Supernova warning! Astronomers have discovered a way to predict when stars will "self-destruct"

Supernova warning! Astronomers have discovered a way to predict the explosive death of stars

Supernovae leave behind striking bubbles.

(Image credit: X-ray: National Aeronautics and Space Administration; / Central Control Center / Massachusetts Institute of Technology / L. Lopez et al.; Infrared: Pa; Broadcast: Natural Science Foundation / National Radio Astronomy Observatory / Synthetic Aperture Radio Telescope)

Isn't it fortunate that astronomers can predict when a giant star will die in a catastrophic supernova explosion? If a giant red star is surrounded by thick material, beware - the star is likely to explode within a few years.

When a massive star approaches the end of its life, it goes through several violent phases. Deep in the star's core, it switches from fusing hydrogen to fusing heavier elements, starting with helium and moving up to carbon, oxygen, magnesium, and silicon. At the end of the chain, the star reaches the core where iron is formed. Because iron consumes energy, rather than giving it away, the star gradually ends, and in less than a dozen minutes, it flips over in a fantastic explosion known as a supernova.

But for all the commotion going on inside a star, from the outside it can be hard to determine what's going on. Towards the end of their lives, these massive stars expand to their maximum size and become incredibly bright -- tens of thousands of times brighter than our sun. But because the star's surface is so puffy, their exterior temperature actually drops, making them look like red giants.

The most famous example of such a proximal star is in the constellation Orion. If it were placed within our solar system, this star, which is only 11 times more massive than our sun, would stretch out to the orbit of Jupiter. It could go supernova any day now, but for astronomers, "any day" could happen in a million years. Although we know that stars of this type will eventually detonate in a supernova, there are no estimates more precise than that. Or, at least, that was the case in the past.

Time bomb

Now, a team of astronomers has developed a method to detect supernovae that may disappear within a few years. Their results were published on the preprint database arXiv and published in the Monthly Notices of the Royal Astronomical Society.

They specifically looked at a few dozen unique supernovae called Type II-P, which remain bright long after their initial explosion compared to other supernovae.

In some cases, astronomers reviewed old star catalogs and found images of stars before they exploded, and they all seemed to be red supergiants like Orion. This clearly showed that such stars were supernova candidates and could explode at any time.

Stars that produce these types of supernovae are thought to have dense envelopes of material before they exploded. The density of this material is orders of magnitude greater than what has been measured around Orion. It is this material that heats up from the initial shock wave that causes the brightness to be retained; there is more around to keep shining after the first signs of the explosion.

This dense material also makes this type of supernova visible much sooner than its more exposed cousin. When the explosion initially occurs, the shock wave hits the material surrounding the star, causing the shock wave to lose steam as it passes through. While initially the supernova is energetic enough to release high-energy radiation, such as X-rays and gamma rays, after the shock wave mixes with the surrounding material, the radiation released is in optical wavelengths.

Therefore, these dense layers of material around stars also seem to indicate that a supernova is about to occur.

Super Cocoon

But how long did it take for this material to form? The researchers looked at two models. In one model, the star blew high-speed winds from its surface, which slowly separated its own debris over decades and spread it out, forming the shroud. In the second model, the star exploded violently before going supernova, sending up to one-tenth the mass of our Sun into orbit in less than a year.

The researchers then simulated how all this material would affect our image of the star. In either case, once the star has formed its shield, it will be severely obscured from detection by our current imaging techniques.

Because we have some direct images of the supernova taken less than 10 years before it went off, astronomers concluded that the slow and steady model doesn't work. Otherwise, the star would have been obscured.

All of this means that once a supergiant star has built up a thick layer of material around itself, it will likely go supernova within a few years. So if you happen to be traveling through the universe and encounter this exact situation, consider yourself forewarned.

BY:Paul Sutter

FY:jane

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