Back when I wrote Measuring the Universe, the most distant object then known had a measured redshift, z, of 5.64. That particular distance record was broken while the book was still in press, and since then numerous objects – primarily galaxies, but also quasars and gamma-ray bursts – have been detected at z > 5.64.
Today, the record holder for “most distant object” changed hands once again. Astsronomers using NASA’s Hubble Space Telescope measured the redshift of the galaxy GN-z11 to be 11.09. This is a HUGE redshift. It corresponds to an age of about 13.4 billion years. In other words, we are seeing the object as it was just 400 million years after the Big Bang!
As galaxies go, GN-z11 is quite small: about 25 times smaller than our own Galaxy and with only 1% of our Galaxy’s mass in stars. Nevertheless, it is surprising that a galaxy as large as this could form so soon after the Big Bang. Presumably we will learn more about the conditions that gave rise to these early galaxies as astronomers push the distance record back to z = 12 and beyond. Exciting times!
The inset in this field of galaxies shows GN-z11, the farthest galaxy ever seen (to date). We see the galaxy as it appeared 13.4 billion years in the past. The expansion of the universe has shifted the light from the GN-z11’s young, blue stars to the red.
(Credit: NASA, ESA, P. Oesch, G. Brammer, P. van Dokkum, and G. Illingworth)
Well that didn’t last long. Last week I blogged about the discovery of a new most distant galaxy, and explained how in the years since the publication of Measuring the Universe the redshift of the most distant known object had been pushed back from 5.64 to about 11. A few days later and astronomers announce that the new record holder is at a redshift of 11.9!
The new result comes from UDF12, the Ultra Deep Field 2012, a survey program that points Hubble at a tiny patch of sky (just one-tenth the diameter of the full Moon) in the constellation Fornax. The aim is to take the deepest ever image of the heavens. Astronomers on UDF12 use Hubble’s Wide Field Camera 3 to take infrared pictures with huge exposure times. Very gradually, they build up images of incredibly distant objects. And one of the objects they imaged, UDFj-39546284, has a redshift zof about 11.9: the light that Hubble detects now set off from the galaxy when the Universe was just 380 million years old.
The Hubble Ultra Deep Field, with the redshifts and positions of seven galaxies indicated. The UDF12 program suggests that one of these galaxies has a redshift of 11.9 – the most distant object yet seen.
(Credit: NASA/ESA/R. Ellis/Hubble UDF12 project)
Perhaps the most interesting aspect of this work is that the stars already contain heavy elements, which must have originated in the nuclear reactions taking place in an earlier generation of stars. Even at these redshifts we still haven’t seen the first generation of stars.