A ghostly light in the sky is haunting the scientists

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Some stars, in deepest space, are wandering aimlessly leaving behind them a ghostly glow that scientists call a “ghost light”: these celestial bodies have no gravitational link with a galaxy, which is a real mystery for astronomers. Were they born already without constraints, lost within the cluster of galaxies in which they continue to move, or did they only find themselves wandering at a later time? And what are the causes of this bizarre phenomenon? A new study may finally give answers to the many questions of the experts.

Hubble photographs wandering stars and their ghostly light

Looking at some huge ones galaxy clustersscientists have noticed the presence of a mysterious glow to which they have given the name of “ghost light”: it comes from some stars that move freely within these clusters, without gravitational links with the galaxies among which they continue to wander. I’m “homeless” starscompletely adrift in the deepest intergalactic space, and the only trace they leave of their passage is precisely the strange luminous haze recently captured by NASA telescopes.

To understand when and how these stars started their incessant journey through the galaxiesastronomers conducted a thorough investigation: thanks to the Hubble telescope, which works with infrared, looked for intracluster light – as the brightness belonging to stars without a galaxy is called – in 10 giant clusters, some as distant as 10 billion light-years from us. That is, they have made a real journey back in time, observing how this glow is present in the galaxy clusters – some of which appear to our eyes as they must have been billions of years ago.

In this way, the scientists discovered that the galaxy orphaned stars they have been wandering since time immemorial. The ratio between the intracluster luminosity and the total luminosity of each cluster is more or less constant for all observed clusters – even the most distant ones. “This means that the stars were already homeless in the early stages of cluster formation,” he explains James Jee, a professor at Yonsei University in Seoul and co-author of the article published on natures. If the removal of the stars from their galaxy of origin took place in successive phases, we should in fact see their number (and consequently the luminosity) increase as the clusters age.

When and how the stars started wandering

Astronomers have thus discovered that these stars without galaxy they began their wanderings billions of years ago, when the clusters were in their “infancy” period. This is a fundamental detail: this will in fact allow scientists to use them to study the dark matter present within the cluster itself. However, it remains to be understood how intracluster stars “untied” from their home galaxy and have begun to move in the deepest space, without any connection.

There are many hypothesis that experts have advanced: it is possible that the stars have moved away after a traumatic event, such as the merger of two galaxies, or that they have been torn away from their galaxy as it orbits the center of the cluster. “Current theories fail to explain our results” – says Professor Jee however – “Somehow they must have been released in large quantities into the early Universe. In their first years of formation, galaxies were very small and therefore they could lose stars quite easily due to a weaker gravitational grip“.