Gravitational Waves Could Probe Inflation

ASTROWATCH

Compiled by Marc Türler, INTEGRAL Science Data Centre and Geneva Observatory Gravitational waves could probe inflation

“In the beginning was the Word,” opens the universe after hybrid inflation. According the gospel of John, and this finds some to the researchers, many extensions of resonance in the possibility of detecting the Standard Model of particle physics gravitational waves from the Big Bang itself expect this process, both in string and at frequencies typical of sound waves. supersymmetric theories. Careful listening to this background signal They suggest that such a process would would probe the inflation phase of the very lead to the formation of high-energy early universe. bubble-like structures, which would collide Astronomy is a science based on and generate a stochastic background of photons. First limited to visible light and gravitational waves. Taking into account then broadening to include radio waves, the the expected downshift of this radiation field of investigation has exploded during by 24 orders of magnitude due to the recent decades. Windows on the sky at new cosmic expansion since that time, their wavelengths have opened one by one thanks calculation predicts a maximum intensity to the use of satellites to avoid absorption of gravitational waves at frequencies from by the Earth’s atmosphere. However, at about 1 Hz for a low-scale inflation model up any wavelength, the quest towards the to about 10 MHz for a high-scale model. beginning of time stops abruptly 380 000 Artist’s view of LISA, a joint ESA and NASA This frequency range is too high to be years after the Big Bang, when the emission project to be the first space mission to accessible to the future Laser Interferometer of the cosmic microwave background (CMB) detect gravitational waves. (Courtesy ESA.) Space Antenna (LISA), a joint mission occurred. This is when the universe became of ESA and NASA, but there is hope to transparent and there is no hope of looking Einstein’s general theory of relativity predicts detect the expected signal with other further back in time via electromagnetic that these distortions of space–time projects, on the ground with the Advanced radiation. Although earlier events like propagate with the speed of light. Although Laser Interferometer Gravitational Wave inflation may leave some imprint in the studying the change of period of tight Observatory or in space with NASA’s map of the CMB (CERN Courier May 2006 double-pulsar systems has demonstrated proposed Big Bang Observer. There is no p12), a direct messenger from the very early their existence (CERN Courier March 2004 doubt that the detection of gravitational universe must be of a different nature. p12), direct detection is still to be achieved waves from the first 10–34 s of the universe Primordial neutrinos from the time of despite the great effort invested to detect would be a new milestone in science, Big Bang nucleosynthesis would be a good these subtle disturbances of space–time. allowing physicists to confront their models candidate for such a messenger, but their A theoretical study by Juan Garcia-Bellido with observations. very low energy and interaction cross- and Daniel Figueroa from the Universidad section makes them currently undetectable. Autonoma de Madrid, Spain, sheds a new Further reading Gravitational waves are another candidate light on the expected amplitude and spectral J Garcia-Bellido and D G Figueroa 2007 attracting a great deal of interest as a property of primordial gravitational waves. Phys. Rev. Lett. in press [http://arxiv. possible witness of the very early universe. The study focuses on the violent reheating of org/abs/astro-ph/0701014].

Picture of the month This beautiful false-colour infrared view of the Eagle Nebula (Messier 16) located 7000 light-years away in the Serpens constellation was taken by NASA’s Spitzer Space Telescope (CERN Courier January/February 2004 p19). The famous “Pillars of Creation” captured by the Hubble Space Telescope in 1995 are overlayed and their location is shown on the background image. The other dust column observed by Hubble 10 years later is also visible to the left of the image (CERN Courier June 2005 p12). Careful analysis of the reddish central area reveals an excess of heat thought to be due to a supernova explosion, which could have been seen to explode 1000–2000 years ago and would destroy the majestic pillars, from our point of view, 1000 years from now. (Courtesy NASA/JPL-Caltech/N Flagey [IAS/ SSC] and A Noriega-Crespo [SSC/Caltech].)

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