Awesome Antennae!

By Phil Plait | July 8, 2010 7:30 am

The Antennae Galaxies are probably the most famous and beautiful example of a cosmic traffic accident in the sky: two spiral galaxies undergoing a massive collision. Davide De Martin took the Hubble images of this pair and reprocessed them as part of his Sky Factory project:


Holy wow! These galaxies are very roughly 45 million light years away, which is relatively close. That means images from Hubble yield vast details. For example, the reddish-pink star-forming bursts, triggered by the collisions of huge dust and gas clouds, are obvious. Long streamers of visible-light-blocking dust can be seen, as well as many individual, massive and bright stars. The overall yellowish glow is from the collected light of tens of billions of stars like the Sun; too faint to be seen on their own, but adding up to provide the background for the more dynamic and dramatic goings-on.

antennae_deepThe Hubble image only shows the cores of the colliding pair, but wider and deeper images, like this one shown on the right, show why they’re called the Antennae: the gravity of the interacting pair has drawn out two long streamers of stars and gas, called tidal tails. This is commonly seen when two galaxies collide.

The two galaxies have already passed through each other, the major event happening hundreds of millions of years ago. Eventually, over the next few hundred million years, these two galaxies will merge to form one more massive elliptical galaxy. The cores will eventually consolidate, and the supermassive black holes that lie there unseen in their cores will also merge, making a slightly bigger black hole.

And if you think this sounds like some fantastic science fiction scenario, bear in mind that this same fate almost certainly awaits us: we’ll collide with the Andromeda Galaxy in a billion years or two. When we do, we’ll look a lot like this! So take a good look now. Your great-great-greatnth descendants may not need a Hubble to be able to watch something like this; they’ll just go out their front door and look up.

Image credits: Davide de Martin, NASA.

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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (24)

  1. Cz-David

    Is this picture taken in visible light or false color?

  2. A billion years, hmmm… I need to mark my calendar.

  3. Messier Tidy Upper

    Great photo. :-)

    if you think this sounds like some fantastic science fiction scenario, bear in mind that this same fate almost certainly awaits us: we’ll collide with the Andromeda Galaxy in a billion years or two. When we do, we’ll look a lot like this! So take a good look now. Your great-great-greatnth descendants may not need a Hubble to be able to watch something like this; they’ll just go out their front door and look up.

    Could we see something earlier than that with interactions between any other local group galaxies such as the Magellanic Clouds?

  4. kvnvk

    I’ll second the “wow” sentiment Phil, just an incredibly amazing, awe-inspiring image.

  5. Might one posit that a pair of merging galactic center black holes will be an, ah, energetic event if for nothing else than the pair’s gravitational potential energy?

  6. Your great-great-greatnth descendants may not need a Hubble to be able to watch something like this; they’ll just go out their front door and look up.

    What would it actually look like from within? Would they see anything defined, or just a Milky Way in turmoil?

  7. ddemartin

    Cz-David, it was taken through BVI-Halpha filters, it is not visible light, but very similar to that.

  8. rob

    along the lines of what organiker said. shouldn’t merging of galactic center black holes be a good source of gravity waves? how often do galaxies collide? are there enough that we don’t have to wait too long to detect gravity waves from them? hmmm…probably not or one of the gravity wave experiments would have detected it by now, or gravity waves are still below the sensitivity of the experiments. stoopid GR!

  9. CW

    I believe Dr. Pamela Gay said in an Q&A episode of AstronomyCast podcast that we are (or will be) monitoring the Antennae galaxies for gravity waves.

  10. Just me

    OMG!!! I see the FSM!!!

  11. RMcbride

    Wow! This is just astounding to have in our “back yard”. But just to show how little I know isn’t there thought to be an upper limit of black holes? And what happens when that limit is reached?

  12. jcm

    But when the Milky Way the Andromeda Galaxy finally collide, will people actually be able to notice it?

  13. Messier Tidy Upper

    @11. RMcbride Says:

    Wow! This is just astounding to have in our “back yard”. But just to show how little I know isn’t there thought to be an upper limit of black holes? And what happens when that limit is reached?

    Upper limit to Black holes? Not as far as I know.

    A black hole (singularity) is what results when the upper limits of other possibilities for gravitational collapse have been reached and / or exceeded.

    A white dwarf cannot exist over a certain mass (1.4 or 5 solar mass) – Chandrasekhar limit. If a white dwarf somehow exceeds that limit then it will explode and be totally destroyed as a type Ia supernovae or, (stellar core collapse in the beginning only?) become a neutron star instead.

    A neutron star too cannot exist over a certain mass limit (3 solar masses I think, off the top of my head, but could be mistaken there) either or it’ll collapse into a black hole.

    (Is there a supernova version of this or could they form theoretical quark or strange stars? Maybe?)

