The large peanut shell-shaped bulge at the centre of the disc galaxy NGC 128. Image credit: Sloan Digital Sky Survey / Aladin Sky Atlas / A. Graham, B. Ciambur (Swinburne University of Technology).Astronomers at Swinburne University of Technology, Melbourne, Australia, 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.
A model of the galaxy NGC 128, based on a NASA/ESA Hubble Space Telescope image. The inner structure has been enhanced to make it more visible. Image credit: B. Ciambur (Swinburne University of Technology).Using data from the NASA/ESA 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.”
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 five times smaller. Image credit: Sloan Digital Sky Survey / B. Ciambur (Swinburne University of Technology) / NASA / ESA.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.
“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.
A zoom-in with the NASA/ESA Hubble Space Telescope into the core of NGC 2549 reveals the inner peanut shell-shaped structure in this galaxy. Its outer peanut shell is three times bigger. Image credit: Sloan Digital Sky Survey / B. Ciambur (Swinburne University of Technology) / NASA / ESA.“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.”
Planetary scientists have discovered pieces of opal in a meteorite found in Antarctica, a result that demonstrates that meteorites delivered water ice to asteroids early in the history of the solar system. Opal, familiar on Earth as a precious stone used in jewellery, is made up of silica (the major component of sand) with up to 30 percent water in its structure.
Dazzling Venus and much fainter Mars have a close encounter with a young Moon in the constellation of Pisces at UK dusk on Tuesday 31 January. The trio form an equilateral triangle small enough to be encompassed by the field of view of a 7x binocular low in the west-southwest for a couple of hours from 7pm GMT.
At a ceremony held today in Germany, the European Southern Observatory and the ACe Consortium signed the largest contract ever in ground-based astronomy for key components of the 39-metre aperture European Extremely Large Telescope (E-ELT). The 85-metre-diameter, 5000 tonne dome and telescope structure will take telescope engineering into new territory.
