PDA

View Full Version : Quasars appear absolutely stationary?



Mike45
2007-Oct-24, 07:31 PM
An article at discovermagazine.com has an astronomer (Chopo Ma) saying that if "one of them [quasars] were shooting laterally across the sky at the speed of light, it would, to us, appear motionless."
Wow, so the article is telling us about how astronomers use these quasars for measuring the Earth, but what else could they be used for?
Also, how long would it have to travel laterally at c before we would notice any differences in it's location (assuming it's, say... 14 billion light years away)?
The scale of our universe will never cease to blow my mind. :shifty:

here's a link: Quasars Say Earth Is 1/2 a Pinkie Smaller (http://discovermagazine.com/2007/oct/quasars-say-earth-is-1.2-a-pinkie-smaller)

antoniseb
2007-Oct-24, 07:38 PM
Let's say it's twelve billion light years away, and moving at 0.9c laterally.
Each year it would seem to move about 70 trillionths of a radian... except that time dilation will slow down the movement event further.

Cougar
2007-Oct-24, 08:12 PM
...but what else could they be used for?
These super-bright beacons at super-distances are like probes of the most distant regions of the universe. By studying all the absorption lines in their spectra, one can tell how much, at what distances, and what kinds of gases are between here and there.

Cougar
2007-Oct-24, 08:43 PM
Another example is the "application to gravitationally lensed images of quasars. Misalignment between lens and quasar yields aymmetrically displaced images. Since quasars are variable light sources, different time delays result for the displaced images. However, differences in time delay are due to both (1) the path-length difference between the quasar and Earth for the light from different images; (2) the Shapiro gravitational time delay for the light rays traveling in slightly different gravitational potentials. The 2nd factor implies model-dependent assumptions. The computed H0 value is usually below or in agreement with the HST Key project H0=72 +/-8 Km s-1 Mpc-1.

-- Using Quasars for Cosmology (http://sait.oat.ts.astro.it/MSAIS/3/PDF/218.pdf)