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Old 11-10-2010, 01:26 AM   #1
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Default Gigantic, mysterious structure in the center of Milky Way (Fermi Bubbles)

Using data from NASA's Fermi Gamma-ray Space Telescope, scientists have recently discovered a gigantic, mysterious structure in our galaxy. This feature looks like a pair of bubbles extending above and below our galaxy's center. Each lobe is 25,000 light-years tall and the whole structure may be only a few million years old.

Source: NASA’s Media Release | Briefing Materials


Click on images to see larger versions
From end to end, the newly discovered gamma-ray bubbles extend 50,000 light-years, or roughly half of the Milky Way's diameter, as shown in this illustration. Hints of the bubbles' edges were first observed in X-rays (blue) by ROSAT, a Germany-led mission operating in the 1990s. The gamma rays mapped by Fermi (magenta) extend much farther from the galaxy's plane. Credit: NASA's Goddard Space Flight Center                                                                 
A giant gamma-ray structure was discovered by processing Fermi all-sky data at energies from 1 to 10 billion electron volts, shown here. The dumbbell-shaped feature (center) emerges from the galactic center and extends 50 degrees north and south from the plane of the Milky Way, spanning the sky from the constellation Virgo to the constellation Grus. Credit: NASA/DOE/Fermi LAT/D. Finkbeiner et al.The bubbles display a spectrum with higher peak energies than the diffuse gamma-ray glow seen throughout the sky. In addition, the bubbles display sharp edges in Fermi LAT data. Both of these qualities suggest that the structure arose in a sudden, impulsive event. Credit: NASA/DOE/Fermi LAT/D. Finkbeiner et al.
First, the data are smoothed to eliminate features smaller than 2 degrees across, then the contrast is increased (stretched). Even without additional processing, the edge of the southern bubble can be seen. Next, astronomers mask out bright point sources, such as pulsars and distant galaxies. Then, using models developed from Fermi LAT observations, astronomers remove the diffuse gamma-ray emission from the image. This reveals the entire new structure, which is further brightened by another contrast stretch. Credit: NASA/DOE/Fermi LAT/D. Finkbeiner et al.


Gamma-ray Space Telescope has unveiled a previously unseen structure centered in the Milky Way. The feature spans 50,000 light-years and may be the remnant of an eruption from a supersized black hole at the center of our galaxy.

"What we see are two gamma-ray-emitting bubbles that extend 25,000 light-years north and south of the galactic center", said Doug Finkbeiner, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., who first recognized the feature. "We don't fully understand their nature or origin".

The structure spans more than half of the visible sky, from the constellation Virgo to the constellation Grus, and it may be millions of years old. A paper about the findings has been accepted for publication in The Astrophysical Journal.

Finkbeiner and his team discovered the bubbles by processing publicly available data from Fermi's Large Area Telescope (LAT). The LAT is the most sensitive and highest-resolution gamma-ray detector ever launched. Gamma rays are the highest-energy form of light.

Other astronomers studying gamma rays hadn't detected the bubbles partly because of a fog of gamma rays that appears throughout the sky. The fog happens when particles moving near the speed of light interact with light and interstellar gas in the Milky Way. The LAT team constantly refines models to uncover new gamma-ray sources obscured by this so-called diffuse emission. By using various estimates of the fog, Finkbeiner and his colleagues were able to isolate it from the LAT data and unveil the giant bubbles.

Scientists now are conducting more analyses to better understand how the never-before-seen structure was formed. The bubble emissions are much more energetic than the gamma-ray fog seen elsewhere in the Milky Way. The bubbles also appear to have well-defined edges. The structure's shape and emissions suggest it was formed as a result of a large and relatively rapid energy release - the source of which remains a mystery.

One possibility includes a particle jet from the supermassive black hole at the galactic center. In many other galaxies, astronomers see fast particle jets powered by matter falling toward a central black hole. While there is no evidence the Milky Way's black hole has such a jet today, it may have in the past. The bubbles also may have formed as a result of gas outflows from a burst of star formation, perhaps the one that produced many massive star clusters in the Milky Way's center several million years ago.

"In other galaxies, we see that starbursts can drive enormous gas outflows", said David Spergel, a scientist at Princeton University in New Jersey. "Whatever the energy source behind these huge bubbles may be, it is connected to many deep questions in astrophysics".

