Oct 27 - Cosmic Mergers & Acquisitions: Mergers and Black Holes and the Growth of Galaxies

Our speaker this week was Dr. Jenny Greene, a Professor of Astrophysics at Princeton University.

Much of Jenny’s research concerns some of the most mind-boggling objects in the Universe: the supermassive black holes that exit at the centers of most galaxies. Millions to billions of times more massive than the Sun, these huge black holes are thought to play a crucial role in the development of galaxies.

Jenny began by reviewing what a black hole is: an incredibly dense object. She used the visual of compressing the Sun to the size of Jupiter, then the Earth, then Manhattan; as it gets smaller, the speed you need to escape its gravity gets larger and larger until it exceeds the speed of light. Since nothing moves faster than that, nothing can escape from a black hole.

Even though we can’t see black holes directly, Jenny showed us evidence of the supermassive black hole in the center of our Galaxy. Careful observations of the Galactic center reveal stars moving at phenomenal speeds. Measuring their positions over decades, astronomers can reconstruct their motions and show that they must be orbiting an incredibly dense but invisible object: a black hole.

Astronomers can’t directly see stars moving in other galaxies but their collective motions can be measured very precisely and it is clear that almost all galaxies require a supermassive black hole in their centers to explain these observations. Interestingly, it seems like the black holes’ sizes ‘know about’ the galaxy that they live in: the mass of the black hole can be predicted if the mass of the galaxy is known. How is this possible? Galaxies grow mostly by merging with other galaxies. This process brings in lots of new stars and gas. The gas both forms new stars and feeds the black hole, but as the black hole eats it forms an ‘accretion disk’ of very hot gas that heats up the remaining gas, eventually causing both star formation and its own growth to stop. In this way the size of the galaxy and the size of the black hole can become related.

If this picture is correct we should also see evidence of pairs of black holes, since each galaxy should have brought one along with it. Jenny described one way she and her students have been looking for these binary black holes. When they get close together, they will be orbiting each other at very high speeds — probably thousands of kilometers per second. The light from their accretion disks will be shifted to redder and bluer colors periodically due to the Doppler shift; if we can observe these color-changing black holes it would be good evidence in favor of our cosmological picture. So far the observations haven’t found anything but astronomers are still looking!





-- David Hendel (graduate student)

Sept 29 - Galactic Archeology

Our speaker this week was Keith Hawkins, a Simons Postdoctoral Fellow based in the astronomy department here at Columbia. Keith is a Galactic Archeologist. He searches for clues to the past of our galaxy, the Milky Way, similar to the way an archeologist seeks to learn about ancient civilizations and cultures. 

Keith started by telling us about the "fossils" he uses to study the galaxy - stars! Stars are fossils in two ways. First, at the great distances involved on the scale of the Milky Way, we see stars not how they are but rather how they were up to hundreds of thousands of years ago, before humans even evolved on the Earth. This is because light moves at finite speed and needs time to reach us from the distant galaxy. Second, many types of stars live for hundreds of millions or billions of years and so their composition provides clues to what was going on at the time when they formed.

Next we learned about the tools used in galactic archeology. We heard about the methods used to measure distances, chemistries, and velocities of stars: parallax and spectra. Keith demonstrated parallax by having the audience hold up a finger and close each eye in sequence; the finger appears to move relative to the background. This is analogous to how astronomers measure distances, except observations taken on opposite sides of the Earth's orbit, 6 months apart, replace winking. The amount the star appears to move relates to its distance from us. Spectra, obtained by splitting a star's light and measuring how bright it is at different colors, contain a wealth of information. Dark bands in the rainbow are often visible. These bands correspond to light being absorbed by different elements in the star's atmosphere, so examining their pattern can tell an astronomer which and how much of the elements are in the star. The specific chemical signature of a star can pinpoint its place of birth or prove association with other stars. The bands in the spectrum may also be shifted to redder or bluer colors than normal; the direction and amount of shift is due to the Doppler effect and indicates the velocity of the star relative to us.

