Accretion Induced Collapse Process Research Articles

On the formation of eccentric millisecond pulsars by accretion-induced collapse of massive white dwarfs

ABSTRACT Millisecond pulsars (MSPs) are believed to be old neutron stars that have undergone spin-up by the accreting material from the donor. However, the discovery of eccentric MSPs (eMSPs) in the Galactic field challenges such a scenario of producing MSP–white dwarf systems only in a circular orbit. As the orbital periods and companion masses of these eMSPs are located in a narrow range, it is reasonable to postulate that they have the same origin. Although many models have been proposed to interpret the origin of eMSPs, the origin of the narrow range of the orbital period is still an open question. The accretion-induced collapse (AIC) of the oxygen–neon white dwarf is considered to be an important pathway to form MSPs, as it is expected to result in the formation of MSPs in a circular orbit due to tidal circularization. Here we revisited this scenario using binary population synthesis including the specific circularization calculation. Our results indicate that binaries with insufficient circularization in this scenario can evolve into eMSPs. The narrow initial binary parameters required by insufficient circularization can naturally account for the narrow range of the orbital period. Although the evolution of the white dwarf AIC process is not yet well understood, the characteristic of a narrow range in the orbital period of eMSPs can still set constraints on the physics of their evolution.

Assessing the complexity of orbital parameters after asymmetric kick in binary pulsars

The dynamical characterization of the Millisecond Pulsar (MSP) parameters is a key issue in understanding these systems. We present an analytical analysis of the orbital parameters of binary MSPs with long periods (Porb>2 d) and circular (e≤ 0.1) orbits, produced by an asymmetric kick model imparted during the Accretion Induced Collapse (AIC) of white dwarfs process. It turns out that the distribution of orbits peaks up to Porb,f≤ 90 d with strong circularization. Considering the different assumptions about the distribution of companion He stars 3M⊙≤Mcom≤5M⊙, the binary will affect the setups of the balance condition of minimum energy. Our analytical approach is just a first approach to the more complete models required for describing all binary parameters after an asymmetric kick. Therefore, we have also run some numerical simulations in order to compare their results with the analytical studies. We aim to initiate a first exploration of the full complexity of the problem, when combining a variable kick time and a variable kick vector direction. Indeed, the numerical simulations show patterns resembling the complex behavior found in chaotic scattering problems. Although we deal with a deterministic problem and bounded orbits, the regular characteristic orbits are found in more realistic phases during the AIC process. In addition, the overall process can show complex behaviors strongly associated with the internal kick mechanisms. This would lead us to identify the nature of regular orbits and their orbital morphology.

The single-degenerate model for the progenitors of accretion-induced collapse events

It has been suggested that the accretion-induced collapse (AIC) of an oxygen-neon white dwarf (ONe WD) to a neutron star is a theoretically predicted outcome in stellar evolution, likely relating to the formation of some neutron star systems. However, the progenitor models of AIC events are still not well studied, and recent studies indicated that CO WD+He star systems may also contribute to the formation of neutron star systems through AIC process when off-centre carbon ignition happens on the surface of the CO WD. In this work, I studied the single-degenerate (SD) model of AIC events in a systematic way, including the contribution of the CO WD+He star channel and the ONe WD+MS/RG/He star channels. Firstly, I gave the initial parameter space of these SD channels for producing AIC events in the orbital period--secondary mass plane based on detailed binary evolution computations. Then, according to a binary population synthesis approach, I gave the rates and delay times of AIC events for these SD channels based on their initial parameter space. I found that the rates of AIC events in our galaxy are in the range of $\sim0.3-0.9\times10^{-3}$\,yr$^{-1}$,and that their delay times are $>$30\,Myr. I also found that the ONe WD+He star channel is the main way to produce AIC events, and that the CO WD+He star channel cannot be ignored when studying the progenitors of AIC events.

ONe WD+He star systems as the progenitors of IMBPs

AbstractPrevious theoretical studies can only explain part of the observed intermediate-mass binary pulsars (IMBPs) with short orbital periods. Note that an ONe white dwarf (WD) accreting mass from a He star may experience the accretion-induced collapse process and eventually form IMBPs, known as the ONe WD+He star scenario. By investigating the evolution of a large number of ONe WD+He star binaries, we found that the ONe WD+He star scenario can form IMBPs including pulsars with 5 – 340 ms spin periods, and the orbital periods range from 0.04 to 900 d. Compared with the observed IMBPs, this scenario can cover almost all of the IMBPs with short orbital periods. Thus, we suggest that the ONe WD+He star channel is responsible for the formation of IMBPs with short orbital periods.

