APOD: North Star: Polaris and Surrounding Dust (2021 Apr 28)

[APOD Robot]

North Star: Polaris and Surrounding Dust

Explanation: Why is Polaris called the North Star? First, Polaris is the nearest bright star toward the north spin axis of the Earth. Therefore, as the Earth turns, stars appear to revolve around Polaris, but Polaris itself always stays in the same northerly direction -- making it the North Star. Since no bright star is near the south spin axis of the Earth, there is currently no South Star. Thousands of years ago, Earth's spin axis pointed in a slightly different direction so that Vega was the North Star. Although Polaris is not the brightest star on the sky, it is easily located because it is nearly aligned with two stars in the cup of the Big Dipper. Polaris is near the center of the eight-degree wide featured image, an image that has been digitally manipulated to suppress surrounding dim stars but accentuate the faint gas and dust of the Integrated Flux Nebula (IFN). The surface of Cepheid Polaris slowly pulsates, causing the star to change its brightness by a few percent over the course of a few days.

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[alter-ego]

IFN → Integrated Flux Nebula

[Ann]

North Star: Polaris and Surrounding Dust. Image Credit & Copyright: Bray Falls.

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Comet C/2014 Q2 Lovejoy near the north celestial pole on May 29, 2015, with Polaris glowing nearby. Credit: Rogelio Bernal Andreo

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There is indeed a lot of dust in the vicinity of Polaris. This dust is really the Integrated Flux Nebula, and I refer you to alter-ego's post to check the link for more information on it.

Personally I've always found the color of Polaris slightly blah, since it's neither blue nor red. Polaris is in fact almost perfectly Sun-colored. The B-V index of the Sun is 0.656 ± 0.005, and the B-V index of Polaris is 0.636 ± 0.003. Same difference!

Well, the Sun is a white star, as I keep insisting. And Polaris looks very white in Bray Falls' image, as does its halo. That's very well done!

However, there are a lot of pictures out there where Polaris looks rather blue. I don't know why, since this obviously isn't a blue star. Is it at all possible that all the IFN surrounding it may create a bluish halo around the star? Or could it be that it is easy and tempting to process the image so that the halo of Polaris looks blue?

I can't resist showing you one of the pictures where Polaris, or at least its halo, looks blue. It is an image by Rogelio Bernal Andreo, and in this picture, Polaris was visited by Comet C/2014 Q2 Lovejoy with its green coma, blue tail and short rather green-looking antitail. Nice!!

Ann

[Prof. Greg Parker]

Intergalactic Flux Nebula!!!!!!!!!!!!!!!!! For God's sake

[rstevenson]

IFN → Integrated Flux Nebula

They’re just checking that we actually read what they write. Yeah, that’s it!

Rob

[orin stepanek]

North Star: Polaris and Surrounding Dust. Image Credit & Copyright: Bray Falls.

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Comet C/2014 Q2 Lovejoy near the north celestial pole on May 29, 2015, with Polaris glowing nearby. Credit: Rogelio Bernal Andreo

---

There is indeed a lot of dust in the vicinity of Polaris. This dust is really the Integrated Flux Nebula, and I refer you to alter-ego's post to check the link for more information on it.

Personally I've always found the color of Polaris slightly blah, since it's neither blue nor red. Polaris is in fact almost perfectly Sun-colored. The B-V index of the Sun is 0.656 ± 0.005, and the B-V index of Polaris is 0.636 ± 0.003. Same difference!

Well, the Sun is a white star, as I keep insisting. And Polaris looks very white in Bray Falls' image, as does its halo. That's very well done!

However, there are a lot of pictures out there where Polaris looks rather blue. I don't know why, since this obviously isn't a blue star. Is it at all possible that all the IFN surrounding it may create a bluish halo around the star? Or could it be that it is easy and tempting to process the image so that the halo of Polaris looks blue?

I can't resist showing you one of the pictures where Polaris, or at least its halo, looks blue. It is an image by Rogelio Bernal Andreo, and in this picture, Polaris was visited by Comet C/2014 Q2 Lovejoy with its green coma, blue tail and short rather green-looking antitail. Nice!!




