Blobs, black holes, and exploding stars!

By Phil Plait | June 24, 2009 11:52 am

How do galaxies form?

Seems like a simple question, right? We live in a galaxy — a sprawling city of gas, dust, and over a hundred billion stars — and we see hundreds of billions of them in the sky, so you’d think we have a decent handle on how these objects came to be.

That turns out not to be the case. Their formation is more complicated than you might expect, but a new set of observations reveals an important clue in the birth process of the largest discrete objects in the Universe.

First, the cool image:

galaxy blobs

OK, so it’s not the most photogenic thing in the world. But what is it?

Deep optical images of young galaxies reveal that they are surrounded a vast cloud of hydrogen gas, many times larger than the galaxy itself. In a fit of nomenclaturial acumen, astronomers have dubbed these "blobs". The thing is, to be seen at all from this great distance, the blobs must be tremendously luminous, and there’s no clear source of energy for them. Something must be powering them, but what?

There were two competing ideas: one was that the gas is simply cooling as it falls in to the galaxy, and that gas radiates away its heat in the form of light (similar to the way a hot iron bar will radiate its heat away as infrared light). That will then power the gas on the outside, causing it to glow. The other idea was that there is some central source of power deep inside the galaxy itself, lighting up the blobs like a light bulb in a smoke-filled room.

But which is it? Ah, enter these new observations.

The image on the left is of such a young galaxy with a blob around it. This image is optical (from Japan’s Subaru telescope and Hubble) plus deep infrared (taken using the Spitzer Space Telescope). You can see the blob, falsely colored yellow, and the denser galaxy embedded in it. Look at the upper left part of the blob: see that reddish glow? What could that be?

The image on the right reveals it. That is the same picture, but added in (in blue) are observations using the Chandra X-ray Observatory. X-rays are only produced through very energetic and violent sources, such as matter swirling around a black hole, or exploding stars. That would certainly explain what’s powering the blobs’ light! But usually these events also produce a lot of optical light. Why don’t we see that?

The reddish glow in the left hand picture is the key. That indicates the galaxy is loaded with dust, made when stars are born and when the explode, too. Dust absorbs optical light, and what does get through can be highly reddened.

So now it looks like we have a complete picture of what’s going on here: as a galaxy forms from an infalling blob of gas a million light years across, a supermassive black hole coalesces in the center. Matter falls in, swirling madly around it, pouring out X-rays. Just outside this central region of the galaxy, stars are born at tremendous rates, creating lots of dust. The most massive stars explode in just a few million years, also blasting out X-rays, but also making even more dust. The dust blocks our optical view of the bright sources, but the X-rays still can leak out in quantities sufficient to heat up and light up the surrounding blobs of gas. What this means for the galaxy at large is that this huge amount of energy dumped into the blobs may slow and eventually reverse the infall, shutting off the process which forms the galaxy itself.

What we’re seeing here may be the last birth throes of a galaxy.

What I love about all this — besides the fact that we can know anything at all about what’s going on in an object a million light years across, billions of light years away, and billions of years in the past — is that we need all these observations together to figure this stuff out. The optical light alone presents us with a mystery, and the IR observations help but don’t solve the problem. But when you add the X-ray observations, they reveal the solution.

And think on this… the blobs we’re talking about here are huge, dwarfing the galaxies that are forming from them. They contain billions of times the Sun’s mass in raw gas, the building material of stars in a nascent galaxy. And these immense clouds are being lit up by not just supernovae — which are terrifying all by their lonesome, dumping out energy at rates that would turn the Earth into a crispy ember — but also by gigantic black holes smack dab in their galaxy’s hearts, which are blowing out energy in quantities to rival or exceed the supernovae themselves.

Yet all that power, the true source of energy illuminating the clouds so much we can see them from across half the Universe, is hidden from our telescopes. Or at least it was, until we learned to slip the surly bonds of Earth and loft our eyes into space, where X-rays can travel freely, unimpeded by our pesky atmosphere.

The universe is complex, and if we truly want to understand it, we will need to continue to explore it, and use the combined might of our scientific equipment to investigate it. There are hidden treasures out there, and the more we probe, the more we’ll find.

