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Morgan Macleod NASA Einstein Fellow Harvard-Smithsonian Center for Astrophysics

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Morgan Macleod NASA Einstein Fellow Harvard-Smithsonian Center for Astrophysics Accretion onto compact objects during common envelope phases Morgan MacLeod NASA Einstein Fellow Harvard-Smithsonian Center for Astrophysics collaborators: Andrea Antoni, Aldo Batta, Soumi De, Jonathan Grindlay, Phillip Macias, Gabriela Montes, Ariadna Murguia-Berthier, Eve Ostriker, Enrico Ramirez-Ruiz, James Stone October 3, 2018 Common envelope interactions transform binary systems Example: formation of merging pairs of neutron stars Pair of massive stars (>8x sun’s mass) much closer pair of neutron stars ? draws the binary closer together gravitational wave inspiral Orbital transformation is key in formation of compact binaries Common envelope interactions transform binary systems Example: formation of merging pairs of neutron stars Pair of massive stars (>8x sun’s mass) much closer pair of neutron stars Common Envelope Phase Drag on surrounding Orbit stabilizes as gas tightens the orbit envelope is ejected Evolution to contact NS Companion Common envelope interactions transform binary systems Today’s topic: transformation of compact objects during these interactions by accretion Dense environment implies that accretion is possible. Accretion and BH spin LIGO measurements of projected spins (Farr+ 2017) χe↵ (e.g. King & Kolb 1999) Analytic predictions: inspiral and accretion In the frame of the orbiting object: Hoyle & Lyttleton (1939), Flow is gravitationally focussed Bondi & Hoyle (1944) toward the compact object 2GM R a ⇠ v2 1 (Edgar 2004) …interacts with a “column” of gas with 2 Area = ⇡Ra Hoyle-Lyttleton Accretion 405 THE EFFECT OF INTERSTELLAR MATTER ON CLIMATIC VARIATION BY F. HOYLE AND R. A. LYTTLETON The effect of interstellar matter on climaticReceived variation 19 Apri409l 1939 by the sun's gravitational attraction, and the action of collisions in this con- densation can be shown to give the sun an effective capture radius much larger than its ordinary radius. 1. INTRODUCTION There is direc(a) Calculationt astronomica of the capture radiusl evidenc of the sune for the existence of diffuse clouds of matter Imagine the cloud to be streaming past the sun, from right to left in the figure, anind leinterstellat the velocity of anr yspace element .o f itAn relativy esectio to the sunn whe ofn atht greae tMilk distanceys Way containing a large number of bstare v. Consides usuallr the pary t showof the clous dregion that if undeflectes in dwhic by theh su nn woulo stard passs appear, and the extent of these within a distance o~ or less of its centre. It is clear that collisions will occur to thpatchee left of thse suisn becausofteen th large attractioe comparen of the latterd wil witl produch eth tweo opposinaveragg e apparent distance between the streamstarss ofthemselve particles and thes effec (seet of ,suc foh collisionr examples is to destro, yRussell the angula,r Dugan, and Stewart (2), p. 820). The existence of the so-called cosmical cloud in interstellar space, sharing in the general motion of the galaxy, is now well established, and observational investiga- tion shows that the obscuration referred to above occurs also on a galactic scale. Thus the diffuse obscuring clouds appear as irregularitieHow sthe in thsune genera gravitationallyl cosmical captures cloud. The dimensions of such regions are comparablinterstellare with the distancegas ands betwee how thisn might the stars, and may be very much greater. In some affectinstance solars the systempresence evolutionof such clouds is revealed by their illumination by a star or stars lying in, or near them, so that the matter then can be directly observed. In shape the clouds are very irregular; some appear like long dark lanes, while other tracts are devoid of Fig. 1. any particular form. momentum of the particles about the sun. If after collision the surviving radial component of the velocity is insufficient to enable the particles to escape, such particleSincs will eeventuall the yexistenc be swept intoe th eo fsun suc. Supposeh cloud, for examples appear, that ans to be general in the galaxy it is elemenof importanct of volume of thee clouto d consideA whose initiar l thangulae effectr momentus mtha is vo~t losecouls d be produced if a star passed this momentum through its constituent particles suffering collisions at C; then ththrouge effectiveh radiu onse a ocafn them be calculate. Thd suce frequench that the velocity oy fradiall s u cyh a toccurrence C is s for a particular star would less than the escape velocity at this distance. The element describes a hyperbola whosclearle equationy depen, with thed usua upol notationn th, mae ydistributio be written n of the clouds in space, and the intervals between these event- = s1 +woul e cos 6.d accordingly be irregular. But it is to be observed