Mini Black Holes Might Reveal 5th Dimension

A space telescope scheduled for launch in 2007 will be sensitive enough to detect theoretical miniature black holes lurking within our solar system, scientists say.

By doing so, it could test an exotic five-dimensional theory of gravity that competes with Albert Einstein's General Theory of Relativity. That is, of course, if the tiny black holes actually exist.

The idea, recently detailed online in the journal Physical Review D, is being proposed by Charles Keeton, a physicist at Rutgers University in New Jersey, and Arlie Petters of Duke University in North Carolina.

The Randall-Sundrum braneworld model, named after the scientists who created it, states that the visible universe is a membrane embedded within a larger universe, like a strand of seaweed floating in the ocean. Unlike the universe described by General Relativity—which has three dimensions of space and one of time—the braneworld universe contains an extra fourth dimension of space for a total of five dimensions.

If the braneworld theory is true, it would "upset the applecart," Petters said. "It would confirm that there is a fourth dimension to space, which would create a philosophical shift in our understanding of the natural world."

The braneworld theory predicts the existence of tiny black holes seeded throughout the universe, remnants of the Big Bang. Thousands of them should exist in our solar system. General Relativity, in contrast, predicts that such primordial black holes evaporated long ago.

The researchers predict that braneworld black holes are about the size of an atomic nucleus but have masses similar to that of a tiny asteroid.

Petters and Keeton say their theory is testable. The mini-black holes should warp the fabric of space-time differently from other types of black holes—thos of stellar-mass and the supermassive variety—due to their close association with the fifth dimension. Light, specifically gamma-rays, should be distorted differently when they whiz past braneworld black holes compared to conventional black holes.

"Our calculations show that braneworld black holes will give you a certain ripple in the gamma rays that would be different from general relativity," Petters told SPACE.com.

The researchers think that the Gamma-ray Large Space Telescope (GLAST) scheduled for launch in 2007 should be sensitive enough to detect the gamma ray distortions.

GLAST Overview
http://glast.gsfc.nasa.gov/science/overview.html

GLAST will have an imaging gamma-ray telescope vastly more capable than instruments flown previously, as well as a secondary instrument to augment the study ofgamma-ray bursts. The main instrument, the Large Area Telescope (LAT), will have superior area, angular resolution, field of view, and deadtime that together will provide a factor of 30 or more advance in sensitivity, as well as provide capability for study of transient phenomena (Table 1-1). The GLAST Burst Monitor (GBM) will have a field of view several times larger than the LAT and will provide spectral coverage of gamma-ray bursts that extends from the lower limit of the LAT down to 10 keV. The basic parameters of the GBM are compared to those of the Burst and Transient Source Experiment (BATSE) instrument on CGRO in Table 1-2. With the LAT and GBM, GLAST will be a flexible observatory for investigating the great range of astrophysical phenomena best studied in high-energy gamma rays. NASA plans to launch GLAST in September 2007.

The anticipated advances in astronomy and high-energy physics with GLAST are described briefly below. They are among the central subjects of NASA's Structure andEvolution of the Universe (SEU) research theme and the Department of Energy's non-accelerator research program. The GLAST mission is also supported by the physics andastrophysics programs in the partner countries of France, Germany, Italy, Japan, and Sweden. NASA recognizes the scientific goals of the GLAST mission as part of the SEUCosmic Journeys planned for study of black holes and dark matter. Of course, with its capabilities, GLAST certainly may yield important unanticipated findings. The missionwill be supported by a vigorous, multidisciplinary guest investigator program to maximize the discovery potential.

The Scientific Case for GLAST

The Universe is largely transparent to gamma rays in the energy range of GLAST. Energetic sources near the edge of the visible Universe can be detected by the light of theirgamma rays. There is good reason to expect that GLAST will see known classes of sources to redshifts of 5, or even greater if the sources existed at earlier times. Thesmall interaction cross sections for gamma rays also means that gamma rays can provide a direct view into nature's highest-energy acceleration processes. Gamma rayspoint back to their sources, unlike cosmic rays, which are deflected by magnetic fields.

Blazars and Active Galactic Nuclei

EGRET discovered that blazar-class active galactic nuclei (AGNs) are bright and variable sources of high-energy gamma rays. In fact, the bulk of the luminosity for manyblazars is emitted in GLAST's energy range. The emission is believed to be powered by accretion onto supermassive black holes at the cores of distant galaxies. GLAST willincrease the number of known AGN gamma-ray sources from about 70 to thousands. Moreover, it will effectively be an all-sky monitor for AGN flares, scanning the full skyevery three hours. It will greatly decrease the minimum time scale for detection of variability, and will offer near-real-time alerts for spacecraft and ground-basedobservatories operating at other wavelengths. Using EGRET, AGN flares were measured to vary on the shortest time scales -- eight hours -- that were able to be determinedwith statistical significance.

Unidentified Sources

GLAST will enable identification of the EGRET sources for which no counterparts are known at other wavelengths by providing much smaller error boxes. More than 60% of theEGRET sources are unidentified. Considering their distribution on the sky, less than one third of these are extragalactic (probably blazar AGNs), with the rest most likely withinthe Milky Way. Recent work suggests that many of these unidentified sources are associated with the nearby Gould Belt of star-forming regions that surrounds the solarneighborhood. Apparently-steady sources are likely to be radio-quiet pulsars Ð and GLAST will be able to directly search for periods in sources at least down to EGRET's fluxlimit. Transient sources within the Milky Way are poorly understood, and may represent interactions of individual pulsars or neutron star binaries with the ambient interstellarmedium. Some of the unidentified EGRET sources may be associated with recently discovered Galactic microquasars. GLAST will be able to explore these source classes indetail.

