Local Bubble

About: Local Bubble is a research topic. Over the lifetime, 572 publications have been published within this topic receiving 17126 citations.

A New Electron-density Model for Estimation of Pulsar and FRB Distances

Abstract: We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H II regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.

3D mapping of the dense interstellar gas around the Local Bubble

Abstract: We present intermediate results from a long-term program of mapping the neutral absorption characteristics of the local interstellar medium, motivated by the availability of accurate and consistent parallaxes from the Hipparcos satellite. Equivalent widths of the interstellar NaI D-line doublet at 5890 A are presented for the lines-of-sight towards some 311 new target stars lying within ∼350 pc of the Sun. Using these data, together with NaI absorption measurements towards a fur- ther ∼240 nearby targets published in the literature (for many of them, in the directions of molecular clouds), and the ∼450 lines- of-sight already presented by (Sfeir et al. 1999), we show 3D absorption maps of the local distribution of neutral gas towards 1005 sight-lines with Hipparcos distances as viewed from a variety of different galactic projections. The data are synthesized by means of two complementary methods, (i) by mapping of iso-equivalent width contours, and (ii) by density distribution calculation from the inversion of column-densities, a method devised by Vergely et al. (2001). Our present data confirms the view that the local cavity is deficient in cold and neutral interstellar gas. The closest dense and cold gas "wall", in the first quadrant, is at ∼55-60 pc. There are a few isolated clouds at closer distance, if the detected absorption is not produced by circumstellar material. The maps reveal narrow or wide "interstellar tunnels" which connect the Local Bubble to surrounding cavities, as predicted by the model of Cox & Smith (1974). In particular, one of these tunnels, defined by stars at 300 to 600 pc from the Sun showing negligible sodium absorption, connects the well known CMa void (Gry et al. 1985), which is part of the Local Bubble, with the supershell GSH 238+00+09 (Heiles 1998). High latitude lines-of-sight with the smallest absorption are found in two "chimneys", whose directions are perpendicular to the Gould belt plane. The maps show that the Local Bubble is "squeezed" by surrounding shells in a complicated pattern and suggest that its pressure is smaller than in those expanding regions. We discuss the locations of several HI and molecular clouds. Using comparisons between NaI and HI or CO velocities, in some cases we are able to improve the constraints on their distances. According to the velocity criteria, MBM 33−37, MBM 16−18, UT 3−7, and MBM 54−55 are closer than ∼100 pc, and MBM 40 is closer than 80 pc. Dense HI clouds are seen at less than 90 pc and 85 pc in the directions of the MBM 12 and MBM 41−43 clouds respectively, but the molecular clouds themselves may be far beyond. The above closest molecular clouds are located at the neutral boundary of the Bubble. Only one translucent cloud, G192−67, is clearly embedded within the LB and well isolated. These maps of the distribution of local neutral interstellar NaI gas are also briefly compared with the distribution of both interstellar dust and neutral HI gas within 300 pc.

A photographic study of pool boiling in the region of the critical heat flux

Abstract: A photographic study was made to investigate the boiling phenomena in the neighborhood of the critical heat flux. The system consisted of an electrically heated zirconium ribbon, insulated on its underface, suspended in a pool of water at its saturation temperature. Measurements of bubble diameters, bubble positions relative to the heating surface, local bubble frequencies, and contact angles at known times intervals were obtained from the film. Results indicate that at high heat fluxes the primary forces acting on a bubble leaving the surface are the buoyancy and drag forces. A dimensionless relationship is developed relating bubble velocity, bubble diameter, and contact angle at breakoff. Drag coefficients for freely rising vapor bubbles a saturated liquid are found to be representable by the usual drag coefficient-Reynolds number curves for solid bodies. Jakob's plot of bubble frequency vs. bubble diameter at breakoff is extended to high heat-flux values, and a relationship proposed by Deissler at the critical heat flux is found to yield reasonable agreement with the experimental data.

The local interstellar medium

Abstract: Observations and theoretical models of the local interstellar medium (LISM), defined as the region within a column density contour of 10 to the 19th H atoms/sq cm, are reviewed. The existence and nature of the Local Bubble and its boundary are examined; and consideration is given to the LISM as an active supernova remnant, confined bubbles, theoretical models of the LISM, cavity geometry, clouds within the Local Bubble, solar-backscatter and other observations of local clouds, ionization mechanisms in clouds, and the implications of clouds for the evolution of the LISM.

Progress on Establishing the Spatial Distribution of Material Responsible for the 1/4 keV Soft X-Ray Diffuse Background Local and Halo Components

Abstract: In this paper we present a new look at the distribution of emission responsible for the soft X-ray diffuse background (SXRB) using ROSAT all-sky survey data. This is prompted by the demonstration of the existence of extensive 1/4 keV emission in the Galactic halo that was not considered in the most successful previous model, in which the bulk of the observed 1/4 keV X-rays originated in a Local Hot Bubble (LHB) that surrounds the Sun. The basic distribution can be represented by two angularly varying Galactic components (the LHB and an X-ray halo) and an isotropic extragalactic component. In addition, there are the distinct enhancements of supernova remnants, superbubbles, and clusters of galaxies. Using the negative correlation between the SXRB and DIRBE-corrected IRAS 100 μm intensity, we find a LHB that is similar to previous models, although it is possibly more limited in extent. The emission of the LHB varies by a factor of ~3.3 with direction and produces ROSAT 1/4 keV intensities between ~250 and ~820 × 10-6 counts s-1 arcmin-2 (typically brighter at higher Galactic latitudes), with inferred emission measures of ~0.0018 to 0.0058 cm-6 pc (assuming thermal ionization equilibrium). The distribution of the emission temperature of the LHB is peaked at 106.07 K with a range of ±12% at FWHM. While this variation is small and is perhaps due to systematic uncertainties in the analysis, there is a suggestion of a cooler region in the anticenter direction consistent with previous studies. We derive halo plus extragalactic intensities that vary from ~400 to 3000 × 10-6 counts s-1 arcmin-2 outside the absorbing gas of the Galactic disk. As the low end of the range is comparable to what is expected for the extragalactic background, this implies that the halo emission varies considerably over the sky, with inferred emission measures ranging from near zero to >0.02 cm-6 pc. The distribution of emission temperatures in the halo, again derived from thermal equilibrium emission models, peaks near 106.02 K and varies over ±20% at FWHM.