APOD: Star Cluster R136 Bursts Out (2016 Jan 24)

[APOD Robot]

Star Cluster R136 Bursts Out

Explanation: In the center of star-forming region 30 Doradus lies a huge cluster containing some of the largest, hottest, and most massive stars known. These stars, known collectively as star cluster R136, were captured in the featured image in visible light by the Wide Field Camera 3 in 2009 peering through the Hubble Space Telescope. Gas and dust clouds in 30 Doradus, also known as the Tarantula Nebula, have been sculpted into elongated shapes by powerful winds and ultraviolet radiation from these hot cluster stars. The 30 Doradus Nebula lies within a neighboring galaxy known as the Large Magellanic Cloud and is located a mere 170,000 light-years away.

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[/b]

[Ann]

Click to view full size image

A near infrared image of the R136 cluster, obtained at high
resolution with the MAD adaptive optics instrument at ESO’s
Very Large Telescope. R136a1 is resolved at the center with R136a2 close by,
R136a3 below right, and R136b to the left.
Credit: ESO/VLT

R136 is an absolutely incredible cluster. According to wikipedia, R136 contains the brightest and most massive star known:

RMC 136a1 (usually abbreviated to R136a1) is a Wolf-Rayet star located at the center of R136, the central condensation of stars of the large NGC 2070 open cluster in the Tarantula Nebula. It lies at a distance of about 50 kiloparsecs (163,000 light-years) in the Large Magellanic Cloud. It has the highest mass and luminosity of any known star, at 265 M☉ and 8.7 million L☉, and also one of the hottest at over 50,000 K.

Another amazing thing about NGC 2070, whose central condensation is R136, is the fact that this entire cluster apparently only contains one single red supergiant, seen in today's APOD at the upper left edge of the cluster. Unless, of course, the red star is a foreground star. If it isn't, then the red star is the Betelgeuse of NGC 2070. But in R136 proper, there are no red giants of any kind.


There are lots and lots of other amazing facts about R136:

1) The estimated mass of the cluster is 450,000 solar masses, suggesting it may become a globular cluster in the future.

2) R136 has around 200 times the stellar density of a typical OB association such as Cygnus OB2.

3) None of the member stars are significantly evolved and none are thought to have exploded as supernovae. (Just think of the fireworks show this cluster will put on in a couple of million years!)



All in all, R136 is a truly incredible cluster!

Ann

[Boomer12k]

Wow...Spectacular...
Brontosaurus Nebula...
:---[===] *

[messier.palette]

What an absolutely spectacular view! Gorgeous...

And Ann, thanks for the wealth of colorful info. Oh, and I love how you iconed the image with the golden Betelgeuse in there

A feast for the imagination!

I'll probably be spending the next while chasing down your info sources. Good times Awhile back, I tried to wrap my mind around Wolf-Rayet stars, but I admit, I don't really understand them. The Universe is such an amazing place, and we're so fortunate to be living in a location where we can see so much of it.

The thing that really baffles me is how R136a1 can be so massive (the most massive known) when its radius isn't all that much bigger than our own little sun. (If the sun is one solar radius, then R136a1 is only about 29, whereas plenty of stars are much, much "bigger" ... maybe they're fluffier!)

[Chris Peterson]

The thing that really baffles me is how R136a1 can be so massive (the most massive known) when its radius isn't all that much bigger than our own little sun. (If the sun is one solar radius, then R136a1 is only about 29, whereas plenty of stars are much, much "bigger" ... maybe they're fluffier!)

With a radius 32 times that of the Sun, R136a1 has 33,000 times the volume. But it only has 260 times the mass of the Sun. That means the Sun is over 100 times denser. It's R136a1 that's fluffy.

[MarkBour]

So, what would have happened 2 million years ago (+light travel time) to create this wonder? A huge compression, shock, or swirling of proto-stellar material?

[Glima49]

So, what would have happened 2 million years ago (+light travel time) to create this wonder? A huge compression, shock, or swirling of proto-stellar material?

