In 2019, astronomers released the first direct image of a black hole, an achievement that made headlines and baffled around the world. The black hole was supermassive – millions of times the mass of our Sun – at the heart of a relatively nearby galaxy known as M87. On March 24, 2021, the Event Horizon Telescope – the same global collaboration that captured M87’s black hole – released it. out a new image with polarized light of this black hole. The polarization of light gives astronomers one signature (a representation) of the magnetic field of a black hole, for the first time.
The astronomers published their results in two peer-reviewed articles (here and here) Astrophysical Journal Letters on March 24, 2021, with a third soon to be accepted (here) for publication.
The black hole in M87 emits huge jets – matter that is ejected at almost the speed of light – from its core. These observations are key to understanding how this happens, these astronomers said. Astronomer Monika Moscibrodzka from Radboud University in the Netherlands said in a statement:
We now see the next crucial piece of evidence for understanding how magnetic fields behave around black holes, and how activity in this very dense region of space can power powerful jets that extend far beyond the galaxy.
Another astronomer involved in the project – Andrew Chael of the Princeton Center for Theoretic Science – further explained:
The newly published polarized images are essential to understand how the magnetic field allows the black hole to ‘eat’ matter and launch powerful jets.
When you measure light coming from an astronomical source, sometimes some of it is polarized, just like the light passing through polarized sunglasses. Rather than lenses, they are magnetic fields in hot regions of space that polarize astronomical light. So if you use telescopes to measure how the light is polarized, you get instant information about the magnetic fields that created it.
Another team member of this black hole study – Jason Dexter of the University of Colorado, Boulder – explained:
The observations suggest that the magnetic fields at the edge of the black hole are strong enough to push back the hot gas and help it resist gravity. Only the gas sliding through the field can spiral inward to the event horizon.
M87 is a huge elliptical galaxy – it consists mainly of older stars and does not show the familiar spiral pattern of disk galaxies – that is relatively close 55 million light years from us, in the Virgo cluster. It is about twice the mass of our Milky Way Galaxy and contains about 10 times more stars. Another special thing about this galaxy is that it has an unusual number of globular clusters, about 12,000, which is comparable to the more modest number of 200 in the Milky Way.
M87’s supermassive black hole is one of the most massive known in direct relation to the size of its host galaxy.
In short, astronomers have taken a new image of the supermassive black hole at the center of the nearby galaxy M87, this time with the signatures of the magnetic fields.
Source: Initial results from the M87 Event Horizon telescope. VII. Polarization of the ring
Source: Initial results from the M87 Event Horizon telescope. VIII. Magnetic field structure near The Event Horizon
Source: Polarimetric properties of Event Horizon Telescope Targets from ALMA