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NASA's Hubble, Chandra Find Clues that May Help Identify Dark Matter

For Release: March 26, 2015


Six Galaxy Clusters
Credit: X-ray: NASA/CXC/Ecole Polytechnique Federale de Lausanne, Switzerland/D.Harvey & NASA/CXC/Durham Univ/R.Massey; Optical & Lensing Map: NASA, ESA, D. Harvey (Ecole Polytechnique Federale de Lausanne, Switzerland) and R. Massey (Durham University, UK)
Press Image and Caption

Using observations from NASA's Hubble Space Telescope and Chandra X-ray Observatory, astronomers have found that dark matter does not slow down when colliding with itself, meaning it interacts with itself less than previously thought. Researchers say this finding narrows down the options for what this mysterious substance might be.

Dark matter is an invisible matter that makes up most of the mass of the universe. Because dark matter does not reflect, absorb or emit light, it can only be traced indirectly by, such as measuring how it warps space through gravitational lensing, during which the light from a distant source is magnified and distorted by the gravity of dark matter.

The leading theory is dark matter is spread throughout clusters of galaxies and is frequently very close to each other. To learn more about dark matter and test such theories, researchers study it in a way similar to experiments on visible matter -- by watching what happens when it bumps into other objects. In this case, the colliding objects under observation are galaxy clusters.

Researchers used Hubble and Chandra to observe these space collisions. Specifically, Hubble was used to map the distribution of stars and dark matter after a collision, which was traced through its gravitational lensing effect on background light. Chandra was used to detect the X-ray emission from colliding gas clouds. The results are published in the March 27 edition of the journal Science.

"Dark matter is an enigma we have long sought to unravel," said John Grunsfeld, assistant administrator of NASA's Science Mission Directorate in Washington. "With the combined capabilities of these great observatories, both in extended mission, we are ever closer to understanding this cosmic phenomenon."

Galaxy clusters are made of three main ingredients: galaxies, gas clouds, and dark matter. During collisions, the gas clouds surrounding galaxies crash into each other and slow down or stop . The galaxies are much less affected by the drag from the gas and, because of the huge gaps between the stars within them, do not slow each other down.

"We know how gas and stars react to these cosmic crashes and where they emerge from the wreckage. Comparing how dark matter behaves can help us to narrow down what it actually is," said the study's lead author David Harvey of the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland.

Harvey and his team studied 72 large cluster collisions. The collisions happened at different times and were viewed from different angles -- some from the side, and others head-on.

The team found that, like the galaxies, the dark matter continued straight through the violent collisions without slowing down. This means dark matter does not interact with visible particles and flies by other dark matter with much less interaction than previously thought. Had the dark matter dragged against other dark matter, the distribution of galaxies would have shifted.

"A previous study had seen similar behavior in the Bullet Cluster," said team member Richard Massey of Durham University in the United Kingdom. "But it's difficult to interpret what you're seeing if you have just one example. Each collision takes hundreds of millions of years, so in a human lifetime we only get to see one freeze-frame from a single camera angle. Now that we have studied so many more collisions, we can start to piece together the full movie and better understand what is going on."

With this discovery, the team has successfully narrowed down the properties of dark matter. Particle physics theorists now have a smaller set of unknowns to work around when building their models.

"It is unclear how much we expect dark matter to interact with itself because dark matter already is going against everything we know," said Harvey. "We know from previous observations that it must interact with itself reasonably weakly." Dark matter may have rich and complex properties, and there are still several other types of interactions to study. These latest results rule out interactions that create a strong frictional force, causing dark matter to slow down during collisions.

The team also will study other possible interactions, such as dark matter particles bouncing off each other like billiard balls and causing dark matter particles to be ejected from the clouds by collisions or for dark matter blobs to change shape. The team also is looking to study collisions involving individual galaxies, which are much more common.

"There are still several viable candidates for dark matter, so the game is not over. But we are getting nearer to an answer," said Harvey. "These astronomically large particle colliders are finally letting us glimpse the dark world all around us, but just out of reach."

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

An interactive image, a podcast, and a video about the findings are available at:

For more Chandra images, multimedia and related materials, visit:

Media contacts:
Felicia Chou
Headquarters, Washington

Ray Villard
Space Telescope Science Institute, Baltimore, Md.

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.

Visitor Comments (26)

I propose that the gravitational anomalies we observe and lead to speculation of "dark matter" are caused by the presence of a parallel universe, overlapping with our universe. This parallel universe was formed - like our own- after the "Big Bang" in the interuniversal medium IUM . It is of the "multiverse 2" type and does not lie beyond our horizon- as is commonly assumed.

Posted by Dr Rudi D Neirinckx on Saturday, 04.1.17 @ 17:34pm

I am 82 years old, and for the last 60 years I have been contemplating where does Gravity get its Energy from. I am well aware of all the usual answers given. I have come to the conclusion that dark matter energy is the energy gravity requires. The entire universe
is contained in a sea of dark m e. We should be concentrating on Gravity.

Posted by George Eames on Friday, 12.30.16 @ 16:57pm

To go along with Mr. Stephen, I can see that dark energy created and destroyed is a possibility. Now with that, what determines the creation destruction of the energy? Many things can be said, great article.

Posted by Igy on Tuesday, 12.13.16 @ 03:08am

I think dark matter could be the walls of universe having a extremely strong gravitational field. The gravity could be so much strong that it would even absorb light and since the light is not reflected back it appears dark to us.

Posted by Tarun Suryawanshi on Thursday, 12.1.16 @ 09:14am

In my opinion, dark matter is the opposite of "normal" matter and dark energy is the opposite of the "normal" energy we are accustomed to. Therefore, if what we have discovered in the past about the laws and properties of matter and energy is true, then the equivalent that violates those laws and properties is dark matter. Eg if matter can neither be created nor destroyed then dark matter can be created and destroyed etc. Let's try to unlearn or twist this in an attempt to unravel the mystery.

