Scientists suggest that a counter-intuitive, hypothetical species of black holes may negate the standard model of cosmology,where dark energy is an inherent and constant property of spacetime that will result in an eventual cold death of the universe. “It’s the big elephant in the room,” says Claudia de Rham, a theoretical physicist at Imperial College London about dark energy, the mysterious, elusive phenomena that pushes the cosmos to expand so rapidly and which is estimated to account for 70% of the contents of the universe. “It’s very frustrating.”
Generic Objects of Dark Energy
Astronomers have known for two decades that the expansion of the universe is accelerating, but the physics of this expansion remains a mystery. In 1966, Erast Gliner, a young physicist at the Ioffe Physico-Technical Institute in Leningrad, proposed an alternative hypothesis that very large stars should collapse into what could be called Generic Objects of Dark Energy (GEODEs). These appear to be black holes when viewed from the outside but, unlike black holes, they contain dark energy instead of a singularity.
In 1998, two independent teams of astronomers discovered that the expansion of the Universe is accelerating, consistent with the presence of a uniform contribution of Dark Energy. Research fellow Kevin Croker, and mathematician Joel Weiner at the University of Hawaiʻi at Mānoa, showed that if a fraction of the oldest stars collapsed into GEODEs, instead of black holes, their averaged contribution today would naturally produce the required uniform dark energy.
Fast forward to today, a team of researchers at the University of Hawai’i at Mānoa led by Croker have made a novel prediction—the dark energy responsible for this accelerating growth comes from a vast sea of compact objects spread throughout the voids between galaxies. This conclusion is part of a new study published in The Astrophysical Journal.
In 2019, Kroker proposed that objects like Powehi, the recently imaged supermassive compact object at the center of galaxy M87, might actually be GEODEs. The Powehi GEODE, shown to scale, below would be approximately 2/3 the radius of the dark region imaged by the Event Horizon Telescope. This is nearly the same size expected for a black hole. The region containing Dark Energy (green) is slightly larger than a black hole of the same mass. The properties of any crust (purple), if present, depend on the particular GEODE model. (Photo: EHT collaboration; NASA/CXC/Villanova University)
Mimic Black Holes
In the mid-1960s, physicists first suggested that stellar collapse should not form true black holes, but should instead form Generic Objects of Dark Energy (GEODEs). Unlike black holes, GEODEs do not ‘break’ Einstein’s equations with singularities. Instead, a spinning layer surrounds a core of dark energy. Viewed from the outside, GEODEs and black holes appear mostly the same, even when the “sounds” of their collisions are measured by gravitational wave observatories.
Because GEODEs mimic black holes, it was assumed they moved through space the same way as black holes. “This becomes a problem if you want to explain the accelerating expansion of the universe,” said Croker, lead author of the study. “Even though we proved last year that GEODEs, in principle, could provide the necessary dark energy, you need lots of old and massive GEODEs. If they moved like black holes, staying close to visible matter, galaxies like our own Milky Way would have been disrupted.”
Croker collaborated with UH Mānoa Department of Physics and Astronomy graduate student Jack Runburg, and Duncan Farrah, a faculty member at the UH Institute for Astronomy and the Physics and Astronomy department, to investigate how GEODEs move through space.
“Entirely New Class of Phenomenon”
The researchers found that the spinning layer around each GEODE determines how they move relative to each other. If their outer layers spin slowly, GEODEs clump more rapidly than black holes. This is because GEODEs gain mass from the growth of the universe itself. For GEODEs with layers that spin near the speed of light, however, the gain in mass becomes dominated by a different effect and the GEODEs begin to repel each other.
“The dependence on spin was really quite unexpected,” said Duncan Farrah. “If confirmed by observation, it would be an entirely new class of phenomenon.”
The team solved Einstein’s equations under the assumption that many of the oldest stars, which were born when the universe was less than 2 percent of its current age, formed GEODEs when they died. As these ancient GEODEs fed on other stars and abundant interstellar gas, they began to spin very rapidly. Once spinning quickly enough, the GEODEs’ mutual repulsion caused most of them to ‘socially distance’ into regions that would eventually become the empty voids between present-day galaxies.
This study supports the position that GEODEs can solve the dark energy problem while remaining in harmony with different observations across vast distances. GEODEs stay away from present-day galaxies, so they do not disrupt delicate star pairs counted within the Milky Way.
“Ancient GEODEs Consistent with Number of Ancient Stars”
The number of ancient GEODEs required to solve the dark energy problem is consistent with the number of ancient stars. GEODEs do not disrupt the measured distribution of galaxies in space because they separate away from luminous matter before it forms present-day galaxies. Finally, GEODEs do not directly affect the gentle ripples in the afterglow of the Big Bang, because they are born from dead stars hundreds of millions of years after the release of this cosmic background radiation.
“It was thought that, without a direct detection of something different than a Kerr [Black Hole] signature from LIGO-Virgo [gravitational wave observatories], you’d never be able to tell that GEODEs existed,” said Farrah. Croker added, “but now that we have a clearer understanding of how Einstein’s equations link big and small, we’ve been able to make contact with data from many communities, and a coherent picture is beginning to form.”
Source: Astrophysical Journal (2020). DOI: 10.3847/1538-4357/abad2f
Journal information: Astrophysical Journal
The Daily Galaxy, Max Goldberg, via University of Hawaii at Manoa
Image credit at top of the page: The universe is 7% of its current age at the bottom, 24% in the middle, and the universe today is displayed at the top. Volker Springel and the Max-Planck-Institute for Astrophysics