The global collaboration that provided us with not one, but two images of supermassive black holes has now peered into one of the brightest lights in the Universe.
The Event Horizon Telescope (EHT), an array of telescopes comprising radio antennas around the world, studied a distant quasar called NRAO 530, whose light traveled 7.5 billion years to reach us.
The resulting data show us the quasar mechanism in incredible detail and, astronomers say, help us understand the complex physics of these amazing objects and how they generate this brilliant light.
Quasars – a term that is short for “quasi-stellar radio sources” – are a type of galaxy believed to be powered by a very active supermassive black hole at the center. This means that the black hole is surrounded by material that is falling on it at a furious rate.
Black holes themselves do not emit light, but the material around an active black hole does. Gravity and friction cause the material to heat up and ignite as it circulates around the black hole like water down a drain. But that is not all.
Not all material falls into the black hole. Some of it is funneled and accelerated along magnetic field lines outside the event horizon – the “point of no return” beyond which not even light can reach escape velocity.
When this material reaches the poles, it is blasted out into space as powerful jets of plasma, traveling at speeds of a significant percentage of the speed of light, known as relativistic speed. These thin collimated jets also glow brightly… but we don’t fully understand how they are created and powered, and the role played by magnetic fields.
Enter the EHT. It is not an individual instrument or array, but a collaboration of radio telescope facilities around the world that combine to effectively form an Earth-sized radio telescope, much like an astronomical Voltron.
This telescope is a mighty thing. In 2019, it gave humanity our first image of the event horizon of a black hole, the heart of a galaxy called M87 55 million light-years away. Then, last year, it delivered an image of the supermassive black hole at the center of our own galaxy, the Milky Way, Sagittarius A*.
Both images took years to make. The observations of NRAO 530 actually took place in April 2017; the international team used it as a calibration target to take pictures of Sgr A*. This quasar is a popular calibration target for the center of the Milky Way, as the two objects appear quite close together in the sky.
It is these observations that a team – led by astronomers Svetlana Jorstad of Boston University and Maciek Wielgus of the Max Planck Institute for Radio Astronomy in Germany – has now used to peer into the heart of NRAO 530. Across such a vast distance in time and space. in space, researchers were able to see the heart of the quasar in unprecedented detail.
“The light we see has traveled towards Earth for 7.5 billion years through the expanding Universe, but with the power of the EHT we see the details of the source’s structure on a scale as small as a single light year,” he explains. Wielgus.
NRAO 530 is a rare type of quasar known as an “optically violent variable” quasar and is known to have a powerful and highly relativistic jet. It is also classified as a blazar; it is a blazar oriented such that the jet points directly or almost directly at us.
Blazars pose no danger, but they can be quite challenging to study, like observing a linear laser beam.
The EHT images show a bright feature at the southern end of the jet; researchers believe this is the “core” of radio, the point where the jet is launched at a specific wavelength of light. This core has two components, which cannot be seen in longer wavelengths of light, but are clearly visible in EHT observations.
From their observations, the team was able to determine the polarization of light emitted by different parts of the structure. This refers to the orientation of light oscillations, which can be affected by the magnetic fields through which it travels.
This allowed the team to map the magnetic fields in the jet, finding evidence that the magnetic field has a helical structure.
“The outermost feature has a particularly high degree of linear polarization, suggesting a very well-ordered magnetic field,” says Jorstad.
To date, NRAO 530 is the most distant object the EHT has studied, and the results hold promise for future studies of distant objects, as well as more detailed studies of blazars and quasars.
The research was published in The Astrophysical Journal.