Cosmus homepage  
Home Page Downloads Projects Tech Notes About Us

Stars around the Supermassive Black Hole at the Galactic Center

This demo shows the observed and predicted orbits of thirteen stars that were used by astronomers at the Keck/UCLA Galactic Center Group to predict the position of a huge black hole at the center of the Milky Way.

Our thanks to Andrea Ghez and Jessica Lu for providing this data.

Download: starsaroundblackhole.zip (5.5Mb) Regular and GeoWall versions of this demo for Windows and Linux. If your computer can't handle that, try this smaller version (1.5Mb) which has a tenth of the timesteps.

In this visualization (see screenshot, above right), the stars and their orbits are shown in a box of length about 16 000 astronomical units. Specifically, the box length is 2 units, where each unit is an "arcsecond distance from the black hole. The center of our galaxy is about 8000 parsecs (or 8 kiloparsecs) from Earth. And at that distance, 1 arcsecond is ~0.04 parsecs = 8000 astronomical units (AU)." (Quote from an email of Jessica Lu, 8 Sep 2004.)

You can turn orbits, stars, and a date ticker on and off.

Installing the demo

Unzip starsaroundblackhole.zip to create a new folder called 'starsaroundblackhole'. Go into it. If you're running Windows, just click on stars.bat or stars_geowall.bat for a regular screen or a GeoWall respectively. If you're running Linux, type the following:

 chmod +x data/partiview
 chmod +x *.csh
 ./stars.csh      (or ./stars_geowall.csh)

Using the demo

See this FAQ for the usual Partiview navigation instructions.

The demo should come up with a screen that looks like this:

The floating menu, also called the command window, can be moved around or minimized as you please.

Click on the button labelled 'g2=orbits' to toggle the orbits on and off.

Click in the space labelled 'Cmd' at the bottom of the menu (or just press TAB) and then type 'run' (and ENTER) to start the stars rotating. Alternatively, press the button that looks like a 'Fast-Forward sign'. It's just below and left of the 'feed' button near the right hand side of the menu.

Click on the button 'lbl' at the top of the menu to turn the date on and off. Alternatively, type 'label on' or 'label off' in the menu.

How this was made

Lu & Ghez provided the raw data file stars13.dat. This has the x-y-z positions of 13 stars, with every 14th line having the year and time index number. The whole data file has about 15 000 timesteps.

Dinoj wrote the perl file dat2pv.pl to convert files in the above format to Partiview format. It also multiplies all distance values by 100. (The box is of length 2*100, so that's ok.)

  perl dat2pv.pl stars13.dat somename K

Typing the above produces files somename.cf, somename_stars.speck and somename_orbits.speck using 1/K of all timesteps. The speed is changed so the total period of the simulation is the same - in this case, 15 seconds. Once you also have the files white.cmap and halo.rgb and a partiview binary, then typing 'partiview myfile.cf' brings up the pretty pictures.


This visualization was made and documented by Dinoj Surendran during an internship for Randy Landsberg of the Kavli Institute for Cosmological Physics at the University of Chicago.

Contact us at randy@oddjob.uchicago.edu
©2004