Ann

Yes; a lot of dust; but makes for a beautiful photo! So nice; in fact it'll become a wallpaper for a day!

[RJN]

IFN → Integrated Flux Nebula

Yes, thank you. This has now been fixed on the main NASA APOD. Apologies for the oversight.
- RJN

[neufer]

IFN → Integrated Flux Nebula

Yes, thank you. This has now been fixed on the main NASA APOD. Apologies for the oversight. - RJN

North Star: Polaris and Surrounding Dust. Image Credit & Copyright: Bray Falls.

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The molecular structure of human interferon-alpha

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IFN may mean:

• Interferon, a type of signaling proteins
  
  Information Fuzzy Networks, a machine learning algorithm
  
  Leibniz Institute for Neurobiology (Leibniz-Institut für Neurobiologie), Germany
  
  Institutet för Näringslivsforskning, Research Institute for Industrial Economics, Sweden
  
  Instituto di Fotonica e Nanotecnologie, Institute for Photonics and Nanotechnologies, Trento, Italy

<<Interferons (IFNs) are a group of signaling proteins made and released by host cells in response to the presence of several viruses. In a typical scenario, a virus-infected cell will release interferons causing nearby cells to heighten their anti-viral defenses. More than twenty distinct IFN genes and proteins have been identified in animals, including humans.

IFNs belong to the large class of proteins known as cytokines, molecules used for communication between cells to trigger the protective defenses of the immune system that help eradicate pathogens. Interferons are named for their ability to "interfere" with viral replication by protecting cells from virus infections. IFNs also have various other functions: they activate immune cells, such as natural killer cells and macrophages; they increase host defenses by up-regulating antigen presentation by virtue of increasing the expression of major histocompatibility complex (MHC) antigens. Certain symptoms of infections, such as fever, muscle pain and "flu-like symptoms", are also caused by the production of IFNs and other cytokines.>>

[johnnydeep]

IFN → Integrated Flux Nebula

Hold on a minute. That very short WikiPedia page says this - in entirety:

Integrated flux nebulas are a relatively recently identified astronomical phenomenon. In contrast to the typical and well known gaseous nebulas within the plane of the Milky Way galaxy, IFNs lie beyond the main body of the galaxy.

The term was coined by Steve Mandel who defined them as "high galactic latitude nebulae that are illuminated not by a single star (as most nebula in the plane of the Galaxy are) but by the energy from the integrated flux of all the stars in the Milky Way. These nebulae clouds, an important component of the interstellar medium, are composed of dust particles, hydrogen and carbon monoxide and other elements."

So, is this IFN between us and Polaris, or well behind it (or perhaps both)? Which also begs the question or what "beyond the main body of the galaxy" means. Perpendicular to the plane of the Milky Way, you don't have to go very far to get "beyond" the main body (a few hundred lys max), but along the plane you do (a few tens of thousands of lys minimum). Polaris is 433 lys away, but in what direction relative to the plane of the Milky Way?

[neufer]

IFN (or galactic cirris)

---

So, is this IFN between us and Polaris, or well behind it (or perhaps both)? Which also begs the question or what "beyond the main body of the galaxy" means. Perpendicular to the plane of the Milky Way, you don't have to go very far to get "beyond" the main body (a few hundred lys max), but along the plane you do (a few tens of thousands of lys minimum). Polaris is 433 lys away, but in what direction relative to the plane of the Milky Way?

The IFN (or galactic cirris) is mostly supernova debris well behind Polaris.

See: https://www.cosmotography.com/images/ga ... irrus.html

[VictorBorun]

I can't resist showing you one of the pictures where Polaris, or at least its halo, looks blue. It is an image by Rogelio Bernal Andreo, and in this picture, Polaris was visited by Comet C/2014 Q2 Lovejoy with its green coma, blue tail and short rather green-looking antitail. Nice!!

Ann

Click to view full size image

Still I am confused as to what's where.
Is Polaris at 400 ly distance already out of the galaxy disk?
Is only background Integrated Flux Nebula (IFN) out of the galaxy disk?
Is the nebula really Integrated Flux ? It looks like locally frontlighted to my eye.

