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We present a multiwavelength observation of a cool core that does not appearto be associated with any galaxy, in a nearby cluster, Abell~1142. Its X-raysurface brightness peak of $\lesssim2$ keV is cooler than the ambientintracluster gas of $\gtrsim3$ keV, and is offset from its brightest clustergalaxy (BCG) by 80 kpc in projection, representing the largest known cool core-- BCG separation. This BCG-less cool core allows us to measure the metallicityof a cluster center with a much-reduced contribution from the interstellarmedium (ISM) of the BCG. XMM-Newton observation reveals a prominent Feabundance peak of $1.07^{+0.16}_{-0.15}$ Z$_{\odot}$ and an $\alpha/$Feabundance ratio close to the solar ratio, fully consistent with those found atthe centers of typical cool core clusters. This finding hints that BCGs play alimited role in enriching the cluster centers. However, the discussion remainsopen, given that the $\alpha/$Fe abundance ratios of the orphan cool core andthe BCG ISM are not significantly different. Abell~1142 may have experienced amajor merger more than 100 Myr ago, which has dissociated its cool core fromthe BCG. This implies that the Fe abundance peak in cool core clusters can beresilient to cluster mergers. Our recent IRAM 30-m observation did not detectany CO emission at its X-ray peak and we find no evidence for massive runawaycooling in the absence of recent AGN feedback. The lack of a galaxy maycontribute to an inefficient conversion of the ionized warm gas to the coldmolecular gas.

The composition and thermal properties of a cool core lacking a brightest cluster galaxy