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Powerful Galaxies Found in Infrared
demachina writes "NASA's Spitzer Infrared space telescope has discovered 'a mysterious population of distant and enormously powerful galaxies radiating in the infrared spectrum with many hundreds of times more power than our Milky Way galaxy.' They are 80% of the way back to the big bang. They found them by comparing a visible and infrared scan of the sky and looking at the places where there was a big infrared signature and no visible one. They are shrouded in dust."
... or is it hilarious to see the pop-up ads that are linked to words like "radio", "satellite" and "software"? Their content is so commercial, and so divorced from relation to the scientific news of the article, that instead of being ads, they become parodies of themselves.
- Peter Ravn Rasmussen
Spitzer Space Telescope Finds Bright Infrared Galaxies
by Larry Klaes
Ithaca NY (SPX) Mar 02, 2005
A Cornell University-led team operating the Infrared Spectrograph (IRS), the largest of the three main instruments on NASA's Spitzer Space Telescope, has discovered a mysterious population of distant and enormously powerful galaxies radiating in the infrared spectrum with many hundreds of times more power than our Milky Way galaxy.
Their distance from Earth is about 11 billion light years, or 80 percent of the way back to the Big Bang.
Virtually everything about this new class of objects is educated speculation, the researchers say, since the galaxies are invisible to ground-based optical telescopes with the deepest reach into the universe.
"We think we have an idea of what they are, but we are not necessarily correct," says Cornell senior research associate in astronomy Dan Weedman.
Among the more probable ideas are that these mysterious bodies are ultraluminous infrared galaxies, powered either by an active galactic nuclei (AGN) or by a starburst, a massive burst of star formation.
AGNs are powered by the in-fall of matter to a massive black hole, while massive starbursts often are triggered by the collision of two or more galaxies.
What makes the objects studied by the Spitzer team stand out is that previously known AGNs are "not nearly as powerful, far away, or as dust-enshrouded" as these bodies are, says Weedman.
The Cornell Spitzer team's discovery is published in the March 1 issue of the Astrophysical Journal Letters (ApJL), published by the American Astronomical Society. The Spitzer telescope, which went into an Earth-trailing orbit around the sun in August 2003, is the last of NASA's Great Observatories, the Hubble being the first.
The IRS team used data obtained by the National Science Foundation's telescopes at Kitt Peak National Observatory, for the National Optical Astronomy Observatory (NOAO) Deep Wide-Field Survey.
The team also used a catalog of infrared sources obtained in a survey in early 2004 by another of the Spitzer telescope's instruments, the Multiband Imaging Photometer for Spitzer (MIPS).
From the thousands of MIPS sources in a three-degree square patch of the sky -- about one-fourth the size of the bowl of the Big Dipper - in the constellation Bootes the Herdsman, the IRS team selected and observed 31 that are quite bright in the infrared but invisible in the NOAO survey.
"The NOAO Deep Wide-Field Survey is the best available optical survey for comparing to our data," Weedman says. "It would have been much more difficult to make this discovery without such a wide area of comparison. These NOAO data allowed us to compare the sky at infrared and optical wavelengths and find things that had never been seen before."
The Bootes area was chosen by the NOAO team because of the absence of obscuring dust in our galaxy, presenting a clear view of the distant sky. The presence of these mysterious, infrared, bright, but optically invisible, objects was first hinted at in 1983 in a paper by James Houck, Cornell's Kenneth A. Wallace Professor of Astronomy and principal investigator for the IRS.
Houck was interpreting data from another space probe he was involved with, the Infrared Astronomical Satellite (IRAS), the first astronomy mission devoted to searching the heavens for infrared sources. More than a decade later these strange objects were again recorded by the European Space Agency's Infrared Space Observatory.
"Spitzer is more than 100 times more sensitive than IRAS for detecting objects at infrared wavelengths," says Houck.
"These celestial bodies are so far from our Milky Way galaxy that we detect them as they were when the universe was just 20 percent of its current age," says Sarah Higdon, a research associate in Cornell's Department of Astronomy, who led the group that developed the software package for analyzing Spitzer data.
