In the grand cosmic theater of our universe, nothing is as dramatic as the death of a star. Yet, the fate of our very own sun has been a topic of speculation and debate among astronomers for decades. As it exhausts its nuclear fuel in approximately 5 billion years, the sun will no longer be able to resist its own gravitational pull. Its outer layers will disperse, possibly obliterating Earth, while its core shrinks into an incredibly dense state, leaving behind a stellar remnant. The question that has intrigued scientists worldwide: could our sun ultimately transform into a black hole, a celestial entity with a gravitational pull so powerful that not even light can escape?
Contrary to popular belief, the sun simply lacks the necessary qualifications to become a black hole, says Xavier Calmet, a black hole expert and physics professor at the University of Sussex in the U.K. "It is very simple: the sun is just not heavy enough to become a black hole," Calmet explains. The main prerequisite for a star to morph into a black hole is attaining the right amount of mass. Stars with initial masses greater than about 20 to 25 times the mass of our sun are the ones with the potential to undergo the gravitational collapse needed to form black holes. This threshold, named the Tolman-Oppenheimer-Volkoff limit, suggests that a dying star must leave behind a core approximately two to three times the sun’s mass to create a black hole.
The Sun’s Fate: A Black Hole or a White Dwarf?
In the next 5 billion years, our sun is predicted to reach the end of its nuclear-fuel-burning life. This will lead to the celestial body no longer being able to sustain itself against its own gravity. The outer layers of our star will disperse, potentially obliterating Earth in the process, while its core will collapse into a highly dense state, leaving behind a stellar remnant.
Not Quite a Black Hole
If the gravitational collapse of a stellar core is complete, the stellar remnant morphs into a black hole, a region of space and time with a gravitational influence so strong that not even light can escape its confines. However, will our sun transform into a black hole when it meets its end? In simple terms, "no," as the sun lacks the conditions necessary for this transformation.
"The sun is just not heavy enough to become a black hole," states Xavier Calmet, a black hole expert and physics professor at the University of Sussex, U.K. Various factors determine whether a star can morph into a black hole, including its composition, rotation, and the processes that govern its evolution, but the primary requirement is sufficient mass.
The Role of Mass and Stellar Evolution
"Stars with initial masses greater than about 20 to 25 times the mass of our sun have the potential to undergo the gravitational collapse needed to form black holes," explains Calmet. This threshold, known as the Tolman-Oppenheimer-Volkoff limit, was first calculated by J. Robert Oppenheimer and his colleagues. Scientists currently believe that a dying star must leave behind a stellar core that is approximately two to three times the mass of the sun to create a black hole. Therefore, theoretically, if the sun were twice its current mass, it would have a chance at becoming a black hole, right? Sadly, no.
Red Giants and White Dwarfs
When a star depletes its nuclear fuel at its core, the nuclear fusion of hydrogen to helium continues in its outer layers. As the core collapses, the outer layers expand, and the star enters the red giant phase. In approximately 6 billion years, when the sun becomes a red giant, it will expand to around the orbit of Mars, potentially consuming the inner planets, including Earth. Over time, the red giant’s outer layers will cool and spread out to form a planetary nebula around the sun’s smoldering core.
However, the sun will never reach the fusing-iron stage, which is characteristic of massive stars that form black holes. Instead, it will morph into a white dwarf, a dense, Earth-sized star, according to Calmet. Therefore, Earth will never experience the thrill and terror of being swallowed by a black hole, unless, of course, the entire universe is already residing inside one.
The Sun’s destiny as a white dwarf rather than a black hole, while scientifically fascinating, also offers some small comfort. It reassures us that our planet will not be consumed by a black hole formed by our Sun, a fate that could be considered even more terrifying than climate change or asteroid impact. However, the fact that the Sun will one day expand into a red giant, potentially engulfing Earth, is a stark reminder of the transient nature of our existence in this vast universe.