The image of a dark heart surrounded by a flame-orange halo of white-hot plasma and gas looks like any number of artists’ renderings within the previous 30 years. But this time, it is the actual deal.
On Wednesday, years-long operate by the Event Horizon Telescope alliance was introduced.
Scientists have been puzzling over invisible”dark stars” since the 18th century, but never has been spied by means of a telescope, much less photographed.
The supermassive black hole today immortalised by a far-flung network of radio telescopes is 50 million light-years away in a galaxy known as M87.
“it is a space that people could have barely imagined,” Frederic Gueth, an astronomer in France’s National Centre for Scientific Research (CNRS) and also co-author of studies detailing the findings, told AFP.
Most speculation had centred on the other candidate targeted by the Event Horizon Telescope — Sagittarius A*, the black hole in the centre of our galaxy, the Milky Way.
In contrast, Sag A* is only 26,000 light-years out of Earth.
Locking down a picture of M87’s supermassive black hole in such space is comparable to photographing a pebble on the Moon.
European Space Agency astrophysicist Paul McNamara called it an”outstanding technical achievement”.
It was also a team effort.
“Rather than constructing a giant telescope which would fall under its own weight, we combined many observatories,” Michael Bremer, an astronomer at the Institute for Millimetric Radio Astronomy (IRAM) in Grenoble, told AFP.
Earth at a thimble
Over a few days in April 2017, eight radio telescopes in Hawaii, Arizona, Spain, Mexico, Chile, and the South Pole zeroed in on Sag A* and M87.
Knit together”like fragments of a giant mirror,” in Bremer’s words, they formed a virtual observatory a few 12,000 kilometres across — about the diameter of Earth.
In the long run, M87 was more photogenic. Just like a fidgety child, Sag A* was too”active” to catch a clear picture, the investigators said.
“The telescope is not looking at the black hole per se, but the substance it has captured,” a luminous disc of white-hot gas and plasma called an accretion disk, said McNamara, who was not part of the group.
“The light from behind the black hole gets bent like a lens.”
The unprecedented picture — so often imagined in science and science fiction — was analysed in six studies co-authored by 200 specialists from 60-odd institutions and published Wednesday in Astrophysical Journal Letters.
“I never believed that I would see a real one in my lifetime,” explained CNRS astrophysicist Jean-Pierre Luminet, author in 1979 of their first digital simulation of a black hole.
Coined from the mid-60s by American physicist John Archibald Wheeler, the expression”black hole” refers to a point in space where matter is so compressed as to create a gravity field where even light can’t escape.
The more mass, the bigger the hole.
In exactly the same scale of compression, Earth would fit in a thimble. The Sun would measure a mere six kilometres edge-to-edge.
A successful result depended in part on the vagaries of weather during the April 2017 monitoring period.
“For everything to work, we had to have clear visibility at each [telescope] location globally”, stated IRAM scientist Pablo Torne, remembering collective anxiety, tiredness and, finally, relief.
‘Hell of a Christmas present’
Torne was at the controls of the Pico Veleta telescope in Spain’s Sierra Madre mountains.
After that, is was eight weeks of nail-biting while scientists at MIT Haystack Observatory in Massachusetts and the Max Planck Institute for Radio Astronomy in Bonn crunched the information.
The Universe is full of electromagnetic”noise”, and there was no guarantee M87’s subdued signs could be pulled from a mountain of data so voluminous it could not be delivered via the web.
There was one glitch.
“We had been desperately waiting for the data in the South Pole Telescope, which — because of extreme weather conditions during the southern hemisphere winter — didn’t arrive till six months afterwards,” recalled Helger Rottmann in the Max Planck Institute.
It came, to be exact, on December 23, 2017.
“When, a couple of hours after, we noticed that everything was there, it had been just one hell of a Christmas gift,” Rottmann said.
It would take another year, however, to piece together the information into an image.
“To be absolutely sure, we did the job four times with four different teams,” explained Gueth.
Each team came up with precisely the exact same spectacular, history-making image of a dark circle encased in a flaming-red halo.