From what I know, many small dwarf galaxies have their gas saved for later as they are small and dwarfed by the giant spiral galaxies like the Milky Way and Andromeda which binge-eat their star forming gas. Roughly 10 billion years ago, the Milky Way was possibly comparable to the LMC, dotted with pink star-forming regions all much bigger than the Orion Nebula. In the smaller galaxies, due to them being left alone, it seems this gas is vaulted until something, we're not sure what, maybe a close encounter with another galaxy, suddenly switches on star formation. Now these galaxies have all their lifetime supply of gas forming new stars. That's probably why smaller galaxies such as IC 10 and NGC 1569 are considered starburst galaxies as they are blanketed with star forming regions, and can easily form nebulae larger and brighter than anything in the Milky Way. Plus the Large and Small Magellanic Clouds are interacting with each other and the Milky Way and the Triangulum Galaxy and IC 10 are interacting with Andromeda. I also know that the gas in small galaxies is less constrained and turbulent than in the Milky Way and therefore a small group of stars has plenty of room to blow out a nebula hundreds of light years across. This is exactly the case for the open cluster NGC 602 in the wing of the Small Magellanic Cloud. This nebula is 200 light years across, and quite bright, unlike anything we find in our galaxy. It is located at the edge of a ring of nebulosity known as the Flying Bat Nebula, and the small grouping of hot bright stars at the edge of this ring of nebulosity easily shock-heats the surrounding gas, which is then ionized by the radiation and stellar wind from the stars forming a cavity.



Here are a couple of previous APODs discussing this:
2013 Dec 26
2016 Jan 14

[messier.palette]

The thing that really baffles me is how R136a1 can be so massive (the most massive known) when its radius isn't all that much bigger than our own little sun. (If the sun is one solar radius, then R136a1 is only about 29, whereas plenty of stars are much, much "bigger" ... maybe they're fluffier!)

With a radius 32 times that of the Sun, R136a1 has 33,000 times the volume. But it only has 260 times the mass of the Sun. That means the Sun is over 100 times denser. It's R136a1 that's fluffy.

Lol, yeah, it might be at that! Good info

But where I was really going with my thoughts above was that as "massive" as R136a1 is in its spot at the top of the Most Massive Star list, compared to a bunch of other stars that are so much much much bigger in radius, it is puny.

Okay, here's more specifically what baffles me:

We've established that R136a1 is about 30 solar radii, plus or minus, depending on who you reference. (Our sun = 1 solar radii.)

Yet even with a "30" it doesn't even come close to getting on the "Largest Stars List." You've got stars on there like...

- UY Scuti -----------1,708 solar radii (top of the list)

- Betelgeuse -----------950 solar radii (approx. halfway down the list)

- lowest on the list is ------700 solar radii

So R136a1's measly little 28-32 (or so) solar radii baffles me. It is The Most Massive, and yet, it is dwarfed by a whole boatload of larger stars. Gobs of them. So it is fun to think about their comparative fluffiness LOL.

In fact, didn't I read somewhere that one reason they haven't quite pinned down Betelgeuse's distance is because it is so hard to really measure where a star stops and starts in all those clouds of [fluffy?] gas trying to decide whether to condense or blow away? I can't wait to learn what Gaia thinks about Betelgeuse.

Forgive my language if it isn't exact. I'm just a hobbyist, and new here. Don't know much about any of this at all, and I've never had a single class. Just hanging out, sightseeing.

[Ann]

So, what would have happened 2 million years ago (+light travel time) to create this wonder? A huge compression, shock, or swirling of proto-stellar material?

The thing to understand about LMC is that it has been forming stars rather furiously for the last three billion years, but before that it was rather quiescent. For billions of years it just "sat" there in its (comparatively) vast reservoir of gas. In his book The Galaxies of the Local Group (Cambridge Astrophysics Series), Sidney van den Bergh refers to a study by Geisler et al (1997). According to that study, the LMC formed a few globular clusters some 11.5 billion years ago, but after that time it formed few stars at all until it started virtually starbursting about 3 billion years ago. And it has just kept on churning out new stars ever since then.

