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)

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)

May 8: “Al Otro Lado del Espectro” (At the Other Side of the Spectrum)

Our last public outreach night of the semester took place on May 8th and it was a very special one since it marked the first Spanish-speaking outreach event in many years. The whole event was conducted in Spanish, including announcements, the presentation, and the activities that took place afterward. It was a mixed audience, consisting of regular attendees, people interested in practicing their Spanish, and Spanish-speakers in the community.  

Alejandro Núñez, a graduate student in the Astronomy Department at Columbia University, gave a talk titled "Al Otro Lado del Espectro" ("At the Other Side of the Spectrum"). Alejandro started the talk by describing the wave nature of light, and introduced concepts such as frequency and wavelength. Then he showed several spectacular images of celestial objects at different wavelengths, starting from the long-wavelength radio waves, all the way to the short-wavelength gamma rays. He included many images of the Sun, other planets, and our Milky Way.  He concluded by showing us the different telescopes capable of observing the different parts of the electromagnetic spectrum.

After the talk, many audience members went to the roof to see Jupiter and M3 through the telescopes, where they had the opportunity to talk with the Spanish-speaking volunteers.  Some  attendees stayed in the lecture hall asking Alejandro a few more questions. In addition, undergraduate student Gladys Velez-Caidedo  showed several movies on the 3D wall.  It was a good turnout and we expect to have similar events in the future.  

-- Ximena Fernandez (graduate student)

Apr 24: Galactic Synthesizers

Tonight Adrian Price-Whelan, Columbia graduate student and National Science Foundation fellow, showed us how he has used simulated galaxies to compose original music. First, he had to describe the basic shapes of galaxies an how stars move inside them since the motions of stars are the basis of his method. Starting with spiral galaxies, we heard about their three main components: a flattened disk of stars moving in orderly, almost circular orbits around the galactic center, a spheroidal bulge at the center of the disk where stars move in every direction with nearly random orientation, and an outer halo which surrounds the disk and spheroid, spanning an enormous volume but containing only 1% of the stars. The shapes of these spiral galaxies were contrasted with that of ellipticals, which are generally more "bloby" and whose stars move mostly with random orientations which are quite unlike the most prominent largest components of spiral galaxies, the disks themselves. Despite their relative featurelessness, ellipticals are typically triaxial - that is, they have different extents in different directions, which leads to a variety of orbits with different shapes including long-axis tubes, short-axis tubes, and box orbits. 

To turn galaxies into synthesizers, Adrian built a computer model of a galaxy of each type and populated them with stars. Each star moves with specific frequencies, both in and out from the center of the galaxy and around it; these frequencies were mapped onto scales, with low notes corresponding to short-axis tube orbits of the elliptical galaxies and halo stars of spiral galaxy, mid-tones made by the disk and long-axis tube stars, and high notes produced by box orbits and stars in the spheroid. As the simulation advances the stars ring their notes in a manner similar to plucking a guitar string, while encoding actual physical information about the shape of the galaxy they orbit in to sound. You can listen to his compositions over on Soundcloud: spiral galaxies, elliptical galaxies.

Following Adrian's talk, Columbia graduate student Emily Sandford presented some slides describing variety of Earth-Sun-Moon arrangements and how they lead to solar and lunar eclipses, which then smoothly transitioned into a discussion of the Kepler space telescope since it uses a very similar principle to find planets around other stars - it precisely measures the dimming caused by an extra-solar planet passing between its host star and the Earth. Upstairs, undergraduate Gladys Velez-Caidedo and post-doctorate researcher Shy Genel ran the 3D wall, illustrating a wide variety of astronomical phenomena.

-- David Hendel (graduate student)

Feb 27: Neutron Stars

This past Friday, Slovko Bogdanov, a research scientist at Columbia University, gave a great talk telling us all about neutron stars. While stars are kept from gravitational collapse by the burning of their nuclear fuel, when this fuel source runs dry, look out! The resulting supernova can outshine the light from an entire galaxy. Neutron stars are the result of this process -- when a massive star collapses, the remainder is so compact that it can fit the mass of the Sun into a star the size of Manhattan. We looked at a number of supernova remnants and learned out about the discovery of fast spinning pulsars. We also learned about an event in December 2004 where a starquake in a magnetar (a highly magnetized neutron star with magnetic fields more than 100,000,000 times stronger than anything scientists can create) released a blast of gamma-radiation so strong that it had the same ionizing effect on our atmosphere that strong solar flares do -- but from a distance of 50,000 light years. Yikes!

