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Meet the largest structure ever discovered in our galaxy

It’s not every day that you discover a huge structure that stretches more than half way across the sky. But this exact thing happened to the international team of astronomers I was leading, as we pored…

Two lobes of charged particles (light blue) have been discovered coming from the galactic centre. Ettore Carretti, S-PASS, Axel Mellinger, Eli Bressert.

It’s not every day that you discover a huge structure that stretches more than half way across the sky. But this exact thing happened to the international team of astronomers I was leading, as we pored over observations taken with the CSIRO’s Parkes Radio Telescope recently.

What we have discovered are giant outflows of charged particles emanating from the central regions of our galaxy, as reported in our paper published in Nature earlier this month.

So where do these charged particles come from? And what can they tell us about our galaxy?

Cones and particles

These outflows of charged particles consist of two lobes extending vertically from the disc plane of the galaxy on either side. Imagine two cones with their narrowest points joined together and you get an idea of what this structure looks like (see image above).

The lobes closely correspond to the gamma-ray bubbles discovered in 2010 using data from NASA’s gamma-ray space telescope Fermi (see image below).

These outflows are huge, stretching 120º across the sky – two-thirds of the way from horizon to horizon. In absolute terms, these outflows are spread across 50,000 light years – half the diameter of the entire galaxy. Quite simply, this is the largest structure ever discovered in our galaxy.

The charged particle lobes closely correspond with the gamma-ray bubbles discovered with NASA’s Fermi telescope. NASA


The analysis of the Parkes data shows these structures are outflows of charged particles generated by star formation activity in a narrow area around the galactic centre. The central part of the Milky Way contains a massive amount of star-forming gas and many young and massive stars which form and explode as supernovae.

The lobes also contain three ridge-like, parallel structures corkscrewing around the surface of the lobes. At least one of them looks to be connected back to the galactic centre and its footpoint might be one of the super-stellar clusters orbiting the Galactic centre.

The ridges, we suggest in our Nature paper, are direct outflows coming out from one of these individual super stellar clusters. The other two ridges are not connected back and their footpoints are no longer active.

These ridges might thus be relics of past star-formation activity – a signature of past stellar clusters orbiting the galactic centre.

Detecting the undetected

Many people ask us why these huge structures have not been seen before. This is because the sky was previously observed at a radio frequency that was either too low or too high.

At low frequency the signal is hidden because of a phenomenon called Faraday rotation – when the polarisation angle of light is rotated by material between the source and the observer. At high frequency the signal from the charged particle outflows is too weak and goes undetected.

When we planned our project we were aiming to study the structure of the galaxy and its magnetic field and we decided to observe at an intermediate frequency (2.3 GHz) to overcome the issues mentioned above and unveil the hidden galactic signal.

Researchers used the Parkes Radio Telescope to observe structures within the Milky Way. Alex Cherney/

What has really surprised us is the massive amount of energy contained in the lobes – in the order of the energy expelled by a million supernovae.

To provide a bit of context, each supernova is so bright that it outshines the entire galaxy hosting it. The structure we discovered hosts more energy than is expelled by a million of these stellar explosions.

This massive amount of energy is produced in a compact region (about 600 light years across) at the very centre of our galaxy and is spat out vertically in the form of these outflows to the outskirts of the galaxy – the galactic halo.

This halo was thought to be a quiet place, but we now discover that it is continuously injected with a massive amount of energy. Our study would seem to suggest that the interaction between our Galaxy and its periphery needs to be rethought.

Our data also show that the outflows carry a strong magnetic field with a massive magnetic energy which is generated in the very centre of the galaxy and transported away in the halo.

We suspect this process can play a key role in generating and sustaining the galactic magnetic field, whose origin has been a mystery since its discovery.

How the outflow field we discovered connects to the general field of the galaxy will need to be investigated in future.

