The Hubble eXtreme Deep Field (XDF) may have observed a region of sky just 1/32,000,000th of the total, but was able to uncover a whopping 5,500 galaxies within it: an estimated 10% of the total number of galaxies actually contained in this pencil-beam-style slice. The remaining 90% of galaxies are either too faint or too red or too obscured for Hubble to reveal. As time goes on, the total number of galaxies within this region will rise from ~55,000 up to approximately to ~130,000 as more of the Universe is revealed. (HUDF09 AND HXDF12 TEAMS / E. SIEGEL (PROCESSING))

No Galaxy Will Ever Truly Disappear, Even In A Universe With Dark Energy

As time goes on, every galaxy beyond our local group will speed away from us faster and faster. And yet, more will keep appearing.

The farther away a galaxy is from us in this expanding Universe, the faster it appears to recede away from us. As time goes on, each one of those individual galaxies will both move progressively farther away and appear to speed away at ever-increasing velocities. To put it simply, the Universe isn’t just expanding, but the expansion is accelerating over time. Over the past two decades, it’s become abundantly clear that a new form of energy — dark energy — is not only driving this accelerated expansion, but is the dominant form of energy in our Universe.

And yet, despite all of this, there are more galaxies that we can observe today, 13.8 billion years after the hot Big Bang, than at any prior point in our cosmic history. Even more puzzling: as time goes on, the number of potentially observable galaxies will increase, more than doubling as the cosmological clock continues ticking by. Even as they recede faster and faster, not a single galaxy will ever disappear from our view entirely. Here’s the puzzling science of how this happens.