When the stars align: Astronomers find answers to mysterious action of
ghost stars in our Galaxy

Date:
July 13, 2023
Source:
University of Manchester
Summary:
Scientists have found a source for the mysterious alignment of
stars near the Galactic Center.


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FULL STORY ==========================================================================
A collaboration of scientists from The University of Manchester and the University of Hong Kong have found a source for the mysterious alignment
of stars near the Galactic Centre.

The alignment of planetary nebulae was discovered ten years ago by a
Manchester PhD student, Bryan Rees, but has remained unexplained.

New data obtained with the European Southern Observatory Very Large
Telescope in Chile and the Hubble Space Telescope, published in
Astrophysical Journal Letters, has confirmed the alignment but also
found a particular group of stars that is responsible, namely close
binary stars.

Planetary nebulae are clouds of gas that are expelled by stars at the
end of their lives -- the Sun will also form one about five billion
years from now.

The ejected clouds are 'ghosts' of their dying stars and they form
beautiful structures such as an hourglass or butterfly shape.

The team studied a group of so-called planetary nebulae found in the
Galactic Bulge near the centre of our Milky Way. Each of these nebulae
are unrelated and come from different stars, which were born at different times, and spend their lives in completely different places. However,
the study found that many of their shapes line up in the sky in the same
way and are aligned almost parallel to the Galactic plane (our Milky Way).

This is in the same direction as found by Bryan Rees a decade ago.

The new research, led by Shuyu Tan, a student at the University of Hong
Kong, found that the alignment is present only in planetary nebulae which
have a close stellar companion. The companion star orbits the main star
at the centre of the planetary nebulae in an orbit closer than Mercury
is to our own Sun.

The planetary nebulae that do not show close companions do not show
the alignment, which suggests that the alignment is potentially linked
to the initial separation of the binary components at the time of the
star's birth.

Albert Zijlstra, co-author and Professor in Astrophysics at The University
of Manchester, said: "This finding pushes us closer to understanding
the cause for this mysterious alignment.

"Planetary nebulae offer us a window into the heart of our galaxy and
this insight deepens our understanding of the dynamics and evolution of
the Milky Way's bulge region.

"The formation of stars in the bulge of our galaxy is a complex process
that involves various factors such as gravity, turbulence, and magnetic
fields.

Until now, we have had a lack of evidence for which of these mechanisms
could be causing this process to happen and generating this alignment.

"The significance in this research lies in the fact that we now know
that the alignment is observed in this very specific subset of planetary nebulae." The researchers investigated 136 confirmed planetary nebulae
in the galaxy bulge -- the thickest section of our Milky Way composed
of stars, gas and dust -- using the European Southern Observatory Very
Large Telescope, which has a main mirror diameter of eight metres.

They also re-examined and re-measured 40 of these from the original
study using images from the high-resolution Hubble Space Telescope.

Prof Quentin Parker, the corresponding author from the University of Hong
Kong, suggests the nebulae may be shaped by the rapid orbital motion of
the companion star, which may even end up orbiting inside the main star.

The alignment of the nebulae may mean that the close binary system preferentially forms with their orbits in the same plane.

Although further studies are needed to fully understand the mechanisms
behind the alignment, the findings provide important evidence for the
presence of a constant and controlled process that has influenced star formation over billions of years and vast distances.

* RELATED_TOPICS
o Space_&_Time
# Galaxies # Nebulae # Stars # Astronomy #
Space_Telescopes # Astrophysics # Space_Exploration # NASA
* RELATED_TERMS
o Milky_Way o Globular_cluster o Satellite o Open_cluster
o Galaxy o Cepheid_variable o Barred_spiral_galaxy o
Interstellar_medium

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========================================================================== Journal Reference:
1. Shuyu Tan, Quentin A. Parker, Albert A. Zijlstra, Andreas Ritter,
Bryan
Rees. When the Stars Align: A 5s Concordance of Planetary Nebulae
Major Axes in the Center of Our Galaxy. The Astrophysical Journal
Letters, 2023; 951 (2): L44 DOI: 10.3847/2041-8213/acdbcd ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/07/230713142104.htm

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