APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 4440
Joined: Fri Dec 04, 2009 3:27 am

APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by APOD Robot » Thu Sep 30, 2021 4:05 am

Image The Hydrogen Clouds of M33

Explanation: Gorgeous spiral galaxy M33 seems to have more than its fair share of glowing hydrogen gas. A prominent member of the local group of galaxies, M33 is also known as the Triangulum Galaxy and lies a mere 3 million light-years away. Sprawling along loose spiral arms that wind toward the core, M33's giant HII regions are some of the largest known stellar nurseries, sites of the formation of short-lived but very massive stars. Intense ultraviolet radiation from the luminous massive stars ionizes the surrounding hydrogen gas and ultimately produces the characteristic red glow. To highlight the HII regions in this telescopic image, broadband data used to produce a color view of the galaxy were combined with narrowband data recorded through a hydrogen-alpha filter, transmitting the light of the strongest hydrogen emission line. Close-ups of cataloged HII regions appear in the sidebar insets. Use the individual reference number to find their location within the Triangulum Galaxy. For example, giant HII region NGC604 is identified in an inset on the right and appears at position number 15. That's about 4 o'clock from galaxy center in this portrait of M33.

<< Previous APOD This Day in APOD Next APOD >>

User avatar
Ann
4725 Å
Posts: 11568
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by Ann » Thu Sep 30, 2021 4:18 am

Wow, that's a wonderful portrait of M33, and the image is as beautifully annotated as anyone could ask for! :D 🤩

Thank you, Luca Fornaciari! :D :clap:

Ann
Color Commentator

Luca Fornaciari
Asternaut
Posts: 4
Joined: Sun Oct 06, 2019 2:01 pm

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by Luca Fornaciari » Thu Sep 30, 2021 1:22 pm

thanks a lot :)

User avatar
orin stepanek
Plutopian
Posts: 6883
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by orin stepanek » Thu Sep 30, 2021 2:27 pm

STScI-01EVT8XBYKB28X1EP3WRB4FZCJ.jpg
Reminds me of the Tarantula!
NebulaeTriangulumM33-1.jpg
Beautiful Galaxy; and you can visit all the hydrogen clouds by
clicking on the insets! :D
Thanks again Luca Fornaciari!
You do not have the required permissions to view the files attached to this post.
Orin

Smile today; tomorrow's another day!

User avatar
Fred the Cat
Theoretic Apothekitty
Posts: 725
Joined: Mon Feb 22, 2016 4:09 pm
AKA: Ron
Location: Eagle, Idaho

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by Fred the Cat » Thu Sep 30, 2021 3:45 pm

Cloudy today with a chance of sun tomorrow. Are we any closer to finding out why? :?

The forecast seems bleak for new ideas to rein in the process :?:
Freddy's Felicity "Only ascertain as a cat box survivor"

DL MARTIN

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by DL MARTIN » Thu Sep 30, 2021 3:54 pm

Number 15 is described as having young stars that formed 3 million years ago. Since M33 is coincidentally 3 million ly distant and hence 3 million years ago as we see it one might ask; What does the 3 million years ago reference to the age of the stars refer to? I believe scientific rigour demands clarification. Or is astronomy billing itself as current events!

De58te
Science Officer
Posts: 417
Joined: Mon Sep 30, 2013 6:35 pm

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by De58te » Thu Sep 30, 2021 4:42 pm

DL MARTIN wrote:
Thu Sep 30, 2021 3:54 pm
Number 15 is described as having young stars that formed 3 million years ago. Since M33 is coincidentally 3 million ly distant and hence 3 million years ago as we see it one might ask; What does the 3 million years ago reference to the age of the stars refer to? I believe scientific rigour demands clarification. Or is astronomy billing itself as current events!
The link actually says the new formed stars are relatively young having formed 3 million years ago. Then it goes on to say that NGC 604 is located about 2.7 million light years away. (A little bit closer than M33.) Then we can conclude the stars in NGC 604 star forming region are roughly 300,000 years old as they are pictured in the APOD photo.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18456
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by neufer » Thu Sep 30, 2021 5:11 pm

