Getting Observing Time

If you followed the many interesting discoveries made by us all as part of the Galaxy Zoo team on the forum and the blog, you’ll have noticed that one of the most important things in astrophysics research is getting data. Unlike most other scientists, astrophysicists can’t just take a tiny galaxy into the lab and watch it evolve, perhaps feeding its (now tiny) supermassive black hole to see what happens. All we can do is observe the universe around us, and to do that, we need telescopes.

Observations are a bit like experiments. They are often designed to answer a very specific question. To take an example from Galaxy Zoo: when we first spotted the Voorwerp, and convinced ourselves that it’s real, rather than an artifact on the camera, we had to find out how far away it is by measuring its redshift and perhaps learn something about what it’s made of. To do this, we needed a spectrum, so we went about looking to obtain one. Normally, to get “time” on a telescope takes a lot of effort and waiting; in this case, we managed to convince some colleagues that the Voorwerp was exciting enough for them to forego some of their allocated time to take a peek at it.

So how do you normally get observing time? I’ll take the example of the XMM-Newton time we just got. Depending on the facility, the administrators will issue a “call for proposals” in certain intervals asking for proposals for observations. For most ground-based facilities, this will be twice a year. For many space missions, since they are harder to schedule, this may be only once a year, or even rarer. This “call” outlines the instruments of the facility, what kinds of proposals for time they will accept (lots of large proposals, no large proposals, etc.) and any technical issues proposers should be aware of.

We wanted to learn more about what physics the Voorwerp can teach us and one of the biggest questions about it is whether the supermassive black hole in IC 2497 (the spiral galaxy next to it) has really shut down, or if it is still a quasar and feeding. All indications so far are pointing towards a shutdown, but perhaps the quasar is really hidden by plenty of material in the way. So, we would like to use the X-ray vision of XMM-Newton, a 3.8 ton, bus-sized X-ray space telescope operated by the European Space Agency to take a look and see if any X-rays still get to us. Even if the quasar was highly obscured, some of the X-rays might still get through. It’s a bit like going to the doctor’s – we need an X-ray to diagnose what’s going on.

We thus sat down and wrote a proposal. The call for proposals outlines quite strictly how many pages, figures etc. you can use and what kind of information on the proposed observations they want. A proposal for observations generally consists of two parts: 1) a science justification and 2) a technical justification.

The science justification is an explanation of what you want to observe and what kind of physics you will learn from the observations. In our case, we described the discovery of the Voorwerp, how much excitement it generated with you all, and what we know about it so far. We then outlined precisely what we will learn with XMM-Newton data.

The technical justification following the science case is an explanation of why your proposed observations are really feasible. Will you really gather enough data to answer your question? Will the observations damage the telescope? Are there any other constraints? Are you (gasp!) asking for more time than you really need? All these are important. Even if you have the greatest science case, if you can’t make a convincing argument that your observations will work, you still won’t get time.

Preparing such a proposal is a lot of work. After submission (hopefully before the deadline!), the facility sends out the proposals to an anonymous panel for review (a bit like for scientific papers). This panel reads the proposals and meets somewhere for discussion. They assign each proposal a grade and so rank them. The telescope planners then approve proposals from the top until they’ve filled the available time. The remaining proposals are then rejected. This is actually the fate of most proposals. Popular facilities like XMM-Newton, Hubble or the VLTs are highly “oversubscribed”, regularly receiving five or even ten times more requests for observing time than they can give.

Astrophysicists thus spend a lot of time writing proposals in the knowledge that they’re unlikely to be accepted. Getting time is very precious and of course, every observation is an opportunity for discovery. As you can see from this description, it also takes a long time between applying for time, getting the time, and the actual observations. It’s fairly common to wait for your data for a year.

Luckily, so far Galaxy Zoo has been very successful with getting observing time….