Starship Asterisk*

by **orin stepanek** » Tue May 24, 2022 1:14 pm

Ann wrote: ↑Tue May 24, 2022 8:18 am When I was 15, I grabbed my parents' binoculars and went out to look for Andromeda. At first I just saw some icy white stars against the black sky, until Andromeda sailed into view: It was a soft, mildly yellowish patch, made up, I knew even then, of millions of stars. (Make that billions, Ann.)

I had never given the thought of life on other planets much thought, but when I saw that soft yellowish patch in my binoculars, I almost gasped at the realization that I was looking at millions of stars at a glance. And I was convinced: There is life in that yellowish patch. There is someone there.

And I thought that, yes, maybe there is someone in there who is not unlike myself. Another girl, who lives in Andromeda. I had to restrain myself not to wave at her, as I looked at the place where she lived thought my binoculars.

And I could imagine her waving back to me and saying hi to me.

Saying hi to Andromeda.png

It was only later that I started thinking about what it would actually mean to say hi to someone in Andromeda. Okay, I realized, even back then, that you couldn't just say hi and wave, but you had to send some kind of a signal. Okay. So... it would take that signal some 2,5 million years to go from the Earth to Andromeda. Yikes.

And then, if the girl in Andromeda wanted to answer me, and she sent a signal back to me, it would take another 2.5 million years for her signal to reach me. So I would get the signal back, sort of, some 5 million years after I sent my signal to her.

Yeah, well. Becoming penpals with someone in Andromeda is a bad idea.

Ann

Hey Ann I too believe that there is life; some where out there: also in the MW and other galaxies as well! Hard to find for several reasons: distance; life cycle (over and done?); +! Odds against it though are very remote!

by **Ann** » Tue May 24, 2022 8:18 am

When I was 15, I grabbed my parents' binoculars and went out to look for Andromeda. At first I just saw some icy white stars against the black sky, until Andromeda sailed into view: It was a soft, mildly yellowish patch, made up, I knew even then, of millions of stars. (Make that billions, Ann.)

I had never given the thought of life on other planets much thought, but when I saw that soft yellowish patch in my binoculars, I almost gasped at the realization that I was looking at millions of stars at a glance. And I was convinced: There is life in that yellowish patch. There is someone there.

And I thought that, yes, maybe there is someone in there who is not unlike myself. Another girl, who lives in Andromeda. I had to restrain myself not to wave at her, as I looked at the place where she lived thought my binoculars.

And I could imagine her waving back to me and saying hi to me.

It was only later that I started thinking about what it would actually mean to say hi to someone in Andromeda. Okay, I realized, even back then, that you couldn't just say hi and wave, but you had to send some kind of a signal. Okay. So... it would take that signal some 2,5 million years to go from the Earth to Andromeda. Yikes.

And then, if the girl in Andromeda wanted to answer me, and she sent a signal back to me, it would take another 2.5 million years for her signal to reach me. So I would get the signal back, sort of, some 5 million years after I sent my signal to her.

Yeah, well. Becoming penpals with someone in Andromeda is a bad idea.

Ann

by **orin stepanek** » Mon May 23, 2022 10:15 pm

Very interesting photo today! I prefer the one in ordinary light! That
Yellow is hard to look at!

by **MarkBour** » Mon May 23, 2022 8:06 pm

Ann wrote: ↑Mon May 23, 2022 7:51 pm ... Suppose the Universe is indeed perched at such a false vacuum point, and that it might
catastrophically fall down. The way I understand it, this would be the end of the Universe
as we know it, and we couldn't survive the "fall". How would we know that the end was nigh? How could we tell?

We couldn't, the way I understand it. Because the effects of the catastrophic "fall" would travel everywhere at the speed of light.
...

Ann

Nice point. So, obviously the Star Wars laser blasters are very poorly designed.
If they just made the beam propagate at the speed of light, then Kylo Ren would never have the chance to do this:

Click to play embedded YouTube video.

by **johnnydeep** » Mon May 23, 2022 8:03 pm

Ann wrote: ↑Mon May 23, 2022 7:51 pm
DL MARTIN wrote: ↑Mon May 23, 2022 6:38 pm There is no argument that "now" is subject to location, but observation relegated to a singularity (Earth) affords the application of distance away interpreted as 'ago". Thus, 2.5 M light-years away is also 2.5 M years ago. We are seeing Andromeda as it was at that time. To use the idea that stars are changing without clarifying that it's in the past lacks scientific rigour.
Absolutely everything in space is constrained by the fact that information can't travel faster than the speed of light, some 300,000 kilometers per second. And given the enormous dimensions of the Universe, this is actually quite slow.

