Nature: Clues emerge in mystery of flickering quasars

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MargaritaMc
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Nature: Clues emerge in mystery of flickering quasars

Postby MargaritaMc » Mon Jul 31, 2017 7:24 pm

http://www.nature.com/news/clues-emerge-in-mystery-of-flickering-quasars-1.22376
Clues emerge in mystery of flickering quasars
Some of the Universe's most luminous objects have disappeared much faster than expected.

Some of the brightest objects in the Universe — quasars — are vanishing rapidly. Astronomers now think that they understand this mysterious behaviour¹, ² and the answer could help them to explain how galaxies such as the Milky Way evolve.

Quasars are supermassive black holes at the centres of galaxies fed by huge quantities of gas that shine across the visible Universe. Astronomers have long thought that quasars persist for millions of years before dimming slowly over tens of thousands of years. But in 2014, Stephanie LaMassa, an astronomer now at the Space Telescope Science Institute in Baltimore, Maryland, discovered a quasar that seemed to disappear in less than ten years³. That’s a blink of an eye, astronomically speaking.

Researchers struggled to explain the oddity. Perhaps a massive dust cloud passed in front of the quasar’s bright beacon and momentarily blocked its light. Or maybe a star passed too close to the black hole and was rapidly torn apart, causing a bright flare that scientists mistook for a quasar. It seemed physically impossible that such a bright object could fade in such a short time.

The discovery set in motion the hunt for more of these ‘changing-look’ quasars. The search has identified dozens of these mysterious beasts, some of which have dimmed more dramatically than the first. The two studies published this month on the preprint server arXiv suggest that these quasars blaze out of existence because the amount of gas and dust flowing through their accretion disks — the swirl of hot matter that encircles a black hole — drops dramatically. In effect, the black hole starves.


1. Sheng, Z. et al. Preprint at https://arxiv.org/abs/1707.02686 (2017).

2. Hutsemékers, D. et al. Preprint at https://arxiv.org/abs/1707.05540 (2017).

3.THE DISCOVERY OF THE FIRST "CHANGING LOOK" QUASAR: NEW INSIGHTS INTO THE PHYSICS AND PHENOMENOLOGY OF ACTIVE GALACTIC NUCLEI
Stephanie M. LaMassa, Sabrina Cales et al

Published 2015 February 20

The Astrophysical Journal, Volume 800, Number 2
http://iopscience.iop.org/article/10.1088/0004-637X/800/2/144/meta
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
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Ann
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Re: Nature: Clues emerge in mystery of flickering quasars

Postby Ann » Tue Aug 01, 2017 4:06 am

Hanny's Voorwerp, a quasar ionization echo.
Photo: Hubble.

Very interesting, Margarita, but we have seen hints of rapidly disappearing quasars before. Hanny's Voorwerp is a good example. It is an ionized cloud that glows from the energy it received from a quasar in a nearby galaxy. But the quasar is now gone, and only its ionizing echo remains as Hanny's Voorwerp.

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Re: Nature: Clues emerge in mystery of flickering quasars

Postby neufer » Tue Aug 01, 2017 12:55 pm

MargaritaMc wrote:
http://www.nature.com/news/clues-emerge-in-mystery-of-flickering-quasars-1.22376
Clues emerge in mystery of flickering quasars

Quasars are supermassive black holes at the centres of galaxies fed by huge quantities of gas that shine across the visible Universe. Astronomers have long thought that quasars persist for millions of years before dimming slowly over tens of thousands of years. But in 2014, Stephanie LaMassa, an astronomer now at the Space Telescope Science Institute in Baltimore, Maryland, discovered a quasar that seemed to disappear in less than ten years. That’s a blink of an eye, astronomically speaking.
Ann wrote:
Very interesting, Margarita, but we have seen hints of rapidly disappearing quasars before. Hanny's Voorwerp is a good example. It is an ionized cloud that glows from the energy it received from a quasar in a nearby galaxy. But the quasar is now gone, and only its ionizing echo remains as Hanny's Voorwerp.

If Voorwerpjes were powered by quasars that totally disappeared in less than ten years time [ :!: ] one would expect to see an extremely sharp cutoff line in their "green" oxygen emissions.
Art Neuendorffer

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Re: Nature: Clues emerge in mystery of flickering quasars

Postby Ann » Tue Aug 01, 2017 3:05 pm

Good point, Art, and sorry for "diminishing" your post, Margarita!

It's great to have you back! :D

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Re: Nature: Clues emerge in mystery of flickering quasars

Postby MargaritaMc » Tue Aug 01, 2017 9:07 pm

Ann wrote:Good point, Art, and sorry for "diminishing" your post, Margarita!

It's great to have you back! :D

Ann

¿"Diminishing "? :?: I was simply posting an article about some research that the journal Nature thought worth reporting on!

And, yes, Art, that was a good point.
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
— Dr Debra M. Elmegreen, Fellow of the AAAS


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