by Ann » Wed Jul 31, 2024 5:16 am
Chris Peterson wrote: ↑Tue Jul 30, 2024 11:46 pm
Roy wrote: ↑Tue Jul 30, 2024 10:33 pm
I am well aware that redshift is not a reliable measure of distance. Hubble himself doubted it, even after he compiled his table of values with nearby galaxies that led to the concept of a Hubble constant. Which all Big-bang astronomers use as a distance measure. Halton Arp’s
Seeing Red discusses it extensively.
But the whole point and title of this post is to claim that two galaxies are interacting gravitationally. I look at the pictures, including the one most recently posted by Johnnydeep and I see Arp 142 severely perturbed in the foreground, and an elliptical unperturbed in the background. When I look up the redshift distance, astronomers have no other, my estimate of what I see is confirmed that they are 17 million light years apart. Our galaxy is only 3 million light years from the great galaxy in Andromeda, and we are not perturbing each other.
Footnote about Hubble: he was a Major in the Army in WWI, and trained troops 1917- 1918. Then had a ground-breaking career as an astronomer with the Mt Wilson 100 inch and Mt Palomar 200 inch telescopes.
Cosmological redshift is most certainly a reliable measure of distance. But it comes with an error of plus or minus a few percent.
Halton Arp became a crackpot. It happens to some scientists when they get old.
That the two galaxies are interacting gravitationally is beyond reasonable doubt. There are no other forces that could produce this kind of distortion, and the resultant shapes, tidal tails, and star formation regions are accurately modeled in many similar systems (possibly in this one, as well) with nothing more than gravity.
You are using poor information to assess the distance between the galaxies (Wikipedia is hardly the definitive source!) and totally ignoring the error on the distances. No astronomer would do this. The optical evidence shows that the galaxies are much closer, and the measured values easily support that. And we certainly don't know which galaxy is in the foreground from any information in these images or from redshift measurements.
Like Chris said, it's not possible to say which galaxy of Arp 142 is in the background and which is in the foreground.
However, it is indeed likely that the galaxies are currently well separated from one another. During a merger, two galaxies will approach each other, and then, in a sort of slingshot effect, separate, before approaching each other again. Consider the Youtube video of a simulation of the future merger of the Milky Way and Andromeda:
Click to play embedded YouTube video.
But even during first approach, spiral galaxies will typically become distorted. It's their arms that will become distorted, because spiral arms are often all showoff and fireworks and little substance. That is because spiral arms typically get their light from massive blue stars, which shine fantastically bright even though they are not nearly that fantastically massive.
Consider HD 93129A, a brilliant massive O-type star in the cluster Trumpler 14 in the Carina Nebula. According to Wikipedia, the mass of this star is 110 solar masses. But its luminosity is ~1.5
million times the solar luminosity! You should not take these figures to be exact, but you should understand that with massive stars, you get a lot of bang (light) for the buck (mass).
Spiral arms are elongated structures that are typically not that massive. Therefore they are easily distorted during galactic interactions.
Elliptical galaxies, as well as bright yellow cores of spiral galaxies, are the opposite. They contain extremely few, if any, brilliantly bright massive stars. Instead they get their light from billions and billions small cool red and yellow stars (and a much smaller number of moderately-massive red giant stars).
Consider Proxima Centauri, the nearest star to the Earth apart from the Sun. According to
Wikipedia, the mass of Proxima is 0.12 the mass of the Sun, but its visible light output is only 0.00005 the light of the Sun!
Elliptical galaxies contain billions and billions of small red dwarf stars. Realistically, stars like Proxima Centauri contribute very little of the light output of elliptical galaxies. Most of the light of these galaxies comes from moderately-massive (say, 1-2 solar masses) red giant stars, whose visible light output is typically 30-300 times that of the Sun.
But while stars like Proxima Centauri contribute very little light to elliptical galaxies, they do provide a lot of mass. That's because the mass of red dwarfs is not negligible, unlike their light output, and there are so, so many of them. Therefore, bright yellow or yellow-white elliptical galaxies are massive. Often but not always, they are also quite compact.
The elliptical component of Arp 142 may indeed be quite compact, because its fluffier (and very faint!) outer layers may already have been torn away and lost during its previous interactions with the spiral galaxy of Arp 142.
We have every reason to believe that the two components of Arp 142 are close to one another - say, separated by no more than 500,000 light-years - and that they are indeed interacting.
Ann
[quote="Chris Peterson" post_id=340580 time=1722383171 user_id=117706]
[quote=Roy post_id=340578 time=1722378825]
I am well aware that redshift is not a reliable measure of distance. Hubble himself doubted it, even after he compiled his table of values with nearby galaxies that led to the concept of a Hubble constant. Which all Big-bang astronomers use as a distance measure. Halton Arp’s [b]Seeing Red[/b] discusses it extensively.
But the whole point and title of this post is to claim that two galaxies are interacting gravitationally. I look at the pictures, including the one most recently posted by Johnnydeep and I see Arp 142 severely perturbed in the foreground, and an elliptical unperturbed in the background. When I look up the redshift distance, astronomers have no other, my estimate of what I see is confirmed that they are 17 million light years apart. Our galaxy is only 3 million light years from the great galaxy in Andromeda, and we are not perturbing each other.
