Black hole-accretion disk collision in general relativity: Axisymmetric simulations

Motivated by recent discoveries of X-ray quasiperiodic eruptions, we revisit the collision of a black hole and an accretion disk. Assuming that they are orbiting a supermassive black hole in orthogonal orbits, we perform a general relativistic simulation of the collision, varying the relative velocity <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msub><a:mi>V</a:mi><a:mn>0</a:mn></a:msub></a:math> from <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mn>0.032</c:mn><c:mi>c</c:mi></c:math> to <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mn>0.2</e:mn><e:mi>c</e:mi></e:math> (where <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>c</g:mi></g:math> is the speed of light) with a variety of disk thickness and a realistic local density profile for the disk. Our findings indicate that the mass of the outflow matter from the disk, <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msub><i:mi>m</i:mi><i:mrow><i:mi>ej</i:mi></i:mrow></i:msub></i:math>, is slightly less than the expected value. Meanwhile, the typical energy associated with this outflow <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:msub><k:mi>E</k:mi><k:mrow><k:mi>ej</k:mi></k:mrow></k:msub></k:math> is <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mo>∼</m:mo><m:msub><m:mi>m</m:mi><m:mrow><m:mi>ej</m:mi></m:mrow></m:msub><m:msubsup><m:mi>V</m:mi><m:mn>0</m:mn><m:mn>2</m:mn></m:msubsup></m:math>. Thus, the predicted peak luminosity from disk flares is approximately equal to the Eddington luminosity of the black hole, whereas the peak time and duration of the flares, which are <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mo>∝</o:mo><o:msubsup><o:mi>m</o:mi><o:mrow><o:mi>ej</o:mi></o:mrow><o:mrow><o:mn>1</o:mn><o:mo>/</o:mo><o:mn>2</o:mn></o:mrow></o:msubsup></o:math>, are shorter than that previously believed. We also demonstrate that the property of the outflow matter induced by the incoming and outgoing stages of the black hole collision is appreciably different. We find that a high mass accretion rate onto the black hole from the disk persists for a timescale of <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mo>∼</q:mo><q:msup><q:mn>10</q:mn><q:mn>6</q:mn></q:msup></q:math> Schwarzschild time of the black hole after the collision for <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:msub><s:mi>V</s:mi><s:mn>0</s:mn></s:msub><s:mo>/</s:mo><s:mi>c</s:mi><s:mo>≲</s:mo><s:mn>0.1</s:mn></s:math>, making this long-term accretion onto the black hole the dominant emission process for black hole-disk collision events. Implications of these results are discussed.