Sloan Digital Sky Survey | 2016 Jan 08
You might think that astronomers could easily tell the difference between a black hole and a white dwarf – but nature can be deceptive.
[c][attachment=0]liers.jpg[/attachment][/c][hr][/hr]Astronomers from the Sloan Digital Sky Survey (SDSS) this morning announced the results of a new study that reveals the true origin of puzzling light from nearby galaxies. Results were presented at the 227th meeting of the American Astronomical Society in Kissimmee, Florida.
“We now know that white dwarfs, not central black holes, explain these observations,” says Francesco Belfiore, the lead author of the study and a graduate student at the University of Cambridge. “Because we know that white dwarfs are to blame, we are much closer to understanding how galaxies retire from the star-formation business.”
To solve the mystery, Belfiore’s team looked at the thin interstellar gas that lies between stars in nearby galaxies. They used information from the emission lines of the spectra of that hot, glowing gas to decode what energy source lights it up. Understanding the origin of these emission lines is far from straightforward. In particular, astronomers have long been puzzled by the energy source for a particular state of gas in galaxies: The source must be hotter than newly formed stars but cooler than the radiation from a violently accreting black hole, like a quasar.
The leading theory used to be that this gas was lit by a wimpy active galactic nucleus, which is only accreting very small amounts of gas. This idea was supported by the fact that nuclear regions of many galaxies show such Low-Ionization Nuclear Emission-line Regions, which were therefore called LINERs. ...
With the extensive mapping of low-ionization emission-line regions outside of the nuclei of galaxies, far removed from central supermassive black holes, but close to newly born white dwarfs, the ‘N’ for ‘nuclear’ in the LINER acronym must disappear.
The truth, then, is this: many galaxies are LIERs.