Stephen Hawking's final scientific paper released

London, Oct 11  Stephen Hawkings final scientific paper has been released by physicists who worked with the late British cosmologist on his career-long effort to understand what happens to information when objects fall into black holes.

The work, which tackles what theoretical physicists call "the information paradox", was completed in the days before Hawking's death in March. It has now been written up by his colleagues at Cambridge and Harvard universities and posted online, the Guardian reported on Wednesday.

Malcolm Perry, a professor of theoretical physics at Cambridge and a co-author on the paper, "Black Hole Entropy and Soft Hair", said the information paradox was "at the centre of Hawking's life" for more than 40 years.

The origins of the puzzle can be traced back to Albert Einstein. 

In 1915, Einstein published his theory of general relativity, a tour-de-force that described how gravity arises from the spacetime-bending effects of matter, and so why the planets circle the sun. 

But Einstein's theory made important predictions about black holes too, notably that a black hole can be completely defined by only three features: its mass, charge, and spin.

Nearly 60 years later, Hawking argued that black holes also have a temperature and because hot objects lose heat into space, the ultimate fate of a black hole is to evaporate out of existence. 

"The difficulty is that if you throw something into a black hole it looks like it disappears," said Perry. 

"How could the information in that object ever be recovered if the black hole then disappears itself?"

In the latest paper, Hawking and his colleagues show how some information at least may be preserved. 

The physicists show that a black hole's entropy may be recorded by photons that surround the black hole's event horizon, the point at which light cannot escape the intense gravitational pull. They call this sheen of photons "soft hair".

Among the unknowns that Perry and his colleagues must now explore are how information associated with entropy is physically stored in soft hair and how that information comes out of a black hole when it evaporates.