NSF VLBA Peers Into the “Eye of Sauron” to Solve Cosmic Neutrino Mystery

View Inside The Jet Of A Blazar

Looking inside the plasma jet cone of the blazar PKS 1424+240 with a radio telescope of the National Science Foundation’s Very Long Baseline Array (NSF VLBA). Credit: NSF/AUI/NRAO/B. Saxton/Y.Y. Kovalev et al.

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Unprecedented radio observations reveal why a distant blazar appears sluggish yet blazes in high-energy gamma rays and neutrinos

Using the U.S. National Science Foundation National Radio Astronomy’s Very Long Baseline Array (NSF NRAO VLBA), an international team of astronomers has solved a decade-long puzzle about one of the brightest cosmic neutrino sources in the sky. Their findings, published today in Astronomy & Astrophysics Letters, reveal that the blazar PKS 1424+240 – dubbed the “Eye of Sauron” for its striking appearance – points its powerful jet almost directly at Earth, creating an extreme cosmic lighthouse effect.

Located billions of light-years away, PKS 1424+240 had long baffled astronomers. Despite appearing to have a slow-moving plasma jet in radio observations, it blazes as one of the brightest sources of high-energy gamma rays and cosmic neutrinos ever detected. This contradiction, known as the “Doppler factor crisis,” has challenged scientists’ understanding of how these extreme cosmic accelerators work.

“The NSF VLBA’s extraordinary resolution has allowed us to peer directly into the heart of this cosmic monster,” said Yuri Kovalev, lead author of the study and Principal Investigator of the ERC-funded MuSES project at the Max Planck Institute for Radio Astronomy. “We discovered that this blazar’s jet is aimed at us with pinpoint precision – within just 0.6 degrees of our line of sight.”

The breakthrough came from 15 years of ultra-high-resolution observations using the NSF VLBA, which consists of ten 25-meter radio telescopes stretching from Hawaii to the U.S. Virgin Islands. By combining 42 separate images collected from 2009 to 2025 as part of the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) program, the team created an unprecedented deep view of the blazar’s inner structure.

“This is like looking at car headlights from the Moon – the NSF VLBA’s incredible precision made it possible,” said Jack Livingston, a co-author at the Max Planck Institute for Radio Astronomy. “What we found was a nearly perfect toroidal magnetic field structure threading the jet of plasma,” added Daniel Homan, co-author and professor of Denison University. Alexander Plavin, co-author and research fellow of Harvard University, continued, “It’s creating what looks remarkably like the Eye of Sauron from Tolkien’s Lord of the Rings.”

The extreme alignment of PKS 1424+240’s jet toward Earth creates a relativistic “searchlight” effect, amplifying its brightness by a factor of 30 or more through special relativity. This explains why the source appears as one of the brightest neutrino emitters detected by the IceCube Neutrino Observatory in Antarctica, despite its plasma jet appearing to move slowly in radio images.

The discovery demonstrates the critical role of Very Long Baseline Interferometry (VLBI) in solving cosmic mysteries. The NSF VLBA connects radio telescopes across a continent-sized baseline, creating a virtual telescope with the highest resolution available in astronomy – sharp enough to read a newspaper in New York from Los Angeles.

The research strengthens the connection between relativistic plasma jets, high-energy neutrinos, and the magnetic fields that shape cosmic particle accelerators, marking a significant milestone in multimessenger astronomy – the study of the universe using multiple types of cosmic signals.

You can read the press release from the Max-Planck Institute for Radio Astronomy here.

Source: National Radio Astronomy Observatory (NRAO)/News

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Background Information:

A blazar is a type of active galactic nucleus powered by a supermassive black hole that launches jets of plasma moving at nearly the speed of light. What makes blazars special is their orientation: one of their jets points within about 10 degrees of Earth, making them appear exceptionally bright and allowing scientists to study extreme physical processes.

The original paper:

Y. Kovalev, A. B. Pushkarev, J. L. Gomez, D. C. Homan, M. L. Lister, J. D. Livingston, I. N. Pashchenko, A. V. Plavin, T. Savolainen, S. V. Troitsky: Looking into the Jet Cone of the Neutrino-Associated Very High Energy Blazar PKS 1424+240, A&A Letters, August 12, 2025 (DOI: 10.1051/0004-6361/202555400)

https://doi.org/10.1051/0004-6361/202555400

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Preprint: https://arxiv.org/abs/2504.09287

Further Information/Links:

Multi-messenger Studies of Extragalactic Super-colliders (MuSES), ERC Grant: https://www.mpifr-bonn.mpg.de/muses

Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE) program: https://www.cv.nrao.edu/MOJAVE/

Max Planck Institute for Radio Astronomy (MPIfR): http://www.mpifr-bonn.mpg.de/2169/en

Center for Astrophysics – Harvard & Smithsonian (CFA): https://www.cfa.harvard.edu/

Denison University (DU): https://denison.edu/academics/astronomy

Very Long Baseline Array (VLBA): https://science.nrao.edu/facilities/vlba

European Research Council (ERC): https://erc.europa.eu/homepage

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About NRAO:

The U.S. National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

About the VLBA:

The NSF Very Long Baseline Array is a system of ten identical 25-meter radio telescopes operating as a single instrument. Stretching 5,000 miles from Mauna Kea, Hawaii, to St. Croix in the U.S. Virgin Islands, the VLBA provides the highest resolution images available in astronomy.

Images and additional resources are available at: https://public.nrao.edu/news/

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Astronomers Detect Earliest and Most Distant Blazar in the Universe

VLASS J041009.05−013919.88
Credit: U.S. National Science Foundation/NSF National Radio Astronomy Observatory, B. Saxton

A groundbreaking discovery has revealed the presence of a blazar—a supermassive black hole with a jet pointed directly at Earth—at an extraordinary redshift of 7.0. The object, designated VLASS J041009.05−013919.88 (J0410−0139), is the most distant blazar ever identified, providing a rare glimpse into the epoch of reionization when the universe was less than 800 million years old. This discovery challenges existing models of black hole and galaxy formation in the early cosmos.

J0410−0139 is powered by a black hole with a mass of 700 million times that of the Sun. Multi-wavelength observations show that its radio variability, compact structure, and X-ray properties identify it as a blazar with a jet aligned toward Earth. Blazars are rare and account for only a small fraction of all quasars. The discovery of J0410−0139 implies the existence of a much larger population of similar jetted sources in the early universe. These jets likely enhance black hole growth and significantly affect their host galaxies.

