Astronomers have discovered a mysterious stream of ancient stars at the far ends of the galaxy: a strange stellar race so unlike any we’ve seen before, they may as well be the last of their kind.
This unusual collection of stars – called the ‘Phoenix stream’, after the constellation Phoenix in which they are visible – is what is known as a stellar stream: an elongated chain of stars that existed in shape. spherical, known as a globular cluster. .
Such clusters can be destroyed by the gravitational forces of a galaxy, in which case their globular shape heats up, spreading into a star system, aimed at orbiting away from a distant galactic core. .
Above: The artist’s impression of the stellar stream wrapping around the Milky Way.
Neither stellar streams nor globular clusters are new to science, but there is something about the Phoenix stream that is. Its chemistry is different from any globular group we have ever seen, it almost looks like it is not part of here.
“We can trace the lineage of stars by measuring the different types of chemical elements we detect, just as we can trace a person’s connection to their ancestors through their DNA,” explains astronomer Kyler. Kuehn from the Lowell Observatory in Arizona.
“It’s almost like finding someone with DNA that doesn’t match someone else, alive or dead.”
There are about 150 known globular clusters in the Milky Way, all of which exist in what is called the Galactic Halo – a tenuous spherical structure that achieves a relatively flat galactic disk, where most of the stars of galaxy otherwise clustered.
Outside our halo shores, there are still many stars mounted inside the globular clusters. Each cluster can contain hundreds of thousands of stars, and observations of clusters in the Milky Way have shown that all clusters show a certain consistency in their stellar chemistry: the stars in the clusters are enriched. with ‘heavier’ chemical elements that are more massive. from hydrogen and helium.
After the Big Bang, the theory holds that all the gas in the Universe was made of hydrogen or helium, which would then form the first stars of the Universe. Other elements, such as oxygen, carbon, and magnesium, became possible only later through the fusion mechanisms of subsequent generations of stars.
The chemical legacy of those later fusion mechanisms lies around us, as a certain proportion of heavier elements have been observed in all the globular customers of our galaxy. That is, so far.
This chemical limit – called the earth of metallicity – is not obeyed by the Phoenix flow, which shows less heavy elements in its stars than we thought was theoretically possible for such a celestial structure.
“This flow comes from a cluster that, to our knowledge, should not exist,” explains astronomer Daniel Zucker from Macquarie University in Australia.
Or at least, it shouldn’t exist now, it could be another way to put it.
Observations of the Phoenix River conducted by an international team of researchers as part of the Southern Stellar Stream Spectroscopic Survey Collaboration have shown that its “abundance of metal is substantially underground for empirical metallicity,” the authors explain in their new study.
Until now, the earth of metallicity has been a useful way to classify a scientific constant that appears in all globular groups present. Still, as it happens – but the Phoenix stream no globular cluster is present.
The team thinks it might be alive: a celestial relic of an age that passed away in the early Universe, when the stars made their light in different ways.
“One possible explanation is that the Phoenix spring represents the last of its kind, the remnant of a population of globular clusters born in radically different environments to those we see today,” says astronomer Ting Li from the Carnegie Observatory in Pasadena.
Many questions remain, of course. If the Phoenix flow is a remnant of a relic from the early Universe, is it the only one? Are there others, hidden in the size of the galactic halo?
“In astronomy, when we find a new type of object, it suggests that there are more of them,” says astronomer Jeffrey Simpson from the University of New South Wales (UNSW) in Australia.
If other old travelers are still on the right track, we won’t have forever to find them. Like globular clusters, stellar streams are not immortal things. Once they are stretched into a series of stars, it is only a matter of time before they dissolve, and spread across the galaxy.
“Who knows how many ruins like the Phoenix stream can be hidden in the Milk halo?” asks German astronomer JM Diederik Kruijssen from the University of Heidelberg, who was not involved in the study but wrote a comment on it.
“Now that the first one has been found, the hunt is still going on.”
The findings are reported in Nature.