experiment VIPER and is no longer maintained, is slated to be removed this year as its entire first floor is buried. In a few years MAPO will be taken down too, before it gets covered in snow completely. In the meantime, the drifts on the upwind side of the building are an impressive sight, rather like a frozen, cresting wave.
Upon entering MAPO, one passes through a small cargo unloading area and then enters the machine shop (which takes up almost all of the first floor). Directly above the machine shop are two rooms, one that we share with HEAT (still called the “AMANDA control room” for the AMANDA neutrino experiment, which stopped taking data in 2009) and the other that serves as the Keck control room. The control room contains computers where we can monitor all of Keck operations (the temperatures of various telescope components, the direction the telescope is pointing, etc.), issue commands to the telescope, and do real-time data analysis. Both rooms also contain lab benches that we use for hardware work when we take receivers out of the telescope mount for upgrades and repairs.
Continuing to the left through the control room brings one to the door to the roof and a long hallway full of storage cabinets. Continuing down the hallway brings one to the mount room – the location of the Keck telescope mount, the helium compressors used to keep the five Keck telescope receivers cold, and a server rack containing the six computers that directly communicate with the telescope. It’s a very noisy, active room – the fans from the computers are always running (the computers themselves generate enough heat to keep the room at room temperature) and the cooling system for each receiver makes a chirruping noise, so the net effect is similar to a chorus of mechanical crickets. We don’t spend much time in here unless we are actively doing upkeep and maintenance tasks. If we do need to access the telescope directly, we can climb up into the mount itself by going up a pair of ladders. The video below shows what this looks like.
After coming back out of the mount room and returning down the hallway, one can proceed up to the roof. This is where the most impressive views of Keck are, along with nice views of DSL, the IceCube control center, and the surrounding Antarctic plateau. The roof also has a crane for heavy lifting and a hatch door that opens into the lab below, which we use to transfer receivers downstairs when we take them out of the mount to work on them.
In order to get a view of Keck, one has to enter the groundshield, an impressive aluminum and plywood construction. (The plywood remains unweathered in the cold, dry Antarctic climate.) Together with the forebaffles attached to the end of each receiver, the groundshield blocks any microwave emission from the ground from contaminating our signal. Its design also traps some of the snow that is constantly blown around by the wind, creating a need for one of the least glamorous jobs assigned to South Pole graduate students – shoveling. The five Keck receivers protrude from a central platform that insulates the inside room-temperature environment from the much colder outside air. This platform can tip sideways and swivel back and forth, to look at different regions of the sky and track our particular field as it rotates around the celestial South Pole (due to the Earth’s rotation). The celestial South Pole is directly overhead, as we are right at the geographic South Pole, so stars never set and we can look at the same patch of sky 24 hours per day, every day, all year round. Since we are looking for a signal that originates outside our own galaxy and we don’t want dust and gas within the Milky Way to overpower this signal, we chose to look at one particularly dust-free patch rather than the whole sky. The telescope scans back and forth to cover this field, over and over (as seen in the video below), and we combine all of this data to produce a map of this region. The longer we observe, the less noise we will have in our map.
The Keck telescope started observations in 2011 and has been collecting data ever since, with annual breaks for summer maintenance. It is funded to continue operating through the end of 2016 (although we hope to operate it through 2017 and beyond). It continues to be a world-class microwave instrument and we hope that its data will continue to produce exciting results for years to come!