Recent content by bombadil

In general, most if not all galaxies are thought to contain supermassive black hole's that went through some quasar phase (including our own Milky Way) at some point in the past. We think this is true because there are large-scale galaxy characteristics that correlate with the mass of the...

Thanks mathman for that correction. pmsrw3, thanks for pointing me to the maximum entropy method. Though I'm pretty sure that I'm not dealing with any of the traditional distributions, but I'll look into it.

My goal here is to at least approximately calculate the probability density function (PDF) given the moment generating function (MGF), M_X(t). I have managed to calculate the exact form of the MGF as an infinite series in t. In principle, if I replace t with it and perform an inverse...

I have no idea, can you give us a link to the paper you are reading? I'm guessing they're speaking of objects that are far away and therefore aren't very bright (i.e. low flux). Though it's also possible they're referring to some technical class of objects that are intrinsically faint (i.e...

When it says Quasars are extinct today, it is merely referencing the observational fact that the number of quasars seems to peak at redshifts around z\sim 1 or 2 and at lower redshifts the number of quasars is much lower. Remember that objects with high redshifts are far away and objects with...

Can you be more specific? What do you mean by "split"? As it turns out, understanding why galaxies have the spiral structures they do is a complicated question. A simplistic analysis says that all galaxies should have their spiral arms tightly wound up, but this is manifestly not the case...

Stars that are born orbiting one another will eventually collide because of the loss of energy due to tidal effects and the emission of gravitational waves. The collisions of stellar remnants (neutron stars, black holes, and maybe white dwarfs) are thought to power...

There are several methods for determining the galactic magnetic field. 1. http://en.wikipedia.org/wiki/Faraday_effect#Faraday_rotation_in_the_interstellar_medium" of pulsars as well) 2. http://en.wikipedia.org/wiki/Zeeman_effect" on emission and absorption lines. 3...

Here's the limit I'm thinking of: \lim_{\substack{R\rightarrow 1}} \frac{RP'}{P}, where primes are derivatives w.r.t. R. Also, P= c R J_1(\alpha R) - \frac{R^2 F}{\alpha^2}, where J_1 is a Bessel function of the first kind. Two of the three constants (c,alpha,F) are chosen such...

Say you have a limit in indeterminate form (0/0 or infinity/infinity) and you apply L'Hopital's rule to it and the result is an infinite limit. Is that a valid answer? Can L'Hopital's rule be applied in this way?

Your on the right track. Though your scale factor seems to have one error in it: the \Omega_M^{1/2} in the argument for sin should actually be (\Omega_M-1)^{1/2}. (check out equation 6.26 in "Introduction to Cosmology" by Ryden) Yes, just integrate over 1/a times the speed of light to get...

Great! I'm such an ignoramus when it comes to ODE, I'll have to file away that integrating factor trick. Just for fun, did you notice how you final result looked suspiciously like a conservation of energy? FYI here's how I solved the problem using conservation of energy: When you have a...

Your solving for v(R) and the ode has a v^2 term. Wait a second. I think your right about that substitution. It does make the ode seperable and first order. very nice. .

Okay, so here's the ode I get that looks hairy and scary: F=\frac{dp}{dt}=\frac{d}{dt}\left(\frac{4}{3}\pi R^3 \rho \frac{dR}{dt}\right) and then assuming (as cepheid did in the first post) that dv/dt=vdv/dR, I get: F(R)=4 \pi R^2 \rho v^2+\frac{4}{3}\pi R^3 \rho v \frac{dv}{dR} Am...

gabbagabbahey, Right, the net force must be zero on the bubble as it's center of mass remains stationary. In this context, it's probably more fruitful to think of the force as pressure which is artificially being regulated (which is why F it is an arbitrary function of R).