On March 29th, 2018 we learned about

Kepler telescope finds that short-lived supernovae are likely the result of a dispersed layer of glowing debris

Exploding stars should be easy to spot. Aside from the release of as much energy as our Sun will produce in its entire lifetime, these massive explosions light up their surroundings for weeks as all the nearby debris cools down over time. If you somehow did miss spotting a particular supernova, you might not have to wait long for the next one, as one star is probably exploding every second somewhere in the universe. Despite all this, astronomers were still having trouble with a particular kind of explosion, which broke some of these rules and would instead flicker brightly for just a couple of days then go dark. Unless we knew exactly where to expect such an event, they were often over before any telescope could find them.

Finally seeing a star’s final flicker

The mystery of Fast-Evolving Luminous Transient (FELT) supernovae has been nagging astronomers for over a decade. Many hypotheses were suggested, ranging from gamma-ray bursts to magnetar-boosted supernovae, but every idea was hard to test against such fleeting opportunities to actually observe the event in the first place. Even in cases were a telescope did capture the first flash of light from a FELT, subsequent observations usually wouldn’t be taken until 24 hours later, missing a lot of important details about how these flashes take place.

Enter the Kepler space telescope. This spacecraft was originally designed to hunt for exoplanets by detecting small, short changes in light levels around distant stars, making it a great way to gather data on a FELT-friendly timescale. Instead of detecting small dips in a star’s light as exoplanets pass in front of them, Kepler was able to observe the bursts and quick decay of light from FELT supernovae, getting a snapshot of data every 30 minutes. This allowed astronomers to discard many of their hypotheses about FELT explosions, leading them to a new model that’s apparently a bit more than a single explosion.

A glow from a globe of dust

Based on the details gathered by Kepler, researchers now believe FELT explosions get started before a star is really ready to blow up. As the start begins its final collapse, it may eject a layer of dense dust that ends up orbiting the star as a sort of shell. Once the star does finally pop, close to a year later in this case, its blast wave of kinetic energy hits the dust in the shell, causing it to quickly light up all at once. In these observations, the brightness peaked in a period of just over two days, making it fast even by FELT standards. Less energy will be emitted in that last burst, allowing the visible light to drop off much more quickly than in a “standard” star explosion.

There’s obviously more to learn about FELT supernovae, such as how the outer shell of material interacts with the core that will eventually burst altogether. Fortunately, the fact that the Kepler telescope was able to find this brief event while just looking at one small patch of sky suggests that these types of explosions aren’t horribly rare either. It will hopefully be relatively easy to collect more data and confirm more details about how these stars flicker before going dark forever.

 

Source: Kepler Solves Mystery of Fast and Furious Explosions by Armin Rest , Hubblesite

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