    But a Black Hole is the ultimate gravitational collapse – it is gravity winning an unconditional surrender and completely dominating with nothing preventing it – I don’t think there is *any* theoretical limit on their mass at all.

    We do now of many millions or even hundreds of million solar mass supermassive black holes lying at the centre of the most massive galaxies after all.

  14. MarcusBailius

    Phil, didn’t you forget something?

    You would normally say something under the picture, like “click to engalacticate” for example…

    Fantastic image though.

    It’s stuff like this that’s making me seriously think that I’ll use my own telescope (due to be in its own backyard observatory in the next few months) just for, you know, looking…!

  15. Robert Carnegie

    Increasingly I fear that asking this type of question only marks me out in a way that may be better to avoid, but did anyone else have to look twice at Dr. Plait’s text to establish that his subject today is not a picture of “The Awesome Galaxies”?

    – Well, it -is-, but usually the manic hyperbole is at one remove from the actual material objects, as in “The Amazing Meeting” and indeed, um, “The Amazing Randi” himself. No, but you aren’t studying HIM scientifically. Unless you’re his doctor.

    “Extremely Large Telescope” -is- taking it too far, I think, or would be, except that if we’re in fact talking about “the European Extremely Large Telescope” then the door is still open to people in at least one country outside Europe feeling that they wouldn’t call that “extremely large” in this neighbourhood.

  16. Robert Carnegie

    Maybe you can identify the science fiction novels I’ve been reading, but is there any kind of theoretical black hole that is so large that the entire universe is inside its event horizon? In which case it wouldn’t really be a black hole.

    All right, it’s – well, no, I’ll let you find out in case you haven’t read it up to the big surprise – where the aliens have moved enough black holes together to have comfortable living space amongst them, which somehow amounts to being inside one larger black hole, while the universe runs by outside at what looks to them like accelerated time. Also, they don’t have to stay in there. But in that case there -is- an outside to the black hole as well.

    I think also a creationist cosmology has been proposed – I don’t know how seriously, but they seemed to have spent time on it, anyway – that somehow puts the Solar System in a position to observe a billion years old universe while being itself only in existence since, well, it’s usually 4,004 B.C. Which was surely the only reason even to think about it. That was the date in your bible (or it used to be), so it must be true. This would be the same bible that as far as I recall declares that James I was king of both Britain and France, which is disputed.

    But I think it’s also been proposed elsewhere that the universe effectively lies inside an event horizon, although maybe not by people who know what they’re talking about.

    Which isn’t the same thing as the universe expanding so fast that distant parts of it can never (again) be seen, either.

  17. Stephan Spiegel

    Something I’ve never understood: If the universe is expanding, and all galaxies are moving away from each other (the dots on the expanding balloon in the metaphor), then how come they keep crashing into each other?

  18. Sorry, but those two should have been called the Spunky Monkeys. See b/w image for reasoning.

  19. Anchor

    Gorgeous! This reprocessed job by Davide De Martin is much preferable to the original. Great work (especially with the suppression of the irksome diffraction spikes). It’s CRISP. Wish there was an even high-res version available on their site…

    Phil, you mention something else that reminded me of an issue which has mildly bugged me for many years now. I really have to wonder about the long-standing paradigm that mergers between two big systems necessarily always leads to an ‘elliptical galaxy’ – that is, the cannonically shapeless product which is unblemished by dust or internal structure.

    I’ve looked at countless galaxy images over the years, noted that the morphologies of galaxies are strongly correlated to their local intergalactic environment. I’ve studied plenty of examples of interacting, colliding, merged and otherwise ‘peculiar’ systems as well. But as far as I can tell, I have never seen a single example of a large elliptical galaxy (or an SO or lenticular type for that matter) that is completely structureless and unbesmirched by dust that isn’t located within or near a populous galaxy cluster. It is true that relatively isolated elliptical galaxies do in fact exist, but almost all of them exhibit considerable internal structure and contain dust.

    Studying lots of galaxy simulations over the years it seems clear that while a single merger between major spirals is likely to shuffle up the stellar populations in the end-product quite a bit, an internal structure of some sort (stellar distribution) persists for a very long time. Observation also demonstrates that plenty of dust and star formation continues to persist in systems that would otherwise be classified as “elliptical”.

    This is borne out by quite a few relatively isolated systems such as Centaurus A, which is a classic example of the persistence of structure and LOTS of gas and dust that continues to fuel vigorous star formation. In fact, the structure in Centaurus A appears not only to have retained a disk, but non-optical wavelength images suggest it appears to have restablished some semblance of spirality. The spiral galaxy usually assumed to have merged with the alleged elliptical progenitor probably wouldn’t have retained its original disk plane-orientation, let alone its original spiral structure, but as we see it now after things have settled in for a time, it is not hard to imagine that the gas compenent in each progenitor have reestablished a disk through collisions. One thing is abundantly clear: that gas and dust is still there. It obviously hadn’t all been drained into the central black hole(s) and it wasn’t swept away out of the system either.

