by Ann » Thu Sep 05, 2024 8:04 am
Very nice APOD of the Needle Eye Galaxy and friends! So why is it called the Needle Eye Galaxy? It is because one side of its disk contains a large void like an extremely big eye of a needle!
R. Wagner-Kaiser et. al suggest that a dark matter sub-halo containing a small amount of baryonic ("normal") gas could have collided with (and plunged through?) the disk of NGC 247, pushing away the gas where the sub-halo hit and leaving a "void" at the impact site. Actually, there are a lot of small old red stars in the void, but there is no star formation there whatsoever, and no young blue stars. Read about it
here!
NGC 247 is sometimes described as a dwarf galaxy, but in reality it is not so small. Its diameter is 70,000 light-years, compared with about 100,000 light-years for the Milky Way. But what makes NGC 247 a small galaxy is the fact that it is low in mass. How can we know? It's because it doesn't have a bright yellow center.
The unimpressively non-bright center of NGC 247. Credit: ESA/Hubble & NASA
Every burst of star formation will create a considerable number of small red and orange stars, which are very long-lived and very faint for their mass. Or, conversely, these small stars are impressively massive for the light they produce. Even though most of the light from bright yellow centers of galaxies will come from red giant stars (like Arcturus), bright yellow centers of galaxies always contain an enormous number of small red stars, and therefore, a lot of mass. Conversely, galaxies that lack a bright yellow center are not massive - or they don't contain a lot of baryonic mass, at least!
But while NGC 247 doesn't have an impressively large population of old red and yellow stars, it does have many young blue stars and quite a lot of star formation. Is it true that small galaxies become starburst galaxies more easily than large galaxies? Yes and no!
No, because there are very many small galaxies with no star formation and no young stars:
However, several small galaxies are sitting inside a "well" of hydrogen gas, ready for star formation:
But small galaxies that bring their own reservoir of gas (or, alternatively, blunder into a gas cloud) can be made to convert much of this gas into stars, if the galaxy and the gas receives the right "nudging". This is something that has happened to our brilliantly starforming neighboring galaxy, the Large Magellanic Cloud.
Star formation history of the LMC, according to Sidney van den Bergh.
I copied the picture of the star formation history of the Large Magellanic Cloud from a book,
The Galaxies of the Local Group by Sidney van den Bergh. The book is from the year 2000, and the figure showing the star formation history of the Large Magellanic Cloud seems to suggest that the age of the Universe is well over 15 billion years, whereas the current consensus is that it is less than 14 billion years.
Nevertheless, take a look at the bars showing the amount of star formation in the LMC at various periods in time. The most recent star formation is shown at left and the oldest star formation is at right. As you can see, the LMC formed very few stars for billions of years, until it suddenly "sprang into action" some 2 billion years ago and started forming stars at a breakneck pace.
What happened? Almost certainly, the LMC met and started interacting with the Small Magellanic Cloud, stirring up its own reservoir of gas and then beginning to steal stars and gas from the Small Magellanic Cloud via the Magellanic Bridge. Watch the video below and scroll to 2.53 to see stars flowing from the SMC to the LMC:
Click to play embedded YouTube video.
As for NGC 247, it may have interacted with its larger neighbor, NGC 253, at least in the past. That may have triggered star formation in NGC 247.
And the rest is history!
Ann
Oh, P.S. The nice chain of galaxies at lower left is Burbidge's Chain of Galaxies (as the caption said).
These galaxies appear to be close together and to be interacting. Probably their interaction has spurred star formation, because they are all quite blue! Note that at least three of them are not so massive, because three of them lack bright yellow centers.
Very nice APOD of the Needle Eye Galaxy and friends! So why is it called the Needle Eye Galaxy? It is because one side of its disk contains a large void like an extremely big eye of a needle!
[float=left][img3="NGC 247 and Friends.
Image Credit & Copyright: Acquisition - Eric Benson, Processing - Dietmar Hager"]https://apod.nasa.gov/apod/image/2409/NGC247-Hag-Ben1024.JPG[/img3][/float][float=right][attachment=2]APOD 5 September 2024 annotated.png[/attachment][/float]
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R. Wagner-Kaiser et. al suggest that a dark matter sub-halo containing a small amount of baryonic ("normal") gas could have collided with (and plunged through?) the disk of NGC 247, pushing away the gas where the sub-halo hit and leaving a "void" at the impact site. Actually, there are a lot of small old red stars in the void, but there is no star formation there whatsoever, and no young blue stars. Read about it [url=https://academic.oup.com/mnras/article/443/4/3260/1009521]here[/url]!
NGC 247 is sometimes described as a dwarf galaxy, but in reality it is not so small. Its diameter is 70,000 light-years, compared with about 100,000 light-years for the Milky Way. But what makes NGC 247 a small galaxy is the fact that it is low in mass. How can we know? It's because it doesn't have a bright yellow center.
