強化されたトリプルα反応は,超新星における陽子豊富な核合成を減少させる
Shilun Jin1,2,3, Luke F Roberts4,5, Sam M Austin1,2
1National Superconducting Cyclotron Laboratory, East Lansing, MI, USA.
Nature
|December 3, 2020
まとめ
超新星では 炭素を形成する重要な反応が 高密度の影響により 10倍まで増加します この発見は,重元素合成の現在のモデル,特に中性子-陽子 (νp) プロセスに挑戦しています.
科学分野:
- 核天体物理学
- スター進化
- エレメント合成
背景:
- トリプルアルファ反応は 超新星における重元素の合成に不可欠です
- 以前の研究では 高温でもホイル状態の共鳴が 支配的であると仮定していました
- 高密度での核分裂プロセスのトリプルアルファ反応速度の影響は十分に理解されていません.
研究 の 目的:
- 超新星爆発のトリプルアルファ反応を 調べるためだ
- 核分裂過程がホイール状態と反応速度にどのように影響するかを決定する.
- 核合成の予測,特に中性子-陽子 (νp) プロセスに対する強化されたトリプルアルファ反応速度の影響を評価する.
主な方法:
- 12Cにおけるホイル状態に対する陽子と中性子の散乱効果の理論的調査.
- 核崩壊の超新星流出に見られる条件下でのトリプルアルファ反応率のモデル化.
- 密度依存反応速度の強化を核合成シミュレーションに組み込む.
主要な成果:
- これまでは無視されていた 陽子と中性子の散乱プロセスは 超新星発射で トリプルアルファ反応の速度を 増加させる.
- この増加した速度は,最も内側から放出される物質でnpプロセスによって形成される重陽子豊かな同位体の生成を抑制する.
- 前回の定数因子感受性研究とは異なる,熱力学的条件の進化に依存する.
結論:
- 高密度でトリプルアルファ反応速度のインメディアの貢献は重要であり,超新星核合成モデルに含まれなければならない.
- 観測された強化は,太陽系と古代の恒星における重元素 (Mo,Ruなど) の豊富さの唯一の説明として νp プロセスに疑問を投げかけます.
- 超新星核合成モデルをこれらの新しく理解された反応動力学で洗練するためにさらなる研究が必要である.
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