A new high-resolution study of the hot, charged gas spouting from an enormous black hole provides the most direct evidence yet that such plasma jets are powered by corkscrew-shaped magnetic fields. Researchers say the finding helps clarify the inner workings of blazars, extremely energetic galaxies that flare up unpredictably, driven by central black holes millions of times more massive than the sun.
Researchers believe that large galaxies such as the Milky Way contain supermassive black holes in their cores that drag dust and gas toward them in a disk and fling it back out via jets of ionized gas or plasma moving at up to 99.9 percent of the speed of light. If that jet points toward Earth, researchers call it a blazar, and it is "one of the most impressive high-energy natural laboratories" in the universe, says astronomer Alan Marscher of Boston University's Institute for Astrophysical Research.
Among the consequences of these near light-speed or relativistic jets are flashlightlike beams of high-energy x-rays and gamma rays as well as the illusion of superluminal (faster-than-light) speeds when viewed straight on [click below to listen to "Superluminal Lover," a "gamma-rated" (not X-rated) ode to plasma jets performed by Marscher].
The leading model holds that blazars result from magnetic field lines—think of arcs formed by iron filings near a magnet—poking out from the accretion disk. If the black hole twisted the field lines together like a handful of twist ties, they would store energy similar to that of a twisted spring, Marscher says. Occasionally, material from the disk would get sucked into the magnetic tangle [see animation below].
To figure out exactly what's going on, researchers need to study plasma jets close to the black hole. In their new study, Marscher and his colleagues used the Very Long Baseline Array—a far-flung network of radio telescopes controlled from Socorro, N.M.—to probe deep into the core of BL Lacertae, a blazar 950 million light-years away. They captured a series of radio images revealing a "knot" of plasma shooting out along the blazar's single visible jet during a flare-up late in 2005.
BL Lacertae flared twice during the knot's migration—once as it was building speed and once when it passed through what researchers believe was a standing shock wave farther out in the jet ["X" shape depicted below]. Theoretical models predict that a twisted magnetic field near the black hole would accelerate outgoing plasma along a trajectory shaped like a stretched-out Slinky.
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7 Comments
Add CommentHey , I thought that the accretion disk was rotating rapidly too --that would be rotating the field and the jet plasma with it, causing the jets to spiral out .Would be very interesting to know if they do so in opposing directions . Enlighten me anyone ?
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Edited by Ajay Shah at 04/27/2008 6:06 PM
I think we have a fundamental flaw in this theory. It seems that Messrs Marscher, Hawley and co believe that magnetic fields can exist as insular entities. Hence the suggestion of blazars resulting from mag. field lines "like arcs formed by iron filings near a magnet".
Reply | Report Abuse | Link to thisWe must go back to the laboratory and look at where the majority of magnetic fields exist - not in permanent magnets with iron filings as indicators. No! Electric currents are the originators of most magnetic fields - discovered in the 19th century and essential to modern life to the present day. Every flow of electrons produces perpendicular circular magnetic fields. Ionised gas behaves the same, we all know it is a very good conductor of current, don't we? Kristian Birkeland gave his name to the filamentary behaviour of plasma currents.
So if you spot spiralling magnetic fields in space this MUST indicate the flow of invisible spiralling currents - that's the way nature works! So let's see how the theory needs tweaking to include the true power of the galaxies ie invisible electricity. Who needs invisible 'black holes' when we can DO everything with PLASMA in the lab. The most scalable phenomena in the universe: millimetres to light years, 14 to 27 orders of magnitude.
i must say that i agree with Cigarshaped fully. The theory seems quite straightforward to me although i'm stil a high school student and i have not grasped all the copncets involved.
Reply | Report Abuse | Link to thisIf light cannot escape black holes, how do they emit jets of matter, or is this matter snatched by magnetic fields from the accretion disk before the matter falls beyond the event horizon?
Reply | Report Abuse | Link to thisTo quote SNL church lady: nevermind. I see the answer is in Minkel's interview of Blandford.
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