Very cool... more evidence of Dark Matter!!
Offline Public release date: 16-May-2007
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Contact: Lars Lindberg Christensen
[email protected]
49-893-200-6306
European Space Agency
Hubble sees dark matter ring in a galaxy cluster
 This Hubble Space Telescope composite image shows a ghostly 'ring' of dark matter in the galaxy cluster ZwCl0024+1652. The ring-like structure is evident in the blue map of the cluster's... Click here for more information. |
A team of astronomers used the Hubble Space Telescope to find the best evidence yet for the existence of dark matter, present in the form of a ghostly ring in a galaxy cluster.
The ring had formed long ago during a titanic collision between two massive galaxy clusters. The team's discovery, to be published on 1 June 2007 in the Astrophysical Journal, represents the first record of dark matter distribution that differs substantially from the distribution of ordinary matter.
The cluster ZwCl0024+1652 (referred to as Cl 0024+17 in the publication) is located 5 thousand million light-years away from Earth. The ring, which measures 2.6 million light-years across, was found unexpectedly while the team was mapping the distribution of dark matter within the cluster.
Astronomers have long suspected invisible dark matter to be the source of additional gravity that holds galaxy clusters together. If galaxy clusters relied only on the gravity from their visible stars as the binding force, the clusters would fly apart.
Although it is not known what dark matter is made of, it is hypothesised that it is made of a type of elementary particle that pervades the Universe.
"This is the first time we have detected dark matter with a unique structure, different from that of the gas and galaxies in the cluster," said astronomer M. James Jee of Johns Hopkins University, USA, a member of the team that spotted the dark matter ring.
"Although the invisible matter has been found before in other galaxy clusters, dark matter 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 differently it behaves from normal matter."
During the team's analysis of the dark matter, 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 initially annoyed to see the ring because I thought it was an artefact, which would have implied a flaw in the data reduction," Jee explained. "Even after many iterations of the data, I couldn't believe my result. I've looked at a number of clusters and I haven't seen anything like this before."
Curious about why the ring was in the cluster and how it had formed, Jee found previous research that suggested that the cluster had collided with another cluster one to two thousand million 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 3D structure. The study revealed two distinct groupings of galaxy clusters, indicating a collision between both clusters.
Astronomers have a head-on view of the collision because it accidentally occurred along Earth's line of sight. From this perspective, the dark-matter structure looks like a ring.
The team created computer simulations showing what happens when galaxy clusters collide. As the two clusters smash together, the dark matter falls to the centre 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 highway.
"By studying this collision, we are seeing how dark matter responds to gravity," said team member Holland Ford, also of Johns Hopkins University. "Nature is performing an experiment for us that we cannot 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 it is not an easy task, because it does not shine or reflect light. Its influence can be detected by its gravitational effects on light. To locate dark matter, astronomers study how faint light from more distant galaxies is distorted or bent into arcs and streaks by the gravity of the dark matter in the foreground. This technique is called gravitational lensing. By mapping the distorted light, the mass of the cluster and the distribution of dark matter can be deduced.
"The collision between the two galaxy clusters created a ripple of dark matter which left distinct footprints in the shapes of the background galaxies," Jee explained.
"It is comparable to looking at pebbles on the bottom of a pond with ripples on the surface. The shape of the pebble appears to change as the ripples pass over them. In a similar manner, galaxies behind the ring show changes in their shape 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 suitable tool for this measurement," said team member Richard White of the Space Telescope Science Institute, USA.
Previous observations of another cluster, 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 away from the hot cluster gas, but the dark matter still followed the distribution of cluster galaxies.
ZwCl0024+1652 is the first cluster to show a dark matter distribution that differs significantly from the distribution of both the galaxies and the hot gas.
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Fascinating.
Best part is the Earth may be in a cosmic shower of dark matter, so we may be able to trap some and confirm it's presence and see what it's made of.
That's exactly what I'm working on. Hopefully we'll get results and I can buy my ticket to Stockholm.
Nam et ipsa scientia potestas est.
Explaining the universe by invoking god is like solving an equation by multiplying both sides with infinity. It gives you a trivial solution and wipes away any real information about the original problem.
I'm curious, how are you trying to detect it? Are you using pure material and hoping for decay due to dark matter?
The funny thing about this finding is the observers were at first annoyed with the ring, because they thought it was flawed data. I love the scientists statement:
"I was initially annoyed to see the ring because I thought it was an artefact, which would have implied a flaw in the data reduction," Jee explained. "Even after many iterations of the data, I couldn't believe my result. I've looked at a number of clusters and I haven't seen anything like this before."
Yeah, they were annoyed that they found cosmic radiation due to the big bang, because it caused interference of their radio equipment.
While I'm not exactly able to post the detector design, I can say that using a pure material and hoping for decay would be a horrible way of going about it. There are far too many factors that can come into play.
The way we're doing it depends entirely on the idea you mentioned earlier. Supposedly dark matter exists in a halo around the galaxy, and supposedly we're in the middle of that halo. As our galaxy moves and our solar system rotates through this halo, we're sailing through this dark matter wind at extraordinarily high velocities...
