Aaron M. Geller
Northwestern University & The Adler Planetarium


Below you will find a sample of my visualizations (images, movies and interactives). These files are hosted on Northwestern's Box storage, and please note that Box sometimes degrades the quality of the videos when previewing in the browser. To download the full resolution versions from within Box (after clicking on a link provided below), please click the purple "DOWNLOAD" button near the top right corner. Use freely, but please give appropriate credit.

Black Hole Encounter

Black Hole Encounter : In late 2015, LIGO discovered gravitational waves emitted by two black holes (each with a mass of about 30 times that of our Sun) that spiraled together and merged about 1.5 billion years ago. Astrophysicists are now debating which is the most likely mechanism that can bring two black holes like those observed so close together. One important open question is: are the black holes born together, or do they find each other later in life? This image depicts the latter scenario, where multiple black holes are found within the heart of a dense globular star cluster (which contains hundreds of black holes and nearly a million luminous stars, simulated on a computer and observed here at an age of 2 billion years). During the very close gravitational encounter shown in this image, three black holes and one normal luminous star are engaged in a gravitational dance. One black hole and the normal star will eventually be flung out, leaving two black holes bound together in a very tight binary configuration. This black hole - black hole binary will later spiral together and merge, releasing gravitational waves similar to those observed with LIGO. Close encounters such as the one shown here are believed to happen frequently in globular clusters. In the image, the very strong gravity near the black holes bends the (normally straight) paths taken by the light emitted from the luminous stars, a phenomenon often called "gravitational lensing". Without the black holes, the viewer, who sits at the center of the globular cluster, would see a bright nearby blue-ish star straight ahead with a nearly uniform field of smaller, more distant, stars in all directions.

This image won 1st place and the People's Choice Award 2017 Northwestern Scientific Image Contest!

Credit: Image created by A. M. Geller. Monte Carlo globular cluster simulation performed by S. Chatterjee using the Northwestern CMC code. Black hole ray tracing simulation performed by A. Geller using GeoViS.

When Worlds Collide

When Worlds Collide : "Hot Jupiters" are Jupiter-like planets with orbits close to their host star. Their origins are debated, and some young planetary system may even host multiple Hot Jupiters. Here, we investigate a planetary system of two Hot Jupiters orbiting a Sun-like star. The system is born on the edge of instability, and over time, the planets' mutual gravitational perturbations increase their orbital eccentricities, leading to a dramatic collision that expels much of the planets' gaseous envelopes across the system. We study the initial orbit dynamics using an "N-body" gravitational integrator (Mercury), and the physical collision and thereafter using a hydrodynamics code (Starsmasher). This image (created in Maya) shows the collision remnant nearly one orbit after the point of first contact. Solid lines show the planet orbits just before the collision. The color gradient represents the gas column density. The background image shows the region observed by the NASA Kepler satellite, whose discoveries helped inspire this work.

This image won the People's Choice Award and an Honorable Mention in the 2015 Northwestern Scientific Image Contest! Here it is on Northwestern's DigitalHub. And it is featured on Northwestern's Research Tools website.

See also this version without the rings.

Credit: Image created by A. M. Geller. Simulation performed by J. Hwang, with F. Rasio advising.

Birth of a Solar System

Birth of a Solar System : Gas-rich "proto-planetary" disks surround young, still forming stars, feeding them through accretion of dust and gas. These are the birthplaces of planetary systems.This image shows a simulation of a possible gas disk progenitor for the real exoplanetary system HR8799. Today, HR8799 has four, six-Jupiter-mass planets, 30 million years into their lives, surrounded by a diffuse disk of planetary debris. With computational fluid dynamics simulations such as the one depicted here, we study the early lives of planets, still embedded in their birth proto-planetary disk, in order to understand how planetary systems like HR8799 came to be. In this image (created in Maya), the color follows the temperature, with white tracing the hottest (and generally densest) material. Four planets are clearly visible as hot dense knots, accreting gas and creating spiral patterns in the disk. The background image is 30 Doradus, the most active star-forming region known in the Local Group of galaxies.

Credit: Image created by A. M. Geller and A. Dempsey. Simulation performed by A. Dempsey.

