The galaxy’s giant black hole: astronomers discover an optical illusion

The galaxy's giant black hole: astronomers discover an optical illusion
An artist's interpretation of a black hole. ©NASA, and M. Weiss (Chandra X -ray Center)

Astronomers have now discovered that the recent mystery surrounding the high levels of scandium, vanadium, and yttrium near the galaxy’s giant black hole were an optical illusion.

The initial mystery, which was published in a study last year, surrounded dramatically high levels of the three elements in red giant stars less than three light years away from the galaxy’s giant black hole. Before the optical illusion discovery, the theories to explain this were that it was either a result of the debris caused by neutron star collisions, or that it was the consequence of the disrupted of earlier stars falling into the black hole.

The elements near the black hole

The new discovery that this was an optical illusion comes from a group of astronomers from various universities including Lund University, Sweden, in collaboration with UCLA, California. Spectral lines are the means for finding out which elements are star contains, using the star’s own light. The high levels of scandium, vanadium, and yttrium found in red giant stars near the black hole were actually an optical illusion rather than spectral lines.

Brian Thorsbro, the lead author of the study and a doctoral student in astronomy at Lund University, said: “These giant red stars have used up most of their hydrogen fuel and their temperatures are therefore only half of the sun’s.”

What caused the optical illusion?

The optical illusion in the measurements of spectral lines near the black hole was caused partially by the lower temperatures of the giant stars. The electrons in the elements behave differently at different temperatures which can cause confusion when astronomers try to measure the spectral lines of elements in stars.

The discovery that the presence of these elements in the giant stars near to the black hole was the result of astronomers and atomic physicists working closely together. Nils Ryde is a research leader and astronomer at Lund University. Ryde added “Our research collaboration is world-leading in terms of systematically mapping the elements contained in the huge central star cluster – the star cluster that surrounds the black hole.”


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