Electromagnetic (EM) emission from a massive black hole binary (MBHB) is produced by the gas that is accreted from a surrounding circumbinary disk (CBD), similar to an accretion disk around a single black hole. The binary's gravitational torque clears out a central, low-density cavity in the CBD, and gas from the inner edge of the CBD is periodically stripped into streams that feed the individual black holes, via minidisks around each massive black hole (MBH). Calculating these EM signatures from first principles is challenging, requiring a detailed understanding of the gas, radiation, and magnetic fields within the CBD and minidisks.
Here we performed the first Radiation Magnetohydrodynamic (RMHD) Simulation of a CBD around an equal-mass MBHB. We show that the CBD with radiation makes it thinner, denser and more filamentary than a locally isothermal MHD CBD, and show the importance of radiation for calculating the EM signatures of MBHB.
Here our group performed the first RMHD simulation of a minidisk (led by Dr. Edwin Chan) in a 20 million solar mass MBHB system. Here we found that the minidisk becomes non-axisymmetric, producing anisotropic emission that varies with a half-orbital-period modulation.
Here we performed Radiation Magnetohydrodynamic Simulation of a CBD around a circular binary with mass ratio 10:1. We found that the smaller cavity and the secondary's closer proximity to the inner edge of the CBD, as compared to the equal-mass case, drive higher variability in the far-UV/soft X-ray band of the spectrum, for a MBHB with a total mass of 20 million suns, separated by 100 gravitational radii.
Here we performed RMHD simulations of super-Eddington minidisks around the secondary massive black hole (of 1 million solar mass) in a 10:1 MBHB system. We found strong radiation-driven outflows in these minidisks.
We are exploring circumbinary disks around equal-mass eccentric black hole binaries, with eccentricities ranging from 0.15, 0.45 and 0.75.
Type Ia supernovae are white dwarf stars composed of carbon and oxygen which undergo a thermonuclear explosion, but the nature of the progenitor stars and the mechanism of the explosion is highly debated.
Here we are exploring the double-degenerate channel in which we have two sub-Chandrashekar WDs, each with thin helium shells. During the accretion of He, it detonates on the surface of the primary and wraps around the white dwarf, colliding on the other side. This would lead to the second detonation of carbon, either on the edge or due to shock convergence at the core, and thus leads to a Type Ia supernova event.
Late-time light curves are thought to be powered by the radioactive decay of 57Co and provide an independent method to constrain the progenitors of Type Ia supernovae. We compared five nearby Type Ias with simulation models of near-Chandrashekar and sub-Chandrashekar ar white dwarfs, and saw a clear distinction between the two types of progenitors. The red markers are the near-Chandra models while the blue ones are the sub-Chandra models. Color gradients represent the metallicity of the models.
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