Observations with instruments such as the U.S. National Science Foundation Very Large Array (NSF VLA), the NSF Very Long Baseline Array (NSF VLBA), the Chandra X-ray Observatory, and the Atacama Large Millimeter/submillimeter Array (ALMA) indicate that J0410−0139 exhibits radio emission amplified by relativistic beaming, a hallmark of blazars. Its spectrum also confirms stable accretion and emission regions typical of active black holes. This discovery raises questions about how supermassive black holes grow so rapidly in the universe’s infancy. Models may need to account for jet-enhanced accretion or obscured, super-Eddington growth to reconcile this finding with the known black hole population at such high redshifts.

“This blazar offers a unique laboratory to study the interplay between jets, black holes, and their environments during one of the universe’s most transformative epochs,” said Dr. Emmanuel Momjian of the NSF National Radio Astronomy Observatory, a co-lead of the study, “The alignment of J0410−0139’s jet with our line of sight allows astronomers to peer directly into the heart of this cosmic powerhouse.”

The existence of J0410−0139 at such an early time suggests that current radio surveys might uncover additional jetted quasars from the same era. Understanding these objects will illuminate the role of jets in shaping galaxies and growing supermassive black holes in the early universe.

Source: National Radio Astronomy Observatory (NRAO)/News

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About NRAO

The NSF National Radio Astronomy Observatory (NSF NRAO) is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

For media inquiries or further information, please contact:

NRAO Media Contact: Corrina C. Jaramillo Feldman
Public Information Officer – New Mexico
Tel: +1 505-366-7267
cfeldman@nrao.edu

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Colossal Black Holes Locked in Dance at Heart of Galaxy

Two supermassive black holes are seen orbiting each other in this artist's loopable animation. The more massive black hole, which is hundreds of millions times the mass of our sun, is shooting out a jet that changes in its apparent brightness as the duo circles each other. Astronomers found evidence for this scenario in a quasar called PKS 2131-021 after analyzing 45-years-worth of radio observations that show the system periodically dimming and brightening. The observed cyclical pattern is thought to be caused by the orbital motion of the jet. Credit: Caltech/R. Hurt (IPAC)

Artist's animation of a supermassive black hole circled by a spinning disk of gas and dust. The black hole is shooting out a relativistic jet—one that travels at nearly the speed of light. Credit: Caltech/R. Hurt (IPAC)

Three sets of radio observations of the quasar PKS 2131-02, spanning 45 years, are plotted here, with data from Owens Valley Radio Observatory (OVRO) in blue; University of Michigan Radio Astronomical Observatory (UMRAO) in brown; and Haystack Observatory in green. The observations match a simple sine wave, indicated in blue. Astronomers believe that the sine wave pattern is caused by two supermassive black holes at the heart of the quasar orbiting around each other every two years. (A period of five years was actually observed due to a Doppler effect caused by the expansion of the universe.) One of the black holes is shooting out a relativistic jet that dims and brightens periodically. Note that data from OVRO and UMRAO match for the peak in 2010, and the UMRAO and Haystack data match for the peak in 1981. The magnitudes of the peaks observed around 1980 are twice as large as those observed in recent times, presumably because more material was falling towards the black hole and being ejected at that time.

Tony Readhead / Sandra O'Neill

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Astronomers find evidence for the tightest-knit supermassive black hole duo observed to date

Locked in an epic cosmic waltz 9 billion light years away, two supermassive black holes appear to be orbiting around each other every two years. The two giant bodies each have masses that are hundreds of millions of times larger than that of our sun, and the objects are separated by a distance roughly 50 times that which separates our sun and Pluto. When the pair merge in roughly 10,000 years, the titanic collision is expected to shake space and time itself, sending gravitational waves across the universe.

A Caltech-led team of astronomers has discovered evidence for this scenario taking place within a fiercely energetic object known as a quasar. Quasars are active cores of galaxies in which a supermassive black hole is siphoning material from a disk encircling it. In some quasars, the supermassive black hole creates a jet that shoots out at near the speed of light. The quasar observed in the new study, PKS 2131-021, belongs to a subclass of quasars called blazars in which the jet is pointing toward the Earth. Astronomers already knew quasars could possess two orbiting supermassive black holes, but finding direct evidence for this has proved difficult.

Reporting in The Astrophysical Journal Letters, the researchers argue that PKS 2131-021 is now the second known candidate for a pair of supermassive black holes caught in the act of merging. The first candidate pair, within a quasar called OJ 287, orbit each other at greater distances, circling every nine years versus the two years it takes for the PKS 2131-021 pair to complete an orbit.

The telltale evidence came from radio observations of PKS 2131-021 that span 45 years. According to the study, a powerful jet emanating from one of the two black holes within PKS 2131-021 is shifting back and forth due to the pair's orbital motion. This causes periodic changes in the quasar's radio-light brightness. Five different observatories registered these oscillations, including Caltech's Owens Valley Radio Observatory (OVRO), the University of Michigan Radio Astronomy Observatory (UMRAO), MIT's Haystack Observatory, the National Radio Astronomy Observatory (NRAO), Metsähovi Radio Observatory in Finland, and NASA's Wide-field Infrared Survey Explorer (WISE) space satellite.

The combination of the radio data yields a nearly perfect sinusoidal light curve unlike anything observed from quasars before.

"When we realized that the peaks and troughs of the light curve detected from recent times matched the peaks and troughs observed between 1975 and 1983, we knew something very special was going on," says Sandra O'Neill, lead author of the new study and an undergraduate student at Caltech who is mentored by Tony Readhead, Robinson Professor of Astronomy, Emeritus.

Tightest-Knit Supermassive Black Hole Duo Found in Heart of Distant Galaxy

Ripples in Space and Time

Most, if not all, galaxies possess monstrous black holes at their cores, including our own Milky Way galaxy. When galaxies merge, their black holes "sink" to the middle of the newly formed galaxy and eventually join together to form an even more massive black hole. As the black holes spiral toward each other, they increasingly disturb the fabric of space and time, sending out gravitational waves, which were first predicted by Albert Einstein more than 100 years ago.

The National Science Foundation's LIGO (Laser Interferometer Gravitational-Wave Observatory), which is managed jointly by Caltech and MIT, detects gravitational waves from pairs of black holes up to dozens of times the mass of our sun. However, the supermassive black holes at the centers of galaxies have millions to billions of times as much mass as our sun, and give off lower frequencies of gravitational waves than those detected by LIGO.

In the future, pulsar timing arrays—which consist of an array of pulsing dead stars precisely monitored by radio telescopes—should be able to detect the gravitational waves from supermassive black holes of this heft. (The upcoming Laser Interferometer Space Antenna, or LISA, mission would detect merging black holes whose masses are 1,000 to 10 million times greater than the mass of our sun.) So far, no gravitational waves have been registered from any of these heavier sources, but PKS 2131-021 provides the most promising target yet.

In the meantime, light waves are the best option to detect coalescing supermassive black holes.

