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)

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 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) 

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) 

Sept 26: The Inconstant Moon

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

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

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

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

-- David Hendel (graduate student)