Illuminating Massive Black Holes with White Dwarfs

Transcription

1 Illuminating Massive Black Holes with White Dwarfs Morgan MacLeod! University of California, Santa Cruz!!! in collaboration with:! Jacqueline Goldstein, James Guillochon, Johan Samsing,! Dan Kasen, Stephan Rosswog, & Enrico Ramirez-Ruiz! Black Holes in Dense Star Clusters!!!!!!!!! Aspen Center for Physics, Jan 2015

2 Outline WD tidal disruption! High energy signatures! Optical counterparts! From detectability to identification This talk builds on the work of: (Rosswog+ 2008,2009), (Clausen+ 2011), (Haas+ 2012), (Scherbakov+ 2013), (Cheng+ 2013,2014), (Jonker+2013)!. and yesterday s talk by Thomas Wevers

3 Tidal disruption of stars by massive black holes r t = Mbh M 1/3 R BH r s

4 From fallback to accretion flare ejected Tidal debris tail falls back at rate Ṁ dm de BH-bound After returning to pericenter, material circularizes at ~2rt and accretes viscously. simulation: J. Guillochon

5 Tidal disruption of stars by massive black holes r s r t = Mbh M 1/3 R rs = 2GM bh c 2

6 8 Fig. 7. Snapshots of rest-mass density (in units of the initial entral density of the star) in the orbital plane around the time that he star s center of mass crosses the BH s light ring from simulaions with main-sequence stars, M BH /M =10 6,and L/M BH =2 top), and 3.5 (bottom). Also shown is the position of the set f geodesics from the corresponding model described in Section 5 magenta outline) at the same time as the simulation snapshot. or r apple r T, while, for r>r T, tidal e ects can be comletely ignored. It also does not capture the distribution f the star s mass, which, in general, will be centrally ondensed. In addition, we note that the quantity t geo coordinate dependent (here we use harmonic coordiates as in the simulations). Nevertheless, we find that his model captures the main features of the simulation esults. As an initial point of comparison, in Figures 7 and 9, long with the density from the full simulation results at pproximately the time the star s center(east of mass2014) Fig. 9. Same as Figure 7, but for the head-on collision crosses of a he hite BH s dwarf light withring, a BHwe with also mass include M BH /M the =2 curve10 made 3 (top) upand by he BH/M positions =4 of 10the 3 (bottom). set of geodesics for the corresponding arameters and Direct time. Weswallowing can see that fact this! curve i erent atches the values shape of Rof the andstar r T corresponding quite well all tocases. the model This dicates ain-sequence that the star. model Since assumptions for large by mass BH are ratios fairly good the GW aproximations for these cases. log HrtêrsL WD Sun horizon log M ü D 2 Merloni: Cosmological EvolutionofSMBH Fig. 10. Relative di erence in time for geodesics to cross the BH light ring for model parameters corresponding to a mainsequence star. The top panel corresponds to head-on collisions with di erent mass ratios, while the bottom panel corresponds to a M BH /M =10 6 mass ratio with di erent amounts of angular momentum. IMBHs??? Fig. 8. Same as Figure 3, but for the head-on collision of a white dwarf and a nonspinning BH. 30R ü RG (Merloni 2008) Fig. 1. The local black hole mass function, plotted as M φ M,inordertohighlightthelocationandheight

7 High energy disruption signatures log M yr -1 D WD Sun-Like M Edd 30R ü RG These highly super-edd. accretion flows can launch relativistic outflows which greatly outshine thermal accretion-disk emission (De Colle+ 2012) log M ü D The peak feeding rate in WD disruptions greatly exceeds the Eddington mass accretion rate, and that of MS TDEs: Ṁ peak / M 1/2 M 2 bh R 3/2 Sw J (University of Warwick / Mark A. Garlick) P jet = Ṁc2 ṀEddc 2 (e.g. yesterday s talk by A. Sadowski)

8 High energy disruption signatures 49 observer along the jet axis: log s -1 D DM = M WD DM = 0.1 M WD M bh = M ü MS M Edd log M bh = M : L peak ergs 1 log tedd yr log tpeak h t peak 1h (MacLeod+ 2014) M wd M t Edd 3 months

9 High energy disruption & detection rates (Given The Astrophysical extrapolation Journal, 794:9(14pp),2014October10 of Mbh-sigma relaition ) 4 log Ngal yr MS TDEs WD TDEs Ecc WD TD WD disruptions are a factor of ~100x less common than their main sequence counterparts. 8 log Ngal Lpeak normalized log M bh M log M bh M (MacLeod+ 2014)

10 High energy disruption & detection rates The Astrophysical Journal, 794:9(14pp),2014October10 4 log Ngal yr MS TDEs WD TDEs Ecc WD TD WD disruptions are a factor of ~100x less common than their main sequence counterparts. 8 log Ngal Lpeak normalized 1.0 jetted transients log M bh M But their beamed emission! is ~1000x more luminous (MacLeod+ 2014)