The first such candidate, OJ 287, also exhibits periodic radio-light variations. These fluctuations are more irregular, and not sinusoidal, but they suggest the black holes orbit each other every nine years. The black holes within the new quasar, PKS 2131-021, orbit each other every two years and are 2,000 astronomical units apart, about 50 times the distance between our sun and Pluto, or 10 to 100 times closer than the pair in OJ 287. (An astronomical unit is the distance between Earth and the sun.)

Revealing the 45-Year Light Curve

Readhead says the discoveries unfolded like a "good detective novel," beginning in 2008 when he and colleagues began using the 40-meter telescope at OVRO to study how black holes convert material they "feed" on into relativistic jets, or jets traveling at speeds up to 99.98 percent that of light. They had been monitoring the brightness of more than 1,000 blazars for this purpose when, in 2020, they noticed a unique case.

"PKS 2131 was varying not just periodically, but sinusoidally," Readhead says. "That means that there is a pattern we can trace continuously over time." The question, he says, then became how long has this sine wave pattern been going on?

The research team then went through archival radio data to look for past peaks in the light curves that matched predictions based on the more recent OVRO observations. First, data from NRAO's Very Long Baseline Array and UMRAO revealed a peak from 2005 that matched predictions. The UMRAO data further showed there was no sinusoidal signal at all for 20 years before that time—until as far back as 1981 when another predicted peak was observed.

"The story would have stopped there, as we didn't realize there were data on this object before 1980," Readhead says. "But then Sandra picked up this project in June of 2021. If it weren't for her, this beautiful finding would be sitting on the shelf."

O'Neill began working with Readhead and the study's second author Sebastian Kiehlmann, a postdoc at the University of Crete and former staff scientist at Caltech, as part of Caltech's Summer Undergraduate Research Fellowship (SURF) program. O'Neill began college as a chemistry major but picked up the astronomy project because she wanted to stay active during the pandemic. "I came to realize I was much more excited about this than anything else I had worked on," she says.

With the project back on the table, Readhead searched through the literature and found that the Haystack Observatory had made radio observations of PKS 2131-021 between 1975 and 1983. These data revealed another peak matching their predictions, this time occurring in 1976.

"This work shows the value of doing accurate monitoring of these sources over many years for performing discovery science," says co-author Roger Blandford, Moore Distinguished Scholar in Theoretical Astrophysics at Caltech who is currently on sabbatical from Stanford University.

Like Clockwork

Readhead compares the system of the jet moving back and forth to a ticking clock, where each cycle, or period, of the sine wave corresponds to the two-year orbit of the black holes (though the observed cycle is actually five years due to light being stretched by the expansion of the universe). This ticking was first seen in 1976 and it continued for eight years before disappearing for 20 years, likely due to changes in the fueling of the black hole. The ticking has now been back for 17 years.

"The clock kept ticking," he says, "The stability of the period over this 20-year gap strongly suggests that this blazar harbors not one supermassive black hole, but two supermassive black holes orbiting each other."

The physics underlying the sinusoidal variations were at first a mystery, but Blandford came up with a simple and elegant model to explain the sinusoidal shape of the variations.

"We knew this beautiful sine wave had to be telling us something important about the system," Readhead says. "Roger's model shows us that it is simply the orbital motion that does this. Before Roger worked it out, nobody had figured out that a binary with a relativistic jet would have a light curve that looked like this."

Says Kiehlmann: "Our study provides a blueprint for how to search for such blazar binaries in the future."

The Astrophysical Journal Letters study titled "The Unanticipated Phenomenology of the Blazar PKS 2131-021: A Unique Super-Massive Black hole Binary Candidate" was funded by Caltech, the Max Planck Institute for Radio Astronomy, NASA, National Science Foundation (NSF), the Academy of Finland, the European Research Council, ANID-FONDECYT (Agencia Nacional de Investigación y Desarrollo-Fondo Nacional de Desarrollo Científico y Tecnológico in Chile), the Natural Science and Engineering Council of Canada, the Foundation for Research and Technology – Hellas in Greece, the Hellenic Foundation for Research and Innovation in Greece, and the University of Michigan. Other Caltech authors include Tim Pearson, Vikram Ravi, Kieran Cleary, Matthew Graham, and Tom Prince. Other authors from the Jet Propulsion Laboratory, which is managed by Caltech for NASA, include Michele Vallisneri and Joseph Lazio.

Written by Whitney Clavin

Contact:

Whitney Clavin
(626) 395‑1944
wclavin@caltech.edu

 

 

Source: Caltech - California Institute of Technology/News

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A Blazar In the Early Universe

VLBA image of the blazar PSO J0309+27, 12.8 billion light-years from Earth.
Credit: Spingola et al.; Bill Saxton, NRAO/AUI/NSF. Hi-Res File

 

Full size image for download: VLBA image of the blazar PSO J0309+27
Credit: Spingola et al.; Bill Saxton, NRAO/AUI/NSF.  Hi-Res File

The VLBA image of the blazar PSO J0309+27 is composed of data from three observations made at different radio frequencies. Red is from an observation at 1.5 GHz; green from 5 GHz; and blue from 8.4 GHz. The lower-frequency, or longer wavelength, data show the large-scale structure of the object; the intermediate- and higher-frequency data reveal increasingly smaller structures invisible to the VLBA at the lower frequency. Credit: Spingola et al.; Bill Saxton, NRAO/AUI/NSF. Hi-Res File

The blazar PSO J0309+27 is in the constellation Aries.
Credit: Bill Saxton, NRAO/AUI/NSF.  Hi-Res File

The supersharp radio “vision” of the National Science Foundation’s Very Long Baseline Array (VLBA) has revealed previously unseen details in a jet of material ejected at three-quarters the speed of light from the core of a galaxy some 12.8 billion light-years from Earth. The galaxy, dubbed PSO J0309+27, is a blazar, with its jet pointed toward Earth, and is the brightest radio-emitting blazar yet seen at such a distance. It also is the second-brightest X-ray emitting blazar at such a distance.

In this image, the brightest radio emission comes from the galaxy’s core, at bottom right. The jet is propelled by the gravitational energy of a supermassive black hole at the core, and moves outward, toward the upper left. The jet seen here extends some 1,600 light-years, and shows structure within it.

At this distance, PSO J0309+27 is seen as it was when the universe was less than a billion years old, or just over 7 percent of its current age.

