This image might not look like much, but it’s actually an amazing step forward for solar astronomy. It captures the image of a large sunspot not in visible light, but in microwaves. 

The difference is important because different wavelengths of light are emitted by different layers of the Sun’s surface. The visible light we see everyday mostly originates from the photosphere, which is the lowest or deepest part of the Sun that we can directly observe. Microwaves are emitted by the chromosphere, which is the next layer above the photosphere. The chromosphere is much less dense than the photosphere, and has lots of interesting phenomena such as filaments and prominences, formed by a complex dance of thermodynamics, magnetic fields, and plasma. The chromosphere is also unusual because it’s actually hotter than the photosphere. You might expect the Sun is hottest at its interior, and the farther out you go, the cooler things become. That’s true for the photosphere, but not the chromosphere. The chromosphere is coolest near the photosphere with a temperature of about 4,000 K, but heats up as you move outward, reaching a temperature of 25,000 K. Just how the chromosphere gets so hot remains a bit of a mystery.

The mysterious heating of the chromosphere is also what typically allows us to see it. Although it’s very diffuse, parts of it emit visible light. We typically have to look at the edges of the Sun to see it (or during a solar eclipse) since the brilliant light of the photosphere is so bright. But in microwaves the chromosphere is brighter than the photosphere. The problem has always been that microwaves are observed with radio telescopes, which typically have a low resolution. This new image is from the ALMA observatory, which can capture microwave images with a resolution rivaling that of Hubble. These new images have enough detail that we can start to see some of the complex behavior of the chromosphere.

And that may help us understand just how the chromosphere gets so hot.

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In the cold depths of space, interactions between gas and dust can produce a range of complex molecules. Everything from water and alcohol to the basic building blocks of life. While much of this chemistry occurs in cold molecular clouds, molecules can also be produced in the warm regions surrounding a young star, in what is known as a hot molecular core. A few hot molecular cores have been observed in our galaxy, but recently one was discovered in the Large Magellanic Cloud. Somewhat surprisingly, the molecular composition of this extragalactic hot molecular core is strikingly different from the ones seen in our galaxy. 

The young star in question is known as ST11, and it was recently observed by the ALMA radio telescope array. ALMA is particularly suited to observe complex molecules in space, because it is able to view them at the kind of sub-millimeter wavelengths these molecules often emit. ALMA was not only able to observe the warm dust around ST11, but also molecules such as formaldehyde and nitrous oxide. The region is lacking other molecules such as methanol, which are common in cold molecular clouds. Since the formation of different molecules depends not only on the available elements but also temperature and cloud density, the study of such hot molecular cores allows us to better understand complex molecular interactions in space, which can give us clues about how complex chemistry and even life formed on Earth.

One key difference between the Large Magellanic Cloud (LMC) and our own Milky Way galaxy is that the LMC has a much lower metallicity. This means it has a lower fraction of heavier elements such as silicon, oxygen and iron. These elements are common building blocks of interstellar dust, which is why the LMC has a lower fraction of such dust. A great deal of complex chemistry can happen on the surface of dust grains as it interacts with surrounding gases, and a lower metallicity means such interactions are less common. We see this in the types of molecules forming around ST11. Given the density of ST11’s hot molecular core, the levels of molecules such as formaldehyde and isocyanic acid are a tenth to a thousandth of levels seen in the Milky Way. This demonstrates the central role of dust surface chemistry to the formation of these molecules.

It’s a powerful insight into just how young stars can seed the cosmos with some of the complex molecules we see around us.

Paper: Takashi Shimonishi, et al. The detection of a hot molecular core in the Large Magellanic Cloud with ALMA. The Astrophysical Journal, Volume 827, Number 1 (2016)

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The Hubble Ultra Deep Field is a particularly dark patch of sky about the size of a grain of sand held at arm’s length. It was first imaged by the Hubble telescope in 2004, and was found to contain about 10,000 galaxies in its field of view. Other observations of this patch of sky have been made over the years, so that we now have images ranging from infrared to ultraviolet. The galaxies of the HUDF are among the most distant ever observed, stretching back to the earliest age of galaxies. Since Hubble can only detect light within the roughly visible range, its view of the galaxy formation period is limited. But now the ALMA telescope array has captured the HUDF, and it’s given us a new view of these distant galaxies. 

ALMA is a radio telescope capable of viewing the sky at millimeter and submillimeter wavelengths (just below infrared), which is the type of wavelength that cold gas and dust emit. Since these wavelengths are longer than infrared, ALMA can also see more distant galaxies than Hubble, since the light of distant galaxies are greatly redshifted. The ALMA survey was able to see galaxies rich in carbon monoxide (CO), which is commonly found in large molecular clouds that can trigger star formation (seen in yellow in the image above). Since cold CO gas emits a specific spectral fingerprint, ALMA could also determine the redshift and thus the distance of these star-forming galaxies. They found that more distant galaxies had higher CO levels than less distant ones, which could have triggered the peak period of star formation that occurred when the Universe was about 4 billion years old.

