Quasars are bright masses of light and energy at the center of large galaxies. They usually surround a massive black hole and gobble up superheated gas, emitting vast amounts of light and radio waves in the process.
What happens after this galactic feast is unveiled by a group of astronomers who observed a distant quasar known as SDSS J1011+5442.
The astronomers first observed the quasar in 2003 and measured its spectrum to understand the properties of the gas the black hole swallows. The "hydrogen-alpha" line in the spectrum in particular showed the amount of gas that was falling into the black hole, which is about 50 million times more massive than the sun.
Early last year, the scientists measured another spectrum for the quasar and noticed that there was a huge decline between the years 2003 and 2015. The bright beacon has disappeared.
Using the Sloan Digital Sky Survey (SDSS) telescope In New Mexico, the researchers found that the abrupt change took place in a matter of just a few years after 2010.
Jessie Runnoe, from the Pennsylvania State University, and colleagues considered possible causes for the sudden change. One is that a thick layer of dust may have passed through the host galaxy, obscuring the view of the central black hole. There is no way, however, that any dust cloud could have moved this fast to cause a significant drop in the quasar's brightness in a period of just two years.
Runnoe and colleagues also considered the possibility that the bright quasar they observed about 13 years ago was a temporary flare caused by the black hole ripping a star apart. This, however, cannot explain that the changing-look quasar has been shining for many years prior to its light turning off.
The researchers eventually concluded that J1011 simply ran out of gas. The black hole is still there but it appeared to have consumed all of the gas in its vicinity.
"We report the discovery of a new 'changing-look' quasar, SDSS J101152.98+544206.4, through repeat spectroscopy from the Time Domain Spectroscopic Survey," the researchers reported in their study, which was published in the Monthly Notices of the Royal Astronomical Society on Nov. 18, 2015.
"An abrupt drop in the accretion rate on to the supermassive black hole appears to be the most plausible explanation for the rapid dimming," the researchers concluded.
The researchers were no longer able to detect the quasar's spectroscopic signature as J1011 appeared to have consumed its entire inner disks of gas.
"Essentially, it has run out of food, at least for the moment," said Runnoe, who said it was the first time they have seen a quasar shut off this fast. "We were fortunate to catch it before and after."
