Recent content by harcel

Hi, You would be completely right if we would have a good measure of the redshift/distance/(any other measure of the distance to us) for all objects. For some galaxies we do, for some we don't and for objects in the Milky Way these are absent (and do not correspond to distance, but only to...

Hi Janus, Sure. Stuff moves only at a dynamical time. Your example, nevertheless is highly underestimating the effect though. Stuff at 100.000 ly from the center is VERY far. The exponential fall of of the disk has a scale length of roughly 10.000 ly, so your object is at a position where the...

It is not so very easy to code, as people have a hard time getting distances to all the objects right.

These are 'colors' over some specified range. For stars, it mostly means that the value of any of these combinations is very high or low, it will be so for about every combination (within the convention that in X-Y A is a bluer band than Y). This is not necessarily true though, and the colors...

I use a variety of tools in both IDL and Python. I use the HDF5 output format, which is useful if you have HDF5 viewers (like e.g. hdfview) for first inspection. Compiling Gadget with the HDF5 option can be a bit more cumbersome though... My tools won't be particularly useful for you, as we...

The virial theorem is about the system as a whole, when it is in virial equilibrium. The v_c that you quote here is not a unique number for every star. In case of an isothermal sphere it is, as the mass distribution it has is such that the velocity is constant, as a function of radius. For all...

Yes, it does. At least most of it. The first relation you quote (L~M^3) is wrong, it holds for stars, not for star clusters. For a star cluster (of sufficiently high mass, higher than about 1000 Msun) the mass and luminosity are linearly proportional to each other (makes sense right? N times...

One more helpful website (on installing gadget on snow leopard) may be: http://astrobites.com/2011/04/02/installing-and-running-gadget-2/ Cheers, Marcel

Fewmet is right. Because the Earth is fairly small and rotates fairly slowly, though, the relative velocity of a rock in space and Earth (roughly of order of the orbital velocity of earth) is much bigger than the rotation velocity of Earth on the equator (where it is biggest). So although in...

try http://arxiv.org/list/astro-ph/new every day the newest papers are on there. Is this just for a course? How much 'work' are you supposed to do? It's pretty hard to find something really small that 'needs to be done' (for the main reason that somebody would have don it by now).

I think most are no flinged out in a merger, although it happens in mergers, but all you need is a two-, or preferably three-body interaction, these also just happen in a galaxy that is just quietly sitting there. In a merger more stars will be launched per unit time, but the amount of time...

Hi! So, yes, Gadget does pure Nbody, if you have zero SPH particles, and then it is not at all slower than pure Nbody codes (on the contrary, most Nbody codes don't do trees for the long range gravity). I have installed it on my laptop and desktop (both linux). I have not yet tried it on my...

Hi there, Weird, I work in numerical astrophysical simulations, among which Nbody, and I have never heard of either of these codes. I would advice you (if you want to do gravitational N-body simulations) to use the code Gadget 2, which is freely available on the web. The install may be a...

The visible Universe is not 13.7 billion light years across. This is because the Universe expanded in the course of it's evolution, we would be able to look that far, if the Universe did not expand (then it is just the light travel time from horizon to here, which is easy to calculate). The...