A new snapshot of a black hole reveals its mysterious physics

Two years ago, the Event Horizon Telescope (EHT) made headlines with the announcement of the first direct image of a black hole. Science magazine called the image the 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 that polarization for the first time – a signature of magnetic fields at the edge of the black hole – is expected to provide new insight into how black holes gobble up matter and emit powerful rays from their cores. The new findings are detailed in three articles published in The Astrophysical Journal Letters

“This work is an important milestone: the polarization of light contains information that allows us to better understand the physics behind the image we saw in April 2019, which was not possible before,” said co-author Iván Martí-Vidal. , coordinator of the EHT Polarimetry. Working group and a researcher at the University of Valencia, Spain. “Unveiling this new image with polarized light took years of work because of the complex techniques involved in obtaining and analyzing the data.”

Multiple imaging methods produced the first ever direct image of a black hole in the center of an elliptical galaxy. Located in the constellation Virgo, some 55 million light-years away, the galaxy is called Messier 87 (M87). The collaboration findings were published in six different articles in April 10, 2019 The Astrophysical Journal LettersIt’s a feat that would have been impossible a generation ago, made possible by technological breakthroughs, innovative new algorithms and of course connecting several of the world’s best radio observatories. The image confirmed that the object in the center of M87 is indeed a black hole.

The EHT captured photons orbiting the black hole and spinning at nearly the speed of light, forming a bright ring around it. From this, astronomers could deduce that the black hole is spinning clockwise. The image also revealed the shadow of the black hole, a dark central area in the ring. That shadow is as close as astronomers can get to take a picture of the actual black hole, from which the light cannot escape once it passes 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 more massive 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 stunning confirmation of the general theory of relativity, which shows that those predictions hold up even in extreme gravitational environments.

What was lacking, however, was insight into the process behind the powerful twin jets produced by the black hole that swallowed matter and some of the material that fell into it fell away at almost light speed. (The black hole at the center of our Milky Way is less hungry, that is, relatively quiet, compared to M87’s black hole.) For example, astronomers are still not in agreement about how those jets are accelerated to such high speeds. These new results impose additional constraints around the various competing theories, limiting the possibilities.

In the same way that polarized sunglasses reduce glare from bright surfaces, the polarized light around a black hole provides a sharper view of the area around it. In this case, the polarization of light is not due to special filters (like the lenses in sunglasses), but due to the presence of magnetic fields in the hot area around the black hole. That polarization allows astronomers to map the magnetic field lines at the inner edge and study the interaction between incoming and outgoing matter.

The observations suggest that the magnetic fields at the edge of the black hole are strong enough to push the hot gas back and help it resist gravity. Only the gas sliding through the field can spiral inward to the event horizon. said co-author Jason. Dexter from the University of Colorado, Boulder, who is also a coordinator of the EHT Theory Working Group. That means that only theoretical models that include the property of a highly magnetized gas accurately describe what the EHT collaboration observed.

This story originally appeared on Ars Technica

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