Quasar CTA 102: Historically Bright, Violently Variable

By: Bob King November 23, 2016 38

The normally faint quasar CTA 102, once thought to harbor an advanced civilization and made famous in a 1967 song by the Byrds, is currently bright enough to see in an 8-inch telescope.

Quasar Footprint — This VLBA image of the jet from quasar CTA 102 in Pegasus shows the historically bright outburst. The ticks are one per milliarcsecond. The quasar is about 8 billion light-years away, so we're seeing about 5,000 light-years of jet length here.
*MOJAVE program, M. Lister (Purdue University) et al.*

In the history of SETI, the Search for Extraterrestrial Intelligence, there have been two great false alarms. The first occurred in 1963 when powerful radio waves were detected from the source CTA 102 in Pegasus. Followup observations in 1965 showed that the source's radio emission was varying, prompting then-Soviet astronomer Gennady Sholomitskii to declare that an advanced civilization was behind the transmissions.

Not long after, observations made with the 200-inch Hale Telescope identified the fluctuating object as a quasar, a supermassive black hole at the center of a remote galaxy.

The second false alarm is associated with the discovery of the first pulsar by Jocelyn Bell in 1967. The steady "thunk" of radio signals every 1.33 seconds earned this object the nickname LGM-1, short for "little green men." Pulsars are rapidly rotating neutron stars that beam a narrow beacon of radio waves in our direction every rotation. Some rotate hundreds of times a second and sound like buzzing bees when the signals are converted into sound.

But back to CTA 102. The worldwide buzz about an alien origin for the quasar was still in the air in 1967 when the American rock band the Byrds recorded the song "C.T.A. 102" on their Younger Than Yesterday LP. The lyrics (below) offer a hopeful message, and the upbeat tune ends with a fun twist — be sure to give it a listen. This may be the only song ever recorded about a quasar!

Year over year receiving you
Signals tell us that you're there
We can hear them loud and clear

We just want to let you know
That we're ready for to go
Out into the universe
We don't care who's been there first

On a radio telescope
Science tells us that there's hope
Life on other planets might exist

A Restless Supermassive Black Hole — This artist's impression depicts a quasar emitting a powerful jet of matter thousands of light-years long, similar to the one we observe at CTA 102. Quasars are supermassive black holes that emit radiation across the electromagnetic spectrum when material heats up as it falls into the black hole.
*ESO / M. Kornmesser*

Like many quasars, CTA 102 is subject to variations in its light depending on what the supermassive black hole is consuming and how it goes down. Powerful gravitational and frictional forces cause material in an accretion disk around the hole to radiate tremendous amounts of energy, primarily in X-ray wavelengths, but also in radio, visual, and other forms of light, before it's sucked into the black hole and disappears forever.

Normally, CTA 102 glows weakly at around magnitude +17, a terrifically tough target for most amateur astronomers. But in early November it underwent a dramatic outburst in brightness. I tracked it down Monday night (November 21st) in my 15-inch scope at magnitude +13.8! That's well within range of an 8-inch telescope.

Quasars Have Their Ups and Downs, Too — This light curve of CTA 102, also known as 4C 11.69, shows two sharp peaks in brightness occurring the past five years separated by lulls at magnitude +16 to +17. The past two months, the star has been very active with lots of rapid up and down variations. The date is shown along the bottom; magnitude scale at left.
*AAVSO*

Thomas Balonek (Colgate University) and team reported in Astronomer's Telegram #9732, that "to our knowledge, this is the brightest level reported in over 40 years of optical monitoring by several groups, including the well-documented optical outburst in 2012."

Others have recorded rapid variations in the quasar's light of up to 0.4 magnitude in the span of just two hours. With the Moon out of the sky and the target on the meridian at nightfall this month and early next, I encourage to feast your eyes on this rare event.

A Quasar Right Over Your Head — This map of Pegasus will help you get oriented. CTA 102 is located about 2.5° NW of ζ Pegasi near the star HD 212989, magnitude +7.2. North is up. The quasar's coordinates are RA 22^h 32^m 36.4^s, Dec. +11° 43′ 51″.
*Map: Bob King, Source: Stellarium*

You'd be wise to start your observing session with CTA 102, making an estimate of its magnitude using the provided chart or download and print this sequence of AAVSO charts: B (wide field), D (narrower view) and E (close in). Note that the alternate name, 4C 11.69, is used by the AAVSO. Return an hour or two later, before finishing up for the night, and make another brightness estimate. Given the quasar's erratic behavior, you might just witness it in the act of choking on its food!

Make a Right at the Stepping Stones — Start at HD 212989 and star-hop to my "stepping stones" about 30′ east. From there, move southeast to a flattened triangle, then drop a short distance north to a smaller triangle of stars that includes the quasar. You can also get there using the "pointing finger." Stars are labeled with magnitudes and south is up. Right click, save the large version, and print out to use at the telescope.
*Map: Bob King, Source: Stellarium*

The "CTA 102" comes from the 102nd entry in the Caltech Survey, part A, a very early radio survey done at Owens Valley California, according to Matthew Lister, Professor of Physics and Astronomy at Purdue, who examined the quasar with the Very Long Baseline Array (VLBA). At 8 billion light-years distant, it might be the easiest, most remote object you'll ever see.

But be sure to look quick! There's no telling how long this outburst may last. Using the maps, star-hop to the erstwhile alien beacon with an 8-inch or larger telescope. Once you've arrived in the general vicinity with low magnification (50×-75×) and identified the brighter star patterns, up the magnification to 150x to pinpoint the quasar then increase the power to 200×. High magnification darkens the sky for a clearer, higher contrast view of those ancient photons.

The Byrds may have flown, but CTA 102 remains to thrill the visual observer with raw power and visions of long, long ago.

Resources:

Research into CTA 102
Track the quasar's ups and downs at the AAVSO website. In the Pick a Star box, use 4C 11.69 and click the Recent Observations link.

Comments

Tom Hoffelder

November 24, 2016 at 8:51 am

Wow, a chance to quadruple the age of the oldest photons that have sent signals through my optic nerve! Awesome! Thanks for the article!