Blazars

Sep 06, 2011
An artist's conception of a blazar, whose powerful jet of high velocity particles is generated around a supermassive black hole and aimed almost directly at Earth. A new CfA study has discovered that the infrared colors of blazars are a distinctive and powerful diagnostic tool. Credit: Marscher et al., Wolfgang Steffen, Cosmovision, NRAO/AUI/NSF

(PhysOrg.com) -- A blazar is a galaxy which, like a quasar, has an intensely bright central nucleus containing a supermassive black hole. In a blazar, however, the emitted light sometimes includes extremely high energy gamma rays, sometimes over a hundred million times more energetic than the highest energy X-rays that the Chandra X-ray Observatory can study. The overall emission has several other unique properties as well, including that its intensity can vary dramatically with time.

Astronomers suspect that this bizarre behavior results when matter falling onto the vicinity of the massive black hole erupts into powerful, narrow beams of high velocity charged particles. The intense X-ray and we see, and the variability as well, are thought to be the results of our fortuitously staring right down the throats of such cosmic monsters. But blazars are among the rarest of active nuclei, with only about 2700 known, and the physical processes that trigger and sustain such jets are still not known. Although relatively few, their powerful emissions make them major contributors to the overall picture of the cosmos.

CfA astronomers Francesco Massaro, Raffaele D'Abrusco, Josh Grindlay, and Howard Smith, and a colleague, have come up with a new method to find and study blazars. The recently launched NASA Wide Infrared Survey Explorer (WISE) satellite has just completed an of the whole sky in four infrared colors. The astronomers matched galaxies known to be blazars with objects measured by WISE in regions of the sky where the data have been reduced and made public. In a new paper in The , the team report their discovery that the infrared bands are remarkably effective at finding blazars. Ninety-seven percent of known blazars were easily picked out from thousands of other WISE sources because their colors in the infrared are different from the colors of other kinds of galaxies. In most galaxies the comes from dust, heated either by star formation or ultraviolet radiation from the vicinity of the massive black hole. In a blazar, however, a completely different mechanism is apparently at work: the ejected beam of charged particles, moving in a powerful magnetic field at nearly the speed of light, radiates infrared light of a distinctly different color than dust emission.

Using this new identification method, the team examines one known, extreme gamma ray source whose character had been mysterious in part because the gamma ray detection could not pinpoint the precise position of the source on the sky. The scientists find an infrared source within the position uncertainty whose distinct colors mark it as a blazar, and conclude that the extreme source is probably a blazar located at the position of the infrared source. In a second paper, the astronomers take advantage of this new method to examine the subset of blazars that are gamma ray emitters. It turns out that the infrared colors of this extreme group are even more distinctly identified, and the team discovered a quantitative relationship between the infrared and gamma ray colors. A future paper will consider the physical mechanism(s) producing the infrared, X-ray, and gamma ray emission. The discovery of the distinct infrared colors of blazars opens a new diagnostic tool in the study of these extreme galaxy nuclei.

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User comments : 9

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omatumr
1 / 5 (8) Sep 06, 2011
A blazar is a galaxy which, like a quasar, has an intensely bright central nucleus containing a supermassive black hole . . . and narrow beams of high velocity charged particles, . . .


Like axial jets from ordinary stars and pulsars, . . .

As if axial jets were the way massive neutron-rich central objects release energy from neutron repulsion ["Neutron Repulsion", The APEIRON Journal, in press (2011)].

http://arxiv.org/...2.1499v1

With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo
fmfbrestel
4.5 / 5 (8) Sep 06, 2011
Seriously Oliver, there there is no grand conspiracy to shut up your neutron repulsion theories. Just put out a nice falsifiable hypothesis that can be tested, or give it a rest already.
yyz
5 / 5 (2) Sep 06, 2011
"The discovery of the distinct infrared colors of blazars opens a new diagnostic tool in the study of these extreme galaxy nuclei."

It'll make a great tool to identify new blazars, as illustrated by the WISE discovery mentioned in the article. There are a number of unidentified gamma ray sources with blazar-like properties but no corresponding objects can be found at shorter wavelengths. Finding corresponding blazar candidates at IR wavelengths will open up multiwavelength studies of these newfound galaxies. Looking forward to widespread application of this powerful new tool.
Pressure2
not rated yet Sep 06, 2011
Couldn't there be other explanations other than a massive blackhole powering these intense beams of particles and radiation, like a galactic size magnetic field? Just how would a blackhole eject these intense beams out its poles other than by a magnetic field? If that is case why would you need the blackhole at all? After all a rotating galaxy would create it own magnetic field. Sure a weak field but lightyears in size.

Deesky
3.7 / 5 (6) Sep 07, 2011
Couldn't there be other explanations other than a massive blackhole powering these intense beams of particles and radiation, like a galactic size magnetic field?

No not really. Even if there was such a field, it would be way too weak to produce the observed jets.

A SM black hole distorts space-time around it which twists magnetic field lines into a coil that propels material outward.

Observations have been made of such a jet outburst (in galaxy BL Lacertae, using the VLBA, et al) which shows evidence that streams of particles wind in a corkscrew-like path away from the black hole, in accordance with the leading hypothesis.
vidar_lund
5 / 5 (2) Sep 07, 2011
Couldn't there be other explanations other than a massive blackhole powering these intense beams of particles and radiation, like a galactic size magnetic field?

The jets from Blazars and Quasars are streaming out from objects much smaller than a galaxy. Also the magnetic fields involved are extremely dense and powerful, nothing like you would observe around a galaxy. Finally the rapid changes in luminosity of these objects indicate a very small active core.
Mayday
not rated yet Sep 11, 2011
How close to a blazar would one have to be for the jet to be dangerous?
Then, wouldn't the intersection of two jets double that first distance? And so on? (of course, I'm probably going out a limb assuming that they don't disperse much.)
Might there, in fact, not be entire galaxies that have been sterilized by these thing's random spray?
Interesting universe.
bluehigh
1 / 5 (1) Sep 11, 2011
No not really. Even if there was such a field, it would be way too weak to produce the observed jets.

-Deesky

Why, just because you say so? Any references to back you up?
yyz
5 / 5 (1) Sep 11, 2011
"Might there, in fact, not be entire galaxies that have been sterilized by these thing's random spray?"

Depends on the size of the galaxy getting hosed (and the width of the jet to some extent). In radio galaxy 3C 321, a jet from the main galaxy's AGN appears to interact with a smaller, infalling companion galaxy some 20,000ly distant, causing a hot spot to appear there: http://chandra.ha...7/3c321/

The jet's interaction with the galaxy appears to bend the jet, which continues outward 850,000ly(!) from the nucleus of 3C 321. A paper on this remarkable system has more details: http://hea-www.ha...c321.pdf