Chuck Bednar for redOrbit.com – Your Universe Online
After years of watching, astronomers have recorded the largest-ever flare in X-rays from the supermassive black hole located at the center of the Milky Way, and their discovery brings the scientific community one step closer to understand how black holes behave.
The event was detected by NASA’s Chandra X-ray Observatory and observed by a research team led by Amherst College astronomy professor Daryl Haggard last September. Haggard and her colleagues presented their findings at this year’s meeting of the American Astronomical Society (AAS), held this week at the Washington State Convention Center in Seattle.
Supermassive black holes are the largest type of black holes, and one can be found in every galaxy, the researchers explained. The one at the center of the Milky Way is called Sagittarius A*, or Sgr A*, and they believe that it contains roughly 4.5 million times the mass of our Sun.
Sgr A* has been repeatedly observed by scientists working with Chandra since the US space agency’s telescope was first launched over 15 years ago. Haggard and her colleagues originally had been using Chandra to determine if the supermassive black hole would consume parts of a 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,” the professor explained.
Her team detected a megaflare – an X-ray outburst that was 400 times brighter than usual, and nearly three times brighter than the previous record holder. That event took place in September, and was followed about a month later by a second enormous X-ray flare – one that was 200 times brighter than Sgr A* in its quiet state.
The astronomers have two main ideas about what could be causing the supermassive black hole to erupt so spectacularly. The first is that its gravity has torn apart a few asteroids and ventured too close, and that the debris would become extremely hot and produce X-rays before completely disappearing across the event horizon, or its point of no return.
“If an asteroid were torn apart, it would go around the black hole for a couple of hours – like water circling an open drain – before falling in,” explained co-principal investigator Fred Baganoff from the Massachusetts Institute of Technology (MIT). “That’s just how long we saw the brightest X-ray flare last, so that is an intriguing clue for us to consider.”
If that theory proves true, it would mean that Haggard, Baganoff and their associates had discovered evidence of the largest asteroid ever to be torn apart by Sgr A*. The second theory suggests that the magnetic field lines within the material flowing towards the Sgr A* are packed unusually tightly, which means that they could interconnect and reconfigure themselves.
When this happens, their magnetic energy is converted into the energy of motion, heat and the acceleration of particles, which could have produced a bright X-ray flare. These types of flares have been seen on the Sun, and the flares from the supermassive black hole could well have a similar pattern of brightness to these solar events, the researchers explained.
“At the moment, we can’t distinguish between these two very different ideas,” Haggard said. “It’s exciting to identify tensions between models and to have a chance to resolve them with present and future observations.”
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