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3 years ago

Our Weird and Wonderful Galaxy of Black Holes

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.

The visualization above shows several of these binary systems found in our Milky Way and its neighboring galaxy. with their relative sizes and orbits to scale. The video even shows each system tilted the way we see it here from our vantage point on Earth. Of course, as our scientists gather more data about these black holes, our understanding of them may change.

The close orbit of a star and black hole causes the star to lose part of its outer layers to the black hole. A panning shot comes from behind a glowing star and reveals a black hole pulling a stream of stellar material into a swirling, hot disk around it.

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.

In this visualization, an off-white, round star orbits around a black hole with glowing orange material encircling it. The black hole is pulling glowing white material off the star as they orbit each other. V404 Cygni is a black hole that erupted in 1989 and 2015 with an X-ray nova. It lies at a distance of 8,200 light-years. The black hole has a mass of 12 times the Sun, and its companion star has just under two Sun’s worth of mass. They orbit each other every 6.5 days.

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.

An illustration depicts what astronomers think is happening within a binary system with a high-mass star and a stellar-mass black hole. A huge, blue-white star radiates strands of 'wind' from its perimeter, with a bright object just to its left. The bright object is the shining disk of material that has collected from the star’s wind and swirls around the black hole before falling 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 bright blue star and a black hole with a swirling disk of hot, glowing material orbit each other in this visualization of the Cygnus X-1 system. Cygnus X-1 is the first confirmed black hole. It lies at a distance of 7,200 light-years. The black hole has a mass of 21 times the Sun and its companion star has 40 Sun’s worth of mass. They orbit each other every 5.6 days.

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.

Two very different black hole systems are shown together in this visualization. In one, called GRS 1915, a bright star and a black hole with a large swirling disk of glowing material orbit each other, filling nearly the whole image. They only complete a small portion of their orbit in the few seconds the GIF plays. The second system is much smaller one called H1705. It has a small, bead-sized star orbiting a tiny black hole that has a small disk of material. The small system completes three orbits in the few seconds the GIF plays.

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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