What Is Dark Matter? Colliding Galaxy Clusters May Help Find Answer


Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but accounts for most of the matter in the universe.  Dark matter is estimated to constitute 84.5% of the total matter in the universe. It has not been detected directly, making it one of the greatest mysteries in modern astrophysics.

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Hubble Image of Galactic Collision 

A study of 72 large cluster collisions shows how dark matter in galaxy clusters behaves when they collide.

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Image Showing How two Galaxies Collides

Astronomers have used data from NASA’s Hubble Space Telescope and the Chandra X-ray Observatory to find that dark matter interacts with itself less than previously thought. In an effort to learn more about dark matter, astronomers observed how galaxy clusters collide with each other — an event that could hold clues about the mysterious invisible matter that makes up most of the mass of the universe.

As part of a new study, published in the journal Science on Thursday, researchers used the Hubble telescope to map the distribution of stars and dark matter after a collision. They also used the Chandra observatory to detect the X-ray emission from colliding gas clouds.

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

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Here are images of six different galaxy clusters taken with NASA’s Hubble Space Telescope (blue) and Chandra X-ray Observatory (pink) in a study of how dark matter in clusters of galaxies behaves when the clusters collide. A total of 72 large cluster collisions were studied.  NASA and ESA

According to scientists, galaxy clusters are made of three main components — galaxies, gas clouds and dark matter. During collisions, the gas clouds bump into each other and gradually slow down. Galaxies, on the other hand, are much less affected by this process, and because of the huge gaps between the stars within them, galaxies do not slow each other down.

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

The researchers studied 72 large galaxy cluster collisions and found that, like galaxies, the dark matter continued straight through the collisions without slowing down much, meaning that dark matter do not interact with visible particles.

“There are still several viable candidates for dark matter, so the game is not over. But we are getting nearer to an answer,” Harvey said.

Source : IBT times

ALMA Identifies Gas Spirals as a Nursery of Twin Stars


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With new Atacama Large Millimeter/submillimeter Array (ALMA) observations, astronomers led by Shigehisa Takakuwa, Associate Research Fellow at the Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA), Taiwan, have found spiral arms of molecular gas and dust around “baby twin” stars. Gas motions supplying materials to the twin were also identified. These results unveil for the first time, the mechanism of the birth and growth of binary stars, which are ubiquitous throughout the Universe. The study was published on November 20 in The Astrophysical Journal.

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Fig 1. Gas and dust disks around L1551 NE spotted by ALMA. Credit: ALMA (ESO/NAOJ/NRAO) / Takakuwa et al.

Stars form in interstellar clouds of molecular gas and dust. Previous studies of star formation focused primarily on single stars like the Sun, and a standard picture of single star formation has been established. According to this picture, a dense gas condensation in an interstellar cloud collapses gravitationally to form a single protostar at the center. Previous observations have found such collapsing gas motions feeding material toward the central protostars.

Compared to single star formation, our understanding of binary star formation has been limited, even though more than half of stars with a mass similar to that of the Sun are known to be binaries. It is thus crucial to observe the physical mechanism of binary formation to obtain a more comprehensive understanding of star formation. Theory suggests that a disk surrounding a young binary will feed material to the central “baby twin” in order for them to grow. While recent observations have found such disks (known as “circumbinary disks”), it was not possible to image the structure and gas motions because of the insufficient imaging resolution and sensitivity.

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Fig 2. Comparison of the disks in simulation and observation. The right panel shows the disk image simulated with ATERUI, and the left panel the real ALMA image. Credit: ALMA (ESO/NAOJ/NRAO)/ Takakuwa et al.

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