In April 2019, if only for a moment, the world was enchanted by an ominous void surrounded by a half halo of light. It was the first direct image of a black holeMore specifically, a supermassive gravity abyss at the core of Messier 87, a galaxy in the constellation Virgo, about 54 million light-years from Earth.
Now, an extensive international collaboration of scientists has examined that data more extensively and, after removing some noise, has released the first polarized image of the black hole, revealing the structure of its magnetic fields.
The research is published today in two articles in the Astrophysical Journal Letters. The papers describe the team’s observational setup and the implications of the findings for understanding theoretical interpretations of the black hole at the center of M87. The hole is a blazar, meaning it has a beam of energy and subatomic particles that shoot out of its accretion disk at nearly the speed of light. The jet’s characteristics are determined by the magnetic fields surrounding it, so understanding the structure of those fields provides clues to the more puzzling issue of jet physics.
“Now if we look at the image, look at how those polarized vectors behave, then we can deduce the geometry of the magnetic field,” said study co-author Maciek Wielgus, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, in a video call. “That’s extremely interesting to us from this perspective of jet physics, because we know what we need to make our theoretical models of jet emissions work.”
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You might find that the new photo is very similar to that original bomb photo, but with a little more swirl in the accretion disk (all the stuff that accumulates around a black hole). What the new image describes, however, is a more specific detail of the black hole. The previous view showed the total light from the plasmoid core of M87. When a black hole has weak magnetic fields, the plasma drags the fields in a circular pattern, and light waves oscillate perpendicular to it, as if unobstructed by the fields. But when the magnetic fields are strong, the polarized pattern of the light waves looks different. And if somewhere between those field strengths, the polarized light emitted takes on a more spiral shape.
“What this research shows is that the projected image of the M87 inner accretion current very close to the black hole looks ring-symmetrical or azimuthal,” said study co-author Richard Anantua, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, in the same video call. “With this vertical magnetic field structure, it tells you that the magnetic fields aren’t just, you know, limp and blurry with the rest of the accretion flow … the magnetic fields are the main scaffolding in the relativistic jets.”
The Event Horizon Telescope is not a traditional telescope at all. It is the uniform term for an increasing number of observatories across four continents, timed on atomic clocks, staring together at space. By effectively making a combined telescope the size of Earth itself, we can bob in a method of cosmological exploration called very long baseline interferometryThe math is complicated, but essentially the different observatories all look at one object and then take into account the minute differences in the arrival of light to each dish to measure the object. As the planet rotates, more observatories collect data and can link that data to what has already been recorded. The more data they get, the sharper the image of a black hole becomes.
The astrophysicists on this team have basically pulled back the curtain on the black hole’s behavior, as Dorothy and her crew did the Wizard of Oz. The difference here, however, is that there are a dozen more behind this curtain. They’ve improved the wizard’s outline a bit.
Wielgus said the “holy grail” would be to better see the deepest workings of the M87 core; specifically, the larger-scale conditions that created a huge plasma beam, ejecting it, collimating and accelerating it. Currently, there is too much noise in the image – and the data behind it – to see anything more, like how an overexposed image shows only the most contrasting objects. With more telescopes in the Event Horizon Telescope’s array, the team will be able to see how the geometry of the magnetic field changes, changes and shapes the beam emitted from the galactic core.
“There is a saying that magnetic fields are lazy because they don’t work. So magnetic fields, you know, they don’t exert magnetic forces that are parallel to them. They exert magnetic forces that are perpendicular to them, ”Anantua said. “By the definition of work, if your force is perpendicular to the direction in which you are doing something, it is not doing any work. But magnetic fields are actually so exceptionally lazy that they just work around this and just use the black hole to do the job for them. “
Black hole, far from big nothing, are actually a stage for a remarkable physics, a location where invisible forces shoot out rays longer than any distance you have ever known in the cosmos, seemingly in spite of the hole’s famous inescapable gravity.
“This is a magnetic rail gun,” Maciek said, “true the source of the energy is the rotational energy of the black hole. “