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28 Comments sorted by

    1. Massimo Bini

      Tertiary Education Consultant at Vision Australia

      In reply to Gavin Moodie

      "Structure" definitely implies that the object was built and may even in this context allude (I assume unintentional) to belief in the existence of God. Likewise take the following sentence from the article; "These ridges might thus be relics of past star-formation activity – a signature of past stellar clusters orbiting the galactic centre." A "relic" is a cultural artifact not a naturally forming object or event and "signature" definitely implies the stamp of a creator. We all tend to be lazy in our use of language but it is a shame when such loaded terms are used in a scientific story which is significant in and of itself.

    2. Paul Fourie

      logged in via email

      In reply to Gavin Moodie

      No, structure is correct, it implies intelligent design.

    3. Guy Cox

      logged in via email

      In reply to Massimo Bini

      There is no basis for the implication that 'structure' refers to man-made artefacts. Descriptions of naturally occurring 'structures' go back at least to the seventeenth century (Robert Hooke's Micrographia and the early Philosophical Transactions) and probably much further.

      Likewise 'relic' simply means a surviving part of something which one existed whole, and has no anthropic connection. I can only think that Bini is confused by the rather specific use in the Roman church to means the remains…

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  1. John Griffiths


    Great article, but does no one proof read these before publication?
    "..., as we poured over observations..." should be pored over

    and ".. particle outflows is too week ..." should be too weak

    just sayin'.

    1. Matt de Neef

      Editor at The Conversation

      In reply to John Griffiths

      All fixed John.

  2. Emma Anderson

    Artist and Science Junkie

    No offense to the grammar nazis battling with semantics here but I think this article discusses a topic that is far more interesting than the words used.

    Question 1
    Am I correct in understanding that as a rule of thumb, including our own, that galaxies generally have black holes at their centre?

    Question 2
    Assuming that black holes are at the centre of the galaxy, why do the observations suggest that the energy in question is being projected out of the centre, rather than being - for my lack of better words - sucked into the black hole as a function of the gravity/density type stuff that black holes are known for?

    Question 3
    If my previous understandings are correct - milky way has a black hole at the centre, the energy observed is indeed going 'into' rather than 'out of' the centre - does this mean we are actually on an arm of an ecretion disk (pardon spelling) and do these observations increase our knowledge about what happens within ecretion disks?

    1. Yoron Hamber


      In reply to Emma Anderson

      Emma, if there is a massive super big black hole there it probably also rotates. And that may make it work as a dynamo.

      And black holes aren't that well understood. We don't really have any to study closely, and all of them seem to spin so far, that I know of. Some of them spin close to the speed of light, which in fact makes them beautiful research platforms for relativistic effects. They also produce a phenomena called 'jets' which as a best guess also is related to their spin.

    2. Yoron Hamber


      In reply to Yoron Hamber

      And all of this happens outside a event horizon btw. Inside it you're perfectly correct to assume that nothing from the inside should be able to penetrate that event horizon, except gravity. A black hole is a 'compressed mass' with a infinite gravity at its center, possibly :) Its former star size may have changed, but outside that event horizon the gravity will be the same as for the star it was before the compression happened. It's inside the event horizon we lose track of what may happen in it.

    3. Yoron Hamber


      In reply to Yoron Hamber

      Better expressed. Assume that you could stand on that stars surface before it started to compress :) feeling a gravity of, let's say one. after it becomes a black hole, and if you place yourself at rest with the BH, at the that same distance fro the center you were before it compressed, you should find the gravity you experience to be the exact same, one.
      But going from that circumference toward the event horizon will increase the gravity bending space-time until the even horizon itself where gravity becomes so strong that all paths from there only point one way. Into the center.

    4. Emma Anderson

      Artist and Science Junkie

      In reply to Yoron Hamber

      Ooh thanks Yoron. This stuff is very cool.

      To recap where Im at now

      1. We probably do have a black hole at the centre of our galaxy, but this isn't exactly certain.
      2. Assuming that we do, we are actually on the arm of an accretion disk (spelling now corrected)
      3. Likewise, black holes are capable of both functions: sucking stuff in, and through a dynamo process, shooting jets out;
      3a. The stuff sucked in increase the density and therefore the gravity of the black hole

      Read more
    5. Yoron Hamber


      In reply to Emma Anderson

      One logical explanation to the spin is called angular momentum. Its like a skater rotating with his arms stretched out, as he moves the arm towards his body his rotational speed increase. In the case of a rotating star you can consider the surface of it being its arms outstretched, and as the star compress the arms moves towards a infinitely small 'center' increasing the angular momentum (rotational speed). If that takes care of it all I'm not sure, but it makes sense.

