## Tuesday, 19 July 2011

### The Hubble Space Telescope and Beyond

In 1990 the space shuttle Discovery carried the Hubble Space Telescope (HST) into orbit and 21-years later (after many upgrades and rescue missions by Shuttle crews), it is set to provide us with awe-inspiring images and valuable data until at least 2014. Only time will tell what Hubble’s successor, the James Webb Space Telescope (JWST) due to launch in 2018, will reveal about the mysteries of the cosmos.

Hubble Space Telescope in Orbit

The HST has certainly played a major role in the world of astronomy and physics, with achievements in many different areas of these subjects. Successful missions include researching black holes at the centre of galaxies, observing the formation of planets around new stars, estimating the age of the Universe, detecting the first organic molecule in the atmosphere of a Jupiter-sized exo-planet and providing evidence for the existence of dark energy. I thought I would write a little more about the age of the Universe since this is an area of particular interest to me.

In the early 20th century, Edwin Hubble discovered the expansion of the Universe and also a relationship between the distance d of an object and the velocity v in which it is receding; v=H0d, where H0 is the Hubble Constant. A value for this Hubble Constant can therefore be determined by accurately measuring the velocity and distance of an object such as a galaxy; the Hubble Constant is simply related to the age (Age=1/H0).

The recessional velocity could be accurately measured using the red-shift of the light that it emits (the Doppler Effect on a cosmological scale), however the distance proved a little trickier to find. Certain stars, called Cephieds, pulsate and this pulsation is related to the absolute magnitude of the star which can be used to find the distance. The inaccuracy occurred due to ground-based telescopes not being able to “see” faint enough. Using the ground-based telescopes the age of the Universe was estimated at 7-20 billion years old. There is a lot of uncertainty in these results!

With the launch of HST, the Cepheids could now be observed much more accurately, free from atmospheric effects and light pollution. With this data the Hubble Constant was found to be 71 km s-1 Mpc-1 with a 10% uncertainty1, which corresponds to an age of 9 to 14 billion years, which is much more accurate than previous results. With the use of other experiments this was pin-pointed to 13.7 billion years1.

The HST has also played another important role, and that is in bringing the world of science to the general public, and seeing images from the HST is partly what first sparked my interest in science. I saw beautiful images of galaxies and nebulae and formations of interstellar gas and dust, such as the Pillars of Creation, and I immediately wanted to know what they were, where they came from and how they fit into the grander scale of the Universe.

Pillars of Creation- Image by HST

With the construction of the James Webb Space Telescope, things can only get better. The JWST will see further into the infra-red and hence will see further than Hubble (light from further objects is more red-shifted). The JWST also boasts a larger mirror, allowing it to collect more light and peer ever deeper into space. One disadvantage that I can see to JWST is that its orbit will be much further away from the Earth, it is in fact not going to orbit the earth at all, but the Sun! It orbits the Sun at the same rate as the Earth and so is stationary relative to us on Earth. Due to the immense distance astronauts will not be able repair or modify the JWST, as was possible with Hubble. The future however looks bright.

The orbits of HST and JWST