Astronomy is hard for a lot of reasons. There’s the maths and computer science needed to transform data into information. There is all the stuff you need to know so you know which maths and which software to use, and then there is stupid stuff like how big the sky is and how little of it is being watched at any given moment. Your typical telescope can view an area no larger than your pinky fingernail at arm’s length. That’s not a lot of sky, and given there just aren’t a lot of professional observatories in the world, most of the sky goes unmonitored most of the time.

It is often entirely by luck that we’re able to capture amazing things that happen in detail. Well, a lot of luck coupled with hard work.

Back in 2019, a team of astronomers applied for coordinated time using the Chandra, NuSTAR, ALMA, and VLT telescopes to observe the supermassive black hole Sgr A* in the center of our galaxy. This is a competitive process, and each telescope’s time has to be requested separately. To be able to get time on all these systems at once is pretty much as amazing as their science, which is pretty exciting.

It’s exciting because it appears that while they were observing Sgr A* with four amazing telescopes that span from X-ray to infrared and radio wavelengths, they caught Sgr A* in the act of potentially eating faster than normal. According to the research paper led by H Boyce and published in The Astrophysical Journal: A moderately bright NIR flare was captured on July 18 simultaneous with an X-ray flare that most likely preceded bright submillimeter flux.

Our black hole is always eating a little of this and a little of that. Dust, gas, random bits that don’t amount to a lot — it all adds up to just enough energy getting released as things scream toward the event horizon that the region around Sgr A* shines in colors of light our eyes can’t see, and the more it is eating, the more light is emitted.

And just to repeat myself — the light is coming from the material falling in, not from Sgr A* itself.

And each color of light comes from different, interrelated mechanisms. By seeing how light, or radiation, of different colors peaks in time with different effects happening simultaneously or with various delays, it’s possible to untangle the mechanisms behind each brightening and fading change in flux. This paper was able to identify three possible scenarios to explain what was seen, and future observations should allow us to narrow things down further.

As the researchers say in their summary: Narrowing down the radiation mechanism powering and connecting variability across wavelength regimes brings the field closer to accurately describing the physical mechanisms that power the dramatic flux changes originating near the event horizon.

This team worked hard and was awarded time on an amazing suite of telescopes. They got lucky and they were able to be on target when the black hole took a big bite of something. And because they worked hard and got lucky, we now know more than we knew before.

And next time a team like Boyce’s is able to get multi-telescope observing time, they just might be able to use the JWST. 

More Information

CfA press release

“Multiwavelength Variability of Sagittarius A* in 2019 July,” H. Boyce et al., 2022 May 18, The Astrophysical Journal