Evolving ONe WD+He star systems to intermediate-mass binary pulsars

It has been suggested that accretion-induced collapse (AIC) is a non-negligible path for the formation of the observed neutron stars (NSs). An ONe white dwarf (WD) that accretes material from a He star may experience AIC process and eventually produce intermediate-mass binary pulsars (IMBPs), named as the ONe WD+He star scenario. Note that previous studies can only account for part of the observed IMBPs with short orbital periods. In this work, we investigate the evolution of about 900 ONe WD+He star binaries to explore the distribution of IMBPs. We found that the ONe WD+He star scenario could form IMBPs including pulsars with 5-340 ms spin periods and 0.75-1.38 Msun WD companions, in which the orbital periods range from 0.04 to 900 d. Compared with the 20 observed IMBPs, this scenario can cover the parameters of 13 sources in the final orbital period-WD mass plane and the Corbet diagram, most of which has short orbital periods. We found that the ONe WD+He star scenario can explain almost all the observed IMBPs with short orbital periods. This work can well match the observed parameters of PSR J1802-2124 (one of the two precisely observed IMBPs), providing a possible evolutional path for its formation. We also speculate that the compact companion of HD 49798 (a hydrogen depleted sdO6 star) may be not a NS based on the present work.

Probing the accretion induced collapse of white dwarfs in millisecond pulsars

This paper investigates the progenitors of Millisecond Pulsars (MSPs) with a distribution of long orbital periods (Porb > 2 d), to show the link between white dwarf (WD) binaries and long orbits for some binary MSPs through the Accretion Induced Collapse (AIC) of a WD. For this purpose, a model is presented to turn binary MSPs into wide binaries and highly circular orbits (e < 0.1) through the asymmetric kick imparted to the pulsar during the AIC process, which may indicate a sizeable kick velocity along the rotation of the proto-neutron star. The results show the effects of shock wave, binding energy, and mass loss (0.2M⊙). The model shows the pulsar systems are relevant to AIC-candidates.

ON THE POSSIBILITY OF FORMING ACCRETION INDUCED COLLAPSE IN MASSIVE CATACLYSMIC VARIABLES

We investigate the process of Accretion Induced Collapse (AIC) during the evolution of massive Cataclysmic Variables (CVs) type binaries, which possibly to occur in our galaxy. The relation between spin periods and orbital periods in different nature of compact objects in binaries, is investigated. We study also the implication and application of the AIC process of the MSPs population. We conclude that a significant fraction of MSPs may originate from AIC (4 - 40%). Hence, massive CVs are of key importance for the formation and evolution of binary MSPs, once they reach the Chandrasekhar limit then collapse to becomes an NS, or blow as apart in a supernova, consequently impart significant kick to the companion and creating long orbital periods. In some cases, this process disrupts the system and creates a single MSP.

Deriving fundamental parameters of millisecond pulsars via AIC in white dwarfs

AbstractWe present a study of the observational properties of Millisecond Pulsars (MSPs) by way of their magnetic fields, spin periods and masses. These measurements are derived through the scenario of Accretion Induced Collapse (AIC) of white dwarfs (WDs) in stellar binary systems, in order to provide a greater understanding of the characteristics of MSP populations. In addition, we demonstrate a strong evolutionary connection between neutron stars and WDs with binary companions from a stellar binary evolution perspective via the AIC process.

Investigation of some physical properties of accretion induced collapse in producing millisecond pulsars

We investigate some physical characteristics of Millisecond Pulsar (MSP) such as magnetic fields, spin periods and masses, that are produced by Accretion Induced Collapse (AIC) of an accreting white dwarf (WD) in stellar binary systems. We also investigate the changes of these characteristics during the mass-transfer phase of the system in its way to become a MSP. Our approach allows us to follow the changes in magnetic fields and spin periods during the conversion of WDs to MSPs via AIC process. We focus our attention mainly on the massive binary WDs (M > 1.0Msun) forming cataclysmic variables, that could potentially evolve to reach Chandrasekhar limit, thereafter they collapse and become MSPs. Knowledge about these parameters might be useful for further modeling of the observed features of AIC.

Where do the progenitors of millisecond pulsars come from?

