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Galaxy-sized peanuts? Astronomers use new imaging software to detect double ‘peanut shell’ galaxy

Last Updated on Thursday, 05 May 2016 15:56
Published on Friday, 06 May 2016 00:01

Astronomers at Swinburne University of Technology, Melbourne, have discovered an unusually shaped structure in two nearby disc galaxies. The Swinburne team recently developed new imaging software, making it possible to observe the double “peanut shell shape” formed by the distribution of stars bulging from the centres of these galaxies. The results are published in a new paper in Monthly Notices of the Royal Astronomical Society.

contour-image thumbThe large (peanut shell)-shaped bulge at the centre of the disc galaxy NGC 128. Credit: Sloan Digital Sky Survey / Aladin Sky Atlas / A.Graham, B.Ciambur (Swinburne University of Technology)

 

Using data from the Hubble Space Telescope and the Sloan Digital Sky Survey, the researchers realised that two of the galaxies they were studying – NGC 128 and NGC 2549 – were quite exceptional. They are roughly 200 and 60 million light years away respectively, in the constellations of Pisces and Lynx, and they displayed a peanut shell configuration at two separate layers within the galaxies’ three-dimensional distribution of stars.

 

“Ironically, these peanut-shaped structures are far from peanut-sized,” says Swinburne’s Professor Alister Graham, co-author of the research. “They consist of billions of stars typically spanning up to a quarter of the length of the galaxies.”

 

Although the ‘bulges’ of both galaxies were already known to display a single peanut shell pattern, astronomers had never before observed the fainter second structure in any galaxy.

 galaxy-model thumbA model of the galaxy NGC 128, based on a Hubble Space Telescope image. Credit: B. Ciambur (Swinburne University of Technology)

“They resemble two peanut shells, with one neatly nested within the other; this is the first time such a phenomenon has been observed,” says Bogdan Ciambur, the PhD student who led the investigation.

 

“We expect the galaxies’ surprising anatomy will provide us with a unique view into their pasts. Deciphering their history can tell us about transformations that galaxies like our own Milky Way might experience.”

 

Astronomers believe that peanut shaped bulges are linked to the bar-shaped distribution of stars that is observed across the centres of many rotating galaxy discs. Each of the two galaxies observed contain two such bars, and it is thought that one way the peanut shaped structures may arise is when these bars of stars bend above and below the galaxy’s central disc.

 

“The instability mechanism may be similar to water running through a garden hose: when the water pressure is low, the hose remains still (stars stay on their usual orbits), but when the pressure is high the hose starts to bend (stellar orbits bend outside of the disc plane),” says Mr Ciambur.

 

“By directly comparing real galaxies with state-of-the-art simulations, we hope to better understand how galaxies evolve,” says Mr Ciambur. “The discovery is exciting because it will enable us to more fully test the growth of bars over time, including their lengths, rotation speeds, and periods of instability.

 

The study may also shed new light on the peanut-shaped bulge of our own Milky Way galaxy, which some astronomers suspect contains two stellar bars.

 

“Thankfully we are too distant from our Galaxy’s bulge to get caught up in the dizzying orbits that lead to these interesting peanut shell patterns,” adds Professor Graham. “However, this is an ideal vantage point to study our Galaxy’s stellar bulge.”

 

Media contacts

 

Dr Morgan Hollis
Royal Astronomical Society
Tel: +44 (0)20 7734 3307
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Dr Sam Lindsay
Royal Astronomical Society
Tel: +44 (0)20 7292 3976
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Ms Lea Kivivali
Senior Media and Communications Adviser
Swinburne University of Technology
Melbourne, Australia
Tel: +61 3 9214 5428
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Science contacts

 

Mr Bogdan Ciambur
Swinburne University of Technology
Melbourne, Australia
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Prof Alister Graham
Swinburne University of Technology
Melbourne, Australia
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Images and captions


A model of the galaxy NGC 128, based on a Hubble Space Telescope image. The over-plotted curves of equal brightness (isophotes) resemble the pursed lips of a kissing mouth due to the extended disc running through the twin peanut shell structures. The inner structure has been enhanced to make it more visible.
Credit: B. Ciambur (Swinburne University of Technology)

 

The large (peanut shell)-shaped bulge at the centre of the disc galaxy NGC 128.

Credit: Sloan Digital Sky Survey / Aladin Sky Atlas / A.Graham, B.Ciambur (Swinburne University of Technology)

 

The galaxy NGC 128 is viewed with its disc in an edge-on orientation in this SDSS false-colour image. A (peanut shell)-shaped bulge can be seen around the thin disc. Its inner peanut shell is 5 times smaller. 

Credit: Sloan Digital Sky Survey / B.Ciambur (Swinburne University of Technology) / NASA / ESA

 

A zoom-in with the Hubble Space Telescope into the core of NGC 2549 reveals the inner peanut shell shaped structure in this galaxy. Its outer peanut shell is 3 times bigger.

Credit: Sloan Digital Sky Survey / B.Ciambur (Swinburne University of Technology) / NASA / ESA

 

Further information

 

The new work appears in “Quantifying the (X/Peanut)-Shaped Structure in Edge-on Disc Galaxies: Length, Strength, and Nested Peanuts”, B.C. Ciambur, A.W. Graham, Monthly Notices of the Royal Astronomical Society, Oxford University Press, in press.

A copy of the paper is available from http://mnras.oxfordjournals.org/content/459/2/1276, or from the arXiv astronomy preprint server at http://www.arxiv.org/abs/1603.00019.

 


Notes for editors

 

The Royal Astronomical Society (RAS, www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3900 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter via @royalastrosoc