Echoes of far away light

All About Space - - Launch Pad -

A unique shot taken by the Eu­ro­pean South­ern Ob­ser­va­tory’s VLT Sur­vey Te­le­scope (VST) un­cov­ers two gal­ax­ies right at the be­gin­ning of the merg­ing process. The smash up be­tween the duo has cre­ated a rare ef­fect known as a light echo, where light bounces off the ma­te­rial within each galaxy. The ef­fect is anal­o­gous to the acous­tic echo where re­flected sound ar­rives at the lis­tener with a de­lay af­ter the sound is emit­ted.

The larger galaxy of the two is seen here in yel­low and is known as ShaSS 073. It’s an ac­tive galaxy with an ex­tremely lu­mi­nous, highly en­er­getic core. Mean­while, its less mas­sive com­pan­ion, named ShaSS 622, glows in blue and com­pletes the in­trigu­ing ShaSS 622-073 sys­tem. The pair­ing’s ra­di­a­tion causes a bright glow as it ab­sorbs and then re-emits light, ex­tend­ing across 1.8 bil­lion square light years.

While study­ing the merger, as­tronomers dis­cov­ered that the lu­mi­nos­ity of the large cen­tral galaxy is 20-times lower than required to ex­cite the gas in this way – an in­di­ca­tion that the cen­tre of ShaSS 073 has faded dra­mat­i­cally over the last 30,000 years or so.

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