What happened 3 billion years ago? There is a lot of evidence that suggests that perhaps 3 billion years ago the LMC started interacting with the SMC, the Small Magellanic Cloud. The interaction with the SMC was just the spark the LMC needed to start a forest fire of star formation in its galaxy-sized tank of gas. After "sitting still and doing nothing" for billions of years, the LMC could now put on a brilliant and still ongoing light show of star formation.

According to Sidney van den Bergh and the studies he refers to, star formation in the LMC is slightly on the decline now, but still vigorous.

My point is that nothing special "happened" in the LMC 2 million years ago to make it create R136. An extremely vigorously starforming galaxy formed yet another massive cluster.

A more interesting question is, perhaps, why R136 and the Tarantula Nebula are located where they are located inside the LMC.

Click to view full size image

The Large Magellanic Cloud. Photo: C-141 Imagery

Take a look at the picture at left of the LMC. Two features of the LMC are immediately obvious: the galactic bar and the Tarantula Nebula, ionized mostly by R136. I think there is a definite connection between the bar and R136 of the Large Magellanic Cloud.

Click to view full size image

NGC 4395. http://www.spacetelescope.org/ Alan Sandage.

Take a look at this picture of NGC 4395. (I'm sorry to show you a black and white photograph, which is really against my principles. A beautiful 800 KB RGB image of NGC 4395 by Adam Block is here.)

NGC 4395 has some interesting similarities with the LMC. It is a relatively small, gas-rich, and vigorously starforming galaxy. NGC 4395 also has a bar, even though is bar is nowhere as pronounced as the bar of the LMC.

And where do you find most of the star formation in NGC 4395?

Right. You find it near the end of the bar. Not only that: The most brilliant site of star formation clearly forms the beginning of a spiral arm.

Click to view full size image

NGC 1313. Credit: VLT/ESO.

Take a look at this picture of another small, barred, starforming galaxy, NGC 1313. (I'm sorry to show you a non-RGB color picture, which is also against my principles.)

NGC 1313 has a strong bar. And where do you find its most brilliant site of star formation? Right. You find it near the end of the bar, at the beginning of one of the spiral arms.

I think of R136 and the Tarantula Nebula as the beginning of a spiral arm of the LMC.

So why would there be so much star formation at the end of the bars of barred galaxy? First off, not all barred galaxies are like that. But in the cases where we see brilliant star formation near one or both ends of the galactic bar, I think it is because the bar is (relatively) stiff, and it sweeps up gas and "dumps" it near the end of itself. (In many cases, the bar instead sends gas into the nuclear region of a barred galaxy, where you can see brilliant nuclear rings of star formation.)

So all in all, I think R136 and the Tarantula Nebula can be thought of as the beginning of a spiral arm in the LMC. R136 and the Tarantula Nebula have formed out of all the gas that has been dumped and concentrated near the end of the bar of the LMC.

Ann

[Ann]

But where I was really going with my thoughts above was that as "massive" as R136a1 is in its spot at the top of the Most Massive Star list, compared to a bunch of other stars that are so much much much bigger in radius, it is puny.

Okay, here's more specifically what baffles me:

We've established that R136a1 is about 30 solar radii, plus or minus, depending on who you reference. (Our sun = 1 solar radii.)

Yet even with a "30" it doesn't even come close to getting on the "Largest Stars List." You've got stars on there like...

- UY Scuti -----------1,708 solar radii (top of the list)

- Betelgeuse -----------950 solar radii (approx. halfway down the list)

- lowest on the list is ------700 solar radii

So R136a1's measly little 28-32 (or so) solar radii baffles me. It is The Most Massive, and yet, it is dwarfed by a whole boatload of larger stars. Gobs of them. So it is fun to think about their comparative fluffiness LOL.

In fact, didn't I read somewhere that one reason they haven't quite pinned down Betelgeuse's distance is because it is so hard to really measure where a star stops and starts in all those clouds of [fluffy?] gas trying to decide whether to condense or blow away? I can't wait to learn what Gaia thinks about Betelgeuse.

