In an era when the James Webb Space Telescope is imaging objects from the beginnings of the universe billions of light years away, an astronomer from the University of Victoria has found some of the oldest galaxies are practically neighbours.
Simon Smith, a PhD student at UVic and Nanaimo Astronomy Society’s next guest speaker, specializes in finding extremely tiny, faint and old galaxies and studies how the behaviour of stars within them points to the presence of invisible dark matter.
These ultra-faint dwarf galaxies, comprised of maybe a few hundred to a few thousand stars, produce little light, but Smith says they are critically important to theories about how the universe behaves. They appear to be surrounded by huge clouds of dark matter which comprise an estimated 80 per cent of all mass in the universe.
“[Tiny dwarf galaxies] started forming, basically, at the start of the universe, but then haven’t really done anything much else since then. This is one of the really interesting things about them,” Smith said.
He said the Milky Way galaxy also began forming at the beginning of the universe, but it continued to pull in more mass, stars and dust, "whereas these tiny little galaxies formed but then nothing else really ever happened to them."
He said galaxies tend to form and grow by gravitationally pulling in other smaller galaxies or by drawing in mass in the form of gases and dust that become the raw materials to make new stars internally.
“These little tiny galaxies just don’t have the kind of gravitational dominance to pull in new gas, which then means that they can’t form any new stars,” he said.
It’s unclear why those tiny clusters of stars haven’t grown for billions of years, but they do offer a way to study dark matter. Smith said galaxies such as the Milky Way with its estimated 100 billion stars, and tiny dwarf galaxies are surrounded – in a way encapsulated – by huge volumes of dark matter that becomes more dense the closer it is to a galaxy’s core.
“The Milky Way … is sitting at the centre of a huge massive cloud of dark matter that extends way, way, way farther out than the visible light of the Milky Way and, in the same vein, these little tiny dwarf galaxies that might only be 1,000 stars or 100 stars, are little groups of stars that are sitting in a much larger cloud of dark matter,” he said.
Because dark matter becomes more dense near the centre of galaxies, the densest part of the dark matter is where the galaxy is located.
“So, rather than the dark matter drawing stars away from the galaxy, the dark matter’s actually almost acting like an insulation. It’s this big cloud of material that’s keeping the centre of this whole system really quite gravitationally stable. There’s a lot of mass there that we can’t see and it’s kind of helping keep all these stars encapsulated within,” Smith said.
In his presentation, he will share how he discovers new ultra faint dwarf galaxies and measures how much dark matter surrounds them. Ursa Major III/Unions 1, the faintest system yet discovered, is just about 30,000 light years from Earth and actually orbits the Milky Way. To give an idea of how relatively close Ursa Major III/Unions 1 is, the Milky Way’s diameter is about 105,700 light years, whereas the James Webb Space Telescope sees the light from objects billions of light years away.
“The tiny little ultra dwarf galaxies are kind of a different story,” Smith said. “We see them today in the local universe, just floating around the Milky Way, but based on the way that they look, we can tell that they’ve been relatively unchanged for the last 10-12 billion years. They’re more like fossils. They’re little chunks of galaxy that have all these markers and features that tell us they’re from the beginning of the universe.”
Smith will present in person at Nanaimo Astronomy Society’s meeting at Beban Park Social Centre on Thursday, April 24, at 7 p.m.
To learn more about Nanaimo Astronomy Society and events, visit www.nanaimoastronomy.com.
