A team of scientists led by Dr Stephanie LaMassa of Yale Center for Astronomy & Astrophysics has identified the first changing look quasar, a gleaming object in deep space that appears to have its own dimmer switch.
This artist’s concept shows a changing look quasar. Image credit: Michael Helfenbein / Yale University.
First discovered as radio loud sources in the 1950s, quasars are cores of galaxies where a supermassive black hole is messily feeding.
Orbiting gas and dust whip around the black hole with such ferocity that they give off light in all wavelengths. The magnetic field of the powerful black hole traps particles from this spinning disk and expels them along its poles.
Astronomers see these polar fountains as gigantic jets in radio waves and X-rays.
Even across long distances, the cores of these galaxies shine like stars, which is why they were first given the description of quasi-stellar radio sources.
They reign as the most luminous objects in the entire Universe.
Until now, astronomers have been unable to study both the bright and dim phases of a quasar in a single source.
Dr LaMassa and her colleagues spotted a quasar that had dimmed by a factor of six or seven, compared with observations from a few years earlier.
“We’ve looked at hundreds of thousands of quasars at this point, and now we’ve found one that has switched off. This may tell us something about their lifetimes,” said Prof Megan Urry of Yale Center for Astronomy & Astrophysics, the senior author of a paper accepted for publication in the Astrophysical Journal (arXiv.org preprint).
The scientists noticed the object, catalogued as SDSS J015957.64+003310.5 (J0159+003 for short), during an ongoing probe of Stripe 82 – a 300 deg2 equatorial field of sky that was imaged over 10 times by the Sloan Digital Sky Survey from 2000 to 2008.
“This is like a dimmer switch. The power source just went dim. Because the life cycle of a quasar is one of the big unknowns, catching one as it changes, within a human lifetime, is amazing,” Dr LaMassa said.
Even more significant for astronomers was the weakening of the J0159+003’s broad emission lines. Visible on the optical spectrum, these broad emission lines are signatures of gas that is too distant to be consumed by a black hole, yet close enough to be excited by energy from material that does fall into a black hole.
The change in the emission lines is what told scientists that the black hole had essentially gone on a ‘diet,’ and was giving off less energy as a result.
That’s when the changing look quasar hit its dimmer switch, and most of its broad emission lines disappeared.
“Even though astronomers have been studying quasars for more than 50 years, it’s exciting that someone like me, who has studied black holes for almost a decade, can find something completely new,” Dr LaMassa said.
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Stephanie M. LaMassa et al. 2015. The Discovery of the First ‘Changing Look’ Quasar: New Insights into the Physics & Phenomenology of AGN. ApJ, accepted for publication; arXiv: 1412.2136
