Dec 4 - On the Care and Feeding of Black Holes

Aleksey Generozov, a 4th year PhD student in the astronomy department, introduced us to the majesty of black holes. Black holes are regions in space-time, where gravity is so strong that nothing (particles or even light) can escape from inside; we could make a black hole if we squeezed the entire earth into the size of our fingernails.

Aleksey next described the discovery of a supermassive black hole at the center of our galaxy, the Milky Way. Observing the orbits of stars very close to the galactic center, with very high precision, astronomers concluded that an object very massive (with mass a few million times the mass of the sun) and very compact (that would fit in a sphere with radius smaller than the radius of our solar system) must be hidden in the galactic center. The only feasible explanation was a huge black hole. These days, we are actually on the verge of seeing the radius of the black hole (the event horizon), with a network of radio telescopes positioned around the globe.

And although the black hole at the center of our galaxy is relatively quiet, this is not the case for every galaxy. In the '60s, astronomers discovered some very bright radio sources, equally bright as some nearby stars, which they named quasars (quasi-stars). Later, when the size and distance of these objects were measured, it was realized that the enormous amount of energy is produced when gas falls onto a supermassive black holes at the center of a very distant galaxy. The gas is brought to the central black holes, when two galaxies collide. This also explains why our own supermassive black hole is quiet; It's starving! However, there is some evidence from observations of very high energy photons, that our own black hole had a more spectacular past. The talk concluded with Aleksey and the audience singing along "twinkle-twinkle quasi-star".

After the lecture, the audience had the chance to hear about the K2 mission, which is the second phase of NASA's Kepler space telescope, lead by graduate student Stephanie Douglas. Moreover, they had a chance to further explore galaxies and black holes by watching 3D movies, guided by undergraduate Briley Lewis. The clear sky and the mild temperature gave us a wonderful opportunity for stargazing on Pupin's roof with the help of Adrian Price-Whelan, Emily Stanford, Daniel De Felippis, Rasmi Elasmar, and Richard H Nederlander. Attendees were treated to views of the Andromeda Galaxy, the Pleiades star cluster, and the Red Giant Betelgeuse.

-- Maria Charisi (graduate student)

Oct 30 - Re-tuning the Hubble Diagram

Our lecture this past Friday was by Columbia Astronomy graduate student David Hendel entitled "Re-tuning the Hubble Diagram".  David used stunning Hubble images to demonstrate the diversity in galaxy shapes and discuss how astronomers classify them. He then went on to discuss why this organization, the Hubble Tuning Fork, can be misleading and how galaxies can be transformed from one classification to another.

After the lecture, some stayed for a lecture on our Local Group by Lauren Corlies and Mihir Kulkarni and Richard Nederlander ran the 3D wall and a discussion on stellar structure. Up on the roof, the weather was great for observing. Yong Zheng led volunteers Emily Sandford, Alex Teachey, Aleksey Generozov and Zephyr Penoyre in pointing the telescopes at double star Albireo, the Double Cluster, and the elusive Andromeda Galaxy.

Overall, it was a great way to kick off the Halloween weekend.

-- Lauren Corlies (graduate student)

Sept 18: Hubble IMAX

The Hubble Space Telescope has been humanity's eye on the universe for over 25 years now. In honor of the observatory's birthday this year, last Friday we screened the IMAX film "Hubble" at Columbia. We were moved to a smaller room this year, but one of our biggest crowds ever came out to celebrate Hubble with us.

Hubble was launched in 1990, but was partly disabled until a 1993 servicing mission installed a contact lens (of sorts) that allowed Hubble to reach its full potential. Though the movie included clips from the launch and first servicing mission, it focused on the final shuttle mission to Hubble in 2009 (there were four servicing missions with five shuttle visits in total, not including launch). We watched as the astronauts, including now Columbia Engineering Professor Mike Massimino, persevered through technical and mechanical challenges to replace important instruments and stabilizing gyroscopes. These repairs enabled Hubble to continue its crucial role of observing our universe.

Another highlight of the film was the animated fly through of the iconic Hubble image of the Orion Nebula. The Hubble data on Orion is so detailed that scientists at the Space Telescope Science Institute and the National Center for Supercomputing Applications were able to reconstruct the Nebula in 3D. Although we couldn't show the 3D version, flying through the brightly colored nebula and zooming in to see the gaseous disks around infant stars took everyone's breath away.

