The author and biochemist Isaac Asimov once said that “the most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ but ‘That’s funny…’.” That quote nicely sums up where researchers are after spotting a massive x-ray flare from the black hole at the center of the Milky Way.

Astronomers with NASA’s Chandra project were watching to see how the black hole, called Sagittarius A* (Sgr A*) would interact with a nearby gas cloud known as G2.

“Unfortunately, the G2 gas cloud didn’t produce the fireworks we were hoping for when it got close to Sgr A*. However, nature often surprises us and we saw something else that was really exciting,” said lead researcher Daryl Haggard of Amherst College in Massachusetts in a statement.

On September 14, 2013 Haggard’s team detected a “megaflare” from the black hole. The x-ray flare was three times brighter than the largest flare ever detected from Sgr A* and 400 times brighter than the black hole’s normal state. On October 20, 2014 after the Sgr A* had returned to normal Chandra detected a second flare half as big as the first and 200 times brighter than normal appeared.

The G2 gas cloud, which the researchers was originally studying, reached its closest point to the black hole in the spring of 2014. At that time G2 was still 15 billion miles away. The magaflare in September 2013 was a hundred times closer to the black hole than G2 making it unlikely that it was the cause of the eruption.

Currently the researchers have two theories to explain what caused the flare.

The first theory is that an asteroid was caught in the massive gravity field generated by the black hole. Sgr A* has an estimated mass of 4.5 billion times that of our sun. The debris from the asteroid could have become very hot, producing vast amounts of X-rays before disappearing into the black hole’s event horizon.

“If an asteroid was torn apart, it would go around the black hole for a couple of hours – like water circling an open drain – before falling in. That’s just how long we saw the brightest X-ray flare last, so that is an intriguing clue for us to consider,” said Fred Baganoff of the Massachusetts Institute of Technology in Cambridge, Massachusetts.

The second theory holds that the magnetic field lines within the gas flowing toward and into SgrA* could be becoming entangled. These lines could reconfigure themselves from time to time, causing a burst of X-rays. These types of magnetic flares sometimes occur on the sun and the observed flare from SgrA* have a similar pattern to those solar flares.

“The bottom line is the jury is still out on what’s causing these giant flares from Sgr A*. Such rare and extreme events give us a unique chance to use a mere trickle of infalling matter to understand the physics of one of the most bizarre objects in our galaxy,” said co-author Gabriele Ponti of the Max Planck Institute for Astrophysics in Garching, Germany.

The Chandra team’s results were presented at the 225th meeting of the American Astronomical Society in Seattle.

An interactive image of the megaflare as well as a podcast and video about the findings are available from the Chandra education website.