You'll typically only see the walking dead in horror movies, books and premium TV shows. And while zombies (very thankfully) don't exist, zombie stars definitely do. And astronomers have just found three more of 'em.
What the heck is a zombie star? Well, they're a rare and newly discovered type of star that comes back to life after a supernova – the typical death of a star – to keep on shining. So how do zombie stars work, and what can they teach us about the universe? Read on to find out.
First, Let's Chat About Supernovas
When you think of lifecycles, you probably think of living beings – caterpillars turning into butterflies, tadpoles developing into frogs, and so on. But stars have their own lifecycles, too.
Stars are "born" in clouds of gas and dust called nebulae. Newborn stars start as a series of nuclear reactions, which provide plenty of energy – enough that the star will create heat and light for millions of years.
That energy doesn't last forever, though. Stars eventually burn out, with bigger stars burning out first. Over millions and millions of years, aging stars expand in size and eventually start to burn out that energy.
When the energy runs out, stars can go along one of two general paths. Some smaller stars, like the sun, will go through a (relatively) quiet transition to a small type of star, called a white or brown dwarf.
Larger stars, on the other hand, go out with a bang – literally. They'll burn out in a massive explosion, called a supernova, which can either form a neutron star – a special type of very dense star – or a black hole.
Got It? So Here's Where Zombie Stars Come In
During a normal supernova, all (or virtually all) of the star burns away in the explosion. But when zombie stars have their supernova, things seem to work differently.
Scientists think that the explosion in zombie star supernovas might be smaller than expected – strong enough to burn away much of the original star, but weak enough to leave something behind.
Turns out, they seem to occupy a middle ground between the two star life cycles listed above. While they definitely undergo a supernova, they end up looking like a typical white dwarf (even though most white dwarfs aren't formed by a supernova at all).
What Do We Know About Zombie Stars?
So far? Not too much. But we know that zombie stars seem incredibly rare. One was first described in 2017, and these three newly discovered stars were only found this summer.
We also know that all four zombie stars tend to have a few things in common, like a large size but a low mass. Zombie stars also tend to be made of similar elements – neon, magnesium and oxygen – and their chemical makeup might explain why they come back to life after they explode.
Overall, scientists think that zombie stars might represent a whole new class of star – and understanding them better could uncover a brand new star life cycle. They might also teach us more about supernovas and how different explosions work, as well as affect the universe.
And who knows – we might one day discover that some of the stars you see in the sky aren't typical white dwarves at all, but zombie stars that came back from the dead.