Of Gamma Ray Bubbles and Dark Matter

MILKY WAY’S GAMMA RAY BUBBLES SHAPED BY DARK MATTER?

Amy Shira Teitel
Analysis by Amy Shira Teitel
Tue May 8, 2012 11:37 AM ET

Gamma-ray-bubbles

Dark matter, the elusive stuff that makes up a substantial portion of all the mass in the universe, is largely a mystery to astronomers. They’ve tried finding it and creating it, but so far no conclusive proof as to what exactly it is though most theories state that we interact with it through gravity.

But Christoph Weniger, of the Max Planck Institute for Physics in Munich, has a different theory to explain new possible evidence for dark matter. By carrying out statistical analysis of three and a half years worth of publicly available data from NASA’s Fermi Space Telescope, he’s found a gamma ray line across the sky that he says is a clear signature of dark matter.

Astrophysicists generally think that supermassive black holes, like the one at the center of the Milky Way, release jets that interact with surrounding dark matter. This interaction is thought to be the source of high-energy gamma rays that satellites like Fermi can detect. What satellites can see are the photons produced when these jets interact with dark matter.

Weniger looked for signs of such an interaction in about three and a half years worth of gamma-ray observations carried out by the Fermi satellite’s Large Area Telescope (LAT).

To increase his chances of success he only considered data from those regions of the Milky Way that should generate the highest ratios of dark-matter photons to photons from background sources. He was looking specifically for a peak in energy, a sign that a photon was produced by the collision between and annihilation of two particles; the photon left over should have the same mass as one dark matter particle. This energy would theoretically appear as a very narrow peak, a line in gamma-ray spectra, distinct from the broad energy distribution seen across the visible universe.

That’s just what he found — a line in the gamma ray spectrum.

But he’s quick to admit it’s a provisional result. His data points come from about 50 photons and he’ll need a lot more to prove conclusively that his line is related to dark matter. It’s possible the line he observed is from a known, though no less mysterious, astronomical phenomenon: the pair of enormous gamma-ray-emitting bubbles extending outwards from the plane of the Milky Way.

In December 2010, scientists working with the Fermi Space Telescope found two giant lobes extending from the black hole at the center of our galaxy.

Twenty-five thousand light years high, each bubble spans more than half of the visible sky reaching from the constellation Virgo to the constellation Grus and may be relatively young at just a million or so years old.

The bubbles are a recent find, normally masked by the fog of gamma rays that appears throughout the sky that is a result of particles moving near the speed of light interacting with light and interstellar gas in the Milky Way. Scientists only found the bubbles by manipulating the data from the LAT to draw out the striking feature.

The manipulated images show the bubbles have well defined edges, suggesting they were formed as a result of a large and relatively rapid energy release — the source of which is still unknown. Interestingly, the energy cutoff of the bubbles corresponds to the gamma ray line Weniger found, the one he’s associating with a dark matter signature.

It’s possible the bubbles and the line have the same origin. Or, dark matter might be the cause of the bubbles’ defined endpoint.

Whether or not the two observations turn out to be linked — which of course hinges on conclusive proof of Weniger’s gamma ray line — both are very cool and part of the fascinating and mystery nature of our corner of the universe.

Image credit: NASA-Goddard

from:   http://news.discovery.com/space/dark-matter-and-gamma-ray-lobes-light-up-the-visible-universe-120508.html

Black Holes Before the Big Bang? New Theory

“Some Primordial Black Holes Have Existed Before the Big Bang” — A Radical Theory Proposed

 

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In recent years, cosmologists have begun to think seriously about processes that occurred before the Big Bang. Alan Coley from Canada’s Dalhousie University and Bernard Carr from Queen Mary University in London, published a paper in 2011, where they theorized that some so-called primordial black holes might have been created in the Big Crunch that came before the Big Bang, which supports the theory that the Big Bang was not a single event, but one that occurs over and over again as the Universe crunches down to a single point, then blows up again.

In some circumstances, they say, black holes of a certain mass could avoid this fate and survive the crunch as separate entities. The masses for which this is possible range from a few hundred million kilograms to about the mass of our Sun.

The theory is based on the fact that the Earth, and the rest of the known Universe is occasionally bombarded with unexplained bursts of gamma rays — something that could, according to Coley and Carr, be the result of primordial black holes running out of energy and disintegrating. These small black holes ought to evaporate away in relatively short period of time, finally disappearing in a violent explosion of gamma rays. Some cosmologists say this thinking might explain the gamma ray bursts that we already see from time to time.

Primordial black holes are thought to be of a different type than the regular kind that are formed when a supernova occurs but rather formed in the first “moments” after the Big Bang. Primordial black holes would be smaller and created by the energy of the Big Bang itself and would then have been widely dispersed as the Universe expanded.

In their theory, however, Coley and Carr suggest that some of these black holes, if they actually exist, might have been created by the collapsing Universe as part of the Big Crunch, and then somehow escaped being pulled into the pinpoint singularity comprised of everything else. And then, after the Big Bang, they simply assimilated with the newly formed Universe.

A key problem they agree on is that it would likely be impossible to tell the difference between pre- and post Big Bang primordial black holes.

The theory raises major questions for cosmologists: if the Universe contracts, then blows up, over and over, has this gone on forever? Or is it possible that our view of the Universe is so limited that we’re only seeing one tiny fraction of it, and thus, any theories or explanations we offer, are little more than guesses.

Image at the top of page shows co-orbiting supermassive black holes powering the giant radio source 3C 75. Surrounded by multimillion degree x-ray emitting gas, and blasting out jets of relativistic particles the supermassive black holes are separated by 25,000 light-years. At the cores of two merging galaxies in the Abell 400 galaxy cluster they are some 300 million light-years away.
Such spectacular cosmic mergers are thought to be common in crowded galaxy cluster environments in the distant Universe. In their final stages the mergers are expected to be intense sources of gravitational waves.

More information: Persistence of black holes through a cosmological bounce, B. J. Carr, A.A. Coley, arXiv:1104.3796v1 [astro-ph.CO] http://arxiv.org/abs/1104.3796

The Daily Galaxy via MIT Technology Review

from site:    http://www.dailygalaxy.com/my_weblog/2012/03/some-primordial-black-holes-have-existed-before-the-big-bang-a-radical-theory-says-yes.html#more

 

Strange Signals fr/the Crab Nebula

Shattered Star Sends Mysterious Signal

Shattered Star Sends Mysterious SignalCredit: NASA/JPL-Caltech/R. Gehrz (University of Minnesota)The Crab Nebula, the leftovers of a star that went out in a supernova in 1054, is sending out strange signals that scientists can’t fully explain. According to research published in the Oct. 7, 2011 issue of the journal Science, astronomers have detected pulsed gamma rays from the neutron star within the nebula that are far higher than the scientists expected.

The pulsed gamma rays have energies between 100 billion and 400 billion electronvolts, far higher than the 25 billion electronvolts previously detected. A 400 billion electronvolt photon is almost a trillion times more energetic than the photons that make up visible light. Explaining this high energy is going to require major adjustments to astronomers’ theories of the energy interactions in the nebula.

“The finding shows that the theory is not there yet,” said study researcher Henric Krawczynski, a professor of physics at Washington University in St. Louis. “We know less about these systems than we thought.”

from:    http://www.livescience.com/1-image-day.html