  We update the globular cluster bound on massive ($m_a$ up to a few 100 keV)
axion-like particles (ALP) interacting with photons. The production of such
particles in the stellar core is dominated by the Primakoff $\gamma + Ze\to Ze
+a$ and by the photon coalescence process $\gamma+\gamma\to a$. The latter,
which is predominant at high masses, was not included in previous estimations.
Furthermore, we account for the possibility that axions decay inside the
stellar core, a non-negligible effect at the masses and couplings we are
considering here. Consequently, our result modifies considerably the previous
constraint, especially for $m_a \gtrsim 50$ keV. The combined constraints from
Globular Cluster stars, SN 1987A, and beam-dump experiments leave a small
triangularly shaped region open in the parameter space around $m_a \sim
0.5-1\,$ MeV and $g_{a\gamma} \sim 10^{-5}$ GeV$^{-1}$. This is informally
known as the ALP "cosmological triangle" since it can be excluded only using
standard cosmological arguments. As we shall mention, however, there are viable
cosmological models that are compatible with axion-like particles with
parameters in such region. We also discuss possibilities to explore the
cosmological triangle experimentally in upcoming accelerator experiments.