Forgive my language if it isn't exact. I'm just a hobbyist, and new here. Don't know much about any of this at all, and I've never had a single class. Just hanging out, sightseeing.

As as a lover of all blue things, my interest in red things is sort of lukewarm. And since all the largest stars in the universe are red giant stars, I have not spent that much time trying to understand them.

(An aside here: While the term "red giant" is firmly established and must be used, the stars it refers to are not red, but yellow-orange.)

Anyway. The reason why these stars are huge and red (make that yellow-orange) is that they are massive and evolved. They have long ago given up hydrogen fusion in their cores. Hydrogen fusion is the most effective fusion in existence, and so called main sequence stars (like the Sun) shine by fusing hydrogen to helium in their cores. The less massive the star is, the longer its core hydrogen will last and the longer the star will stay on the main sequence. What will happen in the end to the smallest stars is not quite clear, but it should be noted that not a single red dwarf star of spectral class M (the most common stars in the universe) has used up its core hydrogen and left the main sequence since the universe came into existence some 14 billion years ago.

Click to view full size image

Red giant star with inert core.
Source: http://pics-about-space.com/layers-of-a-red-giant?p=2

But the more massive a star is, the faster it will use up its core hydrogen. This will lead to a series of developments. The star's core will become inert and shrink, which will cause the core temperature to rise. At the same time, the star will expand greatly. Soon afterwards, the hydrogen in a shell around the core will become hot enough to begin fusion.

Click to view full size image

Helium-burning red giant.
Source: http://cse.ssl.berkeley.edu/bmendez/ay1 ... eburn.html

Eventually, the core will become hot enough that the helium in it, the waste product of hydrogen fusion, will start its own fusion process and fuse carbon and oxygen.

But the really massive stars will drive up the temperature in their cores even higher and start fusing ever more heavy elements. At the same time, there will be other kinds of fusion going in in shells around the core.

Click to view full size image

Massive red supergiant with multiple burning shells.
Source: http://starformation.synthasite.com/red-giants.php

Eventually, the star that is massive enough and can make its core temperature rise sufficiently high, will have an interior similar to an onion, with multiple burning shells surrounding a super-hot core. Its outer layers, by contrast, will be bloated and cool.

If the star has the kind of interior as the star in the illustration at left, it will go supernova any minute. After a star has produced an iron core, it has only moments left to live before it explodes as a supernova.

Click to view full size image

Wolf Rayet star. Hubble Legacy Archive, NASA, ESA.
Processing & Licence: Judy Schmidt

However, when a star becomes a truly humongously big red supergiant, is is no longer anywhere near as massive as R136a1. Why is that? It is because evolved stars that have given up core hydrogen fusion lose a lot of mass late in their lives because of their strong stellar winds. At right you can see a special kind of evolved star, a hot, rather small Wolf Rayet star. But like Wolf Rayet stars, red supergiants also lose a lot of mass at the end of their lives.

R136a1, on the other hand, is in the flush of its youth. It is still fusing hydrogen to helium in its core, it has a simple internal structure, and it is hanging on to almost all the mass that it was born with. Things will change soon for R136a1. But for now, it is blasting forth blue-white light forged as gamma-rays in the magnificent depths of its interior.

Ann

[geckzilla]

Heh, source "nature.com"

[messier.palette]

Ann, loved both your new posts above. Thanks for taking the time to offer such a wealth of illustrated info. I truly appreciate it.

I've been studying the shells lately (evolution of stars) but was missing the magnesium layer in the little sketch I made for myself. So that's an additional bonus from your material. The info about the LMC sort of lazing away until "recently" was also fascinating.

Great stuff, all of it.

[messier.palette]

You know Ann, as long as we're on the topic of the LMC and SMC, I read one article, and only one, several years ago about a diverging point of view that possibly instead of being true companions to the Milky Way, they were just "playing through." However, since then, everyone I've read has just continued the usual discussion about them both being satellites of the Milky Way.

