Astronomers have discovered a mysterious stream of old stars at the far edges of the galaxy: a strange stellar breed that, unlike anything we’ve seen before, may very well become the last of its kind.
This unusual collection of stars – called the “Phoenix Stream”, after the constellation Phoenix in which they are visible – is what is called the Stellar Stream: an elongated chain of stars that used to be in a spherical form, known as a globular cluster.
Such clusters can be torn apart by the gravitational forces of the galaxy. In such a case, their globular form deforms and stretches into a haunting caravan of stars, the fate of the distant orbit of the distant orbit of the galactic nucleus.
Above: The artistic impression of a stellar stream around the Milky Way.
Neither stellar currents nor spherical clusters are new to science, but there is something about the Phoenix current. Its chemistry is different from any globular clusters we have ever seen, almost as if they do not belong here.
“We can trace the line of stars by measuring the different types of chemical elements we detect in them, just as we can use DNA to trace a person’s connection to their ancestors,” explains astronomer Kyler Kuehn of the Lowell Observatory in Arizona.
“It’s almost like finding someone with DNA that doesn’t match any other person, living or dead.”
In the Milky Way there are about 150 known spherical clusters, all of which exist in the so-called A galactic halo – a fine spherical structure that surrounds a relatively flat galactic disk where most of the galaxy ‘s stars otherwise gather.
However, in the fringes of holiness, many stars are still collected in spherical clusters. Each cluster can contain hundreds of thousands of stars, and observations of the clusters in the Milky Way have shown that all clusters show some consistency in their stellar chemistry: the stars in the clusters are enriched with “heavier” chemical elements that are more powerful than hydrogen and helium.
After the Big Bang, the theory concludes that all the gas in the universe was formed by either hydrogen or helium, which in turn formed the first stars of the universe. Other elements, such as oxygen, carbon, and magnesium, were only possible much later through the fusion mechanisms of subsequent generations of stars.
The chemical heritage of these later fusion mechanisms is all around us, as some globular customers in our galaxy have seen some of the heavier elements. That means until now.
This chemical threshold – called the bottom of metallicity – is not observed by the Phoenix current, which has less heavy elements in its stars than we thought was theoretically possible for such a celestial structure.
“This current comes from a cluster that we don’t think should exist,” explains astronomer Daniel Zucker of Macquarie University in Australia.
Or it should not exist now, this may be another way to put it.
Observations of the Phoenix flow by an international team of scientists as part of the Southern Stellar Stream Spectroscope Survey showed that “its metallic abundance is well below the empirical level of metallicity,” the authors explain in their new study.
Until now, the metallic park has been a useful way of classifying the scientific constant that has been observed in all current spherical clusters. It’s still the way it is – but the Phoenix stream is not the current ball cluster.
He thinks he may be the only survivor: a celestial relic of a bygone age in the early universe, when the stars gave off light in different ways.
“One possible explanation is that the Phoenix Stream is the last of its kind, the rest of the spherical cluster population, born in a radically different environment than the one we see today,” said astronomer Ting Li of the Carnegie Observatory in Pasadena.
Of course, many questions remain. If the Phoenix stream is the remnant of remnants from the early universe, is it the only one? Are there others hidden in the vastness of the galactic halo?
“When we find a new kind of object in astronomy, it indicates that there are more,” says astronomer Jeffrey Simpson of the University of New South Wales (UNSW) in Australia.
If there are still old passengers on the way, we don’t have to find them forever. Like spherical clusters, stellar currents are not immortal. Once they reach the star, it is only a matter of time before they disintegrate and scatter across the galaxy.
“Who knows how many remnants, such as the Phoenix Stream, can be hidden in the Hall of the Milky Way?” Wonders German astronomer JM Diederik Kruijssen of the University of Heidelberg, who did not take part in the study but wrote a comment.
“Now that he’s found first, he’s a hunter.”
The findings are set out in nature.