September 21 - Clocks of the Universe

Imagine that half of your wedding guests show up at the venue a month before the event because the government’s decision to add a month to this year’s calendar did not reach them. Turns out that such a scenario could not be completely ruled out in ancient Rome. Mihir Kulkarni, our speaker on Friday, opened our eyes to how the way we measure and keep track of time has evolved through history and how different cultures use different systems.

Until recently, no man-made device could match the regularity of celestial movements. As a result, we used the Earth’s spin, its rotation around the Sun and the Moon’s movements to measure time. These measurements became encoded in the calendars that helped regulate human activity, from seeding to religious festivities. Small differences between the actual movement of celestial bodies and that captured by calendars add to the point where they become noticeable and sometimes, disruptive. Such disagreements were often dealt with through ad-hoc adjustments, but ultimately they inspired calendar refinements based on more accurate astronomical models. This way, we learned about hard-to-measure phenomena such as the precession of the Earth’s rotation axis. As the axis wobbles not unlike that of a spinning top, the closest star to the north pole -called the North Star-, changes. This shift occurs on timescales of thousands of years, long compared with a person’s lifespan but measurable through history.

Finally, minute perturbations and secular changes to the Earth’s movement relative to the rest of the universe pose a fundamental limit to the precision with which we can measure time. To beat these limitations, our current time standards do not rely on astronomical calculations anymore, but that has not removed all implementation challenges, as the “Unix 2038 year” problem illustrates.

After the talk, Mihir answered many insightful questions from the audience. You can also find a detailed summary of the talk by Steven Fertig, of the Amateur Astronomers Association of New York, here.

Clouds prevented us from star gazing, but we had the opportunity of touring the Rutherfurd’s observatory facilities lead by Daniel and Matthew while Douglas discussed some counter-intuitive properties of black holes with the support of animations in our 3D wall.

-- Jose Zorrilla (graduate student)

Mar 3 - Las Atmósferas Estelares

(This was our 3rd Annual Spanish-Language Lecture)

Turns out the Sun has an atmosphere, albeit very different from Earth’s. Alejandro Núñez, a graduate student at Columbia University, unveiled what is known about this gaseous envelope, layer by layer. He further described how a flotilla of space probes is helping scientists clarify some remaining mysteries by continuously gathering data from all angles and wavelengths. The most vexing of these unsolved questions is how the corona -the outer layer of the Sun’s atmosphere- can be hundreds of times hotter than the photosphere -its visible surface-, reaching temperatures in excess of a million degrees Celsius. While a detailed description of the heating mechanism still needs to be developed, it seems to be linked to the complex interaction between the Sun’s magnetic field and its atmospheric plasma.

Turns out the Sun is also a star. Thus, we can extrapolate what we learn about the Sun to other stars. As Alejandro explained, we need to do so with caution, for different stars can have diverse levels of magnetic activity. He illustrated this with a discussion on how the red dwarf at the core of the recently discovered multiple planetary system Trappist-1 seems to be much more active than our Sun, and the consequences that this could have for the habitability of the planets orbiting it.

This was the Spanish public lecture of this season, and the audience had the opportunity to stargaze at the Rutherford observatory on Pupin Laboratories’ roof after the talk. The night was cold and partly cloudy, but we managed to get a glimpse of some objects like the Moon and Mizar through some clearings.

-- Jose Zorilla (graduate student) 

Nov 4 - The Cosmic Origins of the Chemicals of Life

We start, as perhaps all good talks should, with Genesis. Daniel Wolf Savin took us through the first three days of creation, from the light of our universes first stars to the formation of water, and maybe even life, on planets like our own. In the lab his team has recreated the chemical conditions of the first stars and used it to infer some of the evolution and distribution of the chemicals that form the building blocks of life. On the way he also gave us pearls of wisdom such as the best way to ensure a healthy supply of Belgian chocolate in your laboratory, and jokes that even he admitted were "good science but bad comedy".

After his stellar ("good science") talk we also heard from astronomy graduate student Moiya McTier, about how space affects all of our everyday lives. Meanwhile up on the roof we had clear skies, with Stephen Mohammed, Jorge Cortés, Danielle Rowland, and Emily Sandford guiding our telescopes to the Moon, Mars and a proliferation of double star systems. And finally but fluently we had Erin Flowers explaining the wonders of the universe in all your favourite dimensions on the 3D wall.

-- Zephyr Penoyre (graduate student)

Oct 7 - Black Hole Duet

"We did it!" says the soundbite, and while the screen fills with fireworks the lecture hall fills with applause. This is the culmination of an almost century long journey between Einstein's first postulates of general relativity to our first detection of gravitational waves last September.

