Billions of years from now, dark energy will push the rest of the Universe out of reach forever. These galaxies will be the last to go.
A look at the night sky, near and far, reveals galaxies everywhere we look.
Throughout the entire observable Universe, an estimated two trillion galaxies exist.
Our Local Group, dominated by Andromeda and the Milky Way, houses about 70 galaxies total.
Over cosmic timescales, gravity will merge us all together into a single, enormous elliptical galaxy.
But beyond our backyard, all the other galaxies, groups, and clusters are accelerating away from us.
Once you go about 4–5 million light years away, dark energy causes space to expand faster than gravity attracts other objects across space.
Over time, every other galaxy will see its distance and recession speed increase from our perspective.
The Virgo cluster, with thousands of galaxies, is the last large cluster that will remain within view.
Other, small groups are more numerous and closer, but recede with the Universe’s expansion.
This includes tightly bound groups, like Sculptor and M81.
It also includes groups with two largely independent major members, like the Centaurus A group or the IC 342/Maffei group.
Still others, like M94, may consist only of free, unbound galaxies.
The closest of all are NGC 55 and NGC 300.
As the Universe expands, they all shall disappear.
Mostly Mute Monday tells the astronomical story of an object or phenomenon in images, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.