Universe's "Missing" Matter May Lurk in Dwarf Galaxies

May 11, 2007

Astronomers believe they may have found a significant portion of the universe's "missing" matter.

The mysterious dark matter may be giving invisible heft to small galaxies formed during galactic collisions, a new study says.

Dark matter is an invisible form of matter that does not give off or reflect light yet accounts for the vast majority of mass in the universe.

Scientists measured the mass of three so-called recycled dwarf galaxies near a massive galaxy that was recently in a collision.

The dwarfs appear to be more than twice as heavy as their visible stars and gas, indicating that they hold a type of dark matter.

The finding is a surprise, because theoretical models have suggested that recycled dwarfs should be free of dark matter, according to Frédéric Bournaud, an astrophysicist with the French research agency CEA, who led the new research.

"It is clear that this questions the standard pictures," he said in an email interview.

Bournaud and colleagues report the finding in the current issue of the journal Science.

Dark Matter Types

Dark matter comes in two forms. About 10 percent is composed of undetected ordinary matter—like what makes up you, me, planets, stars, and interstellar gas—called baryonic matter.

The rest is a mysterious material called non-baryonic dark matter, which makes up more than a quarter of the universe. (See a computer-simulated picture of dark matter.)

While little is known about non-baryonic dark matter, recent research suggests it serves as the scaffolding of the universe upon which galaxies are formed.

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