Two months after the launch in April 1990 of the Hubble Space Telescope (HST), it was found that its primary mirror was not correctly made. The error was of the order of 0.002 mm at the outer edge of the mirror. As a result, the telescope could only take blurred images of faint objects in space. Despite its spherical aberration, its location above the Earth’s atmosphere allowed observations in the ultraviolet wavebands unavailable from the ground-based telescopes. The telescope measured the age and origins of the Universe, observed distant supernovae, and identified celestial bodies in and outside the solar system. It was able to look back one billion years after the Big Bang.
The faint object camera of the European Space Agency (ESA) on the telescope carried out several scientific observations. First, it took a closer look at Supernova-1987A which exploded in February 1987. Second, Hubble provided the most detailed image of a gravitational lens which bends the light from a quasar, eight billion years away.
A shuttle repair mission was successfully undertaken in December 1993 to restore the telescope’s capability and fix a few other problems. The repaired telescope, orbiting 575 km above Earth, was able to see ten times farther than any telescope on Earth. It could spot a coin 1,200 km away! It could register objects 20,000 times fainter than those seen by the naked eye. Stars that are blurred together can be seen separately.
Astronomers can find the clues to the formation and evolution of galaxies by studying the composition, temperature and other features of stars and gas in galaxies. The distance between two galaxies that can be measured accurately has increased 50 million light years as against 10 million light years possible at present.
The repaired Hubble has found indirect signs of the existence of black holes. In NGC 5728 in the Libra constellation, HST has captured on of the most spectacular images that exactly answers the theoretical description of a black hole environment: a disc of hot gas spiraling around the nucleus of a galaxy.
The telescope has provided an excellent image of the nuclear region of another galaxy (NGC 1068) found at 60 million light years. This is considered to be the prototype of a Seyfert Type-2 galaxy. The core shines with a brilliance of a billion suns and yet the glow fluctuates over a few days, implying that the source is only a few light years across. It is likely to have a super black hole!
Hubble has unveiled cosmic sciences of violence Galaxies collide and merge, frequently leading to star formation. Such a scene is happening now in the super giant, NGC 1275, in the Perseus cluster. The telescope has revealed the structure of individual galaxies as they were four billion years ago. It has observed very distant sources from where light took over ten billion years to reach us. A thousand-fold increase in detail is a major advance in observation.
HST has already given new images of Supernova-1994 discovered on 2 April 1994 in the inner regions of the MSI whirlpool galaxy, 20 million light years away in the Canes Venatici constellation. In addition, HST has photographed a mysterious pair of rings of glowing gas around supernova 1987A.
A fundamental reason for observing cosmic phenomena through Hubble is to measure the ‘yardstick’ of the Universe, Viz. the Hubble constant. Edwin Hubble had pointed out that galaxies appear to be receding at speeds in direct proportion to their distance from the observer. However, the real distance between galaxies is not very well known today. By accurately measuring the distance between galaxies, HST will tell astronomers how old the Universe is.
Another repair mission, due in 2008, was delayed by a serous flaw on board the telescope. In 2009, a collision of two satellites created debris in space, posing a risk to repair missions.