A NASA observatory has zoomed-in on the Milky Way's galactic big "sister" and spied 40 X-ray binaries, objects that are believed to be a key factor in the heating of interstellar gases and therefore major drivers of galaxy evolution.
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NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, is a space telescope capable of detecting some of the highest-energy X-rays the universe can generate and when spying on the Andromeda Galaxy (M31), NuSTAR astronomers weren't disappointed.
Andromeda, like the Milky Way, is a more massive spiral galaxy located around 2.5 million light-years away. This may sound like a long way, but Andromeda is our nearest spiral galaxy neighbor. Its relative closeness means missions like NuSTAR can study Andromeda's X-ray emissions in great detail and some new findings were presented today (Jan. 5) at the 227th meeting of American Astronomical Society in Kissimmee, Fla.
"Andromeda is the only large spiral galaxy where we can see individual X-ray binaries and study them in detail in an environment like our own," said Daniel Wik, of NASA Goddard Space Flight Center in Greenbelt, Md. "We can then use this information to deduce what's going on in more distant galaxies, which are harder to see."
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X-ray binaries consist of two stellar objects - typically one star and a stellar remnant, like a neutron star or black hole. As the pair orbit one another, plasma from the star is dragged away by the compact remnant As this plasma falls toward the black hole or neutron star, the gas undergoes rapid and intense heating - a process that can generate high-energy X-rays.
Now, using NuSTAR observations of a nearby galaxy, astronomers can gain a better understanding as to whether the X-ray binaries are composed mainly of black holes or neutron stars and how their radiation compares with the average X-ray emissions from more distant galaxies. This, in turn, can help us understand the heating influence X-ray binaries have on their galactic environment and how the Andromeda galaxy compares with our own.
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"We have come to realize in the past few years that it is likely the lower-mass remnants of normal stellar evolution, the black holes and neutron stars, may play a crucial role in heating of the intergalactic gas at very early times in the universe, around the cosmic dawn," said Ann Hornschemeier, also from NASA Goddard and principal investigator of the NuSTAR Andromeda studies. "Observations of local populations of stellar-mass-sized black holes and neutron stars with NuSTAR allow us to figure out just how much power is coming out from these systems."
"Studying the extreme stellar populations in Andromeda tells us about how its history of forming stars may be different than in our neighborhood," added Fiona Harrison, of Caltech in Pasadena, Calif., and principal investigator of the NuSTAR mission.