It's not always the brightest or most immense bodies in the cosmos that hide the most mysteries. Shrouded by the ghost glow of dwarf galaxies could possibly be secrets that illuminate galaxy formation — and the enigma of dark matter.
Scientists believe that 13.7 billion years ago, extremely dense matter heated to almost as many billions of degrees expanded through the void of space in what became known as the infamous Big Bang theory. A related theory states that soon after this immense event, smaller celestial objects and clusters joined to form galaxies. Unfortunately, evidence for galactic mergers occurring on a small scale is rare. It is thought that independent dwarf galaxies far enough from any larger galaxies that would hold gravitational sway over them could provide a microcosm of the early Milky Way.
Dwarf galaxies are notoriously difficult to observe. The only ones visible in the night sky to non-superpowered human eyes without the lens of a telescope are the Magellanic Clouds that orbit our galaxy. Telescopes powerful enough to detect their dim glow have mostly discovered the celestial carnage of larger galaxies cannibalizing dwarfs in a close enough vicinity.
Astrophysicist Sabrina Stierwalt of the National Radio Astronomy Observatory in Charlottesville, VA has finally been able to shed more light on them, which could open the portal to answering bigger questions.
"The existence of dwarf-only groups suggests that, given time, hierarchical merging will turn some of these groups into isolated intermediate-mass galaxies," she stated in a study published in Nature Astronomy. "Based on the total stellar masses of the [dwarf] groups, and allowing for some additional conversion of gas into stars, these groups could produce isolated galaxies."
The seven clusters of dwarf galaxies Stierwalt's team studied each contain three to five individual galaxies, each of which is anywhere from ten to thousand times more diminutive than the Milky Way. What the researchers believe is that the dwarfs are gravitationally bound and will eventually merge.
They also theorize that dark matter is the invisible force that has gravitational influence over stars and the gases and dust that comprise star stuff — which is why it is considered to be the so important in demystifying how galaxies such as the Milky Way emerged in the early universe. Scientists conclude that there is just not enough gravitational pull in the space for galaxies to have come into being without the force exerted by dark matter.
Dark matter is believed to be the fabric of 95% of the universe, meaning visible matter supposedly accounts for only a fragment of what is really out there. Dwarf galaxies are assumed to have even more dark matter than larger ones because of their tendency to stay in clusters, and even though they tend to be clear of debris because they have ceased giving birth to new stars, the answer to exactly what part dark matter had to play in their emergence is still in the shadows.
While dwarf galaxies provide tantalizing mines for dark matter and astronomers continue trying to seek out evidence of it with telescopes sensitive to the gamma rays its particles are thought to emit, the invisible (at least for now) continues to elude science.