APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

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APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by APOD Robot » Thu Jan 14, 2016 5:08 am

Image Infrared Portrait of the Large Magellanic Cloud

Explanation: Cosmic dust clouds ripple across this infrared portrait of our Milky Way's satellite galaxy, the Large Magellanic Cloud. In fact, the remarkable composite image from the Herschel Space Observatory and the Spitzer Space Telescope show that dust clouds fill this neighboring dwarf galaxy, much like dust along the plane of the Milky Way itself. The dust temperatures tend to trace star forming activity. Spitzer data in blue hues indicate warm dust heated by young stars. Herschel's instruments contributed the image data shown in red and green, revealing dust emission from cooler and intermediate regions where star formation is just beginning or has stopped. Dominated by dust emission, the Large Magellanic Cloud's infrared appearance is different from views in optical images. But this galaxy's well-known Tarantula Nebula still stands out, easily seen here as the brightest region to the left of center. A mere 160,000 light-years distant, the Large Cloud of Magellan is about 30,000 light-years across.

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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by Ann » Thu Jan 14, 2016 6:10 am

This image, originally released on January 10, 2012, is still fascinating after six years. It is particularly interesting to see how round, or perhaps even square, the Large Magellanic Cloud looks in infrared light. Many of the features seen in optical light are gone in this picture, and instead we see the ubiquitous underlying reservoir of dust and gas that is the "foundation" of this galaxy.

But of course, the underlying substance that really keeps this galaxy together is dark matter!

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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by Boomer12k » Thu Jan 14, 2016 8:50 am

WOW....

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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by vladi » Thu Jan 14, 2016 8:51 am

Hi there,
I'm just wondering who's right:
in today's APOD it reads - the Large Cloud of Magellan is about 30,000 light-years across
in the APOD 2011-04-26 it reads - The Large Magellanic Cloud is about 15,000 light-years across

other sources say anything between 5.000 to 30.000 light-years ...

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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by Ann » Thu Jan 14, 2016 9:04 am

vladi wrote:Hi there,
I'm just wondering who's right:
in today's APOD it reads - the Large Cloud of Magellan is about 30,000 light-years across
in the APOD 2011-04-26 it reads - The Large Magellanic Cloud is about 15,000 light-years across

other sources say anything between 5.000 to 30.000 light-years ...
According to Wkipedia, the Large Magellanic Cloud is about 14,000 light-years in diameter.

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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by vladi » Thu Jan 14, 2016 9:11 am

yup, that's what I meant,
http://jumk.de/astronomie/galaxien/gros ... olke.shtml
here it reads 5.000 light-years
still wondering ...

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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by geckzilla » Thu Jan 14, 2016 10:15 am

Depending on how you measure it and presuming the LMC is 160 000 light years away, it could be correct to say it is anywhere from 15 000 to 20 000 light years across. 14 000 isn't too far off, either, if you only want to measure the brighter parts. The thing with galaxies, especially irregular galaxies, is that it is difficult to say for certain where it starts and where it ends. 5 000 I would say is definitely wrong. 30 000 could be a bit on the large side but perhaps not wrong if the distance estimate is a bit more than 160 000.
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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by neufer » Thu Jan 14, 2016 2:02 pm

Ann wrote:
According to Wikipedia, the Large Magellanic Cloud
is about 14,000 light-years in diameter.
It's not at all clear what Wikipedia is claiming:
  • Distance: 163.0 kly (with an accuracy of 2.2%)

    Size (visual): 14,000 ly in diameter :?:

    Apparent dimensions: 10.75° × 9.17° (= ~30 ly × ~26 ly)
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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by Chris Peterson » Thu Jan 14, 2016 3:38 pm

Ann wrote:According to Wkipedia, the Large Magellanic Cloud is about 14,000 light-years in diameter.
Wikipedia is not a primary source. And in this case, it ties its 14,000 ly value to another secondary source, Encyclopedia Britannica Online, which itself doesn't provide a reference at all. So as useful as Wikipedia often is in tracking down scientific information, in this case it isn't even worth referencing at all.
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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by Ron-Astro Pharmacist » Thu Jan 14, 2016 4:15 pm

The dwarf galaxies
The Local Group.jpg
discovered in orbit around the Milky Way are paving the way looking for evidence of dark matter and how it influences our galaxy. These dwarfs may also give information about our galaxy's globular clusters and how they rotate in the halo of the Milky Way.
Globular Clusters.jpg
Pretty interesting seeing the Milky Way and all the structures that affect its overall motion.
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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by Ron-Astro Pharmacist » Thu Jan 14, 2016 9:34 pm

Emanating from the poles of the Milky Way are these Fermi Bubbles. When we first heard about them a few years back I think all our curiosities were spiked. With all the energy being exhausted into discovering the nature of dark matter, I find it almost too convenient that the bubbles are located in an area not altogether in the halo and far from the galactic plane.

