An object called CSL-1 may have a lot to say about the nature of the universe. The odd thing about this double source — evidently a pair of galaxies — is that both galaxies appear identical. They share a common redshift, a similar shape, and their luminosity profiles match that of two giant elliptical galaxies. Moreover, the spectra of the two components seem to be identical.
Is this a double image of the same galaxy? If so, then something tantalizing is going on. String theory, the latest and still evolving explanation for how the universe works, says that there should be gigantic counterparts to the strings that make up the fundamental particles of matter. A single-dimensional string millions of light years in length — think of it as a thread of energy — is one prediction made by string theory, and CSL-1 may indicate the presence of just such a cosmic string.
For a cosmic string would be so energetic that it would warp spacetime around it, with the effect that a string lying between Earth and a distant object would create two different routes for light to reach us. What we would see would be identical images of the same object, separated by a tiny distance. Mikhail Sazhin (Capodimonte Astronomical Observatory, Naples and the Sternberg Astronomical Institute, Moscow) and his colleagues found CSL-1 last year, and now report on their work in a new paper available on the arXiv site.
The key is to determine whether the two images represent the same object, or whether they are simply two extremely similar galaxies in close proximity to each other. Using the European Southern Observatory’s Very Large Telescope (Paranal, Chile), the team recorded detailed spectra of the objects and now present the case that they are identical. Further work will be definitive, and awaits the observing time on the Hubble Space Telescope that the team has now been granted. “The resolution of the HST will allow us to detect the specific signature produced by the cosmic string,” says Sazhin, in an article running in the July 30 issue of New Scientist. “We hope it will reduce the scepticism of other astronomers.”
Centauri Dreams‘ note: the first alternative that leaped to mind here was conventional gravitational lensing; i.e., lensing caused by a massive object between Earth and the distant galaxy. But Sazhin notes that standard lensing models rule out this configuration. “…in this second case, due to the lack of asymmetry in the two images, the lens could not be modelled with the standard lensing by a massive compact source. Actually, the usual gravitational lenses, i.e. those formed by bound clumps of matter, always produce inhomogeneous gravitational fields which distort the images of extended background sources… The detailed modelling of CSL-1 proved that the two images were virtually undistorted.”
Only gravitational lensing produced by a cosmic string seems to fit the data. The Hubble work will be vital because the cosmic string model predicts the images should have sharp edges of a precision not verifiable from Earth-based telescopes. The observations for these tests have not yet been taken, and so the coincidental two-galaxy possibility cannot yet be ruled out.
Image: A computer simulation of cosmic strings run at the University of Southampton (UK). Formed in a tangled mass, the strings would have quickly started to straighten out at speeds close to that of light, under the influence of their enormous tension. Remnants would still be around today: perhaps a few lengths stretching across the the visible Universe, strings so large that they have not had time to disappear, and a debris of smaller oscillating loops. The Southampton work on massively parallel simulations of cosmic strings can be found online.
If the CSL-1 data are confirmed as the result of a cosmic string, this finding would suggest that string theory is correct in its prediction of extra dimensions in the universe. Indeed, the theory makes the startling claim that the universe may be a three-dimensional ‘brane’ afloat in a sea of other dimensions. A collision between two such branes could have caused the Big Bang, and produced at the same time the kind of cosmic strings hypothesized here.
The paper on CSL-1 is Sazhin, M., Capaccioli, M, Longo, G. et al., “Further spectroscopic observations of the CSL-1 object,” available here.