New Particle Physics

The large area and low instrumental background of GLAST will also allow searches for decays of exotic particles in the early Universe and for annihilations of postulatedweakly-interacting massive particles (WIMPs) in the halo of the Milky Way. Much of the isotropic background detected by EGRET will be resolved by GLAST into discrete AGNsources. A truly diffuse, cosmic residual would be a tremendous discovery and could relate to particle decay in the early Universe. Recent theoretical work suggests thatannihilation emission from the lightest supersymmetric particle, a candidate Galactic halo WIMP, could be detectable with GLAST. The signature would be spatially diffuse,narrow line emission peaked toward the Galactic center.

Extragalactic Background Light

The sensitivity of GLAST at high energies will also permit study of the extragalactic background light by measurement of the attenuation of AGN spectra at high energies. This attenuation is from pair production with photons in the background light primarily produced by young stars at visible to ultraviolet wavelengths. Owing to the large size ofthe AGN catalog that GLAST will amass, intrinsic spectra of AGNs will be distinguishable from the effects of attenuation. The measured attenuation as a function of AGNredshift will relate directly to the star formation history of the Universe.

Gamma-Ray Bursts

GLAST will continue the recent revolution of gamma-ray burst understanding by measuring spectra from keV to GeV energies and by tracking afterglows. With itshigh-energy response and very short deadtime, GLAST will offer unique capabilities for the high-energy study of bursts that will not be superseded by any planned mission. GLAST will make definitive measurements of the high-energy behavior of bursts that EGRET could not. Time-resolved spectral measurements with GLAST, combining datafrom LAT and GBM, will permit determination of the minimum Lorentz factors and baryon fractions for the emitting regions, and distinguish between internal and externalshocks as the mechanism for gamma-ray production, and may also permit gamma-ray-only distance determinations. The LAT and the GBM will detect more than 200 burstsper year and provide near-real-time location information to other observatories for afterglow searches. GLAST will have the capability to slew autonomously toward bursts tomonitor for delayed emission with the LAT.

Pulsars

GLAST will discover many gamma-ray pulsars, potentially 250 or more, and will provide definitive spectral measurements that will distinguish between the two primary modelsproposed to explain particle acceleration and gamma-ray generation: the outer gap and polar cap models. From observations made with gamma-ray experiments through theCGRO era, seven gamma-ray pulsars are known. GLAST will be able to search for periodicities directly in all EGRET unidentified sources. Because the gamma-ray beams ofpulsars are apparently broader than their radio beams, many radio-quiet, Geminga-like pulsars likely remain to be discovered.

Cosmic Rays and Interstellar Emission

GLAST will spatially resolve some supernova remnants and precisely measure their spectra, and may determine whether remnants are sources of cosmic-ray nuclei. Cosmicrays produce the pervasive diffuse gamma-ray emission in the Milky Way via their collisions with interstellar nuclei and photons. GLAST will also be able to detect the diffuseemission from a number of local group and starburst galaxies, and map the emission within the largest of these, for the first time. Spatial and spectral studies of thegamma-ray emission will permit the distributions of cosmic-ray protons and electrons to be measured separately and will test cosmic-ray production and diffusion theories.

Solar Flares

GLAST will have unique high-energy capability for study of solar flares. EGRET discovered that the sun is a source of GeV gamma rays. GLAST will be able to determine wherethe acceleration takes place, and whether protons are accelerated along with the electrons. The large effective area and small deadtime of GLAST will enable the requireddetailed studies of spectral evolution and localization of flares. GLAST will be the only mission observing high-energy photons from solar flares during Cycle 24.

Complementarity with Ground-Based Gamma-Ray Telescopes

GLAST in orbit will complement the capabilities of the next-generation atmospheric Cherenkov and shower gamma-ray telescopes that are planned, under construction, orbeginning operation, such as ARGO, CANGAROO III, CELESTE, HESS, MAGIC, MILAGRO, STACEE, and VERITAS. These ground-based telescopes detect the Cherenkov light orair-shower particles from cascading interactions of very high-energy gamma rays in the upper atmosphere. They have very large effective collecting areas (>108 cm2), butsmall fields of view (~1°, with the exception of MILAGRO) and limited duty cycles relative to GLAST. GLAST will monitor the whole sky on timescales of hours and willprovide alerts when flaring AGNs are detected. Some of the next-generation Cherenkov telescopes will have sensitivities extending down to 50ÊGeV and below, providing abroad useful range of overlap with GLAST.

Because of its unique capabilities and the great increment in sensitivity it offers in a largely unexplored region of the electromagnetic spectrum, GLAST draws the interest ofseveral scientific communities. The international high-energy astrophysics and high-energy particle physics communities together have been particularly active in developingthe mission and the necessary technologies.

Instrument Design

The instruments on the GLAST mission are the Large Area Telescope (LAT, principal investigator Peter Michelson, Stanford University) and the GLAST Burst Monitor (GBM,principal investigator Charles Meegan, MSFC, co-PI Giselher Lichti, Max-Planck-Institut für extraterrestrische Physik, Germany). The LAT will have three subsystems: asolid state detector (silicon strip) pair conversion tracker for gamma-ray detection and direction measurement, a CsI calorimeter for measurement of the energies, and aplastic scintillator anticoincidence system to provide rejection of signals from the intense background of charged particles. The LAT will be modular, consisting of a 4 ×4 array of identical towers, and will have more than one million silicon-strip detector channels. The GBM will have 12 NaI scintillators and two BGO scintillators mounted on thesides of the spacecraft. The combined detectors will view the entire sky not occulted by Earth, with energy coverage from a few keV to 30 MeV, overlapping with the lowerenergy limit of the LAT and with the range of GRB detectors on previous missions.

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