Explanation: What will happen as this already bright comet approaches? Optimistic predictions have Comet C/2023 A3 (TsuchinshanâATLAS) briefly becoming easily visible to the unaided eye -- although the future brightness of comets are notoriously hard to predict, and this comet may even break up in warming sunlight. What is certain is that the comet is now unexpectedly bright and is on track to pass its closest to the Sun (0.39 AU) later this week and closest to the Earth (0.47 AU) early next month. The featured image was taken in late May as Comet TsuchinshanâATLAS, discovered only last year, passed nearly in front of two distant galaxies. The comet can now be found with binoculars in the early morning sky rising just before the Sun, while over the next few weeks it will brighten as it moves to the early evening sky.
Well, you know I'm a galaxy girl with galaxies on my mind, but seriously, aren't the two galaxies (NGC 4123 and NGC 4116) more interesting than the Comet Tsuchinshan-ATLAS?
This poor comet hasn't got a lot of bling to show for itself! It has neither got a green coma nor a blue ion tail. Its poor white tail is even growing narrower rather than wider! It's got nothing on handsome comet 12P/Pons-Brooks!
Of course, today's APOD portrait of Comet Tsuchinshan-ATLAS was taken in may, so perhaps comet Tsuch has grown more handsome since then?
Anyway, as the APOD picture was taken, Comet Tsuch was passing between three stars, one orange on the left and two blue-white ones on the right. The orange star is SAO 119231, a red giant some 45 times brighter than the Sun, but the blue-white ones (which aren't really blue at all) are TYC 280-75-1 and TYC 280-99-1, both only about twice as bright as the Sun! They are almost certainly late F-type main sequence stars.
In the APOD, north is not up and east is not to the left. This picture shows the correct orientation:
So how did the comet move? It didn't move up and to the left as in the APOD. I think, although I'm not quite sure, that it moved mostly to the right!
Let's talk a little about the galaxies, NGC 4123 and NGC 4116. You can tell at a glance that these galaxies are not extremely distant. The fact that they look so relatively large compared with a comet with a reasonably well-developed tail shows that they can't be too tiny in the sky. Also they are both very arm-forward, quite spiral-ly, and quite blue. In nine cases out of ten, such galaxies are relatively small. Not puny, but relatively small. According to Principal Galaxy Catalog, the luminosity of NGC 4123, the yellower of the two, is 0.4 times that of the Milky Way, while the luminosity of the even bluer NGC 4116 is 0.3 times that of the Milky Way. I can't swear that these figures are correct, but they sound very reasonable to me.
I've got to show you a closeup of NGC 4116, also by Mark Hanson:
Look at the little yellow spiral galaxy that seems to be nestled in NGC 4116's arms! The little galaxy is clearly a background object with a bright yellow bar. But the entire galaxy looks yellow, partly because it is reddened by dust in the arms of NGC 4116, and partly because it is somewhat reddened by redshift (because this galaxy is clearly a lot more distant than NGC 4116), but it is certainly also possible that this galaxy is intrinsically less blue and more yellow than NGC 4116. Indeed, it looks that way to me. The background spiral galaxy is probably indeed forming stars, but it is almost certainly dominated by an old yellow population. The galaxy also looks well-formed and not "ragged". Therefore the background galaxy is probably also both larger and intrinsically brighter than NGC 4116.
Roy wrote: ↑Mon Sep 23, 2024 1:54 pm
That link to distant galaxies takes one to the hubble deep field, and doesn't identify the galaxies. Ann will know.?
Somehow Otto managed to double post the discussion for this APOD. Ann's comments are in the other one.
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Chris
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Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
II will add my thanks, Ann! Looking at NGC4116's image, I was led to the Wikipedia article on "Galaxy Morphological Classification" , a subject begun by Edwin Hubble, and extended by Gerard De Vaucoleurs (a Noted Astronomer himself, IMHO). It all gives one to think what is causing all this variation?
Rot wrote: ↑Mon Sep 23, 2024 8:31 pm
II will add my thanks, Ann! Looking at NGC4116's image, I was led to the Wikipedia article on "Galaxy Morphological Classification" , a subject begun by Edwin Hubble, and extended by Gerard De Vaucoleurs (a Noted Astronomer himself, IMHO). It all gives one to think what is causing all this variation?
