MeerKAT Radio Telescope Array in South Africa. Credit: NRF SARAO

A research group that included U-M Astronomy’s Dr. Elena Gallo has published its observations of a black hole ejecting material at close to the speed of light. The team was led by the University of Oxford’s Department of Physics and their observations have allowed a deeper understanding as to how black holes feed into and effect their environment.

The group focused their studies on a transient astrophysical system, MAXI J1820+070, which contains a dynamically confirmed black hole within our galaxy and a star which are orbiting one another. Because of the strong gravitational pull of the black hole, it syphons material from the star and accretes it. Through the process of accretion, as material falls onto the black hole through a gravitational interaction, the gravitational potential energy is converted to radiation in an accretion disk – a disk-like structure orbiting the black hole.

Most transient systems only accrete a small amount of material that is not observable with modern technology. However, these systems do occasionally go into outburst during which they are observable. During these outbursts, the system is capable of turning around a fraction of the accreted material and ejecting it outward. MAXI J1820+070 went into outburst in the summer of 2018, at which point the group began to continuously track the ejections to extreme distances from the black hole using a range of radio telescopes. The final angular separation that was observed is among the largest seen from transient astrophysical systems.

In order to make their observations, the group utilized the newly operational MeerKAT telescope in South Africa, as well as other radio telescopes in the UK and US. Dr. Gallo contributed mainly with observations that were obtained with the Very Large Array in New Mexico. The radio observations were complemented by X-ray observations, with NASA’s Neil Gehrels Swift Observatory.

“These observations have enabled us to track the evolution of a black hole outburst better than ever before” said Dr. Gallo, U-M professor of astronomy. “The most interesting aspect is that we discovered that the total energy carried by the ejections is much higher than we thought.”

Together and using all the recorded radio observations, the team was able to better estimate how much energy is contained in the ejections of black holes. Galactic black holes, such as MAXI J1820+070, are considered to be scaled-down versions of supermassive black holes. Understanding the feedback of these systems can help us understand the growth of galaxies and how they evolve over time.

This work is published in the journal Nature Astronomy:


More information: Prof. Elena Gallo