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

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

With a little help from a conveniently placed galaxy cluster, an international team of researchers measured the flash of light emitted from a distant supernova at three different times.

With the data, they can test theories about what the star’s dying light might tell us about its size.

The star itself is far too far away for a telescope to discern in detail. It’s so distant that its light took about 11.5 billion years to traverse the gaping expanse and arrive at our door, entangled amid the bright glow of countless other stars in its own galaxy.

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

Somewhere between here and there, the mess of starlight happened to pass within part of the Abell 370 galaxy cluster – a node of several hundred galaxies about 4 billion light-years away.

If so many galaxies are close together, there will undoubtedly be a large dimple in the cosmic landscape, causing the star’s light to bend slightly as it passes through.

The effect was somewhat like a giant telescope the size of a galaxy, one with a scratched and wrinkled lens distorted by the uneven gravity.

Lubricated in a configuration that an . is called Einstein crossthe original light was magnified and copied, producing subtly different versions of the distant galaxy as it appeared at different times in time.

The researchers discovered the ring of light with a gravitational lens in a 2010 study of stars made by the Hubble Space Telescope. With some clever modelling, the team turned the light into something meaningful, revealing three of the cross’s four points (the fourth was too dim to discern).

An analysis of the light in each smear revealed the swelling glow of an exploding star somewhere within, spanning eight days. One showed the light just six hours after the first eruption.

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

Dying stars of a certain size don’t go quietly into the night. Running out of atomic fuel to fuel their fires, they cool down just enough to collapse their cores with a rage that results in the mother of all nuclear explosions.

Know exactly when a certain star will pop is something that researchers are slowly working on. While the expanding shells of gas and light from supernova explosions aren’t hard to find, it takes a lot of luck to catch a star at the time of its death.

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

This information helps confirm models of how the material around stars interacts with the burst of radiation from within, heating up in an instant before quickly cooling again, allowing them to work backwards to determine the star’s original size based on how it cools down.

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

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

And that’s as close to an invitation to a star’s last fleeting moments as we’ll ever get.

This research was published in Nature.