Maria Charisi, graduate student and guide through the fabric of space-time, took us through the last moments of the life of a binary black hole. The LIGO project has taken almost 50 years, from the first genesis of the theory to the eureka moment of detection, to find gravitational waves. By measuring the minuscule variations in space-time, a fraction of the width of the nucleus of an atom, we can observe the ripples from distant violent collisions between black holes. Since the first detection we've found 2.9 merger events (the last one we're only 90% certain of, the other results ring clearer than a bell) and when we restart it with improvements in a few years we might find as many as 50 more.

After the main lecture Jordan Borgman took us to Tatooine, Luke Skywalker's home planet to talk about how the planets of Star Wars match up with the exoplanets we're discovering in our galaxy. Meanwhile Erin Flowers guided us through 3D visualizations of the universe on all scales.

Up on the roof, Alex Teachey orchestrated a beautiful (mostly) clear night of viewing through the telescopes. In the able hands of Richard Nederlander, Aleksey Generozov and Rose Gibson we had telescopes pointing at Mars, the Moon, and the Double Cluster.

-- Zephyr Penoyre (graduate student)

May 20 - La Escalera de Distancias Cósmicas

Our last public outreach night of the spring semester was a special version, as the whole event was conducted in Spanish. Although the event was targeted to the Spanish-speaking community of New York, the audience was mixed, as some non-Spanish speaking attendees chose to skip the talk and head directly to the roof top to observe the sky. We were lucky enough that night to have bright Jupiter and the Moon easily accessible from our telescopes.

José Zorrilla, a graduate student in the Astronomy Department at Columbia University, gave a talk titled “La Escalera de Distancias Cósmicas” (“The Cosmic Distances Ladder”), in which he explained some of the ideas and methods used in astronomy to determine distances across the universe. He began by explaining the concept of trigonometric parallax and how astronomers use it to measure the distance to nearby stars. He then talked about astronomical objects known as standard candles, such as supernovae and some types of variable stars. These, he explained, can be used to measure much greater distances, to galaxies in the vicinity of the Milky Way and beyond. Lastly, José talked about redshift as a way to measure distances to the most faraway galaxies in the universe. To put it all together, José explained how the different methods rely upon others to determine distances to the most remote objects we know in the universe, hence the term “ladder”. He also pointed out that the discovery of new distance measuring methods has led the revolution in our understanding of the universe and its true extent.

-- Alejandro Núñez (graduate student)

May 13 - The History and Future of Black Holes

Last Friday, NSF Fellow and future NASA Einstein Fellow Dan D' Orazio gave us an engaging tour to the long history of the most exciting and mysterious astrophysical objects. Black holes are objects with very strong gravitational pull, that nothing can escape from them. John Michell was the first to suggest the idea of such a "dark star", in the late 18th century, although this idea went almost unnoticed at the time.

The story continues in the beginning of the 20th century, when Albert Einstein conceived the general theory of relativity, a revolutionary theory to describe gravity. Dan described the early advances of the theory, including the first solution of Einstein's equations for a spherical non-spinning black hole by Karl Schwarzschild, and the skepticism that followed, mainly driven by the famous British astronomer Sir Arthur Eddington. Dan later discussed General Relativity's golden era (the 60s), with several significant contributions by many great physicists, among which the solution of Einstein's equations for a spinning black hole by Roy Kerr and the suggestion that under specific circumstances black hole can emit radiation, the so-called Hawking radiation. Dan also mentioned the history of the term black hole, which was coined in one of NASA's centers, above Tom's Restaurant in our own neighborhood.

By the early 70s, astronomers acquired the first observational evidence for astrophysical black holes with X-ray telescopes. For instance, the X-ray binary Cygnus X-1, in the constellation of Cygnus hosts one of the most nearby black holes. Earlier in the 1950s, astronomers had discovered radio galaxies with very extended jets, which later realized that can only be powered by supermassive black holes, i.e. black holes with a million to a billion times the mass of the sun. A supermassive black hole resides in the center of our galaxy as well and was discovered by detailed observations of the motion of stars in the close vicinity of the galactic center. Dan finished this exciting journey of discovery by describing the most recent breakthroughs, such as the numerical solutions of Einstein's equations 10 years ago and the first direct detection of gravitational waves of two merging black holes by Laser Interferometer Gravitational Observatory (LIGO), just 3 months ago. Even though, so far we had strong evidence for the existence of black holes, the LIGO event serves as the first direct confirmation of black holes.

