As if black holes weren't mind-bending enough, a new hypothesis suggests an entirely new idea for Nature's densest objects. In fact, the idea goes black holes aren't holes at all but black bubbles with very thick skins.
The new idea, presented this week at a meeting of the American Physical Society, was conceived to provide an alternative to the exotic description of where stuff goes when a star collapses and becomes, in present theory, a black hole.
For most of us, the matter of where the matter goes is no less mysterious under the new notion.
Emil Mottola of the Los Alamos National Laboratory and Pawel Mazur of the University of South Carolina suggest that instead of a star collapsing into a pinpoint of space with virtually infinite gravity, its matter is transformed into a spherical void surrounded by "an extremely durable form of matter never before experienced on Earth."
The researchers call the objects gravastars. And, as with a black hole, you wouldn't want to get to close.
"Since this new form of matter is very durable, but somewhat flexible, like a bubble, anything that became trapped by its intense gravity and smashed into it would be obliterated and then assimilated into the shell of the gravastar," Mottola said.
There is no proof that this new form of matter exists, and thus gravastars remain for the moment no more than a potentially convenient proposal. But other astronomers are intrigued, both because black holes themselves remain mere theory, not fact, and because gravastars might explain strange physical observations that black holes don't.
Losing their grip
Black holes were conceived during World War 1 by the German astronomer Karl Schwarzschild, who while serving in the war was scratching solutions to Einstein's theories.
Black holes are theorized to be so dense that nothing, not even light, escapes the gravitational grip. Einstein first thought the idea was nuts. In a way, though, the concept is not as odd as one might think. Astronomers have clearly seen how any large object, such as the Sun or another star bends light and sends it on a new course. Black holes just bend light a whole lot more, folding its photons right into the object, Schwarzschild proposed.
Such excruciating bends cause the warping of both space and time, or space-time, as the theorists put it. Gravastars would be no less forgiving of what we traditionally call reality.
Inside a gravastar, space-time would be "totally warped," the researchers say. Further, the inner space would exert an outward force, which would enhance the durability of the bubble.
Mottola and Mazur have not worked out all the details of how gravastars might form. Yet they say the objects solve a flaw in black hole theory.
Physicists have long struggled to account for the tremendous entropy, or information, that a black hole would harbor. Theory holds that a black hole should have a billion, billion times more entropy sometimes referred to as states, than the star it formed from.
"Where are all these zillions of states hiding in a black hole?" Mottola said in a recent article in New Scientist magazine. "It is quite literally incomprehensible."
Gravastars don't have the same problem, as their entropy is said to be very low.
Remarkable properties
From the outside, a gravastar would appear much like a black hole; visible only by the high-energy emissions it spits from its jowls while consuming matter. Astronomers use X-ray observations, created by such cosmically carnivorous activity, to detect black holes. By noting the small region of space that can't be seen within a sphere inside those emissions, and by looking at the gravitational effects that the space has on surrounding matter, the black hole is deduced.
But inside, the material in a gravastar would have undergone a phase change, something like when water freezes to the solid state. The newly conceived, wildly dense phase of matter is theoretically rooted in a recent discovery.
In 1995, researchers cooled matter to near absolute zero and created a new form of matter called a
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