NuSTAR’s new view of Andromeda’s X-ray binaries

January 5, 2016

NASA’s Nuclear Spectroscope Telescope Array, or NuSTAR, has captured a new image of the Andromeda galaxy that can help scientists better understand the role of stellar black holes and neutron stars in shaping early galaxy formation processes. The results of this research were presented this morning by Daniel Wik of NASA Goddard Space Flight Center at the 227th meeting of the American Astronomical Society in Kissimmee, Florida.

NuSTAR’s scan of a portion of the Andromeda galaxy captured 40 X-ray binary star systems. In these star systems, a donor star sheds matter into its stellar companion, called the accretor, which is a neutron star or black hole. Material falling from the donor star into the gravitational pull of the accretor is heated to such high temperatures that enormous amounts of gravitational potential energy are released as X-rays. NuSTAR’s powerful lens can detect the faintest of these high-energy X-ray binary star systems, even in the Andromeda galaxy, located 2.5 million light-years away. Studying Andromeda’s binaries allows astronomers to differentiate whether companion accretors are black holes or neutron stars and thus better understand the total population of binaries in a galaxy.

“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’s Goddard Space Flight Center in a press release issued by JPL earlier today. “We can then use this information to deduce what’s going on in more distant galaxies, which are harder to see.”

While both NuSTAR and the older Chandra X-ray Observatory scan X-ray energies, one isn’t meant to replace the other but rather, work together to provide astronomers with the most detailed pictures of the universe possible. NuSTAR captures high-energy X-ray views ranging from 7 to 25 kilo-electron volts, whereas Chandra captures low-energy X-ray views ranging from 0.5 to 2 kilo-electron volts. To drive home this point, Dr. Vik likened NuSTAR and Chandra to cops and detectives arriving on a crime scene.  Chandra (the cops in this scenario) identify the crime, as NuSTAR (the detectives) can dig a little deeper to figure out the story.

NuSTAR’s new views of Andromeda will help researchers explore the hypothesis that X-ray binaries may have heated intergalactic gas during the early formation of the universe.

“We have come to realize in the past few years that it is likely the 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. Observations of local populations of stellar-mass black holes and neutron stars with NuSTAR allow us to figure out just how much power is coming out from these systems,” said Ann Hornschemeier, principal investigator of NuSTAR’s Andromeda research.

The research also reveals potential differences between early star formation in Andromeda compared to our Milky Way.