New stars on the horizon

An exciting new discovery might lead to a confirmation of the presence of the farthest known galaxy

Published: Sunday 31 December 1995

The galaxy in question ONE of the curious facts of our universe to how it is that the deeper one in space, the more one travels in time. This is because light (or signals emitted from a distant in space take time to reach us; the signals we recieve must have ted a long time ago.

Thanks to this knowledge, it is now k- to trace back history by simply ey-ing further in space. Astronomer at the European Southern Obser 15 (ESO'S) New Technology Telescope at La Silla Observatory in Chile sighted the remotest galaxy known They have obtained images of a at a redshift of 4.4. A redshift is a of the spectrum created by the waves because of the expanding universe. The greater the distance to be the faster the object moves and, e the light waves shift towards red end of the spectrum. The entire menon could be compared to a !!@'s whistle which increases in pitch a dw train comes nearer (Science, Vol W September 29, 1995)

A redshift of about 4 indicates that MW palaxy emitted light when the universe was approximately a fifth of its age. The search for the galaxy Mimin 1993, when a very high red (4.7) quasar known as a QS0 1202-07 Mediscovered by the Anglo-Australian modkbimidt telescope. The spectrum of the 'Vemar had dark absorption lines indili@ the presence of an object between ;Wffi and the quasar. The astronomer calculated the redshift of the !Vwxmg object; the result turned out be a wonder because the absorbing cloud happened to be part of a galaxy.

absorbing lines were damped Dadened) because of the interactions 11obtween the incoming light and atoms of the matter comprising the galaxy. When the absorption lines were studied, it was noted that apart from containing the expected hydrogen lines, they also had absorption lines corresponding to higher elements like carbon, silicon, sulphur and aluminium. Such higher elements were not produced by the primordial reactions following the big bang; only lighter elements were produced by those reactions. Since these higher elements were produced only by stars, it was inferred that the absorbing object had stars and therefore, could be a galaxy.

To prove this conclusively, one had to analyse the light emitted from the galaxy itself. This was a challenging task because the galaxy was positioned opposite a very bright quasar. To image the galaxy, Sandro D'Odoricyo and his team used the 3.5 m New Technology Telescope. This telescope uses the latest technology of adaptive optics in which the shape of the main mirror changes continually to adjust to the distortions caused by the earth's atmosphere. The images obtained by the telescope are very sharp and distinct.

The team took 20 images of the galaxy and after processing these images, was able to eliminate the quasar's light. What emerged was the image of a spiral or irregular galaxy. Although the galaxy began emitting rays of light when the universe was barely a fifth of its present age, the presence of the heavier elements indicate that not only the process of star formation was already complete, but the stars had already lived their lives and exploded.

spewing out their contents into space. Even though the imaging of such a distant and faint object is a remarkable feat, much remains to be done before the object can be unambiguously identified as a galaxy. The real lynchpin would be the observation of the lines of hydrogen. The emission occurs when the ionised hydrogen regains an electron and emits light. The presence of a strong emission hydrogen line at a redshift of 4.4 will confirm the fact that the associated object is really a galaxy. If confirmed, the achievement shall have a profound impact on our attempts at understanding galactic evolution and dynamics.

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