Astronomers captured the incredibly rare sight of a star just hours after it exploded

Astronomers captured the incredibly rare sight of a star just hours after it exploded

It’s an inconvenient truth in astronomy that no one gets a personal invitation to witness a star’s dying breath. Sighting a star at a critical moment in its demise is a matter of fortune, making it a rare find.

With the help of a conveniently placed cluster of galaxies, an international team of researchers measured the flash of light emitted by a distant supernova at three separate times.

The data will allow them to test theories about what the star’s dying light might tell us about its size.

The star itself is far too distant for a telescope to distinguish in detail. It’s so distant that its light took about 11.5 billion years to cross the gaping expanse, arriving at our doorstep tangled amid the bright glow of countless other stars in its home galaxy.

However, we can observe the changes in the star’s glow, and they reveal some things about how it died. And lived.

Somewhere between here and there, the mess of starlight passed through a section of the galaxy cluster Abell 370 – a node of several hundred galaxies about 4 billion light-years away.

Having so many galaxies close together inevitably creates a large dimple in the cosmic landscape, causing the starlight to bend slightly as it slips through.

The effect looked a bit like that of a giant galaxy-sized telescope, with a scratched and wrinkled lens distorted by uneven gravity.

Coated in a configuration called an Einstein cross, the original light was magnified and copied, producing subtly different versions of the distant galaxy as it appeared at different points in time.

Researchers discovered the gravitationally lensed ring of light in a survey of stars taken by the Hubble Space Telescope in 2010. Using clever modeling, the team turned the light into something sensitive, revealing three of the four points of the cross (the fourth was too faint to discern).

Various images of light emitted by a supernova.
Several images of the supernova. (Chen et al., Nature2022)

An analysis of the light in each smear revealed the puffy glow of an exploding star somewhere inside, staggered over eight days. One showed the light just six hours after the initial burst.

Taken together, the three blurs of light provide detail of the supernova slowly cooling over a week, from a blazing 100,000 degrees Kelvin to a much cooler 10,000K.

Dying stars of a certain size do not go quietly into the night. Depleted of atomic fuel to fuel their fires, they cool just enough for their cores to collapse with a fury that results in the mother of all nuclear explosions.

Knowing precisely when a given star will explode is something researchers are slowly doing. While the expanding shells of gas and light from supernova explosions aren’t hard to find, catching a star at death takes a lot of luck.

Here, astronomers not only got the characteristic flash of a dying star in a galaxy far, far away, but they also got vital details of changes in its light over a short period of time.

This information helps confirm models of how the material surrounding stars interacts with the burst of radiation from within, heating up in the blink of an eye before rapidly cooling again, allowing them to work backwards to determine the original size of the star from the way it cools.

Based on what they learned in this case, the team is confident that the star they witnessed in its final moments had a radius more than 530 times that of our own Sun.

The study not only supports theoretical models for the evolution of supernovae and the stars that produce them, but also paves the way for the analysis of an entirely new population of stars from the early Universe.

And it’s as close as it gets to an invitation to a star’s fleeting last moments.

This research was published in Nature.

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