A long time ago in a galaxy far, far away….
My video hello (2.4Mb mpeg)
Hi, my name is Nino Panagia. I’m a theoretical astrophysicist at the Space Telescope Science Institute. I am interested in many things that the HST observes but find the deep field images particularly fascinating. As we look back in time, I think it’s amazing that galaxies just like ours have been around for such a long time.
Your task is to make an image using data from the HST and find the furthest and youngest galaxies.
The further an object is from us, the longer it takes for its light to reach us. It takes 500 seconds for the Sun’s light to reach us. So we see the Sun not as it is now, but how it was 500 seconds ago.
From knowing the speed
of light and that it takes 500 seconds for light to reach us from the Sun we can
work out how far away the Sun is.
Use your knowledge of distance, speed, time formula and the fact that the speed
of light is 300,000km per second (or 187,000miles per second) to work out the
distance to the Sun.
Light from the next nearest star, Proxima, takes over 4 years to reach us. So when we look at Proxima we are seeing it as it was over 4 years ago. It is as though we are seeing back in time. The further we look, the further we travel back in time.
But as we look at objects further and further away they get dimmer and dimmer and, for Earth-based telescopes, are eventually lost to us in the glow of the atmosphere. However this is not a problem for the HST. It can look further back in time than any other optical telescope. You are about to create an Ultra Deep Field image of a part of the Universe.
We first find a portion of the sky where we can look outside our galaxy without too many stars being in the way.
Here is one in the constellation called Fornax:
The galaxies will be very dim. You will need to make very long exposures – more than a million seconds in total.
There is
something else you need to know. Because the Universe is expanding, the
further a galaxy is away, the more stretched out the light gets – shifting it
to the red end of the spectrum. Would you like some more
to understand redshift?
You will need to take most of the exposures in the red end of the visible spectrum and some of it in the near infra red. You will also capture closer galaxies and a few stars in our own galaxy. To show these clearly, make an exposure in blue light as well.
The HST takes 96 minutes to orbit the Earth. Take a 56 orbit exposure in blue light, a total of 206 orbits in red (56 orbits in red light and150 in a broad band red/ infrared) and 150 orbits in near infrared.
Don’t worry, the pictures will take a while to download but not that long.
How long, in minutes, did the exposures take to make in total?
Save each image in your work file and then import them into Registax. Adjust the result until you see the greatest amount of detail.
The data for your image was obtained using the HST by a team of scientists: S. Beckwith, S. Malhotra, M. Giavalisco, J. Rhoads, M. Stiavelli, R. Somerville, S. Casertano, B. Margon, C. Blades, J. Caldwell, and M. Clampin (STScI), M. Corbin (CSC), M. Dickinson, H. Ferguson, and A. Fruchter (STScI), R. Hook (STScI/ECF), S. Jogee, A. Koekemoer, R. Lucas (STScI), M. Sosey, L. Bergeron and me!
ANALYSING YOUR RESULTS
Print out an inverted copy of the image to analyse your results
Try to spot the stars that are in our galaxy. The brightest ones will have four ‘diffraction spikes’ caused by the support struts of HST’s secondary mirror. Close galaxies will have a blue tinge to them. These galaxies are over 13 billion year old. Some galaxies are reddened by dust (a bit like a red sunset) rather than being far away. The youngest galaxies will tend to be oval or irregularly shaped – they haven’t had time to collide and start spinning like the older spiral galaxies. But being so far away they will appear very small unless they are very large. So you may not be able to make out their shape.
Astronomers have access to other readings to help them work out the red shifts. You can try to spot the extreme red shifted galaxies by flicking between the blue and infrared images.
Download
a PowerPoint viewer for flicking between the images here
Galaxies that are invisible on the blue but bright in IR are good candidates for newborn galaxies. If you can find one that is visible in the IR but invisible in the red wavelengths (encoded green here) then you may have hit the jackpot. On the other hand you may have found just a nearby (relatively) warm patch of hydrogen gas – nobody said discovery was easy!
Download a
PowerPoint Slide to see the result in colour
We are not absolutely sure of our results yet – so don’t be disappointed if yours is not the same as ours. There’s still a lot we don’t know. New space telescopes like the James Webb (scheduled for launch in 2015) will almost make this task too easy. Until then, we have more data to analyse using our NICMOS infrared camera.