A new class of extragalactic objects

Oct 29, 2012
An artist's conception of a blazar. Astronomers have discovered a gamma-ray source that, although in most ways seeming to be a blazar, has no radio emission -- a feature that makes it unique (so far) and very difficult to understand. Credit: NASA-JPL

A blazar is a galaxy with an intensely bright central nucleus containing a supermassive black hole, much like a quasar. The difference is that a blazar can emit light with extremely high energy gamma rays that are sometimes over a hundred million times more energetic than the highest energy X-rays that the Chandra X-ray Observatory studies. The overall emission of a blazar also varies dramatically with time and all known blazars are bright at radio wavelengths.

Astronomers suspect that the bizarre behavior of blazars results when matter falling onto the vicinity of the erupts into powerful, narrow beams of high velocity charged particles. The intense X-ray and we see, and the strong radio emission and variability as well, are thought to be the results of our fortuitously staring right down the throats of the jets. In most other galaxies, infrared radiation comes from dust heated either by star formation or ultraviolet radiation from the vicinity of the massive black hole, rather than a jet.

CfA astronomers Allesandro Paggi, Raffaele D'Abrusco, Josh Grindlay, and Howard Smith and their colleagues recently published a new method to find and study blazars. They discovered that the infrared colors of blazars, as measured by the recent NASA WISE survey satellite, are so unusual that objects with these colors are very likely to be blazars. Ninety-seven percent of known blazars were easily picked out from thousands of other WISE sources by their infrared colors.

There are about 1873 known . About one-third of them are quite mysterious, however, because their very imprecise spatial locations have not allowed them to be associated with particular galaxies that can be studied with . The CfA astronomers discovered that about half of unknown gamma-ray sources could reasonably be identified with infrared emitting blazars, with the WISE coordinates then allowing detailed follow-up observations.

One unidentified gamma-ray source recently flared in emission, prompting the team to see if it too had an infrared blazar-like color counterpart consistent with its location. In a new paper in this week's Astrophysical Journal Letters, the astronomers report finding one. The mystery, however, is that the counterpart is not a known blazar: it has no radio emission, it is not known to vary, and although it is an X-ray emitter the rest of its broad distribution of energy is unlike that of most blazars. It is possible that another galaxy nearby is actually the gamma-ray counterpart, but all of the alternate candidates show even greater disparities. If the WISE source is in fact the counterpart to the gamma-ray burst, its absence of radio emission means that it represents a strange new class of extragalactic source. If it is not the counterpart, its lack of radio emission is still a blazar mystery. Further research is needed to sort resolve the mystery, but the work so far illustrates the powerful capabilities of multi-wavelength research.

Explore further: How baryon acoustic oscillation reveals the expansion of the universe

Related Stories


Sep 06, 2011

(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 ...

WISE mission sees skies ablaze with blazars

Apr 12, 2012

(Phys.org) -- Astronomers are actively hunting a class of supermassive black holes throughout the universe called blazars thanks to data collected by NASA's Wide-field Infrared Survey Explorer (WISE). The ...

Astrophysicists explore a blazar

Mar 18, 2009

An international team of astrophysicists using telescopes on the ground and in space have uncovered surprising changes in radiation emitted by an active galaxy. The picture that emerges from these first-ever ...

Fermi sees brightest-ever blazar flare

Dec 09, 2009

(PhysOrg.com) -- A galaxy located billions of light-years away is commanding the attention of NASA's Fermi Gamma-ray Space Telescope and astronomers around the globe. Thanks to a series of flares that began ...

Giant gamma ray bubbles in our galaxy

Nov 19, 2010

(PhysOrg.com) -- Gamma rays are the most energetic form of light, typically about one hundred billion times as energetic as optical light.

Recommended for you

The Great Cold Spot in the cosmic microwave background

Sep 19, 2014

The cosmic microwave background (CMB) is the thermal afterglow of the primordial fireball we call the big bang. One of the striking features of the CMB is how remarkably uniform it is. Still, there are some ...

Mystery of rare five-hour space explosion explained

Sep 17, 2014

Next week in St. Petersburg, Russia, scientists on an international team that includes Penn State University astronomers will present a paper that provides a simple explanation for mysterious ultra-long gamma-ray ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

3 / 5 (2) Oct 29, 2012
oh look - gamma rays but no radio waves. no known natural mechanism. i guess that means god is responsible right?