To truly understand galaxies, you need to understand how the supermassive black holes at their center work. And that’s often easier said than done. Thankfully, we do have many tools at our disposal, and one of them has now provided a new look into some hidden gems.
The supermassive black holes at the center of IC 3639 and NGC 1448 have an annoying thing in common: Both are shrouded in thick clouds of gas that makes studying them incredibly tricky. But not for NuSTAR (Nuclear Spectroscopic Telescope Array) – NASA's high-energy X-ray observatory is perfectly equipped to pierce the cloud cover.
The galaxies are part of two separate but complementary studies. The analysis of IC 3639 was led by Peter Boorman from the University of Southampton, while NGC 1448 was studied by Ady Annuar from the University of Durham, who presented the findings at the American Astronomical Society's 229th meeting in Texas.
Although hidden from most telescopes, the supermassive black holes in these two galaxies are generating a lot of light and are thus dubbed "active galactic nuclei" (AGNs), as they significantly affect the core of the galaxies. AGNs can be very different from each other depending on how they are obscured by gas.
"Just as we can't see the sun on a cloudy day, we can't directly see how bright these active galactic nuclei really are because of all of the gas and dust surrounding the central engine," Boorman said in a statement.
NuSTAR was able to provide confirmation that there was indeed an AGN within IC 3639, which is located 170 million light-years from Earth, and has given the most accurate measurement of its luminosity. For NGC 1448, only 38 million light-years away, NuSTAR has detected X-rays reflected on the thick gas clouds.
Until now, we couldn’t see these two giants because they are not facing us, but instead are on their side. Their light comes to us reflected, which is why they have been able to keep their mystery for so long.
"These black holes are relatively close to the Milky Way, but they have remained hidden from us until now," added Annuar. "They're like monsters hiding under your bed."
Astronomers have also found a large population of very young stars in NGC 1448, formed at the same time the black hole began feeding. This is very important in understanding how galaxies evolve, as it is believed that there’s a feedback mechanism between star formation and supermassive black holes, and these observations could provide a lot more information to clarify what goes on in these galaxies.