An international team of astronomers led by Cristiana Spingola of the University of Bologna in Italy, observed the galaxy in April and May of 2020. Their analysis of the object’s properties provides support for some theoretical models for why blazars are rare in the early universe. The researchers reported their results in the journal Astronomy & Astrophysics.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Scientific Paper

Media Contact:

Dave Finley, Public Information Officer
(575) 835-7302
dfinley@nrao.edu

 

Source:  National Radio Astronomy Observatory (NRAO)/News

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VLA Gives Tantalizing Clues About Source of Energetic Cosmic Neutrino

Supermassive black hole at core of galaxy accelerates particles in jets moving outward at nearly the speed of light. In a Blazar, one of these jets is pointed nearly straight at Earth. Credit: Sophia Dagnello, NRAO/AUI/NSF

Astronomers pinpoint likely source of high-energy cosmic rays for first time

A single, ghostly subatomic particle that traveled some 4 billion light-years before reaching Earth has helped astronomers pinpoint a likely source of high-energy cosmic rays for the first time. Subsequent observations with the National Science Foundation’s (NSF) Karl G. Jansky Very Large Array (VLA) have given the scientists some tantalizing clues about how such energetic cosmic rays may be formed at the cores of distant galaxies.

On September 22, 2017, an observatory called IceCube, made up of sensors distributed through a square kilometer of ice under the South Pole, recorded the effects of a high-energy neutrino coming from far beyond our Milky Way Galaxy. Neutrinos are subatomic particles with no electrical charge and very little mass. Since they interact only very rarely with ordinary matter, neutrinos can travel unimpeded for great distances through space.

Follow-up observations with orbiting and ground-based telescopes from around the world soon showed that the neutrino likely was coming from the location of a known cosmic object — a blazar called TXS 0506+056, about 4 billion light-years from Earth. Like most galaxies, blazars contain supermassive black holes at their cores. The powerful gravity of the black hole draws in material that forms a hot rotating disk. Jets of particles traveling at nearly the speed of light are ejected perpendicular to the disk. Blazars are a special class of galaxies, because in a blazar, one of the jets is pointed almost directly at Earth.

Theorists had suggested that these powerful jets could greatly accelerate protons, electrons, or atomic nuclei, turning them into the most energetic particles known in the Universe, called ultra-high energy cosmic rays. The cosmic rays then could interact with material near the jet and produce high-energy photons and neutrinos, such as the neutrino detected by IceCube.

Cosmic rays were discovered in 1912 by physicist Victor Hess, who carried instruments in a balloon flight. Subsequent research showed that cosmic rays are either protons, electrons, or atomic nuclei that have been accelerated to speeds approaching that of light, giving some of them energies much greater than those of even the most energetic electromagnetic waves. In addition to the active cores of galaxies, supernova explosions are probable sites where cosmic rays are formed. The galactic black-hole engines, however, have been the prime candidate for the source of the highest-energy cosmic rays, and thus of the high-energy neutrinos resulting from their interactions with other matter.

“Tracking that high-energy neutrino detected by IceCube back to TXS 0506+056 makes this the first time we’ve been able to identify a specific object as the probable source of such a high-energy neutrino,” said Gregory Sivakoff, of the University of Alberta in Canada.

Following the IceCube detection, astronomers looked at TXS 0506+056 with numerous telescopes and found that it had brightened at wavelengths including gamma rays, X-rays, and visible light. The blazar was observed with the VLA six times between October 5 and November 21, 2017.

“The VLA data show that the radio emission from this blazar was varying greatly at the time of the neutrino detection and for two months afterward. The radio frequency with the brightest radio emission also was changing,” Sivakoff said.

TXS 0506+056 has been monitored over a number of years with the NSF’s Very Long Baseline Array (VLBA), a continent-wide radio telescope system that produces extremely detailed images. The high-resolution VLBA images have shown bright knots of radio emission that travel outward within the jets at speeds nearly that of light. The knots presumably are caused by denser material ejected sporadically through the jet.

“The behavior we saw with the VLA is consistent with the emission of at least one of these knots. It’s an intriguing possibility that such knots may be associated with generating high-energy cosmic rays and thus the kind of high-energy neutrino that IceCube found,” Sivakoff said.

The scientists continue to study TXS 0506+056. “There are a lot of exciting phenomena going on in this object,” Sivakoff concluded.

“The era of multi-messenger astrophysics is here,” said NSF Director France Córdova. “Each messenger — from electromagnetic radiation, gravitational waves and now neutrinos — gives us a more complete understanding of the Universe, and important new insights into the most powerful objects and events in the sky. Such breakthroughs are only possible through a long-term commitment to fundamental research and investment in superb research facilities.”

Sivakoff and numerous colleagues from institutions around the world are reporting their findings in the journal Science.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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Media Contact:

Dave Finley, 
Public Information Officer
(575) 835-7302
dfinley@nrao.edu

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Paper:

“Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A”, http://science.sciencemag.org/cgi/doi/10.1126/science.aat1378

Source: National Radio Astronomy Observatory (NRAO)

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Possible Extragalactic Source of High-Energy Neutrinos

Coincidence of a highly energetic outburst of an active galactic nucleus with a neutrino event at PeV energy

Nearly 10 billion years ago in a galaxy known as PKS B1424-418, a dramatic explosion occurred. Light from this blast began arriving at Earth in 2012. Now, an international team of astronomers, including scientists from the Max Planck Institute for Radio Astronomy in Bonn, have shown that a record-breaking neutrino seen around the same time likely was born in the same event. The results are published in "Nature Physics".

Fermi LAT images showing the gamma-ray sky around the blazar PKS B1424-418. Brighter colors indicate greater numbers of gamma rays. The dashed arc marks part of the source region established by IceCube for the Big Bird neutrino (50-percent confidence level). Left: An average of LAT data centered on July 8, 2011 covering 300 days when the blazar was inactive. Right: An average of 300 active days centered on Feb. 27, 2013, when PKS B1424-418 was the brightest blazar in this part of the sky. © NASA/DOE/LAT-Kollaboration

Neutrinos are the fastest, lightest and most unsociable understood fundamental particles, and scientists are just now capable of detecting high-energy ones arriving from deep space. The present work provides the first plausible association between a single extragalactic object and one of these cosmic neutrinos.

Although neutrinos far outnumber all the atoms in the universe, they rarely interact with matter, which makes detecting them quite a challenge. But this same property lets neutrinos make a fast exit from places where light cannot easily escape -- such as the core of a collapsing star -- and zip across the universe almost completely unimpeded. Neutrinos can provide information about processes and environments that simply aren't available through a study of light alone.

Recently, the IceCube Neutrino Observatory at the South Pole found first evidence for a flux of extraterrestrial neutrinos, which was named the Physics World breakthrough of the year 2013. To date, the science team of IceCube Neutrino has announced about a hundred very high-energy neutrinos and nicknamed the most extreme events after characters on the children's TV series "Sesame Street." On Dec. 4, 2012, IceCube detected an event known as Big Bird, a neutrino with an energy exceeding 2 quadrillion electron volts (PeV). To put that in perspective, it's more than a million million times greater than the energy of a dental X-ray packed into a single particle thought to possess less than a millionth the mass of an electron. Big Bird was the highest-energy neutrino ever detected at the time and still ranks second.