In addition to their incredible d
I am a bit confused by your question but here goes my two cents anyway. Infrared radiation like light is an electromagnetic wave that travel thro' space at the rate of 3 x 10^8 m/s respectively. The condition of the new galaxy that we see now is the 'image' of it some million light years ago, that is the time the radiation took to reach earth. So you may be right to speculate that the galaxy might not exist at all.
We know where they are by a process called Red-Shift. Please note that there is nothing called a 'definite' place in space. You can assume any co-ordinate anywhere and provide a relative 'address' to the object of concern. Also, here time is considered as one dimension because in case of stellar bodies, space and time are wrapped (Einstein et al).
http://astron.berkeley.edu/~mwhite/darkmatter/dm.h tml
Infrared "energy" IS light.
Electromagnetic radiation takes many forms: radio, microwave, infrared, visual (what we see as "light"), UV, Xrays, gamma rays. They are all "light".
Sorry to be a pedant.
No gods, no demons, and no masters. Secular Humanism!
You can do spectral analysis to determine the original emission spectra. The stars have emission and absorption lines at certain wavelengths, and these all get shifted by a certain amount. If it was due to redshift alone, we would know it, i'm pretty sure.
Couldn't find a link to the published ApJL paper, but this might be the preprint or related to it.
IAAA (I am an astronomer).
All galaxies (with the exception of the recently discovered and dubiously titled "dark matter galaxy" mentioned here a few days ago) emit light at a wide variety of wavelengths, from radio all the way to gamma rays. The wavelengths at which a star emits is related to its temperature (google "blackbody radiation" or "planck spectrum"); other astrophysical processes can produce or modify passing emissions as well (molecular & plasma clouds, various types of "dead" stars like neutron stars, white dwarfs, etc. can create emissions due to non-blackbody radiation - google "bremstrahllung", "cerenkov", "synchrotron", etc.).
The reason that these particular galaxies are only visible in the infrared is that a) intervening dust reddens emissions across intergalactic (and, for that matter, INTRAgalactic) distances, and b) they are so far away that as the universe has expanded, the light traveling from them has been redshifted - stretched along with the spacetime through which they have been traveling. Thus, what we see as infrared now was originally of much shorter wavelength when it was emitted.
Hope that's useful, let me know if I can clarify.
No gods, no demons, and no masters. Secular Humanism!
That's because you're not an astronomy professor. Radio waves are light, and no one should give me a funny look about it, especially during lecture. Hammering in a basic point like this helps students remember that radio waves travel at the speed of light (NOT SOUND! Oh I see that a lot), suffer diffraction like other wavelengths of light, etc. Of course, I then make a big point of saying how visible light is just EM radiation.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
Because these galaxies are surrounded by dust (likely from massive starbursts, which produce dust). Dust, because of it's scattering properties, preferentially lets long wavelength light pass through it (ie. infrared) but scatters shorter wavelength light (ie. visible light) into other directions. This is the same effect you see when looking at a sunset. The setting sun looks redder because there is dust (small, scattering particles of various sorts) letting more red light through to you than blue light. In these galaxies, it is more extreme.
The effect is called "dust reddening." I have some slides about it for the lastest entry (March 2) for my Astronomy 1050 class at my astronomy webpage if you want to see examples.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
No. The amount of ALL baryonic light emitting (or reflecting) or not is tightly constrained with high confidence by the WMAP result at ~4%. This number may change in the future with more precise CMBE measurements but certainly not by more than mere fractions of a percent.
- "Hear that?! The percolations are imminent! Cease your ingress!"
Referring to radio waves, x-rays, microwaves and any other portion of the EM spectrum as "light" is VERY common in the literature.....
- "Hear that?! The percolations are imminent! Cease your ingress!"
This begs one to ask, if we keep finding these galaxies that are emitting energy but no light, is this dark matter or is it just normal matter that we just haven't been able to find yet? There might be a hell of a lot more dust out there than we thought there was originally.
