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

Ia型超新星（SNe Ia）标志着一颗白矮星或非常古老的致密恒星的完全破裂，但我们还不知道白矮星爆炸的原因，也不知道是哪种双星系统。流行的模型认为，白矮星从一颗正常的伴星吸积，直到达到一颗稳定的白矮星的最大质量，即钱德拉塞卡极限，或者它可能会与另一颗白矮星合并而爆炸。事实上，超新星Ia可能有多种多样的祖先，它们的混合随着恒星年龄的变化而变化。祖星系和爆炸中喷射出的物质的质量决定了超新星的光度如何随时间演变，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谜团。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超新星Ia的环境来限制它们的前身。该计划将利用卡尔·g·詹斯基甚大阵列（VLA）和南非的新MeerKAT望远镜对超新星Ia进行调查，寻找双星前身的特征，以寻找超新星爆炸波与环双星物质相互作用产生的辐射。首席研究员将通过密歇根4-H吸引来自农村背景的学龄青年，在密歇根州立大学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为这些学生提供实际观测经验和项目。在流行的SN 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，而白矮星合并将在相对清洁的环境中爆炸-但在合并或在共同包层阶段被异常密集，离散的壳所包围。该计划将通过以下方式约束Ia型超新星的前身：(1)通过在超新星爆炸后1-2天的早期观测Ia型超新星的射电波长，寻找由双星伴星排出的低密度风，以确定SN光学光曲线中早期“凸起”的原因。(2)利用超新星Ia爆炸后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矮星合并产生的话，这是可以预料的。(3)绘制了SNe Ia-CSM的环二进制环境。观测将确定星周物质（CSM）是否更符合恒星风（非简并伴星的证据）或普通包层（如预期的白矮星合并）。(4)：观测有红巨星伴星的银河系新星。这些系统可以作为预期的射电发射的按比例缩小的测试平台，这些射电发射是由爆炸中的弹射物与CSM之间的相互作用产生的。该奖项反映了美国国家科学基金会的法定使命，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.