The Progenitors of Type Ia Supernovae: New Insights from Radio Observations

Ia型超新星（SNe Ia）标志着白色或非常古老的致密星星的完全分裂，但我们还不知道白色爆炸的原因，也不知道是什么样的星星系统。流行的模型认为，白色矮星从一颗正常的星星吸积，直到它达到稳定的白色矮星的最大质量，称为阿布拉塞卡极限，或者它可能被驱动与另一颗白色矮星合并爆炸。事实上，超新星Ia可能有多种多样的祖先，其混合物随着恒星年龄的变化而变化。母恒星系统和爆炸中喷出的物质质量决定了超新星的光度如何随时间演化，影响了超新星Ia在宇宙学中作为标准烛光的使用。因此，迫切需要确定超新星Ia的祖先，而不仅仅是解决一个长期存在的天体物理学之谜。密歇根州立大学（MSU）的一个研究小组打算通过射电望远镜观测绘制出它们的环境来限制Ia超新星的祖先。该计划将使用卡尔G. Jansky甚大阵列（VLA）和新的MeerKAT望远镜在南非寻找从SN爆炸波与环双星材料的相互作用发射。 首席研究员将通过密歇根州4-H吸引来自农村背景的学龄青年，在MSU天文台的住宅探索日和活动之夜领导项目。密歇根州立大学天文台和天网望远镜网络将被用来为这些学生提供实践观测经验和项目。在流行的超新星Ia模型的背景下，非简并伴星应该用恒星风和新星壳污染它们的环境，而白色矮星合并将在相对干净的环境中爆炸--但被异常密集的离散壳层在合并或共同包络阶段排出。 该计划将通过以下方式限制超新星Ia的前身：（1）通过在超新星爆发后1-2天的早期观测超新星Ia，寻找由双星伴星喷出的低密度风，以确定超新星光学光变曲线早期“颠簸”的原因。(2)利用超新星Ia爆发后1-60年的射电观测，确定超新星Ia是否被最近喷出的普通包层所包围，如果它们是由两颗白色矮星合并产生的话，这是可以预期的。(3)绘制SNe Ia-CSM的环双星环境。观测将确定拱星物质（CSM）是否更符合恒星风（非简并伴星的证据）或共同的包络（如预期的白色矮星合并）。(4)：观测有红巨星伴星的银河新星。这些系统作为缩小规模的测试平台，用于测试爆炸中喷出物与CSM相互作用产生的预期无线电发射。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Type Ia supernovae (SNe Ia) mark the complete disruption of a white dwarf star, or very old compact star, but we do not yet understand why the white dwarf explodes, nor in what kind of binary star system. Popular models alternatively hold that the white dwarf accretes from a normal companion star until it reaches the maximum mass of a stable white dwarf, known as the Chandrasekhar limit, or that it may be driven to explode by merging with another white dwarf. Indeed, SNe Ia may have a diversity of progenitors, with a mix that varies with stellar age. The progenitor system and the mass of the material ejected in the explosion determine how the luminosity of the SN evolves with time, affecting the use of SNe Ia as standard candles in cosmology. Therefore, there is an urgent need to determine the progenitors of SNe Ia, beyond just solving a longstanding astrophysical mystery. A research group at Michigan State University (MSU) intends to constrain the progenitors of SNe Ia by mapping out their environments with radio telescope observations. The program will survey SNe Ia for signatures of the binary progenitor by using the Karl G. Jansky Very Large Array (VLA) and the new MeerKAT telescope in South Africa to search for emission from the interaction of the SN blast wave with circumbinary material. The principal investigator will engage school-age youth from rural backgrounds through Michigan 4-H, leading programs at the residential Exploration Days and activity nights at the MSU Observatory. The MSU Observatory and SkyNet network of telescopes will be used to offer hands-on observing experience and projects to these students.In the context of popular SN Ia models, non-degenerate companion stars should pollute their environments with stellar winds and nova shells, while white dwarf mergers will explode in relatively clean environments---but be surrounded by unusually dense, discrete shells expelled in the merger or during the common envelope phase. This program will constrain the progenitors of SNe Ia by: (1) Searching for a low-density wind expelled by the binary companion by observing SNe Ia at radio wavelengths at very early times, just ~1-2 days after explosion to identify the cause of early "bumps" in SN optical light curves. (2) Determining if SNe Ia are surrounded by recently ejected common envelopes, as might be expected if they are produced by the merger of two white dwarfs, using radio observations of SNe Ia taken 1-60 years after the explosion. (3) Mapping the circumbinary environments of SNe Ia-CSM. Observations will determine whether the circumstellar material (CSM) is more consistent with a stellar wind (evidence of a non-degenerate companion) or of a common envelope (as expected for a white dwarf merger). (4): Observing Galactic novae with red giant companions. These systems serve as scaled-down testbeds for the expected radio emission resulting from the interaction between ejecta in an explosion and CSM.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.