Saturday, May 17, 2014

just where are quasars?

Ian said he wasn't sure the distances of quasars quoted by SkyTools was correct...

I thought of HS1603+3820, which we viewed at the CAO. The Skyhound app actually does not quote a distance per se. It says the redshift (or z) is 2.51. And it says the "light time" is 9.4 Gyr.

z represents redshift, a measure of recessional velocity and inferred distance due to cosmological expansion.

The highest redshift quasar known is ULAS J1120+0641, with a redshift of 7.085, which corresponds to a comoving distance of approximately 29 billion light-years from Earth! It is thought to appear to us as it was only 770 million years after the Big Bang.

You might think that very odd when you consider the best measurement of the age of the universe is 13.8 billion years. Again, the 29 is the "comoving" distance; not the proper distance. It took 12.9 billion years for ULAS J1120+0641's light to reach us.

Comoving distance factors out the expansion of the universe, giving a distance that does not change in time due to the expansion of space (though this may change due to other, local factors such as the motion of a galaxy within a cluster).

Hubble's Law is the primary means we have for estimating the distances of quasars and distant galaxies in which individual distance indicators cannot be seen.

Some say that the conjecture on quasars doesn't add up. Objects with a z more than 3 need to be moving near the speed of light. Also a number of quasars have been found with proper motion. A high amount of proper motion! It used to be said that quasars were the most distant objects detected in the Universe; now it seems that it not the case. Their energy output, given the estimated distances and corresponding brightnesses, climbs into the fantastic. And yet the incredible off-the-chart energies do not rip apart nearby or hosting galaxies.

So, after a brief amount of research, I think I'm going to stand down. It sounds like there's a bit of hocus-pocus mixed in with extreme distance measures.

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