Primordial black holes (PBHs), believed to have formed during the universe’s earliest moments, might be causing significant disruptions in stellar systems today. Their intense gravitational pull can disturb the orbits of wide binary star systems, sometimes leading to extreme consequences, such as ejecting a star and replacing it with the black hole itself. A recent study delves into these interactions and suggests ways we might detect these elusive cosmic entities.
The theory behind PBHs suggests they emerged shortly after the Big Bang, not from the collapse of massive stars, but from fluctuations in the density of matter in the early universe. Areas with exceptionally high density may have collapsed under their own gravity, forming what we now call primordial black holes. These PBHs are thought to vary widely in size, from subatomic particles to objects more massive than our Sun.
The question of whether PBHs contribute to the universe’s dark matter remains a topic of intense debate. While they likely do not account for all dark matter, some scientists believe PBHs could make up as much as 10% of dark matter, particularly in the planetary mass range (10^-7 to 10^-3 solar masses). However, more research is needed to confirm their role in the dark matter puzzle.
Scientists are gradually mapping dark matter across the universe, though its exact nature remains unknown. This 3D density map of dark matter in the local universe, with the Milky Way marked by an X, shows galaxies as dots and indicates the directions of motion derived from the gravitational potential of dark matter. (Image Credit: Hong et al., doi: 10.3847/1538-4357/abf040).
On a large scale, PBHs might blend in with the background of particle dark matter, making them hard to distinguish. However, on smaller scales, the distribution of PBHs differs from that of particle dark matter, suggesting the need for new theories and models. While directly observing PBHs is challenging, studying their interactions with star systems offers a promising alternative.
A recent paper by Badal Bhalla of the University of Oklahoma and a team of astronomers explores how PBHs interact with stellar binary systems, focusing on how these black holes lose energy during these interactions. The study outlines five possible outcomes:
- Hardening: The two bound stars lose energy to the PBH, causing their separation to decrease.
- Softening: The PBH transfers energy to the bound stars, increasing their separation but keeping them bound.
- Disruption: The PBH transfers enough energy to unbind the stars, leaving all objects unbound.
- Capture: The bound stars capture the PBH, forming a new system.
- Exchange: The PBH transfers energy to unbind one star, then loses energy to become bound to the remaining star.
While previous studies have examined the softening, disruption, and capture scenarios, this new research suggests that hardening is unlikely. Instead, the team explores the exchange model, which could lead to a population of PBH binaries within the Milky Way. Some observations even hint at the existence of such systems. The researchers also propose that it might be possible to detect PBHs in binary systems by studying systems with a sub-solar mass PBH. Future observations will be crucial in validating this model and potentially discovering black holes within binary systems, which could lend support to these findings.
Source : Dancing with invisible partners: Three-body exchanges with primordial black holes
