Per Wikipedia’s list of most distant astronomical objects, the most distant object we’ve detected is GN-z11 at 13.9Gly. This is slightly greater than the galaxies seen in Hubble’s Deep Field images, with max redshifts corresponding to a distance of around 12Gly. The radius of the observable universe is 46 Gly; to see something half-way to that distance would be 23Gly. (A distance which filled half the volume would be a bit farther than that). So we’re trying to make a beacon visible at ~2x the maximum distance at which we’ve seen any object so far, so at a minimum it has to be 4x the brightness. But...
GN-z11 came out of an experiment that imaged 0.02 square degrees, and was made visible by lucky gravitational lensing. The Hubble deep field was about 0.04 square degrees. Since we need it to be detected by a broader sky survey, it needs to be significantly brighter.
At these sorts of distances, detecting fluctuations in brightness is mostly out because of the need for long exposures to detect anything at all. And (I could be wrong about this) I don’t think we get very much information about an object’s spectrum until after we’ve singled it out as interesting, so objects can’t use a weird spectrum to stand out.
That leaves the question of how much you can increase the brightness of a galaxy, if you’re willing to disfigure it. That’s not something I know much about, but the requirement that it remain visible for a billion years seems like it would be pretty constraining.
Another issue is that, at sufficiently long distances, a large fraction of the sky is blocked by foreground objects and dust.
I think this might not be possible.
Per Wikipedia’s list of most distant astronomical objects, the most distant object we’ve detected is GN-z11 at 13.9Gly. This is slightly greater than the galaxies seen in Hubble’s Deep Field images, with max redshifts corresponding to a distance of around 12Gly. The radius of the observable universe is 46 Gly; to see something half-way to that distance would be 23Gly. (A distance which filled half the volume would be a bit farther than that). So we’re trying to make a beacon visible at ~2x the maximum distance at which we’ve seen any object so far, so at a minimum it has to be 4x the brightness. But...
GN-z11 came out of an experiment that imaged 0.02 square degrees, and was made visible by lucky gravitational lensing. The Hubble deep field was about 0.04 square degrees. Since we need it to be detected by a broader sky survey, it needs to be significantly brighter.
At these sorts of distances, detecting fluctuations in brightness is mostly out because of the need for long exposures to detect anything at all. And (I could be wrong about this) I don’t think we get very much information about an object’s spectrum until after we’ve singled it out as interesting, so objects can’t use a weird spectrum to stand out.
That leaves the question of how much you can increase the brightness of a galaxy, if you’re willing to disfigure it. That’s not something I know much about, but the requirement that it remain visible for a billion years seems like it would be pretty constraining.
Another issue is that, at sufficiently long distances, a large fraction of the sky is blocked by foreground objects and dust.
This looks like it’s due to a mixup between comoving distance and light travel distance?
GN-z11 seems to be 13.9 billion years old, almost as old as the universe itself, and to be at comoving distance 32 billion light years.