After the movie, we showed a simulated clip of the Andromeda Galaxy colliding with our own (based on Hubble data), along with a cool solar system model built in the Black Rock Desert. On the roof, graduate student Steven Mohammed and four other volunteers who showed off the Andromeda Galaxy and the Ring Nebula. And when one of our 3D projectors on the 13th floor crashed, undergraduate Briley Lewis and grad student Zephyr Peyore thought fast and created a new presentation to educate visitors.

-- Stephanie Douglas (graduate student)

Oct 24: Stripping Stars

This week's Astronomy public lecture was given by post-doc fellow, Nick Stone, from Columbia Astronomy.  His talk "Stripping Stars: The Exciting Lives and Untimely Demise of Stars Near Supermassive Black Holes" led the audience to discover the dynamic processes associated with black holes.  Starting with an introduction to basic dynamics predicted by Newton's laws of motion and then general relativity, Nick familiarized the audience with the concepts of four dimension time-space and interactions between objects via gravity. Then he explained in detail the physics of black hole accretion, and broadened the case to dual-black hole interactions with the help of simulations. Finally, Nick showed what phenomena when we can expect to see as observers on Earth and how we can observe these energetic events in the Universe. 

About 150 people attended the lecture, after which they headed up to the Rutherfurd Observatory for to observe the Pleides open cluster and the spiral galaxy M31 (aka our nearest neighbor, Andromeda). Those who didn't go to the roof were treated to a slideshow on 'Gas Beyond the Milky Way Disk', by graduate student Yong Zheng, which introduced the very diffuse hot gas with more than 10 thousand degrees in the Milky Way potential well.

-- Yong Zheng (graduate student) 

Sept 26: The Inconstant Moon

This week Columbia Astronomy's own outreach director, Summer Ash, discussed the many ways in which the Moon, frequently taken for granted in our night sky, can exhibit surprising and complex dynamics due to its complicated relationship with the Earth. After reminding us of the most well-known variation, lunar phase, she described the months - all six types!

Moving on from illumination effects, Summer described the many ways the orbit of the Moon around the Earth affects how we see it. Since its distance varies, sometimes it seems larger and brighter in the sky that others; this is the origin of the "Super Moon." Additionally, its orbit makes a small angle with the plane of the Earth-Sun orbit, which is why we don't experience eclipses at every new moon. Speaking of eclipses, she reminded us that total eclipses, where the moon completely enters the shadow of the Earth, are the ones you really want to get out of bed and check out. The Moon's red color during such an eclipse is due to the Sun's light being scattered by the Earth's atmosphere, the same reason the Sun looks red-orange at sunset: only red light can make it straight through!

If you were unable to attend the talk, or would like to read more, Summer wrote a blog piece on this same topic which you can read on Starts With a Bang.

After the lecture, graduate student Yong Zheng lead a lively discussion of the Milky Way's gas dynamics while Pratishta Yerakala demonstrated a variety of astronomical phenomena at the 3D wall and Adrian Price-Whelan, Jose Zorrilla, Emily Sandford, Maria Charisi, and Aleksey Generozov ran stargazing from Rutherfurd Observatory atop Pupin Hall. Objects targeted included the Ring Nebula, the Andromeda Galaxy, the Double Cluster and the beautiful visual binary star Albiero. 

-- David Hendel (graduate student)

March 16: Our Galactic Neighborhood

On March 16 at 8 pm, 190 visitors joined us in Pupin Hall to hear from Dr. Gurtina Besla, an expert in predicting the past and future trajectories of galaxies interacting with our own Milky Way galaxy with special emphasis on the Large and Small Magellanic Clouds. She showed us results from her research that have yet to be released indicating the exact manner in which the Andromeda Galaxy and the Triangulum Galaxy will interact and merge with our own galaxy eventually forming a new galaxy: "Milkomeda". Attendees were wowed by the ability for theoretical astrophysicists like Dr. Besla to predict the future of our galactic environment up to 8 billion years from now.

After the amazing lecture, visitors were treated to glimpses from our 3D Wall, a discussion of Astronomy Pictures of the Day, or a tour of our rooftop telescope facilities. Unfortunately, the clouds and haze prevented us from having a view of the heavens this week, but we cross our fingers for future Public Observing nights, the next one scheduled for March 30. Join us then!

--Josh