A dean of the universe galaxy identified - BBC

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oldest known galaxy in the universe at least 13 billion years. To put it another way, if the history of the universe was represented on a meter, it would be at the fifth centimeter. The venerable z8_GND_5296 is his first name, has won the title of Dean after a study conducted by American astronomers detected several candidates in recent years by the Hubble Space Telescope. She is the only one to have passed the “spectroscopic test” of the infrared camera Mosfire the Keck telescope in Hawaii. An approach that was used to validate age, explained Steven Finkelstein and colleagues in an article in the journal Nature.

What was the test? To understand this, it is necessary to return for a moment on the notion of age in astronomy. When talking about an “old 13 billion years” galaxy, we’re not talking about a dying or shriveled galaxy but a star cluster whose light took 13 billion years to reach us. As this cluster is very far from us, we do know that this lad state, a photograph taken in this case, only 700 million years after the big bang. If this galaxy still exists today, it would be “at least 13 billion years.” In other words, the “oldest” astronomical objects are more distant.

immediate consequence determine the age of a galaxy astronomical returns to estimate its distance. However, a galaxy is far more, the more light that reaches us is redshifted. The “spectroscopic test” is to use a particular clearly identified light from a galaxy, the influence of hydrogen, for example, and measure its redshift. Of the 43 galaxies studied by researchers, only z8_GND_5296 issued this type of light.

“This does not mean that the other candidates are not as distant galaxies, but they are probably too dusty for this radiation has escaped,” said Pierre-Alain Duc, an astrophysicist at the CEA. This large amount of dust leaves suggest that elements heavier than helium and hydrogen were much more common than previously thought in the early Universe. The oldest itself seems immersed in a similar cloud of material.

“We are reaching the limits of current instruments”

other hand, our most distant cosmic ancestor is also distinguished by its high activity. “It forms a hundred times more stars than our Milky Way, says the researcher. This is the first time that this distant galaxy as such a rate of star formation. “However, the current cosmological models struggle to explain the presence of so many heavy elements and a large activity of galaxies.

However, the revision of the models will not happen immediately. It will take these results are confirmed by further steps and similar comments on other very distant galaxies. But the race these old galaxies becomes increasingly complicated. “We are reaching the limits of current instruments,” says François Hammer, an astronomer at the Paris Observatory. New instruments, including the future James Webb Space Telescope or E-ELT (European Extremely Large Telescope), are expected to continue this work in space archeology.

To date, only one more distant astronomical object that this galaxy has been identified as a surprise star exploding. The associated flash was issued only 625 million years after the birth of the universe. This star was probably part of a galaxy, but it has never been observed. And do not (yet) been able to reveal its secrets.