r Thate directiooncen thaparalletl ttho thee initiaintervall asymptots e woulcorrespondd si nto general be of the order of the periods of time 7 8 occurring in galactiecos0+c problemsl = 0, , that is, of the order of 10 or 10 years, the average period of revolution of a star in the galaxy26- bein2 g about 2-5 x 108 years. The density of an obscuring cloud and the velocity that a star would have relative to it are known as far as orders of magnitude are concerned from astronomical considerations, and it is shown in the sequel that these clouds may have a considerable effect upon a star's radiation during the time of passage of the star through the cloud. The importance to terrestrial climate of such an effect upon the sun is at once evident, and it is to this aspect of the process that the present paper is directed, though it would seem that encounters between stars and the diffuse clouds may also have some bearing on questions of a more general astronomical nature. If any appreciable change in the sun's radiative power Analytic predictions: inspiral and accretion In the frame of the orbiting star: Hoyle & Lyttleton (1939), Bondi & Hoyle (1944) Flow is gravitationally focussed toward the compact object Mass passing through this region is 2GM M˙ HL = A⇢v Ra 2 ⇠ v 2 1 = ⇡Ra⇢v (mass per time) … and kinetic energy is 3 …interacts with a “column” of gas with E˙ HL = A⇢v 2 = ⇡R2⇢v3 Area = ⇡Ra a 2 = M˙ HLv (energy per time) Inspiral and mass accumulation during common envelope In the frame of the orbiting star: Hoyle & Lyttleton (1939), Bondi & Hoyle (1944) Mass passing through this region is Captured! M˙ HL = A⇢v 2 = ⇡Ra⇢v (mass per time) … and kinetic energy is Dissipated! 3 E˙ HL = A⇢v 2 3 = ⇡Ra⇢v 2 = M˙ HLv (energy per time) Analytic predictions: inspiral and accretion • Energy dissipation drives the orbital inspiral. They are directly related in • Mass capture causes the compact obj. to grow. Hoyle-Lyttleton theory: 2 E˙ HL = M˙ HLv NS Example: Common envelope orbital inspiral implies an accumulated mass: E E ∆MNS M˙ = ⇡ E˙ v2 MNSMcomp ⇡ MNS + Mcomp This is enough mass to cause a neutron star to collapse to a black hole! & 1M (Chevalier 1993) Common Envelope Wind Tunnel 3D (AMR) calculation in FLASH Cartesian geometry stellar limb ~g inject flow with polytropic (HSE) profile specified by (✏ , ,q) PM + absorbing central BC ⇢ M stellar core -y boundary enforces HSE Common Envelope Wind Tunnel γ = Γs =5/3 (MacLeod+, 2017) COMMONCommonENVELOPE WEnvelopeIND TUNNEL Wind Tunnel 13 gle is not constant, but, in fact, widens with increasing dis- placement into the wake. What we observe from the stream- lines in Figure 4 is that material focused onto the wake at larger +x displacements comes from a larger impact param- eter in the -y-direction. Recalling the profiles of Figure 1, this material, originating from deeper within the stellar enve- lope, has higher sound speed. As a result, there is a gradi- ent of upstream Mach number in the y-direction (which can be observed in the lower panels of Figure 2 and 4). The shock opening angle, which depends inversely on this up- stream Mach number, thus broadens as the focussed material is drawn from deeper in the stellar envelope potential well. mass accretion This effect is observable primarily in cases of steep gradient (near the envelope limb), where the derivatives of and ✏ M ⇢ become large. The equation of state of the stellar envelope gas also plays a role in determining flow structure. The flow in the γ = Γs = density gradient 4/3 shown in Figures 4 and 5 is more compressible than the Figure 6. Median mass accretion rates into the sink boundary con- dition defined by Rs =0.05Ra. Shaded regions denote the 5-th to flow in the γ = Γs =5/3 shown in Figures 2 and 3. This results 95-th percentile values of the time-variable M˙ . These are compared in higher densities in the immediate wake of the embedded to the γ =5/3 case result of MacLeod & Ramirez-Ruiz (2015a), object because the pressure does not build up as rapidly upon which adopted = 2 for all simulations (labeled M2015). In all M compression in the focused material. In the steeper-gradient cases, we find that steepening density gradient inhibits accretion, cases of γ = Γs =4/3, we see a nested shock outside of an with typical values for large ✏⇢ of M˙ M˙ . The γ =4/3 cases ⌧ HL accretion line, which differs from the much broader fan of show systematically higher M˙ than γ =5/3, perhaps because pres- material in the ✏⇢ = 2, γ = Γs =5/3 simulation. sure gradients provide less resistance to flow convergence and ac- In all cases, the secondary’s gravitational focus lifts some cretion in the more compressible flow. dense material from the stellar interior against the primary star’s gravity. This gravitational force leads some material (with impact parameter R ) to rise and fall in a “tidal We begin by examining the mass accretion rate into the a bulge” trailing the embedded object.
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