Inside Black Holes

Three recent black hole events and how they shape our universe

Sagittarius A*
A combination of infrared and X-ray observations indicates that a surplus of massive stars has formed from a large disk of gas around Sagittarius A*. X-ray: NASA/CXC/MIT/F.K.Baganoff

Near the middle of the Milky Way, there lives a supermassive black hole called Sagittarius A* (Sgr A) that any day now might eat a gas cloud (called G2) that’s floating towards it at 5 million miles per hour. Here on earth, we have a front row seat to this extremely rare galactic event that will have ripple effects throughout our galaxy.

“As it veers toward the black hole, the doomed cloud will shred and stretch into a piece of string over 100 billion miles long,” explains Dan Evans, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Boston. Evans spoke at Smithsonian’s Future Is Here conference today and gave attendees a tour of black hole events in our galaxy.

First, what exactly is a black hole? It’s a spot in space where a huge amount matter is extremely compressed and the gravitational forces around this spot of matter are so strong that they trap light, hence the name. “Black holes are extremely simple and extremely powerful,” he says. Astronomers characterize black holes based on three key factors: mass, spin, and electrical charge. On the other hand, a black hole feeding on matter emits the same amount of energy as one billion trillion hydrogen bombs per second.  This is called accretion, and here’s a simulation of what that might look like:

Supermassive Black Hole at the Center of the Milky Way Rips Gas Cloud

When a black hole eats matter, scientists expect to see fireworks: sparks of X-ray radiation. Sagittarius A* piques the interest of scientists because it can tell us about how black holes feed. “We know that the black hole used to eat a lot more in our Milky Way galaxy. But, that was hundreds, thousands or even millions of years ago. We’ve never had the technology to actually see something get shredded by a black hole before,” says Evans. “It will be the first time in our history that we will actually see a black hole swallow.” But, there’s debate as to whether G2 is a dust cloud or in fact a star, which could survive the collision. Sadly, that would mean no fireworks display.

Evans studies black holes through stunning images snapped by the Chandra X-Ray Observatory, which detect X-ray radiation waves to reveal black hole signatures across the universe.

In another galaxy amusingly dubbed “Death Star,” Evans and his colleagues found that a jet of particles, electrons and protons, shooting through a black hole in one galaxy was destroying another. “It’s an extraordinary event of galactic violence,” says Evans.

Such powerful phenomena shape the universe we see today. For example, two black holes in another corner of the universe are spinning closer and closer together. When they inevitably collide, they will send a ripple of gravitational waves across the universe.

Humans can’t see black holes with the naked eye, but thanks to a scientific effort to link radio telescopes across the planet to make a giant telescope, that might change. “With a telescope of that size they expect to produce the first image of a black hole’s silhouette,” says Evans. “For the first time, we could actually see a black hole with our own eyes.”

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