Scientists have agreed since the late 1980’s that a quasar is a compact region in the center of a galaxy surrounding a central, supermassive black hole. After they were discovered by the first radio telescopes, quasi-stellar objects (quasars) were almost as great a mystery as the black holes that spawn them.
Scientists now think that quasars are caused by superheating material in an accretion disc around a black hole. As material is drawn toward the gravity of the black hole, it spins and heats up to millions of degrees. The magnetic environment forms twin jets of material that blast out into space — this is called an active galactic nucleus (AGN).
When a black hole runs out of fuel, meaning nothing is close enough to be drawn in, the quasar fades and then shuts down altogether. This process can happen over the course of billions of years, so it is very unusual to see the phenomenon in progress.
However, now researchers report that they have spotted a quasar in the act of dimming. The quasar appears six to seven times dimmer than observations recorded just a few years ago.
C. Megan Urry, Yale’s Israel Munson Professor of Astronomy and Astrophysics, talked about the event.
“We’ve looked at hundreds of thousands of quasars at this point, and now we’ve found one that has switched off. This may tell us something about their lifetimes.”
Yale associate research scientist Stephanie LaMassa first noticed the dimming during a probe of Stripe 82. Stripe 82 is a thin sliver of sky near the Celestial Equator which has been scanned many times.
“This is like a dimmer switch. The power source just went dim. Because the life cycle of a quasar is one of the big unknowns, catching one as it changes, within a human lifetime, is amazing.”
The Yale researchers looked at a variety of data, including optical spectra information and optical photometry, and X-ray spectrum data that had been archived from previous observations. The analysis was necessary to show that the quasar was dimming and was not simply being obscured by gas clouds or other celestial objects.
The findings provide further evidence for leading theories about the behavior of black holes and the method by which quasars are generated. Urry talked about he importance of understanding black holes.
“It makes a difference to know how black holes grow. This perhaps has implications for how the Milky Way looks today.”
The Milky Way has a super-massive black hole at its core but is not currently generating a quasar, which indicates that it is not consuming fuel at the moment. This will likely change when the Milky Way and the Andromeda galaxy collide in about 4 billion years.
[Image via StellarD3]