Milky Way Stars Mapped With Gaia, May Have Numerous Supermassive Black Holes

The European Space Agency released the second batch of data from its Gaia mission Wednesday, which identifies the location of almost 1.7 billion stars in the Milky Way and beyond, making it the most detailed map of stars we currently have. The data also include precise information on the movement of asteroids with the solar system.

The data relate to observations made over 22 months — between July 25, 2014, and May 23, 2016. Gaia, a space observatory launched in 2013 to measure the position and distance of stars, had observed about two million stars in its first data set that was released in 2016. The data in this new release are a lot more precise — the brightest stars were tracked with accuracy similar to an observer on Earth being able to spot a quarter coin on the moon’s surface.

This level of precision allowed astronomers to track the true movement of stars, instead of relying on an approximation using the parallax method — the apparent shift seen in object’s position in the sky, as Earth orbits the sun.

Along with stars’ positions, the data also reveal their brightness and colors, and in the case of about half a million stars, also how those two have changed over time. For about 100 million stars, the data include their surface temperatures and for 87 million or so stars, the effect that interstellar dust has on them.

“The sheer number of stars alone, with their positions and motions, would make Gaia’s new catalogue already quite astonishing. But there is more: this unique scientific catalogue includes many other data types, with information about the properties of the stars and other celestial objects, making this release truly exceptional,” Anthony Brown of Leiden University in the Netherlands, who chairs of the Gaia Data Processing and Analysis Consortium Executive, said in a statement Wednesday.

For instance, the database has information on the positions of over 14,000 asteroids in the solar system that were already known, allowing astronomers to plot their precise orbits. It also includes the locations of 500,000 quasars, the first time their coordinates have been made available in optical wavelengths.

Gaia also observed the motion of stars inside globular clusters in the Milky Way’s halo, as well as those in nearby galaxies — the Small and Large Magellanic Clouds. Using that data, astronomers could plot the orbits of 75 globular clusters in our galaxy’s halo and of 12 dwarf galaxies orbiting our own. This would allow them to study the evolution of the Milky Way and the distribution of dark matter in it.

Highlights from the second release of Gaia data were presented in Berlin, and a series of scientific papers, discussing various aspects of that large volume of data, are scheduled to be published in a special edition of the journal Astronomy & Astrophysics.

In an unrelated study, also about the Milky Way, researchers used a theoretical model to suggest our home galaxy has several supermassive black holes in it. Typically, most large galaxies have a supermassive black hole in their centers, not several.

According to a study published Tuesday in the Astrophysical Journal Letters, a team of researchers suggest that galaxies as massive as our own should contain several supermassive black holes, likely a result of a smaller galaxy merging into a larger one, and bringing with it its own supermassive black hole in the process. This second supermassive black hole would be at the center of the smaller galaxy, but following the merger, could wander throughout the now-larger galaxy.

However, given their predicted locations — far from galactic centers and even outside the galactic disks — these wandering supermassive black holes would be unlikely to accrete any material. And since they are black holes, the lack of accretion would render them effectively invisible.

“We are currently working to better quantify how we might be able to infer their presence indirectly,” Michael Tremmel, a postdoctoral fellow at the Yale Center for Astronomy and Astrophysics, and lead author of the study, said in a statement.

But if there are supermassive black holes darting around the galaxy, does that forebode impending doom for Earth? No, says Tremmel.

“It is extremely unlikely that any wandering supermassive black hole will come close enough to our Sun to have any impact on our solar system. We estimate that a close approach of one of these wanderers that is able to affect our solar system should occur every 100 billion years or so, or nearly 10 times the age of the universe,” he said.