    In basic form, Centaurus A looks like it COULD be an elliptical…if it wasn’t for all that pesky disk of gas and dust, it would resemble many another giant ellipticals. Years ago many classified it as a “peculiar galaxy”.

    I think that in order to produce a modest-sized elliptical galaxy that has little or no residual gas MANY interactions and mergers must take place, so many that the gas is also stripped out of the system due to the resulting tumult of the combination of starburst-spawned supernovae and firing-up active galactic nuclei (quasars and jets, etc) that both produce copious x-rays to heat gas and produce prodigious outflow winds. The likeliest places where that can happen within populous galaxy clusters. Thats is in fact where we actually see a preponderance of ‘clean’ elliptical,

    SO and lenticular galaxies. And we see a smooth morphological transition in galaxies moving away from galaxy clusters to precincts such as ours.

    So? The reason why I bring all this up?

    First of all, I doubt that the coming INTERACTION between the Andromeda galaxy and our Milky Way will produce the popular image of an ‘elliptical galaxy’.

    And NO, it is NOT yet a foregone conclusion that it will be a head-on collision followed inevitably by a merger. We just do not have anywhere near the proper-motion information on Andromeda yet to be able to make such a claim. All we have is line-of-sight doppler measurements indicating that Andromeda is indeed on approach. But the two galaxies are still separated from each other by over 2 million light-years – a distance about twenty times larger than the diameters of the disks of either galaxy: the ‘target’ from each galaxy’s point of view amounts to under 3 degrees!

    A quick calculation shows it would only take a proper motion velocity of 15% or less that of the observed line-of-sight doppler measurement of approach to make the galaxies completely miss the merger scenario.

    Oh, they’d interact and exhibit fantastic tidal distortions, but they won’t merge if the proper motion was anything much higher than 15% of the observed mutual approach velocity.

    Surely astronomers wouldn’t dream of repeating a charismatically dramatic scenario for the distant future that was not explicitly borne out by available data. (Quick, duck! ;). It’s good enough to declare that the Andromeda galaxy is approaching our galaxy, and that raises a certain possibility, to be sure. I’m sorry, but that popular conclusion (as you recount in your excellent book) does not survive careful scrutiny.

    Besides: the Local Group has probably been gravitationally coherent and gyrating around in one form or another for at least 12 billion years, holding its consituents together with dark matter (i hate that term: it should have been dubbed “INVISIBLE MASS”, which is far more accurate. “Dark matter” is more accurately descriptive of dust and planetary objects and debris which still can be SEEN against a light source. We don’t know enough about what the INVISIBLE MASS is in order to identify it necessarily as being due to “matter”). In that last dozen billion years, the progenitors of Andromeda and the Milky Way should easily have had time to make close encounters along mutually ‘elliptical orbits’ several times.

    As potential evidence for that hypothesis, it is probably not a coincindence that each galaxy’s disk plane is rather closely oriented to the other’s: exactly as one might expect had the two galaxies made previous close encounters in the past to mutually orient their disk planes.

    Of course, galaxy trajectories are hardly Keplerian, and there are plenty of perturbations that can throw a monkey wrench into the picture. (One can’t ignore the modest influence of M33 in Triangulum, not far from Andromeda for example). Given that, it COULD end up as a head-on whammy – maybe even on this next round. But nobody can say it is certain. When the next close passage comes I would be surprised if the two galaxies slammed head-on…or even if their peripheries kissed before departing once again, perhaps, to repeat the cycle of the two principle members of the Local Group being, essentially, an example of a binary galaxy system plus hangers-on.

    When the two galaxies manage an interaction, however glancing – or even if they manage the merger – the tidal arms sprouting from them could give relief: if an inhabited planetary system is fortunate enough to be positioned in just the right spot when it happens, to be cast out of harm’s way, observers riding on them would obtain quite a view of the main activity on one entire side of the sky!…without getting overly fried by high-energy radiation from the starburst and AGN activity

    Who knows, but that at least some of the irregular dwarfs in our Local Group are not the reconstituted fragments of previous encounters between the two main players, those initially ripped out along such tidal streams? It could explain certain anomalies regarding the apparent ‘age’ (based on heavy element concentration versus observed star-formation rates) in some of those.

  20. Krzysztof

    Wow–this happens to be my Windows wallpaper image. It recently hit me that you can imagine a hominid skull in it. Coincidence? Nah–it’s definitely a sign of an anthropic universe. [Just kidding!]

  21. Atticus

    Colliding galaxies? Nah.. it’s a false color image of lung cancer.


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