APOD: The Lively Center of the Lagoon Nebula (2020 Jun 01)

[APOD Robot]

The Lively Center of the Lagoon Nebula

Explanation: The center of the Lagoon Nebula is a whirlwind of spectacular star formation. Visible near the image center, at least two long funnel-shaped clouds, each roughly half a light-year long, have been formed by extreme stellar winds and intense energetic starlight. A tremendously bright nearby star, Hershel 36, lights the area. Vast walls of dust hide and redden other hot young stars. As energy from these stars pours into the cool dust and gas, large temperature differences in adjoining regions can be created generating shearing winds which may cause the funnels. This picture, spanning about 15 light years, features two colors detected by the orbiting Hubble Space Telescope. The Lagoon Nebula, also known as >M8, lies about 5000 light years distant toward the constellation of the Archer Sagittarius.

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[Ann]

The Lively Center of the Lagoon Nebula. Image Credit: NASA, ESA, Hubble; Processing & Copyright: Diego Gravinese.

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The Hourglass Nebula in the Lagoon Nebula in a Hubble picture from 1997.

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I'm very glad to see this new picture of the center of the Lagoon Nebula. I was so turned off by the strange colors of the the first Hubble picture of the region around the Hourglass Nebula in the Lagoon Nebula from 1997 that I completely discarded it as an image that I could incorporate in the treasure chest of astroimages in my mind, those that I could extract at another time for later use.

The reason for the strange colors in the 1997 Hubble image is that the picture was made using OIII, Hα, and SII filters and mapped colors were assigned to the filter images. That would be the reason for the sharp yellow color of the Hourglass nebula. To make matters worse, in some versions of the image the sharp yellow hues of the Hourglass were seen against a sharp blue background, and there was an extremely sharp reddish-magenta star located right next to it. The colors struck me as so "unnatural" that I actually couldn't make sense of the image.

In the new image, Hα dominates and looks properly red. There is a range of subtle red colors mixed with bluish hues. The reason for this palette is that the image according to the caption was made from two filter images, probably Hα and OIII. To me this is an improvement of many magnitudes! The brilliantly bright Hourglass Nebula looks white instead of sharply yellow, the background behind it is a soft shade of turquoise instead of sharp blue, and the star next to it looks a bit magenta-pink but certainly nothing like the shade of 1960s hot pink in the 1997 image. The new image makes perfect sense.

Fantastic! Now I can look at the image and think that I understand it. Now I have an "Hourglass in the Lagoon Nebula" image that I can store in my mind for later use.

Ann

[Ann]

The Hourglass Nebula. Photo: ESA.

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The reason why those Hubble palette images look so weird to me is that the deep red Hα emission is assigned the color green, and the quite faint red SII emission is made to look really bright.

I'm still struggling to understand the utterly weird hues of the image of the Hourglass Nebula at right.

But I probably shouldn't even try to understand it. It's not meant to be "realistic", it's meant to bring out different features of the Hourglass Nebula.

Okay. Whatever.

Ann

[JohnD]

"large temperature differences in adjoining regions can be created generating shearing winds which may cause the funnels."

The links show that what is happening and how is not understood, but for a start how do the temperature differences cause "shearing winds" in deep space? 'Winds' on Earth happen when the air has different temperatures in adjoining regions, but that is caused by change in density and the effect of gravity on a planet-bound atmosphere. What sort of wind exists in space?

[Ann]

"large temperature differences in adjoining regions can be created generating shearing winds which may cause the funnels."

The links show that what is happening and how is not understood, but for a start how do the temperature differences cause "shearing winds" in deep space? 'Winds' on Earth happen when the air has different temperatures in adjoining regions, but that is caused by change in density and the effect of gravity on a planet-bound atmosphere. What sort of wind exists in space?

A young stellar object blowing a pair of jets. Photo: ESA/Hubble & NASA, D. Padgett (GSFC), T. Megeath (University of Toledo), and B. Reipurth (University of Hawaii)

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Both components of Eta Carina blow a strong stellar wind. Illustration: I don't know.

