// block 736065 · science · 12 May 2022
The black hole at the centre of our galaxy
The moment this block marks: the start of the EHT press conferences, 09:00 in Washington and 15:00 in Garching, 12 May 2022, 13:00:00 UTC. The first block mined after it is block 736,065, 12 May 2022, 13:06:49 UTC.
For decades, astronomers had watched stars at the centre of the Milky Way orbit something invisible, compact and very heavy, and concluded that it had to be a black hole. It is called Sagittarius A*, it lies about 27,000 light-years from Earth, and it holds four million times the mass of the Sun. Seen from here it is tiny: about the size of a doughnut on the Moon.
The Event Horizon Telescope, the network of radio observatories that had produced the first image of a black hole in 2019, observed it on several nights in 2017. It proved far harder to image than M87*, although much closer: the gas around this smaller black hole circles it in minutes rather than days or weeks, so its brightness and pattern kept changing while the telescopes were recording.
On 12 May 2022, at simultaneous press conferences in Garching, Washington, Santiago de Chile, Mexico City, Tokyo and Taipei, the collaboration showed the result: a bright ring around a dark shadow. It looks remarkably like M87*, even though the black hole of our galaxy is more than a thousand times smaller and less massive, and the size of the ring agreed with the predictions of general relativity.
The first block mined after the conferences began, block 736,065, came nearly seven minutes in, moments before ESO's press release, scheduled for 13:07 UTC, went out. Its hash, like every hash, can be checked on any node.
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