Scientists have reported a “huge leap forward” in understanding light and other electromagnetic radiation emitted by black holes using NASA’s recently deployed $188 million IXPE Space Telescope.
Beams of electrons crash into slower-moving particles, causing a shock wave that results in electromagnetic radiation across frequency bands from X-rays to visible light, according to a research paper published in Nature this week. .
Astronomers first observed near-stellar radio sources, or quasars, in the early 1960s. This new class of astronomical objects was a puzzle. They looked like stars, but they also radiated very strongly at radio frequencies, and their optical spectra contained strange emission lines not associated with “normal” stars. In fact, these strange objects are gigantic black holes at the center of distant galaxies.
Acceleration of particles in the jet emitted by a supermassive black hole. Illustration credit: Liodakis et al/Nature
Advances in radio astronomy and X-ray observation satellites have helped scientists understand that anomalous radiation is caused by a stream of charged particles accelerated to near the speed of light. If it points towards the Earth, the generator quasar can be called a blazar. Their electromagnetic radiation can be observed from radio waves across the visible spectrum to very high frequency gamma rays.
But the mystery remains as to how the very fast particles end up emitting the radiation.
To shed light on the phenomenon, Ioannis Liodakis, a postdoctoral researcher at the University of Turku, Finland, used data from NASA’s Imaging X-ray Polarimetry Explorer (IXPE) space telescope, designed to observe and measure rays X.
Liodakis and his colleagues used the new kit’s ability to measure X-ray polarization (X-ray polarimetry) in an attempt to gain vital information.
By comparing the polarized X-ray data with the optical polarized visible light data, the scientists came to the conclusion that the electromagnetic radiation resulted from a shock wave in the stream of charged particles emitted by the black hole (see figure ).
In an accompanying article, Lea Marcotulli, NASA Einstein Postdoctoral Fellow at Yale University, said: “Such shock waves occur naturally when particles traveling at near light speed encounter materials more slow along their path. Particles traveling through this shock wave lose radiation quickly and efficiently – and in doing so, they produce polarized X-rays. As the particles move away from the shock, the light they emit radiates with progressively lower frequencies and becomes less polarized.
Marcotulli said Liodakis’ work was the first blazar ever seen through the lens of an X-ray polarimeter, and the results were “dazzling”.
“Blazar jets are among the most powerful particle accelerators in the Universe. Their conditions could never be replicated on Earth, so they provide excellent ‘laboratories’ in which to study particle physics. Thousands of blazars have have now been detected, and at every accessible wavelength, but the mechanisms by which the particles are emitted and accelerated remain elusive.Multi-wavelength polarimetric data from Liodakis and colleagues provide clear evidence for the mechanism of particle acceleration… making the authors’ results a turning point in our understanding of blazars.
“This huge leap brings us one step closer to understanding these extreme particle accelerators, the nature of which has been the subject of much research since their discovery.”
In December last year, a SpaceX Falcon 9 rocket launched NASA’s IXPE mission into orbit from Kennedy Space Center in Florida. It is designed to observe remnants of supernovae, supermassive black holes and other high-energy objects.
The project first got the green light in 2017 and was expected to cost $188 million – a modest price tag compared to NASA’s largest missions on the flagship program often valued at more than $1 billion. ®
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