A long time ago in a galaxy half the universe away, a flood of high-energy gamma rays began its journey to Earth. When they arrived in April, NASA's Fermi Gamma-ray Space Telescope caught the outburst, which helped two ground-based gamma-ray observatories detect some of the highest-energy light e... More
A long time ago in a galaxy half the erse away, a flood of high-energy gamma began its journey to Earth. When they ved in April, NASA's Fermi Gamma-ray e Telescope caught the outburst, which ed two ground-based gamma-ray rvatories detect some of the est-energy light ever seen from a galaxy istant.
Astronomers had assumed that t at different energies came from regions ifferent distances from the black hole. a rays, the highest-energy form of light, thought to be produced closest in. But rvations across the spectrum suggest that t at all wavelengths came from a single on located far away roughly five t-years from the black hole, which is ter than the distance between our sun and nearest star.
The gamma rays came from a xy known as PKS 1441+25, a type of active xy called a blazar. Located toward the tellation Boötes, the galaxy is so far its light takes 7.6 billion years to h us. At its heart lies a monster black with a mass estimated at 70 million s the sun's and a surrounding disk of hot and dust. If placed at the center of our r system, the black hole's event horizon he point beyond which nothing can escape ould extend almost to the orbit of .
As material in the disk falls toward black hole, some of it forms dual icle jets that blast out of the disk in site directions at nearly the speed of t. Blazars are so bright in gamma rays use one jet points almost directly toward giving astronomers a view straight into black hole's dynamic and poorly rstood realm.
In April, PKS 1441+25 rwent a major eruption. Luigi Pacciani at Italian National Institute for ophysics in Rome was leading a project to h blazar flares in their earliest stages ollaboration with the Major Atmospheric a-ray Imaging Cerenkov experiment IC), located on La Palma in the Canary nds. Using public Fermi data, Pacciani overed the outburst and immediately ted the astronomical community. Fermi's e Area Telescope revealed gamma rays up 3 billion electron volts (GeV), reaching the highest-energy part of the rument's detection range. For comparison, ble light has energies between about 2 3 electron volts.
Following up on the i alert, the MAGIC team turned to the ar and detected gamma rays with energies ing from 40 to 250 GeV. Because this xy is so far away, we didn't have a ng expectation of detecting gamma rays energies this high. That’s because ance matters for very high-energy gamma -- they convert into particles when they ide with lower-energy light.
The visible ultraviolet light from stars shining ughout the history of the universe forms mnant glow called the extragalactic ground light (EBL). For gamma rays, this cosmic gauntlet they must pass through e detected at Earth. When a gamma ray unters starlight, it transforms into an tron and a positron and is lost to onomers. The farther away the blazar is, less likely its highest-energy gamma rays survive to be detected.
Following the C discovery, VERITAS also detected gamma with energies approaching 200 GeV. PKS +25 is one of only two such distant ces for which gamma rays with energies e 100 GeV have been observed. Its atic flare provides a powerful glimpse the intensity of the EBL from -infrared to near-ultraviolet wavelengths suggests that galaxy surveys have tified most of the sources responsible it. 15 Dec 2015Less