ISU: Double Nucleus in Nearby 'Cocoon Galaxy'

[bystander]

Amateur Astronomer Helps Reveal Rare Galaxy Double Nucleus
Iowa State University | 2020 Feb 07

NGC 4490 3.6μm image showing regions of interest. Apertures are shown surrounding
the optical nucleus (OPT), infrared nucleus (IR), and the giant HII regions A and B. The
large and small cyan crosses mark the locations of the optical and infrared nucleus
respectively. (Credit: AL Lawrence et al, ApJ 2020

---

Allen Lawrence, wrapping up a long career as an electrical engineer, was serious about moving his astronomy hobby beyond the 20-inch telescope he’d hauled to star parties under the dark skies of Texas and Arizona.

So in 2011 – in his late 60s, after 30 years of operating his own consulting firm around Green Bay, Wisconsin – he enrolled in some courses at the University of Wisconsin-Madison. It wasn’t long before he went around Sterling Hall asking about joining a research team.

Jay Gallagher ... offered Lawrence the chance to study one of two galaxy systems. Lawrence picked a nearby system studied since the 1960s and featuring the interaction of two galaxies, a larger one known as NGC 4490 (nicknamed the “Cocoon Galaxy” because of its shape) and a smaller one known as NGC 4485. The system is about 20% the size of the Milky Way, located in the Northern Hemisphere and about 30 million light years from Earth.

After taking a look at some infrared images from NASA’s Wide-field Infrared Survey Explorer, Lawrence said it looked like the larger galaxy had a rare double nucleus. One nucleus could be seen in visible wavelengths, the other nucleus was hidden in dust and could only be seen in infrared and radio wavelengths. ...

Revealing the Double Nucleus of NGC 4490 ~ AL Lawrence et al

• arXiv.org > astro-ph > arXiv:2001.05601 > 16 Jan 2020

[Ann]

Wow, that's fascinating! NGC 4490 has long been one of my favorite galaxies because it is so blue.

Click to view full size image

NGC 4490 3.6μm image showing regions of interest. Apertures are shown surrounding
the optical nucleus (OPT), infrared nucleus (IR), and the giant HII regions A and B. The
large and small cyan crosses mark the locations of the optical and infrared nucleus
respectively. (Credit: AL Lawrence et al, ApJ 2020

Click to view full size image

Optical image of NGC 4490, processed from datafile http://hla.stsci.edu/hlaview.html
Full size here.

[saturno2]

Well, but why it has 2 nucleus?

[Ann]

Well, but why it has 2 nucleus?

Wow, Saturno. I'm going to speculate, okay?

NGC 4490 is a starburst galaxy. That means that it is forming stars at a very high rate, unlike the Milky Way, which is forming stars at a slow and steady pace. According to this page, the size of the interacting pair, NGC 4490 and 4485, is about 20% of the size of the Milky Way. That's tiny indeed. What's more, the blue color and corresponding lack of a massive yellow population, as well as the irregular shape of NGC 4490, suggests to me NGC 4490 is low in mass.

If you have a low-mass system, full of massive blue stars with strong stellar winds, you can get a galaxy that is becoming chaotic because of the strong forces tearing at such a low-mass system. Moreover, there have been two supernovas recorded by human astronomers in NGC 4490, and we can be sure that there have been many others in the relatively recent past, too.

Long story short, if strong and even exposive forces are tearing at a gas-rich system, that can result in high concentrations of gas and dust and violent star formation in the central part of the galaxy some distance away from the "established nucleus". By "established nucleus", I suppose that would refer to a massive (but perhaps not really supermassive) black hole in NGC 4490.

Yes, but a strong burst of star formation, accompanied by the formation of very high-mass stars, could lead to, perhaps, the merger of some very high-mass stars and the ensuing formation of at least a massive stellar-mass black hole. This second at least moderately massive black hole could function as a second nucleus of NGC 4490. The fact that the second nucleus appears to be located inside a large dusty envelope lends some credence to the idea that some violent star formation has been going on here, and that in turn could facilitate the creation of a moderately large black hole.

Again, please remember that I'm just speculating!

Ann

[BDanielMayfield]

Well, but why it has 2 nucleus?

Wow, Saturno. I'm going to speculate, okay?

