In a cosmic
battle of sorts taking place in the centers of galaxies, stellar forces muscle
up and kick out brewing invisible matter. The result, finds a new study, evens
out the amount of invisible matter held in galactic cores, resolving a cosmological
puzzle.
The
invisible stuff, called dark matter, is thought to make up as much as 90
percent of the universe's mass. Astronomers have never directly observed this mysterious
matter, as it doesn't emit or reflect visible light or other
electromagnetic radiation. Instead, they infer its existence based on its
gravitational effects on visible matter like stars and galaxies. (For instance,
dark matter makes galaxies spin faster than otherwise expected.)
Astronomers
have long tried to explain theoretical models that predict there should be much
more dark matter in the central regions of dwarf galaxies than observations
suggest is the case.
"One of
the most troublesome issues concerns the mysterious dark matter that dominates
the mass of most galaxies," said Sergey Mashchenko of the Department of
Physics and Astronomy at McMaster University in Ontario.
Maschenko
and his colleagues used supercomputer simulations to illustrate galaxy
formation early in our cosmic history—about a billion years after the Big Bang,
the theoretical start of the universe as we know it. The simulations
showed the violent processes galaxies suffer at their births, when dense
clouds of gas collapse to form massive stars, which then end their lives
quickly as explosive supernovas.
It is well
established that these massive stars can inject large amounts of energy into their galactic neighborhoods
through the explosions and also constant emissions of charged particles called
stellar winds. The energy can push interstellar gas to nearly sonic speed,
which for gas at a typical temperature is about 6 miles per second (10
kilometers per second).
Still,
debate has persisted over whether this stellar feedback could turn the spike in
dark-matter density (predicted by theory) into the observed flat core in the
central regions of dwarf galaxies.
The
simulations showed that the stellar wind and explosions shock the interstellar
gas, pushing it back and forth like water sloshing in a cosmic bathtub. That
sloshing kicks most of the dark
matter out of the center of a dwarf galaxy in the simulation, bringing into
agreement theoretical predictions and observations.
The
researchers say their results, detailed online last week by the journal Science,
will force cosmologists to rethink the role of interstellar gas in the
formation of galaxies and could lead to a better understanding of dark matter.
advertisement
