Chris's Backyard Astronomy January 2017


     A view
     Earth’s lifetime 

 By Chris Higgins

Happy New Year to everyone. This month I am going to concentrate upon one topic only; something that came to my attention at New Year.  The item in question is described as a QUASAR and makes a year in my life appear
extremely insignificant.

Eyewitness report:

 “Almost Older Than Time. Would we be able to see it?

On Monday the 2nd of January we gathered in Chris's back garden observatory to spot a tiny pinprick of light that had been travelling 8 billion years, yes that's right 8 BILLION YEARS to reach us!
Chris had done his homework, mapped out its position and identified a few pointer stars to help us in our search. The bright moon and lovely Venusstayed handily behind the house so a reasonably dark, clear sky helped us in
our search.

Our luck was in, the pointer stars in the shape of a triangle were in  the (telescope) field of view and using averted vision I spotted our faint target, impossible to grasp the enormous distance through space and time the photons from this QUASAR had travelled. Once spotted it was easier to see it again as we all took turns to look at this black hole in action; a successful night, thanks Chris.”
Susan Feist 

Quasi Stellar Radio Sources (QUASAR)

The name was adopted originally because such objects were first observed by ‘seeing’ their radio waves and so they were assumed to be stars.  Remember, telescopes are not just available to see things with your own eyes but some are capable of detecting lots of other forms of energy.  The Jodrell Bank telescope near Manchester for example was once the greatest radiotelescopes in the world.

Jodrell Bank Radio Telescope: Image credit mattbuck

Up until the 1960s a multitude of radio wave sources out in the sky were listed and catalogued.  Critical to identifying these objects was to accurately log their precise position and then try and get an identification too with a powerful visual telescope.  This proved possible in some cases and as a bonus it was possible to catch the light and determine the spectrum of the object (see my previous column).  Once you have the spectrum you can find out a lot of important information.

However, visual recognition and thus scientific interpretation of some of these QUASARs eluded astronomers.

3C 48

I quote a lot of numbers and acronyms but really it’s not that complicated. QUASAR 3C 48 was the 48th entry in the 3rd Cambridge catalogue of radio sources.  In 1960, using a huge 200 inch telescope, astronomers Sandage, Matthews and Bolton finally pinned this particular radio source to a 16th Magnitude star.

Mount Palomar 200-inch telescope. Image credit: Coneslayer at English Wikipedia

 A refresher on magnitude

Remember, the magnitude scale works counter-intuitively in reverse. Each step is a change of about 2.5 times in brightness.  For example, to us the full Moon looks about 60,000 times brighter than the bright star Vega. On the other extreme QUASAR 3C 48 is about 10,000 times DIMMER than the dimmest star we can see with the naked eye!

Capturing the light from the QUASAR to enable a spectrum to be examined was some feat in those days but they did so.  Sandage though was quoted describing the spectrum as “exceedingly weird”.  What followed was a 3-year period of doubt and false reasoning because the spectrum just could not be interpreted within the range of known objects.

In 1963 two other scientists, Schmidt and Greenstein, re-examined the spectrum of 3C 48 from 1960.  Schmidt had previously examined a spectrum of a similar  
object (3C 273) and was thus experienced in these matters.  What he immediately concluded was not weird but that object 3C 48 showed a “redshift of 0.37”. So, now we need a recap on redshift.

Hearing an ambulance

Recall the last time you stood by as the ambulance sped towards you and then away from you.  We are all familiar with characteristic change in pitch of the siren.  As it approaches you the pitch gets higher then as it leaves you the pitch gets lower.  The lowering of the pitch as the sound source moves away from us is due to a ‘stretching’ of the wavelength caused by the speed of the ambulance relative to us. This is the Doppler effect and applies to all types of radiation including light.

Normal spectrum above and red-shifted spectrum below.  The tell tale absorption lines are moved to the right.
Credit: Georg Wiora (Dr. Schorsch) via Wikimedia Commons

 So Schmidt was saying that the spectrum of QUASAR 3C 48 told us that it was (and still is) moving away at truly phenomenal speed! As we have discussed before, the painstaking work of Edwin Hubble in the 1920s enabled a connection to be made between the speed that an object is receding and its distance.  On doing the maths 3C 48 was located at 4 BILLION LIGHT YEARS distant.

Ancient photons hit Bishop Monkton

This dramatic distance estimation created disbelief in theastronomical community.  Knowing how bright the object looks to us (Magnitude +16) and also knowing its distance, enables us to quite easily determine its true brightness close up and thus its power.  The calculation for most QUASARs shows they have the luminosity of 10
Trillion (10,000,000,000,000) Suns, easily one of the most energetic objects in the Universe!

As you may imagine this stimulated a decade long argument as to whether the observations were true or were these QUASARS just objects in our mown galaxy that demonstrated weird physics?  In more recent times, advancements in technology have enabled astronomers to study ‘normal’ galaxies in the region of these QUASARS and confirm that indeed they are very distant objects.

On the 2nd January 2017 a group of villagers and friends congregated in my humble shed known as the Observatory and eventually, one by one caught a glimpse of light that has taken 8 BILLION years to get here.  I stumbled across a reference to QUASAR 4C 11.69 also known as CTA 102.  It is in the constellation of Pegasus looking west from the village at the moment.

The old 9 inch SCT telescope used to spot the QUASAR

This particular QUASAR was originally falsely classed as a magnitude +17 variable star.  Variable stars are quite common but are usually quite regular in their variability.  Not this one!  Recently its magnitude has changed from +17 to nearly +11, which is an increase in brightness of 250 times.  Think about this for a moment.  This is an object that is TWICE the age of the Earth, more than half the age of the entire Universe as we know it and visible in my 9 inch telescope.  Surely this is the most powerful and oldest thing any of us will witness.

Its brightness currently varies quite substantially on a daily basis so what is it?  CTA 102 was discovered in the early 1960s from its varying radio source but was laughingly thought to be signals from an extra terrestrial intelligence and American folk rock band The Byrds wrote a song about it in 1967 called ‘Younger Than Yesterday’.  It is in fact a giant black hole at the centre of a distant elliptical galaxy and its brightness is determined by what it is currently consuming.  So the recent huge increase in brightness is a burp of cosmic proportions quite possibly as it gulps in stars or even other galaxies.  I write this in the present tense but it is
highly likely this object ‘died’ eons ago and no longer exists.

A QUASAR; a disk of stellar material feeding a huge black hole and artist’s depiction of data via NASA’s Spitzer and Chandra telescopes. Credit: Nasa JPL

The village group found it a challenge to observe but with careful attention to excluding all other light sources and using averted vision. Ibelieve all present witnessed the 8 BILLION year old photons.  Retiring to the kitchen to consume a well earned cuppa, some of us had another peek about an hour later and it had significantly increased in brightness in that time so obviously it had done similar to us.

What next?

A few days later, from the observatory I captured a star field image to show the QUASAR CTA 102 here in the centre of frame against known reference stars.  This is a stack of 20 x 30 second exposures.

QUASAR CTA 102 approximately Magnitude 12. 8th January 2017; Chris Higgins

CTA 102 is now going out of reach. If it is still belching at the same rate in the Autumn we should check back then to see if it has satisfied its hunger.  Feel free to join me. 

Follow my Twitter feed for regular updates on this and new topics from the backyard observatory.

Twitter: @owmuchonomy