Keith finished his talk by describing his research's goal: a complete map of the Galaxy containing information on the positions, motions, and chemical content of millions of stars. He believes this "chemical cartography" will be key to deciphering the history of the Milky Way. 

After the lecture and a lively question and answer session, undergraduate students Briley and Harrison showed 3D astronomy animations on the 13th floor while graduate students Steven, Aleksey and Haley pointed the Rutherford Observatory's telescopes at the Moon, Ring Nebula, and the double star system Albireo.  

-- David Hendel (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)

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)

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 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)

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)

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) 

November 8: Astronomer vs Astronomer

Scientists do not always agree with each other, and many times, scientific progress is made through debates. On Friday, November 8th, graduated student Jennifer Weston gave a public lecture about a few of the greatest arguments in astronomy in the past 150 years, and how they were resolved. One of the biggest debates in the history of astronomy and astrophysics, the 'Great Debate', was about whether the Milky Way, our own galaxy, was the entire universe, or there were other galaxies out there, seen as the "spiral nebulae". The debate was eventually resolved by the work of Edwin Hubble, which shows that the spiral nebulae are not only galaxies outside of our own, but they are also moving away from us at high speeds. 

After the lecture, many people went to the roof where graduate student Adrian Price-Whelan showed off the Moon and Albiero along with Andrew Emerick, Susan Clark, Aleksey Generozov, and David Jaimes. On the 13th floor, visitors enjoyed 3D astronomy movies with Barnard student Gladys Velez-Caicedo. In the lecture hall, graduate student Yuan Li presented a slide show on planets outside the solar system found by NASA's Kepler telescope. 

Join us on November 22 for a lecture by Jeremiah Murphy on supernova explosions.

-- Yuan Li (graduate student)

September 13: Fossils of Formation

On Friday, September 13th, we launched our 2013 Fall Public Lecture & Stargazing series with a talk on the Milky Way. Post-doctoral researcher, Allyson Sheffield, presented what we currently know about the formation of our galaxy. It turns out that galaxies formed in a hierarchical manner after the Big Bang, with small clumps of gas and dust forming stars, then clusters of stars, and eventually protogalaxies and galaxies. In essence, all galaxies form by accreting other galaxies in a process called galactic cannibalism. Allyson's work deals with observing tidal streams surrounding our galaxy and tracing them back in time and space to determine what structures they originally came from. She is currently focusing her efforts on the Triangulum-Andromeda over-density.

After the lecture, many visitors headed to the roof for some clear sky observing of the Moon, Mizar and Alcor, Alberio, and the Ring Nebula while others remained in the lecture hall to hear about the recent news of the Voyager 1 probe entering interstellar space.

Friday's volunteers included graduate students Jinjing Chen in the lecture hall, Adrian Price-Whelen, Susan Clark, Steven Mohammed, Doug Thornhill, and Yuan Li on the roof, and undergraduates Gladys Velez-Caicedo and Varad Srinivasan on the 3D Wall.

Join us for our next event on Friday, Sept. 27th to hear more on Voyager 1!

--Summer Ash, Director of Outreach

April 19: Extragalactic FM

On Friday, April 19th, Ph.D. candidate Destry Saul shared with us the wonders of the Universe as seen  in the radio portion of the electromagnetic spectrum. He introduced the audience to some of his favorite radio images taken with his favorite radio telescopes. Radio telescopes can either be single dish (like Arecibo or Parkes) or arrays (like the VLA or the VLBA). Objects that emit in the radio include galaxies, supernova remnants, and pulsars. Destry's favorite objects include the closest and most powerful radio source, Cygnus A, and the brightest radio supernova remnant, Casseopeia A.

Unfortunately, the skies were quite cloudy, so observing was replaced by tours of our rooftop observatory given by graduate students Adrian Price-Whelan and Steph Douglas. Audience members were also treated to a guided viewing of our 3D Wall by undergraduate Gladys Velez-Caicedo, and a discussion of the other end of the electromagnetic spectrum, X-ray astronomy, by graduate student Yuan Li.

We hope to see you at our next event on May 3rd.

