Home / Science / We may finally know the origins of a mysterious stream that surrounds the Milky Way

We may finally know the origins of a mysterious stream that surrounds the Milky Way

Like Jörmungandr that surrounds the Earth, the entire galaxy is also surrounded. A huge, high-velocity flow of gas is enveloped most of its way around the Milky Way, at a distance of about 200,000 light years.

We know where it comes from, more or less. It has been connected quite definitively with the Large and Small Magellanic Clouds, dwarf galaxies that orbit around and will eventually be cannibalized by the Milky Way. This gives the name to the cosmic serpent: the Magellanic flux.

However, although the Magellanic Flux chemically corresponds to the Magellanic Clouds, there is one aspect that has puzzled astronomers for decades: its mass. There is up to about a billion solar masses of gas in that stream, and the models couldn̵

7;t explain why the two satellite galaxies were losing so much.

“That’s why,” explained astronomer Elena D’Onghia of the University of Wisconsin-Madison, “we have come up with a new solution that is excellent at explaining the mass of the flux.”

According to their new model, the gas does not come from the Magellanic Clouds themselves. Rather, it is extracted from their galactic halos – gigantic clouds of gas and plasma that envelop most galaxies.

magellanic flowA full sky view of the Magellanic stream. (D. Nidever et al., NRAO / AUI / NSF, A. Mellinger, Leiden-Argentine-Bonn Survey, Parkes Observatory, Westerbork Observatory, Arecibo Observatory)

The dance of the Magellanic Clouds and the Milky Way is interesting, with the two satellite galaxies orbiting each other, and then together orbiting the larger Milky Way. This complex interaction is deforming all three galaxies and the Milky Way is thought to be destroying the Magellanic Clouds.

Previously, the interruption of the tides from the Milky Way was thought to have extracted the Magellanic Current as the two dwarf galaxies entered the Milky Way’s sphere of gravitational influence. But this model could only represent about 10 percent of the observed mass of the flow.

“The flow is a 50-year puzzle,” said astronomer Andrew Fox of the Space Telescope Science Institute. “We have never had a good explanation of its origin. The really exciting thing is that we are now getting close to an explanation.”

The novelty here is recent research that suggests that the Magellanic Clouds are massive enough to have their own halos.

The team, led by astronomer Scott Lucchini of the University of Wisconsin-Madison, conducted their own simulations of the Magellanic Clouds orbiting the Milky Way.

They calculated that the halo of hot gas around the Magellanic Clouds – dubbed the Magellanic Crown – would drastically alter the way the Magellanic Flow formed.

According to their simulations, the training was a two-step process. The first phase took place long before the Magellanic Clouds were captured by the Milky Way, but when they were still orbiting each other. The Large Magellanic Cloud has stolen a lot of material from the Small Magellanic Cloud, losing a small amount of gas.

This process took about 5.7 billion years, resulting in a halo of gas valued at about 3 billion solar masses that enveloped the two galaxies as they were captured by the Milky Way. At this point, gravitational forces have planted the seed for the Magellanic Stream, with the halo providing about 10-20 percent of its final mass.

animation mcSimulation animation. (Elena D’Onghia and Scott Lucchini / University of Wisconsin-Madison)

In the second phase, after the two galaxies were captured in the orbit of the Milky Way, the interactions with our galaxy’s gravity and the galactic halo pulled out a fifth of the Magellanic Corona mass to create the rest of the flow.

According to the team’s simulations, this two-stage sequence of events mimics the structure and mass of the Magellanic Stream, including the branch of the stream called the Leading Arm that orbits in front of the two dwarf galaxies.

We have yet to directly detect Magellan’s Crown, but the team’s model provides the toolkit to do so.

The gas cloud should contain highly ionized carbon and silicon states. Using the Hubble Space Telescope, we can look at distant quasars through Magellan’s Corona and analyze their light to see if it has traveled through significant clouds of these materials on its way to the Solar System.

“The lines of sight of the quasars in the background offer the possibility of unambiguous detections of the Magellanic Corona because they are not contaminated by the interstellar material of the Large Magellanic Cloud,” the researchers wrote in their paper.

The research was published in Nature.

Source link