Posted by Stephen Makanga on Tuesday, 06.21.16 @ 14:08pm

No, the blue coloring of dark matter in the images is not photographic or observed, it is applied by the researchers so that we can see the mapping of the dark matter. The dark matter is invisible and only detected by gravitational lensing. The lensing enables researchers to map it, and the mapping is colored blue so we can see it.

Posted by Chris Perrius on Friday, 06.3.16 @ 15:36pm

The article says that they are combining x-ray light with visible light. The blue is visible light not dark matter. That is why it is labeled optical.

Posted by Brandon Turner on Tuesday, 01.12.16 @ 22:53pm

What is the genesis of Dark Matter?
Why call this phenomenon Dark Matter?

Posted by J Yarkpazuo Wolobah, Jr. on Friday, 01.8.16 @ 08:37am

Pijush Banerjee
Given that Dark Matter is still beyond our technology to detect, our observations are based on the gravitational effect on surrounding matter. while theoretically possible that thermal increases would be detectable, our current lack of understanding in the full nature of DM makes a change in thermal properties similarly undetectable, we would have to observe thermal changes in surrounding matter, which are already being affected by the collisions themselves.

Posted by William Bowers on Tuesday, 12.8.15 @ 18:30pm

Following on from what Alex said, is it possible that the moving mass of galaxies warps space time which causes these unexplainable observations of light?

Posted by Tom on Monday, 12.7.15 @ 10:00am

Has dark matter and dark energy been viewed as maybe the same substance, having similar properties to water which can be a vapor, liquid or solid? Could it all be dark energy but be transformed into dark matter as gravity compresses it? Also if the universe was started by one big bang and everything spreads out in a circular motion do all the calculations being made take it account the fact that what we can observe is only a very, very small slice of a much bigger pie and wouldn't each supernova in a sense be a small new big bang in its own right?

Posted by scott on Sunday, 12.6.15 @ 04:35am

What do these observations tell us about what dark matter could be made of?

Posted by Clare Knowles on Friday, 11.13.15 @ 15:45pm

What about dark matter just being areas where there is no space time. Wouldn't those pockets still look like they bend light?

Posted by Alex Anelon on Saturday, 10.10.15 @ 03:17am

The majority of baryons created at atom formation were hydrogen and helium and most of the hydrogen rapidly became molecular. As we are unable to see radiation from molecular hydrogen and helium at astronomical distances, these may account for dark matter.

Posted by Brian Cook on Wednesday, 09.30.15 @ 15:11pm

Matter has to clump together in order to form clouds and stars. Any matter that has not been swept up in this way would be dark but still have effects on acceleration of the universe etc.

Could it be the case that in most of space matter has not clumped together sufficiently to be seen, so is still dark?

Posted by John Rayment on Friday, 09.25.15 @ 09:57am

The blue areas in the image shown to be dark matter are actually computer simulations of where it thinks dark matter is distributed Modelled by observing gravitational lensing.

Posted by Alex on Wednesday, 09.23.15 @ 10:29am

Maybe I just misinterpreted something, but how can we see dark matter if it's dark? It doesn't make sense. Dark matter is invisible, but we know it's there because of its physical effects. But I'm just a 17 year old, so what do I know.

Posted by Christian on Monday, 09.14.15 @ 17:52pm

During collision if gases become very hot can't the Dark matter because they are more dense?

Posted by Pijush Banerjee on Tuesday, 09.8.15 @ 09:35am

Dark invisible energy-matter can be seen surrounding star clusters, from your photos, reflecting light from the stars and varying their density with distance from the center.
The universe and beyond is made of high-energy particles continually in contact with each other varying in density from invisible billions per cc in space to solids requiring trillions per mm 3 in the core of black holes.

Posted by don hill on Tuesday, 09.1.15 @ 23:05pm

Sir, I want to know about dark energy in details. Also I want to research on this subject.

Posted by surajit das on Friday, 08.28.15 @ 15:00pm

As the building blocks of the universe are broken down and defined, so are the assumptions that were used to discover them.

Posted by Chris on Sunday, 06.14.15 @ 08:26am

I am 17, a Jr in high school alternative. My comment may be irrelevant to the conversation, but I would actually like to learn more of dark matter and dark energy.
Can anyone show me to an accurate source that can show me any and all studies on dark matter or dark energy from any early research to any research that has come up in recent years?

Posted by Daniel Castillo on Wednesday, 05.27.15 @ 15:40pm

Sorry, I must be a bit dim today but in what sense is the dark matter blue? I thought the dark matter was dark i.e. black. Can someone explain this? I am feeling like an idiot at the moment.

Posted by Chris on Sunday, 05.24.15 @ 10:22am

To all contributors of this information
Thank you a lot about this article. All your information very excited. Always will be a pleasure explore knowledge with you.

Posted by sergio flores on Thursday, 04.9.15 @ 20:56pm

If, as was described in News Articles about this finding, it is the case that Dark Matter has very little interaction with itself as it passes through itself, how is it that the Blue areas showing the Dark Matter have central points in the clouds which are more dense than the outside, as if it was gravitationally effecting itself like normal matter would.
If it had little to no effect on itself, surely it would be more uniformly distributed.

Posted by David on Wednesday, 04.1.15 @ 15:10pm

Has anyone proposed a theory of dark matter being a product of black hole emissions? Perhaps an exotic particle produced constantly when black holes are created and afterwards during their lifetime.

Posted by Jim on Wednesday, 04.1.15 @ 13:33pm