Astronomers currently recognize two types
of blazars.
Based on other properties
of blazars, the scientists believe that their interpretation of the data is accurate and that they have measured the extremely fast speeds in the three blazar jets.
Observations
of blazars by NASA's Fermi Gamma Ray Telescope spacecraft for the first time detected that gamma rays from distant blazars are indeed attenuated more than gamma rays from nearby blazars, a result announced on November 30, 2012, in a paper published in Science, as theoretically predicted.
Francesco Massaro at the University of Turin in Italy and Raffaele D'Abrusco at the Harvard - Smithsonian Center for Astrophysics in Cambridge, Massachusetts, show for the first time that the mid-infrared colors
of blazars in WISE data correlate to an equivalent measurement of their gamma - ray output.
At the heart
of a blazar lies a supersized black hole with millions of times the sun's mass surrounded by a disk of hot gas and dust.
Looking at a distant galaxy: the radio chart (left) shows the image
of the blazar PKS 1830 - 211 distorted by the gravitational lens effect.
The light
of the blazar behind it passes through this space well and takes a detour — as if it were passing through a lens.
The detail on the right is a simulation of the micro-gravitational lens effect in the gamma ray region; direct observation of the orange ring — it also represents images
of the blazar — is not possible due to its small size.
VLBA sequence
of blazar 0827 +243 over about 8.4 months.
Not exact matches
In the second half
of last year the
blazar CTA 102, which is 7,600 million light years from Earth, brightened considerably, drawing the attention
of all the astronomers who specialise in this kind
of objects.
The infrared / gamma - ray connection led the authors to search for new
blazar candidates among WISE infrared sources located within the positional uncertainties
of Fermi's unidentified gamma - ray objects.
Astronomers suspect many
of these are
blazars, but there isn't enough information to classify them.
The relationship effectively connects the dots for
blazars across an enormous swath
of the electromagnetic spectrum.
«We found that when we plotted Fermi
blazars by their WISE colors in a particular way, they occupied a distinctly different part
of the plot than other extragalactic gamma - ray sources.»
The discovery, which was accomplished by comparing data from NASA's Wide - field Infrared Survey Explorer (WISE) and Fermi Gamma - ray Space Telescope, has enabled the researchers to uncover dozens
of new
blazar candidates.
They could have emerged from gamma - ray bursts, mysterious and short - lived cataclysms that briefly rank as the brightest objects in the universe; shock waves from exploding stars; or so - called
blazars, jets
of energy powered by supermassive black holes.
The High Altitude Water Cherenkov observatory has released its first map
of the high - energy sky, catching pulsars, supernova remnants and
blazars switching on and off
Related sites Abstract
of paper, with link to full text Chandra X-ray Observatory FUSE satellite, used in similar studies
of lower - temperature gas Observations
of Markarian 421
blazar Shull's home page
Astronomer Fabrizio Nicastro
of the Harvard - Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and his colleagues monitored the galaxy Markarian 421, which contains a «
blazar» — an active black hole that aims powerful jets
of energy toward Earth.
Partially dimmed x-rays (dips in graph) from a flaring
blazar (right) reveal two filaments
of hot, diffuse matter in the vast spaces between galaxies.
It so happens that there is a galaxy roughly half way between Earth and the
blazar, which is billions
of light years away.
Fermi has shown that much
of this light arises from unresolved gamma - ray sources, particularly galaxies called
blazars, which are powered by material falling toward gigantic black holes.
In a detailed analysis
of high - energy EGB gamma rays, published April 14 in Physical Review Letters, Ajello and his team show that
blazars and other discrete sources can account for nearly all
of this emission.
This is a
blazar — a rare case in which one
of the two jets happens to be directed towards Earth so that the astronomers look directly into the jet along the longitudinal axis.
It turns out that
blazars are powered surprisingly like the exhausts
of jet engines, albeit on a cosmic scale, says astronomer and lead author Alan Marscher
of Boston University.
