On two nights in April 2017, eight observatories around the planet will function together as one Earth-size telescope to simultaneously observe Sagittarius A* (Sagittarius A star), the supermassive black hole at the center of the Milky Way. Collectively known as the Event Horizon Telescope, this will be humanity’s first attempt to get an image of a black hole.
They’ll be looking for the hole’s event horizon, the boundary that separates the black hole’s iron-grip from the rest of space. Anything, including light, that crosses the event horizon, can never return to the normal universe. The hole swallows all and crunches it into an infinitely small point.
The Event Horizon Telescope will involve radio telescope observatories in North America, Europe, South America and Antarctica. They’ll use a technique called very long baseline interferometry to take the signals collected from the black hole from each location and combine them, effectively creating a instrument equal in size to the maximum separation of the telescopes — essentially the diameter of the Earth!
That’s a BIG scope, sharp enough according to an article in Scientific American, to see a DVD on the moon. If black holes are light-sucking invisible nothings, what exactly do astronomers hope to see? They’ll be looking for the hole’s shadow cast on the bright light given off as matter goes whirling down its maw. Friction on the way down causes material to heat up and emit light, offering a way for us to see the monster lurking at the center.
Despite their enormous masses, most black holes are quite small. A typical hole’s event horizon measures only about 20 miles in diameter. The supermassive contain millions of solar masses and lurk in the centers of many galaxies including the Milky Way. Those can be up to a billion miles across or about the distance of Saturn from the sun. Sagittarius A* contains about 2.6 million times the mass of the sun and is estimated to be no more than 93 million miles across or nearly equal that of Earth’s distance from the sun.
Even a 93-million-mile wide shadow is a small thing when seen from 26,000 light years away, the distance of our solar system from the galactic center. To see something that small, you need a gigantic telescope. That’s where Event Horizon steps in. Data from each instrument will be carefully combined in a central processing center to create the images. Radio was chosen over optical telescopes because radio waves can penetrate the dust and other star gunk between us and the galactic center.
There is still a lot of work to do before next April. Both the Large Millimeter Telescope in Mexico and the South Pole Telescope need new receivers capable of recording the same high-frequency wavelength as the rest of the stations. We’ll stay on this and report back closer to the date of black hole first light.