Enter Members Area

Guildford Astronomical Society

members' only area

QSO 0957+561 A/B The Double Quasar

A long time ago in a galaxy far, far away....Only kidding, or am I?

Here are some edited highlights from the Quasar episode:

The following group of observers from Guildford AS would like to announce the visual observation of this object from the UK, in the early hours of this morning (8:1:2000). As a hurried search failed to uncover any other observations from British amateurs; we think that this may well be the first visual UK observation. In exceptionally transparent (zenithal limiting magnitude 5.7-5.8) and steady skies, (Antoniadi 1) this object, (aka the Double Quasar) was detected by Laurence Hall (LH) using x300 in an 18" f4.5 Dobsonian at 1.15am. The observation was confirmed by: Gavin Stacey (GS); Peter Dean (PD); Adrian Selby (AS); Kevin Mills (KM).

The Double Quasar is easily located as it is a quarter of a degree np NGC3079, a bright edge-on spiral galaxy. A distinctive kite-shaped asterism lies approx. 2' sf. The quasar is usually imaged as a mag 16.5 wide (6") double star. Megastar v4 gives two values for the measured red-shift; z(abs)=1.39 and z(em)=1.41. We would be interested to hear from anyone who can convert these to their equivalent light-year distance values.

All observers reported the quasar as extremely faint, not held with averted vision but instead 'winking' in and out of visibility. Examination of various charts and the details confirmed that the object sighted was at the correct position and matched the published description. Observers LH, GS and PD considered the object to be elongated and fuzzy; however none of us managed to resolve the quasar into its two (mag 17.1 and mag 17.4) components, even when x600 was used.

Subsequent attempts to detect the quasar with x228 and x324 in a 12.5" f4.8 Dobsonian proved tantalisingly inconclusive. LH, GS and PD all confirmed that 'there was something there' at the correct position, but it was at the limit of detectability.

Amongst many other objects seen during the night; Leo 1, a faint mottling seen with x228 in the 12.5" and all seven components of Copelands Septet; spotted using x300 with the 18". All in all, a quite superlative nights fun, even though the temperature dipped to -4 deg C.

We are very surprised that we were able to observe this quasar with certainty under Southern UK conditions. Peter Dean (GAS member)

2) PETE WORKED OUT THE DISTANCE BASED ON THE REDSHIFT VALUE

Hi guys, Just thought you might like to know that I found a redshift to light years converter and QSO 0957 +561A/B, when you plug a redshift of 1.41, a Hubble constant value of 65 and assume Omega=1, is approximately 7.35 billion light years away. Or to put it another way, before those photons finished up in the back of your eye, they'd been travelling for well over 7 billion years...

Umm, I don't know about you, but I rechecked the figures (twice), same answer near enough. Makes you think eh...

Pete (GAS member)
BTW. I posted on uk.sci.astronomy and sci.astro.amateur.

3) HERE ARE TWO REPLIES TO PETE'S POSTING
Megastar v4 gives two values for the measured red-shift; z(abs)=1.39 and z(em)=1.41. We would be interested to hear from anyone who can convert these to their equivalent light-year distance values. Congratulations on your observation of the Double Quasar. The short cut approximation for converting high redshifts to distance is: (Z/1+ Z) X (age of universe). If you plug 15,000,000 into the formula, you end up with a distance of almost 9,000,000 light years. You can also use Ned Wright's Cosmological Converter. With the Hubble constant set at 60, you get a light travel time of almost 8,000,000 light years, roughly in agreement with the first calculation.

Examination of various charts and the details given confirmed that the object sighted was at the correct position and matched the published description. Observers LH, GS and PD considered the object to be elongated and fuzzy; however none of us managed to resolve the quasar into its two (mag 17.1 and mag 17.4) components, even when x600 was used. Steve Gottlieb and I had much the same experience. Although we agreed that the object appeared elongated, neither of us could make a clean split. Glad our Website was helpful to you.

Jim Shields

Congratulations on seeing this historic and enormously important object for yourselves. I am envious. I have observed this object dozens of times in the past 20 years, but always with radio telescopes such as the VLA, never with my own eyes.

For those who don't know about this object, it is the first case of gravitational lensing ever discovered (in 1979, by Walsh, Carswell, and Weymann). A single radio loud quasar at redshift 1.41 is split into multiple images by the gravitation of a cluster of galaxies at redshift 0.39 that lies in the line of sight of the quasar. In 0957, two of the images are nearly equal in brightness and separated by about 6 arcseconds (visible as two images on Sky Survey prints).

Two decades later, the discovery of gravitationally lensed objects and their use to do astrophysics is an industry. Among other things, they can be used to determine the Hubble constant (the results are totally independent of the usual "distance ladder"), and to search for dark matter.

David H. Roberts
Physics Department, MS-057
Brandeis University
Waltham, MA 02454-9110 USA

4) I SENT A MAIL ROUND EXPRESSING MY FEELINGS....
7.35 Billion Light Years,
WWWWWOOOOOOOOOOOOO WWWWW, AAAAAAHHHHH, YIIIIPPPEEEE !!!!!!!!!
Loz
PS. I think I'm going to be unbearably HYPER for a while !

5) PETE REPLIED
Hi Loz,
Actually, I gave you the nearest figures - if you assume a Hubble Constant of 60 (rather than 65)you get a distance of approx 8 billion light years...and nearly 2/3 of the way to The Restaurant at the End of The Universe. ( Note from Loz - I think you meant to say "The Big Bang Burger Bar")>
PS. I think I'm going to be unbearably HYPER for a while!
you and me both...
Pete

6) I POSTED IT ON MY SITE
QSO 0957+561 A/B The Double Quasar - Ursa Major 18" Dob 7mm Nagler 300x 08:01:2000
Visible as a slightly elongated stellar spot:

Receiving a few photons from a gravitationally lensed quasar approximately 7.35 billion light years away is without doubt my deepest observation yet !!!! Unfortunately although I had some tantalising moments trying to observe it in the 12.5" it finally proved just too tricky to confirm.

Luckily my observing partner Gav happens to own an 18" Obsession.........
I think I owe him a few chocolate biscuits !
If your thinking of tackling this one check out the report by Jay McNeil on the Adventures in Deep Space website (see links page on Loz's site).

Loz (GAS member)

 

[Back]