NGC 4490 is a starburst galaxy. That means that it is forming stars at a very high rate, unlike the Milky Way, which is forming stars at a slow and steady pace. According to this page, the size of the interacting pair, NGC 4490 and 4485, is about 20% of the size of the Milky Way. That's tiny indeed. What's more, the blue color and corresponding lack of a massive yellow population, as well as the irregular shape of NGC 4490, suggests to me NGC 4490 is low in mass.

If you have a low-mass system, full of massive blue stars with strong stellar winds, you can get a galaxy that is becoming chaotic because of the strong forces tearing at such a low-mass system. Moreover, there have been two supernovas recorded by human astronomers in NGC 4490, and we can be sure that there have been many others in the relatively recent past, too.

Long story short, if strong and even exposive forces are tearing at a gas-rich system, that can result in high concentrations of gas and dust and violent star formation in the central part of the galaxy some distance away from the "established nucleus". By "established nucleus", I suppose that would refer to a massive (but perhaps not really supermassive) black hole in NGC 4490.

Yes, but a strong burst of star formation, accompanied by the formation of very high-mass stars, could lead to, perhaps, the merger of some very high-mass stars and the ensuing formation of at least a massive stellar-mass black hole. This second at least moderately massive black hole could function as a second nucleus of NGC 4490. The fact that the second nucleus appears to be located inside a large dusty envelope lends some credence to the idea that some violent star formation has been going on here, and that in turn could facilitate the creation of a moderately large black hole.

Again, please remember that I'm just speculating!

Ann

OR, a more common way to get two cores in one galaxy is for this to be the product of two galaxies in the process of merging. This is what the article reported:

The new paper describes “a clear double nucleus structure.” It says both nuclei are similar in size, mass and luminosity. It says both are similar in mass and luminosity to the nuclei observed in other interacting galaxy pairs. And, it says the double nucleus structure could also explain why the galaxy system is surrounded by an enormous plume of hydrogen.

“The most straightforward interpretation of the observations is that NGC 4490 is itself a late-stage merger remnant” of a much-earlier collision of two galaxies, the authors wrote. A merger could drive and extend the high level of star formation necessary to create such a large hydrogen plume.

Speculation can be dangerous.

[Ann]

Well, but why it has 2 nucleus?

Wow, Saturno. I'm going to speculate, okay?

NGC 4490 is a starburst galaxy. That means that it is forming stars at a very high rate, unlike the Milky Way, which is forming stars at a slow and steady pace. According to this page, the size of the interacting pair, NGC 4490 and 4485, is about 20% of the size of the Milky Way. That's tiny indeed. What's more, the blue color and corresponding lack of a massive yellow population, as well as the irregular shape of NGC 4490, suggests to me NGC 4490 is low in mass.

If you have a low-mass system, full of massive blue stars with strong stellar winds, you can get a galaxy that is becoming chaotic because of the strong forces tearing at such a low-mass system. Moreover, there have been two supernovas recorded by human astronomers in NGC 4490, and we can be sure that there have been many others in the relatively recent past, too.

Long story short, if strong and even exposive forces are tearing at a gas-rich system, that can result in high concentrations of gas and dust and violent star formation in the central part of the galaxy some distance away from the "established nucleus". By "established nucleus", I suppose that would refer to a massive (but perhaps not really supermassive) black hole in NGC 4490.

Yes, but a strong burst of star formation, accompanied by the formation of very high-mass stars, could lead to, perhaps, the merger of some very high-mass stars and the ensuing formation of at least a massive stellar-mass black hole. This second at least moderately massive black hole could function as a second nucleus of NGC 4490. The fact that the second nucleus appears to be located inside a large dusty envelope lends some credence to the idea that some violent star formation has been going on here, and that in turn could facilitate the creation of a moderately large black hole.

Again, please remember that I'm just speculating!

Ann

OR, a more common way to get two cores in one galaxy is for this to be the product of two galaxies in the process of merging. This is what the article reported:

The new paper describes “a clear double nucleus structure.” It says both nuclei are similar in size, mass and luminosity. It says both are similar in mass and luminosity to the nuclei observed in other interacting galaxy pairs. And, it says the double nucleus structure could also explain why the galaxy system is surrounded by an enormous plume of hydrogen.

“The most straightforward interpretation of the observations is that NGC 4490 is itself a late-stage merger remnant” of a much-earlier collision of two galaxies, the authors wrote. A merger could drive and extend the high level of star formation necessary to create such a large hydrogen plume.

Speculation can be dangerous.

Obviously, Bruce. Thanks for correcting me!

Ann