Astronomers Find Most Distant Protocluster of Galaxies 129
The Bad Astronomer writes "Using the monster 8.2-meter Subaru telescope, astronomers have identified the most distant cluster of galaxies ever found: a collection of galaxies at a staggering distance of 12.7 billion light years. This is the most distant cluster ever seen that has been confirmed spectroscopically (PDF). Technically, it's a protocluster, since it's so young — seen only a billion years after the Big Bang itself — the cluster must still be in the process of formation."
Re:Well, that's where it was... (Score:5, Informative)
Wrong on several counts. What the 12.7 refers to is when the light left the cluster in question (in billions of years). At the time the light left the cluster it was actually much closer to us than 12.7 light years. The observable universe is actually larger in light years than the time since the Big Bang, due to the expansion of space. This expansion also stretched the travel time for the cluster's light to reach us. Now the cluster (to the extent 'Now' has any meaning) may be 25+ light years away (I apologize for the imprecision, as I don't have the exact figures at hand).
Re:Well, that's where it was... (Score:5, Informative)
Short answer: yes. For anything traveling at luminal speeds, time is not perceived. If you were a photon, it might take you 12.7 billion years to get here, but for you it is an instant.
Re:But, we weren't so far away 12 Billion years ag (Score:2, Informative)
A quick answer is to say that the universe assuredly is expanding faster than the speed of light. Or rather, it's expanding at some rate, and two sufficiently distant points will be receding from one another at the speed of light, or even greater than the speed of light. (You've no doubt heard that "nothing can travel faster than c" but in fact it's really that "energy (hence information) cannot propagate faster than c"... according to relativity spacetime itself can expand at any speed.)
A more detailed explanation can be found by reading this [arxiv.org]. The take-home message is that it's not so intuitive to think about time and distances when spacetime itself is changing as a function of time. Let's say a star is 1 billion light-years (Gly) from Earth. It emits light, and the light travels towards Earth. But since the space in between is expanding while the light is travelling, it will take more than 1 billion years for the light to reach us. And when it does, the star will no longer be 1 billion light-years away, but will be some further distance.
If you look at Figure 1 in the link above, you'll see that what happened is this:
1. When the universe was 1 billion years old, the protocluster emits some light. At this time, the distance from the cluster to Earth (actually, the position where Earth will one day form) is ~2.5 billion light-years.
2. The light travelled outwards, while the universe was expanding.
3. In the present day (age of universe: 13.7 billion years), the light reaches our location. The protocluster (which has now evolved into something else, no doubt) is now at a distance of ~27 billion light-years from us. (Note that currently the edge of the visible universe is ~46 billion light-years away. The universe is only 13.7 billion years old, but the edge is further than 13.7 billion light-years away since, again, that space is moving away from us for that whole time. C.f. comoving distance [wikipedia.org].)