Where did it come from? The best IceCube position only narrowed the source to a patch of the southern sky about 32 degrees across, equivalent to the apparent size of 64 full moons. “It’s like a crime scene investigation”, says lead author Matthias Kadler, a professor of astrophysics at the University of Würzburg in Germany, “The case involves an explosion, a suspect, and various pieces of circumstantial evidence.”

Starting in the summer of 2012, NASA’s Fermi satellite witnessed a dramatic brightening of PKS B1424-418, an active galaxy classified as a gamma-ray blazar. An active galaxy is an otherwise typical galaxy with a compact and unusually bright core. The excess luminosity of the central region is produced by matter falling toward a supermassive black hole weighing millions of times the mass of our sun. As it approaches the black hole, some of the material becomes channeled into particle jets moving outward in opposite directions at nearly the speed of light. In blazars one of these jets happens to point almost directly toward Earth.

During the year-long outburst, PKS B1424-418 shone between 15 and 30 times brighter in gamma rays than its average before the eruption. The blazar is located within the Big Bird source region, but then so are many other active galaxies detected by Fermi.

These radio images from the TANAMI project reveal the 2012-2013 eruption of PKS B1424-418 at a radio frequency of 8.4 GHz. The core of the blazar’s jet brightened by four times, producing the most dramatic blazar outburst TANAMI has observed to date. © TANAMI Collaboration

The scientists searching for the neutrino source then turned to data from a long-term observing program named TANAMI. Since 2007, TANAMI has routinely monitored nearly 100 active galaxies in the southern sky, including many flaring sources detected by Fermi. Three radio observations between 2011 and 2013 cover the period of the Fermi outburst. They reveal that the core of the galaxy's jet had been brightening by about four times. “No other of our galaxies observed by TANAMI over the life of the program has exhibited such a dramatic change”, explains Eduardo Ros, from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany.

Within their jets, blazars are capable of accelerating protons to relativistic energies. Interactions of these protons with light in the central regions of the blazar can create pions. When these pions decay, both gamma rays and neutrinos are produced. "We combed through the field where Big Bird must have originated looking for astrophysical objects capable of producing high-energy particles and light," says coauthor Felicia Krauß, a doctoral student at the University of Erlangen-Nürnberg in Germany. "There was a moment of wonder and awe when we realized that the most dramatic outburst we had ever seen in a blazar happened in just the right place at just the right time."

In a paper published Monday, April 18, in Nature Physics, the team suggests the PKS B1424-418 outburst and Big Bird are linked, calculating only a 5-percent probability the two events occurred by chance alone. Using data from Fermi, NASA’s Swift and WISE satellites, the LBA and other facilities, the researchers determined how the energy of the eruption was distributed across the electromagnetic spectrum and showed that it was sufficiently powerful to produce a neutrino at PeV energies.

"Taking into account all of the observations, the blazar seems to have had means, motive and opportunity to fire off the Big Bird neutrino, which makes it our prime suspect," explains Matthias Kadler.

Francis Halzen, the principal investigator of IceCube at the University of Wisconsin–Madison, and not involved in this study, thinks the result is an exciting hint of things to come. "IceCube is about to send out real-time alerts when it records a neutrino that can be localized to an area a little more than half a degree across, or slightly larger than the apparent size of a full moon," he says. "We're slowly opening a neutrino window onto the cosmos." "This study demonstrates the vital importance of classical astronomical observations in an era when new detection methods like neutrino observatories and gravitational-wave detectors open new but unknown skies", concludes Anton Zensus, director at MPIfR and head of its Radio Astronomy/VLBI research department, also a coauthor of the study.

Source: Max Planck Institute for Radio Astronomy

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Local Contacts

Prof. Dr. Eduardo Ros

Phone:+49 228 525-125

Email: ros@mpifr-bonn.mpg.de  
Max-Planck-Institut für Radioastronomie, Bonn

Prof. Dr. J. Anton Zensus
Director and Head of "Radio Astronomy/VLBI" Research Dept.
Phone: +49 228 525-298 (secretary)
Email: azensus@mpifr-bonn.mpg.de

Max-Planck-Institut für Radioastronomie, Bonn

Dr. Norbert Junkes
Press and Public Outreach Phone:+49 228 525-399
Email: njunkes@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn
 

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Original Paper 

Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event

 

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Links:

• TANAMI
• IceCube
• Fermi
• Univ. Würzburg
• Radio Astronomy / VLBI

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TANAMI is a multiwavelength monitoring program of active galaxies in the Southern sky. It includes regular radio observations using the Australian Long Baseline Array (LBA) and associated telescopes in Chile, South Africa, New Zealand and Antarctica. When networked together, they operate as a single radio telescope more than 6,000 miles across and provide a unique high-resolution look into the jets of active galaxies.

The IceCube Neutrino Observatory, built into a cubic kilometer of clear glacial ice at the South Pole, detects neutrinos when they interact with atoms in the ice. This triggers a cascade of fast-moving charged particles that emit a faint glow, called Cerenkov light, as they travel, which is picked up by thousands of optical sensors strung throughout IceCube. Scientists determine the energy of an incoming neutrino by the amount of light its particle cascade emits.

NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

MPIfR scientists involved in the project are Eduardo Ros and J. Anton Zensus.

VERITAS Detects Gamma Rays from Galaxy Halfway Across the Visible Universe

This artist's conception shows a blazar – the core of an active galaxy powered by a supermassive black hole. The VERITAS array has detected gamma rays from a blazar known as PKS 1441+25. Researchers found that the source of the gamma rays was within the relativistic jet but surprisingly far from the galaxy's black hole. The emitting region is at least a tenth of a light-year away, and most likely is 5 light-years away. Credit: M. Weiss/CfA.   High Resolution (jpg) - Low Resolution (jpg)

Cambridge, MA - In April 2015, after traveling for about half the age of the universe, a flood of powerful gamma rays from a distant galaxy slammed into Earth's atmosphere. That torrent generated a cascade of light - a shower that fell onto the waiting mirrors of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) in Arizona. The resulting data have given astronomers a unique look into that faraway galaxy and the black hole engine at its heart.

Gamma rays are photons of light with very high energies. These gamma rays came from a galaxy known as PKS 1441+25, which is a rare type of galaxy known as a blazar. At its center it hosts a supermassive black hole surrounded by a disk of hot gas and dust.

As material from the disk swirls toward the black hole, some of it gets channeled into twin jets that blast outward like water from a fire hose only much faster - close to the speed of light. One of those jets is aimed nearly in our direction, giving us a view straight into the galaxy's core.

