The Camel, The Cow and the Koala

Jonathan O’Callaghan wrote nice piece in Quanta Magazine about a rare, powerful and fast form of supernova. These stellar explosions burn much hotter - and about 100x brighter than typical supernovae. They also appear to finish burning within days instead of the more typical weeks.

The first of these weird events, dubbed “the Cow” was spotted in 2018. Before another such event - “the camel” - popped this past fall, two other similar events (including the Koala) were noted in the historical data.

Four events does not afford much statistical power, so explanations are still vague. The mainstream hypothesis is a sort of failed, failed supernova, which itself needs some explanation.

When big stars run out of fuel, they slowly shrink into an incredibly dense mass. Eventually this mass gets so dense that gravity causes the star to collapse violently inwards. This sudden, inward rush of material creates a massive amount of heat and energy which induces an outward shock that we see as a bright burst of light: a supernova. The after product of such a nova can be a neutron star or a black hole.

Models and some observational studies suggest that if the star is really big, it simply collapses directly into a black hole without the fuss of a supernova. They just kind of blink out of existence. The supernova process just fails.

How might one explain the Cow, the Camel and the Koala? If the initial collapse of the core of the star directly creates a black hole, that could immediately start drawing in the other rest of the star’s outer layers. If enough of the star’s original material remains, that rapid inflow could generate the energy necessary to drive the powerful explosion.

It’s a process that kind of in between a standard core collapse supernovae and the quick, complete creation of a black hole. In other words, it could be a failed, failed supernova.