Milky Way’s Black Hole Portrait In Progress

This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disk of infalling matter. Using the Event Horizon Telescope, astronomers observed the Milky Way’s black hole earlier this year and are now processing the data to make the first picture of a black hole ever. Credit: ESA/Hubble, ESO, M. Kornmesser

Time to check in to see how things are coming along with the Event Horizon Telescope (EHT). The EHT  involves eight radio telescopes across the globe working together to capture the first image of a black hole.  The bigger the scope, the finer the detail visible in faraway objects. But instead of building a telescope as big as the Earth, clever astronomers can combine data from the widely-separated instruments to create a virtual, Earth-sized radio telescope. Much, much easier. The EHT will see details 2,000 times finer than the Hubble Space Telescope.

That should be big enough to make out the two supermassive black holes targeted by the global array: the solar system-sized one in the center of the Milky Way and the other in M87, a giant elliptical galaxy 50 million light years away in Virgo. That one contains an estimated 6.6 billion solar masses of material.

The supermassive black hole in the center of our galaxy and the one in M87 are the targets of the Event Horizon Telescope. Two views of the Milky Way are shown — face-on from above and edge-on from the side. The solar system lies 26,000 light years from the center. Credit: NASA with annotations by the author

At the moment, the EHT team is processing observations from last April’s weeklong observing campaign that linked together eight telescopes in Hawaii, Arizona, Spain, Mexico, Chile, and the South Pole via the technique of very-long-baseline interferometry (VLBI).  They global array focused on the two supermassive black holes with the magnifying power and sensitivity to make images of the light emitted by hot gas near the holes’ event horizons.

The UA Submillimeter Telescope on Mt. Graham is one of the many radio telescopes that together create a virtual telescope the size of the Earth. Credit: Dave Harvey/UA Steward Observatory

An event horizon is the last place matter does business with the universe as we know it. The point of no return. Pass it and not even light can get out of the hole, exactly the reason it appears black. Once an object crosses the mysterious and invisible boundary, it moves in only one direction — towards the center of the hole called the singularity, where everything gets crushed to a one-dimensional point by the now-terrifying force of gravity. En route, the object will be stretched to the breaking point until it becomes little more than a cloud of swirling particles headed for oblivion.

A computer simulation of superheated plasma swirling around the black hole at the center of our galaxy. The dark shadow at center is what astronomers hope to finally see. Credit: Scott Noble/RIT

Einstein’s general theory of relativity predicts that the EHT should see a silhouette formed by the intense gravity of the black hole warping the light from infalling hot gas. EHT should also be able to see hot blobs of material get stretched and torn into turbulent flows as they orbiting the black hole. Most of the data recorded at sites has been shipped to processing facilities at MIT’s Haystack Observatory and the Max Planck Institute for Radio Astronomy, where they’ll be combined. Project managers are still waiting for the hard disks to arrive from the South Pole Telescope, where they’ve been in storage during the long winter.

Images are expected by early 2018. To stay abreast of developments, please visit the project’s website.