Though I wouldn't pretend to understand much from this source, it appears to suggest them as a potential source of leptons and quarks. It occurred to me after posting the above it's almost as if the bubbles are part of nature's recycling center and the rest is history.
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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by Glima49 » Thu Jan 14, 2016 10:21 pm

I'm wondering why the LMC's emission nebulae easily grow to over 100 light years in diameter, and complexes like the Tarantula Nebula and N11 are over 1000 light years across! I've seen regions like this in other more normal galaxies like M33 and C57, so why do HII regions form larger and easier in smaller galaxies like those than giant galaxies like the Milky Way? N66, a planetary nebula in the LMC is 6 light years across but a planetary nebula that size in our galaxy doesn't get that bright! Same thing with N49 and N63A supernova remnants. So why are they brighter in smaller galaxies than in the Milky Way? Anyone knows?
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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by geckzilla » Thu Jan 14, 2016 11:00 pm

Glima49 wrote:I'm wondering why the LMC's emission nebulae easily grow to over 100 light years in diameter, and complexes like the Tarantula Nebula and N11 are over 1000 light years across! I've seen regions like this in other more normal galaxies like M33 and C57, so why do HII regions form larger and easier in smaller galaxies like those than giant galaxies like the Milky Way? N66, a planetary nebula in the LMC is 6 light years across but a planetary nebula that size in our galaxy doesn't get that bright! Same thing with N49 and N63A supernova remnants. So why are they brighter in smaller galaxies than in the Milky Way? Anyone knows?
A planetary nebula is the result of a single star transitioning into a white dwarf. Large emission nebulas are receiving the energy from many, many stars, often newly formed and very massive stars which are pushing dust and gas around in often irregular bubbles. Sometimes they can look (visually) like planetary nebulas, but they're not very similar. A planetary nebula dims as it expands because there's a lot less energy and material involved. Same with supernova remnants, though there's probably more energy and material to work with there compared to a planetary nebula given the mass of the stars involved to create a supernova. Still, presumably there should be less than what should be surrounding a newly formed cluster of stars. I think it has less to do with galaxy size and more to do with star formation rates. For example, you can find many very huge emission nebulas in the spiral galaxy M51. I just measured one that is easily comparable to the Tarantula.
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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by Ann » Fri Jan 15, 2016 12:59 am

Glima49 wrote:I'm wondering why the LMC's emission nebulae easily grow to over 100 light years in diameter, and complexes like the Tarantula Nebula and N11 are over 1000 light years across! I've seen regions like this in other more normal galaxies like M33 and C57, so why do HII regions form larger and easier in smaller galaxies like those than giant galaxies like the Milky Way? N66, a planetary nebula in the LMC is 6 light years across but a planetary nebula that size in our galaxy doesn't get that bright! Same thing with N49 and N63A supernova remnants. So why are they brighter in smaller galaxies than in the Milky Way? Anyone knows?
The thing to remember here is that most large galaxies in the nearby universe have already used up most of their gas after having formed stars in bout after bout for literally billions of years.
Smithsonian Astrophysical Observatory wrote:
CfA astronomer Matt Ashby joined with a team of astronomers to use the Hubble Space Telescope and the Spitzer Space Telescope to study over 30,000 galaxies in a survey of the sky specifically targeting objects in the early universe. They studied the first few billion years of the universe to determine the distribution of stellar masses and the star formation rates in galaxies at epochs as early as about 800 million years after the big bang. In an impressive piece of observational and analytic skill, the team improved on earlier measurements and found (among other things) that the star formation rate per volume of space peaked about 3 billion years after the big bang and then declined, and that as the universe expanded and aged the star formation rate per unit of available mass also steadily decreased.
Since the universe is almost 14 billion years old, and star formation in the universe peaked about 3 billion years after the Big Bang, star formation in most galaxies has actually been declining for about 10-11 billion years.

