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Essential Science: Milky Way’s 100s of faint satellite galaxies

In a similar way to the Earth orbiting the Sun, our galaxy – The Milky Way – contains satellite galaxies which have their own satellites. By examining this number of galactic neighbors, new research shows at least one hundred of these satellite galaxies. Understanding these cosmic objects could reveal more about dark matter.

New data has been drawn from the European Space Agency’s Gaia mission. Gaia is a space observatory, which was launched in 2013. The spacecraft focuses on ‘astrometry’, the measuring the positions, distances and motions of stars so that a 3D space catalog of 1 billion astronomical objects can be developed.

Large Magellanic Cloud

As an example of a satellite galaxy, there is the Large Magellanic Cloud (LMC). This is a large satellite galaxy that is visible from the Southern Hemisphere. This galaxy appears to have brought around six of its own satellite galaxies with it, as it approached the Milky Way.

Artist's impression of the Milky Way and location of the spiral arms

Artist’s impression of the Milky Way and location of the spiral arms

At a distance of some 50 kiloparsecs (or163,000 light-years), the LMC is the second closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal. Although the LMC is massive for a satellite galaxy, it is only one-hundredth as massive as the Milky Way.

Within the LHC, vast clouds of gas within it slowly collapse to form new stars. This makes the satellite galaxy one of the most varied and colourful cosmic spectacles.

Dark matter

The star cluster Terzan 5  located in the Milky Way s central bulge

The star cluster Terzan 5, located in the Milky Way’s central bulge
ESO/F. Ferraro

Dark matter refers to the matter that makes up around 85 percent of all of the matter in the universe. This matter cannot be ‘seen’, but it is observed through gravitational effects. One of the focal points of interest is the probability that dark matter exerts a strong influence on the structure of the universe.

Research focus

A key research focus using Gaia and trained on the LMC is an investigation into the size and structure of galaxies, which is thought to relate to dark matter halos that surround them. These take the form of smaller dark matter clumps and tracking these reveals more objects surrounding out galaxy that had previously been realized.

Zoomed-in detail of astar-forming region in our Milky Way galaxy on a larger photo that captures 1 b...

Zoomed-in detail of astar-forming region in our Milky Way galaxy on a larger photo that captures 1 billion of the Milky Way’s stars.
Mike Read (WFAU), UKIDSS/GPS and VVV

According to one of the lead scientists, Risa Wechsler: “For the first time, we can look for these satellite galaxies across about three-quarters of the sky, and that’s really important to several different ways of learning about dark matter and galaxy formation.”

Based on this inquiry, the Milky Way may have a further 150 faint satellite galaxies awaiting surrounding it.


The following video reveals more about the research:

Research paper

The study has been published as a white paper, titled “Milky Way Satellite Census — II. Galaxy-Halo Connection Constraints Including the Impact of the Large Magellanic Cloud.” This is a pre-print, pending final publication.

Essential Science

This article is part of Digital Journal’s regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue.

A cannabis plant.

A cannabis plant.
Michael Fischer (cc) via Pexels

Last week we looked into COVID-19 and cannabis use. This was in light of medical data that suggests users of medicinal cannabis are being hit worse by COVID-19 symptoms compared with other members of the population. This may suggest an issue with the lungs or cannabis itself.

The week before we took the opportunity to carry examine the latest COVID-19 news, including how long people potentially remain infectious for; how the virus jumped from bats to humans; and up-to-date hand sanitization advice.

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Written By

Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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