Narrow Results

We summarize properties of the Kerr–NUT–(A)dS spacetime in a general dimension. We also investigate a limit when several rotational parameters in the metric are set equal and study geometry of the resulting spacetime. In dimension D = 6, we found a suitable Killing vector basis, whose algebraic structure proves that symmetries of the spacetime after the limit are further enhanced.

The persistent emission of the anomalous X-ray pulsar 4U 0142+61 extends over a broad range of energy, from mid-infrared up to hard X-rays. In particular, this object is unique among soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) in presenting simultaneously mid-infrared emission and also pulsed optical emission. In spite of having many propositions to explain this wide range of emission, it is still lacking one that reproduces simultaneously all the observations. Filling this gap, we present a model that is able, for the first time, to reproduce simultaneously the entire spectral energy distribution of 4U 0142+61 using plausible physical components and parameters. We propose that the persistent emission comes from an accreting white dwarf (WD) surrounded by a debris disk. This model is thoroughly discussed at Ref. 2 and assumes that: (i) the hard X-rays are due to the bremsstrahlung emission from the post-shock region of the accretion column; (ii) the soft X-rays are originated by hot spots on the WD surface; and (iii) the optical and infrared emissions are caused by an optically thick dusty disk, the WD photosphere, and the tail of the post-shock region emission. In this scenario, 4U 0142+61 harbors a fast-rotator near-Chandrasekhar WD, which is highly magnetized. Such a WD can be formed by a merger of two less massive WDs.

We study the occurrence of delayed Type Ia supernovae in the single degenerate (SD) scenario. We assume that a massive carbon-oxygen (CO) white dwarf (WD) accretes matter coming from a companion star, making it to spin at the critical rate. We assume uniform rotation due to magnetic field coupling. The carbon ignition mass for nonrotating WDs is $M_{\text{ig}}^{\text{NR}}\approx \text{1}\text{.38 }{M}_{\odot }$; while for the case of uniformly rotating WDs it is few percents larger $\left(M_{\text{ig}}^{\text{R}}\approx \text{1}\text{.43 }{M}_{\odot }\right)$. When accretion rate decreases, the WD begins to lose angular momentum, shrinks and spins up; however it does not overflow its critical rotation rate, avoiding mass shedding. Thus, angular momentum losses can lead the CO WD interior to compression and carbon ignition, which would induce a Type Ia supernova. The delay, largely due to angular momentum losses timescale, may be large enough to allow the companion star to evolve to a He WD, becoming undetectable at the moment of explosion. This scenario supports the occurrence of delayed SNe Ia if the final COWD mass is 1.38 M_⊙ < M < 1.43 M_⊙. We also find that if the delay is longer than ∼ 3 Gyr, the WD would become too cold to explode, rather undergo collapse.

We construct mass-radius relations of white dwarfs taking into account the effects of rotation and finite temperatures. We compare and contrast the theoretical mass-radius relations with observational data.