View Full Version : How far is GRB 090429B now?

mkline55

2012-Oct-11, 02:29 PM

The gamma ray burst from GRB 090429B is estimated to have traveled for 13.4 billion years before it reached us. How far away is the originating object (assuming it still exists) today? Is there a specific formula for this calculation?

My understanding of the math is clearly flawed, because I have 13.4 billion light years almost equal to 4100 Mpc, which, using the Hubble constant of about 74.3 (K/s)/Mpc yields a speed of nearly that of light.

StupendousMan

2012-Oct-11, 05:10 PM

Use Ned Wright's Cosmology Calculator:

http://www.astro.ucla.edu/~wright/CosmoCalc.html

antoniseb

2012-Oct-11, 05:19 PM

... My understanding of the math is clearly flawed, because I have 13.4 billion light years almost equal to 4100 Mpc, which, using the Hubble constant of about 74.3 (K/s)/Mpc yields a speed of nearly that of light.

You seem to have made a simplifying assumption that the universe is not expanding... the object in question is getting further away from us at several times the speed of light. This is not because it is moving with respect to its own frame, but because maybe a million miles of new space is between us per second.

speedfreek

2012-Oct-11, 05:48 PM

GRB 090429B has a redshift of z=9.4, which gives it a comoving distance of around 31 billion light-years.

Everything with a redshift higher than z~1.4 has an apparent recession speed that is faster than light.

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