Feb 19 - Ripples in Spacetime

A record crowd packed into the lecture hall tonight to hear Jillian Bellovary talk about gravitational waves and how to detect them. Jillian's research focuses on supercomputer simulations of supermassive black hole binaries, but her presentation focused on much less massive binaries like those whose merger was detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in September. Gravitational waves are very small distortions in spacetime caused when massive objects are accelerated to high speeds. The distortions measured by LIGO were smaller than the radius of a proton -- and those were caused by two ~30 solar mass black holes merging together. Jillian showed simulations of how these ripples in spacetime are created by the two merging black holes.

Jillian also described how LIGO was able to detect these tiny distortions. LIGO is an interferometer, meaning it measures how light waves interfere with each other (either adding together or canceling each other out) after they travel a very long distance in two perpendicular directions. How the interference pattern changes with time tells LIGO scientists how the distance is changing in each direction. If the "arms" of the interferometer lengthen and compress in a particular pattern, then they know they've detected a gravitational wave!

The sky was cloudy, but graduate students Adrian Price-Whelan and Lauren Corlies, along with undergraduates Amanda Quirk and Cierra Coughlin, showed off the Rutherfurd Observatory. Meanwhile, undergraduates Richard Nederlander and Tze Goh screened short films on the 3D Wall. In the lecture hall, volunteers Stephanie Douglas, Maria Charisi, and Danielle Rowland played videos from PhD comics and from members of the LIGO team at CalTech, and answered audience questions about gravitational waves.

--Stephanie Douglas (graduate student)

Jan 29 - BLAST!

Our first event of the year didn't exactly go as planned as our scheduled screening of BLAST! was plagued by technical difficulties. On the other hand, a thoroughly overcast day miraculous cleared up right as our stargazing began so what might have otherwise been a disappointing night turned into one of the better observing sessions we've had this winter! Led by graduate student Yong Zheng, astronomers on the roof had telescopes pointed at the Orion Nebula, Jupiter and the Galilean moons, and the Pleiades star cluster. On the indoor side, undergraduate Gladys Velez-Caicedo, ran our 3D Wall for a packed house.

For those interested in seeing what actually happened with the BLAST experiment, we hope you'll give us another chance and come see us over the summer for our Film & Stargazing series. We will reschedule our screening of the film then (and will bring every back-up system ever invented).

Thanks to everyone who came out for their incredible patience throughout the evening.

-- Summer (Director of Outreach)

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)

Nov 13 - The Dark Matter of Ghost Galaxies

Multiple galaxies are reported missing from around the Milky Way. The cops have no leads on where to find the missing satellite galaxies. The government is keeping tight lipped. Only one investigator, Jana Grcevich, has any clues to offer on where they have gone.

Dwarf galaxies hold the secrets, and dark matter is the prime suspect. Looking at the stars in these galaxies we can work out that there's less dark matter in their centers than we expect. After deep investigation (and at least one car chase) Jana believes that this can explain why we're not seeing these satellite galaxies, and what their absence can tell us about dark matter and our galaxy.

As well as this packed talk, witnesses enjoyed some hair raising on stage demonstrations of what happens when you crash the most massive galaxies in the universe together by Zephyr Penoyre. They we're able to explore the cosmos even deeper with Shy Genel leading them through a 3D exploration of the hearts of stars and the far edges of the galaxy.

And those who braved the cold and the clouds were rewarded with some stunning views of the Pleiades, Double Cluster, Capella and many others, as our brave team of student volunteers ducked and dove between the clouds, under the steady guiding hand of Steven Mohammed.

-- Zephyr Penoyre (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)

Oct 16: Observing Variable Stars

Stella Kafka, Director of the American Association of Variable Star Observers (AAVSO), gave a dynamic talk on variable stars, terming them "the good, the bad, and the explosive". Good variable stars show very regular periodic signals that can be directly tied to physical processes - like stellar pulsations. Bad variable stars have messier variability, such as star spots rotating in and out of view as they evolve. Finally, some stars explode and suddenly brighten by orders of magnitude. They may explode once (supernovae) or experience smaller surface eruptions (classical novae).

The AAVSO has been collecting data on variable stars for over a hundred years since its founding at the Harvard Observatory in 1911. They are an organization of amateurs who observe variable stars, and their data contributes to professional astronomical research. Even interested members of the public without telescopes can contribute (website).

After Stella's talk, undergraduate Tanay Bhandarkar showed recent pictures of Pluto from NASA's New Horizons mission. Post-doc Shy Genel presented movies on the 3D wall. The team on the roof, led by graduate student Yong Zheng, were mostly thwarted by clouds, but managed to briefly observe the Pleiades.

-- Steph Douglas (graduate student)

Oct 2: The Glorious Past of Our Monster Black Hole

Last week, physics graduate student and NASA fellow, Shuo Zhang, introduced us to the monstrous black hole in the center of our galaxy. It is well established that every massive galaxy hosts a supermassive black hole in its center and Milky Way is not an exception. Astronomers analyzing the orbits of stars in the galactic center, enabled by advancements in observing technology, realized that the only feasible scenario for the dark object in the center is the galaxy is a black hole with mass of a few million times the mass of the sun.

The black hole is known as Sagittarius A-star (SgrA*), since it is located near the border of the constellations Sagittarius and Scorpius. Being the closest supermassive black hole we can observe, SgrA* is of great astronomical interest. But is it a typical black hole? SgrA*, is one of the quietest supermassive black holes among all the nearby galaxies. However, that wasn't always the case. Recently, the Fermi Gamma-ray Space Telescope discovered a bubble of gamma-rays surrounding our galaxy, which indicate that 2 million years ago, the black hole was very active, swallowing gas and expelling in at large distances. 

Shuo also mentioned her own work observing the black hole at the center of the galaxy with an X-ray telescope called NuSTAR (a NASA mission, in which Shuo's research group here at Columbia was a major contributor). Shuo observes sporadic X-ray flares, which last for a few seconds. During these flares the black hole becomes hundreds of times brighter and then returns to its quiet state. The origin of the flares is still unknown and it has been suggested that we observe the heated remnants of an asteroid that was ripped apart by SgrA*.

Unfortunately, the weather did not cooperate to allow stargazing. Whoever stayed after the lecture had a chance to see 3D movies of the galaxy lead by undergraduate student Richard Nederlander, or hear a short presentation by graduate student Emily Sanford, about the exciting discovery of water on the surface of Mars.

-- Maria Charisi (graduate student)