The Magnetic Fields of Black Holes Are Much Weaker Than We Thought, Say Scientists
Black holes remain among the most mysterious galactic phenomena for good reason. We know that black holes are points in space where the gravity is so strong that not even light can escape it. We know that they usually form when a giant star explodes and the resultant core collapses under that intense gravity. But when it comes to understanding details of how they work, we know little else.
That's why a new study in which Chris Packham, an associate professor of physics and astronomy at The University of Texas at San Antonio, collaborated with a team lead from the University of Florida, has caught the attention of the scientific community. Packham and the team of University of Florida astronomers observed the magnetic field of a black hole, called V404 Cygni, from multiple wavelengths for the very first time. Much like the Earth's magnetic field, which is created by the earth's hot, liquid iron core, a black hole's magnetic field is created from the energy of exploding stars.
"In 2015, a surge of accretion by the black hole caused the surrounding plasma to brighten suddenly for the first time since 1989, briefly becoming the brightest x-ray source in the sky," says the study. "[Researchers] combined observations from radio, infrared, optical, and x-ray telescopes taken during the outburst. They compared how fast the flux decayed at each wavelength, which allowed them to constrain the size of the emitting region, determine that the plasma within it cooled through synchrotron radiation, and measure the magnetic field around the black hole."
It's the jets of electrons that form when matter breaks down around a black hole that have long left scientists stumped, though. The electrons are launched by the magnetic field, nearly at the speed of light. As matter is broken down around a black hole, jets of electrons are launched by the magnetic field from either pole of the black hole at almost the speed of light. By studying V404 Cygni at those different wavelengths, the team discovered that magnetic fields are much weaker than previously thought, calling into question all other previous models of how black holes operate. Basically, the research showed them that more resarch is needed.
"This measurement is substantially lower than previous estimates for such systems, providing constraints on physical models of accretion physics in black hole and neutron star binary systems," says the study's abstract.
Earlier this month, a black hole was caught burping. Last year, the oldest black hole was discovered, along with another new black hole at the center of our Milky Way galaxy. Scientists have also recently discovered that many objects currently classified as black holes are actually fast-spinning pulsars.