Sextans: The smallest cannibal galaxy discovered until now

October 11, 2018, Instituto de Astrofísica de Canarias
Credit: Instituto de Astrofísica de Canarias

A team at the Instituto de Astrofísica de Canarias (IAC) has discovered a new case of galactic cannibalism in the neighbourhood of the Milky Way, which has caused the merging of two galaxies on the smallest scale so far known.

The Sextans galaxy has a mass some 100,000 times less than that of the Milky Way but has swallowed an even smaller companion. Using data form the Victor M. Blanco Telescope (4m diameter) at the Cerro Tololo Interamerican Observatory and the Landon Clay 6 m telescope, also known as Magellan 2, at the Las Campanas Observatory, both in Chile, they observed clear signs that Sextans had absorbed a smaller stellar system.

When they analyzed the , they observed that the spatial distribution of the blue, metal-poor stars was round and regular, while that of the red, metal-rich stars was much more elliptical and irregular, with an overdensity of stars on the north-eastern side. "The most reasonable explanation of this phenomenon is that two merged, and had different metallicities," explains Luis Cicuéndez, a researcher at the IAC and at the University of La Laguna.

The analysis of the velocities and of indicators of the chemical composition of the stars reveal the presence of a spatial sub-structure in the shape of a ring. This substructure shows a much higher velocity and a different chemical composition than the rest of the stars in the galaxy.

Credit: Instituto de Astrofísica de Canarias
"This finding appears to show that the hierarchical theory of galaxy formation, in which merge to form larger ones, can explain the formation of even the smallest known galaxies, the dwarf galaxies" explains the IAC researcher and co-author of the study Giuseppina Battaglia.

The details of this new discovery are published in the latest volume of the journal Monthly Notices of the Royal Astronomical Society (MNRAS).

Explore further: Galaxies that feed on other galaxies

More information: L Cicuéndez et al. Appearances can be deceiving: clear signs of accretion in the seemingly ordinary Sextans dSph, Monthly Notices of the Royal Astronomical Society (2018). DOI: 10.1093/mnras/sty1748

Related Stories

Galaxies that feed on other galaxies

February 1, 2018

An international team of astronomers led by Giuseppina Battaglia, researcher at the Instituto de Astrofísica de Canarias (IAC), finds signs that the outer halo of the Milky Way contains stellar remains of massive dwarf galaxies ...

Four newly discovered Milky Way neighbors

October 1, 2018

Ultra-faint dwarf galaxies are the smallest, most dark matter dominated, and least chemically enriched stellar systems in the universe, and are important targets for understanding dark matter and galaxy formation. They comprise ...

Hubble peers at a distinctly disorganized dwarf galaxy

April 4, 2016

Despite being less famous than their elliptical and spiral galactic cousins, irregular dwarf galaxies, such as the one captured in this NASA/ESA Hubble Space Telescope image, are actually one of the most common types of galaxy ...

Image: Hubble's compact galaxy with big-time star formation

October 16, 2017

As far as galaxies are concerned, size can be deceptive. Some of the largest galaxies in the Universe are dormant, while some dwarf galaxies, such as ESO 553-46 imaged here by the NASA/ESA Hubble Space Telescope, can produce ...

Recommended for you

Archaeologists discover Incan tomb in Peru

February 16, 2019

Peruvian archaeologists discovered an Incan tomb in the north of the country where an elite member of the pre-Columbian empire was buried, one of the investigators announced Friday.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

The friendly extortioner takes it all

February 15, 2019

Cooperating with other people makes many things easier. However, competition is also a characteristic aspect of our society. In their struggle for contracts and positions, people have to be more successful than their competitors ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.