Magellanic Clouds duo may have been a trio

September 17, 2018

Two of the closest galaxies to the Milky Way--the Large and Small Magellanic Clouds--may have had a third companion, astronomers believe.

Research published today describes how another "luminous" galaxy was likely engulfed by the Large Magellanic Cloud some three to five billion years ago.

ICRAR Masters student Benjamin Armstrong, the lead author on the study, said most stars in the Large Magellanic Cloud rotate clockwise around the centre of the galaxy.

But, unusually, some stars rotate anti-clockwise.

"For a while, it was thought that these stars might have come from its companion galaxy, the Small Magellanic Cloud," Mr Armstrong said.

"Our idea was that these stars might have come from a merger with another galaxy in the past."

Mr Armstrong, who is based at The University of Western Australia, used computer modelling to simulate galaxy mergers.

"What we found is that in this sort of merging event, you actually can get quite strong counter-rotation after a merger takes place," he said.

"This is consistent with what we see when we actually observe the galaxies."

The Magellanic Clouds can be seen in the night sky with the naked eye and have been observed by ancient cultures for thousands of years.

The Large Magellanic Cloud is a relatively small 160,000 light years away from us, while the Small Magellanic Cloud is around 200,000 light years away.

Mr Armstrong said the finding could help to explain a problem that has perplexed astronomers for years--why stars in the Large Magellanic Cloud are generally either very old or very young.

"In galaxies, there are these large objects called star clusters," he said.

"Star clusters contain many, many, many stars that are all of quite similar ages and made in similar environments.

"In the Milky Way, the star clusters are all very old.

"But in the Large Magellanic Cloud, we have very old clusters as well as ones that are very young--but nothing in between."

This is known as the 'age-gap' problem, Mr Armstrong said.

"Because in the Large Magellanic Cloud we see star formation starting again, that could be indicative of a galaxy merger taking place," he said.

Mr Armstrong said the finding could also help explain why the Large Magellanic Cloud appears to have a thick disk.

"Our work is still very preliminary but it does suggest that this sort of process could have been responsible for the thicker disk in the past," he said.

Mr Armstrong said the research was about asking pertinent questions that astronomers could start examining.

"It's about creating a new idea, a new way of looking at an old problem," he said.
The study was released in the journal Monthly Notices of the Royal Astronomical Society, published by Oxford University Press.

Original Publication

'Formation of a counter-rotating stellar population in the Large Magellanic Cloud: a Magellanic triplet system?', in the Monthly Notices of the Royal Astronomical Society published by Oxford University Press on September 18th, 2018. Available from

More Information

The International Centre for Radio Astronomy Research (ICRAR) is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.


High-resolution images and a simulation available from


Benjamin Armstrong (ICRAR-UWA)
Ph: +61 466 688 016

Dr Kenji Bekki (ICRAR-UWA)
Ph: +61 8 6488 7730

Pete Wheeler (Media Contact, ICRAR)
Ph: +61 423 982 018

International Centre for Radio Astronomy Research

Related Astronomers Articles from Brightsurf:

Astronomers are bulging with data
For the first time, over 250 million stars in our galaxy's bulge have been surveyed in near-ultraviolet, optical, and near-infrared light, opening the door for astronomers to reexamine key questions about the Milky Way's formation and history.

Astronomers capture a pulsar 'powering up'
A Monash-University-led collaboration has, for the first time, observed the full, 12-day process of material spiralling into a distant neutron star, triggering an X-ray outburst thousands of times brighter than our Sun.

Astronomers discover new class of cosmic explosions
Analysis of two cosmic explosions indicates to astronomers that the pair, along with a puzzling blast from 2018, constitute a new type of event, with similarities to some supernovae and gamma-ray bursts, but also with significant differences.

Astronomers discover planet that never was
What was thought to be an exoplanet in a nearby star system likely never existed in the first place, according to University of Arizona astronomers.

Canadian astronomers determine Earth's fingerprint
Two McGill University astronomers have assembled a 'fingerprint' for Earth, which could be used to identify a planet beyond our Solar System capable of supporting life.

Astronomers help wage war on cancer
Techniques developed by astronomers could help in the fight against breast and skin cancer.

Astronomers make history in a split second
In a world first, an Australian-led international team of astronomers has determined the precise location of a powerful one-off burst of cosmic radio waves.

Astronomers witness galaxy megamerger
Using the Atacama Large Millimeter/submillimeter Array (ALMA), an international team of scientists has uncovered a startlingly dense concentration of 14 galaxies that are poised to merge, forming the core of what will eventually become a colossal galaxy cluster.

Astronomers discover a star that would not die
An international team of astronomers has made a bizarre discovery; a star that refuses to stop shining.

Astronomers spun up by galaxy-shape finding
For the first time astronomers have measured how a galaxy's spin affects its shape -- something scientists have tried to do for 90 years -- using a sample of 845 galaxies.

Read More: Astronomers News and Astronomers Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to