If you were to fall into a black hole (which we do not recommend), you”d likely find a singularity, or an infinitely small and dense point, at the center.“ That is what physicists have always believed.
But now a pair of scientists suggests that some black holes may not be black holes at all. Instead, they could be strange objects brimming with dark energy, the mysterious force thought to be pushing at the universe’s boundaries, causing it to expand at an ever-increasing rate.
“If what we thought were black holes are actually objects without singularities, then the accelerated expansion of our universe is a natural consequence of Einstein’s theory of general relativity,” said Kevin Croker, an astrophysicist at the University of Hawaii at Mānoa.
In a new study
published online on August 28 in the Astrophysical Journal, Croker and a colleague describe this concept. If they are correct, and the singularity at the heart of a black hole is replaced by a strange energy flinging everything apart, it could change how we think about these dense objects.
The two were not looking to discover what lies within a black hole. Croker and Joel Weiner, a mathematics professor emeritus at the same university, were studying Friedmann’s equations, which are simplified versions of Einstein’s theory of general relativity. (Einstein’s body of equations describing relativity describes how mass and energy warp space-time.) Physicists use Friedmann’s equations to describe the expansion of the universe, in part because the math is simpler than in Einstein’s body of equations describing relativity. To properly write down Friedmann’s equations, the team discovered that ultradense and isolated regions of space, such as neutron stars and black holes, had to be treated mathematically in the same way as all other areas. Previously, cosmologists believed it was reasonable to ignore the internal details of ultradense and isolated regions, such as the inside of a black hole.
“We showed there’s only one way to [construct these equations] correctly,” Croker told Live Science. “And if you do it that one way, which is the correct way to do it, you find some interesting things.”
The new findings
imply that all of the dark energy required for the universe’s accelerated expansion could be contained in these alternatives to black holes. The researchers discovered this in the math after correcting the way Friedmann’s equations were written. In a subsequent paper submitted to The Astrophysical Journal and published on the preprint journal arXiv on September 7, they demonstrated that these alternatives to black holes, known as Generic Objects of Dark Energy (GEODEs), could also help explain anomalies in gravitational-wave observations from 2016.
The math from Friedmann’s equations revealed that these ultradense objects gain weight over time simply because the universe expands, even when there is no nearby material for them to consume. Matter loses weight as space expands, just as light loses energy as it travels through expanding space (an effect known as redshift). Typically, the effect is so small that it cannot be seen. However, the effect becomes noticeable in ultradense material with extremely high pressures inside, also known as relativistic material. Dark energy’s pressure acts in the opposite direction of normal matter and light, so objects made of it (like these hypothetical GEODEs) gain weight over time.
“Light is sort of a weird thing. It behaves counterintuitively, in many ways,” Croker said. “People didn’t expect that this behavior could also be exhibited in other objects. But we showed, yes, you can see it in another object,” namely inside GEODEs.
GEODEs were first proposed as an idea
in the 1960s, but the math behind them was only recently worked out. However, it turns out that these strange objects could provide a simple explanation for observed large black hole mergers. The Laser Interferometer Gravitational-Wave Observatory (LIGO)-Virgo collaboration announced the first-ever observations of a black hole merger in 2016, but the calculated masses of the supposed black holes were unexpected — scientists expected the masses to be much higher or lower.
GEODEs, on the other hand, gain weight over time, unlike traditional black holes. If two GEODEs formed in the younger universe collided, they would have grown larger than typical black holes by the time they collided. The masses of the GEODEs would then match the masses seen in the LIGO-Virgo collision. Instead of imagining a highly specific situation that led to the merger, GEODEs could provide a simpler explanation for the observations.
Not all scientists are convinced, though. The new description of these objects is “counterintuitive and hard to digest,” Vitor Cardoso, professor of physics at Instituto Superior Técnico in Lisbon, Portugal, who was not involved with the study, told Live Science in an email. But, he added, “I like the idea of finding alternatives to black holes — it forces us to strengthen the black-hole paradigm. Also, sometimes it’s hard to find things if we don’t look for them.”
READ MORE: The End of the Universe: How Black Holes Die