I once read that there is a theoretical possibility that the Universe might not be located at its the lowest possible energy state, like this:

...

I'm sure I have simplified the scenario, and I have probably at least partly misunderstood it, too.

But here's the deal: Electromagnetic information travels at the speed of light. We can't make it go faster. So when we say that the distance to Andromeda is 2.5 million light-years, it means that the light we are receiving from Andromeda has been travelling here for 2.5 million years.

It's the way it is. Deal with it.

Ann

Yeah, this is the "false vacuum" idea. See https://en.wikipedia.org/wiki/False_vacuum_decay

https://en.wikipedia.org/wiki/False_vacuum_decay wrote:In quantum field theory, a false vacuum[1] is a hypothetical vacuum that is stable, but not in the most stable state possible (it is metastable).[2] It may last for a very long time in that state, but could eventually decay to the more stable state, an event known as false vacuum decay. The most common suggestion of how such a decay might happen in our universe is called bubble nucleation – if a small region of the universe by chance reached a more stable vacuum, this "bubble" (also called "bounce")[3][4] would spread.

A false vacuum exists at a local minimum of energy and is therefore not stable, in contrast to a true vacuum, which exists at a global minimum and is stable.

by **MarkBour** » Mon May 23, 2022 7:54 pm

The Once and Future Stars of Andromeda

Explanation: This picture of Andromeda shows not only where stars are now, but where stars will soon be. Of course, the big, beautiful Andromeda Galaxy, M31, is a spiral galaxy -- and a mere 2.5 million light-years away.

----------------------------------------

DL MARTIN wrote: ↑Mon May 23, 2022 4:01 pm Again, how can one claim that the stars are as they are now, when what is shown is an image generated 2.5 million years ago?

Today I have to agree with you, mostly.
"This picture of Andromeda shows not only where stars are now, ..."
is a statement that could be misleading to a lay-person, such as myself.
I think the caption is improved, if we just change "are" to "appear to us". So:
"This picture of Andromeda shows not only where stars appear to us now, ..."

I would quibble a bit with your comment: the image was not generated long ago, Hubble captured the image recently (perhaps the image is from July 2019). But I take your point as quite valid. As I imagine the Universe to be, which is probably not how more experienced astronomers think about it ...

the stars we see today in the Andromeda galaxy actually emitted the light we see
around 2.5 million years ago. (Andromeda is 220,00 light years in diameter, so
some of them emitted their light quite a bit earlier than others, when we see an
image of them together.)

Then, if their estimation is correct, that:

These new stars will likely form over the next hundred million years

then we would not guess that those stars have already formed "in reality" and we're just waiting to see their light. Since 100 million is much larger than 2.5 million, then even if we were in Andromeda today, we would not find those stars yet formed.

Of course what you and I are both doing here, is imagining a Universe that over vast expanses has a time dimension and one can imagine a single "now" for the whole of space. This is the Newtonian view that we all began with. One of Einstein's deepest points of philosophy was to realize that this is not always the most helpful way to picture the Universe, as having a monolithic idea of time.

by **Ann** » Mon May 23, 2022 7:51 pm

DL MARTIN wrote: ↑Mon May 23, 2022 6:38 pm There is no argument that "now" is subject to location, but observation relegated to a singularity (Earth) affords the application of distance away interpreted as 'ago". Thus, 2.5 M light-years away is also 2.5 M years ago. We are seeing Andromeda as it was at that time. To use the idea that stars are changing without clarifying that it's in the past lacks scientific rigour.

Absolutely everything in space is constrained by the fact that information can't travel faster than the speed of light, some 300,000 kilometers per second. And given the enormous dimensions of the Universe, this is actually quite slow.

I once read that there is a theoretical possibility that the Universe might not be located at its the lowest possible energy state, like this:

Instead, it is theoretically possible that the Universe might be perched at a "false vacuum state", from which it might fall down:

Suppose the Universe is indeed perched at such a false vacuum point, and that it might catastrophically fall down. The way I understand it, this would be the end of the Universe as we know it, and we couldn't survive the "fall". How would we know that the end was nigh? How could we tell?

We couldn't, the way I understand it. Because the effects of the catastrophic "fall" would travel everywhere at the speed of light. Or to put it differently: One moment everything is fine, the next moment the sky is falling down.