Yet the other idea, which had science and diagrams and velocities and trajectories and all that good stuff to go with it, is still stuck in my mind. You seem far, far better read than me. Have you read anything definitive about this? Do you think there is any remote possibility that the LMC and SMC might be on the road less traveled, just passing by on their way to somewhere most of us haven't considered? Does the Magellanic Stream convince you one way or the other?

[Ann]

Heh, source "nature.com"

Sorry, Geck. I tried to open the page where the picture was posted, and I searched for other versions of the same image. But the page wouldn't open, and I couldn't find any other sizes of the same picture. That's why I chose "nature.com", since I could see that the picture has been published in Nature.

Ann

[Ann]

You know Ann, as long as we're on the topic of the LMC and SMC, I read one article, and only one, several years ago about a diverging point of view that possibly instead of being true companions to the Milky Way, they were just "playing through." However, since then, everyone I've read has just continued the usual discussion about them both being satellites of the Milky Way.

Yet the other idea, which had science and diagrams and velocities and trajectories and all that good stuff to go with it, is still stuck in my mind. You seem far, far better read than me. Have you read anything definitive about this? Do you think there is any remote possibility that the LMC and SMC might be on the road less traveled, just passing by on their way to somewhere most of us haven't considered? Does the Magellanic Stream convince you one way or the other?

I think it is true that the LMC and the SMC have been interacting for a few billion years only. I also think that they have very recently (in astronomical terms) been captured by the Milky Way.

Timothy Ferris wrote:
Looming near the mighty sweep of the southern Milky Way, the Large and Small Magellanic Clouds resemble detached pieces of our galaxy. Astronomers once assumed they had always orbited the Milky Way at approximately their current distances, like the other, lesser satellite galaxies in the Milky Way's gravitational thrall. But new evidence suggests that the Magellanic Clouds have instead spent most of their careers farther away and are currently experiencing a rare close encounter with our galaxy. If so, we may be witnessing the onset of an intergalactic pas de trois—a dance of the sort that can shatter the composure of galaxies, forging billions of new stars and planets while flinging others into the depths of space.
...
For one thing, the clouds are much brighter than our galaxy's other satellites—bright enough to have captured the attention of naked-eye observers like Ferdinand Magellan's chronicler, Antonio Pigafetta, who remarked upon the "many small stars congregated together." They're bright because they're close by and contain lots of stars. The Milky Way's known satellites harbor up to ten million stars each. The Small Magellanic Cloud holds some three billion stars, and the Large Cloud perhaps 30 billion.
...
In 2006 a team of astronomers using the Hubble Space Telescope measured the motion of the Magellanic Clouds by clocking them against background quasars, which lie billions of light-years beyond and so approximate a static background in a universe where nothing really stands still. These measurements suggest the clouds are pursuing lanky, eccentric orbits that would have brought them into proximity with our galaxy only one time previously since the universe began.

Technology Review wrote:
The Large Magellanic cloud is unusually luminous. In fact, there are only two other irregular galaxies in the entire local universe that come close. “In other words the Large Magellanic Cloud seems to be close to the upper luminosity limit for irregular galaxies,” says van den Bergh. That’s unusual too.

In recent years, astronomers have begun to work out just how rare this is. Sky surveys such as the Sloan Digital Sky Survey allow astronomers to work out the distribution of various types of galaxy. They’ve looked at 22581 galaxies like the Milky Way and found that 81% have no satellite galaxies as bright as the Magellanic Clouds, 11% have one such satellite, and only 3.5% host two such satellite galaxies.

That makes the Milky Way very unusual. As van den Bergh puts it: “That the Galaxy should have an irregular companion as luminous as the Large Magellanic Cloud is almost a miracle.”

It seems pretty certain that the Magellanic Clouds have been outside the influence of the Milky Way for most of their existence. That's why they are gas-rich and luminous now, instead of being harassed and dull like the other companions of the Milky Way. But the Magellanic Clouds may have interacted with each other in the past quite forcefully.

