The Lost Stars of the Magellanic Clouds

The two Magellanic Clouds over the Anglo-Australian Telescope (AAT) now including a false-colour image of the Magellanic Bridge (in red) showing the diffuse gas connecting the SMC and the LMC. A black rectangle shows the region observed using the AAT, and here the “lost stars” of the SMC (identified as big dots in the grey-scale image) have been found.

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Using the Anglo-Australian Telescope (AAT), an international team of astrophysicists has confirmed the existence of stars in the Magellanic Bridge, a gaseous structure connecting the two Magellanic Clouds. These “lost stars” were stripped from the Small Magellanic Cloud by the gravitational pull of the Large Magellanic Cloud in a recent nearby encounter.

Our Galaxy, the Milky Way, has two small satellite galaxies around it: the Magellanic Clouds.

Only visible from the Southern Hemisphere, the Small Magellanic Cloud (SMC) and the Large Magellanic Cloud (LMC) seem to be to isolated objects.

However, they are actually connected by a large gaseous structure: the Magellanic Bridge. The material of that bridge has been stripped from the Magellanic Clouds as a consequence of strong gravitational interactions between the two small galaxies and the Milky Way.

Using the 3.9m Anglo-Australian Telescope (AAT), located at Siding Spring Observatory (Coonabarabran, Australia) and managed by the Australian Astronomical Observatory (AAO), an international team of astrophysicists has confirmed, for the first time, the detection of stars within the Magellanic Bridge.

To make this exciting discovery, astronomers used the AAT’s “2dF” robot together with the AAOmega spectrograph to measure around 1500 stars in that region of the sky.

“The 2dF robot, which is pioneer in its class, allows us to simultaneously observe 400 objects in a region of the sky with a diameter of 4 full moons. This makes it possible to obtain high-quality data for thousands of stars in just a few nights” says Dr Ángel López-Sánchez, AAO astronomer and member of the research team.

“The observations at the AAT were made possible thanks to the OPTICON program from the European Union, which allows European astronomers to access facilities in other countries, such the AAT in Australia”, says Dr Ricardo Carrera, researcher at the Instituto de Astrofísica de Canarias (IAC, Canary Islands Institute for Astronomy) and first author of the study.

The AAT observations revealed that some stars within the region where the Magellanic Bridge is located are not moving with the Milky Way. Instead, the movement of these stars agrees with that of the gas of the Magellanic Bridge.

The researchers discovered that these “lost stars” are very old, born between 1 and 10 billion years ago.

The Magellanic Bridge was only formed around 200 million years ago, much more recently than the stars associated with it, meaning that the “lost stars” were actually born within the LMC or the SMC and later stripped from the galaxies.

Some dynamical models explaining the formation and evolution of the Magellanic Bridge already predicted that both stars and gas should be present. These new observations have confirmed, for the first time, that this is true.

“Although preliminary studies suggested the existence of stars within the Magellanic Bridge, the data obtained with the AAT have definitively confirmed the existence of these old ‘lost stars’”, says Dr Carrera.

“An important part of the gas and the stars in the Magellanic Clouds was “stripped” by effect of the gravitational forces. Comparing with dynamical models it is possible to estimate that this happened around 200 million years ago, when the two dwarf galaxies were very close. This was the origin of the Magellanic Bridge”, says Dr Noelia E. D. Noël, lecturer in Astrophysics at the University of Surrey in the UK.

Furthermore, the spectroscopic data provided by the AAT have been also used to estimate the chemical composition of the “lost stars” found within the Magellanic Bridge.

“Combining both the kinematics and the chemical composition of the stars, we can unequivocally conclude that these stars were actually born in the Small Magellanic Cloud”, says Dr Ricardo Carrera.

Galaxy interactions and mergers were very common in the early Universe, and they are still happening today. Indeed, galaxy evolution is largely dominated by these encounters.

“Galaxy interactions can distort or even drastically change the morphology of the galaxies. During these encounters there is an interchange of material between galaxies, new star-forming regions are created, and frequently the gas and stars are also stripped into the space between galaxies, called the intergalactic medium”, says Dr Ángel López-Sánchez.

The results of this research, published in the journal “Monthly Notices of the Royal Astronomical Society”, provide key clues about the mechanisms involved during galaxy interactions.

The AAO is a division of the Department of Industry, Innovation and Science.

Publication details:

Carrera, R., Conn, B.C., Noël, N.E.D., Read, J.I. & López-Sánchez, Á.R. 2017, “The Magellanic Inter-Cloud Project (MAGIC) III: First spectroscopic evidence of a dwarf stripping a dwarf”, Monthly Notices of the Royal Astronomical Society, Volume 471, Issue 4, 11 November 2017, Pages 4571–4578

Paper in arXiv: https://arxiv.org/abs/1707.08397

Paper in MNRAS: https://academic.oup.com/mnras/article/471/4/4571/4055623/The-Magellanic-InterCloud-Project-MAGIC-III-first

Science Contacts:

- Dr Ricardo Carrera

Research Astronomer,

Instituto de Astrofísica de Canarias, Spain and INAF-Observatorio Astronomico di Padova, Italy

P: +49 8293 507 E: ricardo.carrera@oapd.inaf.it and rcarrera_ext@iac.es

- Dr Noelia Noël

Lecturer in Astrophysics,

Department of Physics, University of Surrey, UK

P: +44 1483 68 3590 E: n.noel@surrey.ac.uk

- Dr Ángel López-Sánchez,

Research Astronomer and Science Communication Officer,

Australian Astronomical Observatory and Macquarie University.