"We're looking down the barrel of this relativistic jet," explains Wystan Benbow of the Harvard-Smithsonian Center for Astrophysics (CfA). "That's why we're able to see the gamma rays at all."

One of the unknowns in blazar physics is the exact location of gamma-ray emission. Using data from VERITAS, as well as the Fermi Gamma-Ray Space Telescope, the researchers found that the source of the gamma rays was within the relativistic jet but surprisingly far from the galaxy's black hole. The emitting region is at least a tenth of a light-year away, and most likely is 5 light-years away. (A light-year is the distance light travels in one year, or about 6 trillion miles.)

Moreover, the region emitting gamma rays was larger than typically seen in an active galaxy, measuring about a third of a light-year across. "These jets tend to have clumps in them. It's possible that two of those clumps may have collided and that's what generated the burst of energy," says co-author Matteo Cerruti of the CfA.

Measuring high-energy gamma rays at all was a surprise. They tend to be either absorbed at the source or on their long journey to Earth. When the galaxy flared to life, it must have generated a huge flood of gamma rays.

The finding also provides insight into a phenomenon known as extragalactic background light or EBL, a faint haze of light that suffuses the universe. The EBL comes from all the stars and galaxies that have ever existed, and in a sense can track the history of the universe.

The EBL also acts like a fog to high-energy gamma rays, absorbing them as they travel through space. This new measurement sets an indirect limit on how abundant the EBL can be - too much, and it would have absorbed the gamma-ray flare. The results complement previous measurements based on direct observations.

These results have been accepted for publication in The Astrophysical Journal Letters and are available online.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, 

Contact:

Christine Pulliam
Media Relations Manager
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Source: Harvard-Smithsonian Center for Astrophysics (CfA)

NASA's Fermi Mission Finds Hints of Gamma-ray Cycle in an Active Galaxy

Fermi observations suggest possible years-long cyclic changes in gamma-ray emission from the blazar PG 1553+113. The graph shows Fermi Large Area Telescope data from August 2008 to July 2015 for gamma rays with energies above 100 million electron volts (MeV). For comparison, visible light ranges between 2 and 3 electron volts. Vertical lines on data points are error bars. Background: One possible explanation for the gamma-ray cycle is an oscillation of the jet produced by the gravitational pull of a second massive black hole, seen at top left in this artist's rendering.Credits: NASA's Goddard Space Flight Center/CI Lab. Hi-res image

Astronomers using data from NASA's Fermi Gamma-ray Space Telescope have detected hints of periodic changes in the brightness of a so-called "active" galaxy, whose emissions are powered by a supersized black hole. If confirmed, the discovery would mark the first years-long cyclic gamma-ray emission ever detected from any galaxy, which could provide new insights into physical processes near the black hole.

"Looking at many years of data from Fermi's Large Area Telescope (LAT), we picked up indications of a roughly two-year-long variation of gamma rays from a galaxy known as PG 1553+113," said Stefano Ciprini, who coordinates the Fermi team at the Italian Space Agency's Science Data Center (ASDC) in Rome. "This signal is subtle and has been seen over less than four cycles, so while this is tantalizing we need more observations."

Supermassive black holes weighing millions of times the sun's mass lie at the hearts of most large galaxies, including our own Milky Way. In about 1 percent of these galaxies, the monster black hole radiates billions of times as much energy as the sun, emission that can vary unpredictably on timescales ranging from minutes to years. Astronomers refer to these as active galaxies.

More than half of the gamma-ray sources seen by Fermi's LAT are active galaxies called blazars, like PG 1553+113. As matter falls toward its supermassive black hole, some subatomic particles escape at nearly the speed of light along a pair of jets pointed in opposite directions. What makes a blazar so bright is that one of these particle jets happens to be aimed almost directly toward us.

"In essence, we are looking down the throat of the jet, so how it varies in brightness becomes our primary tool for understanding the structure of the jet and the environment near the black hole," said Sara Cutini, an astrophysicist at ASDC.

Motivated by the possibility of regular gamma-ray changes, the researchers examined a decade of multiwavelength data. These included long-term optical observations from Tuorla Observatory in Finland, Lick Observatory in California, and the Catalina Sky Survey near Tucson, Arizona, as well as optical and X-ray data from NASA's Swift spacecraft. The team also studied observations from the Owens Valley Radio Observatory near Bishop, California, which has observed PG 1553+113 every few weeks since 2008 as part of an ongoing blazar monitoring program in support of the Fermi mission.

"The cyclic variations in visible light and radio waves are similar to what we see in high-energy gamma-rays from Fermi," said Stefan Larsson, a researcher at the Royal Institute of Technology in Stockholm and a long-time collaborator with the ASDC team. "The fact that the pattern is so consistent across such a wide range of wavelengths is an indication that the periodicity is real and not just a fluctuation seen in the gamma-ray data."

Ciprini, Cutini, Larsson and their colleagues published the findings in the Nov. 10 edition of The Astrophysical Journal Letters. If the gamma-ray cycle of PG 1553+113 is in fact real, they predict it will peak again in 2017 and 2019, well within Fermi's expected operational lifetime.

The scientists identified several scenarios that could drive periodic emission, including different mechanisms that could produce a years-long wobble in the jet of high-energy particles emanating from the black hole. 

The most exciting scenario involves the presence of a second supermassive black hole closely orbiting the one producing the jet we observe. The gravitational pull of the neighboring black hole would periodically tilt the inner part of its companion's accretion disk, where gas falling toward the black hole accumulates and heats up. The result would be a slow oscillation of the jet much like that of a lawn sprinkler, which could produce the cyclic gamma-ray changes we observe.    

PG 1553+113 lies in the direction of the constellation Serpens, and its light takes about 5 billion years to reach Earth.

NASA's Fermi Gamma-ray Space Telescope was launched in June 2008. The mission is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

 

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Maryland

Source:  NASA/Galaxies

What Makes Blazars Vary?

An artist's conception of the Fermi spacecraft in orbit. Astronomers have used Fermi to monitor the gamma-ray variability of thirteen blazars, and find evidence that the emission arises in several different zones and/or from several mechanisms. Credit:NASA/Fermi. Hi-Res image

Science Update - A look at CfA discoveries from recent journals

A blazar is a galaxy whose central, supermassive black hole shines intensely as it accretes material from the surrounding region. Although black hole accretion happens in many galaxies and situations, in blazars the infalling material erupts into a powerful, narrow beam of high velocity charged particles that are fortuitously pointed in our direction. These particles produce gamma rays, each photon over a hundred million times more energetic than the highest energy X-ray photons seen by the Chandra X-ray Observatory. Blazars are also generally characterized by having rapid, strong, and incessant variability, among a host of effects resulting from its beam of rapidly moving electrons. 