[float=left][attachment=1]potw1640a[3].jpg[/attachment][c][size=85][color=#0040FF]The unimpressively non-bright center of NGC 247. Credit: ESA/Hubble & NASA[/color][/size][/c][/float][float=right][img3="Even M33 appears to have a considerably brighter yellow center than NGC 247.
Credit: NASA, ESA, and M. Durbin, J. Dalcanton, and B. F. Williams (University of Washington)"]https://cdn.esahubble.org/archives/images/screen/heic1901a.jpg[/img3][/float]
[float=right][img3="And let's not even talk about the brightness of the yellow center of Andromeda! Credit: NASA/ESA & Hubble "]https://upload.wikimedia.org/wikipedia/commons/thumb/7/79/Andromeda_Galaxy_M31_-_Heic1502a_10k.jpg/1200px-Andromeda_Galaxy_M31_-_Heic1502a_10k.jpg?20150113133105[/img3][/float]
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Every burst of star formation will create a considerable number of small red and orange stars, which are very long-lived and very faint for their mass. Or, conversely, these small stars are impressively massive for the light they produce. Even though most of the light from bright yellow centers of galaxies will come from red giant stars (like Arcturus), bright yellow centers of galaxies always contain an enormous number of small red stars, and therefore, a lot of mass. Conversely, galaxies that lack a bright yellow center are not massive - or they don't contain a lot of baryonic mass, at least!
But while NGC 247 doesn't have an impressively large population of old red and yellow stars, it does have many young blue stars and quite a lot of star formation. Is it true that small galaxies become starburst galaxies more easily than large galaxies? Yes and no!
No, because there are very many small galaxies with no star formation and no young stars:
[img3="All-yellow dwarf spheroidal galaxy NGC 147. Credit: Bernhard Hubl."]https://www.astronomy.com/wp-content/uploads/sites/2/2023/02/NGC147.jpg[/img3]
However, several small galaxies are sitting inside a "well" of hydrogen gas, ready for star formation:
[img3="Dwarf irregular galaxy NGC 6822 sits inside a large reservoir of hydrogen gas. NGC 6822 is forming stars, but it is not a starburst galaxy. Credit: ESO, ALMA (ESO/NAOJ/NRAO)/A. Schruba, VLA (NRAO)/Y. Bagetakos/Little THINGS"]https://cdn.eso.org/images/screen/potw1711b.jpg[/img3]
But small galaxies that bring their own reservoir of gas (or, alternatively, blunder into a gas cloud) can be made to convert much of this gas into stars, if the galaxy and the gas receives the right "nudging". This is something that has happened to our brilliantly starforming neighboring galaxy, the Large Magellanic Cloud.
[float=left][img3="Star formation in the Large Magellanic Cloud. Credit: NOIRLab/AURA/NSF"]https://noirlab.edu/public/media/archives/images/screen/noao0140a.jpg[/img3][/float][float=right][attachment=0]Star formation history of the Large Magellanic Cloud Sidney van den Bergh.jpg[/attachment][c][size=85][color=#0040FF]Star formation history of the LMC, according to Sidney van den Bergh.[/color][/size][/c][/float]
[clear][/clear]
I copied the picture of the star formation history of the Large Magellanic Cloud from a book, [i]The Galaxies of the Local Group[/i] by Sidney van den Bergh. The book is from the year 2000, and the figure showing the star formation history of the Large Magellanic Cloud seems to suggest that the age of the Universe is well over 15 billion years, whereas the current consensus is that it is less than 14 billion years.
Nevertheless, take a look at the bars showing the amount of star formation in the LMC at various periods in time. The most recent star formation is shown at left and the oldest star formation is at right. As you can see, the LMC formed very few stars for billions of years, until it suddenly "sprang into action" some 2 billion years ago and started forming stars at a breakneck pace.
What happened? Almost certainly, the LMC met and started interacting with the Small Magellanic Cloud, stirring up its own reservoir of gas and then beginning to steal stars and gas from the Small Magellanic Cloud via the Magellanic Bridge. Watch the video below and scroll to 2.53 to see stars flowing from the SMC to the LMC:
[youtube]https://www.youtube.com/watch?v=5-0DAqqztSc[/youtube]
As for NGC 247, it may have interacted with its larger neighbor, NGC 253, at least in the past. That may have triggered star formation in NGC 247.
[img3="NGC 253 and NGC 247. Image: Wikisky."]https://www.constellation-guide.com/wp-content/uploads/2023/01/NGC-253-and-NGC-247.webp[/img3]
And the rest is history! :D
Ann
Oh, P.S. The nice chain of galaxies at lower left is Burbidge's Chain of Galaxies (as the caption said).
[img3="Burbidge's Chain of Galaxies. Credit: I don't know."]https://www.go-astronomy.com/images/galaxies/galaxy-15.jpg[/img3]
These galaxies appear to be close together and to be interacting. Probably their interaction has spurred star formation, because they are all quite blue! Note that at least three of them are not so massive, because three of them lack bright yellow centers.