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Well, there are all kinds of stellar winds, of course. If the star in the center of the Hourglass Nebula is a very young star, which I believe it is, it could certainly blow a pair of jets. Then again, I don't see any.

If the star in the center of the Hourglass Nebula is a very massive one, which I believe it is, it could blow a strong stellar wind.

Wikipedia wrote:

Massive stars of types O and B have stellar winds with lower mass loss rates ({\displaystyle \scriptstyle {\dot {M}}<10^{-6}}\scriptstyle {\dot {M}}<10^{{-6}} solar masses per year) but very high velocities (v > 1–2000 km/s).

And if there is more than one star forming at or near the center of the Hourglass Nebula, I guess you might get several stellar winds blowing in different directions.

But let me return to the fact that I have such a hard time reading the Hubble picture of the Hourglass Nebula. The weird colors that I referred to in a nother post is definitely one reason, but there is more.

Why doesn't the bright and painfully pink star to the right of the Hourglass Nebula seem to light up its vicinity in the slightest?

Why can't we see any sort of "point brightening" in the Hourglass Nebula? In other words, why don't see the slightest suggestion of a star forming in there?

Yes, yes, I get it. The star is completely hidden by dust. Okay. Or is that tiny red spot sitting in the middle of the dust to the upper left of the bright pink star actually the central star of the Hourglass Nebula?

It looks weird, that's all I'm saying.

Ann

[orin stepanek]

LagoonCenter_HubbleGravinese_960.jpg

Reminds me of a bat in flight with something in front of its face!
Terrible imagination have I

[jisles]

The nearby star is Herschel 36, not Hershel 36.

John

[johnnydeep]

The Lively Center of the Lagoon Nebula

Explanation: The center of the Lagoon Nebula is a whirlwind of spectacular star formation. Visible near the image center, at least two long funnel-shaped clouds, each roughly half a light-year long, have been formed by extreme stellar winds and intense energetic starlight. A tremendously bright nearby star, Hershel 36, lights the area. Vast walls of dust hide and redden other hot young stars. As energy from these stars pours into the cool dust and gas, large temperature differences in adjoining regions can be created generating shearing winds which may cause the funnels. This picture, spanning about 15 light years, features two colors detected by the orbiting Hubble Space Telescope. The Lagoon Nebula, also known as >M8, lies about 5000 light years distant toward the constellation of the Archer Sagittarius.

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Sometimes I just can't point to a feature of an image based on the description given. Like here: "Visible near the image center, at least two long funnel-shaped clouds, each roughly half a light-year long". Just what funnel-shaped clouds is it referring to? At the center of the image I do indeed see two bright triangular regions, but these are voids in the dust clouds (even better seen in Ann's closeup of another APOD), not clouds themselves. So are these voids the "funnel-shaped" clouds?

Also, a more general question: just how dense are these dust clouds? I'm thinking they would be much less dense than water vapor clouds on earth.

[neufer]

Center of the Lagoon Nebula by ESA

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Sometimes I just can't point to a feature of an image based on the description given. Like here: "Visible near the image center, at least two long funnel-shaped clouds, each roughly half a light-year long". Just what funnel-shaped clouds is it referring to? At the center of the image I do indeed see two bright triangular regions, but these are voids in the dust clouds (even better seen in Ann's closeup of another APOD), not clouds themselves. So are these voids the "funnel-shaped" clouds?

Multiple "funnel-shaped" clouds
bound the voids.

[neufer]

...just how dense are these dust clouds?
I'm thinking they would be much less dense than water vapor clouds on earth.

Most cosmic dust particles measure between a few molecules & 10^-7m.

The light-year is ~10¹⁶m
Hence, the optical cross section: σ_d ~ (10^-7 m)²

Optical depth τ_d ~ [σ_d x 10¹⁶m] x ρ_dL ~ 100 ρ_dL

where ρ_d = dust density in grains/m³
and L = length in light years (~10¹⁶m).

The density of the dust cloud through which the Earth
is traveling is approximately ρ_E ~ 10^-6 dust grains/m³
so one can see a few tens of thousands of light years (i.e., a few optical depths).