Unfortunately, due to bad weather stargazing was not possible. However, the audience had a chance to join tours of the Rutherfurd Observatory on the roof of Pupin, lead by graduate students Steven Mohammed and Steph Douglas. Additionally, undergraduate student Richard Netherlander, guided the audience to the majesty of the cosmos through the projections of 3D movies, while, at the lecture hall, Andrew Emerick presented a mini-lecture on reionization and showed a mesmerizing movie about the end of Dark Ages.

-- Maria Charisi (graduate student)

Apr 29 - Explosive Origins of Our Elements

Every single thing we encounter on Earth exists because, at one point, its atoms were processed through stars. This week Sarah Pearson took us through a tour of the origin of the elements, from hydrogen and helium, through every element in our bodies and the world around us. The real stars of tonight's lecture were supernovae, the beautiful explosions that both produce and distribute elements throughout the universe.

Shortly after the Big Bang, the universe consisted almost entirely of hydrogen and helium. At this point, we had a long way to go before enough elements were produced to give rise to the rich chemistry that governs life here on Earth. As Sarah explained, within the first stars, and in every star since then, nuclear fusion smashed together hydrogen and helium to form increasingly heavier, and more complicated elements. However, these elements would still be trapped within the cores of stars if it not were for a weird quirk of physics. As Sarah showed, once iron is produced within stars, they enters its death throws; quickly collapsing then suddenly exploding with tremendous energy....

Sarah showed images observations of supernova remnants, the hot gas left over after a supernova explosion. This gas expands and mixes with its surroundings, carrying elements produced inside the star with it. Over time, after many explosions, these elements mix throughout a galaxy, eventually ending up inside new stars where the cycle continues.

After the talk, we discussed recent updates to the upcoming James Webb Space Telescope (JWST). Lauren Corlies gave an overview of the instrumentation of the JWST, the replacement to the Hubble Space Telescope. Andrew Emerick talked about the science goals of this upcoming mission, from observing exoplanets in the Milky Way to the first stars and galaxies formed near the beginning of the Universe.

-- Andrew Emerick (graduate student)

Apr 1 - New Horizons

This week Lauren Corlies, a sixth year graduate student here at Columbia, took us on a journey to the far reaches of the Solar System with the fastest spacecraft every built.

New Horizons is the fruit of a project spanning decades and left Earth nearly 10 years ago. Launched with the principle goal of a Pluto flyby, Lauren chronicled its path through the inner solar system and the asteroid belt, its close encounter with asteroid 132524 APL, and the gravity assist from Jupiter which enhanced its speed and gave it the energy needed to reach Pluto.

After she described the various scientific instruments onboard New Horizons (which include high-resolution optical, ultraviolet and infrared cameras and spectrometers, magnetic field sensors, particles counters and radio science experiments), Lauren told us about some of the amazing science results from the mission. To name just a few, the New Horizons team has found that Pluto’s atmosphere is much denser than anticipated and contains stratified haze layers of unknown origin; that the bright and heart-shaped “Sputnik Planum” region is a vast plain of nitrogen ice with the consistency of toothpaste where water-ice mountains, kilometers in size, floating like icebergs; and that several of Pluto’s five satellites show signs of being the lumpy remnants from collisions of smaller bodies.

Lauren highly recommended checking out the New Horizons website to see more fascinating pictures from the flyby and the spacecraft’s current status as it exits the solar system.

-- David Hendel (graduate student)

Mar 4 - The Gas that Fills Invisible Space

How do show something that's invisible? How can we view, model and understand those parts of our universe which are beyond the scope of our senses? How can we use a grad's students unwavering desire for pizza to explain our galaxies inexorable gas guzzling?

Yong Zheng took us on a journey from waking up and rifling through the fridge to building a massive galaxy by throwing swirling disks of stars and gas together. With delightful hand drawn cartoons and a many laughs she showed us that there's much more to the Milky Way than meets the eye, and by examining electromagnetic waves way out of the spectrum our eyes can see we can infer the private life of gas streaming in and out of galaxies. Culminating in beautiful films from the Illustris simulation she invited us to consider what interesting and varied information may be hidden just out of sight.

Afterwards Stephanie Douglas, gave a short talk on how clusters of stars passing near the milky way are ripped apart into long thin streams that we see cutting across the night's sky. Our 3D wall was showing off everything beautiful movies on topics ranging from the surface of our sun to collisions between galaxies. Patchy clouds and technical issues made observing tricky, but those who persevered were able to peer at the Orion Nebula and Jupiter using portable telescopes on campus. The roof was also open for tours but sadly conditions made it impossible to view the sky through it.  

