Black holes have hair?

Stephen Hawking’s 74th birthday was a few days ago, and as a gift to the world, he released his much anticipated paper describing ‘soft hair’ on black holes. Let’s back up a little bit:

In August, Dr. Hawking gave a lecture in KTH (Stockholm) to cast some light on the black hole information paradox. This paradox was briefly discussed in a previous post- essentially, when black holes are formed, they retain the ‘information’, i.e. the quantum properties, of the star that collapsed to form it. Over time, the black hole slowly ‘evaporates’ via a process known as Hawking radiation. The paradox occurs when the black hole completely evaporates- where does the original information of the star go?

The information paradox debate is still in the air as no one could really explain where this lost information goes… until now. Maybe. Black holes are empirically considered to be ‘bald’, i.e. they are characterized completely by their mass, charge, and angular momentum. Hawking’s new theory proposes that black holes do indeed contain ‘hair’.. in the event horizon, as opposed to the interior of the black hole.

bh_hair_small-preview
Black hole with hair. We see the various types of input- clearly this information should be stored somewhere in the black hole? Source: Gr@v

While this sounds like something that could be used in the blueprints of the next Death Star, is there any use for this concept? In his new paper (in collaboration with Malcolm Perry and Andrew Strominger), Hawking establishes the math and physics for realizing these hairs- from evaporating black holes to ‘physical process which implant hair on a black hole.’ It seems that these ‘quantum hair imprints’ can be measured from a black hole from the soft photons/gravitons than should reside along the event horizon, and in fact, black holes with differing amounts of soft photons are indeed distinguishable from one another.

Long story short, the theory does seem to cover important tenets of black holes, but more work definitely needs to be done before this theory can be seriously considered amongst the existing information paradox theories. Speaking of, the last link below comprehensively details all relevant quantum information paradox theories in 6 separate categories.. definitely worth a read. Oh, and did I mention that Hawking published this paper for his 74th birthday? A mini tribute from when you were at your finest: Stephen Hawking: Simpsons

 

Links: Hawking’s speech in KTH, Aug 2015

No-Hair Black Hole Theorem

Soft hair on Black Holes

Review on all existing information paradox theories

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