Comments (58)

  1. IVAN3MAN

    The reddish glow in the left hand picture is the key. That indicates the galaxy is loaded with dust, made when stars are born and when the explode, too. Dust absorbs optical light, and what does get through can be highly reddened.

    Err… Phil, I think you meant they, not “the”. ;-)

    Also…

    There were two competing ideas: one was that the gas is simply cooling as it falls in to the galaxy, and that gas radiates away its heat in the form of light…

    That should be into. ;-)

  2. Charlie Young

    I think I’ve read on this blog before that every galaxy has a gigantic black hole at its heart. Do you think that may be true since from what you present here, it looks like you need one to spawn a galaxy?

  3. Something must be powering them, but what?

    There were two three competing ideas: … and god did it

    couldn’t help it… :)

  4. dirk

    Great post, you make this stuff really accessible.

  5. DrFlimmer

    @ Charlie Young

    Accoring to a post from January (I think it was “AAS5: Galaxy grow from black hole seed” – there was the first big discussion with our good fellow Anaconda, some might remember him ;) ) it seems very likely that galactic growth and SMBHs are bound to and depend on each other. There is also some other evidence (like the large number of active galaxies in the past) that every (normal) galaxy contains a SMBH.

  6. Obviously these pictures have captured Nibiru, but the Evil NASA Conspiracy won’t let Phil spill the beans!

    I couldn’t resist either. :-D

  7. Richard

    Very wonderful and very inspiring. This is (bad) astronomy at its best.

  8. I read the first line of this post in the “How is Babby formed?” voice and I can’t stop laughing.

    It’s the simple things in life…

  9. Oded

    Phil, I have a man-crush on you. That was stunning! Thank you so much for these posts, I really get a smile on my face hearing (reading) you blog about these things!! :)

  10. Really nice post, but stunning..

    Amarjit Singh Kullar

  11. JakeC

    How do you tell the difference between a redshifted object and an object colored red due to interfering gasses?

  12. IVAN3MAN

    … but also by gigantic black holes smack dab in their galaxy’s hearts…

    Now, at first, I wasn’t sure about this, but after checking with Wikipedia, I think that should be collective singular: … but also by gigantic black holes smack dab in their galaxies’ hearts…

    If we were referring to a single black hole, then it would be: … but also by a gigantic black hole smack dab in the galaxy’s heart…

    Extract from Wikipedia — Apostrophe:

    Each of these four phrases (listed in Steven Pinker’s The Language Instinct) has a distinct meaning:

    * My sister’s friend’s investments (the investments belonging to a friend of my sister)
    * My sister’s friends’ investments (the investments belonging to several friends of my sister)
    * My sisters’ friend’s investments (the investments belonging to a friend of several of my sisters)
    * My sisters’ friends’ investments (the investments belonging to several friends of several of my sisters)

    Err… I’ll get my coat and see myself out.

  13. Mike

    If Halton Arp is right, these ‘blobs’ are in fact quasars seen up close.

    Created at the centers if AGNs, initially with zero mass, these particles acquire mass by interacting with the universe via Mach’s principle.

    Then, they condense into ‘blobs’ and later acquire structure

    .

  14. dhtroy

    Phil,

    Great article. Even a total non-astronomy noob like myself can understand what you just said. It’s great to gain knowledge of these subjects, so I can pass this information onto my kids, and hopefully put in them the desire to continue to learn about space science.

  15. Torbjörn Larsson, OM

    How do you tell the difference between a redshifted object and an object colored red due to interfering gasses?

    I’m not entirely sure what you mean. But at a guess the hydrogen would be recognized by its emission lines even when redshifted.

    Or are you asking for the redshift of the obstructed object?

  16. Caleb Jones

    Great post! Resonates with me on multiple levels.

    As more and more measurements deeper and deeper into our universe are made I always have the following thoughts/questions:

    My understanding is that since the universe (space) is expanding, there is a finite limit to which we can directly observe objects since at a certain point, the space between us and some distant object will be expanding so fast that information (ie: light, xrays, gamma rays, etc.) cannot traverse it. If this is correct, then we are, in effect, the center of a sphere (or bubble) with no ability to peer beyond it (as far as we know). This doesn’t mean that there is nothing beyond this bubble, but rather just that we cannot observe it.