Certainly some of the dark matter is in baryonic (i.e. normal) matter. In fact, it's interesting to note that the the first "missing matter" found was baryonic. While the rotation curves of spiral galaxies provide the most clear-cut evidence for missing matter at present, the history of the dark matter problem started much earlier, with Fritz Zwicky's observation that clusters of galaxies had to have a lot of mass not shining in the visible spectrum in order to be bound objects; their galaxies were moving too fast for clusters to be gravitationally bound objects otherwise. Then, starting in the 1960s, a significant fraction of that dark matter was found when it was discovered that the space between galaxies in clusters is filled with a 10-100 million degree gas (well, plasma) known as the intracluster medium or ICM. In very large clusters, the ICM can have several times as much mass as the mass of all the cluster galaxies. That was a good sized chunk of the missing matter on cluster scales, right there.
However, despite that, it still left most of the apparent mass of galaxy clusters unaccounted-for, a situation that remains today. And that's been the same story with pretty much all the dim or dark baryonic matter we've found since then: it's crucial to know about, since it has important things to tell us about the evolution of the Universe, the history of galaxy formation, etc., but it doesn't make a big impact on the dark matter problem. Our measurements of the compnents of the density of the Universe are at low redshift, and we don't know what the low-redshift counterparts of these high-redshift ultraluminous IR galaxies are. But if they turn out to be something we haven't yet detected, and thus it turns out we've underestimated the number of low-redshift galaxies by a factor of three (very doubtful), that still won't put an appreciable dent in the dark matter problem. There's just so much dark matter out there to find, compared to the amount of known baryonic matter.
Finally, it's worth noting that if baryonic matter were able to explain away all the dark matter, that would actually pose a serious problem for the standard relativistic hot big bang model. One of the observational lynchpins of the model is its set of predictions for light element abundances. We think we know all the relevant physics at the energies of nuclear processes; that, combined with the evolution of the background Universe as dictated by the Big Bang model, allows one to calculate the abundances of light elements. It turns out that the theory of Big Bang Nucleosynthesis is able to make pretty good predictions for the abundances of hydrogen, helium, lithium, etc., provided the density of the Universe in baryons is within a small range. The predicted values are significantly larger than the contribution to the mass density of the Universe from the luminous matter in galaxies, so we already expected that that there would be some baryonic dark matter. But the predicted values are also much much much smaller than the apparent density of the Universe in dark matter. In other worse, if Big Bang Nucleosynthesis is correct, you expect there to be baryonic dark matter, but you also expect much much more non-baryonic dark matter. Of course, that doesn't mean that all the dark matter isn't baryonic -- nature is under no obligation to follow our theories! -- but the theory's done reasonably well up to know, so it's worth remembering and is a reminder to be careful.
I'll just reply to a few of the questions raised.
The hot intercluster medium IS hot, but temperture is a funny thing in some astronomical settings. In this case, the density of particles is so low, a better vacuum than you'd get in Earth laboratories, that the heat content would be pretty low. You wouldn't get incinerated, for instance. But a conventional thermometer wouldn't work either since it probably wouldn't get into thermodynamic equilibrium. It would radiate away its heat faster than the ambient gas could warm it.
Astronomers have excellent limits on the amount of normal matter, as the parent poster says. We've got an excellent idea what is out there based on emission in the far infrared, interstellar scintillation, absorption line studies, reddening studies, etc. We have very good limits on the Oort cloud density, too, from comet statistics. There are even a number of direct observations based on microlensing surveys, and there's a shadow survey, too, looking at large star fields. In short, we've got pretty good numbers and we're not going to discover that there's more normal dark baryonic matter out there than we already know about.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
"observation that clusters of galaxies had to have a lot of mass not shining in the visible spectrum in order to be bound objects"
What is the problem here? Does an Oort cloud 'shine'? If the interstellar spaces were crowded with planet-sized bodies, would these 'shine'? Can't this 'missing matter' merely be rocky or icy crud between the stars? I've often suspected that interstellar navigation might be *extremely* dangerous due to such obsticals, but wouldn't they count as 'dark matter'?
Certainly rocks and ice would count as dark matter. The trick is figuring out how to put a large fraction of the baryonic mass of the Universe in that form. That's effectively impossible given what we think we know about star formation, galaxy formation and the history of both. Furthermore, we have now (by a variety of techniques) mapped out the way in which the overall mass (and thus the dark matter, since it dominates the mass) is physically distributed in galaxies and clusters; on both scales, it's nothing at all like you'd expect the rocky/icy matter left over from disks around young stars and so forth to be distributed.
