Monster Outflows Of Energy Pouring Out Of Milky Way’s Center
Combined optical and radio image of two huge eruptions of material flowing out of the Milky Way galaxy.
These are new-found outflows of particles (pale blue) from the galactic Center, January 2, 2013. The background image is the whole Milky Way at the same scale. The curvature of the outflows is real, not a distortion caused by the imaging process. Astronomers using CSIRO’s 210-feet Parkes radio telescope in eastern Australia have found monstrous outflows of charged particles coming from the center of our galaxy.
The researchers said that the outflows contain an extraordinary amount of energy, reaching about a million times the energy of an exploding star. The outflows are shooting out at over 600 miles per second. “They are currently not coming in our direction, but go up and down from the galactic plane,” said CSIRO’s Dr. Ettore Carretti. “We are 30,000 light-years away from the galactic center, in the plane. They appear to pose no threat to Earth or the solar system.”
The outflows extend 50,000 light-years from top to bottom out of the galactic plane, which equals half the diameter of the Milky Way. Astronomers said the outflows stretch about two-thirds across the sky from horizon to horizon, and correspond to a “haze” of microwave emission previously spotted by the WMAP and Planck space telescopes.
These telescopes 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 center, 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. “Our observations tell us it’s star-power.”
The outflows appear to have been driven by many generations of stars forming and exploding in the galactic center over the past hundred million years. In order to determine this, astronomers had to measure the outflows’ magnetic fields.
“We did this by measuring a key property of the radio waves from the outflows — their polarization,” said team member Dr. Roland Crocker of the Max-Planck-Institut fuer Kernphysik in Heidelberg, Germany, and the Australian National University.
“The outflow from the galactic center is carrying off not just gas and high-energy electrons, but also strong magnetic fields,” said team member Dr. Marijke Haverkorn of Radboud University in The Netherlands. “We suspect this must play a big part in generating the galaxy’s overall magnetic field.”
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 these eruptions of matter are so vast that 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.
“We come spinning out of nothingness, scattering stars like dust.” – Rumi
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:
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.