Hapless Star Devoured by Black Hole

Black holes: infinitely deep pits from which nothing can escape. They’ve captured the imaginations of scientists, writers, and the general population, and are commonly found in science fiction, pop culture, and common vernacular. But despite our interest in black holes, we actually know very little about them.

This year has been awash with tales of black holes devouring other cosmic entities. In February, NASA reported that the supermassive black hole at the center of our very own galaxy was “snacking” on asteroids. Now, researchers at Johns Hopkins have detected a supermassive black hole approximately two billion light years from us that recently swallowed an entire star.

A black hole is an object with a gravitational pull so strong that nothing, not even electromagnetic radiation, can escape. They were predicted by Einstein’s theory of relativity: a large enough mass compressed into a small enough space will warp spacetime so extremely that it pulls everything within a certain distance into it. Incidentally, Einstein himself did not believe in the existence of black holes, but they were predicted by his theory nonetheless. Supermassive black holes, for those not aware, are black holes that are one million to one billion times the mass of our sun. The black hole at the center of the Milky Way Galaxy -- Sagittarius A* (pronounced A-star) -- is about 4.3 million times the mass of our sun.

The Johns Hopkins researchers detected a “tidal disruption event” in a galaxy two billion light years away from us. A tidal disruption is when a hapless star passes too close to the event horizon of a black hole and is literally pulled apart by the force of the event's gravitational field. Debris from the stellar break-up produces a distinctive flare that can be seen with the proper equipment. They are extremely rare, only occurring once every 10,000 years per galaxy. The experiment that witnessed this particular tidal event has been observing thousands of galaxies simultaneously for such events.
What does this tell us? Astrophysicists can glean a lot of useful information from events like these. Black holes, as their name suggests, are invisible to detection under normal circumstances. Only through their interaction with other cosmic objects can we detect them and learn about them. By analyzing the flare and other data from the star’s absorption, scientists deduced the type of star (a red giant whose outer hydrogen shell had been stripped off), the size of the black hole (3 million solar masses), and its location. (Nature has a full report, behind a paywall.)

Black holes are one of the great mysteries in our universe. Predicted in 1915, we have struggled to detect and study them ever since. Their very nature makes them elusive, but the more we learn, the more integral they seem to be. Most scientists believe that there is a supermassive black hole at the core of every galaxy, and they may be at least partially responsible for galaxy formation. Without black holes, and specifically without Sagittarius A*, we might not be here.

More compellingly, the event horizons of black holes are one of a few rare but critical cases where our major theories of physics break down. In a nutshell, we have two major theories that explain the universe very well: the “Standard Model” of particle physics and general relativity. However, there are a few conditions under which one or both of those systems breaks down. The most important of these conditions is the Big Bang -- the fundamental genesis of our universe. The more we can learn about black holes, the more likely we are to resolve that vital clash. Studying these anomalies could help us answer the ultimate question: how did we come to be here?

We have a long way to go, but findings like these move us forward.  As Neil deGrasse Tyson said, “We are not simply in the universe, we are part of it. We are born from it. One might even say we have been empowered by the universe to figure itself out—and we have only just begun.”

Originally posted at The Inclusive.