"One of the observational lynchpins of the model is its set of predictions for light element abundances."
So is this setting a limit on how 'crowded with crap' the interstellar medium could be? And if we discover that its thicker than this, then relativity is in trouble?
Big Bang Nucleosynthesis sets a limit on how much baryonic matter there can be in the Universe. That limit is in turn consistent with the prediction for the same quantity made from observations of signatures of density fluctuations in the early Universe left in the cosmic microwave background radiation. If it turned out that there was more baryonic matter around than these constraints allow, enough to explain away all dark matter, then that would be a problem for the Big Bang model. There's no evidence of this, however. People have put a lot of effort into detecting various types of baryonic dark matter, with some amount of success; but the quantities involved don't come close to solving the dark matter problem. And it's hard to imagine a physically plausible theory and history of star formation which would allow it.
"it was discovered that the space between galaxies in clusters is filled with a 10-100 million degree gas (well, plasma) known as the intracluster medium or ICM"
Ok so suppose one were in a spacecraft in one of these clouds of 'plasma' and one stuck a thermometer out of the hull, would it *really* show such a high temperature? Would it not be a cold 'vacuum' out there... even thinner and colder than the 'vacuum' of our own solar system?
Or is the high temperature somehow taken as an aggregate temperature for a large volume of space with small quantities of gas particles or ions whizzing about at extremely high speed and therefore the point temperature at any given location in that cloud would actually be quite low?
I'm not sure what you mean by a "cold vacuum," and your comments about temperature don't make sense to me.
Temperature is, by physical definition, a measure of the average kinetic energy of the particles involved. The intracluster medium has 10-100 million degree temperatures ascribed to it because the measures of the kinetic energy of its particles show that it has that much energy. Your thermometer might not show such a temperature, because thermometers work by exchanging heat with the surroundings until they come to thermodynamic equilibrium together; that wouldn't happen for a thermometer stuck into the intracluster medium for a little while since the interaction rate would be pretty low. But the ions and free electrons that make up the intracluster medium really are whizzing around that fast.
We observe the intracluster medium in the X-ray band. An analysis of the energy spectrum of the X-rays emitted shows it to be mainly thermal bremsstrahlung radiation, and from the
> why do we care?
That's a good question, and worth a better answer than I have time do do here (mbrother?). The short answer is that they're so far away that we're actually seeing galaxies as they were very early in the universe. When we look at nearby galaxies, we only see galaxies as they exist after billions (current estimates are, if I'm up to date, that galaxy evolution has been going on for around 13Gy) of years of evolution. By looking FAR AWAY, we're also looking BACK IN TIME, and are thus able to see things we'd otherwise have no ability to observe.
A surprising amount can be gleaned from spectroscopic analysis of faint, red (& ancient) galaxies. What ionization levels are observable? Do we see lots of heavy elements, or none at all? Such observations can also be very powerful probes of the stuff IN BETWEEN here and there. If we can make certain assumptions about the original emissions, then by looking at the OBSERVED emissions, we can infer, to some degree, the conditions in the intervening space (and time) between emitter and collector. There is lots of good work being done in this area currently.
Hope that helps, let me know if I can clarify!
No gods, no demons, and no masters. Secular Humanism!
You're mistaken about the dearth of comets. We observe well over 50 new comets each YEAR since the era of modern astronomy. For designated comets in the past decade, please see the compilation for instance.
The Oort cloud existence is on very solid footing. The numbers I'm aware of are 50-500 Earth masses, and since this is less than 1/1000 of a solar mass spread out over a huge volume, in discrete chunks, we can certainly address the probability of hitting something flying a space ship through it (which was the original question).
Some issues you mention or allude to, like inner Oort clouds, Kuiper belts, etc., are important for understanding the details and placing constraints on the masses invovled to better than an order of magnitude, but an order of magnitude isn't relevant to the question at hand. And hey, an order of magnitude seems pretty good to me. Astronomy is hard!
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)