Nam et ipsa scientia potestas est.
Explaining the universe by invoking god is like solving an equation by multiplying both sides with infinity. It gives you a trivial solution and wipes away any real information about the original problem.
What I'm trying to do is turn off the lights. If dark matter is present, the room will obviously get darker. See you in Sweden.
That's amazing! Wonderful direct evidence for something that seemed so theoretical and vague. It will just be so great if they can figure out what dark matter actually is and get closer to a complete picture of the composition of the universe.
Was that supposed to be a joke, Pineapple?
Lazy is a word we use when someone isn't doing what we want them to do.
- Dr. Joy Brown
No. They call it DARK matter for a reason.
Are you aware of the theory behind it?
Lazy is a word we use when someone isn't doing what we want them to do.
- Dr. Joy Brown
Tilberian, I have seen enough of Cocnuts posts to know, he is just messing with you. He is actually studying astronomy, he HAS to understand what dark matter is, he is just trying to be funny.
Thanks BGH. I was spoiling to tear him a new one if he was going to come in here trying to turn dark matter theory into a weakness for scientific cosmology.
Lazy is a word we use when someone isn't doing what we want them to do.
- Dr. Joy Brown
LOL! I reacted the same way to some of his posts at first.
wow great article, what i read i assume is somewhat outdated. Great to be informed. and very intresting.
This kind of thing really gets me excited. I want to live long enough to hear of something really, really big, you know? If we can actually say what dark matter is, it's hard for me to even start guessing at the implications that would have! It's like Christmas, only Santa Claus is real!
Atheism isn't a lot like religion at all. Unless by "religion" you mean "not religion". --Ciarin
http://hambydammit.wordpress.com/
Books about atheism
yea, same here. I think its great how close we are getting. I think that science will just eventually outdate religion. We are all here to say look ITS ALREADY outdated. lol
A lot of people thought that science had outdated religion as far back as the 19th century. They left one important factor out of their calculations: the human capacity for doublethink.
Lazy is a word we use when someone isn't doing what we want them to do.
- Dr. Joy Brown
I didn't have enough patience to read the article, because I don't think dark matter or energy is real. I think it's just an perfect example of where modern science fails. I think we need to rewrite some laws of motion, to explain these things. I know that we had to create new laws of motion in the microscopic world, so why can't we do so in large scale world, such as galaxies and the universe?
I don't believe in the big bang, because I don't think we need an abstraction known as "dark energy" to explain how "the universe is expanding". Energy doesn't really exist. It's just a mathematical model for explaining how things work.
Trust and believe in no god, but trust and believe in yourself.
But the laws of motion still seem to apply when we look at large structures - it's just that they are behaving as if they have more mass and energy than is apparent to our instruments. Subatomic particles were different - they didn't seem to obey ANY laws of physics consistently.
I think it's a little early to throw the physical law baby out with the apparent anomaly bathwater. Especially given all the experiments that still need to be done to gather enough data to really have some representative understanding of the phenomena.
Lazy is a word we use when someone isn't doing what we want them to do.
- Dr. Joy Brown
Nuff, said.
I don't read the bible because I don't think it real either.
No dark matter? Sorry Gnophilist, there goes your trip to Sweden
Old idea spawns new way to study dark matter
Public release date: 30-May-2007
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Contact: Subo Dong
[email protected]
614-292-6893
Ohio State University
This composite image shows the microlensing event OGLE-2005-SMC-001 as a distant star brightened (left) and dimmed (right) over the summer of 2005, with views taken from two very distant vantage... Click here for more information.
COLUMBUS, Ohio -- An international team of astronomers led by Ohio State University has examined dark matter in the outer reaches of our galaxy in a new way.
For the first time, they were able to employ triangulation -- a method rooted in ancient Greek geometry -- to estimate the location of dark matter and calculate its mass.
The results, reported May 30 at the meeting of the American Astronomical Society in Honolulu, suggest that this technique could help astronomers detect dark matter of a particular mass range for which there were previously no reliable tests.
It could also settle longstanding questions about the composition of dark matter in the outer reaches of the Milky Way -- the so-called galactic "halo."
Dark matter is, by its nature, invisible. But astronomers can watch the sky for those rare moments when dark matter affects visible objects. One such opportunity is a gravitational lensing event -- when one dark object in space acts like a lens to magnify the light from a star shining behind it.
"Astronomers have discovered more than a dozen lensing events that could have been caused by dark matter objects lying in the halo," said team leader Andrew Gould, professor of astronomy at Ohio State. "But because we had no way to estimate their distance, we couldn't tell whether they were really dark objects in our halo, or just garden-variety stars in another galaxy."
This study marks the first time that anyone has triangulated a lensing event by observing it from the ground and from space at the same time.
On Earth, surveyors triangulate an object by observing it from two different vantage points. The two vantage points and the object itself form the vertices of a triangle. Knowing the distance between the vantage points and the angles of the triangle, surveyors can calculate how far away the object is.
To study dark matter, Gould and his team used triangulation a little differently. Over the summer of 2005, they watched a lensing event from two locations: Earth, and NASA's Spitzer Space Telescope, which is orbiting the sun some 25 million miles away. Earth, the Spitzer telescope, and the dark matter formed a giant cosmic triangle.