Astronomers suspect that clues to the inner workings of black holes and accretion disks can be discerned from modeling the details of the variability, but this has been a difficult task. The complexity of the variability indicates that the emitting structures are also complex, and constraining the locations and sizes of the emitting sites has been hampered by a lack of long-term, sensitive observations capable of steady monitoring of the changing activity.

CfA astronomers Malgosia Sobolewska and Aneta Siemiginowska and two colleagues tackled the problem using the Large Area Telescope (LAT), a gamma ray imaging telescope onboard the Fermi spacecraft. LAT is well suited for studying the variability of blazars, and has been taking continuous observations of the gamma-ray sky since Fermi was launched in 2008. It therefore has an excellent set of light curves (plots of the intensity versus time) for blazars. Recent analyses showed that the blazar light seemed to be produced in random processes, at least for the high energy gamma-rays. The problem is that many of brightest blazar episodes are thought to be flares from a distinctly different kind of process than the regular emission, and if so they should be identified as not arising from a single random process. For example, there are hints in two blazars of activity that is preferentially occurring in six- or seven-day intervals, pointing to shocks or colliding ejecta of some kind.

The scientists undertook a systematic analysis of the first four years of the Fermi/LAT dataset for thirteen bright blazars, and they developed new methods that are insensitive to the known observational biases. They find that three blazars have emission consistent with arising from a combination of random processes; in two they constrain the characteristic times to seventeen and thirty-eight days respectively – longer times than ever before seen and suggestive that the gamma-ray and X-ray emissions arise in different zones of the blazar. In four other blazars they report evidence of characteristic timescales faster than one hour, a finding that is not easily understood and, together with their other conclusions, points to new progress and new puzzles in deciphering what makes blazars blaze.

Reference(s): 

"Stochastic Modeling of the Fermi/LAT γ -Ray Blazar Variability," M. A. Sobolewska, A. Siemiginowska, B. C. Kelly, and K. Nalewajko, ApJ 786, 143, 2014

Source:  Smithsonian Astrophysical Observatory

Galaxy's Gamma-Ray Flares Erupted Far From its Black Hole

In 2011, a months-long blast of energy launched by an enormous black hole almost 11 billion years ago swept past Earth. Using a combination of data from NASA's Fermi Gamma-ray Space Telescope and the National Science Foundation's Very Long Baseline Array (VLBA), the world's largest radio telescope, astronomers have zeroed in on the source of this ancient outburst.

 Theorists expect gamma-ray outbursts occur only in close proximity to a galaxy's central black hole, the powerhouse ultimately responsible for the activity. A few rare observations suggested this is not the case.

 The 2011 flares from a galaxy known as 4C +71.07 now give astronomers the clearest and most distant evidence that the theory still needs some work. The gamma-ray emission originated about 70 light-years away from the galaxy's central black hole.

Prior to its strong outbursts in 2011, blazar 4C +71.07 was a weak source for Fermi’s LAT. These images centered on 4C +71.07 show the rate at which the LAT detected gamma rays with energies above 100 million electron volts; lighter colors equal higher rates. The image at left covers 2.5 years, from the start of Fermi’s mission to 2011. The image at right shows 10 weeks of activity in late 2011, when 4C +71.07 produced its strongest outburst. A more frequently active blazar, S5 0716+71, appears in both images.
Credit: NASA/DOE/Fermi LAT Collaboration .  › Larger image - › Larger image (unlabeled)

The 4C +71.07 galaxy was discovered as a source of strong radio emission in the 1960s. NASA's Compton Gamma-Ray Observatory, which operated in the 1990s, detected high-energy flares, but the galaxy was quiet during Fermi's first two and a half years in orbit.

 In early November 2011, at the height of the outburst, the galaxy was more than 10,000 times brighter than the combined luminosity of all of the stars in our Milky Way galaxy.

 "This renewed activity came after a long slumber, and that's important because it allows us to explicitly link the gamma-ray flares to the rising emission observed by radio telescopes," said David Thompson, a Fermi deputy project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.

 Located in the constellation Ursa Major, 4C +71.07 is so far away that its light takes 10.6 billion years to reach Earth. Astronomers are seeing this galaxy as it existed when the universe was less than one-fourth of its present age.

At the galaxy's core lies a supersized black hole weighing 2.6 billion times the sun's mass. Some of the matter falling toward the black hole becomes accelerated outward at almost the speed of light, creating dual particle jets blasting in opposite directions. One jet happens to point almost directly toward Earth. This characteristic makes 4C +71.07 a blazar, a classification that includes some of the brightest gamma-ray sources in the sky.

Boston University astronomers Alan Marscher and Svetlana Jorstad routinely monitor 4C +71.07 along with dozens of other blazars using several facilities, including the VLBA.

The instrument's 10 radio telescopes span North America, from Hawaii to St. Croix in the U.S. Virgin Islands, and possess the resolving power of a single radio dish more than 5,300 miles across when their signals are combined. As a result, The VLBA resolves detail about a million times smaller than Fermi's Large Area Telescope (LAT) and 1,000 times smaller than NASA's Hubble Space Telescope.

In autumn 2011, the VLBA images revealed a bright knot that appeared to move outward at a speed 20 times faster than light.

"Although this apparent speed was an illusion caused by actual motion almost directly toward us at 99.87 percent the speed of light, this knot was the key to determining the location where the gamma-rays were produced in the black hole's jet," said Marscher, who presented the findings Monday, Jan. 7, at the American Astronomical Society meeting in Long Beach, Calif.

VLBA and Fermi provided complementary observations of the blazar outburst.

Top: During the most intense episode of gamma-ray flaring, VLBA radio maps and polarization measurements, among other observations, linked a bright knot in the jet of 4C +71.07 to variations in brightness in visible and gamma-ray light. The knot appeared to move outward at 20 times the speed of light, an illusion caused by motion almost directly toward us at 99.87 percent the speed of light.

Bottom: The rise and fall of the blazar's gamma-ray brightness as recorded by Fermi's LAT in late 2011 and early 2012.

Credit: NASA's Goddard Space Flight Center/A. Marscher and S.Jorstad (BU) . › Larger image

The knot passed through a bright stationary feature of the jet, which the astronomers refer to as its radio "core," on April 9, 2011. This occurred within days of Fermi's detection of renewed gamma-ray flaring in the blazar. Marscher and Jorstad noted that the blazar brightened at visible wavelengths in step with the higher-energy emission.

During the most intense period of flaring, from October 2011 to January 2012, the scientists found the polarization direction of the blazar's visible light rotated in the same manner as radio emissions from the knot. They concluded the knot was responsible for the visible and the gamma-ray light, which varied in sync.

This association allowed the researchers to pinpoint the location of the gamma-ray outburst to about 70 light-years from the black hole.

