Ring of Dark Matter Detected

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NASA Hubble Space Telescope Detects Ring of Dark Matter

The media advisory is reproduced below:

May 9, 2007

Grey Hautaluoma
Headquarters, Washington
202-358-0668

Susan Hendrix
Goddard Space Flight Center, Greenbelt, Md.
301-286-7745

Ray Villard
Space Telescope Science Institute, Baltimore
410-338-4514

MEDIA ADVISORY: M07-51

NASA Hubble Space Telescope Detects Ring of Dark Matter

REENBELT, Md. - NASA will hold a media teleconference at 1 p.m. EDT on May 15 to discuss the strongest evidence to date that dark matter exists. This evidence was found in a ghostly ring of dark matter in the cluster CL0024+17, discovered using NASA's Hubble Space Telescope. The ring is the first cluster to show a dark matter distribution that differs from the distribution of both the galaxies and the hot gas. The discovery will be featured in the May 15 issue of the Astrophysical Journal.

Briefing participants are:
-- Dr. Myungkook James Jee, associate research scientist, Johns Hopkins University, Baltimore
-- Dr. Richard White, astronomer, Space Telescope Science Institute, Baltimore

Reporters should contact Ray Villard at the Space Telescope Science Institute at 410-338-4514 prior to the media teleconference for the call in number and passcode. Audio for the briefing will stream live on the Internet at:

http://www.nasa.gov/newsaudio

At the start of the briefing, images and supporting graphics will be posted on the Web at:

http://www.nasa.gov/mission_pages/hubble/news/dark_matter_ring.html

For more information about the Hubble Space Telescope, visit:

http://www.nasa.gov/hubble

- end -

Source: NASA Media Advisory M07-51

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Hubble Finds Ring of Dark Matter

May 15, 2007 01:00 PM (EDT)

News Release Number: STScI-2007-17


Astronomers using NASA's Hubble Space Telescope have discovered a ghostly ring of dark matter that formed long ago during a titanic collision between two massive galaxy clusters.

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.

"This is the first time we have detected dark matter as having a unique structure that is different from both the gas and galaxies in the cluster," said astronomer M. James Jee of Johns Hopkins University in Baltimore, Md., a member of the team that spotted the dark-matter ring.

The researchers spotted the ring unexpectedly while they were mapping the distribution of dark matter within the galaxy cluster Cl 0024+17 (ZwCl 0024+1652), located 5 billion light-years from Earth. The ring measures 2.6 million light-years across. Although astronomers cannot see dark matter, they can infer its existence in galaxy clusters by observing how its gravity bends the light of more distant background galaxies.

"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 said. "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.

"I was annoyed when I saw the ring because I thought it was an artifact, which would have implied a flaw in our data reduction," Jee explained. "I couldn't believe my result. But the more I tried to remove the ring, the more it showed up. It took more than a year to convince myself that the ring was real. I've looked at a number of clusters and I haven't seen anything like this."

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 Argeleander-Institut fur Astronomie at the Universitat Bonn, 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.

Astronomers have a head-on view of the collision because it occurred fortuitously along Earth's line of sight. From this perspective, the dark-matter structure looks like a ring.

Computer simulations of galaxy cluster collisions, created by the team, show that when two clusters smash together, the dark matter falls to the center of the combined cluster and sloshes back out. As the dark matter moves outward, it begins to slow down under the pull of gravity and pile up, like cars bunched up on a freeway.

"By studying this collision, we are seeing how dark matter responds to gravity," said team member Holland Ford of Johns Hopkins University. "Nature is doing an experiment for us that we can't do in a lab, and it agrees with our theoretical models."

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.

Tracing dark matter is not an easy task, because it does not shine or reflect light. Astronomers can only detect its influence by how its gravity affects light. To find it, astronomers study how faint light from more distant galaxies is distorted and smeared into arcs and streaks by the gravity of the dark matter in a foreground galaxy cluster, a powerful trick called gravitational lensing. By mapping the distorted light, astronomers can deduce the cluster's mass and trace how dark matter is distributed in the cluster.

"The collision between the two galaxy clusters created a ripple of dark matter that left distinct footprints in the shapes of the background galaxies," Jee explained. "It's like looking at the pebbles on the bottom of a pond with ripples on the surface. The pebbles' shapes appear to change as the ripples pass over them. So, too, the background galaxies behind the ring show coherent changes in their shapes due to the presence of the dense ring."

Jee and his colleagues used Hubble's Advanced Camera for Surveys to detect the faint, distorted, faraway galaxies behind the cluster that cannot be resolved with ground-based telescopes. "Hubble's exquisite images and unparalleled sensitivity to faint galaxies make it the only tool for this measurement," said team member Richard White of the Space Telescope Science Institute in Baltimore.

Previous observations of the Bullet Cluster with Hubble and the Chandra X-ray Observatory presented a sideways view of a similar encounter between two galaxy clusters. In that collision, the dark matter was pulled apart from the hot cluster gas, but the dark matter still followed the distribution of cluster galaxies. Cl 0024+17 is the first cluster to show a dark matter distribution that differs from the distribution of both the galaxies and the hot gas.