Interactive Stellar Evolution

Stellar Evolution : I am currently developing an interactive online visualization to explore how stars change with time, using MESA stellar evolution models and visualized using d3. This visualization is intended for use in inquiry-based lessons for high school and undergraduate courses. (This version is a "mock-up" of what the final product will do. Currently there is no real data running through this visuzliation, though most of the functionality is already built in.)

This visualization won 1st place in the proposal category, and was a finalist in the finished works category, in the 2015 Northwestern Data Visualization Challenge!

Credit: Interactive visualization created by A. M. Geller using MESA and d3.

Pleiades simulation

Dynamical Evolution of Star Clusters : I've been working to perfect this story of star cluster evolution and dissolution for many years (see all the different versions below). This particular movie was generated from an interactive visualization that I developed with Mark SubbaRao using Uniview. The interactive version can be shown on a Planetarium dome, or rendered into a movie (as shown here). We have a 3D version of this movie in the Space Visualization Lab at the Adler Planetarium. This movie discusses star cluster dynamics and evaporation, stellar encounters, black hole and neutron star formation, and the HR diagram.

Life of the Pleiades (shown on left):
Format: .mp4, 177 MB, 5 minute 10 seconds
Credit: Created by A. M. Geller and M. SubbaRao, using Uniview; music, narration and audio by A. M. Geller; dynamical calculation with stellar evolution performed using the NBODY6 code.

Pleiades simulation

Here's a movie of one of the interactive visualizations the I made with Mark SubbaRao for the Space Visualization Lab in the Adler Planetarium (and can be seen there in 3D!). This NBODY6 simulation shows the evolution of a star cluster similar to the Pleiades, and this movie highlights how the cluster is dissolving over time. (The camera revolves around the cluster at the end of the movie; the cluster itself is not rotating at that rate!)

The evolution of a Pleiades-like star cluster (shown on left):
Format: .mp4, 43.5 MB, 1 minute 39 seconds
Credit: Interactive visualization by A. M. Geller and M. SubbaRao, using partiview; movie by A. M. Geller; dynamical calculation with stellar evolution performed using the NBODY6 code.

The early evolution of a star cluster

This visualization uses the N-body code NBODY6 to track the stellar dynamics and stellar evolution of a 5000-star cluster from near-birth to an age of about 800 Myr. The early "flashes" are my attempts to represent supernovae. The dynamical and stellar evolution calculations were performed using NBODY6. Disclaimer: Stellar radii are not fully realistic (primarily because of the very large difference between dwarf and giant radii). Also the colors are slightly exagerated.

This visualization was used in an online course through MIT's OpenCourseWare program : 6.S096 2014 Effective Programming in C and C++, taught by Andre Kessler . See Lecture 9.

Dynamical evolution of a star cluster (shown on left),
Also available without the flashes for supernovae:
Format: .mp4, 89.5 MB, 58 seconds
Credit: Movie by A. M. Geller using IDL and MPEG Streamclip; dynamical calculation with stellar evolution performed using the NBODY6 code.

Star Cluster Evolution in Stereo3D

You may also enjoy the "cross-eyed" stereo 3D image on the left, showing a 500-million-year time lapse of a model star cluster similar to our Sun's birthplace. Points show the stars' initial locations, and lines trace their motion under the force of gravity. Stellar surface temperatures are translated into the visible colors that we would see from real stars. The two yellow regions towards the right mark supernovae. Finally, the thick white line highlights the path of a Sun-like star as it escapes from the cluster. The simulation was performed using NBODY6, and the visualization was created with partiview.

The two side-by-side images are from different vantage points, and can be combined to yield a "cross-eyed" 3D image in the middle. (See here for a useful tutorial.) I recommend clicking on (or downloading) the image to see the bigger version. Then try to align the white line first. If you are unable to see the 3D image please enjoy either 2D image or this 2D version.

This image won 4th place in the 2014 Northwestern Scientific Image Contest!

Credit: Image by A. M. Geller using partiview; dynamical calculation with stellar evolution performed using the NBODY6 code.

Starr Cluster Evolution in d3

Here's a relatively new project that we're working on to visualize star cluster evolution using d3. You will see the evolution of the H-R diagram alongside the dynamical evolution of the star cluster, and you can interactively change the time in the model. Plus you can bring up real images of star clusters in our galaxy using World Wide Telescope. It's still a bit of a work in progress (e.g., you may need to zoom out in your browser to see the entire viz), but try it out!

