Nov 10 - Going out in style: Nebulae at the end of a sun-like star’s life

Our speaker this week was Rudy Montez, an astrophysicist at the Chandra X-ray Center of the Smithsonian Astrophysical Observatory in Cambridge, MA. Rudy studies "planetary nebulae," the ghostly shells sloughed off by dying stars.

Rudy began by showing a gallery of beautiful Hubble Space Telescope photographs of planetary nebulae, explaining how the various colors tell us about the composition of the layers of each nebula. He noted that astronomers always expected planetary nebulae to be spherical, because they're believed to form as the outermost layers of a giant star expand away in all directions from the hot core.

But that's not what we see! Real-life nebulae display amazing, complex structure, including dumbbell-shaped bi-polar lobes. Rudy explained that the leading hypothesis to explain the formation of these lobes is that a donut-shaped ring of dust surrounding the dying star blocks the star's outer layers from expanding in certain directions, forcing them out at the opposite openings of the donut hole. The origins of this ring of dust are not quite clear, but they may be leftover debris from a pair of binary stars orbiting each other at the center of what will eventually be the nebula.

Rudy then discussed his area of particular expertise: X-ray observations of planetary nebulae from the Chandra space telescope, which give us a window onto the hottest, densest central regions. He showed beautiful composite images of Chandra, Hubble, and Spitzer data, which illuminate, respectively, the innermost, middle, and outermost regions of planetary nebulae. Three windows onto these extraordinary objects.

Dec 16 - How to Hold a Dead Star in Your Hand

Our speaker, Kimberly Arcand, didn't come from an astronomy background. She began her science career as a biologist studying deer ticks, then moved into computer science before joining the Chandra X-ray Center (CXC), where she is now the visualization lead. Her job is to take the data and turn it into interesting and useful pictures. The data is beamed down from the telescope to NASA and then sent to the CXC as a lot of 1s and 0s. This is cleaned and assembled into black and white images; part of Kimberly's job is to determine how best to color these images to make them informative. Often, Chandra images are colored by the X-ray energy range or the dominant chemical/element.

Color has meaning. Kimberly spends part of her time studying responses to different color schemes, and choosing the right color scheme based on the audience for an image. Scientists think of blue as hottest, but culturally most people associate red with heat. Because Chandra images are important for outreach to the general public, her team picked red for the hottest parts of an image, rather than the blue that the scientists wanted.

Kimberly also told us about her work on visualizing the Cassiopeia A supernova remnant. Chandra (along with the Spitzer infrared telescope and Hubble Space Telescope) has observed this expanding shell of gas over many years, and you can actually see the gas moving outward in images taken several years apart. There is enough data that her team could use software borrowed from brain imaging to make the first 3D model of a dead star. She showed us a movie where we flew through the Cas A remnant. They also made a 3D printed model of the remnant - you can download the free file here if you want to hold your own dead star in your hand.

After the lecture, undergraduate Richard took us on a tour through all the scales of our universe, undergraduate Briley showed short astronomy movies on the 13th floor, and graduate students Alex and Aleksey led tours of the roof. Myself and graduate student Moiya also helped facilitate in the lecture hall.

-- Stephanie Douglas (graduate student)

October 5: X-ray Spectacular!

On October 5th, over 175 people came to Doug Thornhill's talk on the newly launched X-ray telescope NuSTAR. NuSTAR was assembled at the Nevis Laboratories of Columbia University and Doug worked with the NuSTAR team for almost four years as an undergraduate student at Columbia since the beginning of the project. He provided a clear and thorough explanation on how x-ray telescopes work, with a physical demonstration on how light is detected by the telescope. Doug then showed how NuSTAR was built and discussed the scientific goals of the telescope including the survey of super-massive black holes, supernovae remnants and compact objects, as well as the study of the energy transport of our sun.

After the talk, some people stayed in the lecture hall to enjoy the movie "High Energy Vision: The Chandra X-ray Observatory," which is another NASA X-ray telescope launched more than a decade ago. 

As it was a fairly clear night, many people headed up to the roof to view the night sky through the telescopes. Additionally, Columbia undergrad, Bryan Terrazas, showed 3D movies on the 13th floor. 

Join us for our next event on October 19th, when we will hear from Or Graur on how astronomers use the universe as their laboratory.

--Yuan