The common factor that everyone knows about black holes is that entirely everything nearby gets sucked into them.
Almost everything, it turns out.
Image Credit: Princeton University
Even though black holes are defined as objects from which nothing can escape, one of the astonishing predictions of Einstein’s theory of relativity is that black holes can lose energy. They can rotate, and just like a spinning top slows down over time and loses that energy in its rotation, a rotating black hole can also lose energy to its surroundings.
Eliot Quataert, Charles A, Young Professor of Astronomy on the Class of 1897 Foundation, Princeton University
Researchers have extensively accepted this model since the 1970s. They recognized that magnetic fields probably abstract energy from spinning black holes without knowing it is working.
A Princeton astrophysics team has definitively established that energy in proximity to the event horizon of the black hole M87* is exerting an outward force, contradicting the assumption of inward energy flow. Notably, the researchers have devised a method to verify the prediction that black holes shed rotational energy. The investigators have also created a way to test the prediction that black holes lose rotational energy, Quataert said, and to establish it is that energy that produces “the incredibly powerful outflows we see that we call jets.”
These energy outflow jets are basically like million-light-year-long Jedi lightsabers. They can extend 10 times longer than the Milky Way galaxy.
Alexandru Lupsasca, Former Postdoc, Princeton University
The findings were published in The Astrophysical Journal. Andrew Chael, an Associate Research Scholar in astrophysics, is the first author of the paper. He and co-author George Wong are both members of the Event Horizon Telescope team and have played a critical role in emerging the models used to interpret black holes. Chael, Wong, Lupsasca, and Quataert are all theorists affiliated with the Princeton Gravity Initiative.
The team acknowledged Chael for the crucial insight central to their findings: the correlation between the spiral direction of magnetic field lines and the indication of the energy flow direction. Quataert says, “The rest sort of fell into place.”
If you took the Earth, turned it all into TNT, and blew it up 1,000 times a second for millions and millions of years, that’s the amount of energy that we’re getting out of M87.
George N. Wong, Associate Research Scholar, Member, Princeton Gravity Initiative
For many years, scientists have been aware that as a black hole begins to spin, it induces a dragging effect on the fabric of spacetime. This rotational motion causes magnetic field lines interweaving through the black hole to be carried along, resulting in a gradual slowdown of the rotation and the subsequent release of energy.
“Our new, sharp prediction is that whenever you look at an astrophysical black hole if it has magnetic field lines attached to it, there will be energy transfer - truly insane amounts of energy transfer,” states a former associate research scholar at Princeton who is now an Assistant Professor of physics and mathematics at Vanderbilt University.
He has won the 2024 New Horizons in Physics Prize from the Breakthrough Prize Foundation for his black hole research.
Although the energy near the event horizon of M87* is observed to be moving outward, the scientists note that in a different black hole, the energy flow might theoretically be directed inward. The team is confident in the correlation between energy flow and the orientation of magnetic field lines. This prediction about the energy source from the black hole will be subject to testing once the yet-to-be-launched ‘next generation’ Event Horizon Telescope becomes a reality.
Over the last eighteen months, scientists studying black holes globally have been putting forward specifications for a future instrument.
“Papers like ours can play a crucial role in determining what we need. I think it’s an incredibly exciting time,” Wong noted.
The four researchers researched in their paper that they have not conclusively shown that the black hole’s spin “truly powers the extragalactic jet,” though the evidence certainly leans in that direction. Despite their model indicating energy levels consistent with what the jets require, the researchers could not eliminate the possibility of the jet being powered by rotating plasma outside the black hole. “I think it’s extremely likely the black hole powers the jet, but we can’t prove it,” said Lupsasca. ‘Yet.’
A rotating black hole dragging magnetic field lines
An animation showing how the magnetic field lines crossing the black hole’s event horizon twist up as the black hole rotates more quickly. Video Credit: George Wong, Institute for Advanced Study and Princeton University
Journal Reference
Chael, A., et al. (2023). Black Hole Polarimetry I. A Signature of Electromagnetic Energy Extraction. The Astrophysical Journal. doi.org/10.3847/1538-4357/acf92d.