AbstractObservations of a large population of millisecond pulsars (MSPs) show a wide divergence in the orbital periods (from approximately hours to a few months). In the standard view, low‐mass X‐ray binaries (LMXBs) are considered as progenitors for some MSPs during the recycling process. We present a systematic study that combines different types of compact objects in binaries such as cataclysmic variables (CVs), LMXBs, and MSPs. We plot them together in the so called Corbet diagram. Larger and different samples are needed to better constrain the result as a function of the environment and formations. A scale diagram showing the distribution of MSPs for different orbital periods and the aspects for their progenitors relying on accretion induced collapse (AIC) of white dwarfs in binaries. Thus massive CVs (M ≥ 1.1 M⊙) can play a vital role on binary evolution, as well as of the physical processes involved in the formation and evolution of neutron stars and their magnetic fields, and could turn into binary MSPs with different scales of orbital periods; this effect can be explained by the AIC process. This scenario also suggests that some fraction of isolated MSPs in the Galactic disk could be formed through the same channel, forming the contribution of some CVs to the single‐degenerate progenitors of Type Ia supernova. Furthermore, we have refined the statistical distribution and evolution by using updated data. This implies that the significant studies of compact objects in binary systems can benefit from the Corbet diagram.Observations of a large population of millisecond pulsars (MSPs) show a wide divergence in the orbital periods (from approximately hours to a few months). In the standard view, low‐mass X‐ray binaries (LMXBs) are considered as progenitors for some MSPs during the recycling process. We present a systematic study that combines different types of compact objects in binaries such as cataclysmic variables (CVs), LMXBs, and MSPs. We plot them together in the so called Corbet diagram. Larger and different samples are needed to better constrain the result as a function of the environment and formations. A scale diagram showing the distribution of MSPs for different orbital periods and the aspects for their progenitors re

Can eccentric binary millisecond pulsars form by accretion-induced collapse of white dwarfs?

Binary radio pulsars are generally believed to have been spun up to millisecond periods (i.e. recycling) via mass accretion from their donor stars, and they are the descendants of neutron star low-mass X-ray binaries. However, some studies indicate that the formation of pulsars from the accretion-induced collapse (AIC) of accreting white dwarfs (WDs) cannot be excluded. In this work, we use a population-synthesis code to examine if the AIC channel can produce eccentric binary millisecond pulsars (BMSPs) in the Galaxy. Our simulated results indicate that only when the natal MSPs receive a relatively strong kick (>rsim 100 km s −1), can the AIC channel produce ∼10–180 eccentric (e > 0.1) BMSPs in the Galaxy, most of which are accompanied by a helium star. Such a kick seems to be highly unlikely in the conventional AIC process, hence the probability of forming eccentric BMSPs via the AIC channel can be ruled out. Even if a high kick is allowed, the AIC channel cannot produce eccentric BMSPs with an orbital period of ≳20 d. Therefore, we propose that the peculiar BMSP PSR J1903+0327 cannot be formed by the AIC channel. However, the AIC evolutionary channel may produce some fraction of isolated MSPs, and even submillisecond pulsars if they really exist.

The formation of submillisecond pulsars and the possibility of detection

Pulsars have been recognized to be normal neutron stars, but sometimes have been argued to be quark stars. Submillisecond pulsars, if detected, would play an essential and important role in distinguishing quark stars from neutron stars. We focus on the formation of such submillisecond pulsars in this paper. A new approach to the formation of a submillisecond pulsar (quark star) by means of the accretion-induced collapse (AIC) of a white dwarf is investigated. Under this AIC process, we found that: (i) almost all newborn quark stars could have an initial spin period of ∼0.1 ms; (ii) nascent quark stars (even with a low mass) have a sufficiently high spin-down luminosity and satisfy the conditions for pair production and sparking process and appear as submillisecond radio pulsars; (iii) in most cases, the times of newborn quark stars in the phase with spin period < 1( or<0.5) ms are long enough for the stars to be detected. As a comparison, an accretion spin-up process (for both neutron and quark stars) is also investigated. It is found that quark stars formed through the AIC process can have shorter periods (≤0.5 ms), whereas the periods of neutron stars formed in accretion spin-up processes must be longer than 0.5 ms. Thus, if a pulsar with a period shorter than 0.5 ms is identified in the future, it could be a quark star.

Scintillation Velocities of Five Millisecond Pulsars

Millisecond pulsars differ from normal pulsars in their mode of origin and their properties. They are thought to be born either through binary interaction or through accretion-induced collapse (AIC) of white dwarf stars. Several theoretical considerations suggest that these different mechanisms for the origin of millisecond pulsars would lead to different distributions of the space velocities of millisecond pulsars. Therefore, it is important to estimate the average space velocity of millisecond pulsars and compare it with that of normal pulsars. Here we present transverse velocity estimates of five millisecond pulsars obtained from interstellar scintillation observations, carried out with the Ooty Radio Telescope (ORT) at 327 MHz. For the pulsars J0437-4715, B1257+12, B1534+12, J1730-2304, and J2145-0750 we obtain velocity estimates of 231, 225, 191, 56, and 113 km s-1, respectively. The average velocity for these is much smaller than that of the normal pulsars and larger than that expected from the AIC process. Present velocity estimates are closer to other recent measurements of millisecond pulsars.