Biomedical subjects

LX Li

Publications and source records attributed to LX Li.

8 recordsLinked to original sources

PubMed2000

Extracting Energy from Accretion into a Kerr Black Hole.

The highest efficiency of converting rest mass into energy by accreting matter into a Kerr black hole is approximately 31% (Thorne 1974). We propose a new process in which periods of accretion from a thin disk, and the associated spin-up of the black hole, alternate with the periods of no accretion and magnetic transfer of energy from the black hole to the disk. These cycles can repeat indefinitely, at least in principle, with the black hole mass increasing by approximately 66% per cycle and up to approximately 43% of accreted rest mass radiated away by the disk.

Journal Article↗

PubMed2000

Extracting Energy from a Black Hole through Its Disk.

When some magnetic field lines connect a Kerr black hole with a disk rotating around it, energy and angular momentum are transferred between them. If the black hole rotates faster than the disk, ca&solm0;GMH>0.36 for a thin Keplerian disk, then energy and angular momentum are extracted from the black hole and transferred to the disk (MH is the mass and aMH is the angular momentum of the black hole). This way, the energy originating in the black hole may be radiated away by the disk. The total amount of energy that can be extracted from the black hole spun down from ca&solm0;GMH=0.998 to ca&solm0;GMH=0.36 by a thin Keplerian disk is approximately 0.15MHc2. This is larger than approximately 0.09MHc2, which can be extracted by the Blandford-Znajek mechanism.

Journal Article↗

PubMed2000

Screw Instability and the Blandford-Znajek Mechanism.

When magnetic field lines thread a rotating black hole's horizon and connect with remote astrophysical loads, the rotational energy of the black hole can be extracted through the Blandford-Znajek mechanism. Due to the rotation of the black hole, the magnetic field lines are twisted and toroidal components are generated. Thus, poloidal electric currents are induced and the black hole's rotational energy is transported to the astrophysical loads through Poynting flux. The Blandford-Znajek mechanism has been considered to be a possible process for powering extragalactic jets. In this Letter, we show that because of the screw instability of the magnetic field, the toroidal components of the magnetic field, and thus the poloidal currents, cannot exceed the limits given by the Kruskal-Shafranov criterion. This significantly lowers the power of the Blandford-Znajek mechanism when the loads are far from the black hole. So the Blandford-Znajek mechanism can only work efficiently within the neighborhood of the black hole. The implications of the results for the scenario of extragalactic jets powered by the Blandford-Znajek mechanism are discussed.

Journal Article↗

PubMed1995