Intergalactic Wanderers
Whole worlds lie adrift in an unfathomable abyss.
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So we usually think of stars as parts of galaxies, crowded together in stellar megalopolises billions to trillions strong. However, we've since discovered that not every star has a galaxy to call home.
Intergalactic stars were first discovered in the vast Virgo Cluster1—a collection of some 2,000 galaxies of all shapes and sizes some 50 million light-years away from Earth. Between the galaxies of the cluster is an exceptionally dim glow: the light of trillions of orphaned stars, tossed out into deep space by titanic collisions between massive galaxies. As the Virgo Cluster devours its own over billions of years, these table scraps build in number; today, they constitute over half1 of all stars in the cluster.
A cluster of young blue stars adrift in the Virgo Cluster.
Jones et al. (2022)
But there are also some stars which have never known a home. Recently we discovered some blue splotches again in the Virgo Cluster, far away from any galaxies. When we looked at them in Hubble, we found that they were clusters of young stars and star-birthing nebulae2. But what were they doing out in the middle of nowhere?
The scientists who discovered these were able to rule out association with any known Virgo Cluster galaxy and deeper imaging didn't reveal any faint galaxies nearby. Instead, they think that these stars formed from gas torn off ancient galaxies millions of years ago2, which drifted through the Virgo Cluster until eventually collapsing and igniting.
Now what's particularly interesting about these stars is that the concentrations of heavy elements in their atmospheres is similar to that of the Sun2, so they could very well have planets suitable for life. What might beings who evolve on such planets see, deep in the abyss of intergalactic space? Alone outside a galaxy they would have neither constellations nor the Milky Way in their skies. But the Virgo Cluster contains numerous galaxies, many of which are much brighter than our Milky Way. They would appear as glowing spirals and globes scattered across the sky, far larger and far brighter than Andromeda or the Magellanic Clouds appear to us.
While we can only imagine this view today, we may not have to forever. When the Milky Way and Andromeda Galaxy merge in the far future, there's a good chance3 that the tidal forces of the collision will sling the Sun (or what's left of it) out of the merged galaxy. When that day comes, we will be the latest to embark on the lonely journey through the intergalactic void, never to know the glittering crowds of a galaxy again.
References
1 🗞️Witze, A. (2014 November 06). Half of stars lurk outside galaxies. Nature. https://doi.org/10.1038/nature.2014.16288
2 Jones, M. G., Sand, D. J., Bellazzini, M., Spekkens, K., Karunakaran, A., Adams, E. A. K., Battaglia, G., Beccari, G., Bennet, P., Cannon, J. M., Cresci, G., Crnojević, D., Caldwell, N., Fuson, J., Guhathakurta, P., Haynes, M. P., Inoue, J. L., Magrini, L., Muñoz, R. R., ..., & Zaritsky, D. (2022). Young, blue and isolated stellar systems in the Virgo Cluster. II. A new class of stellar system. The Astrophysical Journal, 935(1), 51. https://doi.org/10.3847/1538-4357/ac7c6c
3 Cox, T. J., & Loeb, A. (2008). The collision between the Milky Way and Andromeda. Monthly Notices of the Royal Astronomical Society, 386(1), 461–474. https://doi.org/10.1111/j.1365-2966.2008.13048.x
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