De58te wrote:
Thu Sep 30, 2021 4:42 pm
DL MARTIN wrote:
Thu Sep 30, 2021 3:54 pm

Number 15 is described as having young stars that formed 3 million years ago. Since M33 is coincidentally 3 million ly distant and hence 3 million years ago as we see it one might ask; What does the 3 million years ago reference to the age of the stars refer to? I believe scientific rigour demands clarification. Or is astronomy billing itself as current events!
The link actually says the new formed stars are relatively young having formed 3 million years ago. Then it goes on to say that NGC 604 is located about 2.7 million light years away. (A little bit closer than M33.) Then we can conclude the stars in NGC 604 star forming region are roughly 300,000 years old as they are pictured in the APOD photo.
We can conclude the stars in NGC 604 star forming region are roughly 3,000,000 years old as they are pictured in the APOD photo.

99.99% of astrophysics assigns the age of observed objects in accord with the Earth time in which those observations were made.
Art Neuendorffer

DL MARTIN

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by DL MARTIN » Thu Sep 30, 2021 6:42 pm

If astrophysics defines objects as observed in earth time then doesn't that omit changes that have taken place during the period of transmission. the sun, for example, as observed has undergone 8 minutes of change at source.

User avatar
johnnydeep
Commander
Posts: 883
Joined: Sun Feb 20, 2011 8:57 pm

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by johnnydeep » Thu Sep 30, 2021 8:16 pm

neufer wrote:
Thu Sep 30, 2021 5:11 pm
De58te wrote:
Thu Sep 30, 2021 4:42 pm
DL MARTIN wrote:
Thu Sep 30, 2021 3:54 pm

Number 15 is described as having young stars that formed 3 million years ago. Since M33 is coincidentally 3 million ly distant and hence 3 million years ago as we see it one might ask; What does the 3 million years ago reference to the age of the stars refer to? I believe scientific rigour demands clarification. Or is astronomy billing itself as current events!
The link actually says the new formed stars are relatively young having formed 3 million years ago. Then it goes on to say that NGC 604 is located about 2.7 million light years away. (A little bit closer than M33.) Then we can conclude the stars in NGC 604 star forming region are roughly 300,000 years old as they are pictured in the APOD photo.
We can conclude the stars in NGC 604 star forming region are roughly 3,000,000 years old as they are pictured in the APOD photo.

99.99% of astrophysics assigns the age of observed objects in accord with the Earth time in which those observations were made.
And in any event, the age numbers don't make sense as stated in the disparate references: M33 is 3 mly away, NGC 604 is 2.7 mly away, yet NGC 604 is WITHIN M33, and M33 is only 60 kly wide. All three can't be true. M33 and NGC 604 have to both be at about the same distance, with NGC 604 being at most 30 kly closer or further away.
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."

User avatar
johnnydeep
Commander
Posts: 883
Joined: Sun Feb 20, 2011 8:57 pm

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by johnnydeep » Thu Sep 30, 2021 8:24 pm

So what's really going on in these annoyingly named HII regions? HII regions are composed of singly ionized Hydrogen atoms, meaning they've lost their single electrons, so are now just bare protons. But where do the electrons go? Do they just fly around until they loose enough energy (by emitting a photon of the appropriate wavelength - by which we can see the process by) only to then be recaptured by an almost certainly different proton? Meaning that this is really just a soup of protons and electrons and very short lived neutral HI atoms?
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18456
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by neufer » Thu Sep 30, 2021 10:08 pm

johnnydeep wrote:
Thu Sep 30, 2021 8:24 pm

So what's really going on in these annoyingly named HII regions? HII regions are composed of singly ionized Hydrogen atoms, meaning they've lost their single electrons, so are now just bare protons. But where do the electrons go? Do they just fly around until they loose enough energy (by emitting a photon of the appropriate wavelength - by which we can see the process by) only to then be recaptured by an almost certainly different proton? Meaning that this is really just a soup of protons and electrons and very short lived neutral HI atoms?
1) Electrons are indistinguishable except for the direction of their spin.

2) Protons are indistinguishable except for the direction of their spin.

