Hubble finds evidence of galaxy star birth regulated by black-hole fountain

August 6, 2015 by Ann Jenkins, NASA's Goddard Space Flight Center
Top: Actual Hubble observations of gas density in the central portion of two galaxies. Bottom: Computer simulations of knots of star formation in the two galaxies show how gas falling into a galaxy's center is controlled by jets from the central black hole. Credit: NASA/ESA/M. Donahue/Y. Li

Astronomers have uncovered a unique process for how the universe's largest elliptical galaxies continue making stars long after their peak years of star birth. NASA's Hubble Space Telescope's exquisite high resolution and ultraviolet-light sensitivity allowed the astronomers to see brilliant knots of hot, blue stars forming along the jets of active black holes found in the centers of giant elliptical galaxies.

Combining Hubble data with observations from a suite of ground-based and space telescopes, two independent teams found that that the black hole, jets, and newborn stars are all parts of a self-regulating cycle. High-energy jets shooting from the black hole heat a halo of surrounding gas, controlling the rate at which the gas cools and falls into the galaxy.

"Think of the gas surrounding a galaxy as an atmosphere," explained the lead of the first study, Megan Donahue of Michigan State University. "That atmosphere can contain material in different states, just like our own atmosphere has gas, clouds, and rain. What we are seeing is a process like a thunderstorm. As the jets propel gas outward from the center of the galaxy, some of that gas cools and precipitates into cold clumps that fall back toward the galaxy's center like raindrops."

"The 'raindrops' eventually cool enough to become star-forming clouds of cold molecular gas, and the unique far ultraviolet capabilities of Hubble allowed us to directly observe these 'showers' of star formation," explained the lead of the second study, Grant Tremblay of Yale University. "We know that these showers are linked to the jets because they're found in filaments and tendrils that wrap around the jets or hug the edges of giant bubbles that the jets have inflated," said Tremblay, "And they end up making a swirling 'puddle' of star-forming gas around the central black hole."

Sorting through thickets of stars in elliptical galaxies far, far away
A composite image of the Hydra Galaxy Cluster, including a look at the hot atmosphere of plasma that pervades the cluster, an ultraviolet image of young stars swirling, an optical image of the elliptical galaxy at the heart of the cluster, and a radio image of jets of relativistic plasma. Credit: NASA, the Hubble Space Telescope, Chandra X-ray Observatory, and the Jansky Very Large Array

But what should be a monsoon of raining gas is reduced to a mere drizzle by the black hole. While some outwardly flowing gas will cool, the black hole heats the rest of the gas around a galaxy, which prevents the whole gaseous envelope from cooling more quickly. The entire cycle is a self-regulating feedback mechanism, like the thermostat on a house's heating and cooling system, because the "puddle" of gas around the black hole provides the fuel that powers the jets. If too much cooling happens, the jets become more powerful and add more heat. And if the jets add too much heat, they reduce their fuel supply and eventually weaken.

This discovery explains the mystery of why many elliptical galaxies in the present-day universe are not ablaze with a higher rate of star birth. For many years, the question has persisted of why galaxies awash in gas don't turn all of that gas into stars. Theoretical models of galaxy evolution predict that present-day galaxies more massive than the Milky Way should be bursting with star formation, but that is not the case.

Now scientists understand this case of arrested development, where a cycle of heating and cooling keeps star birth in check. A light drizzle of cooling gas provides enough fuel for the central black hole's jets to keep the rest of the galaxy's gas hot. The researchers show that galaxies don't need fantastic and catastrophic events such as galaxy collisions to explain the showers of star birth they see.

The study led by Donahue looked at far-ultraviolet light from a variety of massive elliptical galaxies found in the Cluster Lensing And Supernova Survey with Hubble (CLASH), which contains elliptical galaxies in the distant universe. These included galaxies that are raining and forming stars, and others that are not. By comparison, the study by Tremblay and his colleagues looked at only elliptical galaxies in the nearby universe with fireworks at their centers. In both cases, the filaments and knots of star-birth appear to be very similar phenomena. An earlier, independent study, led by Rupal Mittal of the Rochester Institute of Technology and the Max Planck Institute for Gravitational Physics, also analyzed the star-birth rates in the same galaxies as Tremblay's sample.

The researchers were aided by an exciting, new set of computer simulations of the hydrodynamics of the gas flows developed by Yuan Li of the University of Michigan. "This is the first time we now have models in hand that predict how these things ought to look," explains Donahue. "And when we compare the models to the data, there's a stunning similarity between the star-forming showers we observe and ones that occur in simulations. We're getting a physical insight that we can then apply to models

Along with Hubble, which shows where the old and the new stars are, the researchers used the Galaxy Evolution Explorer (GALEX), the Herschel Space Observatory, the Spitzer Space Telescope, the Chandra X-ray Observatory, the X-ray Multi-Mirror Mission (XMM-Newton), the National Radio Astronomy Observatory (NRAO)'s Jansky Very Large Array (JVLA), the National Optical Astronomy Observatory (NOAO)'s Kitt Peak WIYN 3.5 meter telescope, and the Magellan Baade 6.5 meter telescope. Together these observatories paint the complete picture of where all of the gas is, from the hottest to the coldest. The suite of telescopes shows how galaxy ecosystems work, including the black hole and its influence on its host galaxy and the gas surrounding that galaxy.