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The Milky Way is visible from anywhere on Earth. While it makes for a lovely milk-like glow across the sky, it is also filled with gas and dust that can limit our view of certain parts of the sky. While we can map out where certain gas and dust is through the Milky Way, making an accurate map is challenging because much of it is cold and diffuse, making it difficult to observe. But with the rise of submillimeter radio astronomy, that’s changing. 

Cold gas and dust emits faint light in the submillimeter range, so to study this material we need good radio telescopes. Unfortunately our atmosphere (mainly water vapor) absorbs these wavelengths, so the radio telescopes need to be located in a dry region at high elevations, such as at Chajnantor plateau in northern Chile. The most famous telescope at Chajnantor is the Atacama Large Millimeter/submillimeter Array (ALMA), which is an array of about 60 antennas. But just down the way from ALMA is the Atacama Pathfinder Experiment (APEX), which has been mapping the gas and dust of our galaxy.

The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) has been scanning the Milky Way at submillimeter wavelengths, and has just released a full map of our galaxy. You can see one of their images above, which shows the wonderful complexity of the Milky Way, with fine tendrils of gas and dust. Creating a map such as this will not only help astronomers better understand our own galaxy, but also allow astronomers to better take the effects of our galaxy into account when looking beyond our neighborhood of stars.

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One of the more powerful techniques of radio astronomy is the use of interferometry to combine the signals of several radio antennas into a single virtual telescope. Through interferometry we can make radio images with resolutions greater than that of the Hubble telescope. But how does interferometry work?

At a basic level, interferometry is simply the combining of signals from two different sources. If the two signals are similar they will combine to make a stronger signal, and if they aren’t they will tend to cancel out. Where this becomes useful for astronomy is that if two signals are out of sync you can shift them (correlate them) so that they are in sync. When the signal is strongest you know they are lined up.

A schematic of an interferometer system based on Thompson et al.

When two radio antennas are aimed in the same direction, they receive the same basic signal, but the signals are out of sync because it takes a bit longer to reach one antenna than the other. That difference depends on the direction of the antennas and their spacing apart from each other. By correlating the two signals, you can determine location of the signal in the sky very precisely. It’s the precision that you need to create a high resolution image.

Two antennas only give you one point in the sky, but with dozens of antennas (such as the array at ALMA) you can get lots of points, one for each paring of antennas. But even that only gets you a discrete set of image points. If the Earth were fixed in relation to the sky, then our radio image would look like a pointillist painting.

But the Earth rotates with respect to the sky, so as time goes by the relative positions of the antennas shift with respect to an astronomical signal. As you make observations over time, the gaps between antennas are filled to create a more solid image. This isn’t easy to do. It takes lots of observations and lots of computing power to combine the images in the right way. At ALMA, for example, it takes a custom built supercomputer that spends all its time correlating signals.

But the results are nothing short of spectacular.

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Chajnantor means “place of departure,” or more poetically “place of ascension” in the Kunza language of the Atacama region. It is a plateau about 5000 meters (16,000 feet) above sea level. Its elevation and arid climate makes for extremely difficult working conditions, but it also makes it perfect for the Atacama Large Millimeter/submillimeter Array, or ALMA.

ALMA is one of the first truly international astronomical endeavors. Rather than being spearheaded by a single nation with others lending primarily financial support, ALMA is a collaboration between the United States (NRAO), Europe (ESO), East Asia (NAOJ) and the Republic of Chile. It’s coordination has been likened to the United Nations. Given ALMA’s 1.4 billion dollar price tag, international collaboration was the only way the project was feasible.

A 12-meter antenna. Yours truly for scale. Credit: Tim Spuck

ALMA consists of more than 60 12-meter antennas as well as 12 7-meter antennas. The 7-meter antennas are designed to be closely spaced, forming the Atacama Compact Array (ACA). Since the antennas use interferometry to create images of the sky, the ACA creates a wide sky view, while the larger array of 12-meter antennas allows us to focus in on particular objects. The antennas can be moved to different locations to allow for different scales and resolutions.

The engineering of ALMA is incredibly ambitious. In order to combine signals from the antennas, a supercomputing correlator had to be built on the plateau. It is the highest altitude supercomputer on the planet. The correlator not only has to account for the arrangement of the antennas, but also the orientation of the Earth relative to the target object. As the Earth rotates, the effective separation of the antennas change. While this gradual change is a computing challenge, it also allows us to create a more complete image of objects.