This behaviour and further findings from observations can be best explained with an interesting assumption: Although the brightness variations in the gamma ray region also originate from the flare ups in the
blazar, they are amplified to different degrees by the gravitational lens effect
of individual stars in the foreground galaxy.
Now, Readhead and his colleagues argue that they're seeing the
blazar's black hole emit tiny burps
of plasma, magnified hundreds
of times by a new kind
of gravitational lens.
Instead
of streaming out
of a metal casing and turbine, a
blazar's jets «are confined and focused by coiled magnetic fields originating near the [supermassive] black hole.»
Bright spots in the map include the Crab Nebula, which hosts a radiation - spewing stellar corpse called a pulsar, and several
blazars, violent active galaxies where colossal black holes accelerate particles to more than 99 % the speed
of light.
Blazars — found in the centers
of some galaxies — and gamma - ray bursts are two identified wellsprings
of these high - energy rays.
Blazars periodically flare when the supermassive black holes in some active galaxies» cores fill with dust and gas, releasing massive amounts
of energy.
«
Blazars are one type
of active galaxy,» said Marco Ajello, a professor
of physics and astronomy and Paliya's advisor.
However, rather than emitting violent bursts
of gamma - ray radiation, like
blazars, Seyfert galaxies are known for their strong ultra-violet emissions.
«It was unexpected — we have only seen that kind
of gamma ray emission from
blazars,» said Dieter Hartmann, a professor
of physics and astronomy and co-author
of the study.
The attached figure illustrates how energetic gamma rays (dashed lines) from a distant
blazar strike photons
of extragalactic background light (wavy lines) and produce pairs
of electrons and positrons.
So, astrophysicists developed an ingenious work - around method: measuring the EBL indirectly through measuring the attenuation
of — that is, the absorption
of — very high energy gamma rays from distant
blazars.
When a high - energy gamma ray from a
blazar strikes air molecules in the upper regions
of Earth's atmosphere, it produces a cascade
of charged subatomic particles.
Not all the high - energy gamma rays emitted by a
blazar, however, make it all the way across billions
of light - years to Earth; some strike a hapless EBL photon along the way.
Thus, measuring how much gamma rays
of different energies are attenuated or weakened from
blazars at different distances from Earth indirectly gives a measurement
of how many EBL photons
of different wavelengths exist along the line
of sight from
blazar to Earth over those different distances.
«We can think
of one
blazar class as a gas - guzzling car and the other as an energy - efficient electric vehicle,» study lead researcher Marco Ajello, an astrophysicist at Clemson University in South Carolina, said in a statement.
This hybrid
blazar idea implies that the luminosity
of BL Lacs should decrease as their core black holes continue to lose energy and spin.
Taking advantage
of the extremely sharp radio «vision»
of the continent - wide VLBA, the scientists tracked individual features in the jets
of three
blazars at distances from Earth ranging from 7.3 to 9 billion light - years.
Blazars are active galactic nuclei — energetic regions surrounding massive black holes at the centers
of galaxies.
«Now, based on independent confirmation by two groups
of astronomers, we see these three
blazars with apparent speeds greater than 25 times that
of light,» Piner added.
The two different classes
of jet - spewing active galaxies called
blazars may, in fact, be a single hybrid type that evolves over time, according to new research.
«This tells us that the physical processes at the cores
of these galaxies, called
blazars, are extremely energetic and are capable
of propelling matter very close to the absolute cosmic speed limit,» said Glenn Piner
of Whittier College in Whittier, California.
«We typically see apparent speeds in
blazar jets that are about five times the speed
of light, and that corresponds to a true speed
of more than 98 percent
of light speed,» Piner said.
Blazars appear to produce more gamma radiation than other types
of active galaxies, but this may be because one
of their jets is pointed toward Earth.
Blazars occur when the jet
of a supermassive black hole is pointing toward Earth.
Blazars are a type
of active galaxy — about 1,000 have been cataloged [source: A Review
of the Universe].