Comprehensive modeling of Type Ia supernova explosions

• Antragsteller: Professor Dr. Friedrich Röpke
• Fachliche Zuordnung: Astrophysik und Astronomie
• Förderung: Förderung von 2007 bis 2016
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 48431991

• Erstellungsjahr: 2016

Zusammenfassung der Projektergebnisse

Type Ia supernovae (SNe Ia) – theoretically associated with thermonuclear explosions of white dwarf stars – are among the brightest events in the Universe. They have been instrumental in determining its geometry by using them as “lighthouses” to determine distances on cosmological scales. Rich observational material was gathered on these fascinating events over the past decade. Our physical understanding of SNe Ia, however, is incomplete. The progenitor system, out of which they arise, has not been identified observationally. Therefore, simulations have to start out from unknown initial conditions. The goal of the project “Comprehensive Modeling of Type Ia Supernova Explosions” was to address this uncertainty by modeling scenarios of these events avoiding free parameters in the explosion description. This relied on state-of-the-art multidimensional simulations that consistently make predictions of observables – an approach that was pioneered in the project that has set new standards in the field. Only this way, a systematic exploration of several options regarding the progenitor structure and the explosion physics could be compared to astronomical data. The project focused to two main tasks. The first was to scrutinize the Chandrasekhar-mass explosion model that at the time of the start of the work was considered the standard scenario. Indeed, the synthetic observables derived from multidimensional simulations were able to reproduce main characteristics of SNe Ia. Analyzed with a tool normally applied in supernova observations, these objects were classified as SNe Ia. The observables of a suite of two-dimensional simulations followed the correlation employed to calibrate SNe Ia in cosmological measurements, however, this was not reproduced in three-dimensional simulations. In addition, there remain shortcomings in other observables such as the predicted colors or line velocities. Such developments reached the group well-prepared and could be handled with minor adjustments to the work plan. The intended broad approach to modeling SN Ia explosion turned out to be successful in exploring alternatives to the former standard Chandrasekhar-mass explosion model as a second main task of the project. Keeping pace with developments in SN Ia observations and progenitor modeling, the work of the group was instrumental in initiating a shift of paradigm. Detonations in sub-Chandrasekhar mass white dwarfs were found to produce observables that match astronomical data at the same level of agreement as conventional Chandrasekhar-mass white dwarf explosions. Two mechanisms to trigger such a detonation were studied: “double detonations” in which the detonation wave is launched from an accreting layer of helium-rich material and “violent mergers”. The later mechanism was first suggested by the group and contrasts previous belief that mergers of white dwarfs would inevitably lead to a gravitational collapse forming a neutron star. These different possibilities compete for the explanation of the bulk of normal SNe Ia. Hence, current efforts focus on identifying ways to distinguish the models based on alternative observables, such as nucleosynthesis imprints, gamma-ray observables, and spectropolarimetry. Another development in SN Ia astronomy was that distinct sub-classes of these events were defined that diverge in their characteristics from the bulk of normal SNe Ia. Mechanisms in the explosion processes were identified in the project that are capable of explaining such peculiar events. In addition, methods developed by the group to simulate thermonuclear supernova explosions were applied to address other astrophysical questions, such as hypothetic conversions of neutron stars into strange quark stars and the origin of newly found astrophysical transients. The results of the project had significant impact on the development of the field of SN Ia modeling and were disseminated in the scientific literature, in frequent presentations at international conferences, in public media, and in a variety of outreach activities.

Projektbezogene Publikationen (Auswahl)

• (2009): The diversity of type Ia supernovae from broken symmetries, Nature 460, 869–872
  D. Kasen, F. K. Röpke, and S. E. Woosley
  
• (2010): An asymmetric explosion as the origin of spectral evolution diversity in type Ia supernovae, Nature 466, 82–85
  K. Maeda, S. Benetti, M. Stritzinger, F. K. Röpke, G. Folatelli, J. Sollerman, S. Taubenberger, K. Nomoto, G. Leloudas, M. Hamuy, M. Tanaka, P. A. Mazzali, and N. Elias-Rosa
  
• (2010): Detonations in Sub-Chandrasekhar Mass C+O White Dwarfs, Astrophysical Journal 714, L52–L57
  S. A. Sim, F. K. Röpke, W. Hillebrandt, M. Kromer, R. Pakmor, M. Fink, A. R. Ruiter, and I. R. Seitenzahl
  
• (2010): Double-detonation sub-Chandrasekhar supernovae: can minimum helium shell masses detonate the core?, Astronomy and Astrophysics 514, A53
  M. Fink, F. K. Röpke, W. Hillebrandt, I. R. Seitenzahl, S. A. Sim, and M. Kromer
  
• (2010): Sub-luminous type Ia supernovae from the mergers of equal-mass white dwarfs with M ∼ 0.9Msun, Nature 463, 61–64
  R. Pakmor, M. Kromer, F. K. Röpke, S. A. Sim, A. J. Ruiter, and W. Hillebrandt
  
• (2011): Violent mergers of nearly equal-mass white dwarf as progenitors of subluminous Type Ia supernovae, Astronomy and Astrophysics 528, A117
  R. Pakmor, S. Hachinger, F. K. Röpke, and W. Hillebrandt
  
• (2012): Constraining Type Ia Supernova Models: SN 2011fe as a Test Case, Astrophysical Journal Letters 750, L19
  F. K. Röpke, M. Kromer, I. R. Seitenzahl, R. Pakmor, S. A. Sim, S. Taubenberger, F. Ciaraldi- Schoolmann, W. Hillebrandt, G. Aldering, P. Antilogus, C. Baltay, S. Benitez-Herrera, S. Bongard, C. Buton, A. Canto, F. Cellier-Holzem, M. Childress, N. Chotard, Y. Copin, H. K. Fakhouri, M. Fink, D. Fouchez, E. Gangler, J. Guy, S. Hachinger, E. Y. Hsiao, J. Chen, M. Kerschhaggl, M. Kowalski, P. Nugent, K. Paech, R. Pain, E. Pecontal, R. Pereira, S. Perlmutter, D. Rabinowitz, M. Rigault, K. Runge, C. Saunders, G. Smadja, N. Suzuki, C. Tao, R. C. Thomas, A. Tilquin, C. Wu
  
• (2012): Normal Type Ia Supernovae from Violent Mergers of White Dwarf Binaries, Astrophysical Journal Letters 747, L10
  R. Pakmor, M. Kromer, S. Taubenberger, S. A. Sim, F. K. Röpke, and W. Hillebrandt
  
• (2013): Three-dimensional delayed-detonation models with nucleosynthesis for Type Ia supernovae, MNRAS 429, 1156–1172
  I. R. Seitenzahl, F. Ciaraldi-Schoolmann, F. K. Röpke, M. Fink, W. Hillebrandt, M. Kromer, R. Pakmor, A. J. Ruiter, S. A. Sim, S. Taubenberger
  
• (2014): Three-dimensional pure deflagration models with nucleosynthesis and synthetic observables for Type Ia supernovae, MNRAS 438, 1762–1783
  M. Fink, M. Kromer, I. R. Seitenzahl, F. Ciaraldi-Schoolmann, F. K. Röpke, S. A. Sim, R. Pakmor, A. J. Ruiter, W. Hillebrandt