Credit: A. M. Geller produced the simulation using NBODY6. Ester Pantaleo coded this up into d3 and created the visualization. Mark SubbaRao and A. M. Geller conceived the idea.

3+2 encounter leading to stellar collision

Stellar Encounters : Within star clusters, close encounters between single and multiple stars can be frequent and may lead to the production of exotic stars like X-ray sources and blue stragglers. I've created a few visualizations of interesting stellar encounters using the small-N-body code FEWBODY, and my own visualization software. In all of these movies, star sizes and colors are based on the actual radii and temperatures of the given stars (with some artistic license taken). Color-coded tails are shown to help keep track of the individual stars. During a collision, I slow down the encounter, and after the collision I pause and rotate the system, both to show more detail of the interaction. I include four examples below. If you have an idea for a different stellar encounter to visualize, please send me an email, and I'll do my best to create a movie of it!

Triple+binary encounter that leads to a collision (shown on left):
Format: .mp4, 7.5 MB, 26 seconds;
Credit: Movie by A. M. Geller using IDL and MPEG Streamclip; dynamical calculation performed using FEWBODY

Binary+single encounter that leads to a collision:
Format: .mp4, 4.9 MB, 49 seconds;
Credit: Movie by A. M. Geller using IDL and MPEG Streamclip; dynamical calculation performed using FEWBODY

Binary+single encounter that leads to an exchange:
Format: .mp4, 5.8 MB, 1 minute 5 seconds;
Credit: Movie by A. M. Geller using IDL and MPEG Streamclip; dynamical calculation performed using FEWBODY

Binary+single encounter that leads to an exchange, followed by a second binary+single encounter that leads to a collision (made by combining the previous two encounters):
Format: .mp4, 11.0 MB, 1 minute 48 seconds;
Credit: Movie by A. M. Geller using IDL and MPEG Streamclip; dynamical calculation performed using FEWBODY

Color-Magnitude Diagram from NBODY6 at 7Gyr

Evolution of the Color-Magnitude Diagram of a Star Cluster : On the left I link to a movie of the evolving color-magnitude diagram from our N-body model of the old open cluster NGC 188. The snapshot on the left shows the cluster at 7 Gyr. Binaries are plotted with blue points, and show the combined light of the unresolved system. Single stars are plotted in black points. The dynamical and stellar evolution calculations were performed using NBODY6, with some modifications to define the binary population and output format.

Color-Magnitude diagram of the NGC 188 N-body model as a function of time (shown on left):
Format: .mp4, 4.1 MB, 17 seconds
Credit: Movie by A. M. Geller using IDL and MPEG Streamclip; dynamical and stellar evolution calculations performed with NBODY6

Blue Straggler Creation Through Mass Transfer

Creation of a Blue Straggler Through Mass Transfer : My artistic representation of a blue straggler being created by mass transfer in a binary star system. The giant star, seen in the upper left of the illustration, has lost hold of its outer envelope. This material is pulled towards its partner, forming an accretion disk, and is eventually consumed by the "proto-blue straggler", seen in the lower right of the illustration. Soon the giant star will donate the remainder of its envelope, leaving only the half-solar-mass white dwarf core (shown peaking through the giant's tenuous envelope) as the companion to the blue straggler. I created this image to accompany our press release for Geller & Mathieu (2011)

This image was featured in news articles for our 2011 Nature Letter.

Click here for a larger image, and if you want a full resolution version, please email me at the address given below.
Format: jpeg
Credit: A. M. Geller

The Late Evolution of Our Solar System

The Late Evolution of Our Solar System : This visualization was originally developed for the Adler Planetarium, and can be seen in their Space Visualization Lab as a 3D interactive show. Here is a movie of that visualization, which shows the evolution of our Sun and Solar System, including all eight planets and Pluto, from the time that the Sun ends its life on the main sequence (about 5 Gyr from now) until it becomes a white dwarf. You will see the Sun become larger and redder as it ascends the giant branch, shrink back down when it begins fusing Helium in its core, and then increase in size again as it makes its ascent up the asymptotic giant branch. You will also see the late thermal pulses during the asymptotic giant phase. Throughout this evolution, the Sun loses mass from a wind--losing nearly half its mass over the course of the simulation. This mass loss causes the planets to migrate outwards with time. For the inner planets, tides compete against this outward migration, as angular momentum is drawn from the orbit and transferred to the spins of the planets and Sun. The thick colored ellipses show the orbits of the planets as they evolve over time. Thin colored ellipses mark their initial orbits, for reference.

