Astronomers never know exactly what to expect when they point a telescope in a specific direction -- and sometimes what they see is completely unexpected.
In this case, astronomers were using the European Southern Observatory's Very Large Telescope in Chile and the W. M. Keck Observatory in Hawaii to observe the supermassive black hole at the center of our galaxy.
It's 26,000 light-years from Earth, but it's the closest black hole we can see, even if it's largely obscured by dust.
They observed it over four nights in April and May.
Here's a timelapse of images over 2.5 hr from May from @keckobservatory of the supermassive black hole Sgr A*. The black hole is always variable, but this was the brightest we've seen in the infrared so far. It was probably even brighter before we started observing that night! pic.twitter.com/MwXioZ7twV
— Tuan Do (@quantumpenguin) August 11, 2019
This black hole, known as Sgr A*, has shown variability before. It's been observed for years in multiple wavelengths of light. But on three of the four nights they observed it in near infrared, which is the most effective way to see variability in the black hole, astronomers noticed "unprecedented" changes.
The study has been accepted for publication in the journal Astrophysical Journal Letters .
The unusually bright flux levels and variability showed peaks that exceeded twice the historical measurements of the black hole. What the astronomers were seeing was an eruption of the black hole unleashing bright radiation.
In addition to these bright levels, on two nights in May they also saw large drops in brightness occur over the course of minutes.
Some of the astronomers involved in the study, including Tuan Do at the University of California, Los Angeles who initially drew attention to the outburst by tweeting about it, have been observing the black hole for years. And they've never seen anything like this.
The data differs from past observations of the black hole that have been collected in other studies.
So, what happened? That's the big mystery and the astronomers don't know the answer.
In the study, they suggest that the statistical models for the black hole and its variability need to be updated to track these changes in luminosity.
"The 2019 measurements push the limits of the current statistical models," the authors wrote in the study.
Another option is that there was a physical change in the black hole's activity. Is this because of an increase in its gathering of material? The astronomers said that more data, especially over multiple wavelengths of light, through the rest of the year and in the future could provide more answers.