M: +61 406 265 917 E: angel.lopez-sanchez@aao.gov.au

Media contact:

- Dr Ángel López-Sánchez,

Research Astronomer and Science Communication Officer,

Australian Astronomical Observatory and Macquarie University.

M: +61 406 265 917 E: angel.lopez-sanchez@aao.gov.au

Images:

Deep images of the Large Magellanic Clouds (LMC, left) and the Small Magellanic Cloud (SMC, right) obtained from Siding Spring Observatory (Coonabarabran, NSW) on 19th September 2017 using amateur astronomy techniques. Bright globular cluster 47 Tucanae is clearly seen at the right of the SMC. 

Caption: Deep images of the Large Magellanic Clouds (LMC, left) and the Small Magellanic Cloud (SMC, right) obtained from Siding Spring Observatory (Coonabarabran, NSW) on 19th September 2017 using amateur astronomy techniques. Bright globular cluster 47 Tucanae is clearly seen at the right of the SMC.

Credit: Ángel R. López-Sánchez (AAO/MQU).

This image is available at: https://www.aao.gov.au/files/public/images/2017-11-30-Fig01-LMCSMC-angelrls.jpg

The two Magellanic Clouds over the Anglo-Australian Telescope (AAT). The Large Magellanic Cloud (LMC) is at the left and the Small Magellanic Cloud (SMC) is at the right of the image. Photo obtained before the morning twilight, 8th September 2015.

Caption: The two Magellanic Clouds over the Anglo-Australian Telescope (AAT). The Large Magellanic Cloud (LMC) is at the left and the Small Magellanic Cloud (SMC) is at the right of the image. Photo obtained before the morning twilight, 8th September 2015.

Credit: Ángel R. López-Sánchez (AAO/MQU).

This image is available at: https://www.aao.gov.au/files/public/images/2017-11-30-Fig02-LMC-SMC-AAT-angelrls.jpg

The two Magellanic Clouds over the Anglo-Australian Telescope (AAT) now including a false-colour image of the Magellanic Bridge (in red) showing the diffuse gas connecting the SMC and the LMC. A black rectangle shows the region observed using the AAT, and here the “lost stars” of the SMC (identified as big dots in the grey-scale image) have been found.

Caption: The two Magellanic Clouds over the Anglo-Australian Telescope (AAT) now including a false-colour image of the Magellanic Bridge (in red) showing the diffuse gas connecting the SMC and the LMC. A black rectangle shows the region observed using the AAT, and here the “lost stars” of the SMC (identified as big dots in the grey-scale image) have been found. Credit: Image of the Magellanic Clouds over the AAT: Ángel R. López-Sánchez (AAO/MQU). Radio image showing the HI gas: M. Putman (Columbia, US) and Leiden/Argentine/Bonn (LAB) survey of Galactic H I (Kalberla & Haud 2015). Grey-scale image: Digital Sky Survey (DSS). Image composition: Ricardo Carrera (IAC/INAF) and Ángel R. López-Sánchez (AAO/MQU).

This image is available at: https://www.aao.gov.au/files/press/2017-11-30-Fig03-LMC-SMC-AAT-gasstars.jpg

The 2dF robot gantry moving the optical fibres, which are illuminated in red. This is a frame of the video timelapse “A 2dF night at the AAT”.

Caption: The 2dF robot gantry moving the optical fibres, which are illuminated in red. This is a frame of the video timelapse “A 2dF night at the AAT”.

Credit: Ángel R. López-Sánchez (AAO/MQU).

This image is available at: https://www.aao.gov.au/files/public/images/2017-11-30-Fig04-2df-gantry-angelrls.jpg

Video timelapse: A 2dF night at the AAT

Caption: A 2dF night at the AAT" assembles 14 time-lapse sequences taken at the 4-metre Anglo-Australian Telescope (AAT) located at Siding Spring Observatory NSW, Australia. This time-lapse video shows not only how the Two Degree Field (2dF) instrument works but also how the AAT and the telescope dome move in tandem, and the beauty of the Southern Sky in spring and summer. The video is 2min 50sec long and combines more than 4000 frames obtained using a CANON EOS 600D with a 10-20mm wide-angle lens. All sequences were taken during September and November 2011 by AAO and MQU astronomer Dr Ángel R. López-Sánchez while he was working as the 2dF support astronomer for the AAT. The music is the song “Blue Raider” from Composer Cesc Villà's album “Epic Soul Factory”.

More info in https://www.aao.gov.au/public/video/2dF-Night-at-AAT

Link to the YouTube video: https://youtu.be/XKoWQtDd14c

Full Media Release in DOC format.