Footnote about Hubble: he was a Major in the Army in WWI, and trained troops 1917- 1918. Then had a ground-breaking career as an astronomer with the Mt Wilson 100 inch and Mt Palomar 200 inch telescopes.
[/quote]
Cosmological redshift is most certainly a reliable measure of distance. But it comes with an error of plus or minus a few percent.
Halton Arp became a crackpot. It happens to some scientists when they get old.
That the two galaxies are interacting gravitationally is beyond reasonable doubt. There are no other forces that could produce this kind of distortion, and the resultant shapes, tidal tails, and star formation regions are accurately modeled in many similar systems (possibly in this one, as well) with nothing more than gravity.
You are using poor information to assess the distance between the galaxies (Wikipedia is hardly the definitive source!) and totally ignoring the error on the distances. No astronomer would do this. The optical evidence shows that the galaxies are much closer, and the measured values easily support that. And we certainly don't know which galaxy is in the foreground from any information in these images or from redshift measurements.
[/quote]
Like Chris said, it's not possible to say which galaxy of Arp 142 is in the background and which is in the foreground.
However, it is indeed likely that the galaxies are currently well separated from one another. During a merger, two galaxies will approach each other, and then, in a sort of slingshot effect, separate, before approaching each other again. Consider the Youtube video of a simulation of the future merger of the Milky Way and Andromeda:
[youtube]https://www.youtube.com/watch?v=4disyKG7XtU[/youtube]
But even during first approach, spiral galaxies will typically become distorted. It's their arms that will become distorted, because spiral arms are often all showoff and fireworks and little substance. That is because spiral arms typically get their light from massive blue stars, which shine fantastically bright even though they are not nearly that fantastically massive.
Consider HD 93129A, a brilliant massive O-type star in the cluster Trumpler 14 in the Carina Nebula. According to Wikipedia, the mass of this star is 110 solar masses. But its luminosity is ~1.5 [i][b]million[/b][/i] times the solar luminosity! You should not take these figures to be exact, but you should understand that with massive stars, you get a lot of bang (light) for the buck (mass).
[img3="Extremely bright HD 93129 surrounded by the lesser stars of Trumpler 14.
Credit: NASA & ESA, Jesús Maíz Apellániz"]https://upload.wikimedia.org/wikipedia/commons/thumb/e/e3/Trumpler_14_by_Hubble.jpg/420px-Trumpler_14_by_Hubble.jpg[/img3]
Spiral arms are elongated structures that are typically not that massive. Therefore they are easily distorted during galactic interactions.
Elliptical galaxies, as well as bright yellow cores of spiral galaxies, are the opposite. They contain extremely few, if any, brilliantly bright massive stars. Instead they get their light from billions and billions small cool red and yellow stars (and a much smaller number of moderately-massive red giant stars).
Consider Proxima Centauri, the nearest star to the Earth apart from the Sun. According to [url=https://en.wikipedia.org/wiki/Proxima_Centauri]Wikipedia[/url], the mass of Proxima is 0.12 the mass of the Sun, but its visible light output is only 0.00005 the light of the Sun!
[img3="Alpha (left) and Beta (right) Centauri. In the red circle below Alpha Centauri, you can see red dwarf Proxima Centauri. Note that Alpha and Proxima Centauri are at almost exactly the same distance from us. (Beta Centauri is much farther away.) Alpha Centauri consists of two Sunlike stars. Credit: Skatebiker at English Wikipedia."]https://upload.wikimedia.org/wikipedia/commons/thumb/6/61/Alpha%2C_Beta_and_Proxima_Centauri_%281%29.jpg/1200px-Alpha%2C_Beta_and_Proxima_Centauri_%281%29.jpg[/img3]
Elliptical galaxies contain billions and billions of small red dwarf stars. Realistically, stars like Proxima Centauri contribute very little of the light output of elliptical galaxies. Most of the light of these galaxies comes from moderately-massive (say, 1-2 solar masses) red giant stars, whose visible light output is typically 30-300 times that of the Sun.
But while stars like Proxima Centauri contribute very little light to elliptical galaxies, they do provide a lot of mass. That's because the mass of red dwarfs is not negligible, unlike their light output, and there are so, so many of them. Therefore, bright yellow or yellow-white elliptical galaxies are massive. Often but not always, they are also quite compact.
The elliptical component of Arp 142 may indeed be quite compact, because its fluffier (and very faint!) outer layers may already have been torn away and lost during its previous interactions with the spiral galaxy of Arp 142.
[img3="Outer layers of elliptical galaxies being distorted, probably because of past or present interactions. Credit: Canada France Hawaii Telescope"]https://www.cfht.hawaii.edu/en/news/EllGal/FlorilegeAtlas3D_CEA-CFHT_Duc.JPG[/img3]
We have every reason to believe that the two components of Arp 142 are close to one another - say, separated by no more than 500,000 light-years - and that they are indeed interacting.
Ann