With the GLAST mission near launch, keep in mind the possibilities of this unique observatory in terms of findings that could revolutionize our view of distant events. GLAST (Gamma-Ray Large Area Space Telescope) will be looking at things we’ve only recently learned about, such as the enigmatic gamma-ray bursts (GRBs) now flagged by the Swift satellite and quickly pinpointed for the use of Earth-based observatories. We know we’re pushing into uncharted waters given that GLAST represents a major step forward over all previous satellites designed to study gamma ray events. And major new instruments usually deliver new classes of objects.
Because of the increase in GLAST’s sensitivity over earlier tools like the EGRET instrument on NASA’s Compton Gamma-ray Observatory (CGRO), the satellite may find thousands of new point sources. And we have plenty of questions already on the table. Gamma-ray bursts, for example, may be the result of black hole mergers, or the merger of a black hole and a neutron star. But it’s also thought that some are markers for the collapse of a massive star into a black hole. What types of stars, then, become GRB’s, and why? What is the mechanism for producing the initial gamma rays in the burst? Because GRBs seem to come in numerous varieties, their study offers fertile ground for years of research.
Or consider dark matter, the leading candidate for which is the hypothetical weakly interacting massive particle (WIMP). Gamma rays may also derive from WIMPS, which according to supersymmetry theory act as their own antimatter particles, annihilating when they interact with each other, and in the process releasing gamma rays and secondary particles. The signature of such annihilations is potentially observable with GLAST’s Large Area Telescope (LAT), assuming that dark matter is indeed composed of WIMPs. Its continuous stream of gamma rays should differ markedly from the milliseconds-to-minutes time frame of GRBs.
Image: According to supersymmetry, dark-matter particles known as neutralinos (which are often called WIMPs) annihilate each other, creating a cascade of particles and radiation that includes medium-energy gamma rays. If neutralinos exist, the LAT might see the gamma rays associated with their demise. Credit: Sky & Telescope / Gregg Dinderman.
One other fascinating possibility in range of this observatory is the question of the speed of light in a vacuum. The special theory of relativity pins the speed of electromagnetic radiation to 299,792,458 meters (186,282.4 miles) per second, and it would be assumed that gamma-ray photons should move at the same speed. Some models of quantum gravity, however, predict that the speed of very-high-energy gamma rays may vary slightly from other forms of light, the result of the turbulence of spacetime at quantum scales. GLAST can thus test a prediction that could nudge us, if only slightly, toward a merger of general relativity and quantum mechanics.
GLAST is now at Cape Canaveral with a planned launch in early June, having been moved to the Hazardous Processing Facility near Kennedy Space Center for fueling. I suppose it’s human nature that manned missions are what snare media attention, but this observatory may turn out to be one of the most significant we’ve launched in terms of probing out to the edges of physics and cosmology. Dark matter may not make CNN, nor will many gamma-ray bursts, but if GLAST can offer up some answers, we may get a far better read on how the universe functions, and if we’re really lucky, some clues to future propulsion possibilities.
Hi Folks;
I was just reading thru my copy of the newest addition of Popular Science about an exotic type of supernova that in theory would leave nothing behind; no neutron star and no black hole.
These hugely luminous supernova that are unusually long lived in terms of their brightness can perhaps be accounted for by a theory that stars with at least 150 times the mass of the Sun will blow themselves completely apart in runaway thermonuclear fusion processes.
Accordingly, as the requisite star evolves and nears the end of its life, the temperature in the deep interior of the star reaches 1.8 billion degrees F. At this temperature, the gamma rays within this ultra hot plasma state decay into electron positron pairs in a reverse process to Fermi-Dirac pair production. This sudden loss of gamma radiation of the corresponding wavelengths suddenly results in a strong loss of internal pressure thus causing the star to collapse. The temperature eventually reaches 5.4 billion degrees at which point a runaway fusion reaction occurs thus resulting in the complete fusioning of the stars material in a titanic explosion that dwarfs the energy release of conventional types of supernova.
These huge supernova are, accordingly, in part responsible for the production of the heavy elements out of which planets including Earth are made. The power of these supernova astounds me. They must be at least 100 times the yield of a Type Ia or carbon detonation supernova. These huge supernova in theory explode in an essentially spherically symmetric pattern..
The observational astronomers are looking for the degree of spectral emissions of radioactive Nickel which is a product of such supernova explosions. I would encourage anyone who wants to pick up a copy of the latest Popular Science Issue. They have a brief article on a new type of cheap chemical rocket engime as well as hyper spectral Earth observing satellites.
Thanks;
Jim
High energy gamma-ray emission from Gamma-Ray Bursts — before GLAST
Authors: Yi-Zhong Fan, Tsvi Piran
(Submitted on 15 May 2008 (v1), last revised 15 May 2008 (this version, v2))
Abstract: Gamma-ray bursts (GRBs) are short and intense emission of soft gamma-rays, which have fascinated astronomers and astrophysicists since their unexpected discovery in 1960s. The X-ray/optical/radio afterglow observations confirm the cosmological origin of GRBs, support the fireball model, and imply a long-activity of the central engine. The high energy gamma-ray emission (>20 MeV) from GRBs is particularly important because they shed some lights on the radiation mechanisms and can help us to constrain the physical processes giving rise to the early afterglows.
In this work, we review observational and theoretical studies of the high energy emission from GRBs. Special attention is given to the expected high energy emission signatures accompanying the canonical early-time X-ray afterglow that was observed by the Swift X-ray Telescope. We also discuss the detection prospect of the upcoming GLAST satellite and the current ground-based Cerenkov detectors.
Comments: An invited review article for Front. Phys. China. (Possible prompt and very early GeV-TeV emission from GRB 080319B are discussed in Sec. V)
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0805.2221v2 [astro-ph]
Submission history
From: Fan Yizhong [view email]
[v1] Thu, 15 May 2008 18:44:54 GMT (672kb)
[v2] Thu, 15 May 2008 21:25:42 GMT (672kb)
http://arxiv.org/abs/0805.2221
Hi Jim and all
Three predictions which I expect to see from GLAST. 1) All large spiral galaxies will have a substantial gamma ray halo. 2) The source of nearly all gamma-ray bursts will eventually be theorized to be SGR Magnetars. They are also believed to be the source of “soft gamma ray repeaters”. A presently little known condition of relativity makes these gamma ray sources seem to be brighter than they really were. 3) High energy galactic jets produce long lived intense gamma radiation of the same intensity as gamma ray bursts.