The team's paper will appear in the June 1 issue of the Astrophysical Journal.
CONTACT

Donna Weaver/Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493/4514

Richard White
Space Telescope Science Institute, Baltimore, Md.
(phone) 410-338-4899
(e-mail) rlw@stsci.edu

Myungkook James Jee
Johns Hopkins University, Baltimore, Md.
(phone) 1-410-516-5497
(e-mail) mkjee@pha.jhu.edu

Lisa De Nike
Johns Hopkins University, Baltimore, Md.
(phone) 443-287-9906
(e-mail) lde@jhu.edu

Source: HubbleSite - Newsdesk

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Hubble Finds Dark Matter Ring in Galaxy Cluster

News Release Number: STScI-2007-17

ABOUT THIS IMAGE:

This Hubble Space Telescope composite image shows a ghostly "ring" of dark matter in the galaxy cluster Cl 0024+17.

The ring-like structure is evident in the blue map of the cluster's dark matter distribution. The map is superimposed on a Hubble image of the cluster. The ring is one of the strongest pieces of evidence to date for the existence of dark matter, an unknown substance that pervades the universe.

The map was derived from Hubble observations of how the gravity of the cluster Cl 0024+17 distorts the light of more distant galaxies, an optical illusion called gravitational lensing. Although astronomers cannot see dark matter, they can infer its existence by mapping the distorted shapes of the background galaxies. The mapping also shows how dark matter is distributed in the cluster.

Astronomers suggest that the dark-matter ring was produced from a collision between two gigantic clusters.

Dark matter makes up the bulk of the universe's material and is believed to make up the underlying structure of the cosmos.

The Hubble observations were taken in November 2004 by the Advanced Camera for Surveys (ACS). Thanks to the exquisite resolution of the ACS, astronomers saw the detailed cobweb tracery of gravitational lensing in the cluster.

Object Names: CL0024+17, ZwCl 0024+1652

Image Type: Astronomical

Credit: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)

Source: HubbleSite - Newsdesk

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Searching for Dark Matter in a Galaxy Cluster

News Release Number: STScI-2007-17

ABOUT THIS IMAGE:

This rich galaxy cluster, catalogued as Cl 0024+17, is allowing astronomers to probe the distribution of dark matter in space. The blue streaks near the center of the image are the smeared images of very distant galaxies that are not part of the cluster. The distant galaxies appear distorted because their light is being bent and magnified by the powerful gravity of Cl 0024+17, an effect called gravitational lensing.

Dark matter cannot be seen because it does not shine or reflect light. Astronomers can only detect its influence by how its gravity affects light. By mapping the distorted light created by gravitational lensing, astronomers can trace how dark matter is distributed in the cluster. While mapping the dark matter, astronomers found a dark-matter ring near the cluster's center. The ring's discovery is among the strongest evidence that dark matter exists.

The Hubble observations were taken in November 2004 by the Advanced Camera for Surveys.

Object Names: CL0024+17, ZwCl 0024+1652

Image Type: Astronomical

Credit: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)

Source: HubbleSite - Newsdesk

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Two Views of Interacting Galaxy Clusters

News Release Number: STScI-2007-17

Image Type: Illustration

Credit: NASA, ESA, M.J. Jee (Johns Hopkins University), and A. Feild (STScI)

Source: HubbleSite - Newsdesk

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Cartwheel Galaxy

News Release Number: STScI-2007-17

ABOUT THIS IMAGE:

A rare and spectacular head-on collision between two galaxies appears in this NASA Hubble Space Telescope true-color image of the Cartwheel Galaxy, located 500 million light-years away in the constellation Sculptor. The new details of star birth resolved by Hubble provide an opportunity to study how extremely massive stars are born in large fragmented gas clouds.

The striking ring-like feature is a direct result of a smaller intruder galaxy — possibly one of two objects to the right of the ring — that careened through the core of the host galaxy. Like a rock tossed into a lake, the collision sent a ripple of energy into space, plowing gas and dust in front of it. Expanding at 200,000 miles per hour, this cosmic tsunami leaves in its wake a firestorm of new star creation. Hubble resolves bright blue knots that are gigantic clusters of newborn stars and immense loops and bubbles blown into space by exploding stars (supernovae) going off like a string of firecrackers.

The Cartwheel Galaxy presumably was a normal spiral galaxy like our Milky Way before the collision. This spiral structure is beginning to re-emerge, as seen in the faint arms or spokes between the outer ring and bulls-eye shaped nucleus. The ring contains at least several billion new stars that would not normally have been created in such a short time span and is so large (150,000 light-years across) our entire Milky Way Galaxy would fit inside.

Object Names: Cartwheel Galaxy, ESO 350-40, AM0035-335

Image Type: Astronomical

Credit: NASA, ESA, and K. Borne (STScI)

Source: HubbleSite - Newsdesk