Probing dark matter crests with white dwarfs and IMBHs

Abstract

White dwarfs (WDs) are the most promising captors of dark matter (DM) particles in the crests that are expected to build up in the cores of dense stellar clusters. The DM particles could reach sufficient densities in WD cores to liberate energy through selfannihilation. The extinction associated with our Galactic Centre, the most promising region where to look for such effects, makes it impossible to detect the potential associated luminosity of the DM-burning WDs because due to distance and extreme extinction the apparent near-infrared magnitudes of the WDs would be fainter than about 30 mag. However, in smaller stellar systems which are close enough to us and not heavily extincted, such as ω−Cen, we may be able to detect DM-burning WDs. In this work we investigate the prospects of detection of DM-burning WDs in a stellar cluster harbouring an intermediate-mass black hole (IMBH), which leads to higher densities of DM at the centre as compared with clusters without one. We calculate the capture rate of WIMPs by a WD around an IMBH and estimate the luminosity that a WD would emit depending on its distance to the center of the cluster. Direct-summation N −body simulations of ω−Cen yield a non-negligible number of WDs in the range of radii of interest. We apply our assumption to published HST/ACS observations of stars in the center of ω−Cen to search for DM burning WDs and, although we are not able to identify any evident candidate because of crowding and incompleteness, we proof that their bunching up at high luminosities would be unique. We predict that DM burning will lead to a truncation of the cooling sequence at the faint end. The detection of DM burning in future observations of dense stellar clusters, such as globular clusters or ultra-compact dwarf galaxies could allow us to probe different models of DM distributions and characteristics such as the DM particle scattering cross section on nucleons. On the other hand, if DM-burning WDs really exist, their number and properties could give hints to the existence of IMBHs.

Active Galactic Nuclei: Boon or Bane for Biota?

“…It must be noted that the flux of X-rays received from a hypothetical AGN in the Milky Way at the Earth is on the order of 10 −3 erg cm −2 s −1 after using Figure 1 of Vasudevan & Fabian (2009) and calculating the flux along the lines of (7); our result is consistent with Amaro-Seoane & Chen (2014). In contrast, the equivalent flux from GRBs at kpc distances is on the order of 10 7 erg cm −2 s −1 (Thomas 2009), but the effects on marine biota are not predicted to be severe (Neale & Thomas 2016), due to the much shorter duration of GRBs and the fact that these organisms are protected beneath liquid water.…”

“…Laviolette (1983Laviolette ( , 1987 argued, on a related note, that the Galactic center has been sporadically active on timescales of ∼ 10 4 years, thus emitting high fluxes of energetic electrons (up to 10 5 times the background value) leading to abrupt changes in Earth's climate and potential mass extinctions. Gonzalez (2005) reviewed the role of AGNs in regulating habitability, and pointed out the possibility that the X-ray fluxes at the Earth arising from a hypothetical AGN in the Milky Way could be comparable to that contributed by the active Sun; this result is also consistent with the subsequent analysis by Amaro-Seoane & Chen (2014).…”

Probing the nature of central objects in extreme-mass-ratio inspirals with gravitational waves

“…The parameter space of EMRIs, however, contains additional parameters that we will neglect for simplicity [20]. Another crucial point to note is that the event rate of high-eccentricity EMRIs is much larger than that of low-eccentricity ones [21][22][23][24]. High eccentricity EMRIs spend enough cycles inside the band of eLISA to be detectable [21,24].…”

“…These drawbacks were partially addressed in Refs. [19][20][21][22][23][24][25][26][27][28][29][30][31], which helped in the development of better waveforms. Owing to the system's extreme mass ratio, a way to generate realistic EMRI waveforms is to use black hole perturbation theory, governed by Teukolsky equation.…”

Secular evolution of compact binaries revolving around a spinning massive black hole

“…This "mass segregation" process guaranteed that three body encounters in the core can frequently occur [20], producing binary BHs at high rates [21].Kozai-Lidov mechanism has an important secular effect in hierarchical triple systems, and plays an important role in dynamical evolution of triples. GWs emit-ted by highly eccentric orbits of compact binaries excited from the Kozai-Lidov mechanism might be detectable by , pulsar timing arrays [25][26][27], and also future space-based GW observatories such as LISA [28]. Even though Kozai-Lidov mechanism has been extended to more general cases [29][30][31][32] in the past decades, the effect of spin is absent in the literature.…”