Sources and Radiations of the Fermi Bubbles
Two enigmatic gamma-ray features in the galactic central region, known as Fermi Bubbles (FBs), were found from Fermi-LAT data. An energy release, (e.g., by tidal disruption events in the Galactic Center, GC), generates a cavity with a shock that expands into the local ambient medium of the galactic...
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| author | Vladimir A. Dogiel Chung-Ming Ko |
| author_facet | Vladimir A. Dogiel Chung-Ming Ko |
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| description | Two enigmatic gamma-ray features in the galactic central region, known as Fermi Bubbles (FBs), were found from Fermi-LAT data. An energy release, (e.g., by tidal disruption events in the Galactic Center, GC), generates a cavity with a shock that expands into the local ambient medium of the galactic halo. A decade or so ago, a phenomenological model of the FBs was suggested as a result of routine star disruptions by the supermassive black hole in the GC which might provide enough energy for large-scale structures, like the FBs. In 2020, analytical and numerical models of the FBs as a process of routine tidal disruption of stars near the GC were developed; these disruption events can provide enough cumulative energy to form and maintain large-scale structures like the FBs. The disruption events are expected to be <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup><mo>∼</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup><msup><mi>yr</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>, providing an average power of energy release from the GC into the halo of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mi mathvariant="script">E</mi><mo>˙</mo></mover><mo>∼</mo><mn>3</mn><mo>×</mo><msup><mn>10</mn><mn>41</mn></msup></mrow></semantics></math></inline-formula> erg <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi mathvariant="normal">s</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>, which is needed to support the FBs. Analysis of the evolution of superbubbles in exponentially stratified disks concluded that the FB envelope would be destroyed by the Rayleigh–Taylor (RT) instabilities at late stages. The shell is composed of swept-up gas of the bubble, whose thickness is much thinner in comparison to the size of the envelope. We assume that hydrodynamic turbulence is excited in the FB envelope by the RT instability. In this case, the universal energy spectrum of turbulence may be developed in the inertial range of wavenumbers of fluctuations (the Kolmogorov–Obukhov spectrum). From our model we suppose the power of the FBs is transformed partly into the energy of hydrodynamic turbulence in the envelope. If so, hydrodynamic turbulence may generate MHD fluctuations, which accelerate cosmic rays there and generate gamma-ray and radio emission from the FBs. We hope that this model may interpret the observed nonthermal emission from the bubbles. |
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| spelling | doaj-art-03b1d9dac7ed4b139ea6370ac1b2d19d2025-08-20T02:04:44ZengMDPI AGUniverse2218-19972024-11-01101142410.3390/universe10110424Sources and Radiations of the Fermi BubblesVladimir A. Dogiel0Chung-Ming Ko1I.E.Tamm Theoretical Physics Division of P.N.Lebedev Institute of Physics, Leninskii Pr. 53, 119991 Moscow, RussiaInstitute of Astronomy, Department of Physics and Center for Complex Systems, National Central University, Zhongli Dist., Taoyuan City 320317, TaiwanTwo enigmatic gamma-ray features in the galactic central region, known as Fermi Bubbles (FBs), were found from Fermi-LAT data. An energy release, (e.g., by tidal disruption events in the Galactic Center, GC), generates a cavity with a shock that expands into the local ambient medium of the galactic halo. A decade or so ago, a phenomenological model of the FBs was suggested as a result of routine star disruptions by the supermassive black hole in the GC which might provide enough energy for large-scale structures, like the FBs. In 2020, analytical and numerical models of the FBs as a process of routine tidal disruption of stars near the GC were developed; these disruption events can provide enough cumulative energy to form and maintain large-scale structures like the FBs. The disruption events are expected to be <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup><mo>∼</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup><msup><mi>yr</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>, providing an average power of energy release from the GC into the halo of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mi mathvariant="script">E</mi><mo>˙</mo></mover><mo>∼</mo><mn>3</mn><mo>×</mo><msup><mn>10</mn><mn>41</mn></msup></mrow></semantics></math></inline-formula> erg <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi mathvariant="normal">s</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>, which is needed to support the FBs. Analysis of the evolution of superbubbles in exponentially stratified disks concluded that the FB envelope would be destroyed by the Rayleigh–Taylor (RT) instabilities at late stages. The shell is composed of swept-up gas of the bubble, whose thickness is much thinner in comparison to the size of the envelope. We assume that hydrodynamic turbulence is excited in the FB envelope by the RT instability. In this case, the universal energy spectrum of turbulence may be developed in the inertial range of wavenumbers of fluctuations (the Kolmogorov–Obukhov spectrum). From our model we suppose the power of the FBs is transformed partly into the energy of hydrodynamic turbulence in the envelope. If so, hydrodynamic turbulence may generate MHD fluctuations, which accelerate cosmic rays there and generate gamma-ray and radio emission from the FBs. We hope that this model may interpret the observed nonthermal emission from the bubbles.https://www.mdpi.com/2218-1997/10/11/424galactic centerFermi bubblescentral black holestar disruptionsMHD turbulencecosmic rays |
| spellingShingle | Vladimir A. Dogiel Chung-Ming Ko Sources and Radiations of the Fermi Bubbles Universe galactic center Fermi bubbles central black hole star disruptions MHD turbulence cosmic rays |
| title | Sources and Radiations of the Fermi Bubbles |
| title_full | Sources and Radiations of the Fermi Bubbles |
| title_fullStr | Sources and Radiations of the Fermi Bubbles |
| title_full_unstemmed | Sources and Radiations of the Fermi Bubbles |
| title_short | Sources and Radiations of the Fermi Bubbles |
| title_sort | sources and radiations of the fermi bubbles |
| topic | galactic center Fermi bubbles central black hole star disruptions MHD turbulence cosmic rays |
| url | https://www.mdpi.com/2218-1997/10/11/424 |
| work_keys_str_mv | AT vladimiradogiel sourcesandradiationsofthefermibubbles AT chungmingko sourcesandradiationsofthefermibubbles |