Astronomers home in on the heart of the Cosmic Ant

Astronomers, including a team from the UK, using the European Southern Observatory’s Very Large Telescope Interferometer (VLTI) in Chile have uncovered unprecedented detail at the heart of one of the most striking planetary features – the Ant Nebula. The results are presented in a paper in research journal Astronomy and Astrophysics.

The unique ability of the VLTI to see extremely small details has revealed a flat disc of silicates in the centre of the nebula. The disc seems too skinny, however, to explain how the nebula got its intriguing ant like shape. Planetary nebulae are glowing structures of gas cast off by solar-like stars at the ends of their lives. The Ant Nebula consists of a bright core, three nested pairs of lobes and a ring like outflow. It is so unique that it was nicknamed the ‘Chamber of Horrors’ of planetary nebulae in 1950’s.

Many have questioned how a spherical star can produce such complex structures. Astronomers believe that the answer to this requires an understanding of the discs surrounding the central star. The discs may provide detail about the processes at work that lead to the development of the planetary nebulae.

The paper's lead author, Olivier Chesneau from the Observatoire de la Côte d’Azur, France, explains, “The challenge is to actually detect these discs. Most astronomical instruments do not have a sharp enough view to find, let alone study them. The Very Large Telescope Interferometer however, with its exceptionally high spatial resolution, is a powerful disc-hunter.”

Co-author and team member Professor Albert Zijlstra from the Jodrell Bank Centre for Astrophysics, part of the University of Manchester, comments,  "The Ant Nebula shows us what the Sun may be like when it reaches the end of its life, and grew so large to almost engulf the Earth, before ejecting a similar nebula. Will it have the same shape and will the Sun surround itself by a disk looking like the rings of Saturn? We don't know yet.”

Professor Zijlstra adds, “We cannot exclude the possibility that the disk formed when the star of the Ant Nebula swallowed a planet, and this could also happen to the Sun. On the other hand, if the Ant Nebula has a double star at its core, and this causes the disk, than the Sun will look very different."

The disc of the Ant Nebula, which cannot be detected with a single 8.2-m VLT Unit Telescope, was uncovered in the interferometric mode where two 8.2-m Unit Telescopes were used to combine light, through the MID-infrared Interferometric instrument (MIDI). The observations reveal a flat, nearly edge-on disc which extends from about 9 times the mean distance between the Earth and the Sun (9 Astronomical Units or 9 AU) to more than 500 AU. At the distance of the Ant Nebula, this corresponds to having detected structures that subtend an angle of only 6 milli-arcseconds – the equivalent to distinguishing a two-storey building on the Moon.

The dust mass stored in the disc appears to be only one hundred thousandth the mass of the Sun and is a hundred times smaller than the mass found in the bipolar lobes.  “We must therefore conclude that the disc is too light to have a significant impact on the outflowing material and cannot explain the shape of the Ant Nebula”, says Chesneau. “Instead, it looks more like this disc is some remnant of the material expelled by the star.”

The observations also provide unquestionable evidence that the disc is primarily composed of amorphous silicate. “This,” says Chesneau, “most likely indicates that the disc is young, perhaps as young as the planetary nebula itself.”

The astronomers favour the possibility that the large quantity of material in the lobes was propelled by several large-scale events, triggered with the help of a cool stellar companion. The solution of the mystery thus resides in the core of the system, and requires better characterisation of the hot central star and its putative companion, currently hidden from our view by the dusty disc.

Notes for Editors

Link to ESO release (link opens in a new window)

Contacts

• Gill Ormrod
  Science and Technology Facilities Council
  Press Office
  Tel: +44 (0)1793 442 012
  
  
• Prof Albert Zijlstra
  University of Manchester
  Tel: +44 (0)161 306 3925
  
  
• Olivier Chesneau
  Observatoire de la Côte d’Azur
  France
  Tel: +33 4 93 40 53 40

The results are presented in a Letter to the Editor published by the research journal Astronomy and Astrophysics (“A silicate disk in the heart of the Ant” by O. Chesneau et al.). The team is composed of O. Chesneau and A. Spang (Observatoire de la Côte d’Azur, France), F. Lykou, E. Lagadec, and A.A. Zijlstra (University of Manchester, UK), B. Balick (University of Washington, Seattle, USA), M. Matsuura (NAOJ, Tokyo, Japan), N. Smith (University of California, USA), and S. Wolf (Max-Planck-Institute for Astronomy, Heidelberg, Germany).

The Ant Nebula

The Ant Nebula is located about 5 000 light-years away. The central star is as bright as 10 000 Suns and has a temperature of 35 000 degrees Celsius. It is the last phase before this solar-like star will become a white dwarf.

Interferometry

Interferometry works by combining the light of two or more telescopes, so that they act as a single, giant telescope, as large as the entire group. For ESO’s Very Large Telescope Interferometer (VLTI), when combining two of the 8.2-m Unit Telescopes, up to 25 times finer detail can be observed than with the individual telescopes.

Silicates

Silicates are minerals composed of silicon and oxygen, and appear in two flavours: amorphous and crystalline. The latter have symmetry in their structure, whereas the former do not.

Images and captions

• Image 1 - A disc in the Ant nebula.
  © Stephane Guisard / ESO
  
  
• Image 2 - The Ant nebula - fiery lobes protrude from dying, sun-like star.
  Credit: Hubble Space telescope

The images can also be downloaded from the ESO website (link opens in a new window) and the Hubble Space Telescope (link opens in a new window) site.

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