Astronomers discover how tiny dwarf galaxies form ‘fossils’

By Georgina Torbet Published November 9, 2023

Galaxies come in many different shapes and sizes, including those considerably smaller than our Milky Way. These smaller galaxies, called dwarf galaxies, can have as few as 1,000 stars, compared to the several hundred billion in our galaxy. And when these dwarf galaxies age and begin to erode away, they can transform into an even smaller and more dense shape, called an ultra-compact dwarf galaxy.

The Gemini North telescope has recently been studying more than 100 of these eroding dwarf galaxies, seeing how they lose their outer stars and gas to become ultra-compact dwarf galaxies or UCDs.

A dwarf galaxy in the throes of transitioning to an ultra-compact dwarf galaxy as it’s stripped of its outer layers of stars and gas by a nearby larger galaxy. — This illustration shows a dwarf galaxy in the throes of transitioning to an ultra-compact dwarf galaxy as it’s stripped of its outer layers of stars and gas by a nearby larger galaxy. Ultra-compact dwarf galaxies are among the densest stellar groupings in the Universe. Being more compact than other galaxies with similar mass, but larger than star clusters — the objects they most closely resemble — these mystifying objects have defied classification. The missing piece to this puzzle has been a lack of sufficient transitional, or intermediate objects to study. A new galaxy survey, however, fills in these missing pieces to show that many of these enigmatic objects are likely formed from the destruction of dwarf galaxies. NOIRLab/NSF/AURA/M. Zamani

“Our results provide the most complete picture of the origin of this mysterious class of galaxy that was discovered nearly 25 years ago,” said one of the researchers, NOIRLab astronomer Eric Peng in a statement. “Here we show that 106 small galaxies in the Virgo cluster have sizes between normal dwarf galaxies and UCDs, revealing a continuum that fills the ‘size gap’ between star clusters and galaxies.”

Recommended Videos

While astronomers did predict that dwarf galaxies could become UCDs, they hadn’t observed many cases of one transforming into the other. So this study looked for these “missing links” to see how this transition occurred. They found that these in-between galaxies were most often located near larger galaxies, which stripped away stars and gas from the small dwarf galaxies to leave a UCD behind.

“Once we analyzed the Gemini observations and eliminated all the background contamination, we could see that these transition galaxies existed almost exclusively near the largest galaxies. We immediately knew that environmental transformation had to be important,” explained lead author Kaixiang Wang of Peking University.

These objects were spotted using data from sky surveys, which was followed up using observations from Gemini North. That allowed the researchers to pick out the small dwarf galaxies from the many background galaxies visible in the sky.

“It’s exciting that we can finally see this transformation in action,” said Peng. “It tells us that many of these UCDs are visible fossil remnants of ancient dwarf galaxies in galaxy clusters, and our results suggest that there are likely many more low-mass remnants to be found.”

The research is published in the journal Nature.

Topics

Tech News

Georgina Torbet

Space Writer

Georgina has been the space writer at Digital Trends space writer for six years, covering human space exploration, planetary…

Space

How astronomers used James Webb to detect methane in the atmosphere of an exoplanet

An artists rendering of a blue and white exoplanet known as WASP-80 b, set on a star-studded black background. Alternating horizontal layers of cloudy white, grey and blue cover the planets surface. To the right of the planet, a rendering of the chemical methane is depicted with four hydrogen atoms bonded to a central carbon atom, representing methane within the exoplanet's atmosphere. An artist’s rendering of the warm exoplanet WASP-80 b whose color may appear bluish to human eyes due to the lack of high-altitude clouds and the presence of atmospheric methane identified by NASA’s James Webb Space Telescope, similar to the planets Uranus and Neptune in our own solar system.

One of the amazing abilities of the James Webb Space Telescope is not just detecting the presence of far-off planets, but also being able to peer into their atmospheres to see what they are composed of. With previous telescopes, this was extremely difficult to do because they lacked the powerful instruments needed for this kind of analysis, but scientists using Webb recently announced they had made a rare detection of methane in an exoplanet atmosphere.

Scientists studied the planet WASP-80 b using Webb's NIRCam instrument, which is best known as a camera but also has a slitless spectroscopy mode which allows it to split incoming light into different wavelengths. By looking at which wavelengths are missing because they have been absorbed by the target, researchers can tell what an object -- in this case, a planetary atmosphere -- is composed of.

Space

This peculiar galaxy has two supermassive black holes at its heart

The billion-year-old aftermath of a double spiral galaxy collision, at the heart of which is a pair of supermassive black holes.

As hard as it is to picture, with billions or even trillions of galaxies in the universe, entire galaxies can collide with each other. When that happens, one galaxy can be destroyed or the two can merge into one. But even in the case of galaxy mergers, the effects of the collision are often visible for billions of years afterward.

That's shown in a recent image taken by the Gemini South observatory, which shows the chaotic result of a merger between two spiral galaxies 1 billion years ago.

Space

James Webb captures a gorgeous stellar nursery in nearby dwarf galaxy

This new infrared image of NGC 346 from NASA’s James Webb Space Telescope’s Mid-Infrared Instrument (MIRI) traces emission from cool gas and dust. In this image blue represents silicates and sooty chemical molecules known as polycyclic aromatic hydrocarbons, or PAHs. More diffuse red emission shines from warm dust heated by the brightest and most massive stars in the heart of the region. Bright patches and filaments mark areas with abundant numbers of protostars. This image includes 7.7-micron light shown in blue, 10 microns in cyan, 11.3 microns in green, 15 microns in yellow, and 21 microns in red (770W, 1000W, 1130W, 1500W, and 2100W filters, respectively).

A gorgeous new image from the James Webb Space Telescope shows a stunning sight from one of our galactic neighbors. The image shows a region of star formation called NGC 346, where new stars are being born. It's located in the Small Magellanic Cloud, a dwarf galaxy that is a satellite galaxy to the Milky Way.

The star-forming region of the Small Magellanic Cloud (SMC) was previously imaged by the Hubble Space Telescope in 2005, but this new image gives a different view as it is taken in the infrared wavelength by Webb instead of the optical light wavelength used by Hubble.