Two years ago, the Event Horizon Telescope (EHT) was headlined with the announcement of the first direct image of a black hole. Science magazine named the image a breakthrough of the year. Now the EHT collaboration has returned with another innovative result: a new image of the same black hole, which this time shows how it looks in polarized light. The ability to measure this polarization for the first time — a signature of magnetic fields at the edge of the black hole — is expected to provide a new understanding of how black holes swallow matter and emit powerful jets from their nuclei. The new findings were described in three articles published in The Astrophysical Journal Letters.
“This work is an important milestone: the polarization of light involves information that allows us to better understand the physics behind the image we saw in April 2019, which was not possible before,” said the co-author Iván Martí-Vidal, coordinator of the polarimetry EHT Working group and researcher at the University of Valencia, Spain. “The presentation of this new polarized light image required years of work due to the complex techniques involved in obtaining and analyzing the data.”
Several imaging methods produced the first direct image taken of a black hole in the center of an elliptical galaxy. Located in the constellation of the Virgin, about 55 million light-years away, the galaxy is called Messier 87 (M87). The findings of the collaboration were published on April 10, 2019 in six different articles The Astrophysical Journal Letters. It is a feat that would have been impossible a few generations ago, made possible by technological advances, new innovative algorithms and, of course, connecting several of the best radio observatories in the world. The image confirmed that the object in the center of M87 is actually a black hole.
The EHT captured photons trapped in orbit around the black hole, rotating around the speed of light, creating a bright ring around it. From this, astronomers were able to deduce that the black hole rotates clockwise. The image also revealed the shadow of the black hole, a dark central region inside the ring. This shadow is as close as astronomers can get to taking a picture of the actual black hole, from which light cannot escape once it crosses the event horizon. And just as the size of the event horizon is proportional to the mass of the black hole, so is the shadow of the black hole: the larger the black hole, the larger the shadow. (The mass of the M87 black hole is 6.5 billion times that of our sun.) It was a startling confirmation of the general theory of relativity, which showed that these predictions hold even in extreme gravitational environments.
What was missing, however, was knowing the process behind the powerful twin jets produced by the black hole that envelops the matter, expelling some of the material that fell into it at almost the speed of light. (The black hole in the center of our Milky Way is less devouring, that is, relatively quiet, compared to the black hole in M87.) For example, astronomers still disagree on how these jets accelerate. at such high speeds. These new results place additional constraints around the various competing theories, reducing the possibilities.
Just as polarized sunglasses reduce glare from shiny surfaces, polarized light around a black hole provides a sharper view of the surrounding region. In this case, the polarization of light is not due to special filters (such as sunglasses lenses), but to the presence of magnetic fields in the hot zone of the space surrounding the black hole. This polarization allows astronomers to map the lines of the magnetic field at the inner edge and study the interaction between flowing matter and it is made to fly outward.
“Observations suggest that the magnetic fields at the edge of the black hole are strong enough to push the hot gas and help it withstand the pull of gravity. Only gas that slips through the field can spiral inward. to the horizon of events, ”said co-author Jason Dexter of the University of Colorado, Boulder, who is also the coordinator of the EHT theory working group. This means that only theoretical models that incorporate the characteristic of a strongly magnetized gas accurately describe what the EHT collaboration has observed.
This story originally appeared on Ars Technica.
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