27Sep2012

Quasars As A Tool to View the Distant Universe.

Although it is not as easy to map space as it was to map our land masses and oceans here on Earth, we might be a step closer to making this possible.

A collaborative team of researchers from Case Western Reserve University and a further two institutions have found a method, using the light from quasars, that will potentially allow the spread and structure of the universe to be mapped. This method combined with the likely discovery of millions of distant quasars over the next ten years could allow scientists to look back to the universe at a time soon after the Big Bang.

The discovery was made during analysis of the visible light from a small number of quasars – 14 that were recorded by the Massive Compact Halo Objects project, which looked for evidence of the existence of dark matter around the Milky Way – which was measured again and again over a period of hundreds of days. The pattern in variation of light over a period of time – the amount of light would either increase or decrease in a linear manner when graphed – was virtually unchanged from one quasar to the next when the quasar’s redshift was corrected for.

Haydn Hall on the campus of Case Western Reser...

Haydn Hall on the campus of Case Western Reserve University in Cleveland. (Photo: Wikipedia)

Redshift happens as the expanding universe means that the quasars are carried away from us, so their light appears redder and also makes the variation in time seem as if it is slower. Flip this around and by charting the rate at which light from the quasar seems to vary and comparing this to the typical rate at which the quasars sampled did vary, this allowed the researchers to determine the redshift of the quasar.

With the knowledge of the quasar redshift, the researchers were able to work out the size of the universe when the light was emitted compared to its size today.

The information from measuring the redshift of millions of quasars would allow structures in the universe to be mapped out to a large redshift. It is known that the bigger a redshift, the further away and older the light source. The next step is for the researchers to search for larger samples of quasars to check consistency in patterns and that they can be used to determine redshifts across the entire universe.

Previously astronomers have used the bright light emitted by supernovae with redshifts of up to around 1.7 to chart the universe and its accelerating expansion. A star whose redshift was measured as 1.7 would have been giving off its light at a time when the universe was 2.7 times smaller than it is at present. Quasars are much older and a larger distance away.

These quasars have been measured as having redshifts as high as 7.1, which means the light that they gave off, that we see, was when the universe was only an eighth of the size that it is at present.

If this way of calculating quasar redshifts is shown to be applicable to quasars with a higher redshift, this would provide scientists and technicians with millions of markers that would allow them to map how structures grew and evolved, and how the universe expanded out to large distances as it did. Knowing this information could help explain how gravity has assembled the structure of the universe. A knowledge of the rate at which structures grew could also allow it to be determined whether the universe’s accelerated expansion was influenced by dark energy or any adjustment to the laws of gravity.

Supplied by: Jenny Hart for Astro Space News

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