We are much closer to our galaxy’s black hole than we thought

Estimating the exact position of our solar system within the Milky Way is not an easy thing, just because we have no real global view of our galaxy. Given this difficulty, the estimate often undergoes adjustments, often minimal, sometimes more substantial. According to a new map of the Milky Way, the position of the solar system is not what we thought. Not only are we closer to the galactic center – and therefore to the Sagittarius A * supermassive hole, but we are orbiting at a faster rate than previously estimated.

Mapping the Milky Way from our position, ie from within, is a problem that has long stimulated our understanding of the dynamics of celestial objects and gravity. It is relatively easy to map the two-dimensional coordinates of stars and other objects, but the distances between them are much more difficult to determine. And distances are important because they help us determine the intrinsic luminosity of celestial objects.

However, thanks to technical and technological advances, astronomers are constantly improving in the calculation of these distances, in particular through studies exploiting the best technologies and techniques available, whose goal is to refine our three-dimensional maps of the Milky Way, an area known as astrometry. And one of them is the VERA radio astronomy project, led by the Japanese VERA collaboration. The Vera Astrometry Catalog was published in the journal Publications of the Astronomical Society of Japan.

A virtual telescope 2,300 kilometers in diameter

The VERA project (for Very Long Baseline Interferometry Exploration of Radio Astrometry) relies on a number of radio telescopes across the Japanese archipelago, combining their data to efficiently produce the same resolution as a telescope with a satellite dish 2,300 kilometers in diameter. This is the same principle as that of the Event Horizon Telescope (EHT), which produced the very first direct image of the shadow of a black hole.

VERA, whose celestial observations began in 2000, is designed to help us calculate distances to radio-emitting stars by calculating their parallax. Thanks to its incredible resolution, it observes these stars for over a year, and observes how their position changes relative to stars that are much further away as the Earth revolves around the Sun.

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Principle of the parallax calculation with VLBI observation systems (Very Long Baseline Interferometry) such as VERA. Credits: National Astronomical Observatory of Japan

This change in position can then be used to calculate a star’s distance from Earth, but not all parallax observations are created equal. A VLBI system can produce much higher resolution images. For example, VERA has a stunning angular resolution of 10 millionths of an arc second, which should produce astrometric measurements of extraordinary precision. And that’s what astronomers have used to refine our solar system’s position within the Milky Way. Based on the first VERA astrometry catalog of 99 objects released earlier this year, along with other observations, astronomers have created a map of the position and speed of these objects.

From this map, they calculated the position of the galactic center. In 1985, the International Astronomical Union defined the distance to the galactic center as 27,700 light years. Last year, the GRAVITY collaboration recalculated it as being closer, just 26,673 light years away. Lately, measurements based on VERA bring it even closer, at a distance of 25,800 light years. And the solar system’s orbital speed is also faster than previously estimated: 227 kilometers per second, instead of the official speed of 220 kilometers per second.

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Estimated position of the galactic center in relation to the Solar System. Credits: National Astronomical Observatory of Japan

This change might seem insignificant, but it could impact how we measure and interpret the activity of the galactic center – which will hopefully allow us to get a more accurate picture of the complex interactions around Sgr A. *. In the meantime, the VERA collaboration is moving forward. Not only does she continue to observe objects in the Milky Way, but she is partnering with an even larger project, the East Asian VLBI Network. Together, the astronomers hope that the telescopes involved in this project can provide measurements of unprecedented precision.

Source : Publications of the Astronomical Society of Japan

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