The central black hole of our Milky Way is leaking. This supermassive black hole appears to have preserved the remains of a torch-like jet dating back thousands of years. NASA’s Hubble Space Telescope did not photograph the phantom jet but helped find circumstantial evidence that it still grows weakly in a huge cloud of hydrogen and then splashes, like the narrow jet from a pipe aimed at a sandpile.
This is further proof that the black hole, with a mass of 4.1 million suns, is not a sleeping monster but that it periodically hiccups as stars and clouds of gas fall into it. Black holes attract some of the matter into a swirling, orbiting accretion disk where some of the incoming matter is entrained in outgoing jets that are collimated by the black hole’s strong magnetic fields. The narrow “projector beams” are accompanied by a flood of deadly ionizing radiation.
âThe central black hole is dynamically variable and is currently off,â said Gerald Cecil of the University of North Carolina at Chapel Hill. Cecil pieced together, like a puzzle, observations at multiple wavelengths from a variety of telescopes that suggest that the black hole emits mini-jets whenever it swallows something heavy, like a cloud of gas. . The research of its multinational team has just been published in the Journal of Astrophysics.
In 2013, evidence of a squat southern jet near the black hole came from x-rays detected by NASA’s Chandra X-ray Observatory and radio waves detected by the Jansky Very Large Array Telescope in Socorro, New Zealand. -Mexico. This jet also appears to spread through the gas near the black hole.
Cecil was curious as to whether there was a counterjet from the north as well. He first looked at archival spectra of molecules such as methyl alcohol and carbon monosulfide from the ALMA Observatory in Chile (Atacama Large Millimeter / Submillimeter Array), which uses millimeter wavelengths to scan through the veils of dust between us and the galactic core. ALMA reveals a narrow and expanding linear feature in molecular gas that dates back at least 15 light years to the black hole.
Connecting the dots, Cecil then found in Hubble’s infrared images a glowing, swollen hot gas bubble that lines up with the jet at a distance of at least 35 light-years from the black hole. His team suggests that the jet from the black hole sank into it, inflating the bubble. These two residual effects of the fading jet are the only visual evidence of its impact on molecular gas.
When blowing through the gas, the jet hits the material and curves along several streams. “The fluxes escape from the dense gas disk of the Milky Way,” said co-author Alex Wagner of the University of Tsukuba in Japan. “The jet diverges from a pencil beam in tendrils, like that of an octopus.” This flow creates a series of expanding bubbles that span at least 500 light years. This larger “soap bubble” structure has been mapped at various wavelengths by other telescopes.
Wagner and Cecil then ran supercomputer models of the outflow from the jets in a simulated Milky Way disk, which replicated the observations. âLike in archeology, you dig and burrow to find increasingly ancient artifacts until you stumble upon the remains of a great civilization,â Cecil said. Wagner’s conclusion: “Our central black hole has clearly increased its luminosity by at least 1 million times over the past million years. That was enough for a jet to enter the galactic halo.”
Earlier observations from Hubble and other telescopes have revealed that the Milky Way’s black hole erupted around 2-4 million years ago. It was energetic enough to create a huge pair of bubbles towering over our galaxy that glow in gamma rays. They were first discovered by NASA’s Fermi Gamma-ray Space Telescope in 2010 and are surrounded by X-ray bubbles discovered in 2003 by the ROSAT satellite and fully mapped in 2020 by the eROSITA satellite.
Hubble’s ultraviolet light spectra were used to measure the rate of expansion and the composition of the balloon lobes. Hubble spectra later discovered that the burst was so powerful that it illuminated a gaseous structure, called Magellanic Flux, about 200,000 light years from the galactic center. The gas shines from this event even today.
To get a better idea of ââwhat’s going on, Cecil looked at Hubble and radio footage of another galaxy with black hole flow. Located 47 million light-years away, the active spiral galaxy NGC 1068 has a chain of bubble features aligned along a very active black hole flow at its center. Cecil discovered that the scales of radio and X-ray structures emerging from both NGC 1068 and our Milky Way are very similar. “An arc shock bubble at the top of the output of NGC 1068 coincides with the scale of the start of the Fermi bubble in the Milky Way. NGC 1068 could show us what the Milky Way was doing during its surge of power. several million years ago. “
The residual jet characteristic is close enough to the Milky Way’s black hole that it becomes much larger just decades after the black hole reactivates. Cecil notes that âthe black hole only needs to increase its luminosity a hundredfold during this period to fill the jet channel with emitting particles. It would be cool to see how far the jet goes in this explosion. to reach the Fermi gamma ray the bubbles would require the jet to sustain for hundreds of thousands of years because these bubbles are each 50,000 light years in diameter! “
Early black hole shadow images taken with the National Science Foundation’s Event Horizon telescope could reveal where and how the jet is launched.
Video of a mini-jet near the Milky Way’s supermassive black hole: https://www.youtube.com/watch?v=zxqQ4G0NOhI&t=144s