Rare New Galaxy Reveals Black Hole Jet Secrets


A newly discovered galaxy is aiding astronomers in the research into the early evolution of individual galaxies and galaxy clusters. Named Speca, this unique finding is only the second spiral galaxy known to produce “jets” – streams of subatomic particles emitted from the nucleus. What’s more, it’s also one of two which shows this activity happened in separate intervals.

As astronomers know, galaxy jets are formed at the heart of activity where a supermassive black hole is present. While both elliptical and spiral galaxies have known supermassive black holes, only one had been known to produce copious amounts of material from its poles – Messier 87. Now Speca is changing the way researchers look for recurring activity.

“This is probably the most exotic galaxy with a black hole ever seen. It has the potential to teach us new lessons about how galaxies and clusters of galaxies formed and developed into what we see today,” said Ananda Hota, of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), in Taiwan.

Located in a galaxy cluster about 1.7 billion light-years, Speca (an acronym for Spiral-host Episodic radio galaxy tracing Cluster Accretion) made its presence known to Ananda’s researches via an image which joined data from the visible-light Sloan Digital Sky Survey and the FIRST survey done with the National Science Foundation’s Very Large Array (VLA) radio telescope. Subsequent observations with the Lulin optical telescope in Taiwan and ultraviolet data from NASA’s GALEX satellite verified the lobes of material were part of an active, star-forming galaxy. Ananda’s team further refined their studies with information from the NRAO VLA Sky Survey (NVSS), then made new observations with the Giant Meterwave Radio Telescope (GMRT) in India. Each telescope set provided more and more clues to solving the puzzle.

“By using these multiple sets of data, we found clear evidence for three distinct epochs of jet activity,” Ananda explained. But the real excitement began when the low-frequency nature of the oldest, outermost lobes was examined. It was an artifact which should have disappeared with time.

“We think these old, relic lobes have been ‘re-lighted’ by shock waves from rapidly moving material falling into the cluster of galaxies as the cluster continues to accrete matter,” said Ananda. “All these phenomena combined in one galaxy make Speca and its neighbors a valuable laboratory for studying how galaxies and clusters evolved billions of years ago.”

Sandeep K. Sirothia of India’s National Centre for Radio Astrophysics, Tata Institute of Fundamental Research (NCRA-TIFR) said, “The ongoing low-frequency TIFR GMRT Sky Survey will find many more relic radio lobes of past black hole activity and energetic phenomena in clusters of galaxies like those we found in Speca.” Also, Govind Swarup of NCRA-TIFR, who is not part of the team, described the finding as “an outstanding discovery that is very important for cluster formation models and highlights the importance of sensitive observations at meter wavelengths provided by the GMRT.”

Stay close to your radio, folks… Who knows what we’ll hear in the future!

Original Story Source: National Radio Astronomy Observatory News.

12 Replies to “Rare New Galaxy Reveals Black Hole Jet Secrets”

  1. Disk galaxies with episodic bipolar jets are rather rare critters. The authors of the paper note that the galaxy does have appreciable NUV and FUV emission, but overall the galaxy is reddish in color, indicative of absorption by gas and dust in the galaxy’s disk. The farthest radio lobes (3 sets are seen) are estimated to be 1.3 million parsecs apart, while one of the outer lobes has a diameter on the order of 300, 000 parsecs!

    It is speculated that mergers or accretion of material from the Inter Galactic Medium may have been involved in the radio outbursts. X-ray observations are sorely needed here. Whatever the cause of the jets, this galaxy makes a good test subject to study BH-galaxy feedback mechanisms, the authors argue.

    FWIW, the name “Speca” stands for: SPiral-host Episodic Cluster-dominant AGN (?)

    [………………and thanks for the link, Ivan]

  2. This seems physically related to the post on the death of a star. In that case a jet was turned on as well. However, I suspect this case here is far larger in scale, and the turning on of these far larger SMBHs probably involves a catastrophic interaction with nebular regions.


    1. Yeah, but here we see three bipolar outbursts, probably within a period of under 10^7 yr. Three stellar tidal disruptions in that brief period of time? It’s possible, I guess, but somewhat unlikely, it would seem.

    2. Yeah, but here we see three bipolar outbursts, probably within a period of under 10^7 yr. Three stellar tidal disruptions in that brief period of time? It’s possible, I guess, but somewhat unlikely, it would seem.

      1. I would presume this SMBH has some sort of accretion disk, and a disk of material that orbits it further out. The 4×10^6M_{sol} BH in our galaxy currently does not appear to have a disk, but it has stars that orbit it. Presumably there may be periods where this BH has an accretion disk, where there is some jet activity from the Milky Way. If I assume this galaxy Speca has a BH of 10^9M_{sol} the Schwarzschild horizon radius is around where Saturn is in our solar system. The accretion disk would extend far beyond that, and it is like that out to .1 ly there is a belt or disk of material in orbit around the BH.

        I am not that spun up on the physics of accretion disks and the like. As a result I can only speculate. When the accretion disk form tightly around the BH there is probably a fair amount of radiation produced which exerts a pressure on material proximal to the BH. This may reduce the rate at which more outlying material feeds into the accretion disk. So I might conjecture there is a turning on and off or pulsating process.


      2. “I might conjecture there is a turning on and off or pulsating process.”

        Yeah, this on-off process was one of the properties of this system discussed in the paper, especially the timescales involved (10s-100s of millions of years, a cosmic blink, as it were).

        Also, Speca is the Brightest Cluster Galaxy in a poor cluster of galaxies and inhabits (IIRC) the outer fringes of the loose cluster. This is similar to what is seen in many older clusters, with elliptical ‘radio relic’ galaxies located at their periphery. Maybe there is some connection.

        [I see that galaxy guru extraordinaire Bill Keel refereed the paper. Maybe a good word by him and others could get some sorely needed observations of this fascinating system (I’m thinking Hubble & Chandra or XMM, Herschel mebbe, or time on large earthbound scopes).]

      3. I don’t see in the paper where the mass of the BH is estimated. I am presuming it is in the billion solar mass range.

        The plumes that are observed are also I presume due to the interaction of the jets with the intergalactic medium. I have seen images where such jets have pushed huge voids in the medium. I suppose if this cluster were richer we might see more of that.


      4. Possibly that huge 300 kpc diameter radio lobe is the result of the low pressure of the IGM in this small cluster?

        I agree, in a richer galaxy cluster, the interaction with the IGM (and possibly other cluster members ala 3C 321: http://en.wikipedia.org/wiki/3C321 ) would be greater. 😉

      5. After reading more of the paper, I see that this is a rather substantial system (60×29 kpc), a “mature host galaxy”. Curiously, the FUV and NUV is NOT peaked at the nucleus, suggesting overall star formation throughout the disk (see Fig 1a-c) and a non-AGN nucleus at this time.

        An old component of stars is also found among the bright young stars in the disk, so this is a still-evolving galaxy with episodic jet activity in a small cluster of galaxies. I’m looking forward to future follow up on this system.

      6. If I am reading the paper right it seems to indicate that the UV sources are due to accretion shocking. This would suggest an implosion-explosion cycle for the accretion disk. I have read elsewhere that SMBHs might play a role in star burst formation, and this paper appears to bear this out. AGN galaxies might then have a longer lived stellar existence than more quiescent galaxies, such as our own. Then again the level of violence might be a bit much for nice regions such as where our star is located.


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