We’ve Been Underestimating How Many Black Hole Collisions Are Terrorising The Universe
Staring into the void.
By David Nield
Astronomers have found what looks to a fresh trove of supermassive black hole pairs, increasing the number of known pairs by about 50 percent, after new image analysis techniques were used to study two of our most detailed sky surveys.
Finding these black hole pairs is crucial to understanding more about how they form and how galaxies eventually collide, with the new findings giving astronomers five new pairs to analyse.
Supernova Fail: Giant Dying Star Collapses Straight into Black Hole
By Elizabeth Howell
It appears the path to becoming a black hole is more complex than astronomers thought. Rather than exploding into a supernova before collapsing into a black hole, as expected, one giant star skipped the pyrotechnics and went straight to the collapse.
This so-called “massive fail,” spotted in a nearby galaxy, could explain why so few massive stars have been observed going supernova, researchers conducting a new study explained. As many as 30 percent of these massive stars may instead quietly collapse into a black hole.
Black holes are hard to find. Like, really hard to find. They are objects with such strong gravity that light can’t escape them, so we have to rely on clues from their surroundings to find them.
When a star weighing more than 20 times the Sun runs out of fuel, it collapses into a black hole. Scientists estimate that there are tens of millions of these black holes dotted around the Milky Way, but so far we’ve only identified a few dozen. Most of those are found with a star, each circling around the other. Another name for this kind of pair is a binary system.That’s because under the right circumstances material from the star can interact with the black hole, revealing its presence.
If the star and black hole orbit close enough, the black hole can pull material off of its stellar companion! As the material swirls toward the black hole, it forms a flat ring called an accretion disk. The disk gets very hot and can flare, causing bright bursts of light.
V404 Cygni, depicted above, is a binary system where a star slightly smaller than the Sun orbits a black hole 10 times its mass in just 6.5 days. The black hole distorts the shape of the star and pulls material from its surface. In 2015, V404 Cygni came out of a 25-year slumber, erupting in X-rays that were initially detected by our Swift satellite. In fact, V404 Cygni erupts every couple of decades, perhaps driven by a build-up of material in the outer parts of the accretion disk that eventually rush in.
In other cases, the black hole’s companion is a giant star with a strong stellar wind. This is like our Sun’s solar wind, but even more powerful. As material rushes out from the companion star, some of it is captured by the black hole’s gravity, forming an accretion disk.
A famous example of a black hole powered by the wind of its companion is Cygnus X-1. In fact, it was the first object to be widely accepted as a black hole! Recent observations estimate that the black hole’s mass could be as much as 20 times that of our Sun. And its stellar companion is no slouch, either. It weighs in at about 40 times the Sun.
We know our galaxy is peppered with black holes of many sizes with an array of stellar partners, but we’ve only found a small fraction of them so far. Scientists will keep studying the skies to add to our black hole menagerie.
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