NASA/CXC/IAFE/G. Dubner et al. & ESA/XMM-Newton
The ears have it. Many of the glittering shrapnel clouds left behind by the universe’s most violent supernovae seem to have bulging protuberances called “ears” – cute features that have now been enlisted in a debate about how these explosions go off in the first place.
When a massive star runs out of fuel, it blows up, spewing its atmosphere across space. One such event, in the constellation Taurus, was observed by multiple cultures on Earth in 1054, and we still study the debris cloud – the Crab nebula – today. But the details of how exactly a star tears through its own immense gravity to explode are hotly contested.
These so-called core-collapse supernovae are hard to detonate, because the heavy weight of the star’s atmosphere presses down and threatens to hold the impending explosion in. The dominant model of these cataclysms, which has held since 1985, suggests that a shock wave rips through the star’s atmosphere, boosted by a deluge of neutrinos from the core.
Alternatively, Noam Soker at the Technion-Israel Institute of Technology in Haifa has spent the last few years arguing that jets of charged particles emitted from the massive star’s spinning core punch a path out.
Ears, which stick out on either side from supernova remnants, might help settle the debate. Aldana Grichener, Soker’s student at the Technion, set out to find and measure them more systematically in published images of the remains of massive stars.
Jet-propelled bulges
Grichener and Soker have concluded that about a third of core-collapse supernova remnants have a pair of ears, and that these side bulges were probably inflated by jets.
Given their sizes and shapes, they estimate that roughly 10 per cent of all the energy from these supernova explosions goes into blowing up the ears. “It tells you – if the assumption is correct – that jets are quite energetic and play a significant role in the explosion or shortly after,” Soker says.
Other theorists who study this type of supernova explosion are sceptical, though. Adam Burrows at Princeton University in New Jersey thinks that jets may play a part in some explosions, even to the point of inflating the ears – but that the neutrino-boosted shock wave is more important in most of these detonations.
Still, Grichener’s paper is an interesting look at an understudied quirk of supernova remnants, he says: “I agree with the idea of trying to explain these so-called ears. I think it’s interesting and people haven’t emphasised it enough.”
Soker plans to submit the paper to journals, but anticipates the kind of opposition his jet idea often engenders. “We are in the minority among people who work in the explosion mechanisms,” he says. “So we don’t always have an easy time, to put it mildly.”
Quelle: NewScientist