    The questions I have based off of these assumptions are (assuming they’re true):

    1) Is this “bubble”, in effect, our universe?
    2) Does that mean that everything beyond this point is primordial early universe plasma (sorry for the non-technical description)? Or just more of the same (ie: galaxies, nebula, etc.)?
    3) Could the outside edge of this “bubble” be considered an event horizon of sorts?

    Can anyone clear up any misconceptions that I have, confirm that I’m seeing things properly, or otherwise answer these questions?

  17. Charlie Young

    #1 & 12
    Ivan, the grammar Nazi!

  18. TS

    How do you tell the difference between a redshifted object and an object colored red due to interfering gasses?

    The spectral lines will be shifted too, look up “spectral line” on wikipedia and for a nice illustration of it look up “Doppler effect” as well, the illustration can be found about two thirds down the page.

  19. Flying sardines

    @ 3. TechSkeptic Says:

    Something must be powering them, but what? There were two three competing ideas: … and god did it! Couldn’t help it… ;-)

    Nah, everyone knows god* is only 6,000 years old – and these are exponential factors more ancient than that – over actually – aren’t they?

    They predated god by aeons upon eons.

    At least our human gods … which can date back to our creating them at most two million years ago at their oldest.

    BTW. How many billion years of spacetime away are these blobs?
    ——————————–

    * Well at least the most well-known and popular god in the Western world ie. Yahwah-Jehovah-Father&Jesus&HolyGhost -Allah. The Indian and maybe some Chinese gods claim a far greater age up to infinity ..maybe.

  20. davem

    So, is this why galaxies revolve around their centre?

  21. Brandon

    QUESTION: Gravity bends light. So is it crazy to think that one of these galaxies billions of light years away might be our own? The light having gone out really far into space and because of many many interactions with strong gravitational fields somehow get turned around. Kind of like tracing the shape of a water droplet. Or is not possible and I am a little loopy from too much work.

  22. petrolonfire

    Aha! So that’s where The Blob hails from! ;-)

    (Bad 1980′s SF-horror movie ref.)

  23. Grammar Nazi

    Thankyou IVAN3MAN you are quite correct. :-)

    Don’t “see yourself out” – proper English grammar needs all the champions it can get.

  24. Crux Australis

    Jake C: by comparing the spectrum of light given off by the object. If it is redshifted, the Fraunhoffer (dark) lines in the otherwise continuous spectrum will be shifted towards the red (long wavelength) end, when compared to a sample of the same gases in a lab.

  25. StevoR

    The BA wrote :

    “Yet all that power, the true source of energy illuminating the clouds so much we can see them from across half the Universe, is hidden from our telescopes. Or at least it was, until we learned to slip the surly bonds of Earth and loft our eyes into space, where X-rays can travel freely, unimpeded by our pesky atmosphere.”

    That bit in bold is from a poem isn’t it?

    I’ve seen it alluded to before here but which poem & author, anyone?

    Great post BA – How many light years of space and time away are these blobs & proto-galaxies though?

  26. Crux Australis

    Whoops, TS bet me to it. Still, I just finished teaching it to my physics class.

  27. DrFlimmer

    @ Mike:

    You don’t mean this, do you?

    @ Brandon:

    Nice idea ;) But since gravitational lensing is very weak, I would say that it is quite unlikely that we could see ourself out in space. I’m sorry ;)

  28. RTFM!

    @ davem

    “So, is this why galaxies revolve around their centre?”

    Rick Perley of the National Radio Astronomy Observatory explains, “Masses of material from which galaxies were formed had an initial amount of angular momentum. As a developing galaxy’s gas, dust and stars contract into a smaller region of space, it all spins faster — just as a skater twirls more rapidly by pulling her arms in.”

    Essentially, the galaxy revolves around its center because the blob from which it formed already had some amount of angular momentum, and angular momentum must be preserved.

  29. BeckyWS

    Excellent article as always. One thing I am not sure about:

    where Phil says “You can see the blob, falsely colored yellow, and the denser galaxy embedded in it. Look at the upper left part of the blob: see that reddish glow? What could that be?”

