Astronomy Blog

0957+561

Last week the BBC's very glossy science programme Horizon was titled 'What on Earth is Wrong with Gravity?' (available for another 21 hours on the BBC iPlayer). It was presented by man-of-the-moment Dr Brian Cox who, before starting a PhD at the University of Manchester in the late 90s, was in the pop band D:Ream. The band's most (only?) famous hit was Things Can Only Get Better which was used as the anthem to Tony Blair's election victory in 1997. Over the past few weeks and months Brian has been doing an excellent job explaining the issue of the STFC's budget cuts to the press and has appeared on both the Today Programme and BBC North West Tonight. He also does an excellent job talking about the future work of the Large Hadron Collider at CERN.

I had recorded the Horizon programme and was reminded to watch it as my aunty and uncle had been telling me about it over lunch on Saturday. I must say that I found the style to be a bit distracting, and kept wishing that Brian would just talk to the camera rather than in random directions, but the content was pretty good. However, in my astro-geek ways I did spot one mistake in relation to the first gravitational lens discovered.

The lens is actually a luminous galaxy surrounded by others that sit between us and a much more distant quasar (a very active galaxy). As their mass distorts the space-time around them, light heading from the distant quasar past this closer galaxy cluster has its path distorted and bent. The result, in this case, is that two images of the distant quasar are seen rather than just one; one from light bent around one side of the cluster and the second from light going the other way. These two images of the background quasar were first reported in Nature in 1979 by Dennis Walsh (Univ. of Manchester), Bob Carswell (Univ. of Cambridge) and Ray Weymann (Steward Observatory, Texas). The original observation of the lens, named 0957+561, was made with the Lovell Telescope in a survey in 1972 but, due to the resolution of the telescope, the two images looked like one object. A follow up of this survey using optical telescopes at Kitt Peak Observatory showed both images and spectra showed them to be the same object.
OK, back to the Horizon programme and the geeky mistake I was referring to. Whilst at Kitt Peak Brian said "...at first sight it looks like two galaxies. In fact, they gave them different names; 957 and 561." So what is the mistake? Well, 957 and 561 were not the names of the two images. I can see how easy it is to make that mistake if you don't know the conventions. The name is actually that of the object found in the original radio survey and this name refers to its position on the sky. The 0957 part refers to the Right Ascension of the object in hours and minutes (9 hours and 57 minutes) and 561 refers to its declination in decimal degrees (56.1 degrees). This may seem a strange way to do things but it actually does make it easier to find objects on the sky once you start to remember the telephone-number-like names. I find it difficult to remember where objects such as NGC 7027 are but 0836+710 is straightforward to find even if I can't remember what it looks like.

This little slip up in the understanding of naming conventions shouldn't take away from the programme though; it really is trivial and doesn't affect the science content. I am surprised that it slipped through especially considering that Brian works in the same physics department that Dennis Walsh worked in and that is home to a big bunch of radio astronomers. At least the programme made it possible for me to talk to my relatives about fundamental physics over lunch. That doesn't happen a lot.