26 April

1994: On 26 April 1994, an image from the NASA/ESA Hubble Space Telescope (HST) revealed the faint host galaxy of a quasar. The wealth of new detail in the image helped solve a three-decade old mystery about the true nature of quasars, the most distant and energetic objects in the Universe.

The HST image shows clearly that the quasar, called 1229+204, lies in the core of a galaxy that has a common shape consisting of two spiral arms of stars connected by a bar-like feature. The host galaxy is in a spectacular collision with a dwarf galaxy. The collision apparently fuels the quasar 'engine' at the galaxy centre - presumably a massive black hole - and also triggers many sites of new star-formation.

The image is one of a pair of relatively nearby quasars that were selected as early targets to test the resolution and dynamic range of HST's newly-installed Wide Field and Planetary Camera, which contains special optics to correct for a flaw in Hubble's primary mirror.

Quasars are the most distant objects in the universe, and so are among the earliest objects known to have formed in the young universe, more than 12 thousand million years ago. The most widely accepted notion is that quasars are in galaxies with active, supermassive black holes at their centres. However, because of their enormous distance, the `host' galaxies appear very small and faint, and are very hard to see against the much brighter quasar light at the centre. Though a quasar might no be much larger than our Solar System it releases as much energy as millions of stars.

1993: On 26 April 1993, Space Shuttle 'Columbia' was launched on the second German-sponsored Spacelab mission. It lasted until 6 May. Some 88 experiments covered materials and life sciences, technology applications, Earth observations, astronomy and atmospheric physics. Mission specialist Dr Bernard Harris set up the first intravenous line in space, injecting ESA astronaut and payload specialist Hans Schlegel with saline solution as part of a study to replace body fluids lost during adaptation to weightlessness.