What will our Sun look like after it dies? Scientists have made predictions about what the last days of our Solar System will be like and when it will happen. And humans will not be around to see the call of the Sun’s curtain.
Astronomers previously thought the Sun would become a planetary nebula, a luminous bubble of gas and cosmic dust, until evidence suggested it should be a bit more massive.
An international team of astronomers circled it again in 2018 and found that a planetary nebula is, in fact, the most likely solar corpse.
The Sun is about 4.6 billion years old, as measured by the age of other objects in the Solar System that formed around the same time. Based on observations of other stars, astronomers predict that it will reach the end of its life in another 10 billion years.
There are other things that will happen along the way, of course. In about 5 billion years, the Sun will become a red giant. The star’s core will shrink, but its outer layers will expand to the orbit of Mars, enveloping our planet in the process. If it’s still there.
One thing is certain: at that time, we will no longer be there. In fact, humanity only has about 1 billion years left unless we find a way to get away from this rock. This is because the Sun increases in brightness by about 10 percent every billion years.
That doesn’t sound like much, but this increase in brightness will end life on Earth. Our oceans will evaporate and the surface will become too hot for water to form. We will be the most you can get.
It is what comes after the red giant that has proven difficult to identify. Several previous studies have found that for a bright planetary nebula to form, the initial star must have been up to twice as massive as the Sun.
However, the 2018 study used computer modeling to determine that, like 90 percent of other stars, our Sun is more likely to shrink from a red giant to a white dwarf and then end up as a planetary nebula.
“When a star dies, it ejects a mass of gas and dust, known as its envelope, into space. The envelope can be up to half the star’s mass. This reveals the star’s core , which at this point in the star’s life is running out of fuel, eventually shuts down and before finally dying,” explained astrophysicist Albert Zijlstra of the University of Manchester in the UK, one of the authors of the article.
“It is only then that the hot core causes the ejected envelope to glow brightly for about 10,000 years, a short period in astronomy. This is what makes the planetary nebula visible. Some are so bright that they can be seen from extremely great distances measuring tens of millions of light years, where the star itself would have been too faint to see.”
The data model the team created actually predicts the life cycle of different types of stars, to figure out the brightness of the planetary nebula associated with different stellar masses.
Planetary nebulae are relatively common throughout the observable Universe, with famous ones such as the Helix Nebula, the Cat’s Eye Nebula, the Ring Nebula, and the Bubble Nebula.
Cat’s Eye Nebula (NASA/ESA)
They are called planetary nebulae not because they have anything to do with planets, but because, when William Herschel first discovered them in the late 18th century, they looked similar to planets through the telescopes of the time.
Almost 30 years ago, astronomers noticed something peculiar: the brightest planetary nebulae in other galaxies have almost the same level of brightness. This means that, at least theoretically, by looking at planetary nebulae in other galaxies, astronomers can calculate how far away they are.
The data showed this to be correct, but the models contradicted it, which has been troubling scientists since the discovery was made.
“Old, low-mass stars should make much fainter planetary nebulae than young, more massive stars. This has become a source of contention over the past 25 years,” Zijlstra said.
“The data said you could get bright planetary nebulae from low-mass stars like the Sun, the models said that wasn’t possible, anything less than twice the mass of the Sun would give a planetary nebula too faint to see” .
The 2018 models have solved this problem by showing that the Sun is roughly the lower mass limit of a star that can produce a visible nebula.
Even a star less than 1.1 times the mass of the Sun will not produce a visible nebula. Larger stars up to 3 times more massive than the Sun, on the other hand, will produce the brightest nebulae.
For all other stars in the middle, the predicted brightness is very close to the observed one.
“This is a good result,” Zijlstra said. “Not only do we now have a way to measure the presence of stars a few billion years old in distant galaxies, which is a range that is very difficult to measure, but we’ve even figured out what the Sun will do when I die!”
The research was published in the journal Nature Astronomy.
An earlier version of this article was first published in May 2018.