With a single letter seemingly etched in the X-ray glow around it, a giant black hole at the centre of a massive elliptical galaxy is making a mark on its surroundings.
This "H"-shaped structure is found in a detailed new X-ray map of the multimillion-degree gas around the galaxy Messier 84 (M84) created by a team of astronomers from NASA and an international research team including the University of Nottingham.
As gas is captured by the gravitational force of the black hole, some of it will fall into the abyss, never to be seen again. Some of the gas, however, avoids this fate and instead gets blasted away from the black hole in the form of jets of particles. These jets can push out holes, or cavities, in the hot gas surrounding the black hole. Given the orientation of the jets to Earth and the profile of the hot gas, the cavities form what appears to resemble the letter "H".
Astronomers used NASA's Chandra X-ray Observatory to make a map of the hot gas (pink) in and around M84 down to only about 100 light-years away from the black hole in the centre of the galaxy. This gas radiates at temperatures in the tens of millions of degrees. The huge letter "H" is about 40,000 light-years tall – about half the width of the Milky Way. The radio image from the NSF's Karl G. Jansky Very Large Array (VLA) (blue) shows the jets streaking away from the black hole. Optical data from the Sloan Digital Sky Survey (white) shows M84 and neighbouring galaxies.
Researchers studying M84 with Chandra and the VLA found that the jets may influence the flow of the hot gas towards the black hole even more than the gravitational pull from the black hole. For example, matter is falling towards the black hole from the north - along the direction of the jet - at a rate that is only a quarter of that from directions where the jet isn't pointing, to the east and west. One possibility is that gas is lifted along the direction of the jet by the cavities and this slows the rate.
With new scientific techniques we are uncovering unseen parts of the Universe in greater detail than ever before. These new observations show that the hot gas captured by the black hole is a complex mixture of fuelling inflow and jet-driven outflow.
The authors, which included researchers from the University of Nottingham, tested a model called Bondi accretion, where all of the matter within a certain distance from a black hole -- effectively inside a sphere -- is close enough to be affected by a black hole's gravity and start falling inwards. This effect is named after the scientist Hermann Bondi and "accretion" refers to matter falling toward the black hole. The new results show that Bondi accretion is not occurring in M84 because matter would be falling inwards at the same rates in all directions.
M84 is a cousin of Messier 87 (M87) containing the first black hole imaged with the Event Horizon Telescope and is also located in the Virgo Cluster. The supermassive black hole in M84, along with those in our Galaxy, M87, NGC 3115 and NGC 1600, are the only ones close enough or massive enough for astronomers to see details in Chandra images near and inside the Bondi radius (that is, the distance from the black hole where the infall of gas happens). Like the black hole in M87, the M84 black hole is producing a jet of particles, but the X-rays produced by material close to the black hole is over ten times fainter for M84, allowing more detailed study of material near the Bondi radius.
Note: the phenomenon of pareidolia is when people see familiar shapes or patterns in random data. Pareidolia can occur in all kinds of data from clouds to rocks and even galaxies.
A paper describing these results appears in MNRAS. The study was led by Christopher Bambic, a graduate student at Princeton University. Other authors include Helen Russell (University of Nottingham, United Kingdom), Christopher Reynolds (Institute for Astronomy, Cambridge, UK), Andy Fabian (Institute for Astronomy), Brian McNamara (University of Waterloo, Canada), and Paul Nulsen (Center for Astrophysics | Harvard & Smithsonian).
NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
