A legion of other telescopes, including three NASA X-ray observatories in space, were watching while the Event Horizon Telescope collected data for its astonishing new image of the Milky Way's supermassive black hole.
These data are being used by astronomers to understand more about how Sagittarius A, the black hole at the centre of the Milky Way galaxy, interacts with and feeds off its environment some 27,000 light-years from Earth.
When the Event Horizon Telescope (EHT) was surveyed in April 2017 to create the new image, scientists from the partnership used equipment that detects multiple wavelengths of light to peek at the same black hole. They combined X-ray data from NASA's Chandra X-ray Observatory, Nuclear Spectroscopic Telescope Array (NuSTAR), and the Neil Gehrels Swift Observatory with radio data from the East Asian Very Long-Baseline Interferometer (VLBI) network and the Global 3-millimetre VLBI array, as well as infrared data from the European Southern Observatory's Very Large Telescope in Chile for this multiwavelength observing campaign.
NASA Administrator Bill Nelson remarked, "The Event Horizon Telescope has taken yet another stunning image, this time of the massive black hole at the centre of our own home galaxy." "Taking a closer look at this black hole will let us learn more about its cosmic repercussions on its surroundings, and it illustrates the international partnership that will lead us into the future and disclose discoveries we could never have anticipated."
One of the main objectives was to catch X-ray flares, which are thought to be caused by magnetic processes comparable to those on the Sun but can be tens of millions of times more strong. These flares occur on a regular basis in the EHT's observation area, which is slightly larger than Sagittarius' event horizon, the point of no return for matter falling inward. Another purpose was to have a critical look at what's going on on a bigger scale. While the EHT study indicates Sagittarius and the previous black hole it observed, M87, to be strikingly similar, the bigger picture is far more complicated.
"If the new EHT image shows us the eye of a black hole hurricane, then our multiwavelength data reveal winds and rain hundreds, if not thousands, of kilometres beyond," said Daryl Haggard of McGill University in Montreal, one of the multiwavelength campaign's main scientists. "How does this cosmic storm interact with, and even disrupt, its surrounding galaxy?"
One of the most perplexing aspects of black holes is how they absorb, devour, or even expel material orbiting them at near-light speed, a process known as "accretion." This is how planets, stars, and black holes of all sizes begin and grow across the cosmos.
Chandra photos of hot gas around the black hole are important for accretion studies because they show how much material is grabbed from neighbouring stars by the black hole's gravity and how much makes it close to the event horizon. With existing telescopes, no other black hole in the universe, including M87, has this essential information.
"Astronomers can mostly agree on the essentials - black holes have stuff swirling about them, and some of it falls across the event horizon forever," Sera Markoff of the University of Amsterdam in the Netherlands, another multiwavelength observation coordinator, said. "We can go a lot further than this basic picture with all of the data we've acquired."
Scientists in the large international collaboration compared data from NASA's high-energy missions and other telescopes to state-of-the-art computational models that account for factors like Einstein's general theory of relativity, magnetic field effects, and predictions of how much radiation the material surrounding the black hole should generate at various wavelengths.
The simulations and data suggest that the magnetic field around the black hole is strong and that the angle between the line of sight to the black hole and its spin-axis is small – less than 30 degrees. If this is true, it suggests that we are looking down from our vantage point.
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