Categories: Quasars

Astronomers are Starting to Understand the Quasar Lifecycle

Supermassive black holes have a complicated lifecycle. Sometimes they’re “on”, blasting out tremendous amounts of energy, and sometimes they’re “off’, where they sleep like dragons in their caves. By comparing the proportion of high-energy to low-energy waves emitted by quasars, astronomers are beginning to pin down how many black holes are sleeping, and when they’re likely to wake back up.

Here’s how it works. As far as we can tell, every galaxy has a supermassive black hole in its center. When material falls onto this black hole, it compresses and heats up (because the extreme gravity of the black hole is trying to drag a whole bunch of material into a relatively small volume). All that friction drives the release of tons of high-energy radiation, something astronomers call a quasar.

Along with the hard stuff comes radio waves, and we can use radio telescopes like LOFAR (the LOw Frequency ARray) and the WSRT (Westerbork Synthesis Radio Telescope) to detect them.

But the intense radiation blasts material away from the black hole, and it can no longer feed, so the black hole goes to sleep and the quasar shuts off, along with the radio emission.

Astronomers are trying to understand the overall lifecycle, which can take hundreds of millions of years to play out. They want to know how often quasars light up, how long they burn, and when they’re likely to switch on again.

And using a combination of high-frequency and low-frequency radio waves, they’ve got a new tool.

“High frequency radio waves quickly lose their energy…while those in the lower frequency do so much more slowly,” according to Prof. Dr. Raffaella Morganti, first author of the paper The best of both worlds: Combining LOFAR and Apertif to derive resolved radio spectral index images.

By using different radio telescopes to observe different frequencies of radio waves, and using the combined data to measure the ratio of high-frequency to low-frequency waves, astronomers can tell how recently a quasar shut off: the less of the high-frequency stuff, the more time has passed since the last feeding event.

From there, astronomers can build up a survey of active quasars, silent ones, and all the rest in between.

While powerful, the technique will require new radio surveys to observe as many galaxies as possible, to build up a proper population census of the black holes in our universe.

Paul M. Sutter

Astrophysicist, Author, Host | pmsutter.com

Recent Posts

Neutron Stars are Jetting Material Away at 40% the Speed of Light

It’s a well known fact that black holes absorb anything that falls into them. Often…

4 hours ago

Lunar Night Permanently Ends the Odysseus Mission

On February 15th, Intuitive Machines (IM) launched its first Nova-C class spacecraft from Kennedy Space…

14 hours ago

Webb Joins the Hunt for Protoplanets

We can't understand what we can't clearly see. That fact plagues scientists who study how…

16 hours ago

This Supernova Lit Up the Sky in 1181. Here’s What it Looks Like Now

Historical astronomical records from China and Japan recorded a supernova explosion in the year 1181.…

19 hours ago

Hubble Sees a Star About to Ignite

This is an image of the FS Tau multi-star system taken by the Hubble Space…

19 hours ago

This Black Hole is a Total Underachiever

Anyone can be an underachiever, even if you're an astronomical singularity weighing over four billion…

20 hours ago