How will our sun look after its death? Scientists have made predictions about what the last days of our solar system will look like, and when they will happen. We humans will not be around to see the call of the sun canopy.
Previously, astronomers believed that the Sun would turn into a planetary nebula – a luminous bubble of cosmic gas and dust – until evidence suggested it must be a larger mass.
An international team of astronomers flipped it back in 2018 and found that the planetary nebula is indeed the most likely solar corpse.
The Sun is about 4.6 billion years old – measured by the age of other bodies in the Solar System that formed around the same time. Based on observations of other stars, astronomers expect that it will reach the end of its life in about another 10 billion years.
There are other things that will happen along the way, of course. In about 5 billion years, the Sun is set to turn into a red giant. The star’s core will shrink, but its outer layers will extend into the orbit of Mars, engulfing our planet in the process. If it is still there.
One thing is for sure: by then, we won’t be around. In fact, humanity only has a billion years left unless we find a way to get away from this rock. That’s because the sun’s brightness increases by about 10% every billion years.
It doesn’t sound like much, but an increase in brightness would end life on Earth. Our oceans will evaporate, and the surface will become too hot to form water. We’ll be about to get kaput.
It is what comes after the red giant that has proven difficult to identify. Several previous studies have found that in order to form a bright planetary nebula, the protostar must be twice the mass of the Sun.
However, the 2018 study used computer modeling to determine that, like 90 percent of other stars, our Sun is likely to shrink from a red giant to become 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 atmosphere – into space. The envelope can be up to half the star’s mass. This reveals the star’s core, which is turned on at this point in the star’s life. It runs out of fuel, then turns off at The end and before he finally dies,” explained astrophysicist Albert Zelstra of the University of Manchester in the UK, one of the authors of the research paper.
“Only then, the hot core makes the ejected mantle shine brightly for about 10,000 years—a brief period in astronomy. This is what makes planetary nebulae visible. Some are so bright that they can be seen from extremely vast distances measuring tens of millions of light years, where the star is himself too weak to see him.”
The data model the team created actually predicts the life cycle of different types of stars, figuring out the brightness of a planetary nebula associated with different star masses.
Planetary nebulae are relatively common throughout the observable universe, with the most famous being the Helix Nebula, the Cat’s Eye Nebula, the Annular Nebula, and the Bubble Nebula.
They were named planetary nebulae not because they actually had anything to do with the planets, but because when William Herschel discovered the first of them in the late 18th century, they were similar in appearance to the planets through telescopes at the time.
Nearly 30 years ago, astronomers noticed something strange: the brightest planetary nebulae in other galaxies all had the same level of brightness. This means that, in theory at least, by looking at planetary nebulae in other galaxies, astronomers can calculate their distance.
The data showed that this was true, but models contradicted it, which has infuriated scientists since the discovery was made.
“Old, low-mass stars should make fainter planetary nebulae than younger, more massive stars,” Zijlstra said. “This has become a source of conflict over the past 25 years.”
“The data suggests that you can get bright planetary nebulae from low-mass stars like the Sun, and models said that’s not possible, anything less than twice the mass of the Sun would give a planetary nebula too faint to be seen.”
The 2018 models successfully solved this problem by showing that the Sun is approaching the minimum mass of a star that can produce a visible nebula.
Even a star less than 1.1 times the mass of the Sun would not produce a visible nebula. On the other hand, larger stars with a mass up to 3 times the mass of the Sun, will produce the brighter nebulae.
For all other stars located in between, the expected brightness is very close to what was observed.
“This is a good result,” Zijlstra said. “Not only do we now have a way to measure the presence of stars over several billion years in distant galaxies, a range that is remarkably difficult to measure, but we have also discovered what the Sun will do when it dies!”
Publish the research in the journal natural astronomy.
An earlier version of this article was first published in May 2018.
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