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

An inconvenient truth about astronomy is that no one gets a personal invitation to witness the dying breaths of a star. Catching a glimpse of a star at a critical moment of its death is a matter of luck, making it a rare find.

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

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

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

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

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

Having so many galaxies close together will inevitably put a big dent in the cosmic landscape, causing the starlight to bend slightly as it passes through it.

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

Blurred into a configuration called an Einstein crossthe original light was magnified and copied, creating subtly different versions of the distant galaxy as it appeared at different points in time.

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

Analysis of the light in each spot revealed the swelling glow of an exploding star somewhere inside, spread over eight days. One turned on light just six hours after the initial outburst.

Taken together, the three blurs provide details of the supernova’s slow cooling over a week, from a blazing 100,000 degrees Kelvin to a much lower 10,000 K.

Dying stars of a certain size do not go quietly into the night. Depleted of the nuclear 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 just when a given star will explode is something that researchers are slowly working on. While expanding shells of gas and light from supernova explosions aren’t hard to find, catching a star at the moment of death requires a lot of luck.

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

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

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

The research not only supports theoretical models for the evolution of supernovae and the stars that produce them, but also opens the way to analyzing a whole new population of stars from the early universe.

And it’s as close to an invitation to a star’s last fleeting moments as we’re ever going to get.

This research was published in Nature.