NASA has discovered an unprecedentedly large cluster of black holes in our nearest galactic neighbor, Andromeda.
The 26 black hole candidates were spotted with the Chandra X-ray Observatory, which made more than 150 observations spread over 13 years.
Each of the black holes was formed after a star collapsed in on itself. Now, as they suck in material from other stars that orbit or pass nearby, the material gives off X-rays as it is consumed. These X-rays are what Chandra has spotted.
To filter Andromeda's black holes from other X-ray sources—such as neutron stars or much larger black holes that are farther away than Andromeda—the astrophysicists had to look at attributes like the brightness, variability, and color of their emissions.
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