Types Of Compact Objects Research Articles

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

Physics of accretion flows around compact objects

Several physical and astrophysical problems related to accretion onto black holes and neutron stars are briefly reviewed. I discuss the observed differences between these two types of compact objects in quiescent Soft X-ray Transients. Then I review the status of various non-standard objects suggested as an alternative to black holes. Finally, I present new results and a suggestion about the nature of the jet activity in Active Galactic Nuclei. To cite this article: J.-P. Lasota, C. R. Physique 8 (2007).

Remarks on the relative populations of neutron and strange stars

We consider a simple qualitative model to estimate the time-scale forneutron→strange matter decay in dense stellar environments. It is argued that a large mismatch between the former and the microscopic weak interaction time-scale suggests that a dual population of both types of compact objects is unlikely. Assuming the correctness of the strange matter hypothesis all of them should be strange stars. If one instead postulates accretion as the decisive feature for the conversion, a consideration of neutron stars structure indicates a fairly narrow range for the onset of the critical density before the corresponding Chandrasekhar mass is achieved.

VLBI Observations of Compact Extragalactic Radio Sources with Steep Spectra

In recent years it has become clear that the common practice of dividing radio sources into two classes, compact flat-spectrum sources and extended steep-spectrum sources is too simplistic and that compact steep-spectrum sources (CSS) sources which seem to form a separate class in themselves, need to be taken into consideration. A majority of flat-spectrum sources are known to show asymmetric or D2 structures. In contrast to this many CSS sources when observed with subarcsecond resolution show symmetric structures typical of extended steep-spectrum sources. However, further high resolution observations of CSS objects are clearly needed to establish the structural differences, if any, between the two types of compact objects and to understand the interrelationship between the three classes of objects. In this connection we have undertaken a program to observe a sample of 18 CSS sources using the European VLBI network. The sample was selected from the compilation by Peacock and Wall (1982), according to the following criteria: (1) flux density > 1.8 Jy; (2) largest angular size < 1 arc sec; and (3) steep high frequency spectral index (> 0.5) and high degree of low frequency spectral curvature. Our aim was to find out the structures common to these sources and their relation to more commonly observed “centimetre excess” compact objects. Here we will present the preliminary results.