Since Karl Schwarzschild first posited the existence of black holes in a letter to Albert Einstein, scientists have debated what happens to the matter that seemingly disappears when consumed by one. According to the Special Relativity Theory, mass is related directly to energy, and the quantity of energy and mass left over after any reaction must be equal to the amount prior to the reaction, though it doesn’t have to be in the same form. So what happens when a moon, star, or galaxy is swallowed by a black hole? Where does all that mass and energy go, if it can’t actually be destroyed?
According to Quartz, Hawking and his colleagues have a theory. In a paper entitled “Black Hole Entropy and Soft Hair,” Hawking, Malcolm Perry from Cambridge, and Harvard’s Andrew Strominger suggest that the mass may convert to information stored in photons around the edge of the black hole.
The point at which a black hole’s gravitation pull becomes so strong that nothing — even light — can escape its pull is called the event horizon. Hawking and associates theorized that massless energy particles called photons might collect along the event horizon and capture information that represents the objects trapped by the black hole, similar to the way a string of ones and zeroes represents software that performs a function when interpreted by a computer. The mass of the object is transformed into energy, per the theory of Special Relativity.
A Hairy Conundrum: Stephen Hawking’s final paper published, tackles famous paradox. Black holes might have "soft hair," the better to store information. https://t.co/nfQaRV2PGy
— Jennifer Ouellette (@JenLucPiquant) October 11, 2018
The key to this theory is Hawking’s assertion that black holes have temperatures, in addition to the two other characteristics Einstein defined: mass and spin. If they have temperatures, that means they also have entropy, or the amount of disorder in an object as a function of its temperature. Additionally, in 1974, Hawking suggested that black holes emit radiation, a theory that has been born out through observation of powerful gamma-ray jets emitted from certain black holes. He also theorized that over time, emitting all that radiation evaporates the black hole out of existence, leaving the question of where all the matter went.
The photons mentioned above are the “soft hair” described in the research paper, and they may contain the energy representing the mass that no longer physically exists. Perry put it this way, according to the BBC.
“What this paper does is show that ‘soft hair’ can account for the entropy. We don’t know that Hawking entropy accounts for everything you could possibly throw at a black hole, so this is really a step along the way. We think it’s a pretty good step, but there is a lot more work to be done.”
If the theory is right, further research is necessary to determine how the soft hair stores information, and if it does, whether it contains all of the information about objects consumed by black holes or only part of it. Hawking’s final book, Brief Answers to the Big Questions, is due out on October 16 from Bantam.