Andromeda Galaxy: X-ray view

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  • Published: Jan 7, 2016
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Andromeda Galaxy: X-ray view

A better X-ray view

The best high-energy X-ray view yet of a portion of our nearest large, neighbouring galaxy, Andromeda has been captured by NASA's Nuclear Spectroscopic Telescope Array, NuSTAR. The mission revealed 40

The best high-energy X-ray view yet of a portion of our nearest large, neighbouring galaxy, M31, better known as Andromeda, has been captured by NASA's Nuclear Spectroscopic Telescope Array, NuSTAR. The mission revealed 40 "X-ray binaries", intense sources of X-rays comprising a black hole or neutron star feeding from a stellar companion.

The new data from NuSTAR will eventually allow astronomers to explain how these intriguing and highly energetic cosmic systems evolved in the universe. This, in turn, could reveal how important is their role in heating the intergalactic bath of gas and dust from which the first galaxies were formed.

"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," explains Daniel Wik of NASA Goddard Space Flight Center in Greenbelt, Maryland, USA. Wik presented details of the new observations to the colleagues at the 227th meeting of the American Astronomical Society in Kissimmee, Florida, in January. "We can then use this information to deduce what's going on in more distant galaxies, which are harder to see."

Sibling spiral

Andromeda, which lies about 2.5 million light-years from Earth, is often considered the bigger sibling of our own Milky Way galaxy; both of which are spiral systems, and is the only galaxy that can be visible to the naked eye on particularly dark, clear nights. Previously, NASA's Chandra X-ray Observatory, has obtained crisp images of Andromeda at lower X-ray energies than the high-energy X-rays detected by NuSTAR. But, now the combination of Chandra and NuSTAR observations has provided researchers with a powerful data set for homing in on the nature of the X-ray binaries within spiral galaxies.

Power systems

X-ray binaries always contain a living star and a companion dead star or a remnant formed from the explosion of a star much more massive than the Sun. Depending on the precise mass range of that remnant, the system will contain either a black hole or a neutron star. Then, given particular stellar circumstances, material from the companion star can spill over its outermost edges and then be trapped by the enormous gravitation field of the black hole or neutron star. Matter falling into such a field is heated to incredibly high temperatures and generates a huge release of X-rays.

The new view of a wide region of Andromeda has allowed Wik and colleagues to identify the fraction of X-ray binaries containing black holes rather than neutron stars, which they suggest, will help them unravel the demographic of these systems within a spiral galaxy as a whole.

"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," explains principal investigator Ann Hornschemeier of NASA Goddard. "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."

Related Links

AAS Abstracts, 2016, online: "A New Deep, Hard X-ray Survey of M31: Monitoring Black Hole and Neutron Star Accretion States in the X-ray Binary Population of Our Nearest Neighbor"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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