Two years ago, The Event Horizon Telescope (EHT) made headlines with the announcement of the first picture of a black hole. Science magazine named the image its Breakthrough of the year. Now the EHT collaboration is back with another groundbreaking result: a new image of the same black hole, this time showing what it looks like 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 – should provide new insight into how black holes engulf matter and emit mighty jets from their hearts. The new findings were described in Three papers published in Letters from the astrophysical journal.
“This work is a major milestone: the polarization of light carries 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, EHT polarimetry coordinator. Working group and researcher at the University of Valencia, Spain. “Unveiling this new polarized light image took years of work due to the complex techniques involved in obtaining and analyzing the data.”
Multiple imaging methods have produced the first direct image ever taken of a black hole in the center of an elliptical galaxy. Located in the constellation Virgo, about 55 million light years away, the galaxy is called Messier 87 (M87). The results of the collaboration were published on April 10, 2019, in six different articles presented in Letters from the astrophysical journal. It’s a feat that would have been impossible just a generation ago, made possible by technological breakthroughs, 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 indeed a black hole.
The EHT captured trapped photons orbiting the black hole, whirling around at the speed of light, creating a ring of light around it. From this, astronomers were able to deduce that the black hole rotates clockwise. The imagery also revealed the shadow of the black hole, a dark central region inside the ring. This shadow is as close as astronomers can take a photo of the actual black hole, from which light cannot escape once it has crossed 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, showing that these predictions hold up even in extreme gravitational environments.
What was missing, however, was a glimpse into the process behind the powerful twin jets produced by the black hole engulfing matter, ejecting some of the material that fell inside at almost light speed. (The black hole at the center of our Milky Way is less voracious, that is, relatively quiet, compared to the black hole in M87.) For example, astronomers still disagree on how these jets are accelerated to such high speeds. These new results impose additional constraints around the various competing theories, reducing the possibilities.
In the same way that polarized sunglasses reduce glare from bright surfaces, light polarized around a black hole provides a sharper view of the region around it. In this case, the polarization of the light is not due to special filters (like the lenses of sunglasses) but to the presence of magnetic fields in the hot region of space surrounding the black hole. This polarization allows astronomers to map the magnetic field lines at the inner edge and to study the interaction between matter that enters and is blown out.
“The observations suggest that the magnetic fields at the edge of the black hole are strong enough to repel the hot gas and help it resist the pull of gravity. Only the gas that slides across the field can fly inward to the event horizon ”. said co-author Jason Dexter from 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 observed.
This story originally appeared on Ars Technica.
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