11 High energy disruption & detection rates The Astrophysical Journal, 794:9(14pp),2014October10 4 Detection with Swift log Ngal yr MS TDEs WD TDEs Ecc WD TD Ṅ gal 10 6 yr 1 n gal 10 7 Gpc 3 8 log Ngal Lpeak normalized log M bh M z<1: Ṅ swift 1500f beam f MBH yr 1 15 yr 1 (f beam = f MBH =0.1)

12 Optical counterpart: thermonuclear transient Hydrodynamics of WD compression Density slice along major axis,! perpendicular to orbital plane r p = r t /3

13 Optical counterpart: thermonuclear transient Ignition TIDAL DISRUPTION AND IGNITION OF WHITE DWARFS BY BLACK HOLES 415 thermonuclear (Rosswog+ 2009) see also:! (Haas+ 2012,! Cheng+ 2014) 6 How often? rt /3 WD Disruption ance of the central black hole s mass in determining the behavior of a 0.2 M white dwarf passing within β = 5 (same simulations as referred to evolution of the compressed, and tidally disrupted white dwarf in the ρ T plane. The hottest 10% of the particles are identified and their average its of 106 K) is plotted as a function of their average density (in cgs units). These trajectories always start cold and dense (right lower corner) and uring the black hole flyby. If the timescale on which the white dwarf can react (dynamical timescale tg ) is longer than the burning timescale (tb, see e star cannot expand rapidly enough to quench burning. f this figure is available in the online journal.) Unbound Remnant rt Fig. 1. Contours of density distribution in the orbital plane during a close passage of a WD past a MBH. The top panel shows a = 3 encounter, while the lower panel shows and = 4 encounter. The colors represent di erent times, while the contours from thin to thick are at densities of log =1, 3, 5 g cm 3. Compression is more severe and rapid in the = 4 encounter, and the disrupted star rebounds more rapidly. This e ect can, in particular, be traced by the location and size of the log =5 g cm 3 contour. To do: Add text labels to plots, join into one shared set of axes. Make BH size realistic, add dotted line for COM motion. mass loss 2rt Thermonuclear fraction ~1/6 of events Red = Fe - group Fig. 3. Visualization of the unbound remanent of the white dwarf tidal disruption event. Blue shading illustrates the density Fig. 2 dicular time ser maximu beta=3,

14 Optical counterpart: thermonuclear transient Ignition TIDAL DISRUPTION AND IGNITION OF WHITE DWARFS BY BLACK HOLES Sedona MC radiative transfer lightcurve: 415 (Rosswog+ 2009) see also:! (Haas+ 2012,! Cheng+ 2014) 6 WD Disruption ance of the central black hole s mass in determining the behavior of a 0.2 M white dwarf passing within β = 5 (same simulations as referred to evolution of the compressed, and tidally disrupted white dwarf in the ρ T plane. The hottest 10% of the particles are identified and their average its of 106 K) is plotted as a function of their average density (in cgs units). These trajectories always start cold and dense (right lower corner) and uring the black hole flyby. If the timescale on which the white dwarf can react (dynamical timescale tg ) is longer than the burning timescale (tb, see e star cannot expand rapidly enough to quench burning. f this figure is available in the online journal.) Unbound Remnant Red = Fe - group Fig. 3. Visualization of the unbound remanent of the white dwarf tidal disruption event. Blue shading illustrates the density (MacLeod+ in prep)

15 Optical counterpart: thermonuclear transient Spectra & Doppler shifts: observer near orbital plane /2 blueshifted optical L MIN (line blanketing) red color L MAX L MIN 0 redshifted optical L MAX blue color 3 /2 (MacLeod+ in prep)

16 Optical detection with ZTF or LSST ZTF [m thresh =20.5] ~ 0.5 yr -1! LSST [m thresh =25] ~ 240 yr -1 LSST-detectable event! distributions (MacLeod+ in prep)

17 The challenge of identification L [erg/s] SGRs GRBs WD+MBH GRB A GRB A GRB A J J Optical transients have similar photometric properties to other thermonuclear SNe WD+MBH t [s] Figure 8. Luminosity vs. duration adapted from Levan et al. (2014). The High energy transients share phase space of emerging class of ULGRBs WD+MBH e.g. Phillips (1993) Width- Luminosity relation (Drout+ 2013) 5. Absolute magnitude versus m for a variety of SN in the B

18 Co-detection of beamed and thermonuclear transients Jet + supernova with f beam =0.1,! LSST + Swift-like! ~ 30 f MBH yr -1 detection or non-detection can constrain the MBH population & surrounding star cluster properties nebular emission e.g. [OIII] t~100d beamed! emission supernova only thermal! emission (Clausen+ 2011) Figure 5. Light curves of five of the strongest emission lines. These light

19 Conclusions WD tidal disruption: an avenue to select IMBH-transients! IMBHs??? (Merloni 2008) High energy signatures: jets & beamed emission from super-edd feeding! Optical counterparts: thermonuclear transients in deep encounters! Multi-wavelength detections as an avenue to firmly identify transients Detections or non-detections constrain the occurrence of MBHs <10 5 msun surrounded by dense stellar clusters. Thank you!