Hawaiʻi telescope helps reveal first image of Black Hole at the center of the Milky Way Galaxy

The Submillimeter Array on the summit of Maunakea was one of eight telescopes around the world to image the black hole at the center of the Milky Way galaxy.

Astronomers unveiled the first image of the supermassive black hole in simultaneous press conferences around the world today. 

“The result provides overwhelming evidence that the object at the heart of our galaxy is indeed a black hole and yields valuable clues about the workings of such giants, which are thought to reside at the center of most galaxies,” according to the announcement.

The image was produced by a global research team called the Event Horizon Telescope using observations from a worldwide network of radio telescopes, including the Submillimeter Array telescope on the summit of Maunakea. 

The image, described today in a special issue of The Astrophysical Journal Letters, takes an in-depth look at the massive object. “Scientists had previously seen stars orbiting around something invisible, compact and very massive in our galaxy’s core. This strongly suggested that the object — known as Sagittarius A*, or Sgr A* — was a black hole; today’s image provides the first direct visual evidence of it,” according to the announcement.

“It is amazing how well the image of the Sgr A* black hole agrees with the predictions from Einstein’s Theory of General Relativity,” said Ramprasad Rao, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian who is based at the SMA. “These EHT observations have enabled scientists to now have an improved understanding of the processes that are taking place in the center of our own galaxy.”

The black hole itself is completely dark, yet glowing gas around it reveals a tell-tale signature: a dark central region, called a shadow, surrounded by a bright ring-like structure, researchers said in a press release. This new view shows light bent by the powerful gravity of the black hole, which is four million times more massive than the Sun. 

Sagittarius A* is about 27,000 light-years away, appearing to those on Earth to have the same size in the sky as a donut on the Moon. To image it, the team created the powerful EHT, which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope.

Together, the telescopes — including the SMA, a joint operation between the CfA and Academia Sinica Institute of Astronomy and Astrophysics — observed Sgr A* on multiple nights in 2017, collecting data for many hours in a row, similar to using a long exposure time on a camera.

“This research showcases the close cooperation between observatories in Hawai‘i and elsewhere. The SMA has participated in the EHT for more than a decade, supporting the development and refinement of specialized signal processing electronics and observing techniques,” said astronomer Simon Radford, director of SMA operations.

Today’s breakthrough follows the EHT collaboration’s 2019 release of the first image of a black hole, called M87*, at the center of the more distant Messier 87 galaxy.

The latest effort was made possible through the ingenuity of more than 300 researchers from 80 institutes around the world that together make up the EHT Collaboration. In addition to developing complex tools to overcome the challenges of imaging Sgr A*, the team worked rigorously for five years, using supercomputers to combine and analyze their data, all while compiling an unprecedented library of simulated black holes to compare with the observations.

The team is particularly excited to finally have images of two black holes of very different sizes, which offers the opportunity to understand how they compare and contrast. The scientists have also begun to use the new data to test theories and models of how gas behaves around supermassive black holes. This process is not yet fully understood but is thought to play a key role in shaping the formation and evolution of galaxies.

“It’s amazing to finally see this image come to light after over a decade of work assembling the EHT,” said the CfA’s Jonathan Weintroub, an electrical engineer who has built instruments for the SMA for 16 years. “We caught our first glimpse of Sgr A* in 2007 after connecting telescopes in Hawai’i and Arizona. It was after that breakthrough that I became exceedingly confident that imaging black holes was within our grasp.”

Weintroub adds, “Maunakea, the location of the SMA, is a culturally significant site for the indigenous Hawaiian people. My colleagues and I are privileged to study the cosmos from its summit.”

The individual telescopes involved in the EHT in April 2017, when the observations were conducted, were: the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder Experiment (APEX), the IRAM 30-meter Telescope, the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope Alfonso Serrano (LMT), the Submillimeter Array (SMA), the UArizona Submillimeter Telescope (SMT), the South Pole Telescope (SPT). 

Since then, the EHT has added the Greenland Telescope (GLT), which is operated by ASIAA and the CfA, the NOrthern Extended Millimeter Array (NOEMA) and the UArizona 12-meter Telescope on Kitt Peak to its network.