Space.com wrote:

New simulations suggest that the Large Magellanic Cloud (LMC) snatched a stream of stars from its neighbor, the Small Magellanic Cloud (SMC), when the two galaxies collided 300 million years ago.
...
"By reconstructing the scene, we found that the LMC and SMC collided violently hundreds of millions of years ago. That's when the LMC stripped out the lensed stars," Loeb added.

I thought I had read somewhere that the Magellanic Clouds themselves have not been interacting for that many billions of years, but I have been unable to find that source.

Ann

[neufer]

I read one article, and only one, several years ago about a diverging point of view that possibly instead of being true companions to the Milky Way, they were just "playing through."

Magellanic Clouds May Be Just Passing Through
Astronomy, January 9, 2007

<<Astronomers Nitya Kallivayalil and Charles Alcock (Harvard-Smithsonian Center for Astrophysics) and Roeland van der Marel (Space Telescope Science Institute) have made the most accurate measurements to date of the three-dimensional velocities through space of the LMC and SMC. Their surprising results hold profound implications for both the Milky Way and its companions. "We found that the velocities of the LMC and SMC are unexpectedly large - almost twice those previously thought," says Kallivayalil.

The radial velocities (motion along the line of sight) for both Clouds are well known and relatively easy to measure. Much more difficult to measure is the proper motion (motion across the sky), requiring extraordinary precision over the course of several years. Both proper motion and line-of-sight motion must be known to calculate the true 3-D velocity.

By making two sets of observations two years apart with NASA's Hubble Space Telescope, Kallivayalil and her colleagues calculated accurate proper motions for the LMC and SMC. By combining proper motions and radial velocities, they found that the LMC speeds through space at 378 km/sec while the SMC has a speed of 302 km/sec.

There are two possible explanations for these high speeds:

• 1) The mass extent of the Milky Way is larger than previously thought. If the Clouds are gravitationally bound to the Milky Way, then the Milky Way must be much more massive than previous data suggested. The excess mass would pull on the Clouds, keeping them "close at hand."
  
  2) The Magellanic Clouds are not gravitationally bound to the Milky Way. If previous calculations of the Milky Way's mass are accurate, then the Galaxy is not massive enough to hold onto its companions. In a few billion years, they will escape from the Milky Way.

"The Magellanic Clouds may not be true companions of the Milky Way," explains Kallivayalil. "Perhaps they are travelers just passing through the neighborhood.">>

Six years later....

Third-Epoch Magellanic Cloud Proper Motions I: HST/WFC3 data and Orbit Implications

Nitya Kallivayalil, Roeland P. van der Marel, Gurtina Besla, Jay Anderson, Charles Alcock
(Submitted on 4 Jan 2013)

<<We present proper motions for the Large & Small Magellanic Clouds (LMC & SMC) based on three epochs of {Hubble Space Telescope data}, spanning a ∼7 yr baseline, and centered on fields with background QSOs. The new third epoch with WFC3/UVIS increases the time baseline and provides better control of systematics. For the LMC this is sufficient to constrain the internal proper motion dynamics. We combine the results with a revised understanding of the solar motion in the Milky Way to derive Galactocentric velocities: v__{LMC} = 321 ± 24 km/s and v__{SMC} = 217 ± 26 km/s. Our proper motion uncertainties are now dominated by limitations in our understanding of the internal kinematics and geometry of the Clouds, and our velocity uncertainties are dominated by distance errors. Orbit calculations for the Clouds around the Milky Way allow a range of orbital periods, depending on the uncertain masses of the Milky Way and LMC. [Orbital periods] ≲4 Gyr are ruled out, which poses a challenge for traditional Magellanic Stream models. First-infall orbits are preferred (as supported by other arguments as well) if one imposes the requirement that the LMC and SMC must have been a bound pair for at least several Gyr.>>

[Glima49]

So the Magellanic Clouds do not belong to the Milky Way then. Interesting. Also, it seems you guys overlooked an irregular galaxy which could be the LMC's twin. Behold NGC 4449:

Comparable in size and shape to the LMC, but star formation rate is more than the LMC. It is also an emission line galaxy. However, it appears relatively isolated, with no giant companion (Milky Way) or small counterpart (SMC) to trigger starburst formation, what is going on? I'd expect that if it had a giant companion similar to the Milky Way it would probably be the most spectacular other galaxy in the sky save for Andromeda. The true answer could be interactions with dwarf satellite galaxies. Makes me wonder if the LMC would have such galaxies...

