Mark your calendars for the fireworks display to end all fireworks – literally.
According to new research by a trio of astronomers, our Sun will begin its death cycle in about 5 billion years by erupting into an awe-inducingly beautiful cloud of luminous star material visible millions of light years away – a phenomenon known as a planetary nebula.
Their prediction settles an ongoing debate on the fate of the Sun and explains why planetary nebulas pop up in seemingly contradictory parts of the observable universe.
“When a star dies it ejects a mass of gas and dust – known as its envelope – into space," said author Professor Albert Zijlstra in a statement. "The envelope can be as much as half the star’s mass. This reveals the star’s core, which by this point in the star’s life is running out of fuel, eventually turning off and before finally dying.
“It is only then the hot core makes the ejected envelope shine brightly for around 10,000 years – a brief period in astronomy. This is what makes the planetary nebula visible. Some are so bright that they can be seen from extremely large distances measuring tens of millions of light years, where the star itself would have been much too faint to see.”
Writing in Nature Astronomy, Zijlstra and his colleagues explain how their new models use the brightness, or luminosity, of nebulas to infer the past life history of intermediate-age stars – an age range that was notoriously difficult to analyze – and determine how luminous their eventual nebular debris clouds will be. In examining these characteristics, the computer-based model also solves a 25-year-long conflict between what astronomers observed and what their previous theoretical models predicted.
Earlier research had suggested that only stars about twice as massive as our Sun could form a nebula bright enough to be seen a galaxy away, yet high-powered telescopes have detected many bright nebulas in old galaxies known to contain low-mass stars.
“Old, low mass stars should make much fainter planetary nebulae than young, more massive stars. The data said you could get bright planetary nebulae from low mass stars like the sun, the models said that was not possible, anything less than about twice the mass of the sun would give a planetary nebula too faint to see,” Zijlstra explained.
The older models calculated that during its end-of-life evolution, the Sun will expel its outer atmosphere, progressing into a red giant, as all stars do. Yet the remaining core, a white dwarf star, will not produce enough ultraviolet radiation to energize the particles in the envelope, and thus it will not glow.
But after examining the outputs of their luminosity and solar evolution models, the team discovered that the Sun’s remnant core will, in fact, heat up three times faster than previously predicted after ejecting half its mass, allowing it to become a majestic, albeit faint, nebula.
Interestingly, the model shows that our Sun just barely scraped by in terms of the mass cut-off necessary for nebula formation. Stars just a few percent smaller will not become nebula, whereas those at three solar masses and above will form ones that are notably bright.