(Nanowerk News) A collaboration of scientists from the University of Manchester and the University of Hong Kong has discovered the source of the mysterious alignment of stars near the Galactic Center.
The planetary nebula alignment was discovered ten years ago by a Manchester PhD student, Bryan Rees, but remains unexplained.
New data obtained with the European Southern Observatory’s Very Large Telescope in Chile and the Hubble Space Telescope, published in Astrophysics Journal Letter (“When the Stars Align: The 5 σ Concordance of the Major Axis of the Planetary Nebula at the Center of our Galaxy”), have confirmed the alignment but have also found a specific group of stars responsible, namely close binary stars.
A planetary nebula is a cloud of gas ejected by a star at the end of its life – the Sun will also form about five billion years from now. The ejected clouds are the ‘ghosts’ of their dying stars and they form beautiful hourglass or butterfly shaped structures.
The team studied a group of planetary nebulae discovered in the Galactic Bulge near the center of our Milky Way. Each of these nebulae is unrelated and originates from different stars, which were born at different times, and spend their lives in completely different places. However, research has found that many of its shapes line up in the sky in the same way and align almost parallel to the plane of the Galaxy (our Milky Way).
This is in line with what Bryan Rees discovered a decade ago.
New research, led by Shuyu Tan, a student at the University of Hong Kong, finds that alignment exists only in planetary nebulae that have a close companion star. The companion star orbits the main star at the center of the planetary nebula in an orbit closer than Mercury to our own Sun.
Planetary nebulae that do not exhibit any close companions do not display an alignment, indicating that the alignment is potentially related to the early separation of the binary components at the time of star birth.
Albert Zijlstra, co-author and Professor of Astrophysics at The University of Manchester, said: “These findings move us closer to understanding the cause of this mysterious alignment.
“Planetary nebulae provide us with a window into the heart of our galaxy and these insights deepen our understanding of the dynamics and evolution of the Milky Way’s bulge region.
“Star formation in our galaxy’s bulge is a complex process that involves factors such as gravity, turbulence and magnetic fields. To date, we have lacked evidence of which mechanism could cause this process to occur and produce this alignment.
“The importance of this research lies in the fact that we now know that alignment is observed in this very specific subset of planetary nebulae.”
The researchers investigated 136 confirmed planetary nebulae in the galactic bulge – the thickest part of our Milky Way made up of stars, gas and dust – using the European Southern Observatory’s Very Large Telescope, which has a main mirror diameter of eight meters.
They also re-examined and re-measured 40 of them from the original study using high-resolution Hubble Space Telescope images.
Prof Quentin Parker, author of the correspondence from the University of Hong Kong, suggests the nebula may have been formed by the fast orbital motion of a companion star, which may even end up orbiting the main star.
The nebula’s alignment could mean that a close binary system preferentially formed with their orbits in the same plane.
While further studies are needed to fully understand the mechanisms behind this alignment, these findings provide important evidence of a constant, controlled process that has influenced star formation over billions of years and vast distances.