21

Yes. It can be measured in spectra of the moon. A paper The solar gravitational redshift from HARPS-LFC Moon spectra describes the measurment of red-shifts in Iron absorption lines in the spectrum of the moon which result from gravitational redshift from the sun. The difficulty in measuring these redshifts is not their scale (equivalent to motion of about ...


13

tl;dr Because space doesn't contract inside our Solar System. Wavelength increase is proportional to space expansion The prediction of general relativity — one of the most thoroughly tested and succesful theories — is that the wavelength of observed light changes in proportion to the factor by which space expands (Lemaître 1927). If space expands by a ...


6

Yes, there is a "retardation of the co-moving velocity" of particles. It is important to take it into account to understand the time history of peculiar velocities of galaxies and for determining the energy distribution of cosmic rays coming from other galaxies. Peculiar velocities, the difference between an object's velocity and the local rest ...


6

tl;dr No, it's unfortunately not that simple. Cosmological distances The comoving distance to an object observed to have a redshift $z$ — i.e. the coordinates that expand along with the Universe — is calculated by integrating the Friedmann equation, assuming some values$^\dagger$ for the expansion rate $H_0$ and the density parameters $\{\Omega_r,\Omega_m,\...


6

the Quasar Age or Quasar Epoch has ended. As pointed out by James K., the Quasar epoch has not ended. Today quasars are rarer then some Gyr ago, but they are still here. The closest one is about 600 million light years away and it is receding at about 12500 km/s, which is 4% of the speed of light. This fact alone proves that quasars are not a consequence of ...


6

Gravitational waves should be redshifted. The gravitational wave signal of an inspiralling binary system, which drifts across a range of frequencies, does not however yield the redshift of the binary system, since changing the redshift is indistinguishable from changing the mass of the system. In practice, what is usually done is to estimate the redshift ...


5

In the expanding universe the luminosity distance is related to the redshift by, \begin{equation} d_L=c(1+z)\int_0^z \frac{dz'}{H(z')} \end{equation} where $H(z')$ - is the rate of the universe expansion at redshift $z$. You can determine the rate from the Friedmann equations (basically Einstein equations for the cosmological spacetime) \begin{equation} H(z)=...


5

That depends on how accurate you want your answer. The reason is that the angle $\theta$ spanned by a length $L = 1\,\mathrm{Mpc}$ depends on the distance $d$ of that length — in comoving coordinates, $\theta$ keeps decreasing with $d$, just like a normal item, say a bicycle, looks smaller the farther away it is (curiously, in physical coordinates, this is ...


5

It's an observational fact that many disk galaxies have a color gradient with redder (or as you say 'yellow') stars in the central regions and bluer stars in the disk. There are two things that can cause this central redness. Age, older stars being redder than younger stars Metallicity, with red stars being more metal rich than blue stars Whether it's age ...


4

Attractive gravity means a shorter time since the Big Bang, for any given Hubble value. Here's a picture (from lecture notes by Sean Carroll): The averaged distances and speeds of nearby galaxies give us the slope of the curve at the horizontal position marked "now". If you assume they've always moved at that speed, you get the scale factor ...


4

The short answer is that the redshift of stars that are close enough to put into H-R diagrams (or "color magnitude diagrams", if we're being precise, given that you're talking about using colors) is so small that the effects are minimal. The correction to color you're thinking of (called "K correction") depends on the redshift: the ...


3

The de Broglie relation suggests the "wavelength of a particle" is proportional to the reciprocal of its momentum. Like all wavelengths, the de Broglie wavelength is effectively stretched by a factor $(1+z)$, where $z$ is the redshift. The net effect is to increase the wavelength and hence reduce the momentum when measured in the co-moving rest ...


3

$(B-V)_0$ is the intrinsic (unreddened) colour. Reddening is not directly related to redshift because some of it occurs due to the dust in our Galaxy. Thus there is usually some reddening for nearby galaxies that depends on the sightline to them through our Galaxy. The apparent magnitude does not equal the absolute magnitude at $z=0$. Absolute magnitude is ...


3

Neither. You use the Luminosity Distance. $$M = m -5\log D_L + 5$$ This assumes bolometric magnitudes. If you are trying to estimate it in some photometric band then you must also calculate and apply a K-correction that will depend upon the intrinsic spectrum of the source. For $z=11.09$ this cosmology calculator gives a model-dependent luminosity-distance ...


3

Redshifts are plotted because usually that is all that can be measured. Other quantities could be plotted, but since these are inferred from the redshift itself (e.g. density would just mean plotting $(1+z)^3$), or would need to assume particular cosmological models or parameters (e.g. if you plotted look-back time), then it makes sense to stick with ...


2

Since you are presumably using Hubble's law to get the distance to each of the galaxies, the approximate estimate would the "the greater distance ± the smaller distance". But the geometric solution is useful too. Your strategy appears to be something like: Calculate angular separation $\Theta$ from RA and DEC. By trigonometry, the distance is then ...


2

I think you could just take the natural log of your wavelength scale, then re-bin this onto a new log of wavelength scale generate using np.linspace(). Your new scale would be generated using the maximum and minimum values of your raw log of wavelength scale then it is up to you to define the amount of bin in the new homogenous log scale. To re-bin the raw ...


2

The "crisis in cosmology" is a tension between the values of $H_0$ calculated from high-$z$ and low-$z$ astronomical data. This paper modifies ΛCDM cosmology by making $H_0$ a function of $z$. That makes no sense given how $H_0$ is defined. $H$ is already a function of $z$, and $H_0=H(z{=}0)$ by definition. The assumption that $H_0$ depends on $z$ ...


1

The electromagnetic spectrum is a continuous distribution of frequencies/wavelengths. Photometry is the science of light as perceived by the human eye, so it is very relevant for observing astronomical objects with telescopes, etc... In astrophotometry, one cuts the electromagnetic spectrum into bins, called "magnitudes." The specific ranges of ...


1

Yes, you multiply those integrals by the Hubble distance. It's like a cosmological base distance. You generally can't calculate those integrals by algebra, you have to use a numerical method, like Simpson's rule. The tricky part is choosing a set of $\Omega$ (unitless) density parameters to plug into this equation: $$E(z) = \sqrt{\Omega_r(1+z)^4 + \Omega_m(1+...


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