Gaia could detect free-floating black holes passing near stars in the Milky Way
The thing with black holes is that they are hard to see. Usually we can only detect their presence if we can detect their gravity. And if there are rogue black holes just traveling through the galaxy and not tied to another luminous astronomical object, it would be terribly difficult to detect them. But now we have a new potential data set to do this.
Gaia has just released its massive 3rd dataset containing astrometry data for over 1.5 billion stars, about 1% of the total number of stars in the galaxy. According to a new paper by Jeff Andrews of the University of Florida and Northwestern University, it may be possible for Gaia to detect disturbances caused by a rogue black hole that briefly interacts with one of its 1.5 billion stars in the catalog. Unfortunately, it is unlikely that such an interaction actually occurred during Gaia’s observation time.
This article is the third in a series exploring how the wealth of new Gaia data could potentially be used to find companions to some of its stars. Luminous stars are Gaia’s specialty, but many have “dark companions” that are not as detectable as their luminescent partners. Not all of these dark companions are black holes — some may be dead stars that have already used up their fuel supply, but weren’t massive enough to form a black hole.
The first paper looked at how scientists could use Gaia’s data to pick up signatures from those dark companions. The second focused on whether the data contained hints of very long binary orbital relationships with orbital periods lasting longer than the observation timeline. Both studies point to valid analyzes that someone will no doubt undertake now that the Gaia data is released. However, they fail to address what is potentially the most interesting of all dark companions: black holes.
Estimates put the number of black holes in the Milky Way at between 10 million and 1 billion, between 0.01% and 1% of the likely total number of stars in the galaxy. But most of these are only the size of a star and extremely difficult to detect using conventional data. Their appeal is arguably noticeable in Gaia’s dataset.
Gaia itself collects astrometry data, which detects the position, movements and magnitudes of stars. Any interaction, no matter how fleeting, with a black hole could potentially affect one of these stats. It’s just a matter of understanding what to look for.
That may not be as simple as the complex math and “extreme assumptions” that make the details of the Andrews papers clear. He notes that about 300,000 stars in Gaia’s catalog exhibit acceleration events. However, he also notes that, with some very general assumptions about the Milky Way’s dark matter content, none of those 300,000 observed accelerations are likely due to interactions with a rogue black hole.
But that doesn’t mean it isn’t possible to detect such an interaction with Gaia. Andrews even believes it’s possible, with some more assumptions about how the galaxy itself is structured. A rogue black hole temporarily interacting with a luminous star is just a rare event that Gaia most likely failed to capture during its observation period. But if another scientist finds evidence of such an interaction hiding in the data or another mission further in the future manages to collect the evidence, such a discovery would be a boon to black hole science.
Video: Gaia, the surveyor with billions of stars
Jeff J. Andrews, Weighing the Darkness III: How Gaia Will, But Probably Won’t, Detect Astrometrically Free-floating Black Holes. arXiv:2206.04648v1 [astro-ph.HE]† arxiv.org/abs/2206.04648
Quote: Gaia was able to detect free-floating black holes passing near stars in the Milky Way (June 2022, June 28) retrieved June 28, 2022 from https://phys.org/news/2022-06-gaia-free-floating- black-holes-stars.html
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