A galaxy not so far, far away…

ASTRO 3D researchers from the University of Melbourne have discovered that an ultra-bright galaxy thought to have been 13 billion years old is actually much younger (and closer).

The Brightest of Reionising Galaxies (BoRG) survey team found used the Hubble Space Telescope to observe two galaxies (BoRG 0116+1425 747 and BoRG 0116+1425 630). They originally thought they were more than 13.2 billion years old when the Universe was about 5% of its current age.

The galaxies were identified using redshift – the change in colour observed from a given point as an astronomical object moves away. The further away something is, the redder its observed light becomes.

The redshift observed for these two galaxies indicated that the light had been emitted by them a very long time ago. In fact, BoRG 0116+1425 630 was estimated to be the oldest bright young galaxy ever detected.

Astrophysicists Rachael Livermore and Michele Trenti and their colleagues from the BoRG team tested these findings by using follow-up imaging and measurements using Hubble Space Telescope with a filter that helps discriminate between low- and high- photometric redshift solutions for these galaxies.

The colour composite image on the left is taken in near-infrared light and shows the location of the two candidate galaxies initially thought to be at a distance of more than 13.2 billion light-years from Earth. The close-up images on the right show a zoom-in of the two galaxies. The top row uses data from the initial discovery, while the bottom row shows the colours using additional, more precise observations. Based on data taken with the NASA/ESA Hubble Space Telescope. (Credit: R Livermore, M Trenti, and the BoRG team via U. Melbourne)

Their results confirmed that BoRG 0116+1425 747 as a highly probable distant bright galaxy. However, they discovered that BoRG 0116+1425 630 is likely to be an “interloper”, relatively nearby and much younger than previously thought.

Livermore, who led the research says “Now that we have a better measurement of the colours, it looks as though the brightest galaxy is actually relatively nearby – we see it only nine billion years back in time, whereas it was previously thought to be 13 billion.”

The researchers say this discovery has profound implications for models of how galaxies formed when the Universe was in its infancy and that ultra-bright galaxies in the early Universe may be less common than scientists initially thought.

You can read the paper at ArXiv, and it was published in the Astrophysical Journal Letters.