Exploring Black Holes: Introduction to General Relativity makes a quick, directed thrust through general relativity and black holes. Brings preliminary insights concerning the history and structure of the Cosmos. A concise, direct examination of general relativity and black holes, Exploring Black Holes provides tools that motivate tools that motivate readers to become active participants in carrying out their own investigations about curved spacetime near earth and black holes. The authors use calculus and algebra to make general relativity accessible, and use quotes from well-known personalities, including Einstein, to offer further insight. Five chapters introduce basic theory. The book also includes seven projects regarding the analysis of major applications. Discussions provide the background needed to carry out projects. The book's projects guide readers as they fill in steps, compute outcomes and carry out their own investigations. For astronomers, mathematicians and people interested in learning about the relativity of black holes.
An artist's impression of an active galaxy that has jets. The central engine is thought to be a supermassive black hole surrounded by an accretion disc and enshrouded in a dusty doughnut-shaped torus. The torus of dust and gas can be seen orbiting a flatter disc of swirling gas. In the center, the supermassive black hole is surrounded by a flat accretion disc of rapidly orbiting material. The jets are emitted at right angles from the plane of the disc. Courtesy NASA E/PO, Aurore Simonnet, Sonoma State University.
Researchers from the U.S. Department of Energy's Los Alamos National Laboratory and the University of South Carolina have provided a hypothesis that "black holes" in space are not holes at all, but instead are more akin to bubbles.
Researcher Emil Mottola of Los Alamos' Theoretical Division today presented a new explanation for black holes at the American Physical Society annual meeting in Albuquerque, N.M. Pawel Mazur of the University of South Carolina is Mottola's co-author. The researchers' explanation redefines black holes not as "holes" in space where matter and light inexplicably disappear into another dimension, but rather as spherical voids surrounded by an extremely durable form of matter never before experienced on Earth. Mazur and Mottola call the extraordinary objects Gravastars.
The Gravastar explanation for black holes helps provide answers to some of the daunting questions raised by traditional black-hole descriptions. Based on earlier-held astrophysical explanations, black holes form in space when stars reach the end of their lives and collapse in on themselves. According to black hole theory, the matter from these dying stars occupies a tiny amount of space -- a mere pinpoint -- and creates a mind-boggling gravitational field so powerful that nothing can escape, not even light.
Mottola and Pawel suggest that while some degree of collapsing does take place in a dying star, the collapse proceeds only to a certain point. At that point, the intense gravity of the dying star transforms the star's matter into an entirely new phase. Mottolla describes this phase as similar to a Bose-Einstein condensate, a phase of matter recently observed in a laboratory setting and the subject of scientific excitement in the past few years.
On Earth, a Bose-Einstein condensate forms when matter is plunged to very low temperatures approaching Absolute Zero, the theoretical temperature at which all atomic motion -- the motion of electrons, protons and all other subatomic particles within an individual atom -- is believed to cease. When matter is cooled sufficiently to become a Bose-Einstein condensate, the atoms that make up the matter enter a strange new phase. The atoms all reach the same energy state, or quantum state, and they coalesce into a blob of material called a "super atom." The properties of Bose-Einstein condensates are the subject of intense study and many physicists are working to understand them.
Mottola and Mazur believe that dying stars collapse to the "Event Horizon" -- in essence the point of no return for objects entering the gravitational field of a black hole. At this point, the matter in the dying star transforms to a new state of matter that forms a Gravastar. According to the two researchers, the dying star's matter creates an ultra-thin, ultra-cold, ultra-dark shell of material that is virtually indestructible. The new form of gravitational energy in the interior is akin to a Bose-Einstien condensate, although it appears on the inside to be a bubble of vacuum, hence the term Gra (vitational) Va (cuum) Star, or Gravastar.
"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. "However, any matter in the vicinity that fell onto the surface could be re-emitted as another form of energy, which would make Gravastars potentially much more powerful emitters of radiation than black holes, which simply swallow the material."
The space trapped inside the Gravastar's shell is a similarly uncanny conceptually. The interior of the Gravastar would be totally warped space-time (the traditional three dimensions plus time). According to the researchers, this interior space would exert an outward force on the shell, adding to its durability.
Although unconventional, Mottola and Mazur's Gravastar explanation for black holes does solve at least one serious quandary created by black hole theory. Under a black-hole scenario, the amount of entropy created in a black hole would become nearly infinite. Physicists have struggled for years to account for the huge entropy of black holes, and largely have failed. Unlike their black hole counterparts, Gravastars would have a very low entropy.
Black Holes and Time Warps: Einstein's Outrageous Legacy -
By Kip S. Thorne, Frederick Seitz, with an introduction by Stephen Hawking.
Mottola and Mazur continue to refine their theory and are working on a concept behind rotating Gravastars. They even suggest that the universe we now know and live in may be the interior of a Gravastar.
"These are fascinating concepts to think about," Mottola said. "I look forward to exploring this hypothesis further."
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy.