Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Astronomers have the first direct proof that dark matter exists

22.08.2006
University of Arizona astronomers and their colleagues got side-on views of two merging galaxy clusters in observations made with state-of-the-art optical and X-ray telescopes.

"Nature gave us this fantastic opportunity to see hypothesized dark matter separated from ordinary matter in this merging system," said UA Steward Observatory astronomer Douglas Clowe, leader of the study.

"Prior to this observation, all of our cosmological models were based on an assumption that we couldn't prove: that gravity behaves the same way on the cosmic scale as on Earth," Clowe said. "The clusters we've looked at in these images are a billion times larger than the largest scales at which we can measure gravity at present, which are on the scale of our solar system."

Clowe added, "What's amazing about this is that the process of galaxy clusters merging is thought to go on all of time. That's how galaxy clusters gain mass. But the fact that we caught this thing only 100 million years after it occurred -- so recently that it barely registers on the cosmic time scale -- is tremendous luck."

Astronomers have known since the 1930s that most of the universe must be made up of something other than normal matter, the stuff that makes stars, planets, all things and creatures. Given the way that galaxies move through space and scientists' understanding of gravity, astronomers theorize that the universe must contain about five times more dark matter than normal matter.

But for the past 70 years, no one had any direct empirical evidence that dark matter even exists.

"Astronomers have been in the somewhat embarrassing position of saying that we understand the universe, although more than 80 percent of it is something we don't know anything about," said UA astronomy Professor Dennis Zaritsky, a member of the discovery team.

"Either most of the matter in the universe is in some invisible, undiscovered form we call 'dark matter' that causes galaxies to move as they do, or we just don't understand the fundamental laws of gravity," Zaritsky said.

When galaxy clusters merge, the galaxies themselves are so sparsely scattered in space that they don't collide, Clowe said. "Even if two galaxies do pass through each other, the distance between the stars is so great that even stars won't collide. Galaxies basically plow through each other almost without slowing down."

Most of a galaxy cluster's normal mass is in its diffuse hot gas. Galaxy clusters typically contain 10 times as much ordinary mass in gas as in stars. So when galaxy clusters merge, the hot gas from each cluster exerts a drag force on the other, slowing all the gas down, Clowe said.The upshot is that the galaxies themselves continue speeding through space, leaving the gas behind.

Observations made with NASA's Chandra X-ray Observatory showed the bulk of ordinary matter is in the hot gas clouds left in the wake of the galaxies. Part of this million-degree plasma of hydrogen and helium, the part from the smaller cluster, forms a spectacular bullet-shaped cloud because a bow shock, or supersonic shock wave, is created in the 10 million mph collision.

But when the astronomers mapped the region of the sky around the galaxies in optical light, they discovered far more mass near the galaxies, ahead of the gas cloud. They analyzed gravitational lensing of distant galaxies in images taken with NASA's Hubble Space Telescope, the European Southern Observatory's 2-meter Wide-Field Imager and one of the twin 6.5-meter Magellan telescopes that a consortium that includes UA operates in Chile.

Gravitational lensing is a phenomenon caused by gravity bending distant starlight. When the astronomers analyzed the shapes and patterns of the distorted light, they discovered the mass of non-luminous, or dark, matter that causes the lensing is far greater than the mass of ordinary matter in the gas cloud.

Clowe and Zaritsky said that dark matter particles are not expected to interact with either normal matter or dark matter particles except through gravity. Hence, they would pass through the collision just as galaxies do.

"We see that dark matter has careened through the collision efficiently," Zaritsky said.

"We're actually using this system to test the idea that dark matter particles are collisionless," Clowe said.

"The bottom line is, there really is dark matter out there," Zaritsky said. "Now we just need to figure out what it is."

The team is publishing the research in a forthcoming issue of the Astrophysical Journal Letters. In addition to Clowe and Zaritsky of UA's Steward Observatory, team members include Marusa Bradac of the Kavli Institute for Particle Astrophysics and Cosmology in Stanford, Calif., Anthony Gonzalez of the University of Florida, and Maxim Markevitch, Scott Randall and Christine Jones of the Harvard-Smithsonian Center for Astrophysics.

Lori Stiles | University of Arizona
Further information:
http://www.arizona.edu
http://chandra.harvard.edu
http://chandra.nasa.gov

More articles from Physics and Astronomy:

nachricht First Juno science results supported by University of Leicester's Jupiter 'forecast'
26.05.2017 | University of Leicester

nachricht Measured for the first time: Direction of light waves changed by quantum effect
24.05.2017 | Vienna University of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>