AAS Post #5: The warm heart of the Milky Way

By Phil Plait | January 10, 2006 9:21 am

Holy cow, look at that! You want an explanation of what you’re looking at? You know the drill: sit back, relax, and have a listen.

Regular readers may remember a flurry of entries here about the Spitzer Space Telescope, an orbiting observatory that can detect infrared light. IR, as it’s called, tends to be given off by warm dust in space (by warm I mean astronomically warm: maybe from Antarctic temperatures to room temperature or so). You can do some observations of IR from the ground, but our air has this annoying tendency to absorb light at these wavelengths, so in effect we’re blind down here to astronomical IR (though we can breathe, so there are advantages to air as well).

That’s why Spitzer is in orbit. Though it’s not a particularly large telescope (its mirror is less than a meter across, smaller than most ground-based professional ‘scopes), its vantage point over our atmosphere gives it remarkable views of space.

Like that picture at the top of this entry. What you’re seeing there (click for access to much higher-res images) is the inner 900 x 600 light years of our Galaxy, the Milky Way. For comparison, the Earth is roughly 25,000 light years from the center, and the whole Galaxy is 100,000 light years across. So this image represents the inner 1% of the whole shebang.

The wealth of science in this image is astounding. It’s a composite of three IR “colors”, each of which is sensitive to different processes. The flavor of IR nearest to visible light is emitted by both dust and stars. But as you go farther into the IR, the stars disappear and the dust really gets bright. By adding together these colors, a rich tapestry is created. Nearly all the stars in this image are red giants and red supergiants, stars in their declining years (where the Sun will be in a few billion years). Some will simply fade away, while others will explode as supernovae. When they do, they create so much energy it can blow gas clear out the Galaxy. Super-bright stars also blow off winds of gas that can slam into the junk (more gas and dust) between the stars, driving it out of the Galaxy the same way a snowplow pushes snow off your driveway. The tendrils of dust above and below the Galactic center display this silent wind.

In the center, the Milky Way is glowing brightly in IR. In the middle of that spot, far too small to see on this scale, is a black hole 4 million times the mass of the Sun. It’s too far away from us to hurt us, but it strongly affects the objects within a few hundred light years of its terrible grip. Gas, dust, and stars are streaming around it at speeds of hundreds of kilometers per second, heating up the surrounding neighborhood, causing it to glow in IR. Much higher-resolution images show some of this better. Sometimes, as material gets very near the black hole, it heats up as it falls in. The material releases this energy, sparking flares of emission we can detect even from our relatively safe vantage point of 250 quadrillion kilometers away.

To understand this better, astronomers started a multi-telescope campaign to observe the black hole, which included Spitzer (IR), Hubble (visible light), XMM-Newton (high-energy X-rays), INTEGRAL (super high-energy gamma rays) and many ground-based ‘scopes. By observing at all these different energies, astronomers can figure out quite a bit about the physical mechanisms going on. The big mystery is not that the stuff near the black hole there is glowing, but why it’s not glowing very much. Some galaxies boom out from their cores (we call them active galaxies), but ours doesn’t. I suppose that’s a good thing, as this tends to make the galaxy a bit inhospitable for folks like us.

Understanding all this a big task, but the tools we wield are mighty. It’s amazing that we can study an object enshrouded in gas and dust at all that distance, but perhaps most wondrous is that when we do, the vista is as beautiful as it is.’

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

Comments (19)

  1. Ozastro

    That is soooo cool :)

    Love your AAS blogs.

  2. Michelle Rochon

    Very cool indeed! I always found the center of the milky way awesome. :)
    By the by Mr. Phil, I think your troll posted a comment again in the previous post.

  3. Nigel Depledge

    Nice blog entry, Phil. You got a bit poetic towards the end there.

    Plus, those pics are way cool.

  4. Will

    Very beautiful pix by themselves; when one considers the distance and the technology involved to surmount that, it is even more astounding. I still can’t grasp fully the concept of a black hole, however. I don’t see how an object with so much gravitational influence can form in the first place. I suppose once that is discovered, then folks will fully understand gravity. Anyhow, I’m glad you keep the explaining as elementary as you do, otherwise I’d be waaay out in left field myself – almost like our solar system is in relation to our galaxy…

  5. Yes, very poetic.
    I love sentences like “super high-energy gamma rays”

  6. Chip

    Love to have a wallpaper of that view. (Not in the computer – on the actual wall!)

  7. Kevin from NYC

    now that I set as my XP background. (not the other one)

  8. Philippec

    These pictures are really astoundingly beautiful!!!

    Thank you for bringing all these wonderful pictures to our attention!!

    I was wondering, what would the sky look like, if our sun was near the center of our galaxy, somewhere in that picture (assuming we would be able to live there to see it)? there seems to be an awful lot of matter down there….

  9. SFwriter

    I had a look at the 6000×4800 resolution image and zoomed it 6400% (sic). I was using 4 pixels per star (about 5mm x 5mm each) to examine stars, and I could see how far off centre each star was from the group of pixels’ intersection point. I didn’t even know such high rez photos were available… I was toying with the idea of zooming to 12,800% or 25,600% to see if I could do a spectographic analysis by naked eye… :-) I REALLY love my FIREFOX webrowser and the add-ons that are available for it… I never suspected I would use such high zooming capabilities before…

  10. Dori

    Each time I see an astronomical picture I’m reminded of the quote from “Hamlet”: “There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy.” Thanks for the incredible picture, Phil, and thanks even more for doing all you can to combat ignorance. (Including mine– I figure a day when I don’t learn SOMETHING new is a day wasted!)

    By the way, this is my first post ever to ANY blog– I’m a 54-year-old housewife. But this photo truly inspired me!

  11. TJ

    This type of science is so unbelievably awesome, I could spend days just gazing at the photos. *sigh*

  12. Lucid

    Not as pretty as the Large Magellanic from a day or so ago! :)

  13. Marlayna

    I’ve always been mystified by the beauty of the universe. Why do we perceive these things as beautiful? Is it because we know the science behind it all? Is it a matter of scale? I find it strange.that the universe is so beautiful…

  14. Karen M.

    Spitzer has opened our eyes so much over the past couple years.

    Thanks for sharing the science and your thoughts on such an awesome picture. We can look at other galaxies and thing “that MIGHT be like our home galaxy…”, but this is IT. Our home is so small in comparison to the rest of the universe, it boggles the mind.

    I appreciate you setting up the blog on Feedblitz, too, it is very convenient!

    Karen M., Baltimore, MD

  15. Can you be any more boring? Yawn.

  16. SFwriter

    If we were more boring, would you go away? I’m sure we could make the effort to be much duller just to be rid of you…

  17. Nigel Depledge

    “Sophie Anderton” said:
    “Can you be any more boring? Yawn.”

    Obviously not so boring that you didn’t bother to read the comments. Which say more about you than they do about us.

    Phil – it looks like you’ve acquired another troll.

  18. Irishman

    Nigel Depledge Said:
    >Phil – it looks like you’ve acquired another troll.

    Same one, new name.


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