[neufer]

So the Magellanic Clouds do not belong to the Milky Way then. Interesting.

• Maybe.

Also, it seems you guys overlooked an irregular galaxy which could be the LMC's twin. Behold NGC 4449:

http://asterisk.apod.com/viewtopic.php? ... 3&p=169127

[bystander]

Heh, source "nature.com"

Sorry, Geck. I tried to open the page where the picture was posted, and I searched for other versions of the same image. But the page wouldn't open, and I couldn't find any other sizes of the same picture. That's why I chose "nature.com", since I could see that the picture has been published in Nature.

Ann

http://apod.nasa.gov/apod/ap140701.html

[Ann]

Thanks, bystander.

Ann

[Ann]

So the Magellanic Clouds do not belong to the Milky Way then. Interesting.

• Maybe.

Also, it seems you guys overlooked an irregular galaxy which could be the LMC's twin. Behold NGC 4449:

http://asterisk.apod.com/viewtopic.php? ... 3&p=169127

Click to view full size image

NGC 4449. Image: R. Jay GaBany.

That's a great image by R. Jay GaBany! NGC 4449 is interacting after all.

Click to view full size image

NGC 1313. Image: Volker Wendel & Bernd Flach-Wilken.

NGC 1313 is another LMC-like but seemingly isolated galaxy that is putting on a real fireworks show. Maybe, like NGC 4449, NGC 1313 is interacting with a tiny companion of its own, one that hasn't been discovered yet. But NGC 1313 was the APOD of March 30, 2010, and APOD Robot wrote that NGC 1313 appears to be alone.

Ann

[messier.palette]

Thanks for all the info on star evolution and on The Clouds everyone! I've just read through this whole thread three *more* times and am still trying to absorb the new information. What exciting times we live in - thanks for putting together these sources and thoughts. Love the images too. Will look at them often in the coming days. Thank you, thank you, thank you, all of you.

[Ann]

So, what would have happened 2 million years ago (+light travel time) to create this wonder? A huge compression, shock, or swirling of proto-stellar material?

I may have been a bit hasty when I said that nothing special happened in the LMC 2 million years ago. The gas that turned into R136 and NGC 2070 could well have been buffeted and compressed by supernovas in an older cluster nearby, Hodge 301.

Wikipedia wrote:
Hodge 301, along with the cluster R136, is one of two major star clusters situated in the Tarantula Nebula, a region which has seen intense bursts of star formation over the last few tens of millions of years. R136 is situated in the central regions of the nebula, while Hodge 301 is located about 150 light years away, to the north west as seen from Earth. Hodge 301 was formed early on in the current wave of star formation, with an age estimated at 20-25 million years old, some ten times older than R136.

Since Hodge 301 formed, it is estimated that at least 40 stars within it have exploded as supernovae, giving rise to violent gas motions within the surrounding nebula and emission of x-rays. This contrasts with the situation around R136, which is young enough that none of its stars have yet exploded as supernovae; instead, the stars of R136 are emitting fast stellar winds, which are colliding with the surrounding gases. The two clusters thus provide astronomers with a direct comparison between the impact of supernova explosions and stellar winds on surrounding gases.

So Hodge 301 and all its supernovas may have helped create the conditions that gave rise to R136. Of course, that leaves another question unanswered: What happened that gave rise to Hodge 301?

Ann

[Glima49]

Oops. I meant Flying Lizard, not Flying Bat. Flying Bat is the popular name of Sh2-129. Back on the topic.