[Tex/LaTex] Beamer: missing \endcsname inserted \end{frame}

Question

I am getting this error while compiling this code:
I have already tried checking the equations and looking for missing }, but without success.
This is the first time I am using the beamer environment. Here is a minimum example which reproduces the error.

\documentclass{beamer}

\usepackage[utf8]{inputenc}
\usepackage{default}

\begin{document}
\begin{frame}\frametitle{Onde Gravitazionali da sistemi binari}
\begin{columns}
\begin{column}
\begin{itemize}
   \item $P_{gw}=-\frac{dE_{orb}}{dt}$
   \item $\dot{\omega}_{gw} = \frac{12}{5}\, 2^{\frac{1}{3}} \left(\frac{G M_c}{c^3}\right)^{\frac{5}{3}}\omega_{gw}^{\frac{11}{3}}$
  \end{itemize}
  \end{column}
  \begin{column}
   \includegraphics[scale=0.4]{separation(t).png}
  \end{column}
 \end{columns}
\end{frame}

\end{document}

Answer 1

The column environment takes an argument for the width of the column:

\begin{column}{0.4\textwidth}