Here one can see only a few tenths of a light year

so that ρ_d ~ 0.1 dust grains/m³

[mike hewitt]

Check out the monkey's head just left of the 2 bright stars near the top....

[De58te]

Here's something curious. Nature it is said abhors straight lines. What are those two thin lines at the top left. You can see them better with the high definition version. Scroll to the top left corner. There is a thin line almost the same angle as the star spike but at least 5 times longer. Scroll a bit to the right and you see a second line that almost makes a v shape. Could these be a star spike which is just off the top edge but very much closer to the Earth? Or are they actually meteor shooting stars just happened to be caught by the Hubble?

[Ann]

Sometimes I just can't point to a feature of an image based on the description given. Like here: "Visible near the image center, at least two long funnel-shaped clouds, each roughly half a light-year long". Just what funnel-shaped clouds is it referring to? At the center of the image I do indeed see two bright triangular regions, but these are voids in the dust clouds (even better seen in Ann's closeup of another APOD), not clouds themselves. So are these voids the "funnel-shaped" clouds?

Hourglass Nebula with funnels.png

I guess these might be the funnels.

Ann

[johnnydeep]

Sometimes I just can't point to a feature of an image based on the description given. Like here: "Visible near the image center, at least two long funnel-shaped clouds, each roughly half a light-year long". Just what funnel-shaped clouds is it referring to? At the center of the image I do indeed see two bright triangular regions, but these are voids in the dust clouds (even better seen in Ann's closeup of another APOD), not clouds themselves. So are these voids the "funnel-shaped" clouds?

Hourglass Nebula with funnels.png

I guess these might be the funnels.

Ann

Perhaps. But if so, I think I'd call them "fingers" instead.

[MarkBour]

Capture1.jpg

Here's something curious. Nature it is said abhors straight lines. What are those two thin lines at the top left. You can see them better with the high definition version. Scroll to the top left corner. There is a thin line almost the same angle as the star spike but at least 5 times longer. Scroll a bit to the right and you see a second line that almost makes a v shape. Could these be a star spike which is just off the top edge but very much closer to the Earth? Or are they actually meteor shooting stars just happened to be caught by the Hubble?

There is a much brighter star just off the top edge of the image. I believe you're talking about the long diffraction spikes emanating from it. I wanted to determine the name of that star to remark on it, but I'm not very knowledgeable as to how to do that. I think folks would use SIMBAD, but I did not figure out how to find the name of that star.

Anyway, at the right is an image of a slightly wider field of view of the lagoon nebula, with the region of today's APOD sketched in red on it. Would a pair of diffraction spikes from that star be the lines you're asking about?

[johnnydeep]

Center of the Lagoon Nebula by ESA

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Sometimes I just can't point to a feature of an image based on the description given. Like here: "Visible near the image center, at least two long funnel-shaped clouds, each roughly half a light-year long". Just what funnel-shaped clouds is it referring to? At the center of the image I do indeed see two bright triangular regions, but these are voids in the dust clouds (even better seen in Ann's closeup of another APOD), not clouds themselves. So are these voids the "funnel-shaped" clouds?

Multiple "funnel-shaped" clouds
bound the voids.

Thanks. Yeah, that makes more sense and I see it now. Confirmed by Ann's reply as well.

[johnnydeep]

...just how dense are these dust clouds?
I'm thinking they would be much less dense than water vapor clouds on earth.

Most cosmic dust particles measure between a few molecules & 10^-7m.

The light-year is ~10¹⁶m
Hence, the optical cross section: σ_d ~ (10^-7 m)²

Optical depth τ_d ~ [σ_d x 10¹⁶m] x ρ_dL ~ 100 ρ_dL

where ρ_d = dust density in grains/m³
and L = length in light years (~10¹⁶m).

The density of the dust cloud through which the Earth
is traveling is approximately ρ_E ~ 10^-6 dust grains/m³
so one can see a few tens of thousands of light years (i.e., a few optical depths).

