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The search for life in the Universe is a fundamental problem of astrobiology and modern science. The current progress in the detection of terrestrial-type exoplanets has opened a new avenue in the characterization of exoplanetary atmospheres and in the search for biosignatures of life with the upcoming ground-based and space missions. To specify the conditions favourable for the origin, development and sustainment of life as we know it in other worlds, we need to understand the nature of global (astrospheric), and local (atmospheric and surface) environments of exoplanets in the habitable zones (HZs) around G-K-M dwarf stars including our young Sun. Global environment is formed by propagated disturbances from the planet-hosting stars in the form of stellar flares, coronal mass ejections, energetic particles and winds collectively known as astrospheric space weather. Its characterization will help in understanding how an exoplanetary ecosystem interacts with its host star, as well as in the specification of the physical, chemical and biochemical conditions that can create favourable and/or detrimental conditions for planetary climate and habitability along with evolution of planetary internal dynamics over geological timescales. A key linkage of (astro)physical, chemical and geological processes can only be understood in the framework of interdisciplinary studies with the incorporation of progress in heliophysics, astrophysics, planetary and Earth sciences. The assessment of the impacts of host stars on the climate and habitability of terrestrial (exo)planets will significantly expand the current definition of the HZ to the biogenic zone and provide new observational strategies for searching for signatures of life. The major goal of this paper is to describe and discuss the current status and recent progress in this interdisciplinary field in light of presentations and discussions during the NASA Nexus for Exoplanetary System Science funded workshop ‘Exoplanetary Space Weather, Climate and Habitability’ and to provide a new roadmap for the future development of the emerging field of exoplanetary science and astrobiology.
Recently, many superflares on solar-type stars were discovered as white-light flares (WLFs). A correlation between the energies (E) and durations (t) of superflares is derived as t∝E0.39, and this can be theoretically explained by magnetic reconnection (t∝E1/3). In this study, we carried out a statistical research on 50 solar WLFs with SDO/HMI to examine the t-E relation. As a result, the t-E relation on solar WLFs (t∝E0.38) is quite similar stellar superflares, but the durations of stellar superflares are much shorter than those extrapolated from solar WLFs. We present the following two interpretations; (1) in solar flares, the cooling timescale of WL emission may be longer than the reconnection one, and the decay time can be determined by the cooling timescale; (2) the distribution can be understood by applying a scaling law t∝E1/3B−5/3 derived from the magnetic reconnection theory.
We have made aperture synthesis observations of 12CO(J=1−0) emission IRAS 21282+5050, CRL 618 and M 1–7 using the Nobeyama Millimeter Array (NMA). We observed with 3 or 2 configurations and obtained an angular resolution of 3″.2 × 3.1, 3″.6 × 3″.5 and 4″.3 × 3″.8.
Observations of the structure and the velocity field in the L1551 bipolar flow were made with the 45m telescope at Nobeyama in the 115GHz 12CO J = 1 – 0 line with high spatial resolution. It was found that the bipolar flow lobes have a clear hollow cylindrical structure and show evidence of a helical velocity field. They appear to rotate in the same direction as the CS disk found by Kaifu et al. (1984). The velocity of the flow in the bipolar directions increases with distance up to ∼ 3′ from the central object, IRS 5. These characteristics coincide with those predicted by the magnetodynamic theory proposed by Uchida and Shibata and indicate the essential importance of the magnetic field in producing such flows and also in the star-formation process itself through the enhancement of angular-momentum loss.
Pulsar may be regarded as a discharge tube by electron-positron pair creation. On this viewpoint we carry out two numerical calculations. The obtained magnetic field is consistent with the flow. We find that pulsars emit their rotational energy through three modes simultaneously. The three modes are (1)relativistic acceleration and following gamma-ray emission in the closed current circuit in the magnetosphere, (2)wind of the electron-positron pair plasma, and (3)dipole radiation.
We have made 15″ resolution observations of CO J = 1-0 emission toward L723 and S140 using the Nobeyama 45-m radio telescope. The maps resolved the molecular flow structures clearly. The outflow in the S140 molecular cloud was resolved to be a bipolar structure with its axis being nearly perpendicular to the elongation of the dense core observed in CS emission and to the direction of the infrared polarization. The blueshifted and redshifted components in L723 were resolved into two pairs of bipolar outflows with a point-symmetric structure.