3) There will always be electrons & protons that find each other at slow enough velocities that they will combine into an excited neutral hydrogen atoms which then emits spectral lines (e.g., the H-alpha line at 656.3 nm).

4) This is hot (~10,000 K) soup/plasma of protons & electrons with a few short lived neutral HI atoms lighting it up for us.

5) https://www.syfy.com/syfywire/a-fog-of- ... e-know-why
https://en.wikipedia.org/wiki/H_II_region wrote: <<An HII ("H two") region is a region of interstellar atomic hydrogen that is ionized. It is typically a cloud in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per cubic cm. HII regions consist of about 90% hydrogen. The strongest hydrogen emission line, the H-alpha line at 656.3 nm, gives HII regions their characteristic red colour. (This emission line comes from excited un-ionized hydrogen.) The lifetime of an HII region is of the order of a few million years. Radiation pressure from the hot young stars will eventually drive most of the gas away. In fact, the whole process tends to be very inefficient, with less than 10 percent of the gas in the HII region forming into stars before the rest is blown off. Contributing to the loss of gas are the supernova explosions of the most massive stars, which will occur after only 1–2 million years.

HII regions may be of any shape, because the distribution of the stars and gas inside them is irregular. The short-lived blue stars created in these regions emit copious amounts of ultraviolet light that ionize the surrounding gas. HII regions—sometimes several hundred light-years across—are often associated with giant molecular clouds. They often appear clumpy and filamentary, sometimes showing intricate shapes such as the Horsehead Nebula.

Stars form in clumps of cool molecular gas that hide the nascent stars. It is only when the radiation pressure from a star drives away its 'cocoon' that it becomes visible. The hot, blue stars that are powerful enough to ionize significant amounts of hydrogen and form HII regions will do this quickly, and light up the region in which they just formed. The dense regions which contain younger or less massive still-forming stars and which have not yet blown away the material from which they are forming are often seen in silhouette against the rest of the ionised nebula. Bart Bok and E. F. Reilly searched astronomical photographs in the 1940s for "relatively small dark nebulae", following suggestions that stars might be formed from condensations in the interstellar medium; they found several such "approximately circular or oval dark objects of small size", which they referred to as "globules", since referred to as Bok globules. Bok proposed at the December 1946 Harvard Observatory Centennial Symposia that these globules were likely sites of star formation. It was confirmed in 1990 that they were indeed stellar birthplaces. The hot young stars dissipate these globules, as the radiation from the stars powering the HII region drives the material away. In this sense, the stars which generate HII regions act to destroy stellar nurseries. In doing so, however, one last burst of star formation may be triggered, as radiation pressure and mechanical pressure from supernova may act to squeeze globules, thereby enhancing the density within them.

Typically HII regions reach temperatures of 10,000 K. They are mostly ionised gases with weak magnetic fields with strengths of several nanoteslas. A number of HII regions also show signs of being permeated by a plasma with temperatures exceeding 10,000,000 K, sufficiently hot to emit X-rays. X-ray observatories such as Einstein and Chandra have noted diffuse X-ray emissions in a number of star-forming regions, notably the Orion Nebula, Messier 17, and the Carina Nebula. The hot gas is likely supplied by the strong stellar winds from O-type stars, which may be heated by supersonic shock waves in the winds, through collisions between winds from different stars, or through colliding winds channeled by magnetic fields. This plasma will rapidly expand to fill available cavities in the molecular clouds due to the high speed of sound in the gas at this temperature. It will also leak out through holes in the periphery of the HII region, which appears to be happening in Messier 17.

The precursor to an HII region is a giant molecular cloud (GMC). A GMC is a cold (10–20 K) and dense cloud consisting mostly of molecular hydrogen. GMCs can exist in a stable state for long periods of time, but shock waves due to supernovae, collisions between clouds, and magnetic interactions can trigger its collapse. When this happens, via a process of collapse and fragmentation of the cloud, stars are born.