-- Zephyr Penoyre (graduate student)

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)

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 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)

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)

Nov 21: Constellations R Us

This week, Irene Pease guided the audience through the constellations on the sky. Irene Pease has works as an astrophysics educator and leads astronomy classes as a Brooklyn’s Friendly Neighborhood Astronomer. During the lecture, Irene Pease showed us the distributions of constellations on the dark night sky in well-populated cities (e.g., New York) where city light has been a plague. Ancient sky across different cultures, such as Egyptian, European and Chinese, were compared, which amazingly showed great similarities in the definitions of constellations. She then introduced the modern constellations which were defined by Interactional Astronomical Union (IAU). The celestial sphere are divided into 88 official constellations, most of which inherit their names from their Graeco-Roman predecessors (e.g., Orion, Leo), while those in Southern sky have more modernized names (e.g., Microscopium). By using a ball and a cartoon paper to mimic the earth and horizon, Irene also explained the rotation of the celestial sky relative to the earth and the different paths of stars across the sky as viewed by observers at different latitudes. 

After the lecture, a video “The First Earth-sized World of Alpha Centrauri” was shown to the audience. This 7-minute long video introduced the first earth-sized planet orbiting around the star Alpha Centauri. On the roof, observations of double-star Alberio, open cluster Pleiades were led by graduate student, Jose Zorrilla. 

-- Yong Zheng (graduate student)

Nov 7: Juggling with Black Holes

This week, Hubble Postdoctoral Fellow Andreas Kupper described the dynamics of multiple massive objects in the same system.  When two massive objects are near each other, they exert gravitational forces on each other and their motions can be described analytically - that is, the motions at all times can be calculated by hand from basic theories.  When three or more massive objects interact gravitationally, the interactions become complicated and can only be modeled using computer simulations. Andreas showed the results of a few of his simulations - after the objects orbit chaotically around each other for a while, one object (usually the one with the lowest mass) is thrown out of the system with a very high velocity.  The remaining objects end up closer together, and this process, called scattering, is thought to be responsible for bringing massive objects like black holes and neutron stars close enough together that they can merge into an even more massive object. 

After the lecture, audiences were treated to a showing of LIGO: A Passion for Understanding, a 20 minute film about a project to detect gravitational waves coming from closely interacting massive objects.  After the film, graduate student Aleksey Generozov and I answered questions about gravitational waves and LIGO.   Graduate student Yong Zheng was the roof captain, sharing glimpses of the Moon, Albireo and the Ring Nebula while undergraduate Pratishta Yerakala took attendees on a 3D tour of the Universe with the 3D wall.

-- Steph Douglas (graduate student)

Oct 10: Explosive Lighthouses

This week, Columbia Astronomy's 4th year graduate student, Maria Charisi, gave a talk on gamma-ray bursts, or GRB for short. Gamma-rays are a kind of electromagnetic wave, like optical light, but with very short wavelengths, even shorter that of X-rays.

Maria started by telling us the history of how GRBs were discovered. The first GRBs were found by detectors which were built to detect nuclear explosion on the Earth during the Cold War. However, scientists found no correlation between these events and any nuclear explosions on the Earth. So this problem was passed assigned to astronomers to find out if they were related to any astronomical events. At first theorists proposed many mechanisms for GRBs, from neutron star collisions to alien space wars. Astronomers also argued about the location of these events. Some believed they were galactic; others believed they were cosmological. The varieties of theories and beliefs were due to the fact that the location distribution and distance of the GRB events were still unknown. With the launch of the Compton Gamma-Ray Observatory in the mid 90's and the Swift Gamma-Ray Burst Mission in the early 21st century, and with the red-shifts measured from spectra, astronomers finally concluded that GRBs are extremely luminous events that happen all over the Universe. 

Maria then described findings from more recent studies on GRBs. GRBs only last for a short time in the gamma-ray band, but astronomers believed there should be afterglows in other wavelengths, just like charcoals will glow as a fire burns out. They did follow-up observations of GRBs in the optical and infrared bands and found evidence of these afterglows. From the duration distribution of the bursts, astronomers split the GRBs into two different categories: short bursts which lasts less than 100 seconds, and long bursts which last a few hundreds seconds. 

The physical image of GRBs is still not clear today. One of the most widely believed theories is that when two compact objects collide, for example a neutron star and a black hole, tremendous energy is produced and ejected from two jets. If we happened to be in the line of sight of these jets, we would detect a GRB.

After the lecture, graduate student Jingjing Chen showed the first half of a PBS movie called 'Alien Planets Revealed' which discussed transit method of detecting exoplanets used by the Kepler mission. Unfortunately, the weather was not good for stargazing, so graduate students Jeff Andrews and Aleksey Generozov gave tours of the Rutherfurd Observatory instead while undergraduate Erin Flowers and post-doc Robyn Sanderson presented a variety of astronomical phenomena with the 3D wall. 

-- Jingjing Chen (graduate student)