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An international team of astronomers, led by astrophysicist Francesco Tombesi, at NASA’s Goddard Space Flight Center in Greenbelt, Maryland has discovered what causes galaxies to acquire large bulges in their centers: outflows from supermassive black holes that lie in the bulges.
A black hole is an invisible tiny “hole” in space. It is a former star that collapses on its own gravity, which is so strong that nothing, even light, can escape — hence the name “black hole,” coined by physicist John Wheeler in 1967. Black holes feed on objects surrounding them: nebulas, planetary objects, light — anything. Whatever enters a black hole gets spewed out eventually in the form of jets of x-rays and radiation. These jets allow astronomers to view the black hole’s spectrum, which tells them what elements the black hole swallowed and spat out.
Over the years, astronomers have learned that galaxies, even our very own Milky Way, contain supermassive black holes — black holes that are really, really big — at their centers. Surrounding the supermassive black holes are large clouds of gas, where stars are born left and right. The gravity of these black holes also attract fast moving stars, creating the galaxies’ bulges, which then grow large. As to how this is has puzzled astronomers for years.
Tombesi and his colleagues have encountered a distinct kind of “outflow” from the clouds of gas after studying the spectrographs of forty-two galaxies from the All-Sky Slew Survey Catalog from NASA’s Rossi X-Ray Timing Explorer Satellite. In spectroscopy, astronomers look at absorption spectra — essentially pictures of the electromagnetic spectrum — which present light absorbed from the light sources, such as stars, nebulas, galaxies, and, in this case, black holes. With the absorption spectra, astronomers can gauge the light source’s composition of elements by looking for any black lines that vertically cross the spectrum.
While researching the spectra of x-rays from the forty-two galaxies, Tombesi and the team learned that the supermassive black holes absorbed fluorescent iron. They then found out that 40% of these galaxies had such an outflow flow, which suggests that the outflow is common in black holes at the center of galaxies. The x-rays’ wavelengths were shorter than their normal length, indicating that the galaxies were blueshifted (i.e. moving towards us). This outflow was dubbed “ultra-fast outflows,” or UFOs, by Tombesi according to NASA.
“They have the potential to play a major role in transmitting feedback effects from a black hole into the galaxy at large,” Tombesi says in NASA’s press release.
Ultimately, he and his colleauges learned that UFOs halt supermassive black holes’ growth by taking away the mass it would potentially eat. Furthermore, UFOs can slow down or even completely discontinue star formation in the galactic centers by removing gas from the galactic bulge.
Tombesi and his team hope to further study UFOs and their development with Japan’s Astro-H X-ray telescope, which is scheduled to be launched in 2014.