CSIRO: Our Galaxy's "geysers" are towers of power

bystander · Post by **bystander** » Wed Jan 02, 2013 9:50 pm

Our Galaxy's "geysers" are towers of power
CSIRO | 2013 Jan 02

[attachment=0]GalacticOutflowCSIRO.jpg[/attachment]
"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. The outflows were were detected by astronomers from Australia, the USA, Italy and The Netherlands. They report their finding in today's issue of Nature.

"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. But the outflows pose no danger to Earth or the Solar System.

The speed of the outflow is supersonic, about 1000 kilometres a second. "That's fast, even for astronomers," Dr Carretti said. "They are not coming in our direction, but go up and down from the Galactic Plane. We are 30,000 light-years away from the Galactic Centre, in the Plane. They are no danger to us."

From top to bottom the outflows extend 50,000 light-years [five hundred thousand million million kilometres] out of the Galactic Plane. That's equal to half the diameter of our Galaxy (which is 100,000 light-years — a million million million kilometres — across).

Seen from Earth, the outflows stretch about two-thirds across the sky from horizon to horizon. 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."

Galactic geysers fuelled by star stuff
ICRAR | 2013 Jan 02

Giant magnetized outflows from the centre of the Milky Way - Ettore Carretti et al

Nature 493(7430) 66 (03 Jan 2013) DOI: 10.1038/nature11734

http://asterisk.apod.com/viewtopic.php?t=21966

bystander · Post by **bystander** » Thu Jan 03, 2013 9:16 pm

The Milky Way's Old (and Huge) Faithfuls
Slate Blogs | Bad Astronomy | 2013 Jan 03

[i]Combined optical and radio image of two huge eruptions of material flowing out of the Milky Way galaxy.[/i] [url=http://www.csiro.au/~/Media/CSIROau/Portals/Media%20Releases/2012/Our%20Galaxys%20geysers%20are%20towers%20of%20power/GCoutflows_radio_telescope/High_Resolution.jpg][b][i]Click to embiggen.[/i][/b][/url] [b][i]Credits: Axel Mellinger, Central Michigan Univ (optical image); Ettore Carretti, CSIRO (radio image); S-PASS survey team (radio data); Eli Bressert, CSIRO (composition).[/i][/b]
The Milky Way galaxy—our home galaxy—is erupting. Two monumental geysers are blasting out of its heart in opposite directions, and astronomers recently got the clearest view of them ever seen.

The image above shows the Milky Way in visible light, as we see it on a very dark night—stars, gas, and dust strewn across the sky. Superposed on that is the radio emission from those vast winds of material blasting outward (which is invisible to the eye; it's colored blue so you can see it). Those radio waves were detected by the Parkes radio telescope in Australia. These winds have been seen before using both radio telescopes and Fermi, an orbiting observatory that detects gamma rays (the highest energy form of light), but only at low resolution. Until now they haven't been mapped so clearly and in such detail.

The scale of this image is difficult to grasp. I’ve cropped it here to let you see the structures, but if you look at the original image it shows the whole sky…and you can see these eruptions of matter are so vast they stretch across two-thirds of the entire sky!

I’m actually rather stunned at this. If you had radio-vision, and you could see these streams of matter, you’d have to physically turn around to see the whole thing end-to-end. In real numbers, the material is about 50,000 light years long—half the length of the galaxy itself—and is rushing away from the center of the galaxy at a mind-numbing 1000 kilometers per second!

When I read that, the hair on the back of my neck stood up. My first thought was, “What the frak could power something that vast?”

And then I found out: the geysers contain the energy equivalent of a million exploding stars!

At that point I may have blacked out for a moment or two. If you want to know what humbles an astronomer, then this is pretty much your go-to scenario.

It’s hard to express the colossal nature of this. Think of it this way: Take all the energy the Sun emits every second (enough to power the entire Earth’s needs for nearly a million years). Now multiply that by 31 million, the number of seconds in a year. Now multiply that by 10 billion, the numbers of years the Sun will be around. It’s a huge number, staggering, and that’s still only about 1% of the energy output of a single supernova. That means these geysers contain a hundred million times the Sun’s entire lifetime supply of energy.

See? That’s why I was overwhelmed.

I’ll note that these geysers present no danger at all to us here on Earth. If they did, we’d have been zapped a long time ago; this structure is pretty old, millions of years old at least. But we’re a long way from the action; the core of the galaxy, where the geysers are generated, is 26,000 light years away, and the material itself is not headed anywhere near us. We’re safe.

So still, what could possibly generate this much energy? For a long time it was thought to be the supermassive black hole we know exists in our galaxy’s center; matter falling in can be ejected away at high velocity. Another competing idea was that vigorous massive star formation over millions of years would generate huge winds of material, boosted even more when those stars died as supernovae. We know this happens on a smaller scale in the galaxy; bubbles of gas and dust erupting outwards have been seen before, like in this image from the Herschel space telescope:

[i]Far-infrared Herschel observatory image of cold dust and gas in the Milky Way. Note the blowout at the lower left.[/i] [url=http://spaceinimages.esa.int/var/esa/storage/images/esa_multimedia/images/2010/05/stellar_pregnancy_and_birth_in_the_milky_way/9790278-3-eng-GB/Stellar_pregnancy_and_birth_in_the_Milky_Way.jpg][b][i]Click to embiggen.[/i][/b][/url] [url=http://www.esa.int/Our_Activities/Space_Science/Herschel_reveals_the_hidden_side_of_star_birth][b][i]Credit: ESA/Hi-GAL Consortium[/i][/b][/url]
At the lower left is a small herniated region (colored blue in this false-color far-infrared image) caused by supernovae and the winds from new stars blowing material out of the galaxy. Even though this is pretty big on a human scale (many light years across), it’s peanuts compared to the Parkes observation. Still, the idea is the same.

And the new Parkes observations finally do resolve this. As the material blows out from the galaxy it carries with it a magnetic field. Careful analysis of the affect of that field on the material using the Parkes data shows the energy source to be star formation, and not winds from the black hole. The shape and structure of the geysers indicate there must have been several different episodes of star formation, in fact, and not just one long, continuous event.

I’ll note I’ve been reading about these competing ideas for a long time, and the debate has been pretty strong. Until now, it wasn’t clear which was right, so it’s nice to see this resolved.

And it’s amazing, too: It’s incredible to think that something with so much power could have been hiding from us for so long; it’s only because it’s spread out over so much sky that we missed it.

Such an incredible image, on such a scale! It’s wonderful to know that we can learn so much about our own home. Even better, it reminds us that we still have so much more left to learn.

That’s yet another reason I love science so much. It’s a magnificent puzzle that never ends. There's always another piece of it waiting to be found around the corner, and there's always more to learn.