Not only the observable universe is not heavy enough to explain its current configuration, but calculations show that the previously thought mass is actually smaller by 10 to 20 percent, which brings even more questions into discussion.

The subject involving the mass of the observable universe is one of the hottest topics among the astronomers for years, and still eludes current physics, in our understanding of the origin, the structure and the ultimate fate of the universe.

In 2002, a team of astronomers at UAH reported finding large amounts of extra "soft" X-rays coming from the vast space in the middle of galaxy clusters. X-ray emitting atoms were thought to be dispersed thinly through space, filling billions of billions of cubic light years, their cumulative mass adding as much as 10 percent to the mass of the universe, mass needed to explain the extra gravitational pull observed in the galaxies, without which such structures could not exist and rapidly disintegrate before they could ever form.

Several studies made on images provided by multiple space telescopes, including the Chandra X-ray telescope, reveal potential problems regarding this theory. The X-ray analysis can not associate the observations with the spectral emission lines.

The explanation for such a phenomena is that the actual X-ray emissions are not caused by large clouds of X-ray emitting atoms, but rather energy resulted from electrons smashing into photons, which will cause no spectral emissions. This poses a big problem, since the X-ray emission make a large part of the previous observations, used in the theories to estimate the mass of matter present in the universe.

To make matters even worst, it seems that the energy emitted by the electron could have been "puffed up" the clusters. The previous calculations using the energy coming from galaxy clusters were used to estimate how large a cloud of gas must be to reach equilibrium, and form a galaxy. Too much gas, and the cloud will collapse too fast, too little gas and the gravitational pull would not be strong enough to keep it from falling apart, and will disperse.

These complications related to the light mass of the universe excess soft X-ray energy coming from galaxy cluster which are especially massive around iron and other metals, and the possible non-thermal X-rays emitted from electrons colliding with photons that can mask the spectral lines will eventually trigger a new theory and the recalculation of the mass present in the universe.