jueves, 27 de octubre de 2011

Astronomy - Enigmatic Radio-Waves Near Milky-Way's Central Region May Hold Clues to Enduring Mystery


Twenty years ago, astronomers discovered a number of enigmatic radio-emitting filaments concentrated near the center of the Milky Way Galaxy. These features initially defied explanation, but a new study of radio images of the Galactic center may point to their possible source. These mysterious "filaments" of radio-wave emission may hold the ultimate proof of the existence of dark matter, researchers have said. A recent report suggests the filaments' emission arises from dark matter particles crashing into each other.

The filaments --regions of high magnetic fields that emit radio waves of high frequency--have been a mystery to astronomers since they were first discovered in the 1980s. The region within 900 light-years of the Milky Way Galaxy's core is crisscrossed with glowing filaments 1 to 3 light-years thick and 10 to 100 light-years long. They are a recent discovery, known only since the invention of modern radio and infrared telescopes that can "see" through the visually opaque dust clouds shrouding the galaxy core. The latest radio telescope probes of this region show that the filaments are associated with pockets of star-formation.

"There's a long literature about these objects, and there have been some ideas as to what might generate their emission - but frankly no one really knows," said Dan Hooper, an astrophysicist at the Fermi National Accelerator Laboratory (Fermilab) in the US and co-author of the paper, which is under review by academics.

One explanation for this emission would be what is called synchrotron radiation, which arises when charged particles are accelerated in a magnetic field. There are several ideas that could account for the emission which do not invoke dark matter - so called "astrophysical" mechanisms.

Dan Hooper and his colleagues suggest that electrons created when high-energy dark matter particles collide into each other could be clue the what gives rise to the synchrotron radiation detected here on Earth.

"One thing it explains that the astrophysical possibilities don't is that the filaments that are closer to the galactic center are brighter than those that are farther away," Dr Hooper told BBC News. "We would say that's because there's more dark matter as you come closer to the galactic centre - it provides a natural explanation for that."

In the model that the team has developed, the electrons in all the filaments that were studied should have a high energy - between five and 10 billion electron volts (GeV).

"The question is: why would all of these filaments which are different astrophysically, contain different stuff, located in different places - all sorts of different properties - all have electrons with that much energy?" said Hopper. "In the dark matter explanation, that's easy - dark matter is the same everywhere."

"That's definitely one of the strengths of this model; the results seem promising," Sukanya Chakrabarti, an astrophysicist from the University of California, Berkeley told BBC.

However, theoretical models of a substance that has never been detected necessarily require a number of educated guesses and estimates - guesses that could radically affect whether or not a given theory stands up.

Dark matter particles of energies as high as 10 GeV are in severe conflict with the recent results reported by the Fermi-LAT collaboration at the Rome Fermi symposium for an analysis of nearby dwarf spheroidal galaxies.

The results from detections in underground experiments on Earth are also not widely agreed to point to a dark matter explanation, but Hooper said forthcoming results from the Cresst experiment in Italy will lend further credence to his team's theory.

"Many of these filaments have only limited data available about them," said Dr Hooper. "I hope this paper inspires radio astronomers to look more carefully at these objects."

Filaments The combined radio image (left) from the Very Large Array and Green Bank Telescope. The linear filaments near the top are some of the nonthermal radio filaments (NRFs) studied by the researchers. Other features, such as supernova remnants (SNRs) and the area surrounding our Galaxy's supermassive black hole (Sgr A) are shown.

Image Credits: Credit: NRAO/AUI/NSF
Source: The Daily Galaxy - BBC and physicstoday.org

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