X-Ray Vision

If you actually had the ability to see X-Rays, the world around you would look pretty boring.  Actually it would be invisible, since nothing around you gives off X-rays.  You might be able to see an imaging device if you live or work near a medical office, but that’s about it.  If you looked at the night sky, you would see many interesting sources of X-Ray light, mostly from active black holes in our own galaxy and beyond.  Recently a high-resolution scan of the Andromeda Galaxy revealed a plethora of sources, showing where black holes and neutron stars are feeding in our closest neighbor galaxy.

NASA’s Nuclear Spectroscope Telescope Array, or NuSTAR, has imaged a swath of the Andromeda galaxy — the nearest large galaxy to our own Milky Way galaxy. Credit: NASA/JPL-Caltech/GSFC

Using NASA’s Nuclear Spectroscope Telescope Array (NuSTAR), astronomers have discovered a population of 40 X-Ray binaries in Andromeda, where a black hole or Neutron star is feeding on a stellar companion.

“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, Maryland, who presented the results at the 227th meeting of American Astronomical Society in Kissimmee, Florida. “We can then use this information to deduce what’s going on in more distant galaxies, which are harder to see.”

Because Andromeda, M31, is the closest large galaxy to our own, we can study it’s properties to learn more about how distant galaxies behave.  We also are seeing Andromeda in the present epoch of the universe, giving us a baseline for how spiral galaxies behave now and allowing us to compare the properties to spiral galaxies from the distant past.  Since Andromeda is only 2.5 Million light years away, we are viewing it as it was 2.5 Million years ago, which is like a second to a human being, since astronomical time is so vast.

In an X-Ray binary system, two massive stars have been orbiting each other for a long time, until one of them dies and becomes a black hole or neutron star.  Since the other star is still in it’s main sequence or Red Giant phase, it’s material can be sucked up by the denser companion.  This accretion of material produces incredibly hot gas that can be seen as X-Rays across the Universe.

All of this work is important, as it teaches us how the early universe evolved into the galaxies we see today. “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 of NASA Goddard, the principal investigator of the NuSTAR Andromeda studies.

NuSTAR will continue to probe the depths of Andromeda and other galaxies, in order to pinpoint how the X-Ray sources have behaved throughout the history of the universe.


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