First look images made by the new Vera C. Rubin Observatory in Chile confirm the detection of a massive stellar stream around Messier 61, a grand spiral galaxy located some 53 million light years away.
The images demonstrate Rubin’s unprecedented ability to detect galactic stellar streams in a way that has heretofore eluded astronomers. And they are just a preview of the unique 8.4-meter telescope’s coming attractions, says the lead author of a paper detailing the images in Research Notes of the American Astronomical Society.
This stream originated as a dwarf galaxy: about a hundred million times as bright as the Sun, lead author Aaron Romanowsky, professor of physics and astronomy at San José State University in California, tells me via email. And the width and length of the stream are about ten thousand by 170 thousand light years, which exceeds the diameter of our own Milky Way Galaxy, he says.
The Rubin Observatory imaged the stream during the observatory’s main camera commissioning, currently underway atop a dark mountaintop in the deserts of northern Chile.
Faint objects such as the stream around M61, in the southern constellation of Virgo, become crystal clear with the Rubin telescope’s imaging.
It’s a basic prediction of modern astronomy that all galaxies should be surrounded by such streams, but except in a few cases, telescopes have not been powerful enough to see them, says Romanowsky.
Complex Interaction
One of the areas of the sky that Rubin targeted is the Virgo cluster, a grand collection of nearby galaxies, which can be seen in these images to be interacting in complex ways, says Romanowsky. The central region of M61, about 1500 light years across, is a complex region of gas and clumps of intense star formation in a mini spiral-like structure, he says.
Constant Accretion
Giant spiral galaxies like the Milky Way Galaxy constantly accrete dwarf galaxies that disrupt into stellar streams, the paper’s authors note.
As for how the stream in M61 compares with similar stellar streams in our own Milky Way?
Some twenty-five years ago, astronomers discovered a dwarf galaxy of the Milky Way, known as the Sagittarius Dwarf Elliptical Galaxy. This dwarf galaxy, which is still in the process of disrupting and being absorbed by our own galaxy, forms the Sagittarius Stream, similar to the stellar stream found in M61.
It’s thought to have had significant effects on our own galaxy; it’s even possible that it triggered the birth of our own solar system, says Romanowsky.
The gravitational interactions between dwarf galaxies and large spiral galaxies like our Milky Way are continually creating starbursts and stellar streams. In fact, M61 has long been known to harbor a ten-million-year-old galactic starburst in its center.
A Galactic Storm
This “galactic storm” or “starburst” represents the latest in a series of episodes over the past billion years, which funneled gas toward M61’s supermassive black hole at its center, says Romanowsky.
Why is this work important in understanding galaxy populations in general?
Our modern understanding of the cosmos is that it assembles hierarchically; under the influence of gravity bigger structures are built from smaller ones, says Romanowsky. Tidal streams such as the one in M61 are part of the invisible web of cosmic forces that support our very existence, with parts of the web now becoming visible through the Rubin Observatory, he says.
A Future Merger
We are hoping that future work with computational modeling of the stream’s orbit will help us understand how and when this dwarf galaxy was drawn into the larger spiral galaxy, and what the future outcome will be as it fully merges into M61, says Romanowsky.
The Bottom Line?
Our own Milky Way does not currently have such intense activity, but the archeological record of its stars shows similar episodes in its past, which could be due to the influence of the Sagittarius Stream, says Romanowsky.
