by Ann » Wed Oct 16, 2019 7:08 am
k.w.jung wrote: ↑Tue Oct 15, 2019 10:39 pm
Dear sir,
In stephan's quintet, as the distance of NGC 7320 is about seven times closer than the other four galaxies, it's quite understandable that individual stars of NGC 7320 is visible and the other four look fuzzy. However, colliding galaxies NGC 7714 and NGC 7715 are neighbors and it seems indvidual stars of NGC 7714 are visible and NGC 7715's are not. Why is that?
NGC 7714.
NASA, ESA, Hubble Legacy Archive; Processing & Copyright: Rudy Pohl
Hi, k.w.jung! You can't see NGC 7715 in the APOD, because it isn't visible in the APOD.
The reason why you thought that NGC 7714 was two individual galaxies is that it is made up of two distinct stellar populations. One of the populations is young and blue and made up of relatively few but very bright stars which can be seen as individuals in the Hubble picture. The other population is made up of huge numbers of old faint reddish stars, which look like one unresolvable mass of yellow light in the Hubble image.
My guess, for what it's worth, is that NGC 7715 was a relatively low-mass but gas-rich galaxy that swooshed past (or even crashed into) NGC 7714, dumping a lot of gas onto the more massive NGC 7714 in the process. This would have triggered a mighty burst of star formation in NGC 7714, creating many of the bright blue stars in the galaxy. NGC 7715, by contrast, would have found itself depleted of much of its gas, dooming it to stay small and faint due to a lack of starforming material.
Of course, most likely NGC 7714 and NGC 7715 will merge in the future.
Ann
[quote=k.w.jung post_id=296212 time=1571179197]
Dear sir,
In stephan's quintet, as the distance of NGC 7320 is about seven times closer than the other four galaxies, it's quite understandable that individual stars of NGC 7320 is visible and the other four look fuzzy. However, colliding galaxies NGC 7714 and NGC 7715 are neighbors and it seems indvidual stars of NGC 7714 are visible and NGC 7715's are not. Why is that?
[/quote]
[float=left][img2]https://apod.nasa.gov/apod/image/1910/Ngc7714_HubblePohl_1080.jpg[/img2][c][size=85]NGC 7714.
NASA, ESA, Hubble Legacy Archive; Processing & Copyright: Rudy Pohl[/size][/c][/float][float=right][img2]https://upload.wikimedia.org/wikipedia/commons/thumb/5/52/NGC_7714_NGC_7715_hst_12170_R390B300.png/480px-NGC_7714_NGC_7715_hst_12170_R390B300.png[/img2][c][size=85]NGC 7715 (upper left) and NGC 7714 (lower right).
Source: https://commons.wikimedia.org/wiki/File:NGC_7714_NGC_7715_hst_12170_R390B300.png
[/size][/c][/float]
Hi, k.w.jung! You can't see NGC 7715 in the APOD, because it isn't visible in the APOD.
The reason why you thought that NGC 7714 was two individual galaxies is that it is made up of two distinct stellar populations. One of the populations is young and blue and made up of relatively few but very bright stars which can be seen as individuals in the Hubble picture. The other population is made up of huge numbers of old faint reddish stars, which look like one unresolvable mass of yellow light in the Hubble image.
My guess, for what it's worth, is that NGC 7715 was a relatively low-mass but gas-rich galaxy that swooshed past (or even crashed into) NGC 7714, dumping a lot of gas onto the more massive NGC 7714 in the process. This would have triggered a mighty burst of star formation in NGC 7714, creating many of the bright blue stars in the galaxy. NGC 7715, by contrast, would have found itself depleted of much of its gas, dooming it to stay small and faint due to a lack of starforming material.
Of course, most likely NGC 7714 and NGC 7715 will merge in the future.
Ann