NUMO and JAEA have been conducting a joint research since FY2011, which is aimed
to enhance the methodology of repository design and performance assessment in
preliminary investigation stage for the deep geological disposal of high-level
radioactive waste. As a part of this joint research, we have been developing
glass dissolution models which include various processes derived from
glass-overpack-bentonite buffer interaction, considering the precipitation of
Fe-silicates associated with steel overpack corrosion, and Si transport through
altered layer of glass. The objective of this modeling work is to show
comprehensively the lifetime of the vitrified waste due to glass matrix
dissolution timescales through sensitivity analysis, and to identify the
feature/process that most strongly influences the lifetime, and to identify
future R&D issues that would help to improve the nuclide transport
analysis with confidential value and the safety case in future. The sensitivity
analysis suggested that the duration of the glass dissolution might be predicted
in the ranges from 3.8×103 to 1.9×105
years. Also, the results indicated that the precipitation of
Fe–silicate has the strongest influence on the long-team behavior of
We propose a mechanism of amplification of magnetic fields and plasma heating in clusters of galaxies. Recent observations indicate the existence of ~ μG magnetic fields in clusters of galaxies (e.g., Kronberg 1994). There should be some mechanism which locally amplify magnetic fields. In clusters of galaxies, individual motions of galaxies may create locally strong field region by stretching and tangling the magnetic fields threading the galaxies. Magnetic reconnection taking place in the tangled magnetic fields may convert the kinetic energy of the galaxy motion into the inter-galactic plasma heating (Makishima 1996).
Several weeks after the explosion of supernova (SN) SN1987A, the UV flash of the SN illuminated a ring-like structure in the circumstellar material at about 0.65 ly from the SN. The interaction between the stellar winds from the SN progenitor is considered to be the candidate for the formation of the circumstellar structure. In the case that the stellar winds are spherically symmetric, the interaction should result in a shell-like structure. However, Washimi, Shibata & Mori (1996) show that the magnetic field in the winds causes an anisotropy which leads to the formation of a ring-like structure. When the fast wind of the blue supergiant phase of the progenitor sweeps up the surrounding slow wind of the red-supergiant phase, the magnetic field as well as the wind material are piled up in the interaction region. Since the magnetic energy increases in proportion to the square of the amplitude, the magnetic field exhibits its effect prominently at the interaction region; due to the magnetic pressure force the material at lower latitudes is compressed into a ring-like structure. It is suggested that this magnetic process can also explain the newly observed pair of rings of the SN1987A nebula. We note that the idea of a magnetic field effect is consistent with the radio observation of a supernova remnant, detected by Staveley-Smith et al. (1992) at about 1200 days after the explosion. This radio emission is explained by the collision of the supernova blast wave with the shocked blue wind. This position corresponds to the averaged expansion speed of the supernova ejecta ∼ 0.08 ly which is consistent with the estimation by Shigeyama and Nomoto (1990). The estimated magnetic-energy density by the minimum-energy argument is ∼ 4 × 10–8f–4/7N m–2, where f is the fractional volume of the radiating acceleration region, suggesting a magnetic field of a few milli-Gauss or more (Chevalier 1992). This field intensity is consistent with an intensity of ≈ 2 · 10–4 Gauss obtained between the reverse shock and the contact surface shown, if one takes into account a further enhancement of the field due to the sweeping-up process by the supernova blast wave. When the SN ejector collides with the ring at the end of this century or at the beginning of the next one, we can also expect more intense radio emission at rather middle and high latitudes where the magnetic intensity is greater, rather than at the equator where the ring-like structure is located.
Recent general-relativistic MHD simulations of jets ejected from black-hole magnetospheres (for both Schwarzschild and Kerr holes) have revealed that (1) strong shock waves are formed in the accretion flow inside 3rs, (2) jets show two-layered shell structure consisting of a gas-pressure driven jet and a magnetically driven jet, the former being accelerated from a high-pressure region heated by strong shocks, and (3) in the case of a Kerr hole, magnetically driven jets are produced from the ergosphere by the effect of frame dragging.
We present a scenario for the origin of the hot plasma in our Galaxy, as a model of a strong X-ray emission (LX(2 – 10keV) ~ 1038 erg s−1), called Galactic Ridge X-ray Emission (GRXE), which has been observed near the Galactic plane. GRXE is thermal emission from hot component (~ 7 keV) and cool component (~ 0.8 keV). Observations suggest that the hot component is diffuse, and is not escaping away freely. Both what heats the hot component and what confines it in the Galactic ridge are still remained puzzling, while the cool component is believed to be made by supernovae. We propose a new scenario: the hot component of GRXE plasma is heated by magnetic reconnection, and confined in the helical magnetic field produced by magnetic reconnection or in the current sheet and magnetic field. We solved also the 2-dimensional magnetohydrodynamic (MHD) equations numerically to study how the magnetic reconnection creates hot plasmas and magnetic islands (helical tubes), and how the magnetic islands confine the hot plasmas in Galaxy. We conclude that the magnetic reconnection is able to heat up the cool component to hot component of GRXE plasma if the magnetic field is localized into intense flux tube with Blocal ~ 30 μG (the volume filling factor of f ~ 0.1).