Hints of the bubbles appear in earlier spacecraft data. X-ray observations from the German-led Roentgen Satellite suggested subtle evidence for bubble edges close to the galactic center, or in the same orientation as the Milky Way. NASA's Wilkinson Microwave Anisotropy Probe detected an excess of radio signals at the position of the gamma-ray bubbles.
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Old 11-10-2010, 02:20 AM   #2
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I wonder what Finkbeiner and co. were originally looking for. This is quite a remarkable discovery they've come across.
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Old 11-10-2010, 02:42 AM   #3
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Originally Posted by Izack View Post
 I wonder what Finkbeiner and co. were originally looking for. {...}
They were looking for "something" -

SPACE.com: Huge Bubbles Found at Milky Way's Heart Could Signal a Black Hole Eruption:
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"We were definitely looking for something," Finkbeiner told reporters today (Nov. 9). "Some hints of this signal had been seen before, but not convincingly."
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Old 11-14-2010, 11:10 AM   #4
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"Gigantic" isn't sufficient to qualify the size of those "bubbles" That's an enormous, almost unthinkable amount of energy It reminds us how little we know about our Universe !
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Old 11-14-2010, 03:48 PM   #5
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 "Gigantic" isn't sufficient to qualify the size of those "bubbles"

You'd rather have the size in the number of double decker busses?
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Old 11-14-2010, 04:21 PM   #6
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The number of double decker buses all filled with BBC journalists that have been writing out the size of the bubbles since the H.sapiens sapiens started gossiping... (and yes, this is a random comment)
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Old 11-14-2010, 05:02 PM   #7
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Originally Posted by RisingFury View Post
 You'd rather have the size in the number of double decker busses?
If I set the bubbles as spheres with a diameter of 25000 ly, and the size of a double-decker-bus be (4 * 10 * 2.5)m³ = 100 m³ the size of both bubbles is about 1.39E59 double-decker-busses.
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Old 11-14-2010, 08:10 PM   #8
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Originally Posted by RisingFury View Post
 You'd rather have the size in the number of double decker busses?
I think, for better imaginability, the best thing to compare it with would be US Public Debt. These Galactic size bubbles can probably be close to a match for that really enormous bubble!
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Old 11-14-2010, 10:10 PM   #9
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oh yeah those old things. i knew those were there
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Old 11-14-2010, 10:11 PM   #10
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We're rapidly bubbling off-topic... do any of you remember the childhood shock of trying to imagine infinity or very very large numbers?
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Old 11-14-2010, 10:21 PM   #11
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I always found infinity pretty easy to comprehend for some reason. However I do remember the shock I felt when I became able to comprehend things that extend beyond the scope of the common notion "infinity."
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Old 05-08-2012, 08:27 PM   #12
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Discovery News: Milky Way's Gamma Ray Bubbles Shaped by Dark Matter?:
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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.

{...}
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Old 05-30-2012, 09:34 AM   #13
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Center for Astrophysics: Ghostly Gamma-ray Beams Blast from Milky Way's Center

Universe Today: Ghostly Jets Haunt the Milky Way’s Black Hole:
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This artist's conception shows an edge-on view of the Milky Way galaxy and newly discovered gamma-ray jets extending from the central black hole. Credit: David A. Aguilar (CfA)

A ghost is haunting the Milky Way’s central black hole, revealing the galactic nucleus was likely much more active in the relatively recent past. Scientists using the Fermi space telescope have found faint apparitions of what must have been powerful gamma-ray jets emanating from our galaxy’s center.

“These faint jets are a ghost or after-image of what existed a million years ago,” said Meng Su, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), and lead author of a new paper in the Astrophysical Journal. “They strengthen the case for an active galactic nucleus in the Milky Way’s relatively recent past.”

This is the first time this type of jet has been detected from the Milky Way’s black hole. Scientists know that other active galaxies have cores that glow brightly, powered by supermassive black holes swallowing material, and often spit twin jets in opposite directions.

The two beams, or jets found by Fermi observations extend from the galactic center to a distance of 27,000 light-years above and below the galactic plane.
The newfound jets may be related to mysterious gamma-ray bubbles that Fermi detected in 2010. Those bubbles also stretch 27,000 light-years from the center of the Milky Way. However, where the bubbles are perpendicular to the galactic plane, the gamma-ray jets are tilted at an angle of 15 degrees. This may reflect a tilt of the accretion disk surrounding the supermassive black hole.

