AAS #9: Black hole jet of doom from Cen A

By Phil Plait | January 9, 2008 11:00 am

Centaurus A is a nearby galaxy which is bit of mess. Actually, it’s an incredible mess. 12 million light years away, it looks at first like an elliptical galaxy, an unassuming football of billions of stars. A closer look reveals a dark dust lane across the middle, which is our first hint things are amiss: ellipticals tend not to have very much dust, but Cen A has it in bucketloads (as you can see in the picture on the left, courtesy Chandra and AURA/NOAO/NSF).

Cen A has been known to harbor a central supermassive black holes — all big galaxies, including our own, have one. But Cen A’s is active: it is currently feeding off gas and dust, gobbling down huge amounts of matter. This material forms a gigantic flattened disk as it swirls around the hole. This disk is under the influence of a witch’s brew of forces magnetic, gravitational, and even mechanical: friction heats the disk fiercely, and it gets so hot it glows in visible, ultraviolet, and even X-rays.

It’s not clear exactly how these forces interact, but they can combine to focus twin beams of matter and energy, titanic jets that scream outwards from the disk. The jets come from the part of the disk just before the matter takes the Final Plunge, before it falls into the black hole.

The Chandra X-ray Observatory has taken deep images of Cen A, revealing new details about the jets emanating from its central black hole. The jet to the upper left is aimed more or less at us (never fear, it’s way too far away to hurt us), and you can see the counterjet as a shorter stubbier line of light to the lower right. The jets may be equal in size and intensity, but weird effects (due to Einsteinian relativity) make the one aimed away from us appear to be dimmer.

A closer-in view of the jet shows that it is plagued with knots, clumps of emission. These are probably due to shock waves, when faster material is ejected from the vicinity of the black hole and slams into slower moving material. This dumps vast amounts of energy into the material, reheating and re-accelerating it outwards. The magnetic fields of the material keeps it focused, and the shock wave re-energizing keeps it moving up, up, and away from the black hole. These jets can be many thousands of light years long, so the energies involved are fantastic, almost incomprehensible.

But, in fact, there are comprehensible. Jets like these are incredible, but we are beginning to understand them. Observations like this one from Chandra are aiding astronomers’ understanding of how matter behaves when it’s On The Brink.

Comments (12)

  1. Michael Lonergan

    I don’t know….. If that jet is pointed towards us, I’ll feel it. I’m really sensitive the things like that. Maybe that’s what that itching has been about.

    Seriously, I thought all Black Holes were active? If there is matter around, wouldn’t they be taking it in?

  2. k9_kaos

    This is, to me, one of the most beautiful galaxies. I think it looks a little bit like the London Underground logo in the upper image.

    “Seriously, I thought all Black Holes were active? If there is matter around, wouldn’t they be taking it in?”

    Not all black holes are active – the supermassive black hole at the centre of our galaxy is rather quiet, but I think that’s because there isn’t a lot of matter close enough to it for it to “suck it in”. When matter is far enough from a black hole, I believe I heard that the gravitational attraction of the matter to the black hole isn’t strong enough for the black hole to “suck in” the matter (but still strong enough for the black hole’s gravity to peturb the matter’s trajectory through space), so the matter would just pass by or orbit the black hole.

    Is this sort-of right, Phil?

  3. Chris G

    APOD for 10-Jan-2008 has small X-ray, Radio and Optical images, plus larger composite image of Centaurus A:

    http://antwrp.gsfc.nasa.gov/apod/ap080110.html

  4. SF Reader

    Right, from a reasonable distance black holes are just a gravity well and a radiation source, it’s not like it has arms that are reaching out to suck up everything in the neighborhood.

    If stuff isn’t on a trajectory to fall in (just like comets usually don’t fall into the Sun or hit the Earth), then it doesn’t.

  5. Doug

    Ok, I’m confused and I’m supposed to know this stuff. If the jet is pointed “more or less at us,” why does it appear to have an angular extent? Shouldn’t it be a compact point with a whopping blue shift ?

  6. Buzz Parsec

    Doug – Yeah, if it was pointed *directly* at us, that’s what it would look like, but if it’s off by 10-20 degrees, we would see it as a line or as a long thin isosceles triangle pointing at the black hole.

    Re active vs. inactive black holes: Think of a cow quietly roaming around a pasture munching on the grass vs. the WB Tasmanian Devil on a rampage devouring everything in sight. The kicker is the cow and Taz are really the same thing; when Taz has eaten just about everything around, he turns into the cow, and if the cow gets into the cornfield, suddenly she turns into a Tasmanian Devil.

  7. Doug

    On the jet. Not buying the “more or less at us” part. Look at the angular extent. It’s on the order of the size of the entire galaxy. I could make a strong case that it it pointed 45 or 50 degrees away from us. What is needed is velocities along the jet to get a handle on the pointing. But just from the morphology it looks too extended to say it is pointing “at us.”

  8. Hi, Phil. I sent you an e-mail a week and a half ago, requesting permission to translate some of your posts into Spanish, especially when you talk about a new image released from a telescope or a space mission, because he way you explain and relate the science behind the image and make the info so entertaining and didactical is amazing. So I thought it would be great if I could translate them to Spanish and post them in the blog of my local astronomy club:

    http://www.astroelche.es

    I would also link to the post in my personal blog. The post would include a link to your original one, and it would be said that you’re the original author and I only made the translation.

    So well… this is one of those posts I’d like to translate. Can that be done?

  9. blizno

    “On the jet. Not buying the “more or less at us” part. Look at the angular extent. It’s on the order of the size of the entire galaxy. I could make a strong case that it it pointed 45 or 50 degrees away from us. What is needed is velocities along the jet to get a handle on the pointing. But just from the morphology it looks too extended to say it is pointing “at us.”

    I have seen some “casual” physics on this site in other stories.
    Phil, I request that you use more rigor in your descriptions. Lots of your readers are layfolk who don’t have any idea how to deal with the jargon you know like the backs of your own eyelids, but some of us have had training in the sciences. For those of us familiar with science and engineering, casual usage throws us off and we have to struggle to interpret your writings in real terms.
    I’m being picky here, but I get confused when somebody who is obviously among the top tier of scientists writes something sloppy. I understand that you’re trying to make it accessible for everybody, but is there some way to work in a “double standard” where you describe the wonderful discovery in easily accessible terms and then also in scientifically rigorous terms?

    This isn’t a criticism, it’s a request. I adore your site and I visit it almost every day to read of some new, amazing observation about our glorious universe and/or to learn of the latest atrocity committed by the RR in their unpatriotic, anti-American agenda to destroy US democracy and replace it with a priesthood of their own choosing.
    Keep up the good work! We are counting on you.

  10. Ed

    I wrote Peter Edmonds at Harvard and he stated thet the jet actually emanated from beyond the event horizon. Now it seems to me that if they originate past the event horizon, they are not comong from the black hole. So what’s the fuss? Personally I think that someone on the other side threw a rock into the black hole, and it gained so much speed that it came out on this side!

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