    Which bit is the galaxy inside the blob? I can only see variations in density of the blob! Is the galaxy just where the red glow is or more extensive?

    Thanks to anyone who might be able to help.

  30. Charlie Young

    #23 petrolonfire and also a 1950′s SF movie before that.

  31. Kids looking for science fair project topics related to astronomy should keep in mind that the more we learn about the universe the more questions seem to develop. The same thing is going to happen when you create a science fair project. Even after you have completed your experiment and analyzed your data you are bound to have more questions then you answered.

  32. I’m calling Godwin’s on the Grammar Nazis. ;-)

  33. «bønez_brigade»

    Phil spake thusly,

    [...]in an object a million light years across, billions of light years away, and billions of years in the past[...]

    <floodgates=open>

    Errrm…
    Phil, your total explanation — hand it over (, please). The question about it during your (very entertaining) Skeptically Speaking interview also left me wanting the lengthy blog post on this topic.

  34. Talawallah

    Great post. This is exactly why I come back here every day.

  35. Petrolonfire

    @33 : How about the soup nazi from ‘Seinfeld’? ;-)

    @ 31 : Okay, didn’t know about that one… Was it better worse or just as bad as the later one?

  36. IVAN3MAN

    StevoR:

    How many light years of space and time away are these blobs & proto-galaxies though?

    Distance Estimate: About 3.526E+9 parsecs (11.5 billion light-years)*.

    BeckyWS:

    Which bit is the galaxy inside the blob? I can only see variations in density of the blob! Is the galaxy just where the red glow is or more extensive?

    Extract from Chandra.Harvard.Edu:

    [...] A galaxy located in the blob is visible in a broadband optical image (white) from the Hubble Space Telescope and an infrared image from the Spitzer Space Telescope (red). Finally, the Chandra X-ray Observatory image in blue shows evidence for a growing supermassive black hole in the center of the galaxy. Radiation and outflows from this active black hole are powerful enough to light up and heat the gas in the blob. Radiation and winds from rapid star formation occurring in the galaxy is believed to have similar effects. Clear evidence for four other active black holes in blobs is also seen.


    *Source: Chandra.Harvard.Edu.

  37. Semantic Nazi

    Deep optical images of young galaxies reveal that they are surrounded a vast cloud of hydrogen gas, many times larger than the galaxy itself. In a fit of nomenclaturial acumen, astronomers have dubbed these “blobs”. … a galaxy forms from an infalling blob of gas a million light years across,

    a) Only one million light years across? I thought our Galaxy – & galaxies in general were larger than that? 100, 000 million light years for our Milky Way diameter total – right? Or am I thinking of the number of stars or something else?

    b) “Blobs” make me think of something that’s semi-solid or semi-liquid. I would’ve thought ‘cloud’ or ‘puff’ of gas was a better descriptive /more accurate term?

    c) The term “nazi” – other than the historical evil political party – seems to have developed a slang or modern meaning of somebody who is a stickler for accuracy or detail. A nazi is a nit-picking, obssessive, perfectionist who (rather anally) corrects others mistakes although frequently only in a certain specific area, eg. grammar, conduct at a soup restaurant, semantics, etc .. Somehow, I don’t think “Godwin’s law” (a rather dubious notion in any case) applies here. ;-)

  38. StevoR

    @ 35 IVAN3MAN : Thanks! :-)

  39. IVAN:

    another option: “galaxy’s hearts” could be effective if it were a Timelord Galaxy. :)

    as for Petrolonfire: the first movie IMHO was better, with Steve McQueen(!) starring.
    Actually, the comedy Beware The Blob was one of my favorites with Larry “Dallas” Hagman doing a cameo AND directing.

    J/P=?

  40. Robert Carnegie

    The part I don’t get:

    “There were two competing ideas: one was that the gas is simply cooling as it falls in to the galaxy, and that gas radiates away its heat in the form of light (similar to the way a hot iron bar will radiate its heat away as infrared light). That will then power the gas on the outside, causing it to glow.”

