Selections from 2020: Expanding the Universe with GEODEs


Editor’s note: In these last two weeks of 2020, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

Implications of Symmetry and Pressure in Friedmann Cosmology. III. Point Sources of Dark Energy that Tend toward Uniformity

Published September 2020

Main takeaway:

A study led by Kevin Croker (University of Hawai’i at Mānoa) explores the possibility that the first generation of massive stars in the universe — Population III stars — collapsed at the end of their lives not into black holes, but instead into GEneric Objects of Dark Energy (GEODEs). These point sources of dark energy, distributed between galaxies, would explain the universe’s accelerating expansion.

Why it’s interesting:


Some theories propose that objects we’ve previously thought were black holes, like the central object in the galaxy M87 recently imaged by the Event Horizon Telescope, might instead be GEODEs. The inset diagram shows the structure of a GEODE. [EHT collaboration; NASA/CXC/Villanova University]

Scientists have long attempted to explain the universe’s accelerating expansion and the nature of dark energy. A great challenge is finding a solution that’s consistent with all observations — especially those that inform our understanding of the formation of structure in the early universe. Croker and collaborators demonstrate that, because rapidly spinning GEODEs repel each other, they tend to move away from galaxies and into the empty spaces between clusters of matter. This means that the formation of GEODEs at redshifts of z = 8 to 20 doesn’t disrupt the observed structure formation within the universe — so the GEODE scenario is neatly consistent with our observations across a broad range of scales.

Why the existence of GEODEs is tough to prove:

GEODEs are exotic theorized objects that consist of a spinning layer surrounding a core of dark energy — but, to us, they should largely appear to mimic black holes! Just like black holes, they are massive but don’t produce light, so they’re ordinarily invisible. The collision of two GEODEs is expected to produce a gravitational-wave signal that looks just like that from two black holes merging. For this reason, the discovery that GEODEs and black holes move differently through space is especially intriguing — this might provide us with a way to distinguish them.


K. S. Croker et al 2020 ApJ 900 57. doi:10.3847/1538-4357/abad2f