Herschel data links mysterious quasar winds to furious starbursts

December 7, 2017
This image is an artist's impression of a radio-loud quasar in a star-forming galaxy. The quasar is powered by the supermassive black hole at the galaxy's centre. As gas is drawn into an accretion disc around the black hole it heats to very high temperatures and radiates energy across the electromagnetic spectrum, preferentially in the direction of two powerful jets. In addition, the galaxy is making stars at a prolific rate of hundreds per year. For comparison, our Milky Way Galaxy makes 1-2 stars per year. Credit: ESA/C. Carreau

Astronomers have used ESA's Herschel Space Observatory to solve a decades-old mystery about the origin of powerful cool gas winds in the hot environs of quasars. The evidence linking these powerful winds to star formation in the quasar host galaxies may also help resolve the mystery of why the size of galaxies in the Universe appears to be capped.

Since their discovery in the 1960s quasars have provided a treasure trove of questions for astronomers to answer. These energetic sources – up to 10 000 times brighter than the Milky Way – are the nuclei of distant galaxies with supermassive black holes at their heart. As gas is pulled into an accretion disc towards the black hole it heats to very high temperatures and radiates energy across the electromagnetic spectrum from radio to X-rays – in this way the signature luminosity of the quasar is born.

For five decades, astronomers have studied the spectra of quasars to uncover the origin of the electromagnetic radiation they emit and to trace the path the light has traversed to reach us.

A valuable tool in understanding this journey are the in the quasars' radiation spectra. These lines indicate the wavelength ranges which have been absorbed as the radiation travelled from source to observer, giving clues to the material it passed through. Over time, the study of these lines has traced the composition of galaxies and gas clouds that lie between us and these distant luminous objects, but one set of absorption lines has remained unexplained.

Astronomers have observed absorption lines in many quasars that are indicative of absorption en route by cool gas with heavy metal elements like carbon, magnesium and silicon. The lines signal that the light has travelled through winds of cold gas travelling at speeds of thousands of kilometres per second within the quasars' host galaxies. Whilst knowledge that these winds exist is nothing new their origin, and why they are able to reach such impressive speeds, has remained an unknown.

Credit: ESA/Herschel/NASA/JPL-Caltech; acknowledgement T. Pyle & R. Hurt (JPL-Caltech)

Now, astronomer Peter Barthel and his PhD student Pece Podigachoski, both from the Groningen University Kapteyn Institute, together with colleagues Belinda Wilkes from the Harvard-Smithsonian Center for Astrophysics (USA) and Martin Haas at Ruhr-Universität Bochum (Germany) have shed light on the cold winds' origins. Using data obtained with ESA's Herschel Space Observatory the astronomers have shown, for the first time, that the strength of the metal absorption lines associated with these mysterious gas winds is directly linked to the rate of within the quasar host galaxies. In finding this trend the astronomers are able to say with some confidence that prodigious star formation within the host galaxy may be the mechanism driving these mysterious and powerful winds.

"Identifying this tendency for prolific star formation to be closely related to powerful quasar winds is an exciting find for us," explains Pece Podigachoski. "A natural explanation for this is that the winds are starburst driven and produced by supernovas – which are known to occur with great frequency during periods of extreme star formation."

This new connection not only solves one puzzle about quasars but may also contribute to unravelling an even bigger mystery: why does the size of galaxies observed in our Universe appear to be capped in practice, although not in theory.

"Aside from the question of which processes are responsible for the gas winds, their net effect is a very important topic in today's astrophysics," explains Peter Barthel. "Although theories predict that galaxies can grow very large, ultra-massive galaxies have not been observed. It appears that there is a process which acts as a brake on the formation of such galaxies: internal gas winds for example could be responsible for this so-called negative feedback."

Theory predicts that galaxies should be able to grow to masses a hundred times larger than any ever observed. The fact that there is a deficit of behemoths in the Universe implies that there is a process depleting galaxies' gas reserves before they are able to reach their full potential. There are two mechanisms likely to lead to this depletion of gas: the first is the supernova winds associated with starbursts, the second, the winds associated with the supermassive black hole at the heart of every quasar. Although both mechanisms are likely to play a role, the evidence of correlation between cold gas winds and star formation rate found by this team suggests that in the case of , star formation, which requires a steady supply of cold gas, may be the key culprit in sapping the galaxy of gas and supressing its ability to grow the next generation of .

"This is an important result for quasar science, and one that relied on the unique capabilities of Herschel," explains Göran Pilbratt, Herschel Project Scientist at ESA. "Herschel observes light in the far infrared and submillimetre enabling the detailed knowledge of the in the observed that was needed to make this discovery."

Explore further: Astrophysicists detect ultra-fast winds near supermassive black hole

More information: Peter Barthel et al. Starburst-driven Superwinds in Quasar Host Galaxies, The Astrophysical Journal (2017). DOI: 10.3847/2041-8213/aa7631

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Tuxford
1.4 / 5 (9) Dec 07, 2017
why does the size of galaxies observed in our Universe appear to be capped in practice, although not in theory.