    Apparently that’s the wrong idea, but why does gas cool as it falls into the galaxy?

    I’d suppose:

    (1) The galaxy’s gravity draws in the very rarefied gas from outside, compresses it, and by “the combined gas law” it’s hotter. Or just because individual particles of gas acquire kinetic energy, accelerating as the galaxy pulls on them.
    http://en.wikipedia.org/wiki/Gas_Laws

    (2) Having been heated, the gas proceeds to cool down by radiation.

    (3) The gas outside the galaxy is heated by the radiation.

    Am I being dumb?

  41. Bjoern

    @Caleb Jones:
    1) Is this “bubble”, in effect, our universe?
    Properly speaking, it is the “observable universe”, and the “universe” is everything, including the stuff beyond this bubble. But many astronomers, especially when giving public talks or writing for the lay audience, say often only “universe” when in fact they mean “observable universe”.

    2) Does that mean that everything beyond this point is primordial early universe plasma (sorry for the non-technical description)? Or just more of the same (ie: galaxies, nebula, etc.)?
    Just more of the same – we suspect. (everything else would violate the Cosmological Principle) Obviously, we can’t know!

    3) Could the outside edge of this “bubble” be considered an event horizon of sorts?
    Yes. In fact, it’s often called the “cosmological horizon”. But don’t take the analogy with Black Holes too far…

  42. Bjoern

    @Semantic Nazi:
    Galaxies usually have diameters of about 10,000 light years up to about 1 million light years. You are indeed thinking of the number of stars – 100,000 million stars in a galaxy is a good estimate.

  43. Unspeakably Violent Jack

    @ StevoR:

    The line about slipping the surly bonds of Earth comes from a poem “High Flight” by John Gillespie Magee – then a fighter pilot with the RCAF.

    High Flight
    Oh! I have slipped the surly bonds of Earth
    And danced the skies on laughter-silvered wings;
    Sunward I’ve climbed, and joined the tumbling mirth
    of sun-split clouds, — and done a hundred things
    You have not dreamed of—wheeled and soared and swung
    High in the sunlit silence. Hov’ring there,
    I’ve chased the shouting wind along, and flung
    My eager craft through footless halls of air….
    Up, up the long, delirious, burning blue
    I’ve topped the wind-swept heights with easy grace
    Where never lark nor even eagle flew—
    And, while with silent lifting mind I’ve trod
    The high untrespassed sanctity of space,
    Put out my hand, and touched the face of God.

  44. Chambered

    Hey, Caleb Jones, yes your understanding is pretty correct. It’s called our “Observable Universe”. A good place to start would be http://en.wikipedia.org/wiki/Observable_universe

  45. Richard

    @Caleb Jones #17

    1) The region you describe consists of everything we can currently observe directly. Nothing outside it can affect us, so in that sense it is the universe. Because space is expanding, it shrinks over time.*
    2) Beyond it lies more of the same. We know this because a) the above expansion means some of it used to be within observation range; and b) all observed deviations from universal isotropy are minuscule. On an interesting side note, we have indirect observations from things beyond range by their effects on things we can see! http://dsc.discovery.com/news/2008/09/25/universe-dark-flow.html
    3) It is absolutely an event horizon, exactly analogous to those surrounding black holes. 2a above is best described as event horizon crossings.

    * or at least, its contents are increasingly dominated by expansion-derived “dark energy”

  46. Bjoern

    @IVAN3MAN:
    I’d take the distance given there with a grain of salt (or, better, with a heap of salt…). What they give is essentially the distance which the light (err… X-rays) travelled until it reached us; in the press release they say that the light was emitted about 11.5 billion years ago. But that does not mean that the distance of that object to us right now is 11.5 billion light years!

    I searched a bit, and I think the original paper on which this press released is based can be found here: http://arxiv.org/abs/0904.0452

    Using the red shift z = 3.09 given there and putting that into Ned Wright’s cosmological calculator (including the other cosmological parameters provided in the paper), I get:

    light travel time: 11.421 Gyr (close enough)
    comoving radial distance: 21.002 Gly

    The latter one is much more sensible to call “distance”, I’d say. This is the actual distance of this object to us, right now, which has to be used in Hubble’s law.