[De58te]

IFN → Integrated Flux Nebula

Polaris is 433 lys away, but in what direction relative to the plane of the Milky Way?

Well this is not official. I am just doing this in my head. Where is Polaris compared to the galactic plane? The solar system is tilted approx 60 degrees to the galactic plane. Now the Earth itself is tilted 23 degrees to the ecliptic. So a guess, when the solar system at one side is 30 degrees from the galactic north pole then Polaris is another 30 plus 23 degrees on the other side of galactic north or 53 degrees away from north. If I recall the constellation that truly is north of the galactic plane is Coma Berenice or visibly nearby the star Arcturus in Bootes.

[neufer]

Polaris is 433 lys away, but in what direction relative to the plane of the Milky Way?

Well this is not official. I am just doing this in my head. Where is Polaris compared to the galactic plane? The solar system is tilted approx 60 degrees to the galactic plane. Now the Earth itself is tilted 23 degrees to the ecliptic. So a guess, when the solar system at one side is 30 degrees from the galactic north pole then Polaris is another 30 plus 23 degrees on the other side of galactic north or 53 degrees away from north. If I recall the constellation that truly is north of the galactic plane is Coma Berenice or visibly nearby the star Arcturus in Bootes.

• Galactic Latitude : 26.46°
  Galactic Longitude : 123.28°

The Milky Way runs through the nearby constellation of Cassiopeia.

[Ann]

I can't resist showing you one of the pictures where Polaris, or at least its halo, looks blue. It is an image by Rogelio Bernal Andreo, and in this picture, Polaris was visited by Comet C/2014 Q2 Lovejoy with its green coma, blue tail and short rather green-looking antitail. Nice!!

Ann

Click to view full size image

Still I am confused as to what's where.
Is Polaris at 400 ly distance already out of the galaxy disk?
Is only background Integrated Flux Nebula (IFN) out of the galaxy disk?
Is the nebula really Integrated Flux ? It looks like locally frontlighted to my eye.

At a distance of 400 light-years, Polaris could be out of our Galaxy's thin disk.

COSMOS - The SAO Encyclopedia of Astronomy wrote:

First noticed in star counts, the thick disk contains about 10% of the stellar mass of the Milky Way and has a scale height of ~ 1,000 light years (the thin disk has a scale height of only ~ 400 light years).

Ann

[Ann]

IFN (or galactic cirris)

---

So, is this IFN between us and Polaris, or well behind it (or perhaps both)? Which also begs the question or what "beyond the main body of the galaxy" means. Perpendicular to the plane of the Milky Way, you don't have to go very far to get "beyond" the main body (a few hundred lys max), but along the plane you do (a few tens of thousands of lys minimum). Polaris is 433 lys away, but in what direction relative to the plane of the Milky Way?

The IFN (or galactic cirris) is mostly supernova debris well behind Polaris.

See: https://www.cosmotography.com/images/ga ... irrus.html

This image shows the dramatically different view of our sky when viewed in far infrared light. At this wavelength of 100 microns, the light from stars is imperceptible against the cool glow of vast dust clouds warmed by the stars' light. In visible light such dust blocks our view of more distant stars and galaxies, but in far-infrared light it glows dramatically. Significantly, some of it also reflects blue light that can be captured in very deep optical exposures. Image credit: IRAS/COBE

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The link you gave us, Art, took us to a page showing us this infrared image of the Milky Way. There is an important source of some kind to be seen "above" the plane of the Milky Way, to the right.

There are also a few sources "below" the plane of the Milky Way, but I'm more interested in the source above it.

Does anyone know what it could be?

Ann

[VictorBorun]

I feel I miss something.
The background nebula behind Polaris is Integrated Flux Nebula, but may lie within the thick Milky Way disk and have plenty of stars to frontlight parts of it locally.
OK.
But why label such nebula an Integrated Flux at all?

