A 9-Month Hubble Space Telescope Near-UV Survey of M87. II. A Strongly Enhanced Nova Rate near the Jet of M87

TL;DR

This study reports a significantly higher rate of classical novae near M87's jet, with detailed analysis ruling out some explanations and suggesting possible jet-induced star formation as a cause.

Contribution

First detailed survey showing a strong nova rate enhancement near M87's jet, challenging existing explanations and proposing new hypotheses.

Findings

Novae are strongly concentrated along M87's jet.

Nova characteristics are similar regardless of proximity to the jet.

The enhanced nova rate near the jet remains unexplained.

Abstract

The 135 classical novae that we have discovered in M87 with two $\textit{Hubble Space Telescope}$ imaging surveys appear to be strongly concentrated along that galaxy's jet. Detailed simulations show that the likelihood that this distribution occurred by chance is of order $0.3\%$. The novae near the jet display outburst characteristics (peak luminosities, colors and decline rates) that are indistinguishable from novae far from the jet. We explore whether the remarkable nova distribution could be caused by the jet's irradiation of the hydrogen-rich donors in M87's cataclysmic binaries. This explanation, and others extant in the literature which rely on increased binary mass transfer rates, fail by orders of magnitude in explaining the enhanced nova rate near the jet. An alternate explanation is the presence of a genuine surplus of nova binary systems near the jet, perhaps due to jet-induced star formation. This explanation fails to explain the lack of nova enhancement along M87's counterjet. The enhanced rate of novae along M87's jet is now firmly established, and unexplained.