Because ALMA focuses on millimeter wavelengths, it is perfectly suited to image cold molecular clouds, both in interstellar regions and surrounding young stars. Since it can image these clouds with the resolution similar to that of the Hubble telescope, it’s able to provide an incredible view of things like planets forming around other stars.

ALMA has only begun what is intended to be a 30-year mission to study the universe. As the largest international astronomy collaboration, it is perhaps fitting that it resides at Chajnantor, as it will likely be a place of departure toward some incredible astronomical discoveries.

This post was made possible in part by the ACEAP project, funded by the National Science Foundation.

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Yesterday we arrived at the Atacama region of Chile, and are staying in the small town of San Pedro. Atacama is perhaps the driest region in the world, and San Pedro is at an elevation of about 8,000 feet. That combination can be quite a punch. Fortunately we’ve been at a similar elevation the past couple of days at CTIO, so that isn’t too bad. The arid air, however, is a different story. Hydration is key at this point.

While Cerro Tololo had an almost overwhelming beauty to it, Atacama is a bit different. Magnificent desolation, to paraphrase Buzz Aldrin. But the arid and high conditions of the region are exactly why ALMA is here.

But that’s a story for tomorrow. For now it’s time to have a bit more water, and get some sleep.

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Neil Armstrong didn’t go to the Moon. He was sent to the Moon by a skilled and hardworking team known as NASA. Armstrong wasn’t just along for the ride, but he didn’t do it alone. We don’t remember most of the NASA team, but we do remember Armstrong.

The same is true with modern big science. We read about the results, and we might see a quote or two from the primary scientists, but there’s an entire team that makes the scientific findings possible. We remember the show, but not the team behind the curtain.

We can now observe planets forming around other stars. Data gathered at ALMA, and funded by NSF.

Take, for example, the Atacama Large Millimeter/submillimeter Array (ALMA). It currently has 64 telescopes working together to study the sky at microwave wavelengths. It’s done some amazing work so far, and it will continue to do amazing work for at least the next 30 years. ALMA is only possible through a collaboration between Europe, the United States and Japan. Each of these have a corresponding research organization (ESO, NRAO, and NAOJ), and each of these organizations are funded through different governmental institutions. In the case of the U.S. it’s the National Science Foundation (NSF), the same institution that’s funded my trip to Chile.

There are hundreds of people working directly at ALMA. That doesn’t count those that coordinate behind the scenes, including the U.S. Embassy in Chile. Large science projects such as ALMA require both financial and political power to make it happen, and it’s only possible through international collaborations. If you’ve ever served on a committee at work you’ll understand just how amazing these big science collaborations actually are.

But the vast majority of people supporting ALMA and it’s science will never be mentioned in a press release, nor interviewed regarding their contribution to science. But their work behind the curtain is absolutely necessary. Without them, ALMA and other big projects like it wouldn’t be possible.

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Every now and then in astronomy we’ll get an image that lets us actually see phenomena we have previously just deduced from other observations. The image above is one of them. It was taken by the Atacama Large Millimeter/submillimeter Array (ALMA), and shows an exoplanetary system in the process of forming. This isn’t an artistic rendering, it’s an actual image.

We’ve known for a while that planetary systems form along with a star. Known as the nebular model, the basic idea is that as a star forms within a large nebula (known as a stellar nursery) the surrounding gas and dust form an accretion disk around the star. Over time, protoplanets form within these disks, eventually clearing the system and becoming a planetary system such as our own solar system. We have a lot of evidence to support this model. We’ve observed stars forming within nebulae, and we have computer simulations showing how stars form an are cast out of a stellar nursery.  We’ve observed protoplanetary disks around young stars, and we have computer simulations showing how protoplanets begin forming within these disks. We’ve also found lots and lots of exoplanets. So we’ve known that out in the universe there are young stars where protoplanets are actively forming, we just haven’t observed them directly. Until now.

This particular image is of a star known as  HL Tauri. It is a young T-tauri type star about 450 light years away. The image was taken at wavelengths on the order of a millimeter, which is particularly good at penetrating the nebular material surrounding the young star. Because ALMA is an array of telescopes spread across 15 kilometers, it can capture images with a higher resolution than Hubble.

The ALMA telescope array. Credit: ALMA (ESO/NAOJ/NRAO), C. Padilla

It’s the detail of this image that is astounding. Not only can you clearly see the disk, you can actually see gaps in the disk. These gaps are due to protoplanets either clearing the region of their orbit, or creating resonances within the disk to produce gaps, similar to the way Jupiter produces Kirkwood gaps in the asteroid belt. This image is crystal clear evidence of protoplanet formation, just as the nebular model predicts.

ALMA is still in its early stages. In a way, it is one of ALMA’s baby pictures as it gets up to speed. It also happens to be a baby picture of a whole new solar system.

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