${ \newcommand{\nodea}{\node[draw,circle] (a) {$p1$}
;}\newcommand{\nodestara}{\node (sa) {$\bigstar$}
;}\newcommand{\nodeb}{\node[draw,circle] (b) {}
;}\begin{tikzpicture}[auto]
\matrix[column sep=.3cm, row sep=.3cm,ampersand replacement=\&]{
  \& \nodea \\ 
  \nodeb \& \nodestara \\
};

\path[ultra thick, red] (a) edge (b);
\end{tikzpicture}}$