Astronomers said that they observed the supermassive black hole closest to Earth glowing with "unprecedented brightness" — and they aren't quite sure why.

The black hole, known as Sagittarius A* or Sgr A*, is 4 million times as massive as the Sun and about 26,000 light-years from Earth. Although no visible light can escape the gravitational pull of a black hole, astronomers are able to observe the hot gas that's about to fall into it in near-infrared, the portion of the infrared spectrum closest to light detectable by the human eye.

"So we observed basically four nights of observation this year. On one of the nights, its brightness was about twice as bright as the brightest measurement in the past 20 years," said Tuan Do, an associate research scientist and deputy director of the galactic center group at UCLA, who led the study. "That indicates that perhaps something interesting is happening physically in the region of the black hole."

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But Do said what exactly caused the sudden change in brightness is still a mystery.

"That's the big question, that's what we're all super excited to try to figure out," Do said. "We really don’t know at this point and only really with more data can we have a firm physical explanation."

Do suggested two potential explanations for what may have caused the black hole to light up. A star called SO-2 and another object called G2 got very close to Sgr A* in recent years, which could've ejected gas into the region that the black hole absorbed potentially causing the recent fireworks.

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The study has been peer reviewed and Do expects it will be published in the journal Astrophysical Letters very soon. But more research needs to be done to determine exactly what caused the light show, and Do said the window for observation is starting to close.

"We don’t often get to watch things change over such short time scales," Do said. "A lot of other telescopes have also observed the black hole this summer I'm really excited to see what the results might be."

Follow N'dea Yancey-Bragg on Twitter: @NdeaYanceyBragg