How do galaxies grow? One of the most common ways seems to be by merging with other nearby galaxies (a hot research topic that Rita’s talked about in more detail). Seems simple enough, but to really understand how this happens you need to look at a large number of them, at various stages of the merging process.
One way to approach this is by studying active galactic nuclei (AGN) – the extremely bright central regions seen in some galaxies caused by accretion onto their supermassive black holes. Mergers are thought to trigger AGN by funneling cold gas onto the black hole and creating the accretion disc. However, both of the incoming galaxies involved in the merger have their own central black holes, so, if this funelling happens before they themselves merge together, two AGN could be ignited. If you could find systems like this, ideally with a range of separations, what you’ll actually have is a snapshot of many different merging stages. Plus, since AGN only live for a short time, you’ll also be able to get a handle on how long all this takes.
Hundreds of these dual-AGN systems have been detected, but only a small proportion contain AGN that are closer together than 10 kiloparsecs, meaning that we’re missing information on the final stages of the merging process. The situation improved recently with the publication of a paper reporting a pair that are separated by only 4.8 kiloparsecs. One source isn’t enough though to draw conclusions about mergers in general of course, but finding one should make it easier to find more. When it comes to AGN, sometimes two are better than one.
R.C. McGurk, C.E. Max, D.J. Rosario, G.A. Shields, K.L. Smith, S.A. Wright (2011). Spatially-Resolved Spectroscopy of SDSS J0952+2552: a confirmed Dual AGN Submitted to ApJL DOI: arXiv:1107.2651
On Saturday 2nd July I, and several thousand over people headed to Jodrell Bank for a unique event: Jodrell Bank Live. Their tagline “where music meets science” meant we’d be treated to sets from, among others, OK Go, British Sea Power and the amazing Flaming Lips, interspersed with sciency bits featuring their fancy new visitor centre and the giant Lovell Telescope (the dish that I’d happily take home with me if I could). I’ve been meaning to write about this since I got back, but I couldn’t figure out how to convey what happened. Luckily for me though they’ve made a highlights movie:
The part at the end where the crowd chant “science, science, science” came after Dr Tim O’Brien taught everyone about pulsars. It was strangely moving!
One of the (clearly very few) benefits of living in Honolulu is that twice a year we get to witness an astronomical phenomenon that only happens in the tropics. The phenomenon is known as Lahaina Noon and in layman’s terms it’s when the Sun is directly overhead. Outside the tropics while the Sun gets to its highest point in the sky at local noon, this high point isn’t high enough for it to be directly overhead. Over the course of a year, any point in the tropics will have the Sun pass overhead twice every year on either side of the Summer Solstice.
The most immediately cool thing about Lahaina Noon is that shadows are cast straight down. Hence some things have minimal shadows while others have none. It’s quite strange to be in bright sunlight and seeing a signpost casting no shadow. Does that make it a vampire signpost or something? Anyway I went to Ala Moana Park today and took some pictures of things with no or minimal shadows,
It should be noted that the name Lanhaina Noon was chosen as part of a contest run by The Bishop Museum who have a very nice planetarium. Lahaina means “cruel Sun” and also a a town on Maui. Lahaina Noon in Lahaina is on the 18th of July at 12:32, a more comprehensive list of Lahaina Noon times for the islands is here.
Today, at 15:26 GMT, the space shuttle Atlantis is scheduled to make its last ever flight and bring the shuttle program to an end. At the moment though, it’s likely that bad weather is going to postpone the launch until later in the weekend. When it does go ahead I’ll be watching live, and waving it off, via NASA TV: http://www.nasa.gov/multimedia/nasatv/ustream.html.
We don’t have the same history of manned space flight in the UK (despite this some of us still made it into space), but there’s still a lot of love for the shuttle here. Top Gear even had a go at building their own. It nearly worked too…:
As this is the last mission there’s a lot of sadness in the air. I don’t know whether each launch still feels so special because they never, as was the original aim, became routine. There have been shuttles around for my whole life and it’s going to be strange not to hear them talked about anymore. When you’re a kid interested in space, adults always assume you want to be an astronaut, and that always used to feel possible. It feels a little less so today.