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.

6a00d8341bf7f753ef01b7c702511b970b

Hubble Image of Galactic Collision 

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

andromeda_compressed

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.”

Featured Image -- 838

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

New Signal May Be Evidence of Dark Matter


Space-Planets-Homeworld-Space-Planets-Universe-1152x2048

(Click Image to Doanload)

Scientists say they may have discovered a possible dark matter signal coded in the X-rays emanating from two bright objects in the sky.

The findings, set to be published next week in Physical Review Letters, could offer tangible evidence for the existence of dark matter — and help researchers build new tools to search for and study this mysterious stuff.

When it comes to matter in the universe, dark matter is like a backroom political power broker: You never see it, but behind the scenes, it’s been throwing its weight around. The effects of its gravitational influence can be seen in the large-scale structures of the cosmos. Dark matter makes up about 84.5% of the matter in the universe while all the stuff we actually see — stars, galaxies, planets, ourselves — makes up the remaining 15.5%. The enormous galaxies and clusters of galaxies that populate the universe are bantamweights compared to the massive, unseen dark matter ‘halos’ that anchor them.

Dark matter’s formidable gravitational influence is the only way that the strange stuff can be detected, because it’s invisible — it does not interact with light. Physicists have no idea what it’s made of, although they’ve looked for it by building detectors in underground former gold mines, sending satellites into space and other methods.

But now, a team led by researchers at Leiden University in the Netherlands and the École Polytechnique Fédérale de Lausanne in Switzerland say they’ve discovered a signal that could be a sign of dark matter.

The scientists looked at X-ray emissions coming from the Andromeda galaxy and the Perseus galaxy cluster, collected by the European Space Agency’s XMM-Newton space telescope. After accounting for all the light particles (called photons) emanating from known sources in the Andromeda galaxy, they were left with a strange set of photons that had no known source. The found the same light signature emanating from the Perseus cluster. And when they turned their attention to the Milky Way, they found signs of this signal in our home galaxy, as well.

“It is consistent with the behavior of a line originating from the decay of dark matter particles,” the authors wrote in a pre-print of the study.

This weird light signal, they think, could be coming from the destruction of a hypothetical particle called a sterile neutrino (which, if it exists, might help explain dark matter). But it’s going to take a lot of follow-up study to determine whether this signal is a scientific breakthrough or an anomalous blip.

“Future detections or non-detections of this line in multiple astrophysical targets may help to reveal its nature,” the study authors wrote.

Japan’s upcoming Astro-H mission, they said, might allow them to do just that.

Source :Science Tech Today