941 research outputs found
Access to social and health services as a health opportunity. Effects of pandemic on older people
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A Tale of Two Populations: Rotating Radio Transients and X-ray Dim Isolated Neutron Stars
No full textWe highlight similarities between recently discovered rotating radio transients and X-ray dim isolated neutron stars. In particular, it is shown that X-ray dim isolated neutron stars have a birthrate comparable to that of rotating radio transients. On the contrary, magnetars have a formation rate that is too low to account for the bulk of the radio transient population. The consequences of the recent detection of a thermal X-ray source associated with one of the rotating radio transients on the proposed scenarios for these sources are also discussed
Climate change in a critical planetary perspective: Dipesh Chakrabarty and the Anthropocene vs. Capitalocene controversy
No full textThe essay traces Dipesh Chakrabarty’s reflections on the Anthropocene, the epoch of “anthropogenic” climate change, to discuss them in light of the critiques developed in ecomarxist circles, particularly by Jason W. Moore, Andreas Malm, and Alf Hornborg. Chakrabarty, a well-known exponent of postcolonial studies and keen critic of globalization processes, points out that the “globe” of “globalization” is not the same “globe” of “global warming,” but rather “the planet” – the Earth-system – with its many forms of life. A complex trajectory of deliberation leads the author to question the “geological agency” of human beings and, ultimately, argue that the climate crisis can be better understood and addressed from a “planetary perspective" (rather than a humanocentric one) capable of placing “life in general” at the center of discussion. In their critiques of the Anthropocene narrative, Moore, Malm, and Hornborg speak instead of a “Capitalocene.” Through comparison with this critical stance, the essay highlights and discusses some of the theoretical premises underpinning Chakrabarty’s thinking so as to advance the hypothesis of a critical planetary perspective. Such a perspective recognizes capitalism as an ecological regime and climate change as a political challenge in which the problem of human domination over the rest of nature is clearly intertwined with the problem of domination and privilege in interhuman relations
Millisecond pulsars around intermediate-mass black holes in globular clusters
No full textGlobular clusters (GCs) are expected to be breeding grounds for the formation of single or binary intermediate-mass black holes (IMBHs) of ≳100 M⊙, but a clear signature of their existence is still missing. In this context, we study the process of dynamical capture of a millisecond pulsar (MSP) by a single or binary IMBH, simulating various types of single-binary and binary-binary encounters. It is found that [IMBH, MSP] binaries form over cosmic time in a cluster, at rates ≲10−11 yr−1, via encounters of wide-orbit binary MSPs off the single IMBH, and at a lower pace, via interactions of (binary or single) MSPs with the IMBH orbited by a typical cluster star. The formation of an [IMBH, MSP] system is strongly inhibited if the IMBH is orbited by a stellar mass black hole (BH): in this case, the only viable path is through the formation of a rare stable hierarchical triplet with the MSP orbiting exterior to the [IMBH, BH] binary. The [IMBH, MSP] binaries that form are relatively short-lived, ≲108−109 yr, since their orbits decay via emission of gravitational waves. The detection of an [IMBH, MSP] system has a low probability of occurrence, when inferred from the current sample of MSPs in GCs. If next-generation radio telescopes, like Square Kilometre Array (SKA), will detect an order of magnitude larger population of MSP in GCs, at least one [IMBH, MSP] is expected. Therefore, a complete search for low-luminosity MSPs in the GCs of the Milky Way with SKA will have the potential of testing the hypothesis that IMBHs of the order of 100 M⊙ are commonly hosted in GCs. The discovery will unambiguously prove that BHs exist in the still uncharted interval of masses around ≳100
On the dynamical capture of a MSP by an IMBH in a globular cluster
No full textGlobular clusters (GCs) are rich of millisecond pulsars (MSPs) and might also host single or binary intermediate mass black holes (IMBHs). We simulate 3- and 4-body encounters in order to test the possibility that an IMBH captures a MSP. The newly formed system could be revealed from the timing signal of the MSP, providing an unambiguous measure of the BH mass. In current surveys, the number of expected [IMBH,MSP] binaries in the Milky Way is ~0.1. If next-generation radio telescopes (e.g. SKA) will detect ~10 times more MSPs in GCs, we expect to observe at least one [IMBH,MSP] binary
Blue stragglers, young white dwarfs, and UV-excess stars in the core of 47 Tucanae
No full textWe used a set of archived Hubble Space Telescope/WFPC2 images to probe the stellar population in the core of the nearby galactic globular cluster (GGC) 47 Tuc. From the ultraviolet (UV) color magnitude diagrams (CMDs) obtained for similar to 4000 stars detected within the Planetary Camera (PC) field of view we have pinpointed a number of interesting objects : (1) 43 blue stragglers stars (BSSs), including 20 new candidates; (2) 12 bright (young) cooling white dwarfs (WDs) at the extreme blue region of the UV-CMD; and (3) a large population of UV-excess (UVE) stars, lying between the BSS and the WD sequences. The colors of the WD candidates identified here define a clean pattern in the CMDs, which define the WD cooling sequence. Moreover, both the location on the UV-CMDs and the number of WDs are in excellent agreement with the theoretical expectations. The UVE stars discovered here represent the largest population of anomalous blue objects ever observed in a globular cluster-if the existence of such a large population is confirmed, we have finally found the long-searched-for population of interacting binaries predicted by the theory. Finally, we have investigated the feasibility of the optical identification of the companions of the binary X-ray sources recently detected by Chandra and of binary millisecond pulsars (MSPs) residing in the core of 47 Tuc. Unfortunately, the extreme faintness expected for the MSP companions, together with the huge stellar crowding in the cluster center, prevents statistically reliable identifications based only on positional coincidences
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