The Life and Death of Stars That Capture Primordial Black Holes ✦
Context
The dark matter problem remains one of the central challenges in modern astrophysics. Stephen Hawking proposed that dark matter could consist of primordial black holes (PBHs) formed in the early universe. The asteroid-mass range (10^17–10^23 g) is particularly intriguing, as constraints there are weak. The capture of such PBHs by stars, including red dwarfs, opens a new way to detect them. The timescales are on the order of the Hubble time, discovered by Edwin Hubble.
Methods
The authors used a combination of analytics, stellar evolution models, and 3D simulations. Back in the mid-20th century, Subrahmanyan Chandrasekhar developed the theory of dynamical friction, applied here to calculate the braking of a PBH inside a star. Interaction with a giant planet (exoplanet) enables efficient PBH capture. The modeling covers the entire cycle, including a possible explosion akin to a supernova (but without a radioactive tail), and generation of gravitational waves from remnant mergers, which could be detected by LIGO.
Results
Capture is effective only with a third body—e.g., a giant planet. For a solar-type star with a Jupiter analog, the critical PBH mass for inspiral within its lifetime is about 10^22 g. In the core, the PBH grows via quasi-spherical Bondi accretion at low efficiency. If enough angular momentum accumulates before the star is consumed, a disk forms. This transition occurs at a PBH mass of 0.01–1 M⊙, with spin reaching a* ≈ 0.8. Then, jets and winds launch, destroying the star in minutes. Monte Carlo modeling shows that roughly half of systems undergo the explosive scenario, while the rest end in quiet consumption. Explosive events can produce X-ray/gamma-ray flashes, a UV peak at ~1 day, and radio afterglow. Jet power could reach 10^50 erg/s. These explosions may resemble low-luminosity gamma-ray bursts. Also predicted are gravitational-wave signals from mergers of substellar black holes—a potential target for LIGO.
Implications
The results show that stars with PBHs inside do not evolve monotonically but can end in a bright transient, providing a new class of predictions for observational astrophysics. This links dark matter physics, high-energy astrophysics, and gravitational-wave astronomy.
Future development
Future studies should compute detailed light curves and spectra of such explosions, and refine capture rates accounting for realistic distributions of planetary systems. It is important to investigate how often jets remain ultra-relativistic and pierce the envelope.
Impact
This discovery will impact dark matter searches, interpretation of rare transients (such as low-luminosity GRBs), and gravitational-wave surveys like LIGO.
Next steps
Next steps include modeling jet propagation through the envelopes of stars, computing population rates given the PBH mass function, and searching for candidates in archival transient data.
Key open problems
The work directly addresses unsolved problems: the nature of dark matter, mechanisms of core-collapse supernovae, and the origin of intermediate-mass black holes.
🎯 If a primordial black hole of 10^16 g were at the Sun's center, it would grow so slowly that it would only reach the disk stage after 10 billion years—roughly the age of our star. So our Sun could be a 'Hawking star' with no visible consequences... for now.
🎬 The idea of a star devoured from within by a microscopic black hole echoes Arthur C. Clarke's novel 'Rendezvous with Rama,' where an alien artifact uses a black hole as a power source. In the 2009 'Star Trek' film, red matter creates black holes inside planets, causing them to collapse.
Key numbers
- PBH mass window: 10^17–10^23 g
- critical mass for capture: ~10^22 g
- PBH mass at disk formation: 0.01–1 M⊙
- spin at disk formation: ≈0.8
- maximum jet power: up to 10^50 erg/s