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The Evolution of the BL Lacertae Objects
Astrophysics · Submitted 18 Mar 1999
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We compute scales long and uniform enough to yield an intrinsically slow population evolution, giving rise to number counts of ``Euclidean'' or flatter shape; even longer timescales apply to the additional, analogous process involving the inner accretion disk directly.
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The abstract, sentence by sentence
The BL Lac population is set apart from the rest of the active galactic nuclei by a number of peculiar features, including remarkably little signs of cosmological evolution. We focus on this feature, and take hint from the observations to reconsider extraction of the primary energy from a Kerr hole via the Blandford-Znajek (BZ) process; in fact, we stress how this can power the emitting jets of the BL Lac objects in a regime of low accretion. We show that the timescale for the BZ process to exhaust the rotational energy of the hole spans many gigayears in all such sources. We compute scales long and uniform enough to yield an intrinsically slow population evolution, giving rise to number counts of ``Euclidean'' or flatter shape; even longer timescales apply to the additional, analogous process involving the inner accretion disk directly. Such slow evolution takes place in ambients and at epochs (z \lsim 1) where interactions of the host galaxies with companions become rare or weak. On the other hand, at higher z, we argue that frequent interactions of the hosts within groups enhanced, each for some 10^{-1} Gyr, the accretion rates and the emissions from the disks, attaining power levels that are typical of the radio-loud quasars. But such interactions were also likely to disorder the large-scale magnetic field in the disk and to decrease angular momentum of the hole, thus limiting the lifetime of all BZ emissions to under a few gigayears. Then the stronger evolution of the flat-spectrum radio-loud quasars was driven, similar to the radio-quiet ones, by the interaction rate decreasing rapidly with z.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The BL Lac population is set apart from the rest of the active galactic nuclei by a number of peculiar features, including remarkably little signs of cosmological evolution. | background 1.00 | 0.10 | 0.09 | asserted 1.00 |
| s1 | We focus on this feature, and take hint from the observations to reconsider extraction of the primary energy from a Kerr hole via the Blandford-Znajek (BZ) process; in fact, we stress how this can power the emitting jets of the BL Lac objects in a regime of low accretion. | contribution 0.95 | 0.70 | 0.17 | hedged possibility 0.43 |
| s2 | We show that the timescale for the BZ process to exhaust the rotational energy of the hole spans many gigayears in all such sources. | result 0.99 | 0.89 | 0.25 | asserted 1.00 |
| s3 | We compute scales long and uniform enough to yield an intrinsically slow population evolution, giving rise to number counts of ``Euclidean'' or flatter shape; even longer timescales apply to the additional, analogous process involving the inner accretion disk directly. | result 0.89 | 0.92 | 0.30 | asserted 1.00 |
| s4 | Such slow evolution takes place in ambients and at epochs (z \lsim 1) where interactions of the host galaxies with companions become rare or weak. | interpretation 0.70 | 0.27 | 0.10 | asserted 0.90 |
| s5 | On the other hand, at higher z, we argue that frequent interactions of the hosts within groups enhanced, each for some 10^{-1} Gyr, the accretion rates and the emissions from the disks, attaining power levels that are typical of the radio-loud quasars. | interpretation 0.67 | 0.40 | 0.10 | asserted 0.56 |
| s6 | But such interactions were also likely to disorder the large-scale magnetic field in the disk and to decrease angular momentum of the hole, thus limiting the lifetime of all BZ emissions to under a few gigayears. | interpretation 0.72 | 0.46 | 0.14 | hedged possibility 0.95 |
| s7 | Then the stronger evolution of the flat-spectrum radio-loud quasars was driven, similar to the radio-quiet ones, by the interaction rate decreasing rapidly with z. | interpretation 0.93 | 0.58 | 0.27 | asserted 0.97 |
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Original abstract
The BL Lac population is set apart from the rest of the active galactic nuclei by a number of peculiar features, including remarkably little signs of cosmological evolution. We focus on this feature, and take hint from the observations to reconsider extraction of the primary energy from a Kerr hole via the Blandford-Znajek (BZ) process; in fact, we stress how this can power the emitting jets of the BL Lac objects in a regime of low accretion. We show that the timescale for the BZ process to exhaust the rotational energy of the hole spans many gigayears in all such sources. We compute scales long and uniform enough to yield an intrinsically slow population evolution, giving rise to number counts of ``Euclidean'' or flatter shape; even longer timescales apply to the additional, analogous process involving the inner accretion disk directly. Such slow evolution takes place in ambients and at epochs (z \lsim 1) where interactions of the host galaxies with companions become rare or weak. On the other hand, at higher z, we argue that frequent interactions of the hosts within groups enhanced, each for some 10^{-1} Gyr, the accretion rates and the emissions from the disks, attaining power levels that are typical of the radio-loud quasars. But such interactions were also likely to disorder the large-scale magnetic field in the disk and to decrease angular momentum of the hole, thus limiting the lifetime of all BZ emissions to under a few gigayears. Then the stronger evolution of the flat-spectrum radio-loud quasars was driven, similar to the radio-quiet ones, by the interaction rate decreasing rapidly with z.
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