Tremblay's paper appeared in the Monthly Notices of the Royal Astronomical Society; Donahue's paper appeared in the Astrophysical Journal.

Explore further: How do galaxies die?

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1.6 / 5 (7) Aug 06, 2015
The researchers show that galaxies don't need fantastic and catastrophic events such as galaxy collisions to explain the showers of star birth they see.

Merger maniacs unite! Down take this news lamely. Fight back. Say it ain't so! It just must be from collisions!

OK, a feedback mechanism is partially at work. Duh. But where is the origin of the gas that keeps the process going? From within or without? Astronomers simply assume it must all be from without. It is just another assumption, consistent with merger mania.
5 / 5 (1) Aug 06, 2015
What model do you propose Tux? Just curious.
1 / 5 (5) Aug 07, 2015
What model do you propose Tux? Just curious.

Ah, curiosity can be dangerous, since you might not like the answer: A Continuous Creation model by LaViolette. It really disturbs the faith of the merger maniacs. See my comments from:
1 / 5 (4) Aug 08, 2015
Quite honestly, this does provide at least *observational* evidence for an electric star-formation theory. These jets have a measurable electric current flowing through them which is massive - I think 10^18 amps of current - and helically shaped magnetic field lines, most likely along with the current flows in parallel, i.e. a Birkeland current. Z-pinches in the current could be responsible for, at the very least, condensing the plasma in the jets and initiating their fusion reactions - or, as I find it more likely, sustaining their electrical activity.

I find this idea even more likely after the discovery that brown dwarfs, or "failed stars," have demonstrated auroral activity - which, the most logical conclusion would suggest means they are interactive with Birkeland currents, the same way planets in our solar system are.

Also, "self-regulating cycle" sounds pretty much like a "circuit" to me...
Aug 08, 2015
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3.7 / 5 (9) Aug 08, 2015
Quite honestly, this does provide at least *observational* evidence for an electric star-formation theory.

AGN feedback, something which has featured in galaxy formation models for over a decade. Proposed and then studied in the "mainstream" for years and yet suddenly is evidence for the Electric Universe despite no prior mention of it. Talk about intellectual dishonesty.
Aug 08, 2015
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1 / 5 (3) Aug 08, 2015
Talk about intellectual dishonesty.

(1) Alfven was discussing star formation and interstellar clouds since at least '77 (2) Ralph Juergen's began talking about his idea of the electric star and the involvement of galactic Birkeland currents since '79.

(3) The nature of the feedback mechanism being discussed is what lends itself, *observationally*, as support for Alfven's ideas of galaxy formation and the EU's ideas of star formation. Everything I said about the currents found in these jets, the helically-shaped magnetic fields that structure them, and the filaments that wrap around the jets, all come from either articles posted *on this site* or from arxiv papers. And they are also all proposed as critical influences by Alfven/EU in stellar formation. If they're likewise elements of the SM, then great, no one says they're mutually exclusive and no one is being intellectually dishonest.
1 / 5 (3) Aug 08, 2015
What the hell happened to the idea that competing models and theories are *good* for science? I've become significantly less hostile in both my attitude while posting, and my criticism are the SM since I made this account. I post lucidly and rationally about my interest in Alfven's ideas and the EU's ideas, and I believe that research into these ideas have their place in astrophysics and cosmology.

If you think I'm dishonest, go back and look over the entire history of posting on this site. I'm very open about my position as an amateur, and about my very scholastic intent to approach alternative ideas.
1 / 5 (4) Aug 08, 2015
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1 / 5 (4) Aug 08, 2015
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3.5 / 5 (8) Aug 08, 2015
(1) Alfven was discussing star formation and interstellar clouds since at least '77 (2) Ralph Juergen's began talking about his idea of the electric star and the involvement of galactic Birkeland currents since '79.

So what? None of that is relevant, tell me where they claimed AGN shut down star formation. The article speaks about the similarity between simulations and these observations. Not electric galaxy formation, mainstream hydrodynamics and gravity.

The whole point of AGN feedback is motivated by standard models, by dark matter simulations no less. There is no electric model which is developed enough to predict a stellar mass function, there's no point of adding feedback to a model which doesn't exist.
1 / 5 (2) Aug 08, 2015
Of course it is relevant - the feature's being described here, and in my post, were suggested by both Alfven and Juergen's as elements of their own model of star formation and galactic activity. The fact that these observations help support an AGN feedback mechanism is great - that doesn't exclude the reality that they also support electric galaxy formation either. That was literally the entire point of my post.

You're treating these observations as if they may be exclusively be considered as support for one model or the other, and I'm not. The filaments, electric currents, and helical magnetic fields associated with these jets and the subsequent star formation is *observational* evidence for the electric galaxy model proposed by Alfven. If - two decades later - astronomers suggested an AGN feedback mechanism which this *also* supports, then great. Both can exist at the same time.
3.3 / 5 (7) Aug 09, 2015
What you don't seem to understand is that these observations only support AGN feedback against hydrodynamic galaxy formation without feedback. If you claim it's all electrical then you cannot make that connection because the simulations which were compared to would both be wrong. The comparison would be completely moot and you couldn't conclude anything about star formation and AGN.

It is a model dependent test. If you claim that model is wrong the test isn't still valid. These results absolutely do not support electric anything, they don't say anything about it at all. If you want to make a suite of electrical simulations and use those to interpret these observations for the presence of AGN feedback be my guest.

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