Galactic tentacles of DOOM

By Phil Plait | October 7, 2008 12:37 pm

Today is a good day for awesome images. Check out M86 and NGC 4438:

NOAO image of galaxies M86 and NGC 4438

These two galaxies lie in the Virgo Cluster, a city of galaxies about 50 million light years away. Life is crowded in the cluster, and collisions between galaxies are common.

Now, that line sounds pretty mundane, but think about it: entire galaxies collide! They slam into each other at hundreds of kilometers per second! Billions of stars interact gravitationally! Gas clouds impact creating cosmic fireworks on an epic scale! AIIIIEEEE!!!!!!

Phew. OK. That’s outta my system now.

So we see galaxy collisions all the time, but sometimes the evidence is weak. NGC 4438 is the galaxy on the left, and it’s all twisty and distorted. M86 is a more normal looking elliptical. But looking at the gas content of M86 has indicated something is going on; it’s heated up pretty well, and distorted. But it wasn’t until now we could see why.

That image above is from a 4 meter telescope in Arizona. It has a camera that allows it to collect a lot of light over a big area of the sky. When a filter was used that isolates warm hydrogen gas, astronomers found these tendrils connecting the two galaxies. Those tentacles are the shrapnel of the impact, streamed out in the aftermath of the collision… and the galaxies are now 400,000 light years apart. That’s four times the size of our Milky Way.

The sciencey part of this is that they looked for new stars being born in those filaments; that’s common after collisions. However, there aren’t any! The collision happened at such high speed that the gas got really hot, and couldn’t condense to form stars. That has implications for the galaxies themselves. It’s been something of a mystery as to why elliptical galaxies stopped forming stars early in their lives. It’s thought the central supermassive black hole in the center of every galaxy plays a part; as the black hole feeds on matter it blows off a huge wind, blowing out the galaxy’s gas and cutting off star formation.

But now we see that collisions may play a role as well, heating up the galaxy’s gas and preventing it from making stars. It’s hard to say how much each process contributes; early in a galaxy’s life it hasn’t had much time to collide with others, so maybe this becomes important later. And spirals have those black holes too, yet stars still form in them. Obviously, there’s a lot of complicated stuff going on.

Either way, with these new detectors we can look deep into the goings-on of nearby galaxy clusters and learn more about them. And there’s a lot to learn! I’ll note that Virgo is the nearest big cluster, and M86 is visible easily in binoculars, yet here’s something new and surprising to discover about it.

Oh, and that edge-on spiral in the lower right? That’s NGC 4388, which was once thought to be associated somehow with M86. But the filaments seen emanating from it are really high velocity, so something else may be going on there as well.

In a couple of billion years, our Milky Way galaxy will collide with Andromeda in a pretty decently ginormous event. They’ll pass through each other, but then fall back again. Over the course of about five billion more years, and a handful of passes, the two will merge into one massive galaxy. What will happen to us then? Will the Sun fall toward our own central black hole? Or will we get ejected from the galaxy, flung out into intergalactic space?

We don’t know. But I know where you can find out more info… Chapter 8. Mwuhahahahahaha!

Image credit: Tomer Tal and Jeffrey Kenney/Yale University and NOAO/AURA/NSF


Comments (36)

  1. DGKnipfer

    Chapter 8 of what? :)

  2. How many billions of years before the Andromeda/Milky Way collision? We may not be concerned that much about our native sun, but maybe one that we’ve moved to? :)

  3. Zurack

    Chapter 8 of Death from the Skies of course!

    (Woo, my first post!)

  4. Too true. Most of the world seems more concerned with Chapter 13 at the moment…. 😀

  5. Weird stuff

    @ Kevin F.

    Good one.

  6. But what ALSO is really cool (not mentioned in Phil’s post, but in the astro-ph preprint) is the material that appears to be streaming (at high velocity) from the neighboring NGC 4388 in the lower right (color coded green to indicate H-alpha + [NII] emission) toward M86. Not conclusive (as the authors point out in a footnote in the preprint) but this “collision” may be even more complex than first meets the eye.

  7. Well, I see Phil DID mention it (NGC 4388) — apologies — for some reason that did not appear in my web browser (gremlins) on first display. Still, really cool!

  8. Arthur Maruyama

    Larian LeQuella:

    BA did write that the collision will take place “[i]n a couple of billions of years.”

  9. Considering the way Americans count, a couple billion could mean 2, or 700, or 850. We are bad with numbers that have billion associated with them. 😉

  10. Xave

    Astronomy newb here. So what you’re saying is that maybe collisions cause elliptical galaxies to heat up too much to form new stars. So does that mean they don’t cool down at all over time?

  11. Architeuthis

    And now my computer has a new desktop image…. Very cool!

  12. Danniel B.

    Mine too, replacing “black eye galaxy” M64

  13. strahlungsamt

    What are those 2 identical black “lemons” in the picture. There is one at the edge of each of the big galaxies?