Here one can see only a few tenths of a light year

so that ρ_d ~ 0.1 dust grains/m³

Thanks for the details! But as has been the case with some of your past replies, I don't quite follow all this (I still have to look up optical cross section and optical depth for example). But assuming the figures of interstellar visibility are correct (that is, being able to see a few tenths of a light year), given we can't see through a cumulus cloud more than a few hundred meters thick, then, yes, interstellar dust clouds are indeed much less dense than earth water vapor clouds.

PS - and I hope it didn't take too long to compose your reply, what with all those [ sub ]s and [ sup ]s to format!

[Chris Peterson]

...just how dense are these dust clouds?
I'm thinking they would be much less dense than water vapor clouds on earth.

Most cosmic dust particles measure between a few molecules & 10^-7m.

The light-year is ~10¹⁶m
Hence, the optical cross section: σ_d ~ (10^-7 m)²

Optical depth τ_d ~ [σ_d x 10¹⁶m] x ρ_dL ~ 100 ρ_dL

where ρ_d = dust density in grains/m³
and L = length in light years (~10¹⁶m).

The density of the dust cloud through which the Earth
is traveling is approximately ρ_E ~ 10^-6 dust grains/m³
so one can see a few tens of thousands of light years (i.e., a few optical depths).

Here one can see only a few tenths of a light year

so that ρ_d ~ 0.1 dust grains/m³

Thanks for the details! But as has been the case with some of your past replies, I don't quite follow all this (I still have to look up optical cross section and optical depth for example). But assuming the figures of interstellar visibility are correct (that is, being able to see a few tenths of a light year), given we can't see through a cumulus cloud more than a few hundred meters thick, then, yes, interstellar dust clouds are indeed much less dense than earth water vapor clouds.

PS - and I hope it didn't take too long to compose your reply, what with all those [ sub ]s and [ sup ]s to format!

They're not just orders of magnitude less dense than Earth clouds, they're orders of magnitude less dense than Earth's atmosphere (without any dust or aerosols). You'd not see stars through just a few tens of thousands of miles of atmosphere... let alone fractions of light years!

[neufer]

...just how dense are these dust clouds?
I'm thinking they would be much less dense than water vapor clouds on earth.

Most cosmic dust particles measure between a few molecules & 10^-7m.

The light-year is ~10¹⁶m
Hence, the optical cross section: σ_d ~ (10^-7 m)²

Optical depth τ_d ~ [σ_d x 10¹⁶m] x ρ_dL ~ 100 ρ_dL

where ρ_d = dust density in grains/m³
and L = length in light years (~10¹⁶m).

The density of the dust cloud through which the Earth
is traveling is approximately ρ_E ~ 10^-6 dust grains/m³
so one can see a few tens of thousands of light years (i.e., a few optical depths).

Here one can see only a few tenths of a light year

so that ρ_d ~ 0.1 dust grains/m³

Thanks for the details! But as has been the case with some of your past replies, I don't quite follow all this (I still have to look up optical cross section and optical depth for example). But assuming the figures of interstellar visibility are correct (that is, being able to see a few tenths of a light year), given we can't see through a cumulus cloud more than a few hundred meters thick, then, yes, interstellar dust clouds are indeed much less dense than earth water vapor clouds.

Earth cloud droplets measure around ~140 x 10^-7m.

Hence, the optical cross section: σ_d ~2 x 10^-10m²/droplet

Earth cloud droplet density ρ_d = ~0.5 x 10⁹ droplets/m³

Optical depth τ_d ~ σ_d x ρ_d L ~ 0.10 L (where L = length in meters)

Ergo: one can see into a cloud a few tens of meters (i.e., a few optical depths).

[w5dfc]

What is the bright white streak in the NW quadrant?

[TheZuke!]

What is the bright white streak in the NW quadrant?

Everyone knows the Lagoon Nebula is in the Alpha Quadrant!
(Star Trekkie joke).

(Which makes me wonder how Star Fleet was able to convince residents in other quadrants that this is the "alpha" quadrant and therefore their quadrants are secondary.)