As stars are born within a GMC, the most massive will reach temperatures hot enough to ionise the surrounding gas. Soon after the formation of an ionising radiation field, energetic photons create an ionisation front, which sweeps through the surrounding gas at supersonic speeds. At greater and greater distances from the ionising star, the ionisation front slows, while the pressure of the newly ionised gas causes the ionised volume to expand. Eventually, the ionisation front slows to subsonic speeds, and is overtaken by the shock front caused by the expansion of the material ejected from the nebula. The HII region has been born.>>
Art Neuendorffer

User avatar
johnnydeep
Commander
Posts: 883
Joined: Sun Feb 20, 2011 8:57 pm

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by johnnydeep » Fri Oct 01, 2021 2:30 pm

DL MARTIN wrote:
Thu Sep 30, 2021 6:42 pm
If astrophysics defines objects as observed in earth time then doesn't that omit changes that have taken place during the period of transmission. The sun, for example, as observed has undergone 8 minutes of change at source.
Yes, but why does that trouble you? The sun may have imploded at the instant the light that left it hit our eyes, but we wouldn't know that for 8.33 minutes. Likewise, M33 may have just had a member star go supernova, and we wouldn't know that for another 2.7 million years. The vast distances involved in combination with the finite speed of light simply mean that we can't know everything that happens at the moments they are happening. That's how the universe works.
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."

User avatar
johnnydeep
Commander
Posts: 883
Joined: Sun Feb 20, 2011 8:57 pm

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by johnnydeep » Fri Oct 01, 2021 3:11 pm

neufer wrote:
Thu Sep 30, 2021 10:08 pm
johnnydeep wrote:
Thu Sep 30, 2021 8:24 pm

So what's really going on in these annoyingly named HII regions? HII regions are composed of singly ionized Hydrogen atoms, meaning they've lost their single electrons, so are now just bare protons. But where do the electrons go? Do they just fly around until they loose enough energy (by emitting a photon of the appropriate wavelength - by which we can see the process by) only to then be recaptured by an almost certainly different proton? Meaning that this is really just a soup of protons and electrons and very short lived neutral HI atoms?
1) Electrons are indistinguishable except for the direction of their spin.

2) Protons are indistinguishable except for the direction of their spin.

3) There will always be electrons & protons that find each other at slow enough velocities that they will combine into an excited neutral hydrogen atoms which then emits spectral lines (e.g., the H-alpha line at 656.3 nm).

4) This is hot (~10,000 K) soup/plasma of protons & electrons with a few short lived neutral HI atoms lighting it up for us.

5) https://www.syfy.com/syfywire/a-fog-of- ... e-know-why
...
So, I was essentially correct in my simple understanding/explanation. But why did you have to throw in points 1) and 2)? What bearing do they have on their behavior in an HII region? And surely, free protons at least (not entirely sure about free electrons) also can all have different energies or velocities. Never mind that I don't know what "direction of spin" means. All protons have spin of 1/2. And is "direction" what we call the imaginary axis of that spin?
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18456
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by neufer » Fri Oct 01, 2021 5:14 pm

neufer wrote:
Thu Sep 30, 2021 10:08 pm
johnnydeep wrote:
Thu Sep 30, 2021 8:24 pm

So what's really going on in these annoyingly named HII regions? HII regions are composed of singly ionized Hydrogen atoms, meaning they've lost their single electrons, so are now just bare protons. But where do the electrons go? Do they just fly around until they loose enough energy (by emitting a photon of the appropriate wavelength - by which we can see the process by) only to then be recaptured by an almost certainly different proton? Meaning that this is really just a soup of protons and electrons and very short lived neutral HI atoms?
1) Electrons are indistinguishable except for the direction of their spin.

2) Protons are indistinguishable except for the direction of their spin.

3) There will always be electrons & protons that find each other at slow enough velocities that they will combine into an excited neutral hydrogen atoms which then emits spectral lines (e.g., the H-alpha line at 656.3 nm).

4) This is hot (~10,000 K) soup/plasma of protons & electrons with a few short lived neutral HI atoms lighting it up for us.

