APOD: NGC 253: Dusty Island Universe (2016 Nov 03)

[APOD Robot]

NGC 253: Dusty Island Universe

Explanation: Shiny NGC 253 is one of the brightest spiral galaxies visible, and also one of the dustiest. Some call it the Silver Dollar Galaxy for its appearance in small telescopes, or just the Sculptor Galaxy for its location within the boundaries of the southern constellation Sculptor. First swept up in 1783 by mathematician and astronomer Caroline Herschel, the dusty island universe lies a mere 10 million light-years away. About 70 thousand light-years across, NGC 253 is the largest member of the Sculptor Group of Galaxies, the nearest to our own Local Group of Galaxies. In addition to its spiral dust lanes, tendrils of dust seem to be rising from a galactic disk laced with young star clusters and star forming regions in this sharp color image. The high dust content accompanies frantic star formation, earning NGC 253 the designation of a starburst galaxy. NGC 253 is also known to be a strong source of high-energy x-rays and gamma rays, likely due to massive black holes near the galaxy's center.

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[Ann]

While it is true that NGC 253 is a starburst galaxy, the starburst itself is confined to the nuclear region, and in spite of the numerous (and comparatively small) pink emission nebulas, the disk of NGC 253 is not very rich in young stars. James D Wray, who in the 1980s photographed about a thousand galaxies or so through ultraviolet, blue and yellow-green filters, showed that the disk of NGC 253 doesn't emit a lot of UV light.

Click to view full size image

Infrared image of the nuclear starburst of NGC 253.
Source: http://www.gemini.edu/node/12441

To appreciate the small size of the nuclear starburst of NGC 253, consider the image at left, taken through infrared filters J, H and K. Even though infrared light is often able to penetrate dust, the dust hiding the starburst of NGC 253 is so thick that not even this infrared image can completely reveal the starburst underneath. The Hubble telescope, whose infrared capabilities aren't stellar, also had trouble seeing through the dust.

And while the nucleus of NGC 253 is undergoing a starburst, the disk of NGC 253 isn't particularly rich in young stars. The colors of the galaxy are relatively red, too, with a B-V of 0.850 and an U-B of 0.380. Of course, the galaxy is very dusty and therefore dust-reddened, too. The far infrared magnitude of NGC 253 is two and a half magnitudes brighter than its B magnitude, which is a clear signature of dust.

Click to view full size image

M82. Photo: Jason Jennings.

An even more extreme case of a nuclear starburst and a "dead" disk is M82. The central outflow from the nuclear region of M82 is tremendous, the B-V index of M82 is a little redder than that of NGC 253 (0.890 vs 0.850), the U-B index is a little bluer (0.310 vs 0.380), the dust content of M82 may be even higher than that of NGC 253 (the far infrared magnitude is three and a half magnitudes brighter than its B magnitude), and no obvious sites of star formation can be spotted in the disk at all.

It is almost as if a really runaway nuclear starburst may blow the entire galaxy free of gas, dampening or even destroying the galaxy's future starforming ability.

Ann

[aljo]

I don't like the title of this picture. NGC253 is not an island, and it isn't the universe!

[rstevenson]

I don't like the title of this picture. NGC253 is not an island, and it isn't the universe!

"Island universe" is a term invented by the 18th-century philosopher Immanuel Kant, who believed that the "spiral nebulae" astronomers could see in their telescopes were not small clusters of stars near or in the Milky Way, but were much larger and more distant groups of stars, galaxies much like the Milky Way itself. The term may be archaic, but it has an honourable history within astronomy, and is now a useful metaphor.

Rob

[Chris Peterson]

I don't like the title of this picture. NGC253 is not an island, and it isn't the universe!

But it is an island. And while it's not the Universe, it is a universe. Island universe. A lovely, poetic term with historical significance.

[ta152h0]

nice spikes on those stars. Must be a real photo

[Chris Peterson]

nice spikes on those stars. Must be a real photo

As opposed to...?

[Travies0]

I noticed some interesting objects in today's APOD, and I was hoping someone may already know. Just below and diagonally right from NGC 253 there is a distant galaxy with an object in front of it. I thought this appeared strange because it blocks some of the light of the occluded galaxy around the object.

The other interesting thing I noticed was to the right of the lower half of NGC 253, about half way to the end of the image. There is a star, pinkish in color, and there is a reddish-orange object right next to that star. This is likely another star in our own galaxy, or perhaps another distant galaxy. However, could this by chance be an exoplanet orbiting that star, the planet would be quite large if it was...

I like to look for stars in these pictures of distant galaxies to see if maybe an exoplanet can be visible. I can never be certain, but I still enjoy looking.

