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

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

The European Southern Observatory’s GRAVITY instrument discovered clusters of gas swirling around just outside our galaxy’s supermassive black hole. Here’s a graphic representation of the gas in orbit. (Image credit: ESO/Gravity Consortium/L. Calçada)

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.

Furthermore, our solar system is moving faster than previously assumed as it orbits the 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’re still a long way from the Sagittarius A* (Sgr A*) black hole: 25,800 light-years, where one light-year equals around 6 trillion miles (9.5 trillion kilometers).

The research is part of the VERA Experiment, or the VLBI Exploration of Radio Astrometry, which aims to investigate the Milky Way’s three-dimensional structure. Scientists can’t just take a photo of the Milky Way to figure out its structure because we live within it. Instead, in a scientific field known as astrometry, they take exact measurements of stars’ sizes, locations, and orbital velocities (how fast they round the galactic center). The resulting maps can reveal details about our Milky Way, its stars, 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 calculate the distance to a black hole the size of Sgr A*, which has 4.2 million times the mass of the sun? Quite 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 high that it would be like seeing a penny on the moon’s surface with human eyes. VERA, on the other hand, is designed to view things that are considerably farther away than the moon. VERA, for example, can detect a star’s annual positional shift within 10 micro-arcseconds, which is an angle of 1/360,000,000 of the distance between two tick marks on a protractor.

Researchers used four telescopes to precisely measure the positions, sizes, and orbital velocities of Milky Way stars. VERA provided a catalog of 99 objects from the Milky Way. 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. They calculated the more exact velocity of the solar system using this new location.

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.

Sagittarius A* is 2,000 light-years closer to Earth than the International Astronomical Union (IAU) estimated in 1985. Furthermore, our solar system is traveling at 510,000 mph (227 km/s), which is quicker than the previously recorded official speed. Because the scientists used more advanced technology and accounted for how the Earth’s atmosphere blurred previous readings, VERA’s measurements are thought to be more accurate than previous ones.

According to Nicholas Suntzeff, distinguished professor and director of the astronomy program at Texas A&M University, the new discovery also corresponds with a distance measurement published in the journal Astronomy & Astrophysics in 2019, which places Earth around 26,660 light-years from Sgr. A*. Suntzeff questioned why the researchers compared their results exclusively with 1985 data rather than this more recent measurement in GRAVITY, an experiment involving the GRAVITY instrument attached to the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in northern Chile.

Hirota agreed that the findings of VERA should be compared to those of 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 are based on the solar system being hit by a “wind” of dark matter. Some of the dark matter is expected to interact with detectors on Earth. Larger signals will be produced by faster dark matter. If the VERA experiment is true and the solar system is moving faster, dark matter may be easier to detect than scientists presently believe.

The VERA researchers will examine at objects much closer to the Milky Way’s core in their next collaboration. With each measurement, we will have a greater understanding of our place in the universe.

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