Lurking in the depths of a galaxy, hidden from human eyes, lie millions of monsters. They could swallow you up in an instant, sealing you off from the outside world and devouring you atom by atom. This sounds like your typical Hollywood monster movie, but with millions of black holes hidden throughout the galaxy, its more real than you might think. Supermassive black holes, the largest ones that reside at the centers of galaxies, are much easier to see. They are devouring gas and dust rapidly, resulting in bright emission across the electromagnetic spectrum, especially in x-rays. For many galaxies, the black hole can be obscured by thick clouds of dust, but with improvements in technology we can peer into the thick clouds to see the monster within.
Using NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) satellite observatory, astronomers have seen high energy x-ray emission from five new black holes that were previously obscured by the dust in their host galaxy. Looking at nine candidate galaxies that had large amounts of activity in their cores, the telescope was able to peer into the dust and see the x-ray signature that tells us a black hole is feeding within.
Although there are only 5 new detections, the understanding that the universe is homogeneous, meaning it looks roughly the same no matter which direction we observe, suggests that there should be millions of new supermassive black holes that have previously been hidden from view. Using NuSTAR or a larger telescopic survey should reveal many more hidden monsters.
I would call it a big surprise, but it seems logical that we should find a supermassive black hole at the core of most large galaxies, if not all. This new discovery gives us more data in the understanding of how galaxies form, grow, evolve, and eventually die. Someday we will have a clear picture of the largest inhabitants of the vast dark cosmos.