I'm sure I have simplified the scenario, and I have probably at least partly misunderstood it, too.

But here's the deal: Electromagnetic information travels at the speed of light. We can't make it go faster. So when we say that the distance to Andromeda is 2.5 million light-years, it means that the light we are receiving from Andromeda has been travelling here for 2.5 million years.

It's the way it is. Deal with it.

Ann

by **Ann** » Mon May 23, 2022 6:47 pm

DL MARTIN wrote: ↑Mon May 23, 2022 6:38 pm There is no argument that "now" is subject to location, but observation relegated to a singularity (Earth) affords the application of distance away interpreted as 'ago". Thus, 2.5 M light-years away is also 2.5 M years ago. We are seeing Andromeda as it was at that time. To use the idea that stars are changing without clarifying that it's in the past lacks scientific rigour.

The Earth is not a singularity.

Ann

by **Chris Peterson** » Mon May 23, 2022 6:43 pm

DL MARTIN wrote: ↑Mon May 23, 2022 6:38 pm There is no argument that "now" is subject to location, but observation relegated to a singularity (Earth) affords the application of distance away interpreted as 'ago". Thus, 2.5 M light-years away is also 2.5 M years ago. We are seeing Andromeda as it was at that time. To use the idea that stars are changing without clarifying that it's in the past lacks scientific rigour.

We are seeing Andromeda as it is at a certain point in its evolution. Which is all that matters. What we are seeing is not in the past.

by **DL MARTIN** » Mon May 23, 2022 6:38 pm

There is no argument that "now" is subject to location, but observation relegated to a singularity (Earth) affords the application of distance away interpreted as 'ago". Thus, 2.5 M light-years away is also 2.5 M years ago. We are seeing Andromeda as it was at that time. To use the idea that stars are changing without clarifying that it's in the past lacks scientific rigour.

by **Chris Peterson** » Mon May 23, 2022 5:02 pm

DL MARTIN wrote: ↑Mon May 23, 2022 4:01 pm Again, how can one claim that the stars are as they are now, when what is shown is an image generated 2.5 million years ago?

Again, because "now" is when the observation is made. "Now" is defined by the speed of light, and is different in different places.

by **Ann** » Mon May 23, 2022 5:02 pm

johnnydeep wrote: ↑Mon May 23, 2022 3:30 pm
APOD Robot wrote: ↑Mon May 23, 2022 4:06 am The Once and Future Stars of Andromeda

Explanation: This picture of Andromeda shows not only where stars are now, but where stars will soon be. Of course, the big, beautiful Andromeda Galaxy, M31, is a spiral galaxy -- and a mere 2.5 million light-years away. Both space-based and ground-based observatories have been here combined to produce this intriguing composite image of Andromeda, at wavelengths both inside and outside normally visible light. The visible light shows where M31's stars are now -- as highlighted in white and blue hues and imaged by the Hubble, Subaru, and Mayall telescopes. The infrared light shows where M31's future stars will soon form -- as highlighted in orange hues and imaged by NASA's Spitzer Space Telescope. The infrared light tracks enormous lanes of dust, warmed by stars, sweeping along Andromeda's spiral arms. This dust is a tracer of the galaxy's vast interstellar gas -- the raw material for future star formation. These new stars will likely form over the next hundred million years, surely well before Andromeda merges with our Milky Way Galaxy in about 5 billion years.
So, does "dust is used as a tracer for gas" imply that the two are always found together (is dust an inevitable consequence of molecular gas "clumping")? And is star formation caused primarily by gas or dust or both?

In the present-day Universe, all gas is mixed with dust to some extent. And dust is never found completely in isolation, with no gas present. So yes, gas and dust are always found together. Where you see dark dust, there is also a lot of gas present.

Stars are formed from gas, not dust. After all, a star made entirely of ices, silicates and carbon components would find it hard to get any fusion going. But dust helps gas to collapse and form stars.

: Gas is streaming into the center of galaxy NGC 3077, setting off a starburst there. The gas is mixed with dust, making it look dark in optical light. Credit: NASA, ESA, J. Dalcanton and B. Williams.

Ann

by **VictorBorun** » Mon May 23, 2022 4:54 pm

AVAO wrote: ↑Mon May 23, 2022 3:25 pm
Chris Peterson wrote: ↑Mon May 23, 2022 12:41 pm
VictorBorun wrote: ↑Mon May 23, 2022 4:58 am why is the IR frame of the two-frame video monochromatic?
Spitzer Space Telescope must be capturing more than one spectral band channel of data, must not it?
What additional value would combining IR channels provide? The intent it to highlight the dust, and a single channel would seem to be best for that.
"This is the most detailed image of the Andromeda Galaxy ever taken at far-infrared wavelengths. The Herschel infrared space telescope captured the image during Christmas 2010."