Recent X-ray astronomy satellite (e.g., Ginga, ASCA) has revealed that the center of our Galaxy is filled with a large amount of very hot plasmas (a few − 10 keV) on a scale of 100 pc, which are referred to as superhot plasmas. These plasmas are similar to the Galactic Ridge X-ray Emission (GRXE; cf Tanuma et al. 1997), but with larger gas pressure, and their formation mechanism has been a big puzzle. Here we propose a new model, magnetic reconnection model (Fig. 1), to explain the heating as well as the confinement of the Galactic center superhot plasmas, by performing MHD numerical simulations of magnetic reconnection in the situation suitable for the Galactic center. In our model, the magnetic field is amplified by the rotation of the Galactic gas disk (Fig. 2), and inflate from the disk to outside by the Parker instability. The inflating magnetic loop collides with ambient field lines, thus inducing the magnetic reconnection (the same process applied to the solar corona is shown in Yokoyama and Shibata 1995). In this model, energy release per single reconnection event is ΔE ≈ emVrec ≈ 2 × 1051 erg where em = P/β is the energy density of toroidal magnetic field, Vrec = λ2δ is the volume of the event, λ ≈ 60pc is the most unstable wavelength of the Parker instability, and δ ≈ 3pc is the thickness of the Galactic disk. The occurrence rate of this event is f ≈ N/Δτdep ≈ (3 × 104 yr)−1 where N = Vdisk/Vrec is the number of current sheets in the disk, Vdisk is the volume of the disk, and Δτdep is the time scale of energy deposit which is comparable with the time scale of the Galactic rotation. Then, the heating rate is h = fΔE = 2 × 1039 erg s−1 = 100L2–10keV.
Since the discovery of fading X-rays from Gamma-Ray Bursts (GRBs) with BeppoSAX (Piro et al. 1997, Costa et al. 1997), world-wide follow-up observations in optical band have achieved the fruitful results. The case of GRB 970228, there was an optical transient, coincides with the BeppoSAX position and faded (Paradijs et al. 1997, Sahu et al. 1997). These optical observations also confirmed the extended component, which was associated with the optical transient. The new transient are fading with a power-law function in time and the later observation of HST confirmed the extended emission is stable (Fruchter et al. 1997). This extended object seems to be a distant galaxy and strongly suggests to be the host.
Intra-cluster spaces are filled with intra-cluster medium (ICM), whose typical temperature and density are TICM ~ 107.5 K and nICM ~ 10−3 cm−3, respectively (e.g., Sarazin 1988). Recent Faraday rotation measurements have revealed the existence of magnetic fields in ICM with few − 10 μG (e.g., Ge & Owen 1993). In ICM, the plasma β (the ratio of gas pressure to magnetic pressure) is almost “equipartition” value as follows:
NGC 3079 has very luminous water megamaser from the nucleus, the peak of the spectrum being blueshifted by 180 km s−1 from the systemic velocity of the galaxy (Vsys = 1131 km s−1) (Henkel et al. 1984, Haschick & Baan 1985). Core-jet like continuum structure is also found in the nuclear region (Irwin & Seaquist 1988). No velocity drift for main features of water maser (VLSR = 941–975 km s−1) has been shown (Nakai et al. 1995). However, the drift was recently detected for the maser of 1190 km s−1 (Nakai 1997). HI and OH absorptions are detected in the nucleus (Haschick & Baan 1985, Irwin & Seaquist 1991). Thus this galaxy is very unique object to investigate water masers, continuum structure and absorption features all together with VLBI.
X-ray images of rotation-powered pulsars were examined using ASCA Gas Imaging Spectrometer (GIS). The data sets are taken from those available in the ASCA public archive in the performance verification (PV) phase and the guest-observing (GO) phase 1. We detected diffuse X-ray sources in the vicinity of nine pulsars including five new detections. There are large variety in their morphology and spatial size. The high probability of finding such diffuse sources around pulsars suggests that they exist universally for all the active pulsars, and that they are powered by the pulsars. We propose that the pulsar-powered nebula is a good probe to measure the otherwise invisible energy flux dissipating from a pulsar into the surrounding space.
We have performed a 2.5D, nonsteady, general-relativistic MHD simulation. Initially, we assumed a uniform magnetic field, a geometrically thin accretion disk rotating at Keplerian velocity, and a hydrostatic corona around a Schwarzschild black hole. We have investigated the formation mechanism of gas-pressure driven jets expected by Koide et al. and found the strong dependence of jet velocities Lorentz factor of jets) on the ratio of the density of the accretion disk to that of the corona (ρd/ρc), where γ2j - γj ∝ (ρd/ρc)0.75.