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CR7, the distant brighter galaxy


The galaxy displays evidence of the presence, in its interior, of examples of first-generation stars. These massive objects, bright and so far purely theoretical, have produced the first heavy elements of the story.
Using the VLT (Very Large Telescope) ESO, a group of astronomers led by David Sobral, the Institute of Astrophysics and Space Sciences, the Faculty of Sciences of the University of Lisbon in Portugal, and the Leiden Observatory in the Netherlands, He discovered the brightest galaxy ever found in the Universe primeval also finding evidence of the presence of first-generation stars. These massive objects and bright, so far only been predicted by theory, they produced the first heavy elements of the story – the elements necessary to shape the stars today around us, planets and life as we know it. The new galaxy, called CR7, is three times brighter than the brightest distant galaxy known so far.

Artist’s impression of CR7: the brightest galaxy in the early

Credit: ESO

Astronomers have long theorized the existence of a first generation of stars – known as Population III stars – born from the primordial matter of the Big Bang. The name Population III was born because astronomers had already classified the stars of the Milky Way as Population I (Sun-like stars, rich in heavy elements and distributed on disc) and Population II (older stars, with a lower content of heavy elements and present in the halo, in the central bulge and in globular clusters). All heavier chemical elements – oxygen, nitrogen, carbon and iron, essential for life – were produced inside stars. This means that the first stars must have formed the unique elements that already existed: hydrogen, helium and traces of lithium. These Population III stars were huge – several hundreds or thousands of times more massive than the Sun – and transient burning – having to explode as supernovae after only two million years. But so far the search for physical evidence of their existence has been inconclusive. It is hard to find these stars because they should have a very short life, and to have been light at a time when the Universe was opaque.
Experts have peeked in the ancient Universe, to a period known as re-ionization, roughly 800 million years after the Big Bang. Instead of carrying out a study small but deep, in a small area of the sky, they have expanded the view to produce the most extensive survey of distant galaxies cha never been attempted. Their study was made possible thanks to expanded collaboration with VLT Observatory WM Keck Telescope and Subaru as well as the Hubble Space Telescope of the NASA / ESA. The team found – and confirmed – a number of very young galaxies and surprisingly bright.
One of these, indicated as CR7, it was an object exceptionally rare, the galaxy far more brilliant ever observed in this phase of the Universe. With the discovery of CR7 and other bright galaxies, the study could already be considered a success, but further investigations have provided news stimulants. The nickname is de CR7 COSMOS Redshift 7, a measure of its position in terms of cosmic time. The larger the redshift, the more distant the galaxy and we see further back in the history of the Universe. A1689-ZD1, one of the oldest galaxies ever observed, has a redshift of 7.5. CR7 is in the COSMOS field, a small patch of sky in the constellation Sextant studied very intensively. The nickname was also inspired by the great Portuguese footballer, Cristiano Ronaldo, also known as CR7. The galaxy is three times brighter than the previous record, Himiko, who was thought to be a one of a kind in this era so remote. Galaxies with dust, in the later stages of history of the Universe can radiate more total energy than CR7, in the form of infrared radiation from warm dust. The energy of CR7 is mainly in the visible and ultraviolet light.
The X-shooter and SINFONI on the VLT found in CR7 strong emission of ionized helium but – surprisingly – no sign of heavy elements in a galaxy of brilliant. This means that the team discovered the first significant evidence of the presence of groups Population III stars which have the ionized gas within a galaxy in the Universe primal. The team considered two alternative theories: that the light source was an AGN or star Wolf-Rayet. The lack of heavy elements and other evidence refute these theories. The team also considered that the source could be a black hole produced by direct collapse, exotic objects and still purely theoretical. The lack of an emission line large and the fact that the brightness of helium and hydrogen were much greater than had been expected for a black hole also indicate that this hypothesis is unlikely. The lack of X-ray emission would be further evidence against this hypothesis, but further observations.
“The discovery has challenged the very beginning of our expectations,” said Sobral, “because we did not expect to find a galaxy so bright. Next, finding a piece at a time the nature of CR7, we realized that not only had found the distant galaxy brighter, but we also started to realize that she had all the necessary requirements for the Population III stars. These stars are those that have formed the first heavy elements that eventually enabled us to be here. It could not be more exciting than that. ”
Within CR7 we were found clusters of stars bluer and a bit ‘more red, indicating that the formation of Population III stars has occurred in waves, as expected. What the team has observed directly was the last wave of Population III stars, as if to say that these stars should be easier to find than previously thought: they are among the normal stars, the brightest galaxies, not only in the early galaxies smaller and weaker, so faint as to be really difficult to study.
Jorryt Matthee, second author of the article, he concluded: “I always wondered where we come from. Since childhood I wanted to know where the elements came from: calcium in my bones, the carbon in my muscles and the iron in my blood. I discovered that these were formed at the beginning of the Universe, from the first generation of stars. With this discovery, we’re really starting to see these objects for the first time. “Further observations with the VLT, ALMA and the Hubble Space Telescope of the NASA / ESA are expected to confirm that Population III stars were really observed and to try to identify more examples.

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