But some small galaxies are different. For some reason, some small galaxies have been "left alone" for a long time, say billions of years, and during that time they have formed few stars and "hung on to" most of their gas reservoir. Then suddenly, and for some reason, their star formation is kick-started. Now they have lots of gas to play with, and they can form fireworks of new stars. In his book The Galaxies of the Local Group, Sidney van den Bergh wrote that the Large Magellanic Cloud formed few stars for the first 10-11 billion years of its existence, and then it kick-started its star formation about 3 billion years ago. It has been sparkling with brilliant young stars ever since then. I also recommend an article in Scientific American about the Magellanic Clouds, both LMC and SMC, which turn out to be quite unusual as satellite galaxies go, precisely because of their high levels of star formation.

You mentioned M33. I don't know very much about M33, but I do know that it is considerably smaller than the Milky Way and Andromeda, and its rate or star formation is much higher than what we find in the Milky Way and Andromeda. Still, the rate of star formation in M33 is lower than it is in the LMC. In all probability, M33 has also "been left alone" for a considerable part of its existence, so it has been able to conserve its reservoir of gas. Now M33 is interacting with Andromeda and has turned up its rate of star formation very much.

Planetary nebulas are not my forte. Nevertheless, if some planetaries in the LMC are particularly bright, there are three possible explanations for that. First, and most likely, the brightest planetaries likely result from the most massive and hottest white dwarfs, which would have collapsed into neutron stars if they had been just a little bit heavier. Since very massive stars are proportionally much more common in the LMC than in the Milky Way, there should be more massive stars turning into particularly hot and massive white dwarfs illuminating very bright planetaries in the LMC than in the Milky Way.

Second, the planetaries in the LMC are typically less metal-rich than the planetaries in the Milky Way, since the stars in the LMC are typically less metal-rich than the stars in the Milky Way. This fact may or may not affect the brightness of the planetaries. The reason why stars in the LMC are typically less metal-rich than the stars in the Milky Way is precisely because there have been long periods of "quiescence" in the LMC, when few stars formed and therefore only low levels of heavier elements were synthesized, few supernovas exploded and sent their load of heavy elements out into the LMC, and even comparatively few red giants sent their heavy metal-enriched gas out into their galactic environments.
Third, astrophotographer David Malin once wrote that the gas in the Milky Way is both more constrained and more turbulent than the gas in many smaller galaxies. And because the gas in small galaxies are typically less constrained and less turbulent than it is in the Milky Way, it is easier for stars to blow large bubbles and generally form large nebulas around themselves. Check out the picture at left of small galaxy NGC 6822 by Brad Bates. NGC 6922 has modest levels of star formation but a huge reservoir of unused gas, which means that it is ripe for a brilliant burst of star formation. Note that many of the newly formed stars in NGC 6822 are surrounded by huge bubbles of ionized gas.

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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by Glima49 » Fri Jan 15, 2016 1:38 pm

Thanks Ann for your write-up. Nice to know there are reasons why planetary nebula N66 is 6 light years across and is still bright and huge, larger than in the Milky Way. Yes, the Milky Way and Andromeda have little gas left for star formation and are considered "dead", doomed to become a lenticular.

Other smaller galaxies however still play along. I just measured an HII region in M74 that is slightly bigger than NGC 604 in M33. According to what I've read, our galaxy's nebulae would maybe have been comparable to the LMC about 10 billion years ago, however we missed this show because Earth and the Solar System were born 4.6 billion years ago. I wish we could've watched it from the very outskirts of a globular cluster back then.

I should note that the thread for the APOD of December 26, 2013 here also discusses the reasons why star formation activity is higher and nebulae in general form easier, larger and brighter in smaller galaxies like NGC 6822, M33, the Magellanic Clouds and IC 10 than in the Milky Way and Andromeda.

If anyone knows of a web page discussing this problem I'd be happy to have a link to it. :)
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Re: APOD: Infrared Portrait of the Large Cloud... (2016 Jan 14)

Post by spaceaman » Sat Jan 16, 2016 4:46 pm

Hi
This might seem like Penny talking to Sheldon but that picture of the large cloud looks to me to be a big bang in progress.