Credit for discovering the OGLE-2005-SMC-001 microlensing event goes to the Optical Gravitational Lensing Experiment (OGLE) led by Andrzej Udalski. OGLE found the event in its very early phase using the Warsaw Telescope at Las Campanas Observatory in Chile, which enabled intensive follow-up observations from the ground and space
The astronomers didn't measure the angles of the triangle to calculate the distance to the object as a surveyor would on Earth. That's because lensing events are all about timing. The dark matter lens is moving, and so astronomers learn about the lens by watching how quickly the light brightens and fades over a brief few days as the lens passes by. Seen from Earth and from the Spitzer telescope, the peak brightness would occur at slightly different times.
So when Gould and his team triangulated OGLE-2005-SMC-001, they didn't directly measure its distance, but rather the velocity with which it was moving across the sky.
Since astronomers know roughly how fast an object in our galactic halo should be moving, compared to an object in another galaxy -- in this case, the Small Magellanic Cloud (SMC) -- they could infer from the velocity whether the lens was a halo object or an SMC object.
They calculated a 95 percent likelihood that the lens was in the halo. That would place the dark matter some 16,000 light years away from Earth. A light year is the distance light travels in a year -- approximately six trillion miles.
Then, by factoring in other information about the timing of the brightness, they were able to determine that the lens in this case was made of two separate dark objects: one roughly seven times more massive than our sun, and the other three times more massive than our sun. The objects circle each other, separated by a distance roughly the same as that between Jupiter and the sun.
All this calculation adds up to one tantalizing possibility: that the dark matter lenses are black holes.
"If this lens is in the halo, it is a 10 solar-mass black-hole binary, which would be very exciting," said Ohio State doctoral student Subo Dong, lead author of the study. "But we cannot completely rule out the possibility of the lens being in the SMC. In fact, there is still a 5 percent chance that it is a pair of ordinary stars in the neighboring galaxy."
At its outermost edges, the Milky Way retains a halo of material left over from when the galaxy first formed billions of years ago. The halo contains gas and very old stars, but its chief ingredient is dark matter. Most astronomers agree that a small minority of halo dark matter -- no more than 20 percent -- could be made of planets, dim stars, or black holes. These are called Massive Compact Halo Objects, or MACHOs.
But there's a gap in astronomers' knowledge when it comes to detecting MACHOs of a particular mass range -- 10-100 solar masses. For those objects, there have been no reliable methods -- until now.
With a combined mass of about 10 solar masses, the two dark objects that Gould's team detected fall within that range. So the method they used could finally enable astronomers to take a survey of 10-100 solar mass dark objects in the halo.
Dong sees a lot of potential for future discoveries with this observational method.
"It will be very interesting to locate and measure the mass of more dark objects in the future by applying this technique," he said. "And we might finally be able to unravel the mystery of MACHOs."
When astronomer Sjur Refsdal of the Hamburg Observatory in Germany proposed using triangulation to study dark matter in 1966, no one could attempt it, because his technique involved combining at least two separate and distant views of an object. Since the launch of the Spitzer telescope in 2003, researchers have had an opportunity to get the right kind of space-based measurement.
Gould is confident that over the next few years, he and his colleagues will be able to capture a few more lens events with the Spitzer telescope, and will gain a better perspective on the variety of dark objects that may populate the halo. But he also looks forward to a new satellite instrument, NASA's SIM PlanetQuest (formerly the Space Interferometry Mission), now set to launch in 2015, which could provide more answers. Gould is on the SIM science team, and leads the project that will use the satellite to search for lensing events.
"Right now we know with a high probability that these objects we found are in the halo, but with SIM we could just directly measure the distance, as well as the mass of the objects," he said. "We wouldn't be dealing with probabilities anymore."
###For this project, Gould and Dong collaborated with other astronomers at Ohio State, as well as Warsaw University Observatory; Spitzer Science Center and Michelson Science Center, both at the California Institute of Technology; Auckland Observatory; Georgia State University; Notre Dame University; Harvard-Smithsonian Center for Astrophysics; University of California, San Diego; Universidad de Concepción in Chile; the Institute of Astronomy at the University of Cambridge; Princeton University Observatory; and the Observatories of the Carnegie Institute of Washington.
The Jet Propulsion Laboratory (JPL), which is managed by the California Institute of Technology (Caltech), operates the Spitzer Space Telescope; observations taken with this telescope were supported by NASA through a contract issued by JPL and Caltech. Other funding for the study came from the National Science Foundation, the Polish Ministry of Science and Higher Education, and NASA. Some computing resources were provided by Cluster Ohio, an initiative of the Ohio Supercomputer Center (OSC), the Ohio Board of Regents, and the OSC Statewide Users Group.
Contact: Andrew Gould, (614) 292-1892; [email protected] and Subo Dong, (614) 292-6893; [email protected]
Ooooooooooooo!! Ahhhhhhhhhhhhh!!
What a find.
Lazy is a word we use when someone isn't doing what we want them to do.
- Dr. Joy Brown