Lola Gayle, STEAM Register
Astronomers using NASA’s Fermi Gamma-ray Space Telescope have discovered five of the most distant gamma-ray blazars yet known, and two of them are hiding huge monsters at their centers.
The light coming from the most distant object began its journey to us when the universe was 1.4 billion years old. To put it into perspective, the age of the universe is estimated to be 13.8 billion years. Previously, the most distant blazars detected by Fermi emitted their light when the universe was about 2.1 billion years old.
A blazar is a very compact quasar typically associated with a supermassive black hole at the center of an active, giant elliptical galaxy. Astronomers consider them to be among the most energetic phenomena in the universe.
Black-hole-powered galaxies called blazars are the most common sources detected by NASA’s Fermi. As matter falls toward the supermassive black hole at the galaxy’s center, some of it is accelerated outward at nearly the speed of light along jets pointed in opposite directions. When one of the jets happens to be aimed in the direction of Earth, as illustrated here, the galaxy appears especially bright and is classified as a blazar. Credit: M. Weiss/CfA
Blazars account for roughly half of the gamma-ray sources detected by Fermi’s Large Area Telescope (LAT). It’s believed their high-energy emissions are powered by matter heated and torn apart as it falls from an accretion disk toward a supermassive black hole with a million or more times the sun’s mass. Some of this material becomes redirected into a pair of particle jets, which blast outward in opposite directions at nearly the speed of light. Blazars appear their brightest when one of the jets happens to point almost directly toward us.
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Earlier observations showed that the most distant blazars produce most of their light at energies right in between the range detected by the LAT and current X-ray satellites, which made finding them extremely difficult.
But in early 2016, the Fermi team released a full reprocessing of all LAT data, called Pass 8, that ushered in so many improvements astronomers said it was like having a brand new instrument. After searching through the LAT data for the most distant sources in a catalog of 1.4 million quasars, a galaxy class closely related to blazars, astronomers were able to eliminate all but the brightest objects at radio wavelengths from the list.
From there, they wound up with a final sample of about 1,100 objects, from which they pinpointed the five new gamma-ray blazars. Expressed in terms of redshift, the new blazars range from redshift 3.3 to 4.31, which means the light we now detect from them started on its way when the universe was between 1.9 and 1.4 billion years old, respectively.
The researchers were then able to collect all the available multiwavelength data on them and derived properties like the black hole mass, the accretion disk luminosity, and the jet power, said lead researcher Vaidehi Paliya from Clemson University in South Carolina.
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The Monster Inside
Two of the blazars are home to billion-solar-mass black holes that challenge current ideas about how quickly such monsters could grow. All of the objects possess extremely luminous accretion disks that emit more than two trillion times the energy output of our sun. This means matter is continuously falling inward, corralled into a disk and heated before making the final plunge to the black hole.
“The main question now is how these huge black holes could have formed in such a young universe,” said fellow researcher Dario Gasparrini from the Italian Space Agency’s Science Data Center in Rome. “We don’t know what mechanisms triggered their rapid development.”
In the meantime, the team plans to continue a deep search for additional examples.
“We think Fermi has detected just the tip of the iceberg, the first examples of a galaxy population that previously has not been detected in gamma rays,” said team member Marco Ajello, also from Clemson University.
Also included on the research team was Roopesh Ojha, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Ojha presented the findings Monday, Jan. 30, at the American Physical Society meeting in Washington, and a paper describing the results has been submitted to The Astrophysical Journal Letters.
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