41) Message boards : MilkyWay@home Science : astronomy (Message 425) Posted 12 Nov 2007 by Nathan Post: No, we will not be doing any n-body work here. However, the results we get from our work here will be able to be used to make n-body simulations better and fit what we see in the data more accurately.

42) Message boards : MilkyWay@home Science : Goal (Message 424) Posted 12 Nov 2007 by Nathan Post: Yes, we've had some discussions about what to do for a screensaver and the disruption would be a good start, at least until we can maybe come up with something better that would be a more realistic interpretation of the work being done. And, yes the project could be expanded beyond tidal debris and could be used to search for anything you can model in density space.

43) Message boards : MilkyWay@home Science : Goal (Message 113) Posted 4 Oct 2007 by Nathan Post: Hi, I'm Nathan, and I'm the astronomy grad student working on this project. I developed the algorithm that studies the data we're working with. I'm excited to see all of the interest in the project so far and hope that it's just the beginning. I've seen a bunch of questions regarding the science we'll be doing, so I'll try and answer those after I give you a brief outline: Galaxies are ever evolving systems that can provide insight into how the universe came to be what it is now. One thing we have learned about galaxies is that they often merge into larger galaxies. We know this because we can observe it (e.g. here and here). However, there is only so much you can learn by looking at these mergers since we only see a two dimensional projection. Therefore, we are going to study the Milkyway since it is the only galaxy where we can study in all three dimensions. We are also in luck for in 1994 Rodrigo Ibata discovered that the Milkyway was currently merging with another galaxy: the Sagittarius (Sgr) Dwarf Ellipsoidal Galaxy. Due to its relative small size compared to the Milkyway, the Sgr dwarf is being tidally disrupted. This means that due to the Milkyway's much stronger gravitational force the Sgr dwarf is being ripped apart and drawn out into long tidal streams that lead and follow the actual core of the Sgr dwarf. You can see a simulation of this disruption and get a better understanding of it here. This tidal debris gives us a unique insight into our Galaxy. In general, we can only tell where a star is and where it is going. However, by studying these streams we can see where the stars were. In this way streams leave a map that allow us to be able to study the gravitational potential of the Milkyway. Also, since the potential is an estimated 90% due to dark matter we will be able to get a good handle on the distribution of the dark matter within the Milkyway. It is this tidal debris that we be studying using Milkyway@home. We have developed a method to be able to isolate and determine the properties of this debris. We also do not plan to limit ourselves to simply studying known streams (this will be the first step though), but to also be able to discover/study new pieces of tidal debris. That should give you an idea of what it is we're doing here, feel free to ask questions. Until then, I'll answer the questions I've seen presented so far: How long will it take to crunch a WU? This will ultimately depend on how we decide to split up the work and what technique we employ. However, most realistically, and to start with at least, we'll be looking at about a 4-8 fold increase over the current WU. So if it's taking you an 15-30 minutes to do the current WU you're looking at 1-2 hours. This is subject to change, however. How long will the program run? The short answer is unlimited. We have an enormous amount of data to study. Also, there will always be more (and better) data collected and many different models for the Galaxy. Therefore there will always be WUs to process using these new models and new data. What time period are we studying? Are we starting at the Big Bang or some other time? We are not doing simulation work. We are doing data analysis. Therefore we are only looking at current snapshots of the Milkyway. Our primary data set will be the Sloan Digital Sky Survey (SDSS) Data Release 6. The results of our work will be able to further simulation research, but that is not this projects goal.

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