This episode is sponsored by The Ridge.

Go to ridge.com/scishow to see their holiday guide, and use promo code “scishow” to get 10% off your next order. [♪ INTRO]. Nebulas are some of the most famous and beautiful objects in space.

They’re huge clouds of gas and dust, and have a tendency to glow in brilliant, multi-colored light. But every now and then, one throws a major mystery our way, like the Stingray nebula. This object is doing something so strange that a researcher studying it called it, quote, “very, very dramatic, and very weird.” This nebula is fading way faster than anyone expected it to.

The Stingray nebula is a planetary nebula, which despite its name, has nothing to do with planets. Instead, they’re a type of cloud that forms as mid-sized stars die. When one of these stars reaches the end of its life, it grows into a huge red giant star, and then eventually starts turning into a remnant called a white dwarf.

In the process, it gives off huge streams of radiation, which blow most of the star’s gas into open space. That gas is the nebula, and at first, it glows super brightly. That’s because, as its star is still becoming a white dwarf, it pumps out tons of ionizing radiation.

That ultimately makes the gas in the nebula super hot and electrically-charged. And super hot means super bright. Eventually, the gases do cool enough to become invisible to the naked eye, but that takes about 10,000 years.

And this is where the Stingray nebula gets weird. The Hubble Space Telescope has observed this nebula a few times over the years, including in 1996 and 2016. And in those 20 years, this object has become significantly dimmer.

Like, anywhere from 29 to 900 times dimmer depending on which type of gas you’re looking at! We’ve never seen anything like this before. But in a paper recently accepted to The Astrophysical Journal, the researchers announced they think they know at least part of what’s going on:.

They think the culprit is the star at the center of the nebula. See, the star isn’t yet a white dwarf. It’s still in the process of dying, and recently, it began expanding and cooling.

That means it’s emitting less radiation, so in turn, the gases forming the nebula are also cooling, and are much dimmer! That said, the mystery isn’t totally solved yet, because now we have another question on our hands:. Why did that central star expand and cool all of a sudden?

The jury is still out on this one, but we do have clues. Like, between 1971 and 2002, we saw the star get incredibly hot, jumping up 40,000 degrees Celsius. And one hypothesis is that it happened because of a sudden burst of helium fusion.

As the dying star burned through its fuel, a shell of helium could have formed around its core, and eventually ignited in what’s called a helium flash or a thermal pulse. If this happens late enough in a star’s life, it could have caused the star to expand, cool, and start emitting less ionizing radiation for a while. Again, this is just a hypothesis, and there are some issues with the physics here.

Like, the star’s current mass doesn’t match up with what we’d expect if it just went through something like this. But if this is what happened, the star might get back to normal stellar death in another few decades, and start producing enough radiation to heat up the nebula again. Or maybe it won’t!

This is such a new situation that we really can’t predict what’s going to happen. If the nebula keeps fading like this, it should be barely visible in only 20 to 30 years. So we’ll have to just keep observing and reobserving to figure out what’s going on.

And in the end, we should learn more about how nebulas evolve over time, and what happens when everything is going a lot faster than expected. Because even though we’ve been studying these objects for hundreds of years, it turns out, we’re just scratching the surface. This episode of SciShow Space is brought to you by The Ridge.

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If you want to learn more, head to Ridge.com/SciShow and use the code “SCISHOW.” You’ll get 10% off and free worldwide shipping, and you’ll be supporting SciShow along the way, too. [♪ OUTRO].