Universe Might Weigh Much Less than We Think

The universe might be many billions of light-years wide, but it could be much lighter than its proportions would lead you to believe, according to new research from the University of Alabama at Huntsville (UAH).

In fact, the UAH research team's findings indicate the universe's mass might be 10 to 20 percent less than previous calculations indicated.

The sudden slimdown comes from new information about the source of x-ray energy radiating from the middle of galaxy clusters, which are the largest cosmological structures in the universe. UAH researchers had previously theorized that both low- and high-energy x-rays came from intergalactic clouds of so-called "warm" gas. However, they now believe the low-energy x-rays might be created in collisions between photons and electrons; the energy generated in those collisions revs up the photons, which are electromagnetic particles, from microwaves to x-rays.

The discovery is like finding out that the many points of light you thought were coming from aircraft carriers were instead generated by light, tiny but very bright fireflies.

"This means the mass of these x-ray emitting clouds is much less than we initially thought it was," said Max Bonamente, an assistant professor in UAH's physics department. "A significant portion of what we thought was missing mass turns out to be these 'relativistic' electrons."

UAH researchers in 2002 had speculated that some of the "missing mass" needed to hold the universe together gravitationally came from x-ray emitting gases in the middle of galaxy clusters. While those gases were believed to be present in amounts less than one atom per cubic meter, spread out over the vast reaches of the universe, they could have accounted for up to 10 percent of the mass and gravity required to bind together galaxies, galaxy clusters and more.

Bonamente's team reached its latest conclusion after analyzing satellite data of a galaxy cluster in the southern sky. The spectra of the low-energy x-rays coming from inside the cluster didn't show the telltale signs of gas atoms and ions. The most logical explanation for the absence of spectral emission lines was that the low-energy x-rays were instead generated from the collisions of electrons and photons, both of which are much tinier than atoms.

The new theory raises even more doubts about the mass of the universe. The electrons causing low-energy x-rays would also generate some of the higher-energy x-rays believed to be coming from intergalactic gases. And the amount of energy coming from electrons might also be leading astrophysicists to overestimate how much mass is in those intergalactic clouds. Finally, x-rays from electrons might be masking spectral emission lines from iron and other metals, meaning the universe might contain more of those elements that previously thought.

"It means we need to revise how we calculate both the gas mass and the total mass," Bonamente said. "We have to follow the evidence and, if that leads us to confusion, well that's OK."

The research team's findings were published in a recent edition of the Astrophysical Journal. Other scientists participating in the study included Jukka Nevalainen of the Helsinki Observatory in Finland and Richard Lieu, also of UAH.

The University of Alabama, Huntsville, "A Big Chunk of the Universe is Missing ... Again." URL:

(http://www.uah.edu/News/newsread.php?newsID=958)