Question 1: What kinds of problems do you come across while working? Please name just one.
I study things which are very distant in the universe. Some of them
are galaxies, which we can see as blobs of light which are really huge
collections of stars -- about 100,000,000,000 of them at a time. Some of
them are dark shadows which we see in front of further, brighter objects
called quasars (sometimes abbreviated as QSOs = quasi-stellar objects).
The shadows actually only occur at certain wavelengths (colors) because
the atoms in the clouds of gas which produce the shadows only absorb light
at those wavelengths. Since the universe is expanding, things which are
further away move faster away from us (like dots painted on a balloon which
is being inflated), which causes the wavelengths of light being absorbed
to become red. The further away something is, the redder the absorbed light.
If we see several shadow clouds of gas toward a distant quasar, then we'll
see wavelengths without light which correspond to each one of the shadows,
with the furthest shadow producing the reddest wavelengths without light.
Take a look at the graphic on this BBC
article for a picture. I'll be happy to explain it to you over
the phone, too. The question I have is: what is the relationship between
galaxies (which are bright) and these shadow-clouds? We call these shadow
clouds "quasar absorption systems".
Question 2: How do you solve those problems? (What is your hypothesis about what will solve the problem?)
Astronomers can take two approaches to figuring out what the relationship between galaxies and quasar absorption systems is. One is, "point the telescope and see". That worked just fine when it was easy to get time on a big telescope. "Big" is a relative term! Galileo made lots of discoveries that way on his early telescopes. One was 26mm (about 1 inch) in diameter, which is not impressive today, but when he was the only person using it to study the sky, he revolutionized astronomy! Unfortunately, big telescopes are scarce, and there are lots of astronomers who want to use each one. So, nowadays we have to think very carefully what we want to do, and convince a committee of fellow astronomers why OUR observing proposal should get time on a telescope, and not the proposal of somebody else! For every night on a ground-based telescope, there might be three or four astronomers who want to use it. For space-based telescopes, which are very few indeed, there might be between six or ten! To write a good proposal, we have to have a theory which can be tested. We should get an answer whether we see something or not. Sometimes the most important experiments have what is called a "null" result, meaning we looked but didn't find anything. We usually have to phrase our hypothesis that way, "Either we see X and so it supports our theory, or we don't see X and it doesn't support our theory." We have to be sure to look carefully enough so that if X is there, that we actually should be able to see it.
So, for my particular case, I want to know: when I look at a quasar and see some absorption systems (shadows), are the galaxies and absorption systems connected? If so, how? Specifically, we can ask:
1) How many galaxies are in the same field in the sky?
2) How far away are they from the quasar (what are their positions on the sky)?
3) Are they at the same distance from Earth as one of the quasar absorption systems?
4) How bright are the galaxies?
5) How likely is it that galaxies are there just by chance? -- This is the key which will show the likelihood that they are connected.
Question 3: When you experiment, what exactly do you do?
I first write a proposal to use a telescope, as I explained above. If I'm lucky enough to get the telescope time (which I do about 25-50% of the time) then:
1) I observe the quasar to look for absorption systems. This involves spreading the light from the quasar out so that I can see its wavelengths (colors) in great detail. Then I look for dark spots (absorption lines), and measure where they are to estimate their distance from Earth. I also measure how big they are, because not all absorption systems are the same. Some have lots of gas in them, some (actually most) have only a little, some (most) have only hydrogen in them and a few have other elements like carbon, magnesium, oxygen etc. I use an instrument called a spectrograph to spread out the light gathered by the telescope's mirror. Then I use a computer to digitally add a number of pictures made by the spectrograph, to bring out fine detail and to make all sorts of small corrections like effects from Earth's atmosphere, effects from Earth's motion around the Sun etc.
2) I look for galaxies in a field around the quasar. This involves hooking up a digital camera to the telescope and taking long-exposure pictures. I use a computer to digitally add them, too, plus make small corrections to bring out fine detail. The field I look at is about 10 or 20 arcminutes across, or about 1/3 to 2/3 of the diameter of the full Moon.
3) I then use a spectrograph to look at each of the galaxies found in step 2. By spreading out the light from a galaxy and looking at how its brightness varies with wavelength, I can estimate how far away it is. This is computer-intensive work, too.
Question 4: When you're done with the experiment, what happens?
Once I have my observations, I use a computer to calculate how far apart the galaxies are from the quasar absorption systems, because I know how far apart the absorption systems and galaxies are from Earth, and their positions on the sky, too. I then use a random number generator to simulate how many quasar absorbers and galaxies should occur there by chance. (I use statistics gathered by other astronomers, or take my own data and shuffle around galaxy positions and quasar absorption system distances.) Once I have my results, then I write them up in an article (sometimes called a paper), like a big, fancy lab report with lots of detail and graphics, and send them to a magazine read by my fellow astronomers (called a journal). You can see some of my papers on my website. The editor of the journal picks some other astronomer -- whose name remains anonymous to me -- and sends my article to be refereed (judged). If the other astronomer is happy with it, great! If the other astronomer wants some small changes for clarification or disagrees with some minor point, then I get a report and either make the changes or try to convince the referee that I'm right. In the end, the referee and I usually come to agreement. But, sometimes the referee says that there is nothing new learned from the article, and rejects it. I can appeal for a new referee, but if a second referee says the same thing, then I've wasted my time. It can take months or even a few years to get an article done, so I'd better be sure to get it done right. At the end of every year, I have to write a report to my department to say how many articles I've published in journals. (There are several journals that we astronomers use.) People keep or lose their jobs depending on how many articles they've published, so it's really important to do good research and get articles approved by referees!
Question 5: Was your hypothesis right or wrong?
Most of the time I'm right, but occasionally I (like any other scientist) can be wrong. If we're very wrong and published an article with incorrect results, we have to print a retraction in the same journal which published our article. That's very embarrassing, and we're not so likely to get time on a telescope next time if it happens too much. But, it happens a little to everyone. It just pays to check our work very, very carefully before we send it to a journal! As for the galaxy-absorption system connection, yes, they're very much connected together, and the close ones (which I have been specializing in lately) are connected together even more so than the distant ones.