Credit: ESA/Herschel/PACS/SPIRE/J. Fritz, U. Gent
https://www.esa.int/ESA_Multimedia/Imag ... n_infrared

In the Far-Infrared image of the Herschel telescope, the dust areas looks much larger and denser than with Spitzer in Mid-Infrared. Which wavelength is best suited for estimating whether stars will soon form? How will WEBB be able to help us?

https://www.esa.int/Science_Exploration ... star_birth

I am afraid that this ESA's presentation is worse than monochrome: it's monochrome colour-coded, with lighter parts coded as yellowish and darker parts as reddish.

Real multi-channel can look like this:
3.4 and 4.6 μm → ██
12 μm → ██
22 μm → ██

: Click to view full size image

by **MarkBour** » Mon May 23, 2022 4:35 pm

johnnydeep wrote: ↑Mon May 23, 2022 3:30 pm
So, does "dust is used as a tracer for gas" imply that the two are always found together (is dust an inevitable consequence of molecular gas "clumping")? And is star formation caused primarily by gas or dust or both?

Well, I'm not an expert, but ...
To make a nice star, all you need is a whole lot of Hydrogen. But a cloud of Hydrogen, even at low temperatures of 10K or less, is not necessarily going to collapse. Generally, something gives it an impetus. Lacking a galaxy collision, which causes massive turbulence overall, there are gentler nudges, like a more local compression on a molecular cloud, due to gravitational or magnetic forces, or a wave of matter from a nearby supernova, compressing part of the cloud. Dust abounds in the present-day universe. Dust particles provide good gravitational seeds for the beginning of a local clumping that eventually becomes a collapse of a local section of the molecular cloud to the density that then becomes a star. (So it's similar to the formation of raindrops in earthly water clouds. When the concentration of suspended H₂O is great enough, it wants to precipitate out. But the raindrops begin to form on the surface of dust particles and then accrete from that point on.)

>>> https://en.wikipedia.org/wiki/Star_formation <<<
A protostellar cloud will continue to collapse as long as the gravitational binding energy can be eliminated. This excess energy is primarily lost through radiation. However, the collapsing cloud will eventually become opaque to its own radiation, and the energy must be removed through some other means. The dust within the cloud becomes heated to temperatures of 60–100 K, and these particles radiate at wavelengths in the far infrared where the cloud is transparent. Thus the dust mediates the further collapse of the cloud.

by **DL MARTIN** » Mon May 23, 2022 4:01 pm

Again, how can one claim that the stars are as they are now, when what is shown is an image generated 2.5 million years ago?

by **johnnydeep** » Mon May 23, 2022 3:30 pm

APOD Robot wrote: ↑Mon May 23, 2022 4:06 am The Once and Future Stars of Andromeda

Explanation: This picture of Andromeda shows not only where stars are now, but where stars will soon be. Of course, the big, beautiful Andromeda Galaxy, M31, is a spiral galaxy -- and a mere 2.5 million light-years away. Both space-based and ground-based observatories have been here combined to produce this intriguing composite image of Andromeda, at wavelengths both inside and outside normally visible light. The visible light shows where M31's stars are now -- as highlighted in white and blue hues and imaged by the Hubble, Subaru, and Mayall telescopes. The infrared light shows where M31's future stars will soon form -- as highlighted in orange hues and imaged by NASA's Spitzer Space Telescope. The infrared light tracks enormous lanes of dust, warmed by stars, sweeping along Andromeda's spiral arms. This dust is a tracer of the galaxy's vast interstellar gas -- the raw material for future star formation. These new stars will likely form over the next hundred million years, surely well before Andromeda merges with our Milky Way Galaxy in about 5 billion years.

So, does "dust is used as a tracer for gas" imply that the two are always found together (is dust an inevitable consequence of molecular gas "clumping")? And is star formation caused primarily by gas or dust or both?

by **AVAO** » Mon May 23, 2022 3:25 pm

Chris Peterson wrote: ↑Mon May 23, 2022 12:41 pm
VictorBorun wrote: ↑Mon May 23, 2022 4:58 am why is the IR frame of the two-frame video monochromatic?
Spitzer Space Telescope must be capturing more than one spectral band channel of data, must not it?
What additional value would combining IR channels provide? The intent it to highlight the dust, and a single channel would seem to be best for that.