    If one wants to have the distance of that object at the time when the X-rays were emitted, one has to divided by 1 + z = 4.09, which gives about 5.13 Gly.

  47. Michael Parmeley

    Am I the only one that read the headline like this the first time? “Boobs, black holes, and exploding stars!”

    Had to shake my head and read it again…

  48. Now I have a craving for Lucky Charms cereal.

  49. Mark

    I’ve seen gas and dust everywhere, but no explanation of what the “dust” is? What elements make up dust?

  50. Semantic Nazi

    @ 43. Bjoern Says:

    June 25th, 2009 at 6:24 am @Semantic Nazi: Galaxies usually have diameters of about 10,000 light years up to about 1 million light years. You are indeed thinking of the number of stars – 100,000 million stars in a galaxy is a good estimate.

    Okay thanks. :-)

  51. Stone Age Scientist

    Hi Phil, thank you for this post. I saw the same picture in a Yahoo! Science article, but you explained the matter better here.

    I find black holes to be a very fascinating subject. I have here a book by Paul Davies, entitled How to Build a Time Machine, which I acquired many years ago as a gift. It was my first steps into the realm of E=mc&sup2; , the relationship between gravity and matter, time/space curves, etc.. And I can tell you, not being a scientist myself, despite my faux nom de plume here, I came out of that book as baffled as when I first began reading it. Nonetheless, it was a pleasurable read, if only to ignite further interest in science and also garner basic knowledge about the secrets of the cosmos.

    A recent question that popped up in my head is, if the gravity of a black hole were so strong that not even light could escape, doesn’t that then translate that matter which falls into the hole would also be travelling at the speed of light, if not at greater speeds due to the intense force that even overpowers light?

    I’m asking this because I am now aware, after recent visits into other scientific sites, that there are camps out there that say it is impossible for matter to reach the speed of light. They even have Einstein’s equation to back them up. I personally do not know what your take on this is. If you are one such proponent, then I mean no offence. (Though of course, if you are a Star Trek fan, I’m guessing you’re open to the possibility of faster-than-light scenarios.)

  52. DrFlimmer

    @ Stone Age Scientist

    The physics of black holes are really entertaining, but also quite complicated since they do not only depend on special relativity but strongly on general relativity.
    First: Yes, a black hole is defined by the boundary that the escape velocity exceeds the speed of light. And since it is, indeed, true that no matter with mass (a rest-mass that is not zero – light has a rest mass that IS zero, e.g.) can reach the speed of light. So a massive particles that once crossed the boundary (called the event horizon) will never come out again!

    However, if a particle comes close to the event horizon there are strange thing happening to it. Since you have severe tidal forces acting on the particle it is streched vertically but in the same time compressed horizontally. The particles becomes very streched – a process that is called “spaghettification” :D .

    The matter that falls into a black hole does not necessarily have to travel with the speed of light – it just can’t get out any more. There are also some other weird effects that act on spacetime itself, which are very complicated and probably hard to understand (frame-dragging as a key-word).

  53. Stone Age Scientist

    Hi DrFlimmer @ #54,

    Yes, the process of spaghettification was explained in the book by Paul Davies. The book went on to elaborate that “it was such stretch-and-squeeze gravitational forces that ripped comet Shoemaker-Levy 9 into fragments before it plunged into Jupiter in 1994.” (page 54)

    There was also this part about spaghettification being less likely to happen for bigger black holes. Mr. Davies wrote “You could just about survive falling to the surface of a black hole with ten thousand solar masses. A supermassive black hole a billion kilometers across would be no problem, but such an object would have a mass equal to a small galaxy – not a very practical proposition for accessing another universe.”

  54. khms

    >33. Shane Says:

    I’m calling Godwin’s on the Grammar Nazis. ;-)

    It doesn’t do what you seem to think it does.

    >38. Semantic Nazi Says:

    Somehow, I don’t think “Godwin’s law” (a rather dubious notion in any case) applies here. ;-)

    Nothing dubious about it – but you also seem to think it says something it doesn’t.

    See, for example, Wikipedia, or the Jargon file, or the relevant FAQ.

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