--Summer Ash (Director of Outreach)

April 5: Eyes in the Sky

On a beautifully clear (almost) spring night, PhD student Ximena Fernandez gave a talk entitled "Eyes in the Sky" to a packed room of over 200 people. Ximena's talk focused on how the combination of space telescopes that operate at a variety of wavelengths have been invaluable in revealing the secrets of our Universe. Starting with our galactic center, she showed how only through the use of infrared and X-ray data have we begun to understand the nature of our galaxy's supermassive black hole. Moving to nearby galaxies, GALEX images revealed the largest known spiral galaxy, which has extended spiral arms thanks to an ongoing interaction with another galaxy. At the end, Ximena presented the newly released Hubble Extreme Deep Field, the single longest exposure in all of astronomy. The image contains over 5 billion galaxies, including the oldest known galaxy to date. The talk ended with a video that zoomed through the image to show the distribution of the galaxies in the picture. You can watch the video here!

After seeing so many wonderful images, the good weather gave everyone the opportunity to see amazing objects with their own eyes.  Most popular were the Orion Nebula and Jupiter.  Some chose to remain in the lecture hall where there was a presentation on the Cosmic Microwave Background and the new results just released by the Planck Telescope.  Finally, there was also the possibility of experiencing our 3D wall. Everyone had a great time and we're looking forward to our next event.

--Lauren Corlies (graduate student)

November 30: Galactic Neighborhoods

On November 30th, about 100 people joined us to hear Columbia Astronomy Professor Jacqueline van Gorkom talk about how galaxies are influenced by their surroundings. Professor van Gorkom is a radio astronomer and does extensive research on galaxies. She showed us how strikingly different galaxies look in dense clusters of galaxies compared with fields. She explained that when a galaxy enters a galaxy cluster filled with hot intra-cluster gas, the cold gas inside the galaxy gets stripped out of it and thus star formation is quenched, which changes the color of the galaxy from blue to red. The audience raised a lot of interesting questions about galaxies and gravity.

After the talk, some people went to see the 3D movies on the 13th floor shown by Columbia undergraduate student Gladys Velez-Caicedo. Unfortunately, the sky was not clear on Friday, but Columbia Astronomy graduate students Adrian Price-Whelan and Jenna Lemonias gave a telescope tour to a group of people on the roof of Pupin. In the lecture hall, graduate student Yuan Li presented a slide show on spiral galaxies and Dr. Jana Grcevich talked about the Big Bang and the expansion of the universe.

Join us on December 14th for the last event of this semester: a panel discussion on Life, the Universe, and Everything!

--Yuan

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

February 3: Top 11 Astronomy Stories of 2011

Last night, graduating grad student, Jana Grcevich, kicked off our Spring lecture series by recapping the "Top 11 Astronomy Stories of 2011." Some of the highlights included: the most massive galaxy cluster found, a possible detection of the Higgs boson, a possible detection of a supermassive black hole devouring a star, the 2011 Nobel Prize in Physics going to three astronomers, and the discovery of over 3000 new exoplanets.

Jana ranked the new planet discoveries as number one on her list and many people would agree. Understanding and determining the available real estate for life to grab a foothold in our galaxy, let alone the rest of the Universe, ranks as one of the top 3 questions asked by humanity since humanity could ponder its own existence. Jana explained how the discoveries were made, by the Kepler space telescope, by stating that it measures the dimming of light from a star to determine the nature of the object causing the dimming due to occultation (the object passing in front of the star). She then focused on some of the gems from this exciting database of planets which included the discovery of a super earth-massed planet (roughly 2.5x) orbiting around its star in the habitable zone - an object known as Kepler 22b. Afterwards, she pointed out some planets orbit around binary stars, giving a shout out to the fans of Star Wars who recall Tatooine’s planetary system. Last, but not least, she displayed the best determination for many planetary systems’ orbits and configurations which showed us that planetary systems similar to our own are actually common place and not rare as previous thought based on the planetary systems discovered before the Kepler mission.

Many good questions were asked from the 140+ attendees last night, proving that a recap of the LAST year’s exciting discoveries was a great way to start off THIS year’s lecture series.

--Duane