  14. JSug

    Pareidolia moment for the day: In the upper center of the image I can clearly see the silhouette of a very familiar spacecraft…

  15. strahlungsamt: “What are those 2 identical black “lemons” in the picture.”

    The meatballs of His Holiness, the Flying Spaghetti Monster, naturally!

  16. Brian T.


    The TARDIS? That’s what it looks like to me, anyway.

  17. Hey, Phil! I love your enthusiasm! I’ve subscribed to your feed for a while. Love the comments in here too, folks!

    (I would like to thank commenter Glen Schneider above for answering my unasked Q about the galaxy in the background with the green tentacles, too!)

  18. Captain Swoop
  19. ozprof

    My first reaction when I saw that image was “that is not a REAL picture surely!!!”

    Having seen so many images of this region, that is one heck of an image!!!!!!

  20. Les Johnson

    Great write-up on one of the many recent discoveries in the field of astronomy.
    Maybe a rest from that anti ID rants for awhile?

  21. jeff kenney

    i love your title “galactic tentacles of DOOM”!!
    i wish i thought of it for the title of the journal article!

  22. OH! “Tentacles”… I thought you said “tes…” Nevermind.

    Amazing image and fantastic (as always) explanation.

  23. Jose

    All I see is a wrist and hand (probably belonging to the Virgin Mary) giving us the finger.

  24. quasidog
  25. Durn it, but the universe is so durned purty. Obviously it has been designed for our, and only our, viewing pleasure. Obviously by designed for us I meant those of us designed with 4 meter telescopes with special cameras that are filtered in such a way that picture can be made that we can see it posted on the godless intertoob.

  26. Nigel Depledge

    Wow, what a spectacular image, and what spectacular imagery you invoke, Phil. I don’t think I can wait 5 billion years to find out what happens to our sun after our galaxy merges with Andromeda (but won’t our sun be going nova at around that time anyway?).

    I particularly like the scale bar : “20 kpc”. Images I deal with usually have a scale bar that says “1 µm” (about a gazillion times smaller).

  27. One of my favorite moments from grad school (yes Virginia, grad school does come with favorite moments) is watching Alar Toomre show us the colliding galaxies simulation film he made with his brother Jüri. It was done in the seventies, had something like 500 stars per galaxy, and was made by photographing an image on a storage oscilloscope screen. Each star was represented by the letter “M” (for “mass”). I think the frame rate they were able to generate was one frame every 10 minutes or so. The result was a nice 16mm film that still looked good when I saw it in the mid-90s. Looked just like the antenna galaxies!

    And now the same thing is done as a screen-saver. For entertainment! With CPU cycles that would otherwise go unused!

    And yes, I know this photo is of gas, not stars, but since actual collisions between stars are so rare in galactic collisions, it’s all gravity in either case.

  28. Wow.

    Do you mind if I ask…

    Those tendrils emanating from NGC 4388 — they’re green. What exactly is being detected there?

    I’m guessing the warm hydrogen in those red tentacles is giving off H-alpha (hence, red). Are the green ones emitting H-beta? Or is it something else?

    (Sorry to go all technical there! :) )

  29. @Invader Xan:

    According to the caption at the NOAO site, “The green filaments seen near the edge-on spiral galaxy in the lower right (NGC 4388) show H-alpha emission with much higher velocities, suggesting that this galaxy might not be related to M86.”

    I assume from context that they mean “higher average radial velocity”, not “larger spread of velocity”.

  30. Clair

    “Now, that line sounds pretty mundane, but think about it: entire galaxies collide! They slam into each other at hundreds of kilometers per second! Billions of stars interact gravitationally! Gas clouds impact creating cosmic fireworks on an epic scale! AIIIIEEEE!!!!!!

    Phew. OK. That’s outta my system now.”

    Phil, I love your enthusiasm! :-)

  31. I don’t see galaxies colliding, just the FSM and his noodly appendage…

  32. Nigel Depledge

    Invader Xan –

    The green colour probably occurs for one of two reasons:

    EITHER the gas is moving rapidly towards us and its emission is very, very blue-shifted,

    OR the entire image is false-coloured (as so many astrophotos are), and this material was coloured green to distinguish it from other components of the image.

    I think the latter is more likely.

  33. Greg

    looks like sunglasses or / either a celestial bra ..virgo’s bra ! lol

  34. anon

    I don’t see galaxies colliding, just the FSM and his noodly appendage…

  35. arabwhipmonk

    As Phil said, these galaxies are now farther apart than our galaxy’s size. I wonder if the galactic magnetic fields interacting during collisions could play a part in the structure we see now. I also wonder how the galactic magnetic fields are related to galaxy shapes.

  36. Re: Andromeda and the Milky Way colliding: probably, but not certainly. We’re working on an answer, so stay tuned!


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