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| A*'s death ray ghosts of 10,000 suns | May 30, 2012 5:13 AM PDT | url |
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Added 1 new A* page:Scientists working with the Fermi Gamma-ray Space Telescope have made another startling discovery, described in Harvard's (the author of the key research paper, Meng Su, is a Harvard astronomer) press release as "Ghostly Gamma-ray Beams Blast from Milky Way's Center."
If you're saying to yourself hey, that's where the supermassive black hole Sgr A* is, you're absolutely right! And if you're saying to yourself say, didn't the Fermi 'scope already recently discover some huge lobes of gamma radiation above and below the galactic core, then you're doubly right! Those were the so-called "Fermi bubbles" that I discussed back in September--big radioactive balls 25,000 light years across, just above and below A*.
This new discovery is very likely related to the process that created the Fermi bubbles, because it's just about the same size! Here's a conceptual illustration of the "Gamma-ray beams" (or what they may once have been--see below) superimposed on the bubbles:
image by David A. Aguilar (CfA) (source)
Now, it's important to note that sharp-looking jets like those in that illustration are *not* what they actually found; if you look at the diagrams in the afore-linked research paper, you'll see that what they detected are very faint, vaguely cylindrical "cocoons" of gamma-ray-scattering space dust radiating outward about 27,000 light years from Sgr A*, tilted at about a 15 degree angle to the galactic pole. They *think* that these are most likely reflections--light echos, I suppose you could say--of relativistic jets of highly energetic plasma shot out of the poles of our galaxy's central supermassive black hole at some time in the past (at least 55,000 years ago, I guess, since at least some of the plasma would have had to travel 27,000 light years out, maybe at just under the speed of light, then its transmitted energy would have had to bounce back about another 27,000 light years to reach us), as we can see shooting out of distant galaxies whose supermassive black holes are actively sucking in (and jetting out) large amounts of material. Astronomers and astrophysicists have for some time now, based on other evidence of past star births and other things we can see around the core, supposed that A* goes "active" like that maybe every 100,000 years, but this is the first time that traces of the tell-tale jets have actually been spotted.
This may also indicate that A* is or was spinning at a different angle than the rest of the galaxy! It isn't clear yet whether the bubbles and the jets were formed in the same event; they could just as well be remnants from separate active periods. From the press release:
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. |
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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. |
Go A*!
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I have the author of the webcomic Variables to thank for pointing out that he and some other webcomic authors have started up a Longform Webcomics subreddit on the popular link-sharing social networking site, reddit. I tossed an A* link in there to see if I could help this new subreddit get going. There are the popular "comics" and less-used "webcomics" subreddits on reddit already, but they tend to favor gag-a-day type comics, which I suppose are better suited to quick bursts of non-committal satisfaction. :) So it would be nice for "long form" webcomic authors such as myself ("long form" just meaning they tell a continuing story from strip to strip) if a thriving subreddit for sharing story comic links should flourish, but I guess we'll see!
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