Afterwards, Columbia Post-Bac David Jaimes gave a slideshow on the recent Rosetta Mission, where after 10 years, we successfully landed a probe on Comet 67P. He showed us some gorgeous close up images of the comet, and described some of the science behind this amazing feat of engineering. Others wandered to our 3D-wall, where we screened several different movies showing simulations of colliding galaxies and more. Up on the roof, the skies were clear and we had clear views of Jupiter, the moon, and the Orion Nebula with our Big and Little Dome telescopes.

-- Jennifer Weston (graduate student)

Feb 13: New Developments in Gravity

It was a pleasure to have Dr. Rachel Rosen, Assistant Professor of Theoretical Physics at Columbia University, give a lecture on the New Developments in Gravity. Dr. Rosen is an expert in areas of research pertaining to field theory, cosmology, and particle physics. She is recognized for her contributions to the theory of massive gravity, a modified theory of gravity. In the lecture, she explained to us that the currently accepted standard theory of gravity is Albert Einstein’s general relativity. In this theory, the graviton (the particle responsible for the force of gravity) is a massless particle. However, Dr. Rosen stated that people have been interested in whether or not it's possible to modify this theory of gravity, particularly at large distances. One way to do this is to give the graviton a mass and make it a massive particle. Recently, it has been shown that it is possible to have theoretically consistent theories in which the graviton has a mass. The recent discovery of dark energy and the associated cosmological constant problem has prompted investigations for long distance modifications of general relativity. Dr. Rosen believes that making the graviton a massive particle may lead us to understand natural phenomena like the observed expansion of the universe.

After the main lecture, graduate student, Stephanie Douglas, gave a brief talk on star-forming regions in open clusters.  She showed images of open clusters such as Trumpler 16, Pleiades, Hyades, Alpha Persei, all ranging in age between 500,000 and 680 million years. Stephanie explained how some of the open clusters have regions that glow differently in different parts of the light spectrum (i.e., visible versus infrared).  She explained that when look at regions obscured by gas and dust in at different wavelengths we can pick out areas where stars are being formed.

After the lecture, audience members headed up to the roof to see the Moon, Jupiter, and the Orion Nebula. Graduate student, Adrian Price-Whelan, set up a digital SLR camera in the Big Dome to demonstrate how it's still possible to see faint sky objects, even from the heart of New York City. The image below was taken through our 14" Meade telescope.

-- David Jaimes (post-back student)

Jan 30: Cosmic Stretchmarks

Tonight Princeton post-doc, and cosmologist, Renee Hlozek explained what light can tell us about the early universe. She showed us this map of light from the early universe, called the Cosmic Microwave Background, which is almost entirely uniform - the temperature fluctuations shown are only a few parts per million. But such uniformity, along with the observation that the universe appears perfectly flat, was a problem for theories about the universe's beginning.  For the temperature fluctuations to be so small, every part of the universe must have been in contact at the beginning. Renee used the example of communication across the big lecture hall - if she asks the person in the front row what the favorite band is of the person in the back corner, the front row person won't know unless she has talked to the other person. 

So scientists came up with the theory of cosmic inflation, which explains the Cosmic Microwave Background very well. But Renee also told us that scientists don't want their theories to simply explain existing data - good theories also make testable predictions for future observations.  And inflation theories predict that we should see a particular type of polarization (the orientation of light rays as they reach our detectors) that isn't produced by any other object in the universe. So if we detect that type of polarization, called B-modes, then we have good evidence for inflation!

Many experiments are studying the Cosmic Microwave Background, and last year one of them announced that they had detected B-modes, but a leaked press release for tomorrow indicates that their supposed detection was probably due to interference from dust in our Galaxy. Renee told us that this is a product of good science - the scientific method involves checking your own and other people's work, to make sure results are accurate.  Renee works on a collaboration using the Atacama Cosmology Telescope, one of many experiments studying the Cosmic Microwave Background. She showed us a picture of the telescope, and also of four women who built one of its instruments. Another instrument currently being added to ACT will also look for B-mode polarization - it may still be out there!

After the main lecture, graduate student Andrea gave a short slideshow on a few asteroids and comets that have passed by Earth recently, and undergraduate Erin showed movies on the 3D Wall.  Graduate students Adrian, Jose, and Emily, along with undergraduate Rasmi, braved an extreme wind chill to let our attendees see Jupiter and the Moon from two dome telescopes on the roof. 

-- Steph Douglas (graduate student)