As to why galaxies look so different, a very short an incomplete answer has to do with mass concentration and star formation.
The young Universe was a busy place, considerably smaller and much, much more gas-rich than it is today. The gas was not uniformly distributed, and there was more of it in some places than in others. In these gas-rich nodes, star formation must have started very early, and it was probably rampant. In this way, galaxies were formed. As the gravitational wells of these early galaxies grew deeper (because more and more mass had gathered there) still more gas accreted onto these galaxies, fueling more and more star formation. There were also many galaxy collisions and mergers, fueling even more star formation.
However, during galactic collisions gas was also lost, as it was ejected out of the galaxies. On top of that, a lot of massive stars exploded as supernovas, blowing still more gas out of the galaxies. Also, as more and more of the galaxies' own gas was turned into stars, the "gas reservoir" of both the galaxies and, to some extent, the Universe, began to dwindle. Star formation began to wind down quite sharply.
As star formation began winding down, the short-lived, brilliantly bright blue stars soon died, and only some of them were replaced, due to the dwindling gas supply. But the small faint red and yellow stars lived on. Bear in mind that every burst of star formation will form a few massive bright blue stars, but many, many light-weight faint red and yellow stars.
Because M87 is located inside a large cluster of galaxies, we can be sure that it has undergone many, many mergers and interactions since it first started forming during the first few hundred million years of the Universe. All the gas that was once present in what is now the Virgo Cluster fueled burst after burst of star formation in the proto-M87 galaxy (or else it may have been an ultraluminous infrared galaxy in its youth, one that created an ultra-mega-copious burst of star formation that formed enormous numbers of stars, created a cocoon of soot and dust around itself, and basically drained itself of gas in one fell swoop). Also, a violent burst of star formation will create hundreds and hundreds of supernovas that will literally blow much of the remaining gas out of the galaxy. The long and short of it is that present-day M87 contains trillions of small old red and yellow stars and 15,000 globular clusters, but no young stars or star formation.
See this Youtube video of galaxy formation:
Click to play embedded YouTube video.
By contrast, there were much smaller pockets of gas formed elsewhere, outside the large clusters, some of them in quite isolated locations. These small pockets of gas typically formed stars quite slowly. Some of them probably underwent a mild starburst in their youth, but then they stopped forming stars, and slowly turned themselves into dwarf spheroidal galaxies:
But then there is another category of galaxies, those that were relatively isolated when they formed, and that formed relatively few stars in their youth. But then something happened. They may have met another, smaller galaxy that either stirred up the "first galaxy's" own gas supply and made it start forming stars, or else the "first galaxy" may have stolen gas from the small intruder, again making the larger (but still smallish) galaxy form stars.
The long and short of it is that small galaxies can hang on to their gas for a longer period than large galaxies typically can (because large galaxies have typically used up most of their gas already). And when a small(ish) galaxy starts forming stars, this can have a dramatic effect on both the shape, the brightness and the color of the galaxy. I found a tiny picture that I'm posting here of a dwarf galaxy that seems to be writhing, as if in pain, due to all its star formation:
In the case of dwarf galaxy F549-1, the galaxy itself is so low in mass and the star formation it has set off is so widespread and massive that the entire galaxy becomes "distorted" because of it. Clearly its companion has something to do with the violent star formation of F549-1, and the companion is itself affected by F549-1 and is itself induced to make stars. Both galaxies are small.
Oh, and... I just found this rather fascinating article by Keith Cooper, where he claims that small galaxies are better at hoarding their gas (rather than blowing it away) because they are more likely to form black holes rather than supernovas! Don't ask me if that is correct!
Some of the biggest, most intense regions of star formation are found in the smallest of galaxies, and scientists believe this is because stars reaching the ends of their lives in the so-called dwarf galaxies are more likely to turn into black holes than explode in supernovas. The contrast is large enough, the team says, that dwarf galaxies experience a 10-million-year delay in blowing all their star-forming material away, a process usually dependent on the forces of supernovas.
It has become obvious in later years that some stars just disappear, without going supernova first. It is possible that these stars have just collapsed into black holes instead of exploding:
Comet Tsuchinshan-ATLAS Approaches