The merger maniac can never understand that the source of his conundrum is that his fantasy model is directly inverted. That the core star at the center of galaxies is the source of matter growing the galaxy, not the sink. So he reaches for unlikely explanations to patch his fanciful world view — such as supernovae winds — in order to avoid mental instability. And mental instability and intellectual embarrassment is his key enemy.

Feedback. LOL. Yes feedback is involved in all processes, including the periodic instabilities in the growing core star, leading to explosive outbursts seeding the galaxy from within, not from without. Once the core grows from within into a super active monster, it is blowing so fiercely that the stars dissipate radially therefrom, shutting down further galactic growth, leaving a bare quasar shining brightly across the universe!
Jeffhans1
not rated yet Dec 07, 2017
Tuxford, we should be able to prove or disprove galaxy growth by observing galaxy mergers and rewinding the event backwards in simulators to see if the galaxies had to have grown during the event to match current observations. If simulations show that the results of mergers had no growth from the center and instead have lost mass to the black holes, that should end the debate one way or another.
Da Schneib
5 / 5 (1) Dec 07, 2017
Very interesting since this data resolves a long-standing debate over the lack of ultra-massive galaxies, strongly bolstering the argument that the gas is disturbed by supernovae caused by the starbursts, not by the supermassive black holes and associated quasar phenomena. The JWST will add its own data to this probably permanently resolving this debate, but the evidence for the starburst providing its own negative feedback is now very strong. This will affect models of galaxy dynamics from now on, I think.
RNP
5 / 5 (1) Dec 08, 2017
@Da Schneib
This will affect models of galaxy dynamics from now on, I think.

Indeed. In fact, nearly all recent models contain SF-feedback and all they will need to do is tune the models in accord with the paper's results. So, the effects will be almost immediate.
Tuxford
1 / 5 (4) Dec 08, 2017
You merger maniacs are rather suddenly jumping on the feedback bandwagon, as if you just discovered a new word that you don't fully comprehend. LaViolette's SQK physics is based on close-loop feedback systems being at the heart of the description of the sub-atomic particle, never mind for larger systems as well, such as galactic systems! LOL. That you don't really understand the implications of closed-loop systems dynamics is stunningly obvious to those few who truly do. For this reason, your comprehension of why new matter could suddenly emerge from the cores of stars will remain beyond your intellectual reach for the foreseeable future.
milnik
1 / 5 (4) Dec 08, 2017
Again it is a question of knowing the structure of the universe !!
In order to understand this structure more easily, we must admit that there is some substance in the universe from which matter is formed. It is AETHER, which the unethical scientists have rejected as something illogical and non-existent. This has shown that they are opponents of the entire spirituality of the university and that they do not know the laws of nature. This is about some quasi-winds, and there is a mess that is thought to be involved and the effects of black holes.
The sequence of formation of everything in the material-energy entity of the universe (MEEU): From Aether, through high vibrations, matter is formed in two "aggregate" states: "solid" -3kg particles and "liquid" -gluones
milnik
1 / 5 (3) Dec 08, 2017
Thus, as the first form of the celestial body, a magnetar (quark-gluon plasma) arises, and thereafter a quasar occurs when magnetic gases break down from the magnet and high energy waves and light are formed, resulting in a pulse or dual star, which converts into a neutron The star, which when it explodes, creates supernames from which atoms form, chemical elements, celestial bodies all the way to the galaxy.
The fact that scientists have discovered some jets of cold gases is a phenomenon when gluons are released from neutrons, disintegrate and form hydrogen atoms by emitting an electron from a neutron, circulating around the remainder (proton) and thus creating a hydrogen, and later all others chemical elements. You need to figure this out if you want to go on. !!
Tuxford
not rated yet Dec 10, 2017
Some recent evidence to re-consider (or not?) (see my comment history):

Winds expelling more material than can be accreted:
https://phys.org/...tml#nRlv
http://phys.org/n...ume.html
https://phys.org/...ter.html
https://phys.org/...axy.html

That the fabled beginning is indeed a fantasy:
https://phys.org/...ant.html

That galaxies have limited growth potential before self-destruction:
https://phys.org/...ous.html

Galactic size is related to core mass, as I earlier predicted:
https://phys.org/...ies.html
https://phys.org/...ars.html

That active cores can periodic:
https://phys.org/...ead.html
Tuxford
not rated yet Dec 10, 2017
And a surprisingly friendly discussion how SQK can explain new matter appearance within our detectable subset of the larger structure of the universe (see comments):
https://phys.org/...tml#nRlv
Da Schneib
not rated yet Dec 10, 2017
So, hmmmm. Seems like starbursts happen often in galaxies without quasars too. So it doesn't seem like starbursts are linked to quasars.

However, in quasars with starburst activity, it seems like we see these spectral features indicating a cold fast wind.

We also see quasars without starbursts and without these spectra features.

This all argues for small to no causal connections either way between quasar activity and starburst activity.
Tuxford
not rated yet Dec 10, 2017
So, hmmmm.
This all argues for small to no causal connections either way between quasar activity and starburst activity.

It argues for a wide variety of states for the quasar and the host galaxy, as logic would predict if both are growing from within, and the growth processes are non-linear.

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