Free Astronomy Magazine May-June 2019

MAY-JUNE 2019 The black hole’s boundary — the event horizon — is around 2.5 times smaller than the shadow it casts and measures just under 40 billion km across. The EHT links telescopes around the globe to form an unprecedented Earth-sized virtual telescope. The EHT offers scientists a new way to study the most extreme objects in the Universe predicted by Einstein’s general relativity during the cente- nary year of the historic experiment that first confirmed the theory. Although the telescopes are not physically connected, they are able to synchronize their recorded data with atomic clocks — hydrogen masers — which precisely time their observations. These observations were collected at a wavelength of 1.3 mm during a 2017 global cam- paign. Each telescope of the EHT produced enormous amounts of data — roughly 350 terabytes per day —which was stored on high-per- formance helium-filled hard drives. These data were flown to highly spe- T his artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. This thin disc of rotating material consists of the leftovers of a Sun-like star which was ripped apart by the tidal forces of the black hole. The black hole is labelled, showing the anatomy of this fas- cinating object. [ESO] cialised supercomputers — known as correlators — at the Max Planck In- stitute for Radio Astronomy and MIT Haystack Observatory to be com- bined. They were then painstakingly converted into an image using novel computational tools developed by the collaboration. “We have taken the first picture of a black hole,” said EHT project director Sheperd S. Doeleman of the Center for Astrophysics | Harvard & Smith- sonian. “This is an extraordinary sci- entific feat accomplished by a team of more than 200 researchers.” Black holes are extraordinary cosmic objects with enormous masses but extremely compact sizes. The pres- ence of these objects affects their environment in extreme ways, warp- ing spacetime and superheating any surrounding material. “If immersed in a bright region, like a disc of glowing gas, we expect a black hole to create a dark region similar to a shadow — something predicted by Einstein’s general rela- tivity that we’ve never seen be- fore,” explained chair of the EHT Science Council Heino Falcke of Rad- boud University, the Netherlands. “This shadow, caused by the gravi- tational bending and capture of light by the event horizon, reveals a lot about the nature of these fasci- nating objects and has allowed us to measure the enormous mass of M87’s black hole.” Multiple calibration and imaging methods have revealed a ring-like structure with a dark central region — the black hole’s shadow — that persisted over multiple independent EHT observations.