April and May were exciting months for cosmologists, as new results brought them one step closer to unravelling the mysteries of the early universe.
April and May were exciting months for cosmologists, as new results brought them one step closer to unravelling the mysteries of the early universe. Observations of fluctuations in the microwave background placed important new constraints on the fundamental cosmological parameters; and for the first time, optical observations showed hints of analogous structure in matter distribution.
Cosmic microwave background radiation (CMB) dates from 300 000 years after the Big Bang, when radiation decoupled from matter. Fluctuations in the CMB are evidence for the first clumping of matter particles – the seeds of the galaxies that we see today. Plotting the observed power as a function of the angular size of contributing regions provides a constraint on
cosmological parameters.
It is predicted that this power spectrum will show a number of peaks. The first, corresponding to the largest clumps of matter in the early universe, can be used to give a constraint on W – the ratio of matter in the universe to the critical level needed to halt its expansion. Subsequent peaks give an indication of the amount of ordinary matter and dark matter in the universe.
Last year’s results from the Boomerang and Maxima balloon experiments provided a map of the first peak, and suggest that W is equal to one, which is equivalent to a flat universe. Now a new analysis of the Boomerang data has revealed other peaks that show that the amount of baryonic, or ordinary, matter is about 5%. Results from the Degree Angular Scale Interferometer, which is based at the South Pole, agree with Boomerang, lending strong support to the inflationary model of the early universe.
The two experiments also suggest that the amount of dark matter present in the universe is between 30% (Boomerang) and 65% (Maxima). These results were announced at the American Physical Society meeting in late April.
Meanwhile, astronomers using the Anglo Australian Telescope (AAT) announced observations of ripples in the matter distribution of the universe, in a structure analogous to the fluctuations in the radiation background. The discovery resulted from a survey of 170 000 galaxies carried out using the AAT’s two degree field instrument.
“What we showed was not just that there are ripples in the matter distribution, but that the strength of these ripples is enhanced at certain wavelengths related to the preference for certain angular scales in the CMB,” said John Peacock of Edinburgh. He added: “These are consistent with the effects of acoustic oscillations and allow us to rule out the higher end of the CMB range for dark matter. We prefer 5% baryons and about 30% dark matter.”