"This is the most detailed image of the Andromeda Galaxy ever taken at far-infrared wavelengths. The Herschel infrared space telescope captured the image during Christmas 2010."

Credit: ESA/Herschel/PACS/SPIRE/J. Fritz, U. Gent
https://www.esa.int/ESA_Multimedia/Imag ... n_infrared

In the Far-Infrared image of the Herschel telescope, the dust areas looks much larger and denser than with Spitzer in Mid-Infrared. Which wavelength is best suited for estimating whether stars will soon form? How will WEBB be able to help us?

https://www.esa.int/Science_Exploration ... star_birth

by **Chris Peterson** » Mon May 23, 2022 12:41 pm

VictorBorun wrote: ↑Mon May 23, 2022 4:58 am why is the IR frame of the two-frame video monochromatic?
Spitzer Space Telescope must be capturing more than one spectral band channel of data, must not it?

What additional value would combining IR channels provide? The intent it to highlight the dust, and a single channel would seem to be best for that.

by **Ann** » Mon May 23, 2022 5:24 am

The APOD is interesting, but the presence of dust (and gas, of which the dust is a tracer) doesn't always promise future star formation. The gas and dusty mixture is sometimes "sterile":

: AM 1316-241 is made up of two interacting galaxies - a spiral galaxy (on the left of the frame) in front of an elliptical galaxy (on the right of the frame). A long outer dust lane in the spiral galaxy seen in silhouette against the elliptical is lacking in obvious star clusters. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and W. Keel.

A long stretch of dust lane in a spiral galaxy seen in silhouette against an elliptical galaxy is seen to contain no significant star clusters at all. In fact, if the spiral galaxy hadn't been backlit by the elliptical, the outer dust lane would not have been known by astronomers.

And galactic collisions do not always lead to massive star formation. Compare the star formation in the Antennae galaxies with the star formation in the merging Cen A system:

: The Antennae galaxies. NASA, ESA, and the Hubble Heritage Team.

: Star formation in the dust lane of Cen A. NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgment: R. O’Connell.

Yes, there is star formation in Cen A. But compared with how much star formation there is in the Antennae, the star formation in Cen A is not too impressive.

And the Antennae themselves are certainly not "equal":

The amount of star formation in NGC 4038 and NGC 4039 is not the same.

For a while there in the future, the merging Milkomeda galaxy will certainly look impressive. But I predict that it will not rival the present appearance of the Antennae galaxies, because neither Andromeda nor the Milky Way is especially gas-rich as galaxies go.

Then again, I'm sure that Gaia has shown that the Milky Way will collide with the Large Magellanic Cloud in some 2 billion years, which will be a giant enough galactic train wreck in itself, and it will send a tsunami of gas into the Milky Way('s black hole). So maybe the MW itself will be flatulent and ready to burst when Andromeda homes in on it, and who knows what will happen then? At least Sgr A* may be swollen and throbbing as it waits for the black hole of Andromeda.

Laser Interferometer Gravitational-Wave Observatory (LIGO), where will you be in 5 billion years' time when we are going to need you the most?

Ann

by **VictorBorun** » Mon May 23, 2022 4:58 am

why is the IR frame of the two-frame video monochromatic?
Spitzer Space Telescope must be capturing more than one spectral band channel of data, must not it?

by **APOD Robot** » Mon May 23, 2022 4:06 am

The Once and Future Stars of Andromeda

Explanation: This picture of Andromeda shows not only where stars are now, but where stars will soon be. Of course, the big, beautiful Andromeda Galaxy, M31, is a spiral galaxy -- and a mere 2.5 million light-years away. Both space-based and ground-based observatories have been here combined to produce this intriguing composite image of Andromeda, at wavelengths both inside and outside normally visible light. The visible light shows where M31's stars are now -- as highlighted in white and blue hues and imaged by the Hubble, Subaru, and Mayall telescopes. The infrared light shows where M31's future stars will soon form -- as highlighted in orange hues and imaged by NASA's Spitzer Space Telescope. The infrared light tracks enormous lanes of dust, warmed by stars, sweeping along Andromeda's spiral arms. This dust is a tracer of the galaxy's vast interstellar gas -- the raw material for future star formation. These new stars will likely form over the next hundred million years, surely well before Andromeda merges with our Milky Way Galaxy in about 5 billion years.

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