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  • Writer's pictureSiheli Siyathra

The Wandering Star

In the year 2017, astronomers spotted a bright star hurtling out of the Milky Way. It was travelling at the speed of 2 million miles per hour. The problem with it was that it was moving against the direction in which most stars travel. Even more bizarre, it consisted of totally different star stuff. The star was made up of heavy metallic atoms. At the same time, most stars consist of way lighter atoms.

The wandering star got the name ‘LP 40-365.’ It was moving so fast, it literally dashed out of our galaxy. This made scientists believe that the star was pushed out by some kind of cosmic disaster. Perhaps a supernova.

A supernova is the largest explosion that can take place in space: an explosion of a star. It happens after irreversible changes start in the core of a star. Supernovas can occur in two ways: in binary star systems and when there’s a single star.

Binary stars are two stars orbiting around the same centre. At one point, one of the stars starts stealing matter from its companion. After some time, this thief accumulates too much matter, which causes it to explode in a supernova. Or it could be a single star that is nearing the end of its life. It’s running out of fuel, which means more and more mass is flowing into the core of the star. At some point, the core becomes so heavy it can’t stand its own gravity. As the core collapses, a huge amount of energy is released in a supernova.

But scientists still can’t figure out how a supernova could send LP 40-365 flying. There are more questions than answers. Was it a companion star that got flung out by a shockwave? Or was it a piece of an exploded star? A new study based on the collected data has shown that the star, which is a white dwarf, keeps slowly rotating around its axis. Astronomers are almost sure that LP 40-365 is indeed just a chunk of space debris. This wandering piece somehow managed to survive one of the fiercest space events.

After making such a conclusion, scientists realized something amazing. LP 40-365’s unusual features could have appeared after it witnessed a supernova. Even though this event happened lightning fast, it changed the entire star. Most stars consist mainly of Hydrogen and Helium. But LP 40-365 is different. It contains heavy elements such as Magnesium, Oxygen, and Neon. It must have been the supernova that added these atoms to the star. Astronomers consider all elements heavier than helium to be metals. This means that, after witnessing the supernova, LP 40-365 became metallic.

There’s also another curious thing: LP 40-365 brightens and dims every 8.9 hours. It might mean that the star pulsates. But usually, stellar pulsations are much less regular. A much more plausible explanation is that the star’s surface is uneven. And, as it spins, some spots are brought into and out of view.

And it’s great news. After astronomers figure out how fast the star rotates, they can understand what happened to it around 5 million years ago, during the supernova.

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