spectra

"The infrared wavelengths of our observations overlap with an important silicate dust feature that's characteristic of some red supergiant spectra," Kilpatrick said.

“This was intriguing, but without a way to obtain spectra of those stars, we could not really establish whether we were witnessing genuine accretion and the presence of disks, or just some artificial effects.”

The team gathered spectra of that star’s light with two optical telescopes.

Firstly, water vapor interferes and overlaps with the absorption spectra of many gases in the standard infrared ranges normally used for detection.

Astronomers can tell whether there’s a black hole in the galaxy by looking at large emission lines in their spectra, created by gas around the black hole swirling at high speed.