# Tag Info

22

To address your last point, there are several stars of which we have been able to resolve images i.e. see the star as more than just a featureless point. There is a list of these stars on Wikipedia (I love that they put the Sun at the top of the list - true but pedantic :-). The farthest away of the stars in the list is Epsilon Aurigae at about 2000 light ...

19

I'll add a theoretical limit to the actual record put forward by John Rennie. To image an object as more than a featureless "point source", it must be resolved by the telescope. The angular resolution $\theta$ of a telescope is: $$\theta\sim1.22\frac{\lambda}{D_{\rm aperture}}$$ $\lambda$ is the wavelength of light, $D_{\rm aperture}$ is the diameter of ...

9

You cut off the sentence that tells you what the numbers mean. "All uncertainties define a 90% credible interval". Crudely speaking, it means that there is a 90% probability of the parameters lying in the quoted range, with the most likely estimate being the headline number. It doesn't really make sense to translate these into Gaussian sigmas (it would be ...

4

I don't think there has even been observational evidence of Kerr-specific effects. While gravitational lensing is well known these days I don't think any of the objects studied have been rotating fast enough for the difference between the Kerr and Schwarzschild metrics to be apparent. Well, not in lensing anyway - Gravity Probe B did measure frame dragging. ...

4

In general, yes you need to know the orbital inclination angle $i$ in order to fully solve the orbit. The radial velocity amplitude $K$ is just modified to $K \sin i$ (where $i=0$ is a face-on orbit). Combining this with the orbital period and Keplerian orbits gives you the "mass function"  \frac{M_1^3 \sin^3 i}{\left(M_1 + M_2\right)^2} = \frac{K_{2}^3 \...

4

The apparent line-of-sight velocity (red shift / blue shift) is $v\cos\theta$ where $\theta$ is the angle between the plane of the stars' orbits and the line-of-sight line from the Earth. If the stars eclipse one another at a certain point in their orbit (eclipsing binaries) then we know that the Earth is in their orbital plane, so $\theta=0$ and the ...

4

Yes, there are lots of optical observations of isolated (non-pulsar) neutron stars. Such observations have been done for many, many years. An early example would be Kulkarni & van Kerkwijk (1998) who detected optical radiation from the counterpart to RX0720.4-3125. http://arxiv.org/abs/astro-ph/9803024 The authors discuss various mechanisms that ...

3

The progenitor bias arises in attempts to study early-type (elliptical) galaxies at higher redshift. The desire is to choose a sample of galaxies at high $z$ that are the analogs of the galaxies that evolved to form the low $z$ sample. The bias arises if one chooses a sample of only early-types at high $z$. Because some late-types eventually evolve into ...

3

Did you notice the caption of the table?

2

The variation in the orbital distance between aphelion and perihelion is not an "uncertainty" - it is certainly variable. The ratio between aphelion distance and perihelion distance is $(1+e)/(1-e)$. The NASA fact sheet http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html gives the eccentricity $e$ to 8 decimal places, so I assume (though I may be ...

2

The technique is to sight in on known frequencies of sources in the Milky Way and other galaxies. Any signal bearing the multiband set of data is subtracted.

2

There have been a few detected in the visible range by Hubble Space telescope and Keck observatory. The magnitude is less than 25 for the Hubble image(PSR0656+14). Neutron stars are very hot, 600,000 or more Kelvin and very small (Hubble star was 28 kilometers in diameter) so their visible luminosity is very low. The emission is redshifted due to General ...

1

I'm not sure if this is exactly what you want, but there's a book called Practical Statistics for Astronomers by J.V. Wall and C.R. Jenkins that might fit the bill. According to the Cambridge University Press website (the book is a part of Cambridge Observing Handbooks for Research Astronomers): Astronomy needs statistical methods to interpret data, but ...

1

The reason the hottest temperatures of the year are later than the solstice is because the land and oceans need time to warm up. Interestingly enough, there's a name for this phenomenon - "the lag of the seasons".

1

Gamma Ray Bursts happen in galaxies, and the ISM in the host galaxy will leave spectral imprints on the GRB afterglow spectrum. This also means that besides being interesting in their own right, GRB afterglows are also valuable light sources for various cosmological uses, including galaxy evolution and IGM analysis.

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