[aljo]

I don't like the title of this picture. NGC253 is not an island, and it isn't the universe!

But it is an island. And while it's not the Universe, it is a universe. Island universe. A lovely, poetic term with historical significance.

If it is an island universe then presumably there are also mainland universes, otherwise why use that adjective? And it is not a universe, which means everything that exists. Any other meaning causes confusion and should be avoided. That is why I am also opposed to the term Multiverse, because multiple universes is a contradiction in terms - someone should come up with a more meaningful term.

[Chris Peterson]

I don't like the title of this picture. NGC253 is not an island, and it isn't the universe!

But it is an island. And while it's not the Universe, it is a universe. Island universe. A lovely, poetic term with historical significance.

If it is an island universe then presumably there are also mainland universes, otherwise why use that adjective?

Why does the existence of islands presuppose a mainland? Consider an ocean planet, 95% covered with water, and just the tips of undersea mountains poking up here and there. Would those not be islands, even without any substantial landmasses?

And it is not a universe, which means everything that exists.

No, that isn't what "universe" means. Like a great many words, it has multiple meanings. It can be a relatively closed population (of anything). It can be an aggregate of stars such as the Milky Way. A set of related elements. Even a very large number. It is a mistake to confuse a universe with the Universe.

Any other meaning causes confusion and should be avoided. That is why I am also opposed to the term Multiverse, because multiple universes is a contradiction in terms - someone should come up with a more meaningful term.

I don't think most people find any confusion in the term. And "multiverse" most certainly contains no contradiction.

[Chris Peterson]

I noticed some interesting objects in today's APOD, and I was hoping someone may already know. Just below and diagonally right from NGC 253 there is a distant galaxy with an object in front of it. I thought this appeared strange because it blocks some of the light of the occluded galaxy around the object.

It's possible this is a foreground star, although it appears somewhat elongated, unlike other stars in the area. But the apparent elongation could be an illusion because of the galaxy behind it. Also very possible is that this is a much more distant galaxy, seen through the larger, closer galaxy. The slight outline around it may be nothing more than a processing artifact giving the illusion that it's actually in front.

The other interesting thing I noticed was to the right of the lower half of NGC 253, about half way to the end of the image. There is a star, pinkish in color, and there is a reddish-orange object right next to that star. This is likely another star in our own galaxy, or perhaps another distant galaxy. However, could this by chance be an exoplanet orbiting that star, the planet would be quite large if it was...

This is just a pair of stars- possibly a binary system, or unrelated and lying at very different distances. There is no possibility of seeing exoplanets in images such as this. They would lie too close to the star to be spatially resolved, and would be orders of magnitude too dim to rise above the noise floor of the image.

[geckzilla]

I don't like the title of this picture. NGC253 is not an island, and it isn't the universe!

But it is an island. And while it's not the Universe, it is a universe. Island universe. A lovely, poetic term with historical significance.

If it is an island universe then presumably there are also mainland universes, otherwise why use that adjective? And it is not a universe, which means everything that exists. Any other meaning causes confusion and should be avoided. That is why I am also opposed to the term Multiverse, because multiple universes is a contradiction in terms - someone should come up with a more meaningful term.

They already do call them galaxies. Island universe is just more poetic. Do you like poetry? Then maybe we have a common ground. Otherwise, we'll just have to disagree.

[Visual_Astronomer]

I was looking at this just last Friday - it is a truly spectacular visual target. Large and bright with a mottled appearance. Not coloured, of course, but in other respects not too different from this picture.

[neufer]

They already do call them galaxies. Island universe is just more poetic. Do you like poetry?

Dusty Island Universe is not particularly poetic (nor very easy to say 5 times fast).

A Dusty Universe Island is easier to state and has a certain air of danger to it.

[ta152h0]

as oopesed to paintings. I still remember the APOD subject in the past regarding paintings vs pictures. Teache bable moment.

[Boomer12k]

I don't like the title of this picture. NGC253 is not an island, and it isn't the universe!

It is an old term... though still used... Island is separate from continuous land, surrounded by water,... this is an "island" in Space, so is the Earth for that matter,... it is a Concept. They are considered...."universes" in themselves... your intestines are a "universe" to your gut bacterial... you have 100 trillion bacteria there. That is like 500 Milky Way Galaxies, if bacteria were Stars.... a veritable Universe. So, we have these terms...

:---[===] *

[Boomer12k]

And a very nice image of it, to be sure...

:---[===] *

[starsurfer]

nice spikes on those stars. Must be a real photo

Those diffraction spikes are real! They're caused by the design of the telescope.