Astronomers say the Milky Way may be catapulting stars into its outer halo

Although powerful, the Milky Way and galaxies of similar mass are not without scars that tell turbulent stories. The University of California, Irvine astronomers, and others have shown that clusters of supernovae can cause scattered and eccentric orbiting suns to rise in outer star halos, overturning commonly held notions of how star systems have formed and evolved during billions of years.

The hyperrealistic and cosmologically self-consistent computer simulations of the Feedback in Realistic Environments 2 project allowed scientists to model interruptions in galactic rotations that would otherwise be ordered. The team’s work is the subject of a study published today in the Monthly notices from the Royal Astronomical Society.

“These highly accurate numerical simulations have shown us that it is likely that the Milky Way galaxy has been launching stars into circgalactic space on exits triggered by supernova explosions,” said lead author James Bullock, dean of the UCI College of Physical Sciences. and professor of physics and astronomy. . “It is fascinating, because when multiple large stars die, the resulting energy can eject gas from the galaxy, which in turn cools, causing new stars to be born.”

Bullock said that the diffuse distribution of stars in the stellar halo that extends far beyond a galaxy’s classic disk is where the system’s “archaeological record” exists. Astronomers have long assumed that galaxies assemble for long periods of time as groups of smaller stars enter and are dismembered by the larger body, a process that ejects some stars into distant orbits. But the UCI team proposes “supernova feedback” as a different source for up to 40 percent of these external halo stars.

Lead author Sijie Yu, Ph.D. from UCI. Physics candidate said the findings were made possible in part by the availability of a powerful new set of tools.

“FIRE-2 simulations allow us to generate movies that make it look like you’re looking at a real galaxy,” he said. “They show us that as the center of the galaxy rotates, a bubble fueled by supernova feedback develops with stars forming at its edge. It appears that the stars are being ejected from the center.”

Bullock said he did not expect to see such an arrangement because stars are balls so tight and incredibly dense that they are generally not subject to being moved relative to the background of space. “Instead, what we are witnessing is that the gas is pushed,” he said, “and that gas subsequently cools and causes the stars to come out.”

The researchers said that while their conclusions have been drawn from simulations of galaxies that form, grow, and evolve to this day, there is actually a fair amount of observational evidence that stars are forming at departures from galactic centers. to their halos.

“In plots comparing data from the European Space Agency’s Gaia mission, which provides a three-dimensional velocity graph of stars in the Milky Way, with other maps showing stellar density and metallicity, we can see structures similar to those produced by the outflow stars in our simulations, “Yu said.

Bullock added that mature, heavier, metal-rich stars like our sun rotate around the center of the galaxy at a predictable speed and trajectory. But low-metallic stars, which have undergone fewer generations of fusion than our sun, can be seen spinning in the opposite direction.

He said that over the lifetime of a galaxy, the number of stars produced in supernova bubble outlets is small, about 2 percent. But during parts of the galaxy stories when starburst events are booming, up to 20 percent of stars are formed this way.

“There are some current projects looking at galaxies that are considered very ‘explosive’ at the moment,” Yu said. “Some of the stars in these observations also appear suspiciously as if they were pushed out of the center.”