Where’s all the missing ordinary matter of the Universe?

January 7th, 2010 - 3:02 pm ICT by ANI  

Large Hadron Collider Washington, January 7 (ANI): An international team of scientists has found that individual galactic objects have less ordinary matter, relative to dark matter, than does the Universe as a whole.

Scientists believe that all ordinary matter, the protons and neutrons that make up people, planets, stars and all that we can see, are a mere fraction - some 17 percent - of the total matter in the Universe.

The protons and neutrons of ordinary matter are referred to as baryons in particle physics and cosmology.

The remaining 83 percent apparently is the mysterious “dark matter,” the existence of which is inferred largely from its gravitational pull on visible matter.

According to University of Maryland astronomer Stacy McGaugh, dark matter is presumed to be some new form of non-baryonic particle - the stuff scientists hope the Large Hadron Collider in CERN will create in high energy collisions between protons.

McGaugh and his colleagues posed the question of whether the “universal” ratio of baryonic matter to dark matter holds on the scales of individual structures like galaxies.

“One would expect galaxies and clusters of galaxies to be made of the same stuff as the universe as a whole, so if you make an accounting of the normal matter in each object, and its total mass, you ought to get the same 17 percent fraction,” he said.

“However, our work shows that individual objects have less ordinary matter, relative to dark matter, than you would expect from the cosmic mix; sometimes a lot less,” he added.

Just how much less depends systematically on scale, according to the researchers.

The smaller an object the further its ratio of ordinary matter to dark matter is from the cosmic mix.

McGaugh said that their work indicates that the largest bound structures, rich clusters of galaxies, have 14 percent of ordinary baryonic matter, close to expected 17 percent.

“As we looked at smaller objects - individual galaxies and satellite galaxies, the normal matter content gets steadily less,” he said.

“The smaller the galaxy, the smaller is its ratio of normal matter to dark matter. Put another way, the smallest galaxies are very dark matter dominated,” he added. (ANI)

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