PureInsight | June 23, 2007
This Hubble
Space Telescope composite image shows a ghostly "ring" of dark matter
in the galaxy cluster ZwCl0024+1652. Credit: NASA, ESA, M.J. Jee and H.
Ford (Johns Hopkins University)
According to a Hubble ESA Information Center News Release on May 15,
2007, an international team of astronomers using the NASA/ESA Hubble
Space Telescope has discovered a ghostly ring of dark matter that was
formed long ago during a titanic collision between two massive galaxy
clusters. "It is the first time that a dark matter distribution has
been found that differs substantially from the distribution of ordinary
matter." "The ring, which measures 2.6 million light-years across, was
found in the cluster ZwCl0024+1652, located 5 billion light-years away
from Earth."
"This is the first time we have detected dark matter as having a unique
structure that is different from the gas and galaxies in the cluster,"
said astronomer M. James Jee of Johns Hopkins University in Baltimore,
USA, a member of the team that spotted the dark matter ring.
"Although the invisible matter has been found before in other galaxy
clusters, it has never been detected to be so largely separated from
the hot gas and the galaxies that make up galaxy clusters," Jee
continued. "By seeing a dark matter structure that is not traced by
galaxies and hot gas, we can study how it behaves differently from
normal matter."
During the team's dark-matter analysis, they noticed a ripple in the
mysterious substance, somewhat like the ripples created in a pond from
a stone plopping into the water.
Curious about why the ring was in the cluster and how it had formed,
Jee found previous research that suggested the cluster had collided
with another cluster 1 to 2 billion years ago. The research, published
in 2002 by Oliver Czoske of the Argelander-Institut für Astronomie at
Bonn University, was based on spectroscopic observations of the
cluster's three-dimensional structure. The study revealed two distinct
groupings of galaxies clusters, indicating a collision between both
clusters.
"Dark matter makes up most of the universe's material. Ordinary matter,
which makes up stars and planets, comprises only a few percent of the
universe's matter."
"The ring's discovery is among the strongest evidence yet that dark
matter exists. Astronomers have long suspected the existence of the
invisible substance as the source of additional gravity that holds
together galaxy clusters. Such clusters would fly apart if they relied
only on the gravity from their visible stars. Although astronomers
don't know what dark matter is made of, they hypothesize that it is a
type of elementary particle that pervades the universe."
Reference: http://www.spaceflightnow.com/news/n0705/15darkmatter/
Translated from: http://zhengjian.org/zj/articles/2007/6/11/44357.html