The astronomers think that the gamma rays were produced when electrons moving near the speed of light within the jet collided with visible and infrared light originating outside of the jet. Such a collision can kick the light up to much higher energies, a process known as inverse-Compton scattering.

The source of the lower-energy light is unclear at the moment. The researchers speculate the source may be an outer, slow-moving sheath that surrounds the jet. Nicholas MacDonald, a graduate student at Boston University, is investigating how the gamma-ray brightness should change in this scenario to compare with observations. "The VLBA is the only instrument that can bring us images from so near the edge of a young supermassive black hole, and Fermi's LAT is the only instrument that can see the highest-energy light from the galaxy's jet," said Jorstad.

NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership. Fermi is managed by NASA's Goddard Space Flight Center. It was developed in collaboration with the U.S. Department of Energy, with contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

The VLBA is operated by the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

The Very Long Baseline Array is a system of ten radio telescopes spanning 5,500 miles that work together as the world's largest dedicated astronomical instrument. Each station consists of an 82-foot-diameter, 240-ton dish antenna and an adjacent control building. Credit: NASA's Goddard Space Flight Center . › Larger image - › Larger image (no labels)

Related Links

• "Active Galaxies Flare and Fade in Fermi Telescope All-Sky Movie" (04.03.09)

• "NASA's Fermi Mission, Namibia's HESS Telescopes Explore a Blazar" (03.18.09)

• Active Galaxies and Quasars on NASA's "Imagine the Universe!"

• The Very Long Baseline Array (VLBA)

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md. 

Text issued as NASA Headquarters Release No. 13-004

J. D. Harrington
NASA Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov

Lynn Chandler
NASA's Goddard Space Flight Center, Greenbelt, Md.
301-286-2806
 lynn.chandler-1@nasa.gov

A New Class of Extragalactic Objects

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.  Low Resolution Image (jpg)

 

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 massive black hole erupts into powerful, narrow beams of high velocity charged particles. The intense X-ray and gamma ray emission 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 blazar 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 gamma ray sources. 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 optical telescopes. 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.

Source: Harvard-Smithsonian Center for Astrophysics

 

NASA's WISE Mission Sees Skies Ablaze With Blazars

This artist's concept shows a "feeding," or active, supermassive black hole with a jet streaming outward at nearly the speed of light. Such active black holes are often found at the hearts of elliptical galaxies. Not all black holes have jets, but when they do, the jets can be pointed in any direction. If a jet happens to shine at Earth, the object is called a blazar. Image credit: NASA/JPL-Caltech. Full image and caption

This image taken by NASA's Wide-field Infrared Survey Explorer (WISE) shows a blazar -- a voracious supermassive black hole inside a galaxy with a jet that happens to be pointed right toward Earth. These objects are rare and hard to find, but astronomers have discovered that they can use the WISE all-sky infrared images to uncover new ones. So far, researchers have found more than 200 new blazars, and they say WISE has the potential to find many more. Image credit: NASA/JPL-Caltech/Kavli. Full image and caption - enlarge image

PASADENA, Calif. - 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 mission has revealed more than 200 blazars and has the potential to find thousands more.

Blazars are among the most energetic objects in the universe. They consist of supermassive black holes actively "feeding," or pulling matter onto them, at the cores of giant galaxies. As the matter is dragged toward the supermassive hole, some of the energy is released in the form of jets traveling at nearly the speed of light. Blazars are unique because their jets are pointed directly at us.

"Blazars are extremely rare because it's not too often that a supermassive black hole's jet happens to point towards Earth," said Francesco Massaro of the Kavli Institute for Particle Astrophysics and Cosmology near Palo Alto, Calif., and principal investigator of the research, published in a series of papers in the Astrophysical Journal. "We came up with a crazy idea to use WISE's infrared observations, which are typically associated with lower-energy phenomena, to spot high-energy blazars, and it worked better than we hoped."

The findings ultimately will help researchers understand the extreme physics behind super-fast jets and the evolution of supermassive black holes in the early universe.

WISE surveyed the entire celestial sky in infrared light in 2010, creating a catalog of hundreds of millions of objects of all types. Its first batch of data was released to the larger astronomy community in April 2011 and the full-sky data were released last month.

Massaro and his team used the first batch of data, covering more than one-half the sky, to test their idea that WISE could identify blazars. Astronomers often use infrared data to look for the weak heat signatures of cooler objects. Blazars are not cool; they are scorching hot and glow with the highest-energy type of light, called gamma rays. However, they also give off a specific infrared signature when particles in their jets are accelerated to almost the speed of light.

One of the reasons the team wants to find new blazars is to help identify mysterious spots in the sky sizzling with high-energy gamma rays, many of which are suspected to be blazars. NASA's Fermi mission has identified hundreds of these spots, but other telescopes are needed to narrow in on the source of the gamma rays.

Sifting through the early WISE catalog, the astronomers looked for the infrared signatures of blazars at the locations of more than 300 gamma-ray sources that remain mysterious. The researchers were able to show that a little more than half of the sources are most likely blazars.

"This is a significant step toward unveiling the mystery of the many bright gamma-ray sources that are still of unknown origin," said Raffaele D'Abrusco, a co-author of the papers from Harvard Smithsonian Center for Astrophysics in Cambridge, Mass. "WISE's infrared vision is actually helping us understand what's happening in the gamma-ray sky."

The team also used WISE images to identify more than 50 additional blazar candidates and observed more than 1,000 previously discovered blazars. According to Massaro, the new technique, when applied directly to WISE's full-sky catalog, has the potential to uncover thousands more.

"We had no idea when we were building WISE that it would turn out to yield a blazar gold mine," said Peter Eisenhardt, WISE project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who is not associated with the new studies. "That's the beauty of an all-sky survey. You can explore the nature of just about any phenomenon in the universe."

Other authors include: A. Paggi and H.A. Smith of Harvard's Smithsonian Astrophysical Observatory; G. Tosti of the University of Perugia, Italy; M. Ajello of Stanford University, Stanford, Calif.; J.E. Grindlay of the Harvard College Observatory, Cambridge, Mass; and D. Gasparrini of the Italian Space Agency, Science Data Center, Italy.

The Kavli Institute for Particle Astrophysics and Cosmology is a joint institute of Stanford University and SLAC National Accelerator Laboratory in Menlo Park, Calif.

JPL manages and operates WISE for NASA's Science Mission Directorate in Washington. The principal investigator for WISE, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program, managed by the Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. Science operations and data processing and archiving take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

More information is online at http://www.nasa.gov/wise and http://wise.astro.ucla.edu and http://jpl.nasa.gov/wise .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
Whitney.clavin@jpl.nasa.gov

J.D. Harrington 202-358-5241
NASA Headquarters, Washington
j.d.harrington@nasa.gov