Mercury and Venus are engulfed by the Sun has the Sun becomes a red giant. (The effect of tides is most evident as Venus is drawn into the Sun.) In this model, the Earth survives. Although it is worth noting that our understanding of the maximum radius that our Sun will reach on the red and asymptotic giant branches, and the strength of tidal dissipation, are both not well known. Slight changes to these parameters in our model can cause the Earth to also be engulfed by the Sun!

You will also see the habitable zone, marked by the wide blue band, evolve with time. Inside the habitable zone, the temperature is such that liquid water can exist on the surface of a planet. As the Sun evolves onto the red giant branch, you will notice the habitable zone quickly move outwards, eventually moving well beyond the orbit of Neptune, due to the rapid increase in the Sun's luminosity. It is clear that, although the Earth is not engulfed by the Sun in this model, liquid surface water (and likely also humans) would not survive this stage of the Sun's evolution.

Finally, note that the time progresses according to the mass loss from the Sun, not linearly as we're more used to. (Specifically the Sun is allowed to lose at most 10-4 solar masses of material per time step.) This is done to highlight the phases of the Sun's life when its structure is changing most rapidly. However the actual time that the Sun spends in these stages is not represented directly by the amount of time spent in the simulation. I intend to include an indicator of the true time in the future. For reference, the total simulation covers about 1.5 Gyr. From the end of the main-sequence phase to the tip of the first giant branch lasts about 1.32 Gyr. Core He burning lasts about 130 Myr, and the asymptotic-giant phase lasts only about 5 Myr

Late Evolution of Our Solar System (shown on left):
Format: .mp4, 114 MB, 2 minutes 31 seconds (this is a prelimiary viz, sorry for the blinking background stars--will try to fix this in the next version)
Credit: Movie by A. M. Geller using partiview and ffmpeg; stellar evolution calculation performed using MESA; equillibrium tides following Hut (1981); dynamical calculation COMING SOON using Mercury; all linked together within AMUSE.

Same movie, but twice the size

Our Solar System in a star cluster

Planets in Star Clusters : We are currently developing a code within AMUSE that will model the dynamical evolution of planetary systems, including our Solar System, in realistic star clusters. This visualization uses the N-body code Huayno to track the dynamics of our Solar System within a VERY dense 100-star cluster. Here stellar masses are chosen from a Salpeter IMF, and the stellar positions and velocites are chosen from a Plummer model. Planets are shown in red, and stars are shown in blue. More recent versions of our code use Mercury and/or Huayno to model the planetary systems, ph4 to model the star cluster, and Bridge to link these systems together.

Dynamical evolution of our Solar System in a star cluster (shown on left):
Format: .mp4, 4.2 MB, 21 seconds
Credit: Movie by A. M. Geller using Python and ffmpeg, dynamical calculation performed within AMUSE using the code Huayno

AoT Chicagox

Astronomy on Tap Chicago : Northwestern/CIERA, the University of Chicago and the Adler Planetarium have joined forces for Astronomy on Tap Chicago! Each FREE event features accessible, engaging science presentations on topics ranging from planets to black holes to galaxies to the beginning of the Universe. I developed the logos and various advertising materials for our Northwestern/CIERA group.

AoT Chicagox AoT Chicagox

Some of my favorite visualizations from others:

Contact Information (jointly appointed):
Northwestern University -- CIERA
2145 Sheridan Road, Evanston, IL 60208-3112, USA
Office: F233 Tech
Phone: (847) 467-5076   |   Fax: (847) 467-0679
Email: a-geller [at] northwestern.edu
The Adler Planetarium
Department of Astronomy
Museum Campus, 1300 S Lake Shore Dr, Chicago, IL 60605, USA
Phone: (312) 542-2410
Email: ageller [at] adlerplanetarium.org