Gravitational Collapse of Accreting Neutron Stars in Binary-Driven Hypernovae

Conceitos Básicos

Accreting neutron stars in binary-driven hypernovae can reach the critical mass for gravitational collapse into a black hole, with the occurrence time depending on the initial angular momentum and accretion efficiency.

Resumo

The article investigates the conditions under which a neutron star (NS) in a binary-driven hypernova (BdHN) can reach the critical mass for gravitational collapse into a black hole (BH).
The key highlights are:

The authors perform 3D smoothed-particle-hydrodynamics (SPH) simulations of BdHNe to calculate the baryonic mass accretion rate onto the newborn NS (νNS) and the NS companion.

They use up-to-date nuclear equations of state (EOS), including those with hyperons, to model the NS interiors and track the evolution of the NS structure during the accretion process.

The simulations show that the time for the NS to reach the critical mass and collapse into a BH (tcol) depends on the initial angular momentum of the NS. For high initial angular momentum (jNS,0 ≳ 1) and efficient angular momentum transfer (χ = 0.9), tcol ranges from a few tens of seconds to hours.

BdHNe I are the most compact (orbital period ~5 mins) and promptly form a BH, releasing ≳10^52 erg. BdHNe II and III do not form BHs, releasing 10^50-10^52 erg and ≲10^50 erg, respectively.

In some compact BdHNe II, either NS can become "supramassive", i.e., above the critical mass of a non-rotating NS.

Magnetic braking can delay BH formation, leading to BH-BH or NS-BH binaries with tens of kyr merger timescales.

Estatísticas

The baryonic mass accretion rate onto the νNS and the NS companion reaches peak values of up to 10^-3 M⊙/s.
The time for the NS to reach the critical mass and collapse into a BH (tcol) ranges from a few tens of seconds to hours, depending on the initial angular momentum and accretion efficiency.

Citações

"BdHNe I are the most compact (about five minutes orbital period), promptly form a BH and release ≳1052 erg."
"BdHNe II and III do not form BHs, release ∼1050–1052 erg and ≲1050 erg."
"Magnetic braking by a 1013 G field can delay BH formation, leading to BH-BH or NS-BH of tens of kyr merger timescale."

Principais Insights Extraídos De

Occurrence of gravitational collapse in the accreting neutron stars of binary-driven hypernovae

by L. M... às arxiv.org 10-03-2024

https://arxiv.org/pdf/2409.05767.pdf

Perguntas Mais Profundas

How do the properties of the binary progenitor, such as the masses of the CO star and NS companion, affect the occurrence and timing of the gravitational collapse?

The properties of the binary progenitor, particularly the masses of the carbon-oxygen (CO) star and the neutron star (NS) companion, play a crucial role in determining the occurrence and timing of gravitational collapse into a black hole (BH). In the binary-driven hypernova (BdHN) model, the mass of the CO star directly influences the amount of material ejected during the supernova (SN) explosion and the subsequent accretion onto the NS. For instance, a more massive CO star (e.g., from a zero-age main-sequence (ZAMS) star of 30 M⊙) can eject a larger mass (up to 7.14 M⊙) compared to a less massive progenitor (e.g., 1.6 M⊙ from a 15 M⊙ ZAMS star). This increased ejection leads to a higher accretion rate onto the NS, which can accelerate its growth towards the critical mass necessary for gravitational collapse.
The timing of the collapse, denoted as ( t_{col} ), is also influenced by the initial angular momentum of the NS and the efficiency of angular momentum transfer during the accretion process. Higher initial angular momentum values can delay the collapse, as the NS may reach the mass-shedding limit and experience a dynamical instability before collapsing into a BH. The simulations indicate that ( t_{col} ) can range from a few tens of seconds to hours, depending on the binary parameters, including the masses of the CO star and NS companion, and their respective angular momenta. Thus, the interplay between the progenitor masses and the dynamics of mass transfer is critical in shaping the evolutionary path leading to gravitational collapse.

What are the observational signatures that could distinguish between BdHNe I, II, and III, and how could they be used to test the predictions of this model?

The observational signatures that could distinguish between BdHNe I, II, and III primarily revolve around the energy output and the characteristics of the associated gamma-ray bursts (GRBs). BdHNe I are expected to be the most energetic, releasing approximately ( 10^{52} - 10^{54} ) erg, and are associated with the formation of a rotating black hole. These events would likely exhibit rapid, intense GRB emissions with a short duration, potentially accompanied by multiple emission episodes due to the accretion dynamics.
In contrast, BdHNe II and III are characterized by lower energy outputs, with BdHNe II releasing around ( 10^{50} - 10^{52} ) erg and BdHNe III emitting less than ( 10^{50} ) erg. The GRBs associated with these events would have longer durations and less intense emissions, reflecting the lower accretion rates and the absence of BH formation.
To test the predictions of the BdHN model, astronomers could analyze the light curves and spectra of GRBs to identify these energy ranges and duration characteristics. Additionally, the presence of associated supernovae, particularly type Ic, could provide further context, as these are expected to accompany BdHNe events. The correlation between the GRB properties and the progenitor characteristics, such as the mass of the CO star and the NS companion, could serve as a robust test of the BdHN model, allowing for a deeper understanding of the underlying astrophysical processes.

Could the formation of supramassive neutron stars in some BdHNe II lead to unique electromagnetic or gravitational wave signatures that could be observed?

Yes, the formation of supramassive neutron stars (NSs) in some BdHNe II could indeed lead to unique electromagnetic and gravitational wave signatures. Supramassive NSs are those that exceed the maximum mass of a non-rotating NS but remain stable due to rapid rotation. In the context of BdHNe II, where the accretion rates are lower than in BdHNe I, it is possible for the NS to accumulate mass without collapsing into a BH, thus reaching supramassive states.
The rapid rotation of these supramassive NSs could produce distinctive electromagnetic emissions, such as pulsar-like signals or enhanced X-ray emissions due to the high-energy processes occurring in their magnetospheres. Additionally, the presence of strong magnetic fields, potentially exceeding ( 10^{13} ) G, could lead to phenomena such as magnetar-like bursts, which would be observable across various wavelengths.
From a gravitational wave perspective, the dynamics of a supramassive NS undergoing mass accretion could generate gravitational waves, particularly if the NS approaches the mass-shedding limit or experiences instabilities. The gravitational wave signatures from such events would differ from those produced by binary neutron star mergers or collapses into BHs, providing a unique opportunity to study the properties of supramassive NSs and their evolutionary pathways. Observations of these signatures could help confirm the BdHN model and enhance our understanding of the end stages of massive star evolution.