dwarf galaxies Archives

September 26, 2024September 26, 2024 by Brian Koberlein

Dark Matter Could a Have Slight Interaction With Regular Matter

A comparison of non-interacting and interacting dark matter. Credit: Gabriel Pérez

The reason we call dark matter dark isn’t because it’s some shadowy material. It’s because dark matter doesn’t interact with light. The difference is subtle, but important. Regular matter can be dark because it absorbs light. It’s why, for example, we can see the shadow of molecular clouds against the scattered stars of the Milky Way. This is possible because light and matter have a way to connect. Light is an electromagnetic wave, and atoms contain electrically charged electrons and protons, so matter can emit, absorb and scatter light. Dark matter isn’t electrically charged. It has no way to connect with light, and so when light and dark matter meet up they simply pass through each other.

July 13, 2024July 13, 2024 by Mark Thompson

Mapping the Stars in a Dwarf Galaxy to Reveal its Dark Matter

Dark matter is curious stuff! As the name suggests, it’s dark making it notoriously difficult to study. Although it’s is invisible, it influences stars in a galaxy through gravity. Now, a team of astronomers have used the Hubble Space Telescope to chart the movements of stars within the Draco dwarf galaxy to detect the subtle gravitational pull of its surrounding dark matter halo. This 3D map required studying nearly two decades of archival data from the Draco galaxy. They found that dark matter piles up more in the centre, as predicted by cosmological models.

June 10, 2024June 10, 2024 by Evan Gough

The Milky Way’s Last Merger Event Was More Recent Than Thought

Our home galaxy as seen by the European Space Agency’s Gaia satellite. Image Credit: ESA/Gaia/DPAC

The Milky Way is only as massive as it is because of collisions and mergers with other galaxies. This is a messy process, and we see the same thing happening with other galaxies throughout the Universe. Currently, we see the Milky Way nibbling at its two satellite galaxies, the Large and Small Magellanic Clouds. Their fate is likely sealed, and they’ll be absorbed into our galaxy.

Researchers thought the last major merger occurred in the Milky Way’s distant past, between 8 and 11 billion years ago. But new research amplifies the idea that it was much more recent: less than 3 billion years ago.

March 29, 2024March 29, 2024 by Evan Gough

The Milky Way’s Smallest, Faintest Satellite Galaxy Found

Hidden in this deep sky image (left) is Uma3/U1, an ultra faint galaxy. It contains fewer than 100 hundred stars, a tiny amount for a galaxy. Credit: CFHT/S. Gwyn (right) / S. Smith (left)

The Milky Way has many satellite galaxies, most notably the Large and Small Magellanic Clouds. They’re both visible to the naked eye from the southern hemisphere. Now astronomers have discovered another satellite that’s the smallest and dimmest one ever detected. It may also be one of the most dark matter-dominated galaxies ever found.

March 25, 2024March 25, 2024 by Brian Koberlein

Dwarf Galaxies Could be the Key to Explaining Dark Matter

Dark matter map in Galaxy Cluster Abell 1689. Credit: NASA, ESA, and D. Coe (NASA JPL/Caltech and STScI)

If you have a view of the southern celestial sky, on a clear night you might see two clear smudges of light set off a bit from the great arch of the Milky Way. They are the Large and Small Magellanic Clouds, and they are the most visible of the dwarf galaxies. Dwarf galaxies are small galaxies that typically cluster around larger ones. The Milky Way, for example, has nearly two dozen dwarf galaxies. Because of their small size, they can be more significantly affected by dark matter. Their formation may even have been triggered by the distribution of dark matter. So they can be an excellent way to study this mysterious unseen material.

February 28, 2024February 28, 2024 by Evan Gough

Dwarf Galaxies Banished the Darkness and Lit Up the Early Universe

The JWST used gravitational lensing to search for the sources of light that triggered the Epoch of Reionization and brought darkness to an end. The white hazy blobs are galaxies in Pandora's Cluster, which acts as the gravitational lens. The red objects are the distant and ancient objects magnified by the lens, some of them warped into arcs. Many of them are early dwarf galaxies, some of them responsible for the Epoch of Reionization. Image Credit: NASA/ESA/CSA JWST

During the Universe’s Dark Ages, dense primordial gas absorbed and scattered light, prohibiting it from travelling. Only when the first stars and galaxies began to shine in energetic UV light did the Epoch of Reionization begin. The powerful UV light shone through the Universe and punched holes in the gas, allowing light to travel freely.