      If we are on arm of it is…

      Read more
    6. Yoron Hamber


      In reply to Yoron Hamber

      And maybe I should add this. A atom may be photographed, but it doesn't answer what it is. Same goes for electrons. They can both for example be 'super imposed' meaning that the two atoms can share the same space. and the orbitals of electrons is best described by the probability of a electron being in a certain place. That's also called probability 'clouds', meaning that the electron in fact is 'smeared out' over its path, not definable to any specific location except by the probability of it being 'there'. all of that belong to quantum effects and they differ from what we see macroscopically.

    7. Emma Anderson

      Artist and Science Junkie

      In reply to Yoron Hamber

      Two atoms sharing the same space sounds bizarre.
      An atom spinning 720 degrees to make a full rotation, like wise.

      Perhaps a dimensional relationship between the two concepts makes sense of both. Such as an atom occupying one unit of ordinary space creates an echo of that space through the angular momentum of its spin. The echo of that space is dimensionally equivalent to ordinary space, meaning, a second atom can occupy that space simultaneously, and from the observer's point, the first atom…

      Read more
    8. Yoron Hamber


      In reply to Emma Anderson

      Don't know Emma :) Your ideas of space echoing is nothing I know of. Space is observer dependent, meaning that my measurements of it, and yours, will differ, the same goes for gravity. Change your coordinate system from standing on a planet to 'free falling' and gravity disappears for you. We use repeatable experiments to define reality, and according to those what you measure is your reality. That's where relativity blows my mind away :)

      Try this one

    9. Ettore Carretti

      Senior Systems Scientist, at CSIRO

      In reply to Emma Anderson

      Emma, our analysis tell the radio lobes we observe are outflows driven by the star formation occurring in the Galactic Centre area, rather than jets from the central super massive black hole. There is a massive amount of star forming gas orbiting the super massive black hole at the centre of the milky way. This gas is sufficiently far from the black hole to orbit around it without falling into it.

      This gas is forming stars at a high rate: it is one of the most active star forming areas of our galaxy. That way, a number of young and massive stars form here and explode as supernovae. It is the energy and the gas expelled by these supernovae that power the outflows we see.

    10. Emma Anderson

      Artist and Science Junkie

      In reply to Ettore Carretti

      Ahhh cool!!

      Okay so I'm a visual thinker and I'll picture see if I'm following you.

      Dead centre: There's a black hole
      Ring 1 near centre: a gap of some sort
      Ring 2 near centre: Lots of gas becoming stars and forming supernovae. Energy shoots out from this process, creating the jets referred to in this article.
      Going out further and further: the galaxy starts to resemble our neighbourhood more and more

      Am I correct in understanding that if the plane of the galaxy is X axis, the jets are Y axis? Or do the jets propel in all directions/radially, or in another pattern?

  3. Dave Phillips

    logged in via Facebook

    This is very very cool, I am out at the Parkes Radio Telescope (as a visitor) and the set up and information is amazing, the program for 2013 is exciting and well documented to see what is coming up and who is working on it. I long for the day we put this science to the forefront of our efforts. The everyday needs of our puny existence on the blue planet pale into the immensity of deep space.

  4. Margo Saunders

    Public Health Policy Researcher

    Wonderful article about something truly awe-inspiring. However, I was hoping to read about the actual implications of this massive amount of energy and its magnetic field. Is this all too far away to matter, or does this discovery have practical implications for space travel, communication, the interpretation of other information about the galaxy, etc.?

  5. Dania Ng

    Retired factory worker

    Excellent article, captivating stuff. Thank you very much.

  6. Mark Amey

    logged in via Facebook

    Great article and gorgeous images.