Our galaxy's supermassive black hole is closer to Earth than we thought

The supermassive black hole hiding in the center of our galaxy is much closer to Earth, about 2,000 light-years closer, than scientists thought, according to new research out of Japan. 

Not only that but our solar system is moving faster than thought as it orbits this galactic center. 

All this doesn't mean you need to worry that Earth is zooming toward the central behemoth or that we will get sucked up by the gravity monster, the researchers noted. We are still quite a ways from the black hole, dubbed Sagittarius A* (Sgr A*): 25,800 light-years, where one light-year is about 6 trillion miles (9.5 trillion kilometers).

Related: The biggest black hole findings

The study is part of the  VERA Experiment, or the VLBI Exploration of Radio Astrometry, whose aim is to explore the three-dimensional structure of the Milky Way. Since we live within the Milky Way, scientists can't just take a snapshot of it to figure out its structure. Instead, they take precise measurements of stars' sizes, positions and orbital velocities — how fast they circle the galactic center — in a scientific field called astrometry. The resulting maps can shed light on details of our Milky Way, the stars in it and possibly the universe.  

Researchers can now “measure distances of stars located farther and 30,000 light-years from our solar system,” said Tomoya Hirota, a professor in the Department of Astronomy at SOKENDAI and the leader of the data analysis team in VERA. 

Measuring a monster

How do you measure the distance to a black hole as monstrous as Sgr A*, weighing in at 4.2 million times the mass of the sun? Very precisely.

To do this, the researchers with VERA used four Very Long Baseline Interferometry (VLBI) telescopes in Japan. These observatories work together to achieve results comparable to one telescope with a diameter about 1,400 miles (2,300 km) across. The resolution is so sharp that when compared to human eyesight, it would be like seeing a penny on the surface of the moon. However, VERA is designed to see things that are much farther away than the moon. For instance, VERA can distinguish the annual positional shift of a star within 10 micro-arcseconds, which is an angle 1/360,000,000 of the distance between two tick marks on a protractor. 

Using the four telescopes, researchers were able to measure the accurate positions, sizes and orbital velocities of Milky Way stars. VERA published a catalog of 99 Milky Way objects. From the catalogued information, they constructed a position and velocity map. This map helped them project orbits around the galactic center and, in turn, hone-in on its location.  With this new location, they figured out the more accurate velocity of the solar system. 

They used this information to reveal our location within the Milky Way and to determine the three-dimensional velocity and spatial structure of the galaxy, which is a barred spiral. 

They found that Sagittarius A* is 2,000 light-years closer to Earth than the International Astronomical Union (IAU) determined in 1985. Furthermore, our solar system is traveling 510,000 mph (227 km/s),which is faster than the earlier, official, recorded speed. VERA’s measurements are thought to be more accurate than past ones because the group used more advanced technology and corrected for how the Earth’s atmosphere blurred earlier measurements. 

The new finding also agrees with a distance measurement reported in the journal Astronomy & Astrophysics in 2019, which put Earth around 26,660 light-years from Sgr. A*, Nicholas Suntzeff, distinguished professor and director of the astronomy program at Texas A&M University, told Live Science. As such, Suntzeff wondered why the team compared their results primarily with the 1985 data rather than this more recent measurement in an experiment called GRAVITY, which involves the GRAVITY instrument attached to the European Southern Observatory's (ESO) Very Large Telescope (VLT) in northern Chile. 

Hirota agreed that VERA findings should be compared  to GRAVITY. "An important point is that we estimate the same parameters independently from the GRAVITY results by using a different method." 

The new findings have implications for solving some of the most enduring mysteries in astronomy.

“These results can be used to estimate other astronomical parameters such as the distribution of dark matter and its density around the solar system, and could even help scientists predict how often we should see hypothetical dark matter particles, if they exist,” said Hirota, whose group has been working to improve astrometry techniques and accuracy for more than 15 years. Many dark matter searches rely on a “wind” of dark matter blowing through the solar system. It is thought that some of the dark matter will interact with Earth-based detectors. Faster dark matter will make larger signals. If the VERA experiment is correct, and the solar system is moving more quickly, it is possible that dark matter might be easier to detect than scientists currently think.

In their next collaboration, the VERA researchers will look at objects even closer to the heart of the Milky Way. With each measurement, we will better know our place in the universe.