[Chris Peterson]

I feel I miss something.
The background nebula behind Polaris is Integrated Flux Nebula, but may lie within the thick Milky Way disk and have plenty of stars to frontlight parts of it locally.
OK.
But why label such nebula an Integrated Flux at all?

As opposed to labeling it what?

[neufer]

This image shows the dramatically different view of our sky when viewed in far infrared light. At this wavelength of 100 microns, the light from stars is imperceptible against the cool glow of vast dust clouds warmed by the stars' light. In visible light such dust blocks our view of more distant stars and galaxies, but in far-infrared light it glows dramatically. Significantly, some of it also reflects blue light that can be captured in very deep optical exposures. IRAS/COBE

---

The IFN (or galactic cirris) is mostly supernova debris well behind Polaris.

See: https://www.cosmotography.com/images/ga ... irrus.html

The link you gave us, Art, took us to a page showing us this infrared image of the Milky Way. There is an important source of some kind to be seen "above" the plane of the Milky Way, to the right.

There are also a few sources "below" the plane of the Milky Way, but I'm more interested in the source above it.

Does anyone know what it could be?

Ann, for all I know your "source" above the plane of the Milky Way is nothing more than a distant galaxy.

However, there are plenty of potential dust sources "within" the plane of the Milky Way (e.g., supernova, Bok globules, EGGs, etc.) if only there was some mechanism to exile this material to "dust heaven" and keep it there permanently. (A normal orbiting dust cloud would have to repetitively pass through the sticky/gaseous "fly paper" of the Milky Way disk and get trapped.)

Since Wikipedia has so little to say on this matter I will throw out my own Cavorite "dust heaven" hypothesis:
.................................................................................................
H. G. Wells 1901 _The First Men in the Moon_ story proposed an anti-gravity material called cavorite.

Now, there is a somewhat analogous "anti-gravity cavorite" material called fine dust in the presence of bright starlight.

Fine enough dust will absorb starlight and act as a solar sail under
the influence of a (analogous "anti-gravity") repulsive radial Force:

• F_R= [L d² - M ρ d³]/R² ... provided L/(Mρd) > 1

where: L= stellar Luminosity, M= stellar Mass, R= stellar Radial distance, d= dust diameter and ρ= dust density.

For example:
Zodiacal light dust particles of diameters (d) less than 10 μm are removed from the inner Solar System by solar radiation pressure.

• Hence, if d<10 μm then L_☉/(M_☉ρd) > 1

These dust particles continue moving away from the Sun and by the time they are ~10 light-years away
they are joined by many other dust particles of diameters (d) less than 10 μm.

In fact, the sphere of radius 10 ly around the Sun contains ~28 L_☉ of luminosity (mostly from Sirius) but only ~7 M_☉ of star mass.
Hence, these smaller (<10 μm) dust particles are joined by larger dust particles of diameters (d) up to ~40 μm.

This L/M ~ 4 L_☉/M_☉ ratio seems about right for the whole (non-dark matter) Milky Way
which has a luminosity of ~ 20 x 10¹⁰ L_☉ and a (non-dark matter) mass of ~ 5 x 10¹⁰ M_☉

Hence, the ~1,000 light-year wide Milky Way disk will shed dust particles of diameters (d) up ~40 μm
until those particles feel the effects of a much wider & more massive dark matter disk
at which point they permanently rest in peace in "dust heaven" (where dark matter pull balances starlight push).

<<Much of the mass of the Milky Way seems to be dark matter, an unknown and invisible form of matter that interacts gravitationally with ordinary matter. Mathematical models of the Milky Way suggest that the mass of dark matter is 1–1.5×10¹² M_☉. The total mass of all the stars in the Milky Way is estimated to be between 4.6×10¹⁰ M_☉ and 6.43×10¹⁰ M_☉. The mass of the Milky Way's interstellar gas is equal to between 10% and 15% of the total mass of its stars. Interstellar dust accounts for an additional 1% of the total mass of the gas. In March 2019, astronomers reported that the mass of the Milky Way galaxy is 1.5 trillion solar masses within a radius of about 129,000 light-years, over twice as much as was determined in earlier studies, and suggesting that about 90% of the mass of the galaxy is dark matter.>>

[VictorBorun]

At a distance of 400 light-years, Polaris could be out of our Galaxy's thin disk.