New observations with the James Webb Space Telescope reveal how it happened. The telescope shows that faint dwarf galaxies brought an end to the darkness.

November 12, 2023November 12, 2023 by Mark Thompson

Mystery Solved. How We Get Ultra-Compact Dwarf Galaxies

This NASA/ESA Hubble Space Telescope image shows the dwarf galaxy M60-UDC1. Lying about 50 million light-years away, M60-UCD1 is a tiny galaxy with a diameter of 300 light-years — just 1/500th of the diameter of the Milky Way! Despite its size it is pretty crowded, containing some 140 million stars. The dwarf galaxy may actually be the stripped remnant of a larger galaxy that was torn apart during a close encounter with its neighbour, a massive galaxy called Messier 60. Circumstantial evidence for this comes from the recent discovery of a monster black hole, which is not visible in this image, at the centre of the dwarf. The black hole makes up 15 percent of the mass of the entire galaxy, making it much too big to have formed inside a dwarf galaxy. — Ultra Compact Dwarf Galaxy M60-UCD1 (Credit NASA/ESA and A.Seth)

I have been fascinated by galaxies for most of my adult life. I find it amazing that, just as we can ascertain the lifecycle of a tree by closely studying the trees in a forest, it is possible to study a sample of galaxies and understand galactic evolution. A team of astronomers using the Gemini North Telescope have recently solved a long standing galactic mystery, namely how we get ultra-compact dwarf galaxies (UCDs to use their catchy acronym).

November 7, 2022November 7, 2022 by Evan Gough

The Perfect Tidal Tail Connects These two Galaxies Seen by Hubble

This image from the NASA/ESA Hubble Space Telescope shows two of the galaxies in the galactic triplet Arp 248. Image Credit: ESA/Hubble & NASA, Dark Energy Survey/Department of Energy/Fermilab Cosmic Physics Center/Dark Energy Camera/Cerro Tololo Inter-American Observatory/NOIRLab/National Science Foundation/AURA Astronomy; J. Dalcanton

Sometimes it’s tempting to imagine a supernatural hand behind the arrangement of celestial bodies. But the Universe is big, huge even, and nature’s flow presents many fascinations.

So it is with the galactic triplet Arp 248, an arrangement of interacting galaxies that’s both visually and scientifically fascinating.

August 7, 2022August 7, 2022 by Carolyn Collins Petersen

Dwarf Galaxies Found Without Influence From Dark Matter

Dwarf galaxy in Fornax. — The dwarf galaxy NGC1427A flies through the Fornax galaxy cluster and undergoes disturbances which would not be possible if this galaxy were surrounded by a heavy and extended dark matter halo, as required by standard cosmology. Courtesy ESO.

Ask astronomers about dark matter and one of the things they talk about is that this invisible, mysterious “stuff” permeates the universe. In particular, it exists in halos surrounding most galaxies. The mass of the halo exerts a strong gravitational influence on the galaxy itself, as well as on others in the neighborhood. That’s pretty much the standard view of dark matter and its influence on galaxies. However, there are problems with the idea of those halos. Apparently, some oddly shaped dwarf galaxies exist that look like they have no halos. How could this be? Do they represent an observationally induced challenge to the prevailing ideas about dark matter halos?

December 8, 2021February 17, 2023 by Matt Williams

A Nearby Dwarf Galaxy has a Surprisingly Massive Black Hole in its Heart

Since the 1970s, scientists have known that within the cores of most massive galaxies in the Universe, there beats the heart of a Supermassive Black Hole (SMBH). The presence of these giant black holes causes these galaxies to be particularly energetic, to the point where their central regions outshine all the stars in their disks combined – aka. Active Galactic Nuclei (AGN). The Milky Way galaxy has its own SMBH, known as Sagittarius A*, which has a mass of over 4 million Suns.

For decades, scientists have studied these objects in the hopes of learning more about their role in galactic formation and evolution. However, current research has shown that SMBHs may not be restricted to massive galaxies. In fact, a team of astronomers from the University of Texas at Austin’s McDonald Observatory recently discovered a massive black hole at the heart of a dwarf galaxy that orbits the Milky Way (Leo I). This finding could redefine our understanding of how black holes and galaxies evolve together.