“The central accretion disk can warp as it spirals in toward the black hole, under the influence of the black hole’s spin,” explained co-author Douglas Finkbeiner of the CfA. “The magnetic field embedded in the disk therefore accelerates the jet material along the spin axis of the black hole, which may not be aligned with the Milky Way.”

The two structures also formed differently. The jets were produced when plasma squirted out from the galactic center, following a corkscrew-like magnetic field that kept it tightly focused. The gamma-ray bubbles likely were created by a “wind” of hot matter blowing outward from the black hole’s accretion disk. As a result, they are much broader than the narrow jets.

Both the jets and bubbles are powered by inverse Compton scattering. In that process, electrons moving near the speed of light collide with low-energy light, such as radio or infrared photons. The collision increases the energy of the photons into the gamma-ray part of the electromagnetic spectrum.

The discovery leaves open the question of when the Milky Way was last active. A minimum age can be calculated by dividing the jet’s 27,000-light-year length by its approximate speed. However, it may have persisted for much longer.

“These jets probably flickered on and off as the supermassive black hole alternately gulped and sipped material,” said Finkbeiner.

It would take a tremendous influx of matter for the galactic core to fire up again. Finkbeiner estimates that a molecular cloud weighing about 10,000 times as much as the Sun would be required.

“Shoving 10,000 suns into the black hole at once would do the trick. Black holes are messy eaters, so some of that material would spew out and power the jets,” he said.

{...}
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Old 01-03-2013, 01:19 PM   #14
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CSIRO: Our Galaxy's "geysers" are towers of power:
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"Monster" outflows of charged particles from the centre of our Galaxy, stretching more than halfway across the sky, have been detected and mapped with CSIRO's 64-m Parkes radio telescope.

{...}

"These outflows contain an extraordinary amount of energy — about a million times the energy of an exploding star," said the research team's leader, CSIRO's Dr Ettore Carretti.

{...}

The speed of the outflow is supersonic, about 1000 kilometres a second. "That's fast, even for astronomers," Dr Carretti said.

{...}

From top to bottom the outflows extend 50,000 light-years [five hundred thousand million million kilometres] out of the Galactic Plane.

{...}

The outflows correspond to a "haze" of microwave emission previously spotted by the WMAP and Planck space telescopes and regions of gamma-ray emission detected with NASA's Fermi space telescope in 2010, which were dubbed the "Fermi Bubbles".

The WMAP, Planck and Fermi observations did not provide enough evidence to indicate definitively the source of the radiation they detected, but the new Parkes observations do.

"The options were a quasar-like outburst from the black hole at the Galactic Centre, or star-power — the hot winds from young stars, and exploding stars," said team member Dr Gianni Bernardi of the Harvard-Smithsonian Center for Astrophysics, in Cambridge, Massachusetts.

"Our observations tell us it's star-power."

In fact, the outflows appear to have been driven by many generations of stars forming and exploding in the Galactic Centre over the last hundred million years.

The key to determining this was to measure the outflows' magnetic fields.

"We did this by measuring a key property of the radio waves from the outflows — their polarisation," said team member Dr Roland Crocker of the Max-Planck-Institut fuer Kernphysik in Heidelberg, Germany, and the Australian National University.

The new observations also help to answer one of astronomers' big questions about our Galaxy: how it generates and maintains its magnetic field.

"The outflow from the Galactic Centre is carrying off not just gas and high-energy electrons, but also strong magnetic fields," said team member Dr Marijke Haverkorn of Radboud University Nijmegen in The Netherlands.

"We suspect this must play a big part in generating the Galaxy's overall magnetic field."

{...}
Slate - Bad Astronomy: The Milky Way's Old (and Huge) Faithfuls

Click on image to enlarge:
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Old 01-03-2013, 01:36 PM   #15
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"The speed of the outflow is supersonic, about 1000 kilometres a second."

'Supersonic' is not the word I would use for 1,000km/s.

Really, really cool findings, though. Outflows driven by "many generations of stars forming and exploding in the Galactic Centre over the last hundred million years." Now there's something to sit around and imagine. Nice picture, too.
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