Cracking the Code: Unraveling the Magnetic Secrets of Black Hole Accretion

Scientists have made a breakthrough in understanding the magnetic field transport processes and the formation of a magnetically arrested disk (MAD) near a black hole. Using multi-wavelength observations of the black hole X-ray binary MAXI J1820+070, researchers discovered that the radio emission from the black hole jet and the optical emission from the outer region of the accretion flow lag behind the hard X-rays from the inner region by about eight and 17 days, respectively. These observations provide direct evidence for the existence of a MAD and shed light on the formation and transport mechanisms of magnetic fields in black hole accretion.