domingo, 6 de enero de 2013

Black Holes "Should Glow with a Ring of Light"



Stephen Hawking's great discovery was that the mysterious regions in space we call black holes radiate heat through quantum effects. Hawking has said that "black holes are not really black after all: they glow like a hot body, and the smaller they are, the more they glow."

Hawking's famous theory says that the temperature of a black hole varies inversely to its mass. The mathematician Louis Crane proposed a scifi-like scenario back in 1994 that billions of years in the future, after all the stars have burned out, that small black holes could be created to generate heat and guarantee survival of the species. 
Confirming Hawking's theory,  Tim Johannsen and Dimitrios Psaltis at the University of Arizona in Tucson calculated in 2010 that black holes ought to be surrounded by a ring of light that comes from photons that have become trapped in a circular orbit about the black hole, just outside the event horizon, which are then scattered by gas and dust falling into the hole.

This ring has some interesting properties. It should be much brighter than the surrounding gas and dust. It should have a diameter that is some ten times the size of the black hole, meaning that it should be visible in images that will soon be available and will provide a direct measure of the black hole's mass.

And most importantly, its shape depends on the properties of the black hole, not on the structure of the gas and dust falling into the hole. That means the shape of the ring is measure of the properties of the black hole and any asymmetry in the ring will be a direct violation of the no hair theorem, say Johannsen and Psaltis.

 "The black hole in the center of the Milky Way, is the ideal candidate for a test of the no-hair theorem due to its high brightness, large angular size, and relatively unimpeded observational accessibility," say Johannsen and Psaltis.

Meanwhile, elsewhere, in Hanover, New Hampshire a bold team of researchers at Dartmouth College proposed a new way of creating a reproduction black hole in the laboratory on a much-tinier scale than their celestial counterparts. 
The new method to create a tiny quantum sized black hole would allow researchers to better understand what physicist Stephen Hawking proposed more than 35 years ago: black holes are not totally void of activity; they emit photons, which is now known asHawking radiation.

"Hawking famously showed that black holes radiate energy according to a thermal spectrum," said Paul Nation, an author on the paper and a graduate student at Dartmouth. "His calculations relied on assumptions about the physics of ultra-high energies and quantum gravity. Because we can't yet take measurements from real black holes, we need a way to recreate this phenomenon in the lab in order to study it, to validate it."

The researchers showed that a magnetic field-pulsed microwave transmission line containing an array of superconducting quantum interference devices, or SQUIDs, not only reproduces physics analogous to that of a radiating black hole, but does so in a system where the high energy andquantum mechanical properties are well understood and can be directly controlled in the laboratory.

"We can also manipulate the strength of the applied magnetic field so that the SQUID array can be used to probe black hole radiation beyond what was considered by Hawking," said Miles Blencowe, another author on the paper and a professor of physics and astronomy at Dartmouth.

"In addition to being able to study analogue quantum gravity effects, the new, SQUID-based proposal may be a more straightforward method to detect the Hawking radiation," says Blencowe.

In a paper published in the August 20 issue of Physical Review Letters, the flagship journal of the American Physical Society

Ref: Testing The No-Hair Theorem With Observations In The Electromagnetic Spectrum: II. Black-Hole Images

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