5) https://www.syfy.com/syfywire/a-fog-of- ... e-know-why
...
johnnydeep wrote:
Fri Oct 01, 2021 3:11 pm

So, I was essentially correct in my simple understanding/explanation.
More or less.
johnnydeep wrote:
Fri Oct 01, 2021 3:11 pm

But why did you have to throw in points 1) and 2)? What bearing do they have on their behavior in an HII region? And surely, free protons at least (not entirely sure about free electrons) also can all have different energies or velocities. Never mind that I don't know what "direction of spin" means. All protons have spin of 1/2. And is "direction" what we call the imaginary axis of that spin?
I didn't quite understand the point of your long question: "Do [the free electrons] just fly around until they loose enough energy (by emitting a photon of the appropriate wavelength - by which we can see the process by) only to then be recaptured by an almost certainly different proton?"

The free electrons certainly must lose some energy in order to be captured by a free proton but most of this loss is due to interactions with weak magnetic fields or non-relativistic near-elastic proton scattering. More important, IMO, is the fact that every electron will eventual pair up with a proton of almost identical velocity. Once this pair weakly bond into an excited hydrogen atom then and only then is there time for the emitting a visible photon of the appropriate wavelength - by which we can see the process.

Also... why did you emphasis: "... by an almost certainly different proton?"

Quantum mechanics states that each spin 1/2 fermion classes (e.g., electrons or protons or ...) consist of indistinguishable particles except for whether they are "spin up" or "spin down." So why emphasize this "change of partners." The only possible importance in this regard is whether the electron's spin direction matches the proton's spin direction in the final ground state neutral hydrogen atom since that allows us to detect the HI 21-centimeter line:
https://en.wikipedia.org/wiki/Hydrogen_line wrote: <<The hydrogen HI 21-centimeter line is the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation has a precise frequency of 1,420.405751768 MHz, which is equivalent to the vacuum wavelength of 21.10611405416 cm in free space. This wavelength falls within the microwave region of the electromagnetic spectrum, and it is observed frequently in radio astronomy because those radio waves can penetrate the large clouds of interstellar cosmic dust that are opaque to visible light. The microwaves of the hydrogen line come from the atomic transition of an electron between the two hyperfine levels of the hydrogen 1 s ground state that have an energy difference of 5.874326184112 μeV. It is called the spin-flip transition.

The 21 cm spectral line appears within the radio spectrum. Assuming that the hydrogen atoms are uniformly distributed throughout the galaxy, each line of sight through the galaxy will reveal a hydrogen line. The only difference between each of these lines is the Doppler shift that each of these lines has. Hence, one can calculate the relative speed of each arm of our galaxy. The rotation curve of our galaxy has been calculated using the 21 cm hydrogen line. It is then possible to use the plot of the rotation curve and the velocity to determine the distance to a certain point within the galaxy. Hydrogen line observations have also been used indirectly to calculate the mass of galaxies, to put limits on any changes over time of the universal gravitational constant and to study the dynamics of individual galaxies.

The line is of great interest in Big Bang cosmology because it is the only known way to probe the "dark ages" from recombination to reionization. Including the redshift, this line will be observed at frequencies from 200 MHz to about 9 MHz on Earth. It potentially has two applications. First, by mapping the intensity of redshifted 21 centimeter radiation it can, in principle, provide a very precise picture of the matter power spectrum in the period after recombination. Second, it can provide a picture of how the universe was reionized, as neutral hydrogen which has been ionized by radiation from stars or quasars will appear as holes in the 21 cm background.

However, 21 cm observations are very difficult to make. Ground-based experiments to observe the faint signal are plagued by interference from television transmitters and the ionosphere, so they must be made from very secluded sites with care taken to eliminate interference. Space based experiments, even on the far side of the Moon (where they would be sheltered from interference from terrestrial radio signals), have been proposed to compensate for this. Little is known about other effects, such as synchrotron emission and free–free emission on the galaxy. Despite these problems, 21 cm observations, along with space-based gravitational wave observations, are generally viewed as the next great frontier in observational cosmology, after the cosmic microwave background polarization.>>
Art Neuendorffer

User avatar
johnnydeep
Commander
Posts: 883
Joined: Sun Feb 20, 2011 8:57 pm

Re: APOD: The Hydrogen Clouds of M33 (2021 Sep 30)

Post by johnnydeep » Sat Oct 02, 2021 8:26 pm

Thanks, neufer. I have more learning to do...
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."