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article imageScientists baffled by mysterious missing stars

By Stephen Morgan     Nov 25, 2014 in Science
Scientists are mystified because a huge group of stars aren't where they're supposed to be and they don't know where they've gone.
When exploring the Universe, scientists have a habit of finding things, but in this case they lost something, or rather, they didn't find something they expected to, which doesn't make sense according to previous theories.
A dilemma already faced scientists before the latest observations by the Hubble telescope. When scanning the stars, they saw that the star clusters in the Milky Way didn't have as many stars as they should. To explain this, they suggested that these stars had been ejected to other regions of our galaxy, but when they recently went looking for them they were nowhere to be seen.
The article on the mystery, which first appeared in Space.com, quotes Frank Grundahl of Aarhus University in Denmark, who co-authored a paper, on the subject. Grundahl said, "If these kicked-out stars were there, we would see them — but we don't!"
The results of his teams' findings now put in question whether the missing stars were ever within the clusters in the first place, either in the inner circles of our Milky Way or in other similar galaxies. If that is the case, it raises questions about the nature of star clusters, which overturns currently accepted theories.
These dense clusters of stars normally orbit the centres of galaxies. They are left over from the beginnings of the universe and are made up of some of its oldest stars. Until now scientists believed that the old stars would have formed into such clusters around the same time and as one homogeneous group. However, these latest observations show that about half of them are a lot younger.
They presumed that the youngesters were created from matter jettisoned by the older stars. In that case, they believed that the number of older stars in the clusters should have been far greater than the younger ones. But the equal divisions of old and young.stars now observed by the research contradicts this.
To explain this anomaly, astronomers thought that the deficit of old stars was the result of them having been expelled to outer regions of the galaxy. And here is the nub of the problem. They just aren't there.
So to test their theory further, they set about studying another galaxy with clusters of stars made up 50/50 of young and old, like our Milky Way. Looking at the Fornax galaxy, some 62 million light years away, they expected the accepted theory to hold true, but it didn't. There weren't enough older stars in outer orbit to validate existing theories.
The theory had more credibility for our own Milky Way, because it is already surrounded by a halo of old stars, where those jettisoned from inner clusters could hide. But Fornax does not have this halo and the older stars should have been easily visible. That they weren't, in turn, raises the question of whether the same is true of own galaxy and others.
Fornax Galaxy
Fornax Galaxy
NASA/ESA
These results also put in doubt the size of the earlier clusters. By the accepted theory, they would have been ten times larger in the past and now the new findings suggest that they must have been much smaller than previously thought.
As phys.org commented, "some of the most mysterious cosmic residents have just become even more puzzling."
These new observations mean that scientists are back to square one. Commenting on the findings, Grundahl said. "Our leading formation theory just can't be right, There's nowhere that Fornax could have hidden these ejected stars."
The new findings can be found in a paper published on Nov 20th in The Astrophysical Journal.
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