COSMOS - The SAO Encyclopedia of Astronomy wrote:
First noticed in star counts, the thick disk contains about 10% of the stellar mass of the Milky Way and has a scale height of ~ 1,000 light years (the thin disk has a scale height of only ~ 400 light years).

Ann

But Polaris Aa, mass of 5.4 suns, spectral type F7Ib, is just 70 million years old.
If Polaris is on a thick disk orbit with its plane crossing the thick disk what cloud could have formed Polaris?
How could that cloud cross the thick gas disk every 230 million year?

[Ann]

At a distance of 400 light-years, Polaris could be out of our Galaxy's thin disk.

COSMOS - The SAO Encyclopedia of Astronomy wrote:
First noticed in star counts, the thick disk contains about 10% of the stellar mass of the Milky Way and has a scale height of ~ 1,000 light years (the thin disk has a scale height of only ~ 400 light years).

Ann

But Polaris Aa, mass of 5.4 suns, spectral type F7Ib, is just 70 million years old.
If Polaris is on a thick disk orbit with its plane crossing the thick disk what cloud could have formed Polaris?
How could that cloud cross the thick gas disk every 230 million year?

I found this link, which is admittedly quite old:

Annette M.N. Ferguson wrote:

The far outer regions of galactic disks allow an important probe of both star formation and galaxy formation. I discuss how observations of HII regions in these low gas density, low metallicity environments can shed light on the physical processes which drive galactic star formation.

Polaris is probably not situated deep in the thick disk of the Milky Way, but rather at the outskirts of the thin disk or in a part of the thick disk that is quite close to the thin disk. Star formation can take place there, so Polaris may indeed have been born close to where it is now located.

Ann

[VictorBorun]

Polaris is probably not situated deep in the thick disk of the Milky Way, but rather at the outskirts of the thin disk or in a part of the thick disk that is quite close to the thin disk. Star formation can take place there, so Polaris may indeed have been born close to where it is now located.
Ann

Galactic orbit for Sun or Polaris is 270 million years, and if the plane of the orbit is crossing the central plane of Milky Way at any small angle then the star must bob from one or another side of the Milky Way central plane every 135 million years: 33 million years of moving away, then 67 million years of soaring, then 33 million years of moving near, then crossing over and so on.

Well, suppose a gas-dust cloud is levitating off the plane because integrated stellar light of the Thin Disk pushes the 10 micrometer dust particles.

Suppose then that such a cloud got disturbed by a supernova, or a tidal force from a dwarf galaxy or from a globular stellar cluster.

Suppose the distutbed cloud started collapsing and formed some stars including Polaris system.

Such a dense object would stop levitating and start falling to the plane. By 70 million years Polaris system would have come close and be now just crossing the plane, would not it?

[Ann]

Polaris is probably not situated deep in the thick disk of the Milky Way, but rather at the outskirts of the thin disk or in a part of the thick disk that is quite close to the thin disk. Star formation can take place there, so Polaris may indeed have been born close to where it is now located.
Ann

Galactic orbit for Sun or Polaris is 270 million years, and if the plane of the orbit is crossing the central plane of Milky Way at any small angle then the star must bob from one or another side of the Milky Way central plane every 135 million years: 33 million years of moving away, then 67 million years of soaring, then 33 million years of moving near, then crossing over and so on.

Well, suppose a gas-dust cloud is levitating off the plane because integrated stellar light of the Thin Disk pushes the 10 micrometer dust particles.

Suppose then that such a cloud got disturbed by a supernova, or a tidal force from a dwarf galaxy or from a globular stellar cluster.

Suppose the distutbed cloud started collapsing and formed some stars including Polaris system.

Such a dense object would stop levitating and start falling to the plane. By 70 million years Polaris system would have come close and be now just crossing the plane, would not it?

Stars don't "levitate", but follow orbits. So there is no reason for Polaris to "fall down".

Ann